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Effects of Functional Groups on Surface Pressure−Area Isotherms of Hydrophilic Silicone Polymers
Abstract
Organic/inorganic hybrid silicone polymers are increasingly used in cosmetics, inks and paints, and fabric care applications owing to their special Si-O bond characteristics. Because of the presence of organic as well as inorganic groups, they show the properties of both, and the presence of hydrophobic as well as hydrophilic character makes them behave like a hybrid polymer. Though they are widely used, the utilization of hydrophilically modified silicones on a large scale has mainly been empirical due to lack of fundamental knowledge about variation in their properties with systematic change in their structure. The choice of moieties for hydrophilic modification of silicones in most of the earlier works has been nonionic based on ethylene oxide and propylene oxide groups, however, very little is known about their ionic counterparts. The current work focuses on understanding the behavior of functionally grafted silicone polymers with respect to the variation in the hydrophilic part of the grafting chain. Hydrophilically grafted silicone polymers form monolayers at the air-water interface, which are stabilized by interactions of functional groups with water. The present work examined the effects of functional group modifications on the conformational behavior of chains at the interface. It was observed that the shape of the chain depends on the available area at the interface (or surface pressure), and there are conformational changes with an increase in the number of molecules per unit area. While a poly(dimethylsiloxanes) (PDMS) chain may undergo stretched to helix transition as predicted earlier, this may not be the case for hydrophilically grafted chains. On the basis of the shape of the surface pressure-area isotherm and correlation with the scaling theory, a gradation in hydrophilicity of functional groups and hence modified silicone chains at the air-water interface is predicted.
... The authors of [10][11][12] developed a model that describes the behavior of organosilicon surfactants in Langmuir layer under compression, in particular, as a function of a change in the surface pressure (Fig. 1). ...
... Upon further compression (step C), the conformation of the siloxane chain changes and forms, in accordance with some authors, helical structures or a bilayer at the interface (Fig. 2). At step D, deformation of the formed surfactant layer takes place; according to one hypothesis, helices undergo deformation, while according to the other one folded layers are formed [10][11][12]. Figure 3 shows surface pressure and surface potential isotherms for the studied dimeric organosilicon compounds with end carboxyl and amino groups (PDMS(СООН) and PDMS(NH 2 )). Regions A, В, C, and D may be distinguished on the surface pressure isotherms by analogy with the published data [10]. ...
... Figure 3 shows surface pressure and surface potential isotherms for the studied dimeric organosilicon compounds with end carboxyl and amino groups (PDMS(СООН) and PDMS(NH 2 )). Regions A, В, C, and D may be distinguished on the surface pressure isotherms by analogy with the published data [10]. ...
The behavior of organosilicon surfactants of different structure in model systems—Langmuir films—at the water/air interface is studied. It is shown that, under the compression of Langmuir films, the conformational states of surfactants of different structure are different. The obtained data make it possible to explain a high stability of polymer suspensions synthesized in the presence of organosilicon surfactants.
... Conformational changes arising from the compression of a PDMS monolayer were analyzed in [4,16,30]. Four typical regions can be discerned on the PDMS π-А isotherm with methyl end groups (Fig. 2a) [21,31]. The modified model of conformational changes (see Fig. 2b) is based on investigation performed by means of sum-frequency vibrational spectroscopy. ...
... In region A (Fig. 2a), individual polymer chains from the conformation are separated from each other [4,21,31]. Oxygen atoms are hydrated, and methyl groups are disordered and arranged in a random way [32]. In region B (Fig. 2a), isolated PDMS chains approach each other to form a monolayer, and the methyl groups of PDMS macromolecules are ordered [4,16,21,31,32]. ...
... Oxygen atoms are hydrated, and methyl groups are disordered and arranged in a random way [32]. In region B (Fig. 2a), isolated PDMS chains approach each other to form a monolayer, and the methyl groups of PDMS macromolecules are ordered [4,16,21,31,32]. In region C, a plateau is observed at π-А isotherm at a surface pressure π of 8.7 mN/m, indicating conformational reconstruction or phase transition in a monolayer [21]. ...
The special features of self-organization and structure formation observed at the interface between different-polarity phases of macromolecules with various hydrophilic-lipophilic balances are reviewed by the example of amphiphilic siloxanes: polymers, oligomers, and low-molecular compounds. The structure of polyorganosiloxanes, the peculiarities of their behavior and conformational changes at the phase interface, and the influence of molecular mass, end groups, hydrophobic bulk substituents, chemical structure of the main (linear or cyclolinear) chain, and the subphase on the surface properties of the compounds mentioned above are analyzed.
... The col loid-chemical properties of these surfactants (namely, a low interfacial tension and the presence of liquid crystalline phases) provide the formation of the strong interfacial adsorption layer on the surfaces of mono mer droplets and polymer-monomer particles (PMPs) and ensure their high stability even at a high concentration of the surfactant. The behavior of sur factants at the interface is determined by both the properties of the main chain and the kinds of func tional substituents at silicon atoms [17]. ...
... During compression, the Langmuir films of PDMS molecules transfer from the planar trans zigzag con formation to the maximally dense helical packing [17][18][19][20][21][22][23][24][25][26]. The second step, corresponding to the detachment of hydrophilic end groups from the sur face of water, appears on the π-A isotherms of such oligomers [17,18]. ...
... During compression, the Langmuir films of PDMS molecules transfer from the planar trans zigzag con formation to the maximally dense helical packing [17][18][19][20][21][22][23][24][25][26]. The second step, corresponding to the detachment of hydrophilic end groups from the sur face of water, appears on the π-A isotherms of such oligomers [17,18]. This circumstance may be respon sible for a decrease in interfacial tension and for stabi lization of polymer dispersions at the boundary with the water phase. ...
The kinetics of methyl methacrylate polymerization in the presence of α,ω-functional polydimethylsiloxanes is investigated. The formation of polymer suspensions with a narrow particle-size distribution is explained by the ability of the surfactants to form strong adsorption layers in the interfacial layers of polymer–monomer particles. This assumption is confirmed by data obtained via the Langmuir method with the use of model systems: thin films of the mentioned organosilicon compounds.
... Under these conditions, the surfactant interfacial layer is characterized by thermodynamic and mechanical reversibility. Several types of conformations for linear chains of PDMS have been suggested in the literature [46,[49][50][51][52][53][54][55][56][57][58][59][60]. Such structures have been established from the NMR 29 Si and NMR 13 C spectra of crystalline PDMS [61,62]. ...
... Several types of conformations for linear chains of PDMS have been suggested in the literature [46,[49][50][51][52][53][54][55][56][57][58][59][60]. Such structures have been established from the NMR 29 Si and NMR 13 C spectra of crystalline PDMS [61,62]. ...
This article presents the results of investigations on heterophase polymerization of vinyl monomers in the presence of organosilicon compounds of different structures. On the basis of the detailed study of the kinetic and topochemical regularities of the heterophase polymerization of vinyl monomers, the conditions for the synthesis of polymer suspensions with a narrow particle-size distribution using a one-step method have been determined.
... The expected behavior for the osmotic pressure of polymer chains in θ -solvent in 3D is π c 3 , [ 1 ] which is not supported by the data shown in Figure 3 . Moreover, using Equation ( 2) and y = 8 from Figure 3 one fi nds that 4/7 ν = rather than the value expected for 3D chains in good solvent, 3/5 ν = , [ 15,16 ] in agreement with experiments [ 30,31 ] and confi rming the essential correctness of Equation ( 1) . ...
... We fi nd that ν is in good agreement with experiments with large N -poly mer chains. [ 22,30,31 ] The reason why quasi-2D scaling behavior is obtained in these 3D systems regardless of solvent quality can be found in the "blob" argument of de Gennes. [ 1 ] As the separation between the planes in Figure 1 is reduced (increasing concentration), the chains begin to overlap and the characteristic length is no longer R G 3 but instead the size of the blobs, ξ , which scales in 2D once h h* < . ...
... Moreover, using eq. 2 and y = 8 from Fig. 3 one finds that = 4 7 ⁄ rather than the value expected for 3d chains in good solvent, = 3 5 ⁄ [15,16], in agreement with experiments [30,31] and confirming the essential correctness of eq. 1. 1) and (2), and reference [24]. For all cases the surfacemonomer interaction was set to aw = 120.0, ...
... Notice that eq. 2 becomes c singular for = 0.5, so the poor solvent limit can never truly be achieved. We find that is in good agreement with experiments with large Npolymer chains [22,30,31]. The reason why quasi -2d scaling behavior is obtained in these 3d systems regardless of solvent quality can be found in the "blob" argument of de Gennes [1]. ...
A scaling relation for the disjoining pressure of strongly confined polymer fluids is proposed for the first time, which yields directly the scaling exponent, nu, of the radius of gyration for polymers. To test the proposed scaling relation we performed extensive particle – based, coarse – grained computer simulations of polymers confined under theta – solvent conditions and found that the value of nu agrees with the expected value for strictly two dimensional chains, nu = 4/7, which points towards the essential correctness of our scaling relation. New approaches are suggested for experimental tests of this scaling law. This work opens up the way to look for other scaling exponents that may reveal new physical regimes and it constitutes an efficient route to determine nu because the scaling exponent can be obtained with chains of a single polymerization degree by simply reducing the distance between the confining plates.
... The expected behavior for the osmotic pressure of polymer chains in θ -solvent in 3D is π c 3 , [ 1 ] which is not supported by the data shown in Figure 3 . Moreover, using Equation ( 2) and y = 8 from Figure 3 one fi nds that 4/7 ν = rather than the value expected for 3D chains in good solvent, 3/5 ν = , [ 15,16 ] in agreement with experiments [ 30,31 ] and confi rming the essential correctness of Equation ( 1) . ...
... We fi nd that ν is in good agreement with experiments with large N -poly mer chains. [ 22,30,31 ] The reason why quasi-2D scaling behavior is obtained in these 3D systems regardless of solvent quality can be found in the "blob" argument of de Gennes. [ 1 ] As the separation between the planes in Figure 1 is reduced (increasing concentration), the chains begin to overlap and the characteristic length is no longer R G 3 but instead the size of the blobs, ξ , which scales in 2D once h h* < . ...
A scaling relation for the disjoining pressure of strongly confined polymer fluids is proposed for the first time, which yields directly the scaling exponent, nu, of the radius of gyration for polymers. To test the proposed scaling relation we performed extensive particle – based, coarse – grained computer simulations of polymers confined under theta – solvent conditions and found that the value of nu agrees with the expected value for strictly two dimensional chains, nu = 4/7, which points towards the essential correctness of our scaling relation. New approaches are suggested for experimental tests of this scaling law. This work opens up the way to look for other scaling exponents that may reveal new physical regimes and it constitutes an efficient route to determine nu because the scaling exponent can be obtained with chains of a single polymerization degree by simply reducing the distance between the confining plates.
... In the case of ionic silicone surfactants, cationic [17,18] and anionic [19] trisiloxanes have been found to behave as excellent foaming agents [20,21]. There has been some work done on the solution properties of cationic [22], anionic [23] and zwitterionic [21] silicone surfactants. However, very little is known about the emulsifying properties of these ionic compounds. ...
... The approximate molecular weight of all the compounds as measured from viscosity was 5000 and a volatile content below 1%. The details on the synthesis of each polymer has been reported earlier [23]. The general structures of the above mentioned silicone surfactants are illustrated in Fig. 1. ...
Silicone oils are widely used in cosmetics and personal care applications to improve softness and condition skin and hair. Being insoluble in water and most hydrocarbons, a common mode of delivering them is in the form of emulsions. Currently most applications use polyoxyethylene (non-ionic) modified siloxanes as emulsifiers to stabilize silicone oil emulsions. However, ionically grafted silicone polymers have not received much attention. Ionic silicones have significantly different properties than the non-ionic counterpart. Thus considerable potential exists to formulate emulsions of silicones with different water/silicone oil ratios for novel applications. In order to understand the mechanisms underlying the effects of hydrophilic modifications on the ability of hybrid silicone polymers to stabilize various emulsions, this article focuses on the phase diagram studies for silicone emulsions.
... Для веществ 7 и 8 область плато на кривых πS 0 (рис. 3) находится в интервале значений π 812 мН/м, значения S 0 изменяются от 2300 до 300 Å 2 (8), от 950 до 100 Å 2 (7). Исходя из приведенных данных, можно предположить, что величина плато характеризует степень деформации молекул кремнийорганических веществ, которая происходит при увеличении поверхностного давления в монослое. ...
The colloid-chemical properties of organosilicon surfactants with different solubility in water were studied. The behavior of organosilicon surfactants of various structures in model systems - Langmuir films at the water-air interface has been studied. The results obtained showed that high stability of polymer suspensions is observed only in the presence of insoluble in water organosilicon surfactants.
... It is fundamentally important that this was achieved at concentrations an order of magnitude lower than those normally used for hydrocarbon surfactants (0.5 ÷ 1.0 wt.% and 3.0 ÷ 5.0 wt.% per monomer, respectively). It was shown in [10,11] that the ability of organosilicon surfactants to provide stability of latex particles at low concentrations in the synthesis of polymer microspheres, ranging from monomer droplets to polymer particles at full conversion of monomer, is due to unusual conditions of formation of interphase adsorption layers on the surface of the particles, while the strength of former determines the stability of the latter. ...
Based on systematic studies of kinetic regularities of heterophase polymerization of styrene and methyl methacrylate (MMA), and study of physical and chemical properties of polymer suspensions, it was established that stable functional polymer suspensions with narrow particle size distribution with diameters from 0.4 to 1.4 μm are formed, when functional organosilicon surfactants are used as stabilizers at 0.5–1.0 wt% surfactant concentration per monomer mass.
Graphical abstract
... They then adopted more ordered conformations with the more hydrophilic oxygen atoms immersed in the subphase and hydrophobic silicone-methyl groups sticking into the air.While most researchers agree on the chain conformation model of regions I and II, more controversy surrounds regions III and IV. Earlier studies using reflected infrared spectroscopy proposed the helix model, which states that upon further compression from region III to IV, the helices slide on each other, which leads to the second increase in surface pressure149,151 . The helical structures of PDMS chains in regions III and IV are similar to the structures found by X-ray diffraction and NMR of PDMS crystals 152,153 . ...
The composition and morphology of cellular membranes are highly dynamic. Potential parameters modulating protein and lipid distributions in different organelles include membrane shapes and the structures of lipids and proteins. Moreover, the concept of "lipid rafts" provides a prevailing view where nanodomains serve as centers for signal transduction, membrane trafficking, and cytoskeletal organization. In this contribution, we first investigated the lipid and protein organizations as a function of membrane curvature. To this end, a system consisting of solid-supported wavy membranes that exhibits a continuous curvature distribution with positive and negative curvature ranges was fabricated. Spatial distributions of ENTH (epsin N-terminal homology) domain and N-BAR (Bin-Amphiphysin-Rvs) domains derived from the proteins Endophilin and BIN-1 were found to vary approximately linearly with membrane curvature. In contrast, streptavidin and fluorescent lipid analogues exhibited homogenous distributions on wavy membranes. Fluorescence recovery after photobleaching and single-molecule tracking experiments revealed that protein domains remain laterally fluid in the curved regions. We next studied the membrane organization with respect to lipid structures, more specifically, the length and degree of saturation of acyl chains of lipids. The ganglioside GM1 binds cholera toxin (CT) on host cells and carries it retrograde from the plasma membrane (PM) through endosomes, the trans-Golgi network (TGN), and the endoplasmic reticulum (ER) to induce toxicity. To elucidate how a membrane lipid can specify trafficking in these pathways, GM1 isoforms with alternate ceramide domains were synthesized and their partitioning between liquid-ordered (Lo) and liquid-disordered (Ld) phases in GUVs was imaged. GM1 with differing ceramides showed distinct phase-partitioning behaviors. Furthermore, crosslinking of GM1 by cholera toxin subunit B (CTB) was found to drive phase partitioning shift from less preferential phase preference to exclusively Ld or Lo phases. To shed light on the stability of lipid domains, factors qwhich affect line tension were discussed and potential line-active molecules were examined. We found that the presence of cone-shaped diacylglycerol decreases line tension, while the commonly used fluorescent lipid, Texas-Red DHPE tends to increase line tension. Additionally, to bridge the connection between thermodynamics to highly dynamic cellular environments, we developed a single liposome-based kinetics system which allowed us to examine membrane binding kinetics of proteins as a function of membrane curvature. Overall, these measurements help provide an integrated view of biophysical and structural parameters underlying organizations of lipids and proteins.
... Note that in all cases the expansion of the compressed samples is not accompanied by a hysteresis, which indicates that no stable structures are formed during the compression. According to the literature data, the isotherms for linear PDMS have two distinctive regions [32]. The first one corresponds to the formation of a monolayer with the surface area per unit equal to 20Å 2 ; the second one is usually considered as a formation of a monolayer consisting of helical PDMS macromolecules, and its further collapse [33]. ...
Comb-like polymethylsiloxanes consisting of a silsesquioxane backbone and dimethylsiloxane side chains were synthesized by means of the “grafting to” method using a linear polyfunctional matrix [SiMe(ONa)O]n and monofunctional oligomers (CH3)3Si[OSi(CH 3)2]nOCOCH3. The effects of architecture of the synthesized methylsiloxane polymers on their physicochemical properties, rheology, and behavior at the air–water interface were studied and compared with those for the linear analogue – polydimethylsiloxane.
... Their distinctive chemistry imparts a range of characteristics, including improved softness, dimensional stability, fabric physical properties, wrinkle recovery, and stretch (Jang & Yeh, 1993). Silicones can also be used to provide hydrophilicity (Mehta, Somasundaran, Maldarelli, & Kulkarni, 2006) or hydrophobicity, static control, lubrication, antimicrobial treatments and anti-slip properties (Abidi, Hequet, & Cabrales, 2009;Gao, Zhu, Guo, & Yang, 2009;Xue, Jia, Zhang, & Ma, 2010). A variety of silicone technologies have different applications in the textile industry (Abidi et al., 2009). ...
Bioinspired membrane molecules with improved physical properties and enhanced stability can serve as functional models for conventional lipid or amphiphilic species. Importantly, these molecules can also provide new insights into emergent phenomena that manifest during self-assembly at interfaces. Here, we elucidate the structural response and mechanistic steps underlying the self-assembly of the amphiphilic, charged oligodimethylsiloxane imidazolium cation (ODMS-MIM+) at the air-aqueous interface using Langmuir trough methods with coincident surface-specific vibrational sum-frequency generation (SFG) spectroscopy. We find evidence for a new compression-induced desolvation step that precedes commonly known disordered-to-ordered phase transitions to form nanoscopic assemblies. The experimental data was supported by atomistic molecular dynamics (MD) simulations to provide a detailed mechanistic picture underlying the assembly and the role of water in these phase transitions. The sensitivity of the hydrophobic ODMS tail conformations to compression─owing to distinct water-ODMS interactions and tail-tail solvation properties─offers new strategies for the design of interfaces that can be further used to develop soft-matter electronics and low-dimensional materials using physical and chemical controls.
Investigation of interfacial proton transport is necessary to elucidate biological systems. As commonly found in biomaterials, the carboxylic acid group was proven to act as a proton-conducting group. This study investigated the influence of carboxylic acid concentration on both interfacial and internal proton transport. Several styrene-based polymers containing the carboxylic acid group were synthesized. The amount of carboxylic acid group in the polymer chain was varied to explore the effects of weak acid concentration on polymer thin films’ electrical properties. The IR p-polarized multiple-angle incidence resolution spectrometry (pMAIR) spectra show the higher ratio of the free carboxylic acid groups rather than cyclic dimers in polymers with a higher concentration of carboxylic acid group, facilitating the more hydrogen bonding networks in films. The water uptake results reveal the similar number of adsorbed water molecules per carboxylic acid group in all thin films. Remarkably, polymer thin films with high carboxylic acid concentration provide internal proton conduction because of the relative increase in the amount of the free carboxylic acid group. In contrast, interfacial proton conduction was found in low carboxylic acid concentration polymers because of the relatively large amount of cyclic dimer carboxylic acid group and poor amount of free carboxylic acid group. This study provides insight into interfacial proton transport behavior according to the weak acid concentration, which might explain proton transport in biological systems.
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The adsorption of proteins and synthetic polymers at the air-water interface (AWI) has broad significance in biomedicine and biotechnology. Protein behavior at the AWI can be guided to control the structure of the two-dimensional biopolymer film. In addition, synthetic polymers affect how plasma proteins act on implant or drug carrier surfaces, and can also decrease the potential for gas embolism. In this thesis, fluorescence microscopy was applied in combination with tensiometry and atomic force microscopy to study plasma proteins at the AWI alone and under the effect of synthetic polymers. First, the morphology of serum albumin layer controlled by the solution conditions was explored by fluorescence microscopy. Heterogeneity at the micron scale was observed for the protein film during adsorption and at reduced concentrations. Moreover, the competition for interfacial area between Pluronic surfactant F-127 and fibrinogen or serum albumin was studied by semi-quantitative confocal fluorescence methods. A transition stage where F-127 and protein underwent lateral phase separation was found. Two competing processes were revealed—the disintegration of protein-rich phase by F-127 and the coalescence of protein phase. Lastly, the interaction of immunoglobulin and the thin film of a widely used polydimethylsiloxane synthetic polymer was studied at the AWI. The compression state of the polymer film was shown to significantly affect protein adsorption and guide proteins into circular domain structures. Overall, this work has demonstrated the wide utility of fluorescence microscopy to study protein-protein and protein-synthetic polymer interactions at the AWI.
Silicone polymers, with their high flexibility, lie in a monolayer at the air water interface as they are compressed until a critical pressure is reached, at which point multilayers are formed. Surface pressure measurements demonstrate that, in contrast, silicones that are end-modified with polar groups take up lower surface areas under compression because the polar groups submerge into the water phase. Boronic acids have the ability to undergo coordination with Lewis bases. As part of a program to examine the surface properties of boronic acids, we have prepared boronic acid-modified silicones (SiBAs) and examined them at the air-water interface to better understand if they behave like other end-functional silicones. Monolayers of silicones, aminopropylsilicones and SiBAs were characterized at the air-water interface as a function of end-functionalization and silicone chain length. Brewster angle and atomic force microscopy confirm domain formation and similar film morphologies for both functionalized and non-functionalized silicone chains. There is a critical surface pressure (10 mN m-1) independent of chain length that corresponds to a first order phase transition. Below this transition the film appears to be a homogeneous monolayer whose thickness is independent of chain length Ellipsometry at the air-water interface indicates that the boronic acid functionality leads to a significant increase of film thickness at low molecular areas that is not seen for non-functionalized silicone chains. What differentiates the boronic acids from simple silicones or other end-functionalized silicones, in particular, is the larger area occupied by the headgroup when under compression, compared to other or non-end-functionalized silicones, which suggests an in-plane rather than submerged orientation that may be driven by boronic acid self-complexation.
Silicones, particularly polydimethylsiloxane (PDMS), are widely exploited for their surface properties. A quantitative review of relevant properties is presented including liquid surface tension measurements, water contact angle studies and solid surface tension determinations from both contact angle and contact mechanics approaches. The properties are considered in the light of the fundamental characteristics of PDMS and related siloxane polymers in order to establish a structure/property relationship of importance in any examination of the surface science of this family of polymers. The central position of PDMS in silicone science and industry follows inevitably from its structure. The combination of small, low-intermolecular-force methyl groups arrayed along the uniquely flexible siloxane backbone produces a polymer whose low surface energy can be equaled or bettered by relatively few other polymers. There is also the additional benefit of greater thermal and oxidative stability than most comparable organic polymers that is important in many applications.
Kinetics of condensation of individual siloxane diols HO[(CH 3)2SiO]xSi(CH3)2OH (x=3,5,6 and 9) with aminoalkyl-alkoxysilanes (RO)2SiR'(CH 2)3NHR'' (R = CH3, CH2CH 3; R' = CH3, OR; R'' = H, (CH2) 2NH2) is described. The second order rate constants point to the significant effect of the siloxane diols chain length on reactivity, which increases for higher homologues (almost an order) of magnitude on coming from x=3 to x=9. The role of substituents at silicon atom is discussed. Three novel functional siloxane oligomers (substrates) are described and characterized.
Polydimethylsiloxanes bearing aminoalkyl groups as terminal or side chain moieties have found a broad application as polymer modifiers, fabric conditioners, release agents, personal care products and hydrophobizing agents. Methods of aminosiloxane synthesis as well as established and future applications of these silicone materials are reviewed.
The interaction between synthetic polymers and proteins at interfaces is relevant to basic science as well as a wide range of applications in biotechnology and medicine. One particularly common and important interface is the air-water interface (AWI). Due to the special energetics and dynamics of molecules at the AWI, the interplay between synthetic polymer and protein can be very different from that in bulk solution. In this paper, we applied the Langmuir-Blodgett technique and fluorescence microscopy to investigate how the compression state of polydimethylsiloxane (PDMS) film at the AWI affects the subsequent adsorption of serum protein, e.g., human serum albumin (HSA) or immunoglobulin G (IgG), and the interaction between PDMS and protein. Of particular note is our observation of circular PDMS domains with micrometer diameters that form at the AWI in the highly compressed state of the surface film: proteins were shown to adsorb preferentially to the surface of these circular PDMS domains, accompanied by a greater than 4-fold increase in protein found in the interfacial film. The PDMS-only film and the PDMS-IgG composite film were transferred to cover glass, and platinum-carbon replicas of the transferred films were further characterized by scanning electron microscopy and atomic force microscopy. We conclude that the structure of the PDMS film greatly affects the amount and distribution of protein at the interface.
Industrial use of enzymes requires high activity, stability, and manageability under technical conditions. Therefore, most biocatalysts are immobilized before use, often by physical adsorption onto a solid carrier. However, a major limitation for the technical use of such immobilizates is the insufficient operational stability under process conditions resulting from enzyme leaching and carrier disintegration. Our group demonstrated recently that for lipase‐catalyzed esterifications these limitations can be largely overcome by the formation of silCoat biocatalysts, composite materials of carrier‐bound enzymes and silicone. Here, we report the successful transformation of this method to the immobilization of carbonyl reductase (CR), an enzyme representing oxidoreductases as a completely different class of biocatalysts. The silCoat biocatalysts cannot be transferred directly to CR because they require an overall hydrophilic surrounding, which opposes the hydrophobicity of silicone. Consequently, the hydrophilization of the material is necessary to achieve reasonable enzyme activity. This was realized by the rational modification of the precursors for silicone formation and applied to increase the leaching stability and mechanical strength of the carrier‐bound CR. The resulting HYsilCoat CR had a significantly longer half‐life than that obtained through the uncoated preparation; the mechanical stability of an alumina carrier was increased by a factor of 120. This enables the consideration of mechanically unstable but environmentally friendly and/or cheap material as an enzyme carrier for industrial use.
Silicone polymers, due to their high lubricity and good spreading properties, are widely used in industrial applications. Being insoluble in water and most hydrocarbons, a common mode of delivering silicones is in the form of emulsions. To stabilize silicones in the emulsion form more efficiently, it is useful to understand the mechanism of emulsion stabilization. Two different mechanisms of emulsion stabilization have been proposed in the past: film formation and precipitation (known as the Pickering mechanism). These two mechanisms are different, and there is a need to further investigate this issue. The aim of the present work was to investigate the mechanism of stabilizing silicone emulsions and to propose a generalized behavior. Several experiments including the measurement of Langmuir isotherms, rheology experiments, phase diagram studies, and microscopy experiments were conducted. All of the above techniques indicated that the functional groups interact strongly with the water phase. The emulsions were found to be stable only if the emulsifiers were soluble in silicone oil or the water phase, and the stability decreased as the emulsifier precipitated. In most cases tested here, the emulsifiers were not observed to precipitate as reported earlier for the Pickering mechanism, and the emulsion stabilization followed film formation. These results should help to predict emulsion stabilization for unknown systems.
We propose the exact values of the tricritical exponents of a collapsing polymer in two dimensions: nu=(4/7, gamma=(8/7, and phi=(3/7. They are obtained in a model of self-avoiding walk on a hexagonal lattice, with random forbidden hexagons, whose percolation threshold gives the exact tricritical point. The infinitely many exact tricritical exponents then derived from Coulomb gas methods are critical exponents of the O(n=1) Ising model below Tc. The numerical check is very good.
Interaction of a Langmuir monolayer of polydimethylsiloxane (PDMS) with different hydrophobic ions added to the aqueous subphase was studied using surface pressure–area and surface potential–area isotherm techniques. For strongly hydrophobic tetraphenylborate (TPB) anions and tetraphenylphosphonium (TPP) cations, a pronounced shift of the monolayer surface potential accompanied by modest variations in the surface pressure isotherms was observed. Effects of TPB and TPP ions were found to be almost identical except the sign of a surface potential shift: it was positive for TPP and negative for TPB. An absolute value of this shift increased with concentration of hydrophobic ions and the monolayer surface density, whereas it was not affected by moderate variations of the subphase ionic strength. An effect of less hydrophobic ions (picrate anion and tetraethylammonium cation) was much less pronounced than that of TPP and TPB. A two-phase distribution model was proposed to describe the behaviour of hydrophobic ions in PDMS monolayer/subphase system. In spite of the extreme simplicity, the model appeared to describe rather well all experimental findings. It was shown that hydrophobic ions are located inside the monolayer. Their surface density is low; however, a shift of the surface potential is pronounced due to the low dielectric constant of monolayer material.
The adsorbed amounts of cyclic and linear poly(dimethylsiloxane) fractions of heterogeneity indices on silica were investigated by Fourier-transform infra-red spectroscopy. It has been found that at low molar masses the adsorption of cyclic polymer is greater than that of the corresponding linear polymer, but at high molar masses the reverse behaviour is found. This is in agreement with the theoretical predictions of van Lent, Scheutjens and Cosgrove. Adsorption of the polymers was investigated in two different solvents, and it was found that the adsorption was greater from hexane than from tetrachloromethane for both linear and cyclic polymers.
It is shown how the molecular weight dependence of the radius of gyration ${R}_{F2}$ of two-dimensional polymeric chains can be derived from surface-pressure isotherms in Langmuir monolayers. ${R}_{F2}$ scales as ${N}^{$\nu${}}$ with $$\nu${}=0.56$ for polymethylmethacrylate and 0.79 for polyvinylacetate. These values are in agreement with the scaling predictions for tricritical and excluded-volume behaviors, respectively. The crossover between the dilute and the intermediate regimes is also clearly observed in one case.
An investigation has been made of the surface properties of some organo-silicon compounds, with particular reference to their orientation on a water surface and their efficiency as boundary lubricants. New silicones of the types CH3[(CH3)2SiO]n . Si(CH 3)2CH2Cl, CH3[(CH3) 2SiO]n . Si(CH3)2CH2OH and CH2OH[(CH3)2SiO]n . Si(CH 3)2CH2OH have been prepared, and their force-area and potential-area curves on water obtained. The results show that at low pressure all the silicone molecules are lying flat on the water surface. At a pressure of 8-10 dynes cm.-1 collapse occurs, and the siloxane chain lifts out of the water. With the hydroxyl compounds the curves obtained show that the molecule is anchored by the -OH group. Close packing of the molecules does not occur even under a pressure of 25 dynes cm.-1 because of the small lateral adhesion between the siloxane chains. The behaviour of silicones as boundary lubricants on steel is discussed in relation to the possible orientation of the monolayers on the metal surface. Silicones are less effective than polar hydrocarbons in reducing metallic contact.
A new family of zwitterionic organofunctional siloxanes of the general formula Me3SiO(SiMe2O)x-(SiMeR(1)O) ySiMe3 (R(1) = (CH2)3NR(2)2+-(CH2) zSO3-; R(2) = CH3, CH2CH3, CH2CH2OH; x = 0-3, y = 1, 2, z = 3, 4) have been prepared and characterized both structurally and as aqueous surfactants. They are prepared by the quaternization of the precursor amino functional siloxane with either cyclic 1,3-propanesultone or cyclic 1,4-butanesultone. They were structurally characterized by elemental analysis, proton and silicon-29 NMR, and IR spectroscopies. Members of this family reduced the surface tension of water to approximately 21 mN/m at concentration levels of 0.005-0.5 wt %. The species where x = 0 and y = 1 displayed very rapid lowering of the surface tension of water. These silicone surfactants demonstrated adequate shelf life stability as the isolated compound or in aqueous solution between pH 5 and 8. Aqueous instability of some of these solutions could be attributed to hydrolysis and subsequent rearrangement of the Si-O-Si bonds in these molecules, yielding hexamethyldisiloxane as a byproduct.
Relationships of film pressure (F) vs. area (A), surface potential (ΔV) vs. A, and the vertical component of the surface dipole moment (μp) vs. A were studied of two groups of liquid polysiloxanes, (CH3)3Si[OSi-(CH3)(R)]nOSi(CH 3)3, spread on water as adsorbed monolayers. In the first group R is either CH3, C2H5, or n-C4H9 and n is 14 or 12; in the second group R is (CH2)2CF3, and n varies as the 25° viscosities of the polymers range from 72 to 1000 cSt. For any given area in the first group, the three surface-physical properties measured decreased in value as the carbon number increased. The F vs. A isotherms of the second group of polymers are similar to one another but are different from the members of the first group. The electrical properties (ΔV vs. A and μp vs. A) show that the net dipole moment per monomer of the (CH2)2CF3 substituted polysiloxanes is oriented with the negative end away from the water, i.e., in the opposite direction from that of the n-alkyl substituted polymers. It was possible to compute, under a given set of conditions, μp of the terminal CF3 group only, and the values are in good agreement with those found by us in an earlier investigation of progressively fluorinated n-alkanoic carboxylic acids adsorbed closely packed on water. All results are discussed in terms of chain length and fluorine subsitution for hydrogen in the alkyl side chains, tactic configuration, effects of steric hindrances of the substituents, and possible molecular arrangements of the various adsorbed polymer chains. It is concluded that the difference in magnitude and sign of μp per close-packed, well-oriented monomer is highly indicative of a major difference in the biochemical and medical properties of these two classes of poly(organosiloxanes).
Detailed surface pressure measurements have been performed in the dilute regime for Langmuir monolayers of atactic poly(methyl methacrylate) chains spread at the air-water interface. Marked deviations from the ideal gas law give clear evidence for attractive interactions between the two-dimensional polymer chains. The second virial coefficient is negative and scales with the chain molecular weight as A22Γ ∝ M2v when the concentration is measured in units of the number of chains Γ = c/M. For chains with molecular weights between 3250 and 18600, we obtain v = 0.57 ± 0.03 for the Flory exponent describing the single-chain conformation RG ∝ Nv. This new, and independent, derivation of the v exponent in two dimensions is in complete agreement with the value based on the concentration dependence of the surface pressure in the semidilute regime. This is the first time that the molecular weight dependence of the second virial coefficient is clearly established for polymer chains in two dimensions.
A method is developed for the detailed atomistic modeling of well-relaxed amorphous glassy polymers. Atactic polypropylene at -40°C is used as an example. The model system is a cube with periodic boundaries, filled with segments from a single "parent" chain. An initial structure is generated by using a modified Markov process, based on rotational isomeric state theory and incorporating long-range interactions. This structure is then "relaxed" by potential energy minimization, using analytical derivatives. Computing time is kept relatively small by stagewise minimization, employing a technique of "blowing up" the atomic radii. Model estimates of the cohesive energy density and the Hildebrand solubility parameter agree very well with experiment. The conformation of the single chains in the relaxed model system closely resembles that of unperturbed chains. Pair distribution functions and bond direction correlation functions show that the predominant structural features are intramolecular and that long-range orientational order is completely absent.
Diffusion coefficients, radii of gyration, and second virial coefficients of short polystyrene chains have been measured by dynamic light scattering, small-angle neutron scattering, and static light scattering. Deviations from the established exponential laws at high molecular weights are observed in all cases. The hydrodynamic behavior can equally well be described by Kirkwood's diffusion equation, if the free draining term is properly taken into account, and by the Yamakawa-Fujii theory of cylindrical wormlike chains. The enhanced increase of A2 for short chains is caused by the inherent chain stiffness. Satisfactory agreement of the Stockmayer-Yamakawa theory with experiment is obtained if a 45% higher Kuhn length is assumed in toluene at 20°C than in cyclohexane at 34.5°C.
Surface pressure π has been measured as a function of surface concentration c for monolayers of linear and cyclic poly(dimethylsiloxane) (PDMS) of molecular weight 730-14 800, spread on water and tricresyl phosphate at 26.0°C. In the transition region where the surface pressure rises much more rapidly than proportional to the surface concentration, the findings for linear and cyclic PDMS were indistinguishable and independent of molecular weight. The findings in this region could be described as power laws with powers corresponding to scaling predictions for the semidilute region of concentrations (coil overlap accompanied by low overall polymer concentration) on near-θ and fairly good surface solvents, respectively. However the second virial coefficient of the surface pressure appeared to be negative for both liquid supports. These observations, the fact that the transition region occurred at quite high fractional surface coverage, and the instability of films from small oligomers suggest that recent interpretations of behavior in the transition region in terms of predictions for a semidilute surface solution are invalid in this case. The existence of a semidilute region of concentrations for polymer monolayers is uncertain in principle. In addition the comparisons of linear and cyclic polymer above the overlap concentration c* lead to the surprising conclusion that even for three-dimensional semidilute solutions, the ratio c/c* is not a universal reduced concentration.
The phase behavior of long hydrophobic A−B type silicone surfactants, Me3SiO−(Me2SiO)m-2−Me2SiCH2CH2CH2−O−(CH2CH2O)nH (SimC3EOn), in water and water + octamethylcyclotetrasiloxane (D4) was investigated by studying phase behavior and small-angle X-ray scattering. Si25C3EO15.8 forms a reverse micellar cubic phase (I2) in water and water + D4 systems. This cubic phase is highly thermally stable in a surfactant−water binary system. The thermal stability decreases monotonically with addition of silicone oil. Although the solubilization of water in the reverse cubic phase is low, a very large amount of excess water can be incorporated in a so-called reverse cubic phase based concentrated emulsion. The emulsion stability is enhanced upon addition of silicone oil. D4 molecules penetrate into the surfactant palisade layer in the reverse micelles forming the I2 phase and expand the effective cross-sectional area per surfactant, aS (penetration). The continuous penetration of oil destabilizes the I2 phase structure, and therefore the melting temperature of the phase decreases. The incorporation of D4 into the I2 phase in the aqueous mixtures of Si14C3EO7.8, Si25C3EO7.8, Si25C3EO12.2, and Si25C3EO15.8 varies with both the hydrophilic and lipophilic chain lengths of silicone surfactants.
The pseudophase separation model is used to describe pH and concentration effects on dimethyldodecylamine oxide (DDAO) solutions. If the protonated and neutral species are treated as separate surfactants, an amine oxide surfactant can be modeled thermodynamically as a binary mixture, the composition of which is varied by adjusting the solution pH. With the Gibbs-Duhem equation written for the micelle pseudophase, activities of the surfactant species at concentrations greater than the critical micelle concentration (cmc) can be calculated directly from experimental titration curves. It is not necessary to introduce an "apparent" pKa for the surfactant in micellar form.
The formation of Langmuir monolayers from poly(dimethylsiloxane) oligomers (molecular weights of 900-4000) terminated with methyl, hydroxyl, epoxide, carboxyl, and amine groups is described. The isotherms (except for oligomers with molecular weights below 1500) show the characteristic transitions commonly observed for methyl-terminated PDMS. In addition, the functionally-terminated materials show a transition associated with orientation of the PDMS chains normal to the surface to form a close-packed monolayer. For oligomers with molecular weights below 1000 this transition overlaps the standard configurational transitions, and the overall shape of the isotherm is determined by the oligomer molecular weight, the functional group, and the nature of the subphase. Most of the materials have cross-sectional areas at collapse of about 100 Å2/chain, consistent with a structure where the molecules form helices oriented perpendicular to the surface of the subphase. Shorter amine-terminated materials have areas as low as 50-60 Å2/chain, consistent with the formation of extended cis-trans caterpillar structures oriented normal to the subphase surface.
We report the first direct measurements of the molecular weight distribution in transferred condensed monolayers of amphiphilic oligomers determined by time-of-flight secondary ion mass spectrometry (TOFSIMS). Two α,ω-functional oligomers of poly(dimethylsiloxane) are investigated, comprising pentylamine and propylcarboxy end groups. Measurements are performed directly on condensed monolayer films transferred to silver-coated substrates using the Langmuir-Blodgett-Kuhn (LBK) technique. These results are compared to the original distributions measured on submonolayer thin films of the original oligomers prepared by spin coating onto silver-coated substrates and to molecular weight determinations provided by end group titration and size exclusion chromatography analyses. Different families of ions are found for the two different thin film preparation methods. A number of tentative assignments are proposed for these masses, based upon consideration of the effects of the LBK film deposition process and the influence of interactions between the end groups and the substrate. The molecular weight distributions for LBK films of both oligomers is found to be narrower and shifted to higher molecular weights than are those for the corresponding spin-coated films. The changes in molecular weight distribution observed are attributed to dissolution of lower molecular weight species into the aqueous subphase during the LBK film deposition process.
Surface activity at the interface of organic liquids with air has been studied by direct observation of the force-area properties of surface films. The all-Teflon film balance developed for this purpose and the special techniques required are discussed. Liquid substrates studied include n-hexadecane, white mineral oil and tricresyl phosphate. On n-hexadecane and tricresyl phosphate, a linear polymethylsiloxane of high molecular weight was spread from solution to form monolayers having limiting cross-sectional areas which agree well with each other and with those found by other methods. Spreading coefficients of four liquids on white mineral oil could be measured using the piston film technique. From these the liquid/liquid interfacial tensions were calculated. For two of these spreading liquids the interfacial tensions against white mineral oil were determined by the ring method and agreed to 0.1 dyne/cm. with the calculated values. Films of zein could be spread from solution on the surface of tricresyl phosphate. The results suggest that this protein can be spread on the organic liquid substrate without the denaturation that accompanies its spreading on water. Many other compounds were found to be surface active on organic liquids. Among these were other silicones, organic silicates, polyacrylates, polyalkylene ethers and fluorocarbon derivatives. A plausible explanation of the defoaming power of polymethylsiloxanes for organic liquids is offered.
The absolute entropy of the chloride ion in six different concentrations of hydrochloric acid, ammonium chloride, sodium chloride, and potassium chloride at a mean temperature of 12.5°C. has been calculated from data obtained from thermocells, using silver-silver chloride electrodes.
Linear organosiloxanes with various substituents differ in their spreading velocities and with respect to the film structure formed on aqueous substrates. The material investigated allows a distinction between siloxanes in which the molecules placed on the subphase in helical form become oriented on the surface of the water to form “spreading chains” and siloxanes in which this is not the case. It is believed that hydrogen bridging is responsible for the orientation effect.
Within the first group, a distinction can be made between polymers which on strong compression are lifted off from the water and can be returned to the helical form, and those in which due to great hydrophilicity of the substituents release of “dry” spreading chains from the water can not be achieved. Methyl-substituted siloxanes, among them especially the dimethyl- and methyl-H-siloxanes, show quick spreading and good orientability. This may explain why these siloxanes play such an important role since the beginning of silicone technology up to the present day as interfacially active substances. But this behavior is not representative for organosiloxanes in general.
The structure of the siloxane skeleton seems to have no decisive influence on the spreading phenomena. Branched or crosslinked methylsiloxanes behave similar to the linear ones and form also, by and large, monomolecular films.
Hydrate phases, i.e., mixed phases of the spread substance and the subphase, play an important part in the interpretation of the force/area (F/A) isotherms.
The structure changes accompanying phase transitions in poly(diethylsiloxane) (PDES) have been studied by WAXS and SAXS techniques using oriented and isotropic samples. PDES may exist in two low-temperature modifications (the monoclinic α1-form and presumably the “tetragonal” β1-form) and two high-temperature modifications (the monoclinic α2-form and the “tetragonal” β2-form). In linear PDES the crystal - crystal transitions α1–α2 and β1–β2 occur near 214 and 206 K, respectively. At higher temperatures α2 (280 K) and β2 (290 K) forms transform into the mesomorphic phase αm that gradually melts at 280–300 K giving an amorphous phase. According to x-ray and density data, αm phase is also characterized by monoclinic structure slightly different from hexagonal packing.
Polymer monolayers spread at the air/water interface were obtained for: poly(monooctyl itaconate) (PMOI), poly(monodecyl itaconate) (PMDI), poly(monododecyl itaconate) (PMDoI), poly(monobenzyl itaconate) (PMBzI), poly(methyldodecyl itaconate) (PMeDoI) and the alternating copolymer (monooctyl itaconate-alt-maleic anhydride) (MOI-alt-MA). By monolayer compression at constant temperature, the respective Langmuir isotherms for these polymers were obtained. For all polymers the zero-pressure limiting area per repeating unit (ru) Ao, and the collapse pressure πc were determined. At low surface polymer concentrations, the monolayers characterization was carried out according to the surface pressure expressed as a function of the surface concentration. The behavior observed was described by the virial expansion development. At the semidilute region, the surface pressure variation was expressed in terms of the scaling laws as a power function of the surface concentration.
Measurements of the two-dimensional surface pressure π have been made as a function of average area per monomer A at areas too small to support a single monolayer, for films of cyclic and linear poly(dimethylsiloxane) (PDMS) spread on the surface of water at temperatures between 6°C and 31°C. The number-average numbers of monomer units were 10 to 196 for the rings and 10 to 1.2 × 105 for the linear chains. The surface pressures were stable with time for films formed from molecules with more than 20 monomer units. For these films, two plateaux of surface pressure linked by a rounded step were observed for both rings and chains, and the step occurred at the same average area per monomer. However, although the levels of the plateaux were the same for films formed from all linear species, increases in levels of the plateaux with decreasing number of monomer units were observed for cyclic species. The temperature coefficient of the surface pressure was negative in all instances, suggesting that surface entropy is gained upon compression. The unstable films formed from the linear and cyclic decamers were also studied. The former displayed a step in the plateau region, the latter did not appear to. The present findings suggest that cyclic and linear PDMS with more than 20 monomer units collapse by a common mechanism. If the long-standing hypothesis that PDMS collapses by adopting a helical configuration is correct, this implies that rings with as few as 20 repeat units on the average coil into helices.
Surface pressure (π) of monolayers of two polyethers, i.e., poly(ethylene oxide) and poly(tetrahydrofuran) at the air-water interface have been measured as a function of surface polymer concentration (Γ) at 22°C using the surface balance with the sensitivity of 0.03 dyn cm−1. Poly(ethylene oxide) and poly(tetrahydrofuran) with sharp molecular weight distributions were used. Both polyether monolayers showed the condensed-type surface pressure-area isotherm. At the lower polymer concentration the surface pressure was interpreted by the virial expansion form and the number average molecular weight can be determined by extrapolation of π/ΓRT to Γ = 0, showing very good agreement with the weight average molecular weight. It was found that the air-water interface at 22°C corresponds to a good solvent condition for both polyethers. At the intermediate polymer concentration the exponent for the concentration dependence of surface pressure was in excellent agreement with that predicted from the scaling concepts.
A homologous series of polydimethylsiloxanes were spread as insoluble monomolecular films on water and on a number of organic liquids. The organic liquids studied as substrates were tricresyl phosphate, propylene carbonate, diethylphthalate, bis(2-ethylhexyl)adipate, and hexadecane. Monolayer stability and insolubility were found to vary with the molecular weight of the polydimethylsiloxane and the polarity of the substrate liquid. Stable, reversible monomolecular films were formed on all substrates by the higher molecular weight polymers (molecular weight > 6,000); however, film stability decreased with decreasing polymer molecular weight and decreasing substrate polarity.The orientations of the polydimethylsiloxane films at the organic liquid/air interfaces, as inferred from these studies, appeared to be functions of the surface composition of the substrate liquids. On tricresyl phosphate and propylene carbonate the high molecular weight polymers adsorbed in a fully extended configuration at large areas/molecule, analogous to their behavior on water. Upon compression the film pressure vs. area/molecule curves suggested they assumed a helical configuration. On the less polar substrates the higher molecular weight polydimethylsiloxanes apparently remained in the helical configuration regardless of the state of compression. Owing to the instability and/or solubility of the lower molecular weight polydimethylsiloxane monolayers on the less polar substrates, no conclusions were made regarding changes in molecular orientation as a function of film pressure.
Silicone surfactants are becoming increasingly important in the pharmaceutical and cosmetic industry, because of their versatility, low cost, and technological advantages. The present study was designed to measure the critical micellar concentration of three non-ionic silicone surfactants, one water-soluble and two lipid-soluble. We measured surface tension with a technique based on drop geometry. Solubility and dispersibility in water were tested in the two lipophilic surfactants with visible and UV light spectrophotometry. The data obtained with all techniques showed a characteristic behavior of lipophilic silicone surfactants, which did not entirely conform to the definition of critical micellar concentration.
Silicone Oil Systems
- Surfactants
Surfactants/Silicone Oil Systems. Langmuir 2001, 17, 5169- 5175.
Concentration dependence of surface pressure of polyether monolayers at the air-water interface Exact tricritical exponents for polymers at the theta point in two dimensions
- M Kamaguchi
- S Komatsu
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- A Takahashi
Kamaguchi, M.; Komatsu, S.; Matsuzumi, M.; Takahashi, A. Concentration dependence of surface pressure of polyether monolayers at the air-water interface. J. Colloid Interface Sci. 1984, 102 (2), 356-360. (33) Duplantier, B.; Saleur, H. Exact tricritical exponents for polymers at the theta point in two dimensions. Phys. ReV. Lett. 1987, 59 (5), 539-542.
Hydrodynamic and thermodynamic behavior of short chain polystyrene in toluene and cyclohexane at 34.5 °C Figure 6. Plot of ln π vs ln Γ in the semidilute region of the surface pressure-area isotherm to obtain the characteristic critical exponent of excluded volume. π ) Γ dν
- K Huber
- S Bantle
- P Lutz
- W Burchard
Huber, K.; Bantle, S.; Lutz, P.; Burchard, W. Hydrodynamic and thermodynamic behavior of short chain polystyrene in toluene and cyclohexane at 34.5 °C. Macromolecules 1985, 18, 1461-1467. Figure 6. Plot of ln π vs ln Γ in the semidilute region of the surface pressure-area isotherm to obtain the characteristic critical exponent of excluded volume. π ) Γ dν/(dν -1)
X-ray investigation of the structure of silicone rubber
- G Damaschun
Damaschun, G. X-ray investigation of the structure of silicone rubber.
Organosilicone having a carboxyl functional group thereon
- A Berger
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Berger, A.; Fost, D. L. Organosilicone having a carboxyl functional group thereon. U.S. Patent 5,596,061, 1997; U.S. Patent 5,807,955, 1998. (28) de Gennes, P. G. Sclaing concepts in polymer physics; Cornell University Press: Ithaca, New York, 1979.
Synthesis and characterization of zwitterionic silicone sulfobetaine surfactants) Banks, W. H. Surface films of polydimethylsiloxanes on organic liquid substrates
- M J Owen
Owen, M. J. Synthesis and characterization of zwitterionic silicone sulfobetaine surfactants. Langmuir 1990, 6, 385-391. (11) Banks, W. H. Surface films of polydimethylsiloxanes on organic liquid substrates. Nature 1954, 174, 365-366.
Exact tricritical exponents for polymers at the theta point in two dimensions Hydrodynamic and thermodynamic behavior of short chain polystyrene in toluene and cyclohexane at 34.5 °C
- B Duplantier
- H Saleur
- K Huber
- S Bantle
- P Lutz
- W Burchard
(33) Duplantier, B.; Saleur, H. Exact tricritical exponents for polymers at the
theta point in two dimensions. Phys. ReV. Lett. 1987, 59 (5), 539-542.
(34) Huber, K.; Bantle, S.; Lutz, P.; Burchard, W. Hydrodynamic and
thermodynamic behavior of short chain polystyrene in toluene and cyclohexane
at 34.5 °C. Macromolecules 1985, 18, 1461-1467.