Phase Separation Behavior Of Mixed Polymer Brushes Grafted Onto Nanoparticles

Mixed polymer brushes grafted onto nanoparticles system has been regarded as a class of materials of the preparation of environmental response characteristic smart surface. Currently the focus of research in this field is mainly concentrated in the preparation of nanoparticles of system and the phase separation of the system in solvent or bulk. Understanding micro-phase separation of this system has significant importance such as better preparation of materials with excellent performance. Self-consistent mean field theory can accurately describe the complex chain topology, multi-component system, as well as thermodynamic equilibrium state phase structure of grafted or mixed system. This research is using SCMFT to research phase separation of mixed polymer brushes grafted onto nanoparticles system under variety of parameters and with different nanoparticles.In the first chapter, we detail the history and progress of research in this area, from the concept of macromolecule to the establishment of the field of polymer brushes, then to mixed polymer brushes system. Finally, we introduce the mixed polymer brushes grafted onto the nanoparticles system.We described the details of the self-consistent mean field theory in the second chapter. With using of this theory, we accurately derivate the self-consistent field theory of the two components mixed polymer brushes system. And we use the pseudo-spectral method combines saddle point approximation to solve the self-consistent equations, and combined with the "masking" techniques to deal with the "hard wall" problem.With this self-consistent field theory and its numerical solution, we have researched a system which is two components of mixed polymer brushes grafted onto an infinitely long cylindrical nanoparticle, in the third chapter. We focus on three factors:radius of cylindrical nanoparticles R (the curvature of the system), the graft density of system a and the interaction parameter of two homopolymer,χ. These calculations are carried out in a three-dimensional space. With different parameters, we obtain a petal structure in XY cross section surface which AB two components appear alternately. And we found that with the increase of the radius R, the period number of this petal structure is from 3 to 6. Then we give the critical transition radius R of different periodic structure with different graft density and the interaction parameter. We have introduced an order parameter S which describes the degree of phase separation of system. And with using of this parameter, we found that the growth of the curvature inhibit the phase separation behavior. At last, we developed the existing polymer brush height statistics theory. We found that the polymer brush height increases linearly with the radius.In the fourth chapter, we have studied a system which is two components of mixed polymer brushes grafted onto a cylindrical nanorod with finite length and two hemispheres in two ends. We focus on the ratio of the length H and the radius R of the nanorod, two homopolymers chain length ratio (symmetric and asymmetric system), and the interaction parameter of two homopolymers,χ. These calculations are also carried out in a three-dimensional space. In the symmetrical chain length system, we obtain a rippled structure, and the XY cross-section of this structure is a petal. We found that the degree of phase separation is increasing with the aspect ratio increases, and the degree of phase separation in cylindrical region is much larger than the spherical region, which confirm our conclusion in the chapter 3, the growth of the curvature inhibited the phase separation. We found that the brush height along the Z axis is higher in the middle and lower in both sides. And as the aspect ratio increases, the height of the entire brush will also rise. In the asymmetric chain length system, we obtain a double layers structure, and with the aspect ratio increases, the inner layer will continue having phase separation to a petal structure which have multiple cycles. We found that the height distribution in this system is similar to the symmetrical system. We found that the maximum value of the order parameter under larger x is in closer position to the nanoparticle surface which the same value position of the lower χ conditions is farther from the nanoparticle surface; this means the system must be phase separation completely at a farther distance to nanoparticle surface. Because of this reason, we did not find the inner layer continue being phase separation to a petal structure in the low χ condition in asymmetric chain length system. By the brush height analysis, we found that the brush height of the whole nanoparticle basically has nothing to do with the system’s interaction parameter χ(interface energy), and mainly affect by system aspect ratio (entropy energy).In the fifth chapter, we study a three-component blend system. And we chose two types of nanoparticles which are infinitely long cylindrical nanoparticle and spherical nanoparticle. In infinitely long cylindrical nanoparticle system, we focus on a cylindrical nanoparticles radius R (related to the curvature), the graft density of system a and interaction parameter χ. We got series petal structures of the three component XY cross-section phase diagram. And we found that with increasing of radius R, the system is from the 4-4-4 structure gradual transition to the 6-6-6 structure. We found that in the three-component system, the order parameter S and brush height h changes are similar to the two-component system in third chapter. In spherical nanoparticle system, we focus on the radius R, the grafting density a and interaction parameter χ. We got an island structure of phase separation, and as the system radius increases, we got the 6-6-6 structure,9-9-9 structure and 12-11-11 structure. The total number of island structure increased because the graft density elevated. We also analyze the brush height, and it increases with the radius R increases, and also with χ increased.In summary, this paper mainly uses the self-consistent mean field theory to study the phase separation of the multicomponent mixed polymer brushes grafted onto different structures of nanoparticles system. By these studies, we can better understand the characteristics of this type of phase separation system, and give better guidance to the preparation of related materials.