Reaction‐Induced Phase Separation of Polymeric Systems under Stationary Nonequilibrium Conditions

Abstract

Cong-Miyata IntroductionFor most cases, materials processing is carried out under various conditions far from equilibrium where the temperature, concentration, or pressure is not constant, but is, in general, a function of time and space. Under such stationary nonequilibrium conditions, coupling among the different variables such as diffusion, concentration, temperature, density, or surface tension distribution can lead to a wide variety of instabilities such as double diffusion, Mullins-Sekerka, RayleighBenard, Rayleigh-Taylor, and so on [1-3]. As a consequence, for a physicochemical system undergoing phase separation far from thermodynamic equilibrium, one can expect the emergence of various exotic morphologies whereby functional materials can be designed and utilized.In this chapter, we will show that, by using ultraviolet (UV) irradiation to induce and maintain phase separation under stationary nonequilibrium conditions, morphologies that cannot be generated under thermal equilibrium conditions can be produced and controlled by taking advantage of the competition between phase separation and photochemical reactions. At first, theories and numerical calculation of phase separation kinetics in both nonreacting and reacting systems are briefly overviewed, together with the experimental results on reaction kinetics in polymeric mixtures. Here, the nonuniform kinetics observed for mixtures in both the bulk and liquid states containing monomers is summarized. Emphasis is particularly given for the autocatalytic behavior of the reaction and its consequence on the phase separation kinetics and the resulting morphology. By taking advantage of the gradient of light intensity in an irradiated sample, morphology with spatially graded structures is constructed and controlled. Emergence of an elastic strain field accompanying the cross-linking process in polymer mixtures is monitored and analyzed by using Mach-Zehnder interferometry. The development and relaxation of this reaction-induced strain field are described, together with its influence on the morphology of the reacting polymer mixtures. Finally, results on the temporal modulation experiments of phase separation are briefly summarized. The conclusions are provided at the end of this chapter, together with some Nonlinear Dynamics with Polymers: Fundamentals, Methods and Applications. Edited by John A. Pojman and Qui Tran-Cong-Miyata

Modeling the Self‐Assembly of Ternary Blends that Encompass Photosensitive Chemical Reactions: Creating Defect‐Free, Hierarchically Ordered Materials

“…(8.1) and is not applicable to blends with photo-controlled crosslinking. (Hence, our model does not account for the reaction-induced elasticity, which has been shown to be important for systems undergoing photo-induced crosslinking [63,64].) To design experiments based on our model systems, one would first need to perform the control experiments for a binary reactive blend to obtain data on the dependence of both the bulk value of the order parameter (similar to the data shown in Figure 8.4a) and the characteristic length scale (e.g., calculated from the expression for the wavenumber in Section 8.3.2) on the intensity of light illumination.…”

“…Such control experiments would allow one to match the characteristic time scale and length scale in the particular experimental system and the dimensionless values in our simulations. We also note that the computer-assisted irradiation (CAI) method [63] recently used to create a twodimensional light pattern to illuminate polymer blends undergoing photo-cross linking could also provide an excellent opportunity for modifying intensity to write with the non-reactive C component in a controlled manner.…”