Pattern Formation And Morphological Evolution Of Microstructure On A Pre-stretched Elastomeric Substrate

Self-assembly of nanostructure brings new opportunity for the synthesis of new materials, and offers new topics for physical and chemical research. It requires further understand on how to control the self-assembly which makes the self-assembly proceeding under well-designed direction. While most of the previous studies of self-assembly of a monolayer have been done on solid substrates, some elastomeric materials lend themselves to be suitable templates for monolayer self-assembly. Such materials are soft and highly stretchable, and the points on their surface for adsorbing molecules can be manipulated mechanically. More studies need to carry out for addressing the surface process on stretchable substrates. Therefore, this thesis develops a phase-field model involving the nonlinear contribution of the finite pre-stretch, studies the evolution of microstructure and pattern formation on a pre-stretched elastomeric substrate, and discusses the possibility of controlling the process of self-assembly on such a substrate. The main content is as follows:We studied two-dimensional phase separation of a binary monolayer of molecules attached onto the surface of a uniformly stretched elastomer substrate. Taking the compositional concentration as order parameter, considering the effect of deformation of the substrate, a continuous phase-field model is adopted to analyze the stability and to simulate the temporal evolution of the monlayer composition. Our numerical results reveal that the uniform pre-stretch strongly affects the phase separation patterns, and leads to preferential growth in the tensile direction. Depending on the concentration of the monolayer and the amount of the pre-stretch, various ordered patterns may be formed, including elongated dots, parallel rod-like domains, and perfectly aligned stripes, etc. The feature sizes of the patterns are determined by the magnitude of the finite pre-stretch. Therefore, we conclude that the phase separation pattern can be well tuned by adjusting the stretch of the substrate in addition to the concentration of the monolayer.Self-assembly of binary monolayers on a pre-stretched substrate with chemically modified surface is simulated via a continuous phase-field model. Indeed, a finite stretch can change the instantaneous elastic property and material anisotropy of the substrate. And chemical modification of surface leads to the change of local average concentration. The result indicates that the chemical modification of surface can guide the nucleation and the pre-stretch can control the growth direction of compositional domains. Various ordered surface structures can be self-assembled by tuning the magnitude of the pre-stretch and the pattern of the surface modification.We study the influence of a uniformly stretched elastomeric substrate and the multi-component of ternary monolayers on the formation of phase separation patterns. The increase of composition leads to a great variety of the energy of system. Incorporating the effects of different mechanisms such as elastic anisotropy and multiple phases, a continuous phase-field model is adopted to simulate the spatio-temporal evolution of the compostional patterns. Our results indicate that the phase separation patterns depend strongly on both the amount of the uniform stretch and the relative percentages of the phases. The unidirectional stretch plays a role of ordering the patterns, while the relative percentages of phases affect the size, distribution and connectivity of the domains.