A Scaling Theory Study On The Effect Of Nanoparticles On The Glass Transition Temperature Of Polymer Melts

Polymer nanocomposites(PNCs)have many advantageous mechanical,optical and electrical properties,so they have been the focus of much attention in the fields of nanomaterial science and engineering.In general,by adding nanoparticles(NPs)into the polymer matrices and tuning the way of interaction between nanoparticles and polymer chains,the dispersity of nanoparticles in the polymer host will be changed,composites having different macro-behaviors could be obtained.The macro-physical properties such as viscoelasticity and glass transition temperature of polymer nanocomposites is determined by their microstructure,so we can modify the dynamic process between nanoparticles and polymer chains to achieve the change of related physical parameters.In detail,the interaction process between nanoparticles and polymer matrices not only influences the diffusion of nanoparticles but also makes the relaxation mode of polymer chains changed,thus leads to the mobility of nanoparticles and the glass transition temperature of polymer melts up or down.The scaling formula built between related physics parameters also quantitatively describe the coupling relations between micro-interaction between nanoparticles and polymer matrices and their macro-properties.This research uses molecular dynamics method to implement dynamical simulations on interaction between polymer and nanoparticles and changes the related physical parameters values,discovered the close relations between changes of system's related physical variables and the concentration of nanoparticles,the concentration of polymer monomers,the interaction strength of monomer-NP.For the system which is restricted in one dimension,the entropic depletion attractions induced by nanoparticles prompts polymer chains to form ordered layering crystallization structures,and the thickness of layering crystallization could be targetedly controllable by varying the concentration of monomers.Then we give two important prerequisites for deciding the polymer crystallization conditions,the stability of crystallization structure is owe to the compensation mechanism that from the translational entropy of nonconnected monomer to the conformational entropy of the crystallized monomers in the system.For the relations between nanoparticles motion and the glass transition temperature of polymer melts,by the analyzing of built scaling relations,it can produce a suppression effect of direct NP-polymer attraction to hamper the NP mobility and exist the critical value of NP-polymer interaction and adsorption duration to decide whether polymer adsorbed on the surface of nanoparticles,with the relaxation process of polymer chains accelerated or slowed down.According to the physical nature of glass transition is the relaxed procedure of polymer chains,from the upper research and analysis,the conclusion which we obtained is: when the interaction value of NP-polymer is lower than the critical value,there is no polymer chains adsorbing on nanoparticle surface,the relaxation of polymer chains is faster and the corresponding glass transition temperature decreased,inversely the polymer chains adsorbed on nanoparticle surface,the relaxation of polymer chains becomes slower and the glass transition temperature increased.Incorporating simulation results with scaling prediction have confirmed this conclusion.