Attraction-repulsion Transition Induced By Self-propelled Particles And The Transport And Ordered Structures Of Nanoparticles

With the development of science and technology level and discipline the mutual infiltration between,polymer chemistry and physics,chemistry,biology,medicine,material,chemical and other closely related disciplines,so the polymeric system are the focus of researchers.In the equilibrium system of self-driven particles,the collective behavior of self-propelled particles can produce special entropy and transport operations for the system.In recent years,the booming of computer technology provides great help for the investigation of polymer system at the molecular level.On the basis of Monte Carlo,Molecular Dynamics and Coarse-Grained model introduced in the chapter two,computational simulation methods are employed to investigate the entropy force and transport of self-propelled particles system.In the chapter three,effective forces between two micro-wedges immersed in an active bath are investigated using Brownian dynamics simulations.Two anti-parallel and parallel wedge-like obstacles are considered respectively,and the effective forces between two wedges rely on the wedge-to-wedge distance,the apex angle of wedge,as well as the particle density.For two anti-parallel wedges,a transition from long-range repulsion to long-range attraction occurs by varying the apex angle,which is also sensitive to the particle density.The optimal apex angle ?r*(or ?a*)and particle density ?*is characterized by the saturated trapping of active particles inside wedge.For two parallel wedges,the effective force also experiences a transition from repulsion to attraction as wedge-to-wedge distance increases.These results originate from the collective trapping effect which is driven by the many-body dynamics of self-propelled particles in confinement(near the boundary)of obstacles.In the chapter four,transport of passive particles induced by chiral active particles in microchannel is investigated by using the overdamped Langevin dynamics simulation in a two-dimensional model system.Due to the chirality of active particles and special structure of microchannel,ratchet transport of passive particles is achieved.Effective transport of passive particles depends on the width of microchannel(d),the density(?)and the angular velocity(?)of chiral active particles.There exist optimal parameters for d and ? at which the transport efficiency for passive particles takes its maximal value.In the chapter five,entropic force is fairly ubiquitous in nature,but the entropic force is not good for system for most cases,so as to reduce the entropic force of the system is very important.In this chapter,we studied the system of self-propelled particles immersed with two stationary large particles(two walls).Self-propelled particles without angular velocity would gather around the large particles(two walls)under the effect of entropic force,which induce a great force between the large particles and self-propelled particles.And because of the asymmetry of the system inside and outside,the interaction force between two large particles(two walls)is large,but it is greatly related with the distance of two large particles(two walls).Otherwise,for the case of self-propelled particles with an angular velocity,the effect of entropic is weak,and the larger angular velocity is,the weaker entropic force is.Self-propelled particles will no longer assemble together.In the chapter six,the conformations of binary nanoparticles(NPs)in semiflexible polymer brushes under compression are investigated by molecular dynamics simulations,and a migration phenomenon of large NPs in semiflexible polymer brushes is observed in our simulations.For flexible polymer brushes,small NPs disperse freely within polymer brushes and large NPs tend to be located at the brush interface during the compression process.However,for semiflexible polymer brushes,both small and large NPs enter polymer brushes at the beginning of compression process.Most of large NPs can penetrate into polymer brushes and migrate towards the grafting surface,while most of small NPs are always located within polymer brushes in the compression process.The micro-spatial distributions of binary NPs are controlled easily by compressing the impenetrable surfaces through the external forces.There is a free-energy barrier located in the middle region between two impenetrable surfaces,and a free-energy well near the grafting surface in the free-energy landscape of a NP within semiflexible polymer brushes.The height of free-energy barrier and the depth of free-energy well depend mainly on the compression degree of two impenetrable surfaces and also rely on the size of NPs as well as the interaction between polymer brushes and NPs.However,for flexible polymer brushes,there only exists a free-energy well near the polymer brush surface during the compression process.In the chapter seven,Molecular Dynamics(MD)simulations are presented for a coarse-grained bead-spring model of ring polymer brushes under compression.Flexible polymer brushes are always disordered during compression,whereas semiflexible brushes fend to be ordered under sufficiently strong compression.Besides,the polymer monomer density of semiflexible polymer brush is very high near the polymer brush surface,inducing a peak value of free energy near the polymer brush surface.Therefore,by compressing nanoparticles(NPs)in semiflexible ring brush system,NPs tend to exhibit a closely packed single layer structure between the brush surface and the impenetrable wall,which provide a new access of designing responsive applications.In the chapter eight:in nature,the spiral structure is widespread.Under the drive of entropy,the polymer chain can form a helical structure under some special circumstances.Molecular dynamics method is used to study the self-assembly behavior of polymer chain induced nano-rod.It is found that the conformation of nano-rod/polymer chain is closely related to the number of nano-rods and the rigidity of the polymer chain.When the nanorods with polymer chains between moderate adsorption,nanorods can form three completely different conformation,especially in semi-rigid polymer chain induced nanorods can form linear array.