Dissipative Particle Dynamics Simulation On Polymer Blends With Graft Compatibilizers

A polymer blend or polymer mixture is a member of a class of materials analogous to metal alloys, in which at least two polymers are blended together to create a new material with different physical properties. Most polymers are mutually thermodynamically unstable and immiscible because of low blending entropy. To solve the problem, compatibilizers, which usually are copolymers, are introduced to the system, leading to modification and strong adhesion at interface. The compatibilizing efficiency of compatibilizer can be affected by its molecular architecture, composition and the interaction with the homopolymers etc. So it is really necessary and urgent to figure out the factors affected the efficiency of compatibilizers. There are several factors should be considered that it is time-consuming and uneconomical to be studied in laboratory. Computer simulations provide efficient ways to study the polymer blend with compatibilizers systematically.In this thesis, the dissipative particle dynamics (DPD) is used to study the compatibilizing process and the effect of graft copolymer compatibilizers on A and B blends varied in volume ratio. For a validation with our former experiment work, the coarse-grained polymers A and B were constructed based on polystyrene (PS) and nylon6(PA6) with QSPR (quantitative structure-property relationship) method. The results are as follows:As the PS/PA6compositions are varied, the mesoscale simulations predict the morphologies like ordered structures of body centered cubic (BCC), hexagonally perforated lamellar (HPL), ordered bi-continuous double diamond (OBDD) and hexagonal packed cylinders (HPC). The agreement between mesoscopic morphologies with SEM of PS/PA680/20,60/40and50/50proves practicability of DPD simulation on PS/PA6blend.Simulation results show that compatibilizers contribute to form fine and uniform domains for dispersed-matrix morphologies by preventing the dispersed phase domains from collision, adherence and coalescence, and help to make the density distribution more homogeneous in ternary blends. By comparing the evolution of PS/PA6(90/10) blends with and without compatibilizers, the addition of compatibilizer can accelerate the dynamic equilibrium process. For compatibilizers with the same backbone and number of grafts, the ones with longer grafts exhibit higher efficiency. However, too long graft chain may make the efficiency reduced due to swelling effect.Compatibilizers would create absorbed layers in polymer melts at the interface, and the ones with less but longer grafts contribute to form thick layers, and are conducive to higher compatibilizing efficiency.Virtual graft copolymers B-g-A were added in A/B90/10blends with the same parameters as PS and PA6. It is found that when the backbone of the graft copolymer was miscible with the dispersed phase, the one with medium length (1/5of the homopolymer B in this simulation) exhibits higher efficiency. And for a given backbone/graft composition, graft copolymers with less but longer grafts exhibit higher efficiency. B-g-A is more effective than A-g-B in preventing the dispersed phase domains from collision, adherence, and coalescence, leading to form smaller domain of dispersed phase.