Langmuir (Langmuir)

Publisher: American Chemical Society, American Chemical Society

Journal description

Langmuir is devoted to reporting new and original experimental and theoretical research of interest to chemists and chemical physicists in the fields of surface and colloid chemistry. Coverage includes such topics as micelles, visicles, emulsions, gels, surfacants, colloids, crystal growth, nucleation, liquid crystals, imaging spectroscopy, electro-chemistry, biological colloids & interfaces, biopolymers, nanostructures, multicomponent systems, and materials. In addition to these structures, Langmuir also carries articles on theory, simulation, modeling and experimental developments. Along with national award-winning lectures, Langmuir regularly features letters, articles, reviews, commentaries, notes, and special issues.

Current impact factor: 4.38

Impact Factor Rankings

2015 Impact Factor Available summer 2015
2013 / 2014 Impact Factor 4.384
2012 Impact Factor 4.187
2011 Impact Factor 4.186
2010 Impact Factor 4.268
2009 Impact Factor 3.898
2008 Impact Factor 4.097
2007 Impact Factor 4.009
2006 Impact Factor 3.902
2005 Impact Factor 3.705
2004 Impact Factor 3.295
2003 Impact Factor 3.098
2002 Impact Factor 3.248
2001 Impact Factor 2.963
2000 Impact Factor 3.045
1999 Impact Factor 2.937
1998 Impact Factor 2.813
1997 Impact Factor 2.852
1996 Impact Factor 3.47
1995 Impact Factor 3.143
1994 Impact Factor 3.232
1993 Impact Factor 2.628
1992 Impact Factor 2.638

Impact factor over time

Impact factor
Year

Additional details

5-year impact 4.42
Cited half-life 6.70
Immediacy index 0.79
Eigenfactor 0.21
Article influence 1.16
Website Langmuir website
Other titles Langmuir (Online), Langmuir
ISSN 1520-5827
OCLC 39280622
Material type Document, Periodical, Internet resource
Document type Internet Resource, Computer File, Journal / Magazine / Newspaper

Publisher details

American Chemical Society

  • Pre-print
    • Author cannot archive a pre-print version
  • Restrictions
    • Must obtain written permission from Editor
    • Must not violate ACS ethical Guidelines
  • Post-print
    • Author cannot archive a post-print version
  • Restrictions
    • If mandated by funding agency or employer/ institution
    • If mandated to deposit before 12 months, must obtain waiver from Institution/Funding agency or use AuthorChoice
    • 12 months embargo
  • Conditions
    • On author's personal website, pre-print servers, institutional website, institutional repositories or subject repositories
    • Non-Commercial
    • Must be accompanied by set statement (see policy)
    • Must link to publisher version
    • Publisher's version/PDF cannot be used
    • If mandated sooner than 12 months, must obtain waiver from Editors or use AuthorChoice
    • Reviewed on 07/08/2014
  • Classification
    ​ white

Publications in this journal

  • Qi Wei, Fanhua Hu, Liyuan Wang
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    ABSTRACT: A few kinds of 2-diazo-1-naphthoquinone-4-sulfonates of poly (4-hydroxylstyrene) were prepared to form one-component i-line photoresists. In the laser interference lithography experiments of some of the photoresists, nano tunnels were observed aligned in the inner of the resist film. The shape and size of the nano tunnels keep virtually unchanged even under increased exposure dose, indicating that the exposure energy is confined within the tunnel space. The formation of the nano-tunnels is resulted from the effect of standing wave and permeation of the developer from the surface into the deep of the resist films.
    Langmuir 05/2015; DOI:10.1021/acs.langmuir.5b00194
  • Paul Chapman, Robert E Ducker, Claire R Hurley, Jamie Kayne Hobbs, Graham J Leggett
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    ABSTRACT: Poly(oligoethylene glycol methyl ether methacrylate) (POEGMEMA) brushes, grown from silicon oxide surfaces by surface-initiated atom transfer radical polymerization (SI-ATRP), were end-capped by reaction with sodium azide leading to effective termination of polymerization. Reduction of the terminal azide to an amine, followed by derivatization with the reagent of choice, enabled end-functionalization of the polymers. Reaction with bromoisobutryl bromide yielded a terminal bromine atom that could be used as an initiator for ATRP with a second, contrasting monomer (methacrylic acid). Attachment of a nitrophenyl protecting group to the amine facilitated photopatterning: when the sample was exposed to UV light through a mask, the amine was deprotected in exposed regions, enabling selective bromination and the growth of a patterned brush by ATRP. Using this approach, micropatterned pH-responsive poly(methacrylic acid) (PMAA) brushes were grown on a protein resistant planar poly(oligoethylene glycol methyl ether methacrylate) (POEGMEMA) brush. Atomic force microscopy analysis by tapping mode and Peak Force quantitative nanomechanical mapping (QNM) mode allowed topographical verification of the spatially specific secondary brush growth and its stimulus-responsiveness. Chemical confirmation of selective polymer growth was achieved by secondary ion mass spectrometry (SIMS).
    Langmuir 05/2015; DOI:10.1021/acs.langmuir.5b01067
  • Gustavo González-Gaitano, Marcelo Alves da Silva, Aurel Radulescu, Cecile A Dreiss
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    ABSTRACT: Inclusion complexes between cyclodextrins (CDs) and polymers - so-called pseudopolyrotaxanes (PPR) - are at the origin of fascinating supramolecular structures, which are finding increasing uses in biomedical and technological fields. In this work, we explore the complexation of a range of cyclodextrins with Tetronic T1307, a four-arm block-copolymer of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) with a pH-responsive central ethylene diamine spacer, and its impact on micellisation and sol-gel transition. At low concentrations, small-angle neutron scattering (SANS) combined to dynamic light scattering (DLS) measurements show the presence of spherical micelles with a highly hydrated shell and a dehydrated core. Increasing the temperature leads to more compact micelles and larger aggregation numbers, while acidic conditions induce a shrinking of the micelles, with fewer unimers per micelle and a more hydrated corona. At high concentrations, T1307 undergoes a sol-gel transition, which is suppressed at pH below pKa,1 (4.6). SANS data analysis reveals that the gels result from a random packing of the micelles, which have an increasing aggregation number and increasingly dehydrated shell and hydrated core. Native CDs (α, β, γ-CD) can complex T1307, resulting in the precipitation of a PPR. Instead, modified CDs compete with micellisation, to an extent that is critically dependent on the nature of the substitution. 1H and ROESY NMR combined to SANS demonstrate that di-methylated β-CD can thread onto the polymer, preferentially binding to the PO units, thus hindering self-aggregation by solubilizing the hydrophobic block. The various CDs are able to modulate the onset of gelation and the extent of the gel phase, and the effect correlates with the ability of the CDs to disrupt the micelles, with the exception of a sulfated sodium salt of β-CD, which, while not affecting the CMC or CMT, is able to fully suppress the gel phase.
    Langmuir 05/2015; DOI:10.1021/acs.langmuir.5b01081
  • Kathleen McEnnis, Anthony D Dinsmore, Thomas P Russell
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    ABSTRACT: Particles adsorbed on microscopic polystyrene (PS) capillary bridge surfaces were observed to investigate their motion under capillary forces arising from a nonuniform shape. Capillary bridges were created by placing thin PS films, heated above the glass transition temperature (Tg), between two electrodes with an air gap between the surface of the PS and the upper electrode. Silica particles, 100 nm in diameter, were placed on the surface of the PS capillary bridges, and the sample was heated above the Tg of PS to enable particle motion. Samples were cooled to below Tg, and the locations of the particles were observed using scanning electron microscopy. The particles did not preferentially locate around the center of the capillary bridge, as predicted by others, but instead segregated to the edges. These results indicate that the forces driving particles to the three-phase contact line (air/PS/electrode surface) are greater than those locating particles around the center.
    Langmuir 05/2015; DOI:10.1021/acs.langmuir.5b00372
  • Taro Yoshikawa, Verena Zuerbig, Fang Gao, René Hoffmann, Christoph E Nebel, Oliver Ambacher, Vadim Lebedev
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    ABSTRACT: Mono-sized (~4 nm) diamond nanoparticles arranged on substrate surfaces are exciting candidates for single photon sources and nucleation sites for ultra-thin nanocrystalline diamond film growth. The most commonly used technique to obtain substrate supported diamond nanoparticles is electrostatic self-assembly seeding using nanodiamond colloidal suspensions. Currently, monodisperse nanodiamond colloids, which have a narrow distribution of particle sizes centering on the core particle size (~4 nm), are available for the seeding technique on different substrate materials such as Si, SiO2, Cu, and AlN. However, the self-assembled nanoparticles tend to form small (20 - 100 nm) aggregations on any of those substrate materials. In this study, this major weakness of self-assembled diamond nanoparticles was solved by modifying the salt concentration of nanodiamond colloidal suspensions. Several salt concentrations of colloidal suspensions were prepared using potassium chloride as an insert electrolyte and examined for the seeding on SiO2 surfaces. The colloidal suspensions and the seeded surfaces were characterized by dynamic light scattering and atomic force microscopy, respectively. Also, the interaction energies between diamond nanoparticles in each of the examined colloidal suspensions were compared based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. From these investigations, it became clear that the appropriate salt concentration suppresses the formation of small aggregations during the seeding process owing to the modified electrostatic repulsive interaction between nanoparticles. Finally, mono-sized (<10 nm) individual diamond nanoparticles arranged on SiO2 surfaces have been successfully obtained.
    Langmuir 05/2015; DOI:10.1021/acs.langmuir.5b01060
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    ABSTRACT: Gas-phase equilibrium adsorption of D- and L-serine (Ser) mixtures and D- and L-phenylalanine (Phe) mixtures has been studied on the naturally chiral Cu{3,1,17}(R&S) surfaces. (13)C-labeling of the L-enantiomers (*L-Ser and *L-Phe) has enabled mass spectrometric enantiodiscrimination of the species desorbing from the surface following equilibrium adsorption. On the Cu{3,1,17}(R&S) surfaces, both equilibrium adsorption and the thermal decomposition kinetics of the D- and *L-enantiomers exhibit diastereomerism. Following exposure of the surfaces to D-/*L- mixtures, the relative equilibrium coverages of the two enantiomers is equal to their relative partial pressures in the gas phase, θD⁄θ*L = PD⁄P*L . This implies that adsorption is not measurably enantiospecific. The decomposition kinetics of Ser are enantiospecific while those of Phe are not. Comparison of the observation with those of aspartic acid, alanine and lysine suggests that enantiospecific adsorption on the natural chiral Cu surfaces occurs for those amino acids that have side chains with functional groups that allow strong interactions with the surface. There is no apparent correlation between amino acids that exhibit enantiospecific adsorption and those that exhibit enantiospecific decomposition kinetics.
    Langmuir 05/2015; DOI:10.1021/acs.langmuir.5b00707
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    ABSTRACT: Monodisperse, nonmagnetic, asymmetrical composite dumbbells in a suspension of magnetic nanoparticles (ferrofluid) were aligned by application of an external magnetic field to the ferrofluid. The asymmetrical composite dumbbells were prepared by two-step soap-free emulsion polymerization consisting of the first polymerization to coat spherical silica cores with cross-linked polymethylmethacrylate (PMMA) shell and the second polymerization to protrude a polystyrene (PSt) lobe from the core-shell particles. A chain structure of nonmagnetic dumbbells oriented to the applied magnetic field was observed at nanoparticle content of 2.0 vol% and field strengths higher than 1.0 mT. A similar chain structure of the dumbbells was observed under application of alternating electric field at strengths higher than 50 V/mm. Parallel and orthogonally combined applications of the electric and magnetic fields were also conducted to examine independence of the electric and magnetic applications as operational factors in the dumbbell assembling. Dumbbell chains stiffer than those in a single application of external field were formed in the parallel combined application of electric and magnetic fields. The orthogonal combination of the different applied fields could form a magnetically aligned chain structure of the nonmagnetic dumbbells oriented to the electric field. The present work experimentally indicated that the employment of inverse magnetorheological effect for nonmagnetic, anisotropic particles can be a useful method for the simultaneous controls over the orientation and the positon of anisotropic particles in their assembling.
    Langmuir 04/2015; DOI:10.1021/acs.langmuir.5b00737
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    ABSTRACT: Blockage of pipelines by formation and accumulation of clathrate hydrates of natural gasses (also called gas hydrates) can compromise project safety and economics in oil and gas operations, particularly at high pressures and low temperatures such as those found in subsea or arctic environments. Cyclopentane (CyC5) hydrate has attracted interest as a model system for studying natural gas hydrates, because CyC5, like typical natural gas hydrate formers, is almost fully immiscible in water; and thus CyC5 hydrate formation is governed not only by thermodynamic phase considerations but also kinetic factors such as hydrocarbon/water interfacial area and mass & heat transfer, as for natural gas hydrates. We present a macro-scale investigation of the formation and adhesion strength of CyC5 hydrate deposits on bilayer polymer coatings with a range of wettabilities. The polymeric bilayer coatings are developed using initiated chemical vapor deposition (iCVD) of a mechanically-robust and densely-cross-linked polymeric base layer (poly-divinyl benzene or pDVB) that is capped with a covalently-attached thin hydrate-phobic fluorine-rich top layer (poly-perfluorodecylacrylate or pPFDA). The CyC5 hydrates are formed from CyC5-in-water emulsions, and differential scanning calorimetry (DSC) is used to confirm the thermal dissociation properties of the solid hydrate deposits. We also investigate the adhesion of the CyC5 hydrate deposits on bare and bilayer polymer-coated silicon and steel substrates. Goniometric measurements with drops of CyC5-in-water emulsions on the coated steel substrates exhibit advancing contact angles of 148.3º ± 4.5º and receding contact angles of 142.5º ± 9.8º, indicating the strongly emulsion-repelling nature of the iCVD coatings. The adhesion strength of the CyC5 hydrate deposits reduced from 220±45 kPa on rough steel substrates to 20±17 kPa on the polymer-coated steel substrates. The measured strength of CyC5 hydrate adhesion is found to correlate very well with the work of adhesion between the emulsion droplets used to form the CyC5 hydrate and the underlying substrates.
    Langmuir 04/2015; DOI:10.1021/acs.langmuir.5b00413
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    ABSTRACT: Little is known concerning the interface between a polyelectrolyte multilayer, PEMU, and its substrate. Recent models suggest that excess polymer charge, compensated by counterions, remains buried within the PEMU, especially for thicker films having a nonlinear component to their growth. We report a novel approach for making free-standing multilayers of poly(diallyldimethylammonium) (PDADMA) and poly(styrenesulfonate) (PSS): after assembly on aluminum substrates, films were released by brief immersion in aqueous alkali. The multilayers were then flipped, allowing access to the initially buried substrate/PEMU interface. Experiments were performed to show that this method of release, one of many established for PEMUs, perturbed the surface and bulk of the film minimally. Film/solution and film/substrate interfaces were compared using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). AFM was used to record topography and perform nanoindentation, while XPS provided surface elemental composition. All three methods revealed data consistent with an excess of PDADMA at the buried interface. This excess PDADMA was then complexed with additional PSS to yield "nanosandwiches" of nonstoichiometric PEMU between layers of stoichiometric PEMU.
    Langmuir 04/2015; DOI:10.1021/acs.langmuir.5b00975
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    ABSTRACT: The kinetic signature of the β-relaxation of Poly(methyl methacrylate) (PMMA) is investigated by friction force microscopy. The variation in friction force was measured as a function of scan velocity, temperature (300 K-410 K) and applied load using both sharp and blunt probe tips. The friction data shows distinct maxima, which can be ascribed to the β-relaxation of PMMA. The contact area was varied over the ranges of approximately 20 to 70 nm² and 12000 to 43000 nm² through the use of probe tips with radii of approximately 15, 18, 1350 and 2650 nm. Kinetic analysis shows that the apparent activation energy of the β-relaxation decreases with the tip radius. Accompanying finite element simulations indicate that for the sharp tips a substantial sub-volume of the polymer underneath the tip exceeds the yield stress of PMMA. This suggests that for small contact sizes and high stresses the activation barrier of the β-process decreases through the activation of the α-process by material yielding.
    Langmuir 04/2015; DOI:10.1021/acs.langmuir.5b00735
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    ABSTRACT: We report non-circular, stable liquid propagation patterns in a stable displacement process in a confined thin patterned porous layer. For constant fluid injection rates, the average front location of the interface r(t) exhibits a power-law behavior r ∝ t(1/2); however, when surface tension effects become important, the interface displays non-circular shapes, e.g. square, rectangular, or octagonal, and maintains the same shape during most of the injection process. The interface shape is controlled by the value of a dimensionless group representing the strength of surface tension stresses relative to stresses accompanying injection. Furthermore, we show that the propagation patterns of the interface can be controlled by the relative orientation of the different porous layers.
    Langmuir 04/2015; DOI:10.1021/acs.langmuir.5b00958
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    ABSTRACT: With the aim to develop a facile strategy to prepare functional drug carriers to overcome multidrug resistance (MDR), we prepared heparin/protamine/calcium carbonate (HP/PS/CaCO3) hybrid nanovesicles with enhanced cell internalization, good serum stability, and pH sensitivity for drug delivery. All the functional components including protamine to improve the cell uptake, heparin to enhance the stability, and CaCO3 to improve drug loading and endow the system with pH sensitivity were introduced to the nanovesicles by self-assembly in an aqueous medium. An antitumor drug (doxorubicin, DOX) and a drug resistance inhibitor (tariquidar, TQR) were coloaded in the nanovesicles during self-assembly preparation of the nanovesicles. The drug loaded nanovesicles, which had a mean size less than 200 nm, exhibited a pH-sensitive drug release behavior. In vitro study was carried out in both nonresistant cells (HeLa and MCF-7) and drug-resistant cancer cells (MCF-7/ADR). Because of the enhanced intracellular and nuclear drug accumulation through effective inhibition of the P-gp efflux transporter, DOX/TQR coloaded nanovesicles showed significantly improved tumor cell inhibitory efficiency, especially for drug-resistant cells. These results suggest the self-assembled nanovesicles have promising applications in multidrug delivery to overcome drug resistance in tumor treatments.
    Langmuir 04/2015; DOI:10.1021/acs.langmuir.5b00542
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    ABSTRACT: Self-assembled monolayers (SAMs) of phosphonic acids (PAs) on transparent conductive oxide (TCO) surfaces can facilitate improvement in TCO/organic semiconductor interface properties. When ordered PA SAMs are formed on oxide substrates, interface dipole and electronic structure are affected by the functional group properties, orientation, and binding modes of the modifiers. Choosing octylphosphonic acid (OPA), F13-octylphosphonic acid (F13OPA), pentafluorophenyl phosphonic acid (F5PPA), benzyl phosphonic acid (BnPA), and pentafluorobenzyl phosphonic acid (F5BnPA) as a representative group of modifiers, we report polarization modulation-infrared reflection-absorption spectroscopy (PM-IRRAS) of binding and molecular orientation on indium-doped zinc oxide (IZO) substrates. Considerable variability in molecular orientation and binding type is observed with changes in PA functional group. OPA exhibits partially disordered alkyl chains but on average the chain axis is tilted ~57° from the surface normal. F13OPA tilts 26° with mostly tridentate binding. The F5PPA ring is tilted 23° from the surface normal with a mixture of bidentate and tridentate binding; the BnPA ring tilts 31° from normal with a mixture of bidentate and tridentate binding, and the F5BnPA ring tilts 58° from normal with a majority of bidentate with some tridenate binding. These trends are consistent with what has been observed previously for the effects of fluorination on orientation of phosphonic acid modifiers. These results from PM-IRRAS are correlated with recent results on similar systems from near-edge x-ray absorption fine structure (NEXAFS) and density functional theory (DFT) calculations. Overall, these results indicate that both surface binding geometry and intermolecular interactions play important roles in dictating the orientation of PA modifiers on TCO surfaces. This work also establishes PM-IRRAS as a routine method for SAM orientation determination on complex oxide substrates.
    Langmuir 04/2015; DOI:10.1021/acs.langmuir.5b00129
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    ABSTRACT: A surfactant-induced autophobic effect has been observed to initiate an intense depinning behavior at the initial stage of evaporation in both pure water and nanofluid sessile droplets. The cationic surfactant adsorbing to the negatively charged silicon wafer makes the solid surface more hydrophobic. The autophobing-induced depinning behavior, leading to an enlarged contact angle and a shortened base diameter, only takes place when the surfactant concentration is below its critical micelle concentration (cmc). The initial spreading degree right before the droplet retraction, the retracting velocity of the contact line and the duration of the initial droplet retraction are shown negatively dependent on the surfactant concentration below cmc. An unexpected enhancement in the initial depinning was found in the nanofluid droplets, possibly resulted from the hydrophilic interplay between the graphite nanoparticle deposition and the surfactant molecules. Such promotion of the initial depinning due to the nanoparticle deposition makes the droplet retract even at a surfactant concentration higher than cmc (1.5cmc). The resulted deposition formed with the presence of the depinning behavior has a greatly enhancement for coffee-ring formation as compared with the one free of surfactant, implying that the formation of a coffee ring does not require pinning of the contact line in the entire drying process.
    Langmuir 04/2015; DOI:10.1021/acs.langmuir.5b00288
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    ABSTRACT: An azide-functionalized shape memory elastomer, poly(octylene diazoadipate-co-octylene adipate), has been grafted with poly(oligio ethylene glycol) methacrylate (poly(OEGMA)) brushes via aqueous ARGET (activators regenerated by electron transfer) ATRP. Swelling of the substrate facilitated a high grafting density, which yielded an incompressible brush layer on top of the shape-memory substrate. Upon heating the substrate above the Tm to return to the primary shape, uniaxial wrinkles perpendicular to the direction of strain with sizes of 27-33 μm appear in addition to randomly oriented features formed on the temporary shape after grafting. Swelling equilibration time (t1) and grafting reaction time (t2) were varied to control wrinkle formation and size. In this manner, we were able to create unique, anisotropic hierarchical surface structures with different length scales and patterns.
    Langmuir 04/2015; DOI:10.1021/la504826w
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    ABSTRACT: Poly(acrylic acid)/azobenzene microcapsules were obtained through distillation precipitation polymerization and selective removal of silica templates by hydrofluoric acid etching. The uniform, robust and monodispersed microcapsules, confirmed by transmission electron microscopy and scanning electron microscopy, had reversible photoisomerization under ultraviolet (UV) and visible lights. Under UV irradiation, azobenzene crosslinking sites in the main chain transformed from trans- to cis- isomer, which would induce the shrinkage of microcapsules. These photomechanical effects of azobenzene moieties were applied on the encapsulation and release of model molecules. After loading with Rhodamine B (RhB), the release behaviors were completely distinct. Under steady UV irradiation, the shrinkage adjusted the permeability of capsule, providing a novel way to encapsulate RhB molecules. Under alternate UV/visible light irradiation, a maximal release amount was reached due to continual movements of shell networks by cyclic trans-cis photoisomerization. Also, microcapsules had absolute pH responsiveness. The diffusion rate and the final release percentage of RhB both increased with pH value. The release behaviors under different irradiation modes and pH values were in excellent agreement with the Baker-Lonsdale model, indicating a diffusion controlled release behavior. Important applications are expected in development of photo-controlled encapsulation and release systems, as well as in pH-sensitive materials and membranes.
    Langmuir 04/2015; DOI:10.1021/acs.langmuir.5b01180
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    ABSTRACT: Perfluorinated alcohols and acids such as Hexafluoroisopropanol (HFIP), Trifluoroethanol, Trifluoroacetic acid, Pentafluoropropionic acid, and Heptafluorobutyric acid induce coacervation and phase separation in aqueous solutions of a wide variety of individual and mixed amphiphiles1 (Khaledi et. Al, Langmuir, 2013, 29, 2458). This paper focuses on HFIP-induced complex coacervate formation in the mixtures of anionic polyelectrolytes, such as sodium salt of poly (methacrylic acid) (PMA) or poly (acrylic acid) (PAA) and cationic surfactants of alkyltrimethylammonium bromides. In purely aqueous media and over a wide concentration range, mixtures of PMA and CTAB form the catanionic complex (CTA+ PM-) that is insoluble in water (white precipitate). Upon addition of a small percentage of HFIP, the mixture goes through phase transition and formation of two distinctly clear liquid phases. The phase diagram for the HFIP-PMA-CTAB coacervate system was studied. The coacervate volume was determined as a function of system variables such as charge ratio, total and individual concentrations of the system components. These results, combined with the chemical composition analysis of the separated aqueous top-phase and coacervate bottom-phase shed light on the formation mechanism. The results suggest that exchange of counterions and ion-pair formation play critical roles in the coacervation process. This process facilitated by HFIP through solvation of the head groups and dehydration of the hydrophobic moieties of the catanionic complex. Due to the presence of HFIP, coacervation occurs over a wide range of concentrations and charge ratios of the oppositely charged polyelectrolyte and surfactant.
    Langmuir 04/2015; DOI:10.1021/acs.langmuir.5b00444
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    ABSTRACT: Nanosilver with closely controlled average particle diameter (7 - 30 nm) immobilized on nanosilica is prepared and characterized by X-ray diffraction, N2 adsorption and transmission electron microscopy. The presence of Ag2O on the as-prepared nanosilver surface is confirmed by UV-vis spectroscopy and quantified by thermogravimetric analysis and mass spectrometry. The release of Ag(+) ions in de-ionized water is monitored electrochemically and traced quantitatively to the dissolution of a preexisting Ag2O monolayer on the nanosilver surface. During this dissolution, the pH of the host solution rapidly increases, suppressing dissolution of the remaining metallic Ag. When however a nanosilver suspension is exposed to a CO2-containing atmosphere, like ambient air during its storage or usage, then CO2 is absorbed by the host solution decreasing its pH and contributing to metallic Ag dissolution and further leaching of Ag(+) ions. So the release of Ag(+) ions from the above closely-sized nanosilver solutions in the absence and presence of CO2 as well under synthetic air containing 200 - 1800 ppm CO2 is investigated along with the solution pH and related to the antibacterial activity of nanosilver.
    Langmuir 04/2015; DOI:10.1021/la504946g
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    ABSTRACT: Aggregation of rodlike colloidal particles is here investigated through the aggregation process by either increasing ionic strength or decreasing surface charge density of cellulose nanocrystals (CNC). The form factor of the nanoparticles is characterized up to the Guinier plateau using small angle neutron scattering (SANS) extended to very small scattering vector Q. Ionic strength, above the threshold of screening charges, brings aggregative conditions that induced fractal organizations for both charged and uncharged CNC. These two structures display respective fractal dimensions of 2.1 for charged CNC at high ionic strength, and 2.3 for desulfated CNC over more than a decade of the scattering vector Q irrespective of salinity revealing a denser structuration for neutral particles. This is discussed in the framework of aggregation of rodlike particles with aspect ratio higher than 8. Furthermore, dilution of the rod gel led to disentanglement of the network of fractal aggregates with a subsequent macroscopic sedimentation of the suspensions, with a characteristic time that depends on ionic strength and surface charge density. It revealed a percolation threshold around 2.5 g/L and the metastable out-of equilibrium character of CNC suspensions.
    Langmuir 04/2015; DOI:10.1021/acs.langmuir.5b00851
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    ABSTRACT: Porous aluminum oxide (PAO) is a nanoporous material used for various (bio)technological applications, among which as a chip for culturing cells. Tailoring its surface properties via covalent modification is a way to expand and refine its application. Specific and complex chemical modification of the PAO surface requires a stepwise approach, in which a secondary reaction on a stable initial modification is necessary to achieve the desired terminal molecular architecture and reactivity. We here show that the straightforward initial modification of the bare PAO surface with bromo-terminated phosphonic acid allows for the subsequent preparation of PAO with a wide scope of terminal reactive groups, making it suitable for (bio)functionalization. Starting from the initial bromo-terminated PAO, we prepared PAO surfaces presenting various terminal functional groups, such as azide, alkyne, alkene, thiol, isothiocyanate, and N-hydroxysuccinimide (NHS). We also show that this wide scope of easily accessible tailored reactive PAO surfaces can be used for subsequent modification with (bio)molecules, including carbohydrate derivatives and fluorescently-labeled proteins.
    Langmuir 04/2015; DOI:10.1021/acs.langmuir.5b00853