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ABSTRACT: Mesoscale simulations are performed to study the complexes between a dendrimer and a vesicle of amphiphilic molecules. In particular, the assembled structures and dynamics of these complexes are investigated by tuning vesicle size and the surface tension of vesicle membrane. Our simulations demonstrate that a dendrimer-based bulge containing amphiphilic molecules forms in the vesicle membrane when a dendrimer adheres to a vesicle. We find that vesicle size and the surface tension of the vesicle membrane permit effective accesses to control the shape change of the bulge structure with respect to various hydrophobic interactions in the complexes. The analysis for the energy of the vesicle reveals that the change of elastic energy induced by various densities of amphiphilic molecules in the membrane plays an important role in this bulge-shape control. Because both charged dendrimers and vesicles are effective nanodevices for targeted drug delivery, our findings shed light on the effective means of developing multitasking nanocarriers as targeted drug delivery platforms.
Nanoscale 08/2011; 3(9):3812-8. · 5.91 Impact Factor
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ABSTRACT: Janus nanoparticles with two chemically different compartments have been shown to be a unique class of building blocks in solution. Here we perform mesoscale simulations to explore the self-assembly of Janus nanoparticles with widely varying architectures in diblock copolymers. We demonstrate that the coassembly of these amphiphilic building blocks forms novel and tunable structures at the interfaces of block copolymers, and consequently influences the interface stabilization and structural evolution kinetics. Our simulations suggest that Janus nanoparticle self-assembly at block copolymer interfaces yields considerable control over the creation of polymer nanocomposites with improved shear behavior. In this context, the approach is a viable strategy for creating functional materials with enhanced processing properties.
ACS Nano 02/2010; 4(2):913-20. · 10.77 Impact Factor
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ABSTRACT: Understanding the interactions of dendrimers with biological membranes is of fundamental importance in determining their potential biomedical applications like drug delivery vehicles and gene therapeutic agents. Herein we perform systematically mesoscopic simulations to investigate the interactions and binding structures in complexes comprised of charged dendrimers with lipid bilayer membranes. For these purposes, various interaction strengths between the outer-dendrimer hydrophilic component and lipid heads and those between the inner-dendrimer hydrophobic component and lipid tails are used in the simulations. The external force is also induced into the complexes by stretching the membranes to examine the influence of the dendrimer binding on the stabilization of the lipid bilayer membranes. Our simulations demonstrate that the increasing attraction between outer dendrimer and lipid heads leads to wider spread of dendrimer along the membrane surface, while the attraction between the inner dendrimer and lipid tails has a great effect on the insertion of the dendrimer into the bilayer membrane. It is found that the dendrimer can induce a hole in the tense bilayer membrane at earlier time for a stronger attraction between the hydrophobic dendrimer component and lipid tails, which prompts the failure of the membrane affected by the external forces or surroundings. The findings could provide some guidelines for the design of the dendrimers with defined molecular architectures and prompt the understanding for the stabilization of the tense membranes and the potential cytotoxicity of the charged dendrimers in the dendrimer−lipid bilayer membrane complexes.
08/2009;
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ABSTRACT: Dendrimers have successfully proved themselves as functional nanodevices for drug delivery because they can render drug molecules a greater water solubility, bioavailability, and biocompatibility. It has recently been suggested that the structural changes of cell membranes (e.g., local lipid density and actual pore or hole) could affect the permeability across them for dendrimers. However, to understand these effects requires direct measurements in a single cell and is thus very difficult and more challenging. Here we use mesoscopic simulations to investigate the tension-mediated complexes comprising charged dendrimers and lipid bilayer membranes. The structures of membranes are alternated by adjusting their surface tensions. Our simulations demonstrate that the permeability of charged dendrimers can be effectively enhanced in the tense membranes, and the permeability in the actual hole is several times higher than that in the lipid-poor section. The possible mechanism of charged dendrimer-induced pore nucleation in the tense membranes is evaluated. The findings have implications in tuning intracellular delivery rates and amounts in nanoscale complex and chemotherapeutics.
ACS Nano 08/2009; 3(8):2171-6. · 10.77 Impact Factor
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Small 07/2009; 5(11). · 8.35 Impact Factor
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Macromolecular Chemistry and Physics 06/2009; 210(12):1003 - 1010. · 2.36 Impact Factor
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ABSTRACT: Dissipative particle dynamics (DPD) approach is used to investigate the conformational behaviors and interactions of the complex between a cylindrical polyelectrolyte brush (CPB) and linear polyelectrolytes (LPs) with opposite charges. The effective complex between CPB and LPs and its dependence on the amount and length of LPs are examined. It is found that the CPB conformation presents collapse and reswelling with the increasing amount of LPs. The collapse is caused by the replacement of monovalent CPB counterions by LPs and the condensation of LPs on the CPB which reduce the osmotic pressure inside the brush. The swelling of the collapsed CPB is induced by the excluded volume effects of additionally absorbed LPs and LP counterions. The results show that the addition of LPs can not enhance the effective complex between the CPB and LPs when the total charge of LPs exceeds that of CPB. Our simulation also demonstrates that the increase of the LP length leads to a shrinking of the CPB which consequently exhibits rod-like or spherical conformations. The most effective complex between a CPB and LPs can be reached only when the contour length of LPs is not less than that of the CPB side chain.
Langmuir 05/2009; 25(6):3808-13. · 4.19 Impact Factor
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ABSTRACT: Using a dissipative particle dynamics approach, we study the conformations and interactions of a cylindrical polyelectrolyte brush (CPB) with added salt. The effects of counterion valency on the conformational behaviors of the CPB are analyzed in detail by considering various parameters like the distribution of bond lengths, the mean distance between two grafting points, the order parameter of side chains, etc. The lyotropic behavior of the CPB is also investigated through examining the backbone persistence. Our simulations demonstrate that the presence of the multivalent counterions can induce the collapse of the CPB, leading to various conformations. We identify a horseshoe to helical to coil-like conformation transition with increasing counterion valency. An important factor for the collapse of the CPB is the fact that the strong condensation of counterions induced by the higher electrostatic correlations decreases the osmotic pressure inside the brush. It is found that the ratio of the backbone persistence to the diameter of the CPB, l(p)/d, can only be affected to a slight extent by changing the counterion valency and the side chain length. These results may provide a valuable guideline that can be used to tailor the microstructure of the systems and to yield desired macroscopic behaviors.
The Journal of Physical Chemistry B 05/2009; 113(15):5104-10. · 3.70 Impact Factor
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ABSTRACT: High crystallinity and controlled porosity are advantageous for many applications such as energy conversion and power generation. Despite many efforts in the last decades, the direct synthesis of organic-inorganic composite materials with crystalline transition metal oxides is still a major challenge. In general, molecules serve as inorganic precursors and heat treatment is required to convert as-synthesized amorphous composites to stable crystalline materials. Herein, an alternative approach to the direct synthesis of crystalline polymer-metal oxide composites by using a spherical polyelectrolyte brush as the template system is presented. Pre-synthesized electrostatically stabilized rutile nanocrystals that carry a positive surface charge are used as inorganic precursors. In this approach, the strong Coulomb interactions between anionic polyelectrolyte brush chains and cationic crystalline rutile colloids, whose surfaces are not capped and therefore reactive, are the key factors for the organic-inorganic crystalline composite formation. Stepwise calcination first under argon and followed with a second calcination in air lead to the complete removal of the polymer template without collapse and porous rutile balls are obtained. The results suggest that any colloids that carry a surface charge might serve as inorganic precursors when charged templates are used. It is expected that this hierarchical route for structuring oxides at the mesoscale is generally applicable.
Small 04/2009; 5(11):1326-33. · 8.35 Impact Factor
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ABSTRACT: Surface-directed phase separation via a two-step quench process in asymmetry polymer mixtures is numerically investigated by coupling the Flory-Huggins-de Gennes equation with the Cahn-Hilliard-Cook equation. Two distinct situations, i.e., the minority component is preferred by the surface and the majority component is preferred by the surface, are discussed, respectively. The morphology and evolution dynamics of the phase structure, especially the secondary domain structure, are analyzed. The wetting layer formation mechanisms during the two-step quench process are examined. The simulated results demonstrate that different secondary domain structures in these two situations can be induced by the second quench with deeper quench depth, which can be used to tailor phase morphology. It is also found that, in the second quench process, the evolution of the wetting layer thickness can cross over to a faster growth when the preferential component is the minority component. In this situation, the formation mechanism of the wetting layer will change and is eventually determined by the second quench depth. However, when the preferential component is the majority component, a deeper second quench depth corresponds to a slower growth of the wetting layer thickness. The chemical potential is calculated to explain the difference regarding the growth dynamics of the wetting layer thickness between these both situations.
The Journal of Physical Chemistry B 08/2008; 112(29):8499-506. · 3.70 Impact Factor
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ABSTRACT: Lamellar structure via two-step surface-directed phase separation in polymer blend films is numerically investigated in three-dimensional (3D) space, which is more physically appropriate for the experimental situation than that in two-dimensional (2D) space [L.-T. Yan and X. M. Xie, J. Chem. Phys. 128, 034901 (2008)]. The 3D phase morphology and its evolution dynamics in both critical and off-critical conditions have been studied. The wetting layer formation mechanism during the second quench has been concerned. The effects of noise on the ordered phase structures have also been examined. The simulated results in 3D space give a more certain evidence that the lamellar structure can be induced by the surface or interface when the system is in the equilibration state with very shallow quench depth first and then imposed on a further quench depth in the unstable region of the phase diagram. It is found that the lamellar structure can also be induced in the polymer blends with off-critical condition. The simulated results demonstrate that the formation of the lamellar structure can present two basic processes and obey logarithmic growth law at the initial and metaphase stages. The results also show that a stronger thermal noise corresponds to a smaller region with the lamellar structure.
The Journal of chemical physics 07/2008; 128(22):224906. · 3.09 Impact Factor
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ABSTRACT: The two-step quench process of surface-directed spinodal decomposition is numerically investigated by coupling the Flory-Huggins-de Gennes equation with the Cahn-Hilliard-Cook equation. The phase dynamics and formation mechanisms of the wetting layer in two-step surface-directed spinodal decomposition have been concerned in detail. The results demonstrate that a parallel strip structure forms near the wetting layer and propagates into the bulk, when the first quench depth is very shallow and the bulk does not undergo phase separation, and the second quench depths are various points with deeper quench depths. In this case, the wetting layer turns to be unchangeable at the intermediate and later stages of the second quench process, compared to the growth with a time exponent 1/2 during the first quench process. When the first quench depth is deeper and phase separation occurs in the bulk during the first quench process, it is found that a deeper second quench depth can stimulate a more obvious secondary domain structure, and the formation mechanism of the wetting layer changes from logarithmic growth law to Lifshitz-Slyozov growth law.
The Journal of Chemical Physics 05/2008; 128(15):154702. · 3.33 Impact Factor
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ABSTRACT: The phase separation of polymer blend films on the stripe patterned surface is numerically investigated by coupling the Flory–Huggins−de Gennes equation with the Cahn−Hilliard−Cook equation. The kinetic pathway and its mechanisms are analyzed in both real space and reciprocal space. Compared to experimental measurements, the simulated results exhibit more complete kinetic pathways of pattern-directed phase separation. It is found that the extreme fluctuation of the chemical potential at the edges of stripes leads to the formation of the branch structure. Our simulated results indicate that the phase inversion, occurring not only in the polymer/air interface but also in the bulk, can extensively affect the relations between the isotropic phase separation and the periodic structure. The analysis in reciprocal space shows that the evolution of the phase morphologies in the polymer/air interface obeys a 1/3 power law for a thick film, consistent with the experimental results. It is also found that the amplitude change of the first diffraction peak can reflect the kinetic pathway of the phase structure in the polymer/air interface very well. A narrower strip periodicity corresponds to an earlier phase inversion and an earlier appearance of the droplet arrays in strips.
04/2008;
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ABSTRACT: A novel process for obtaining ordered morphology on the basis of two-step surface-directed spinodal decomposition is numerically investigated. The formation mechanism and evolution dynamics of this process are also discussed in detail. The calculated results of the chemical potential demonstrate that the equilibration state at the first quench affects the competition between the surface potential and the chemical potential in the bulk, leading to a surprising lamellar structure at the second further quench. It is also found that the lamella formation obeys the logarithmic growth. These results could provide a new approach for fabricating ordered structure of polymer materials and stimulate experimental studies based on this subject.
The Journal of Chemical Physics 02/2008; 128(3):034901. · 3.33 Impact Factor
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ABSTRACT: Focusing on the off-critical condition, the quench depth dependence of surface-directed phase separation in the polymer binary mixture is numerically investigated by combination of the Cahn-Hilliard-Cook theory and the Flory-Huggins-de Gennes theory. Two distinct situations, i.e., for the wetting, the minority component is preferred by the surface and the majority component is preferred by the surface, are discussed in detail. The simulated results show that the formation mechanism of the wetting layer is affected by both the quench depth and the off-critical extent. Moreover, a diagram, illustrating the formation mechanisms of the wetting layer with various quench depths and compositions, is obtained on the basis of the simulated results. It is found that, when the minority component is preferred by the surface, the growth of the wetting layer can exhibit pure diffusion limited growth law, logarithmic growth law, and Lifshitz-Slyozov growth law. However, when the majority component is preferred by the surface, the wetting layer always grows logarithmically, regardless of the quench depth and the off-critical extent. It is interesting that the surface-induced nucleation can be observed in this case. The simulated results demonstrate that the surface-induced nucleation only occurs below a certain value of the quench depth, and a detailed range about it is calculated and indicated. Furthermore, the formation mechanisms of the wetting layer are theoretically analyzed in depth by the chemical potential gradient.
The Journal of Chemical Physics 03/2007; 126(6):064908. · 3.33 Impact Factor
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ABSTRACT: The diffusion effects on chain-extension reactions using carboxyl-terminated polyamide-12 as a model reactant with bisoxazolines were investigated by the stochastic Monte Carlo method. Thus, complicated direct modeling and numerical calculations were avoided. The chain-length dependence and detailed diffusive behavior were discussed in depth. The diffusion effects retarded the progress of chain-extension reactions and led to lower coupling efficiency. The simulated results indicated that the diffusion effects could make the final molecular weight distributions wider. In the presence of diffusion and with the progress of the coupling efficiency, peaks in the evolution curves of the weight-average molecular weight and valleys in the evolution curves of the polydispersity index were observed, respectively, when the coupling efficiency was low enough. These phenomena were different from those without diffusion effects and were analyzed in detail. The critical entanglement chain length had strong effects on the simulated results of the diffusion effects, especially when its value was near the average chain length. The results also showed that the effects of the reactant degradation made the molecular weight distribution of the reaction system wider and weakened the diffusion effects on the coupling reaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2902–2911, 2006
Journal of Polymer Science Part B Polymer Physics 08/2006; 44(19):2902 - 2911. · 1.53 Impact Factor
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ABSTRACT: The diffusion effects on chain extension reactions, using carboxyl-terminated polyamide12 (PA12, say CA in this paper) as a model reactant with bisoxazolines (OO), were simulated by the stochastic Monte Carlo (MC) method. The chain length dependence and detailed diffusive behavior of each chain were considered based on the reptation theory. It is found that the diffusion effects retard the progress of chain extension reactions and, lead to a lower coupling efficiency and a lower molecular weight. The simulated results indicate that the diffusion effects can make the final molecular weight distribution (MWD) wider. In the presence of diffusion and with the progress of p, peaks in the evolution curves of weight-average molecule weight (M w) and valleys in the evolution curves of polydispersity index, d, are observed, respectively, when p is small enough, which is different from those without diffusion effects, and has been analyzed in detail in this paper. The results also show that the effects of reactant degradation make the MWD of the reaction system wider, and weaken the diffusion effects on the coupling reaction.
05/2006;
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Macromolecular Theory and Simulations 04/2006; 15(3):226 - 237. · 1.71 Impact Factor
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ABSTRACT: The surface-directed spinodal decomposition (SDSD) in binary polymer mixture with different quench depths is investigated by numerical simulations, combining Cahn−Hilliard−Cook (CHC) theory with Flory−Huggins−de Gennes theory. The formation mechanisms of the wetting layer with different quench depths are discussed. The simulated results demonstrate that the growth of the wetting layer can exhibit pure diffusion-limited growth law, logarithm growth law, and Lifshitz−Slyozov (LS) growth law with the increasing quench depth, which reproduces experimental observations. Furthermore, the detailed ranges of these three regimes are determined on the basis of simulated results. The growth law of the wetting layer is pure diffusion-limited growth law when χN < 2.01. In the case of 2.08 ≤ χN, the growth of the wetting layer obeys LS growth law. However, when 2.01 ≤ χN < 2.08, the logarithm growth law of the wetting layer is favored. The simulated results also demonstrate that the evolution of the polymer morphology in the parallel cross sections near the substrate surface obeys LS growth law. Moreover, the orientation effect of the surface on the dynamic behavior of these cross sections with deeper quench depth is more remarkable than that with shallower one.
02/2006;
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Macromolecular Theory and Simulations 11/2005; 14(9):586 - 595. · 1.71 Impact Factor
