A novel mesoscopic simulation model is proposed to study the liquid crystal phase behavior of the anisotropic rodlike particles with a soft repulsive interaction,which possesses a modified anisotropic conservative force type used in dissipative particle dynamics.The influences of the repulsion strength and the particle shape on the phase behavior of soft rodlike particles are examined.In the simulations,we observe the formation of the nematic phase and smectic-A phase from the initially isotropic phase.Moreover,we find that shorter soft rodlike particles with anisotropic repulsive interactions can form a stable smectic-B phase.Our results demonstrate that the soft anisotropic purely-repulsive potential between the rodlike particles can reflect the interaction nature between soft rodlike particles in a simple way and is sufficient to produce a range of ordered LC-like mesophases.
Molecular dynamics simulations are useful tools to unveil molecular mechanisms of polymer phase separation,self-assembly,adsorption,and so on.Due to large molecular size and slow relaxation of the polymer chains,a great amount of issues related to large-distance chain displacement cannot be tackled easily with conventional molecular dynamic simulations.Systematic coarse-graining and enhanced sampling methods are two types of improvements that can boost spatiotemporal scales in polymer simulations.We present two typical ways to obtain the coarse-graining potential either by fitting to correct liquid structures or by fitting to available thermodynamic properties of polymer systems.The newly proposed anisotropic coarse-grained particle model can be used to describe aggregation and assembly of polymeric building blocks from disk-like micelles to Janus particles.We also present a stochastic polymerization model combined with coarse-grained simulations to investigate the problems strongly influenced by the coupling of polymerization and excluded volume effects.Finally,a facile implementation of integrated tempering sampling method is illustrated to be very efficient on bypassing local energy minima and having access to true equilibrium polymer structures.
LI YanChunWANG YongLeiLI ZhanWeiLIU HongLü ZhongYuan
The effect of silica nanoparticles on the morphology of(10/90 wt%) PDMS/PBD blends during the shear induced coalescence of droplets of the minor phase at low shear rate was investigated systematically in situ by using an optical shear technique.Two blending procedures were used:silica nanoparticles were introduced to the blends by pre-blending silica particles first in PDMS dispersed phase(procedure 1) or in PBD matrix phase(procedure 2).Bimodal or unimodal droplet size distributions were observed for the filled blends during coalescence,which depend not so much on the surface characteristics of silica but mainly on blending procedure.For pure(10/90 wt%) PDMS/PBD blend,the droplet size distribution exhibits bimodality during the early coalescence.When silica nanoparticles(hydrophobic and hydrophilic) were added to the blends with procedure 1,bimodal droplet size distributions disappear and unimodal droplet size distributions can be maintained during coalescence;the shape of the different peaks is invariably Gaussian.Simultaneously,coalescence of the PDMS droplets was suppressed efficiently by the silica nanoparticles.It was proposed that with this blending procedure the nanoparticles should be mainly kinetically trapped at the interface or in the PDMS dispersed phase,which provides an efficient steric barrier against coalescence of the PDMS dispersed phase.However,bimodal droplet size distributions in the early stage of coalescence still occur when incorporating silica nanoparticles into the blends with procedure 2,and then coalescence of the PDMS droplets cannot be suppressed efficiently by the silica nanoparticles.It was proposed that with this blending protocol the nanoparticles should be mainly located in the PBD matrix phase,which leads to an inefficient steric barrier against coalescence of the PDMS dispersed phase;thus the morphology evolution in these filled blends is similar to that in pure blend and bimodal droplet size distributions can be observed during the early coalescence.These results imply that
