A comparative study of the target search of end monomers of real and Rouse chains under spherical confinement.

We study the dynamics of the end monomers of a real chain confined in a spherical cavity to search for a small target on the cavity surface using Langevin dynamics simulation. The results are compared and contrasted with those of a Rouse chain to understand the influence of excluded volume interactions on the search dynamics, as characterized by the first passage time (FPT). We analyze how the mean FPT depends on the cavity size Rb, the target size a, and the degree of confinement quantified by Rg/Rb, with Rg being the polymer radius of gyration in free space.

Crystallization and melting of unentangled poly(ε-caprolactone) cycles containing pendants.

The Rouse model provides a basic framework to understand the chain dynamics of polymers, which is confirmed to be more suitable for exploring the linear dynamics of unentangled polymers. The crystalline morphology governed by chain dynamics and crystallization kinetics is expected to differ in linear and cyclic polymers. Cyclic poly(ε-caprolactone)s (c-PCLs) containing two bi-anthracenyl group pendants with molecular weights close to the critical molecular weight () were synthesized to investigate the chain dynamics based crystallization and melting behavior by DSC, POM, and simultaneous small-angle X-ray scattering/wide-angle X-ray scattering (SAXS/WAXS) investigations during heating of the isothermally crystallized samples.

Effects of end groups and entanglements on crystallization and melting behaviors of poly(ε-caprolactone).

The topology including end groups, entanglement loops, and tie molecules has a significant impact on the rheological and crystallization behavior and consequently on the functionality of a polymer. Unentangled, weakly entangled, and strongly entangled poly(ε-caprolactone)s (PCLs) with end groups and various molecular weights were synthesized. POM and DSC were used to observe spherulite growth and characterize thermal properties during crystallization and melting.

Explicit analytical form for memory kernel in the generalized Langevin equation for end-to-end vector of Rouse chains.

The generalized Langevin equation (GLE) provides an attractive theoretical framework for investigating the dynamics of conformational fluctuations of polymeric systems. While the memory kernel is a central function in the GLE, explicit analytical forms for this function have been challenging to obtain, even for the simple models of polymer dynamics. Here, we achieve an explicit analytical expression for the memory kernel in the GLE for the end-to-end vector of Rouse chains in the overdamped limit.

Diffusive Escape of a Nanoparticle from a Porous Cavity.

Narrow escape from confinement through a nanochannel is the critical step of complex transport processes including size-exclusion-based separations, oil and gas extraction from the microporous subsurface environment, and ribonucleic acid translocation through nuclear pore complex channels. While narrow escape has been studied using theoretical and computational methods, experimental quantification is rare because of the difficulty in confining a particle into a microscopic space through a nanoscale hole. Here, we studied narrow escape in the context of continuous nanoparticle diffusion within the liquid-filled void space of an ordered porous material.

Individual circular polyelectrolytes under shear flow.

Individual circular polyelectrolytes in simple shear flow are studied by means of mesoscale hydrodynamic simulations, revealing the complex coupling effects of shear rate, electrostatic interaction, and circular architecture on their conformational and dynamical properties. Shear flow deforms the polyelectrolyte and strips condensed counterions from its backbone. A decrease in condensed counterions alters electrostatic interactions among charged particles, affecting shear-induced polymer deformation and orientation.

Structural Mechanism for Viscosity of Semiflexible Polymer Melts in Shear Flow.

The viscosities of semiflexible polymers with different chain stiffnesses in shear flow are studied via nonequilibrium molecular dynamics techniques. The simulation reproduces the experimentally observed results, giving a complete picture of viscosity as chain stiffness increases. Analysis of flow-induced changes in chain conformation and local structure indicates two distinct mechanisms behind a variety of viscosity curves.

Effect of functionality on unentangled star polymers at equilibrium and under shear flow.

The properties of unentangled star polymers with arm length Nf = 20 beads and functionality f (3 ≤ f ≤ 60) are investigated at equilibrium and under shear flow by coarse-grained molecular dynamics simulations. At equilibrium, the star polymer shows a crossover from a linear, freely penetrable, extremely soft object to a spherical, slightly hard object with an impenetrable center with increasing f. The results confirm that the arm relaxation is essentially independent of f and stars of large f form a liquid-like structure.

GPU-Accelerated Molecular Dynamics Simulation to Study Liquid Crystal Phase Transition Using Coarse-Grained Gay-Berne Anisotropic Potential.

Gay-Berne (GB) potential is regarded as an accurate model in the simulation of anisotropic particles, especially for liquid crystal (LC) mesogens. However, its computational complexity leads to an extremely time-consuming process for large systems. Here, we developed a GPU-accelerated molecular dynamics (MD) simulation with coarse-grained GB potential implemented in GALAMOST package to investigate the LC phase transitions for mesogens in small molecules, main-chain or side-chain polymers.

Topological constraints of network chains in telechelic associative polymer gels.

We present an analysis of topological constraints of network chains, in particular entanglements, in ABA telechelic associative polymer gels generated by Brownian dynamics technique with a B selective solvent. We find two fundamental types of entanglements formed by bridge chains: first, two or more bridge chains linking different micelles impose topological constraints on each other because they cannot cross, denoted as type-I entanglement; second, two or more bridge chains linking a pair of micelles are twisted together, denoted as type-II entanglement. More complex constraints are composed of both types.

Effects of excluded volume and hydrodynamic interaction on the deformation, orientation and motion of ring polymers in shear flow.

A ring polymer is a classical model to explore the behaviors of biomacromolecules. Compared with its linear counterpart in shear flow, the ring polymer should be more sensitive to excluded volume and hydrodynamic interaction attributed to the absence of chain ends. We carried out multiparticle collision dynamics combined with molecular dynamics simulation to study the effects of excluded volume and hydrodynamic interaction on the behaviors of ring polymers in shear flow.

Temperature-Dependent Immobilization of a Tungsten Peroxo Complex That Catalyzes the Hydroxymethoxylation of Olefins.

A tungsten peroxo complex stabilized by the bidentate picolinato ligand has been synthesized and then immobilized successfully on imidazole-functionalized silica. The immobilized tungsten-based catalyst was employed as an efficient catalyst for the one-pot synthesis of β-alkoxy alcohols from olefins and methanol with H O . Regarding the catalyst evaluation and the results of characterization by the various methods, it was demonstrated that the immobilization of tungsten peroxo complex was highly temperature-dependent.

Simulation studies on architecture dependence of unentangled polymer melts.

The dependences of the properties of linear, ring, star, and H-shaped polymer melts on architecture are investigated by nonequilibrium molecular dynamics simulations. We find that zero-shear viscosities η0 for various architectures follow a universal relation, η0=Cη〈Rg0 (2)〉, where Cη is a constant and 〈Rg0 (2)〉 the equilibrium mean-square radius of gyration, in the unentangled regime. This law is also found valid for asymmetrical polymers but invalid for polymers with a hard core, such as stars with many arms and short arm lengths.

Gold nanoparticles embedded in silica hollow nanospheres induced by compressed CO2 as an efficient catalyst for selective oxidation.

Metal nanoparticles embedded in hollow materials are important due to their wide applications in catalysis. In this work, we disclosed a nontraditional synthetic pathway to prepare silica hollow nanospheres by hydrothermal treatment in the presence of compressed CO2. Especially, the silica hollow nanospheres with an outer diameter of about 16 nm and an inner pore size of 7 nm were obtained using 1.

Shear thinning behavior of linear polymer melts under shear flow via nonequilibrium molecular dynamics.

The properties of both untangled and entangled linear polymer melts under shear flow are studied by nonequilibrium molecular dynamics simulations. The results reveal that the dependence of shear viscosity η on shear rate γ, expressed by n ~ γ(-n), exhibits three distinct regimes. The first is the well-known Newtonian regime, namely, η independent of shear rate at small shear rates γ < τ0(-1) (where τ0 is the longest polymer relaxation time at equilibrium).

Traditional chinese medicine in cancer care: a review of case series published in the chinese literature.

Traditional Chinese medicine (TCM) has been widely used in cancer in China. Case series report a series of cases exposed to a certain intervention. To understand the current situation of case series of TCM for cancer, we performed this review.

Monte Carlo simulation of self-assembly of symmetric ABC three-arm star copolymers under cylindrical confinement.

Self-assembly of symmetric ABC three-arm star copolymers confined in cylindrical nanopores is investigated by means of a lattice Monte Carlo simulation method. The dependence of morphologies on the degree of confinement and preference of pore surface is studied systematically. For the symmetric ABC three-arm star copolymers which form polygonal cylinder structures with periodic spacing L(0) in bulk, various novel structures are observed inside the nanopores.

Self-assembly of T-shaped rod-coil block copolymer melts.

Self-assembled behavior of T-shaped rod-coil block copolymer melts is studied by applying self-consistent-field lattice techniques in three-dimensional space. Compared with rod-coil diblock copolymers with the anchor point positioned at one end, the copolymers with the anchor point at the middle of the rod exhibit significantly different phase behaviors. When the rod volume fraction is low, the steric hindrance of the lateral coils prevents the rods stacking into strip or micelle as that in rod-coil diblock copolymers.

Simulated morphological landscape of polymer single crystals by phase field model.

The novel phase field model with the "polymer characteristic" was established based on a nonconserved spatiotemporal Ginzburg-Landau equation (TDGL model A). Especially, we relate the diffusion equation with the crystal growth faces of polymer single crystals. Namely, the diffusion equations are discretized according to the diffusion coefficient of every lattice site in various crystal growth faces and the shape of lattice is selected based on the real proportion of the unit cell dimensions.

Rigidity effect on phase behavior of symmetric ABA triblock copolymers: A Monte Carlo simulation.

The phase behavior of symmetric ABA triblock copolymers containing a semiflexible midblock is studied by lattice Monte Carlo simulation. As the midblock evolves from a fully flexible state to a semiflexible state in terms of increase in its persistence length, different phase behaviors are observed while cooling the system from an infinite high temperature to a temperature below T(ODT) (order-disorder transition temperature). Within the midblock flexibility range we studied (l(p)N(c) View Article and Find Full Text PDF

Self-assembly of rod-coil-rod ABA-type triblock copolymers.

Self-assembled behavior of symmetric ABA rod-coil-rod triblock copolymer melts is studied by applying self-consistent-field lattice techniques in three-dimensional space. The phase diagram is constructed to understand the effects of the chain architecture on the self-assembled behavior. Four stable structures are observed for the ABA rod-coil-rod triblock, i.

Study of self-assembly of symmetric coil-rod-coil ABA-type triblock copolymers by self-consistent field lattice method.

The self-assembly of symmetric coil-rod-coil ABA-type triblock copolymer melts is studied by applying self-consistent field lattice techniques in a three-dimensional space. The self-assembled ordered structures differ significantly with the variation of the volume fraction of the rod component, which include lamellar, wave lamellar, gyroid, perforated lamellar, cylindrical, and spherical-like phases. To understand the physical essence of these phases and the regimes of occurrence, we construct the phase diagram, which matches qualitatively with the existing experimental results.