查看更多>>摘要：We study the effect of chain rigidity on tailoring the nanoparticle locations for neutral and selective particles embedded in the lamellar morphology formed by semiflexible diblock copolymer chains using self-consistent field calculations.The nanoparticles are modeled through a cavity function,and the semiflexible chains are represented by the continuous Kratsky-Porod chain model.In general situation,the nanoparticles prefer to stay at the interface in order to reduce the interface areas and thus the system free energy.However,the particle distribution at the do-main center is subtle,and the underlying physics is intrinsically different depending on the polymer flexibility.In the case of flexible chains,the entropy just contributes a constant shift to the free energy when the nanoparticles move around the domain center indicating that the local metastable state if appears at the domain center is wholly attributed to the local minimum in the enthalpy.If the polymers are rigid,the variation of the particle distribution at the domain center has a close relation with the polymer rigidity and nanoparticle size.In the case of strongly rigid polymers with small nanoparticles,a nearly uniform particle distribution at the domain center is observed,while in other cases,a local enhance-ment of particle distribution there is found.In contrast to the case of flexible chains,further analysis reveals the crucial role of entropy in control-ling the shape of particle distributions at the phase domain.Specifically,the local metastable state appears in the domain center is determined by the large entropy there which arises from the weak coupling of bond orientations that allows the polymer chains to be relatively relaxed.When the particle becomes selective,its distribution in the phase domain exhibits a shift almost uniformly rather than changes its profile,and the un-derlying physics still holds.In all,our study establishes a strong coupling between the chain rigidity and effect of entropy.
查看更多>>摘要：The polymer with nanoparticles tethered at each end is a unique modelfor unraveling the effect of chain ends on the polymer dynam-ics.We investigated the rheological behavior of this kind of polymer by using nonequilibrium molecular dynamics simulation.The effect of poly-mer lengths and nanoparticle radii on the complex moduli and viscosity was examined.The dependence of complex moduli on the frequency be-comes less pronounced as the polymer is short or the nanoparticle is large.The shear thinning behavior was revealed for these systems,and the scaling exponent of complex viscosity with respect to the frequency was found to change from-1/2 to-3/4 as the polymer shortens or the nanoparticle enlarges.The rheological behavior was further explained by analyzing the mean square distance of nanoparticles.The simulation re-suIts were compared with the existing experimental finding,showing an agreement.The work provides information for understanding the chain end effect on polymer rheology.
查看更多>>摘要：To understand the dynamic process of polymerdetachment,it is necessary to determine the mean detachment time of a single break-able link,which is modeled as a spring.Normally,this time can be viewed as the escape of a Brownian particle from the potential well of the spring.However,as the free dangling length of the polymer chain increases,the conformational entropy of the chain is affected by geometric confinement.It means that the wall exerts a repulsive force on the chain,resulting in accelerated link detachment from a macroscopic perspec-tive.In this work,we investigate the effect of entropy on the detachment rate in the case where the substrate is spherical.We demonstrate that spherical confinement accelerates chain detachment both inside and outside the sphere.An analytical expression for the mean detachment time of breakable links is given,which includes an additional pre-factor that is related to the partition function.Additionally,we analyze the expres-sions for entropic forces inside the sphere,outside the sphere,and on a flat wall,comparing their magnitudes to explain the difference in mean detachment time.
万方数据
维普