Experimental studies on polymer materials with spatially graded structures are reviewed in this paper. A wide variety of principles and experimental methods utilized to prepare and control these specific structures of polymer materials are summarized and discussed. In particular, the method of using light to generate and control these gradient morphologies in the micrometer scales is summarized with great detail for binary polymer mixtures. Finally, recent studies on copolymers with various gradient compositions at nanometer length scales are also summarized in this review.

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