[Show abstract][Hide abstract] ABSTRACT: Graphene oxide (GO) was successfully incorporated into a hybrid lyotropic liquid crystal matrix formed by two kinds of surfactants n-dodecyl tetraethylene monoether (C12E4) and 1-dodecyl-3-methylimidazolium bromide ionic liquid (C12mimBr). By changing the ratios of C12E4 and C12mimBr, two types of C12E4/C12mimBr LLC matrixes (lamellar and hexagonal phase) were formed and the effects of the concentration of GO and temperature on the properties of GO/C12E4/C12mimBr LLC composites were systematically investigated by using polarized optical microscopy (POM) observations, small-angle X-ray scattering (SAXS) and rheological measurement. Both POM observations and SAXS results indicated that GO can be well-dispersed in the hybrid LLC matrixs at room temperature. Moreover, after the incorporation of GO, the temperature tolerance of GO/C12E4/C12mimBr LLC composites were enhanced compared with pure C12E4/C12mimBr hybrid LLC and aggregated GO was not observed in the hybrid hexagonal C12E4/C12mimBr LLC matrix with the increase of temperature while it can be observed in the hybrid lamellar C12E4/C12mimBr LLC matrix. The results of rheological measurements showed that the addition of GO were helpful for enhancing the mechanical properties of C12E4/C12mimBr LLC. Thus, the success preparation of GO/hybrid LLC composites can highly improve the temperature resistance of these materials and widen the applications of GO/LC materials in nanotechnology, electrochemical, drug delivery systems and bioengineering areas.
[Show abstract][Hide abstract] ABSTRACT: Sodium deoxycholate/graphene oxide (NaDC/GO) composite hydrogels were prepared in varying salinity. The hydrogels were characterized in detail by phase behavior study, transmission electron microscopy (TEM) observations, scanning electron microscopy (SEM) observations, X-ray powder diffraction (XRD) mesurements, Fourier transform infrared (FT-IR) spectra and rheological measurements. It was found that the introduction of GO to NaDC hydrogel enhances the mechanical strength of the composite hydrogel. When contacted with methylene blue solution, methylene blue can be absorbed inside the gel accompanied with a swelling of the gel. On the contrary, the hydrogel forms by NaDC only dissolves in methylene blue solution, forming a homegeous solution. Further study reveals that the gelation of NaDC/GO composite gel can be accelerated by an increase in salinity. This work may open the door for a variety of applications of NaDC/GO composite hydrogels such as in biotechnology, drug delivery and sewage treatment.
Colloids and Surfaces A Physicochemical and Engineering Aspects 07/2015; 483. DOI:10.1016/j.colsurfa.2015.07.044 · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this Letter, the kinetic Monte Carlo simulations are employed to study the microscopic mechanisms of patterning molten organic particles based on liquid behavior on templated surfaces. The simulated results show that the binding energy difference between the organic particle and templated surface plays a key role in the anisotropic wetting of organic particles. And the square root of time law between the spreading distance and simulated time on different temperatures is well consistent with experimental observation. We also note that the geometry effect of channel edge has very significant effect on the dependence of spreading velocity on template dimensions.
Chemical Physics Letters 05/2015; 628. DOI:10.1016/j.cplett.2015.04.007 · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The site-selective deposition behavior of perylene onto a self-assembled monolayers (SAMs) patterned substrate was studied using the equilibrium and steered molecular dynamics simulations. Four kinds of different densely packed SAMs were constructed on silicon oxide substrates as the patterned templates. Equilibrium MD simulations showed that the packing density of alkyl chains on the substrate could influence the deposition behavior of the organic molecules. The potential of mean force (PMF) of the deposition process of perylene onto different density packed SAMs, which was calculated by the umbrella sampling with the weighted histogram analysis method (WHAM), determined the favorite location of perylene on the SAM. The equilibrium and non-equilibrium MD methods gave the same conclusion about the deposition positions of organic molecules on the patterned substrate. In summary, this comprehensive study is expected to provide useful information for the synthesis of new functional materials.
[Show abstract][Hide abstract] ABSTRACT: Carboxyl asphaltene is commonly discussed in the petroleum industry. In most conditions, electroneutral carboxyl asphaltene molecules can be deprotonated to become carboxylate asphaltenes. Both in crude oil and at the oil/water interface, the characteristics of anionic carboxylate asphaltenes are different than those of the carboxyl asphaltenes. In this paper, molecular dynamics (MD) simulations are utilized to study the structural features of different asphaltene molecules, namely, C5 Pe and anionic C5 Pe, at the molecular level. In crude oil, the electroneutral C5 Pe molecules prefer to form a steady face-to-face stacking, while the anionic C5 Pe molecules are inclined to form face-to-face stacking and T-shaped II stacking because of the repulsion of the anionic headgroups. Anionic C5 Pe has a distinct affinity to the oil/water interface during the simulation, while the C5 Pe molecules persist in the crude oil domain. A three-stage model of anionic C5 Pe molecules adsorbed at the oil/water interface is finally developed.
Energy & Fuels 12/2014; 28(12):7368-7376. DOI:10.1021/ef5020428 · 2.79 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The aggregation behaviors of two trisiloxane-tailed surface active ionic liquids in water have been investigated by coarse-grained (CG) molecular dynamics simulation on the basis of MARTINI force field. The new CG model is developed from the optimized molecule computed by using density functional theory. Direct comparison of angles and bonds obtained from all-atom (AA) simulations with those calculated from the CG model has been conducted to validate the latter model. Excellent agreement between AA and CG demonstrates that the potential of the new CG model can represent the complex system well. The long time CG simulation has been performed to understand the formation process of micelles when dissolving ionic liquids in water. Vesicles were observed at the final stage of the simulation and their partially truncated views and density profiles were obtained to describe the structure in detail.
Journal of Dispersion Science and Technology 11/2014; 35(11). DOI:10.1080/01932691.2013.856319 · 0.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The TiMgAlCu mixed oxides, based on hydrotalcite-like compounds, was developed as novel SOx removal catalysts for FCC (fluid catalytic cracking) process. The mixed oxides were prepared by modified co-precipitation method and estimated for SOx removal under conditions similar to those of FCC units. XRD, TG/DTA and N2 adsorption analysis were performed to investigate the physicochemical and textural properties of the samples. The analysis results indicated that all the samples exhibit good dispersion of metal oxides in the matrix. The SOx adsorption–reduction tests showed that the novel TiMgAlCu catalysts with 15%Ti and 1% Cu had a good performance on SOx removal. Moreover, the particle size had obvious effect on the adsorption activity of sulfur remove catalysts and the best fit particle size is from 100 to 300 μm.
Ceramics International 09/2014; 40(8):11559–11566. DOI:10.1016/j.ceramint.2014.03.112 · 2.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Two kinds of carbon materials，i.e., graphene and graphene oxide (GO), were successfully incorporated into a lyotropic liquid crystal (LLC) matrix formed by n-dodecyl tetraethylene monoether (C12E4). The properties of graphene/C12E4 and GO/C12E4 LLC composites were characterized by UV-vis absorption, transmission electron microscopy (TEM) observations, polarized optical microscopy (POM) observations, small-angle X-ray scattering (SAXS) and rheological measurements. SAXS results indicate that both graphene and GO are well-dispersed in the C12E4 LLC matrix and some interactions occur between C12E4 LLC matrix and graphene (or GO) sheets. Moreover, it is demonstrated that graphene interacts with the hydrophobic part of C12E4 LLC while GO mainly interacts with the hydrophilic part of C12E4 LLC because of the different properties of graphene and GO. Integration of graphene and GO into C12E4/PEG systems by a spontaneous phase separation method reveals the different interaction mechanisms of graphene and GO with C12E4 LLC. It can be concluded that the mechanical and electrical properties of the C12E4 LLC have been largely improved by the incorporation of graphene and GO, which opens the door for wide applications in nanotechnology, electrochemical and biochemical areas.
[Show abstract][Hide abstract] ABSTRACT: In enhanced oil recovery (EOR), the micro-oil droplet heavily affected the stability of foam and prevented foam flooding. In this paper, the oil bridge-stretching mechanism of foam rupture was described through molecular dynamics with the aim of providing supplements to the experiments at the molecular level. Two important phenomena for foam rupture have been pointed out by the simulation. One is about the pseudoemulsion film, representing the stability of the oil-water-air three phase interface. The bound water connecting the headgroups of the surfactant through strong H-bonding interactions played a vital role in the stability of the pseudoemulsion film. These water molecules could hinder the disappearance of the water phase in the pseudoemulsion film. The additional energy barrier, which was influenced by the surfactant concentration, also played a vital role in preventing the destruction process. The other factor is about the oil bridge, which appeared after the destruction of the pseudoemulsion film. The external horizontal force stretched the bridge resulting in the destruction of the bridge. The process was decided by the properties of the oil molecules. In the simulation, the stretching force was divided into three stages including the initial increasing force, the middle equilibrium force and the final decreasing force. Especially the second equilibrium force, which stretched the middle of the oil bridge so that it became thin, was vital to the foam rupture. The concentration and properties of the oil molecules were the crucial factors for foam rupture. The simulated results offer important supplements to experiments.
[Show abstract][Hide abstract] ABSTRACT: The adsorption of polyelectrolyte surfactant mixture of sodium poly(acrylic acid) (NaPAA) and dodecyl trimethyl ammonium bromide (C(12)TAB) at the air/water interface was studied using molecular dynamics simulation. In our simulations, the transition from monolayer adsorption of a polymer surfactant complex to a multilayer structure was observed with increasing surfactant concentration at the interface. For the multilayer structure, the two polyelectrolyte chains were linked by two layers of surfactant molecules which adopted a tail-to-tail arrangement. The results indicated that the electrostatic interaction was the main driving force for the binding of surfactants to the polyelectrolyte, meanwhile the hydrophobic interaction between surfactant tails induced a layer-by-layer packing arrangement at high surfactant concentration. The dynamic properties of inorganic ions implied that the complex of polyelectrolyte and surfactant was an ion-exchange process. Our conclusions are in accordance with experimental results on polyelectrolytes and ionic surfactants.
Colloids and Surfaces A Physicochemical and Engineering Aspects 07/2014; 454(1):104–112. DOI:10.1016/j.colsurfa.2014.04.009 · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Carbon nanotubes (CNTs) were incorporated into a lyotropic liquid crystal (LLC) matrix at room temperature through spontaneous phase separation. The phase separation process occurred in n-dodecyl tetraethylene monoether (C12E4) solutions induced by the hydrophilic polymer, poly(ethylene glycol) (PEG). It was found that the molecular weight of PEG has a significant effect on the CNTs-C12E4 system, which not only influences the phase behavior of the system but also changes the properties of the CNTs-LLC composites. Polarized optical microscopy (POM) images, combined with small-angle X-ray scattering (SAXS) results, indicate that CNTs incorporate within the layers of the lamellar LLCs without destroying the structure of LLCs. Moreover, UV-vis absorption, Raman spectra and rheological measurements were performed to investigate the characteristic properties of the CNTs-LLC composites. This study not only gives a more comprehensive understanding of polymer-induced phase separation, but also expands the potential uses of CNTs-LLC composites in nanotechnology.
[Show abstract][Hide abstract] ABSTRACT: The adsorption of the anionic surfactant, sodium dodecylsulfate (SDS) in poly(ethylene oxide) (PEO) brush was studied by molecular dynamics simulations. Our simulations revealed that surfactant can adsorb in polymer brush as micellar aggregates and the polymer would reside at the hydrocarbon-water interface of SDS micelles. This association between surfactant and polymer was mainly driven by the hydrophobic interaction between the polymer and surfactant tails. In the simulation, with the increasing of surfactant concentration, a plateau value representing saturated adsorption was observed. The height of polymer brush was mainly affected by the adsorbed surfactant at low grafting density of polymer; however, it was primarily controlled by the grafting density at high grafting density. Our conclusions at the molecular level were in close agreement with experiment about the adsorption of surfactant in polymer brushes.
[Show abstract][Hide abstract] ABSTRACT: In this paper, the detachment mechanism of alkane molecules from one hybrid hydrophobic and hydrophilic solid surface was studied by molecular dynamics simulation. First, some alkyl chains were linked through C-O bonds with silica surface to get one half-hydrophobic one, and the other half-hydrophilic area was still same as silica surface, thus one modified hybrid hydrophobic and hydrophilic silica surface was constructed. Second, some alkane molecules were adsorbed on the hybrid surface to get one whole hydrophobic oil layer, and the detachment mechanism of alkane molecules on the surface was discussed in aqueous solution using molecular dynamics. The simulated results showed that the key to the detachment of alkane molecules is the formation of water channel in oil layer between water phase and solid surface. In the detachment process, water molecules can penetrate oil layer to the silica surface through the strong H-bonding interaction among water molecules in water channel, and soon these molecules can form a gel layer along the silica surface by fast diffusion under the H-bonding interaction and electrostatic interaction between water molecules and silica surface. At last, the half-hydrophilic area on hybrid surface becomes hydrophilic again after the oil layer's detachment, and alkane molecules aggregate on the modified surface linked the alkyl chains. For the hybrid surface, some of alkane molecules insert into the interstice among the alkyl chains, and thus the oil drop cannot be dispatched thoroughly from the surface linked alkyl chains in aqueous solution. Our results showed that the detachment mechanism of oil from hybrid surface is different, compared with the whole pure hydrophilic surface.
The Journal of Chemical Physics 04/2014; 140(16):164702. DOI:10.1063/1.4870930 · 2.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Template directed growth of functional organic molecules is a recently developed technique to generate organic micro/nano-structures on surfaces. Using templates of a metal patterned substrate, two different mechanisms were observed: area selective nucleation on predefined patterns with molecules nucleated on top of patterns and step-edge induced area selective growth on the substrate. Until now, much work has been done to investigate the microscopic mechanism of the former one. However, little attention was paid to the latter one. Here in this work, a series of kinetic lattice Monte Carlo simulations were conducted to get deeper insight into the microscopic mechanism of step-edge induced area selective growth. The time-resolved process of structure formation, the relationship between nucleation control efficiency and template size, and different growth regimes were studied. The results agree well with experimental speculation while selecting appropriate interactions.
[Show abstract][Hide abstract] ABSTRACT: In this paper, the solubilisation process of pyrene molecule, as the fluorescence probe molecule, in cetyltrimethylammonium bromide (CTAB) surfactant micelle solution is studied by molecular dynamics (MD) method. When one pyrene molecule is in the micellar solution, it can be adsorbed into the micelle spontaneously and vertically. The probe molecule mainly locates in the interior cavity or the palisade layer of the micelle. When two pyrene molecules exist in the micellar solution, they transfer from the interior to the palisade layer. Although strong π–π interactions exist between the pyrene molecules, the pyrenes separate to each other in the palisade layer in two-third simulated time.
[Show abstract][Hide abstract] ABSTRACT: At present, rubrene, which exhibits a high charge mobility, has become one of the most promising organic semiconductors because of its potential applications in organic thin-film transistors (OTFTs). The performance of organic molecule crystalline films is governed by both their molecular packing state phase and their molecular structures, which are greatly influenced by the growth process and inducing layer. In this paper, molecular dynamics (MD) simulations were performed to study the deposition behavior and crystallization of rubrene films. Four systems with different self-assembled monolayers (SAMs) were constructed to investigate the microscopic configuration of rubrene deposition, their interfacial reactions, and to further discuss how the template structures affect the crystallization of rubrene molecules. Our results suggest that the phase states of the inducing layer exhibit a significant effect on the rubrene growth. The theoretical results are consistent with the experimental findings and provide theoretical assistance on the further design of appropriate inducing layers for the crystallization of organic molecules.
[Show abstract][Hide abstract] ABSTRACT: The microscopic behaviors of a water layer on different hydrophilic and hydrophobic surfaces of well ordered self-assembled monolayers (SAMs) are studied by molecular dynamics simulations. The SAMs consist of 18-carbon alkyl chains bound to a silicon(111) substrate, and the characteristic of its surface is tuned from hydrophobic to hydrophilic by using different terminal functional groups (-CH3, -COOH). In the simulation, the properties of water membranes adjacent to the surfaces of SAMs were reported by comparing pure water in mobility, structure, and orientational ordering of water molecules. The results suggest that the mobility of water molecules adjacent to hydrophilic surface becomes weaker and the molecules have a better ordering. The distribution of hydrogen bonds indicates that the number of water-water hydrogen bonds per water molecule tends to be lower. However, the mobility of water molecules and distribution of hydrogen bonds of a water membrane in hydrophobic system are nearly the same as those in pure water system. In addition, hydrogen bonds are mainly formed between the hydroxyl of the COOH group and water molecules in a hydrophilic system, which is helpful in understanding the structure of interfacial water.
[Show abstract][Hide abstract] ABSTRACT: Molecular dynamics simulations and quantum mechanics calculation were employed to study the deposition behavior of organic luminescent molecules rubrene onto bare dioxide silicon substrate and self-assembled monolayers (SAM) patterned substrate. A mixed system was constructed to investigate the edge-induced area-selective growth. Our simulation results suggest that the functionalized SAM decoration on the substrate surface exerts significant effect on the growth behavior and crystallinity of rubrene molecules. In the mixed system, the rubrene molecules diffused and preferetially deposited along the step-edge of SAM and formed a typical π-conjugated structure by standing up-right.
Chemical Physics Letters 05/2013; 571:38–43. DOI:10.1016/j.cplett.2013.03.075 · 1.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this paper, we report a facile synthesis of mesoporous silica nanomaterials by utilizing cetyltrimethylammonium bromide (CTAB)/sodium dodecylbenzenesulfonate (SDBS) vesicle systems as templates. The porous nanostrucures with varied morphologies, including nanocapsules and nanospheres can be successfully fabricated by simply regulating the volume ratio (R) of ethanol to ethyl ether. In addition, we also investigated the influences of vesicular solution concentration on the nanomaterial morphologies with two different vesicle systems. A vesicle-templating mechanism was proposed to explain the formation of porous silica nanostructures.
Colloids and Surfaces A Physicochemical and Engineering Aspects 05/2013; 424:59–65. DOI:10.1016/j.colsurfa.2013.02.014 · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The prevention of nonspecific protein adsorption was a big challenge in biomedical and marine fields. Recent studies of the mechanisms of non-fouling materials have identified a strong correlation between material surface hydration and resistance to nonspecific protein adsorption. To investigate the molecular mechanism of two typical non-fouling materials PDMS and pSBMA on molecular level, a series of molecular dynamics simulations were conducted. This work concentrated on the structure properties and dynamic behaviors of water molecules that belong to the non-fouling membranes' surface hydration layers. Water's behavior near the membrane were analyzed in energetic, dynamics and structure aspects: PMFs (potential of mean force) between hydration layer water and polymer surfaces indicated pSBMA has more advantages on binding water molecules energetically; the analyzing of diffusion coefficients, residence time, and dipole residence time of hydration layer water showed pSBMA has slower dynamics properties which demonstrate water molecules were tightly bonded by pSBMA; the illustration of atoms density profile, hydrogen bond and their number distribution showed a rich hydrogen bond network structure around pSBMA. Based on above, following conclusions were then speculated: 1) the hydration layer near non-fouling membrane has a strong relationship with the nonspecific protein adsorption which forms a physical and energy barrier during particles in solution (including proteins) come into contact with non-fouling membranes. 2) Comparing with PDMS, pSBMA as a zwitterionic polymer can bind water molecules more strongly via both electrostatic and hydrogen bonding. And the caging effects of water network formed around pSBMA can also reduce water molecules' mobility. All these lead to a stable hydration layer that prevents non-specific protein adsorption. Simply, pSBMA generated a more energetic advantaged, tightly bounded and structured water layer by electrostatic, hydrogen bonding and caging effect. This hydration layer prevents protein from approaching the surface, resulting in a better non-fouling surface than PDMS.