Static And Dynamic Properties Of A Linear Polymer Chain In Confined Environment With Nanoparticles

Dependent on the restriction degree and the restricted condition,the static and dynamic properties of the confined polymer chain exhibit a series of unique regularity,which is an important research topic of soft condensed matter physics,polymer physics and biophysics.The mixture of polymers and nanoparticles(NPs)has important scientific and technical significance in many fields,such as suspension polymers with colloid or NPs,proteins or biopolymers in cells,and polymer nanocomposites formed by polymer filled with NPs.Because of the interaction between NPs and polymers,the properties of glass transition temperature,crystallization behavior and mechanical properties of polymers are significantly different from those of the bulk polymer.Polymer nanocomposites combine perfectly the rigidity,dimensional stability and thermal stability of inorganic materials with the elasticity and machinability of polymer materials,which has become one of the important methods to obtain high performance composites.In addition,the translocation phenomenon of polymer chain through the nanopores exists widely in various life processes,and the research on the translocation has many potential applications in DNA sequencing,molecular separation and structure research.In this thesis,the static and dynamic properties of polymer chains in the environment of the low concentration mobile NPs and that of semi-flexible polymer chains in the environment of randomly distributed immobile NPs,and the factors affecting the translocation time of polymer chains through repulsive nanopores are studied by using the molecular dynamics simulation method.The polymer chain is modeled as coarse grained bead-spring model,and Lennard-Jones interactions are taken into account for the interactions between polymer and NPs as well as between polymer and nanopore.The thesis is divided into five chapters.Chapter 1 presents a review introduction on polymer in confined environment,Brownian motion and anomalous diffusivity of polymer,statistical,and dynamical properties of polymer,and polymer nanocomposite(PNC).Chapter 2 gives a detail description of our simulation models and methods.The main simulation results on a polymer chain in the environment with low concentration mobile NPs,semiflexible polymer chain in a crowded environment with randomly distributed immobile NPs,and temperature dependence of the translocation time of polymer through repulsive nanopores were presented in Chapter 3,Chapter 4,and Chapter 5,respectively.The main results are outlined below:(1)In the environment with a low concentration mobile NPs,with the increase of the interaction between polymer and NPs,a phase transition for the polymer chain changing from the expand random coil to the compact globule is observed.This phase transition is caused by the increase of the contact between the polymer and the NPs due to the attraction of the NPs.The normal diffusion of polymers can be observed regardless of the size and concentration of the NPs and the interaction strength between the polymer and NPs.The results show that the normal diffusion of polymer is independent of the state of polymer,but the diffusion coefficient decreases with the increase of the interaction between polymer and NPs.(2)In the crowded environment with randomly distributed immobile NPs,the static and dynamic properties of semiflexible polymers are dependent on the chain stiffness(k?),polymer-NP interaction(?PN),and concentration of NPs(CNP).The mean square radius of gyration<RG2>can be increased,decreased,or unchanged,dependent on these three variables.For a fully flexible polymer(k?=0),<RG2>changes non-monotonously with ?PN and CNp.Whereas for a semiflexible polymer(k??10 with its persistence length larger than inter-particle distance of NPs),<RG2>decreases monotonously or remains unchanged with increasing ?PN or CNP,indicating the softening of polymer by NPs.Moreover,the translational diffusion and rotation of polymer were retarded by NPs.Subnormal diffusion behaviors are observed for both fully flexible polymer and semiflexible polymer at sufficiently large ?PN.The effect of NPs on the translational diffusion is more obvious for the fully flexible polymer because more monomers are in contact with NPs for the fully flexible polymer.On the other hand,the effect of NPs on the rotation is more obvious for the semiflexible polymer because it contacts with more NPs.The rotational relaxation time ?R of semiflexible polymer increases faster with increasing spN or CNp than that of fully flexible polymer.(3)The mean translocation time<?>for polymer chain translocating through nanopore is highly dependent on the temperature T and the minimal<?>is located near the coil-globule transition temperature.Moreover,the scaling behaviors<?>?N? and<?>?F-?(N the polymer length and F the driving force inside the nanopore)are dependent on T:Universal values ? = 1.4 and ? = 0.85 are observed for the polymer in the random coil state,while for the polymer in the compact globule state,? decreases from ? = 2 at weak driving to 1.2 at strong driving for short N and 8 increases with decreasing T in low F region,but universal exponents ?= 1.6 for long N and ? = 0.85 in large F region were observed.Results show that polymer's conformation plays very important role in controlling the translocation time of polymer chain.