Blend polymer blends, patterned domain

Fig. 4.8, Schematic representation of the spin-diffusion process by a wave-front in (a) a compound consisting of different domains, e.g., a polymer blend (b) a regular structure with long-range order (e.g., a crystal) and (c) a microscopically disordered compound. The resonance frequency is encoded into the density of the filling pattern and simultaneously into the direction of the long elliptical axis, symbolizing that it can be determined either by the isotropic shift or the orientation of the shift tensor. Quasi-equilibrium is reached in (a), if the wave has extended over a typical domain size in (b) after the spin-diffusion wave has reached the next neighbors and in (c) after the wave has sampled all possible orientations, leading to the typical pattern for amorphous compounds discussed below.

Microcontact Printing to create a pattern of lines with a periodicity of 4 pm. With this pattern, they illustrated near complete directed assembly of polystyrene (PS)/poly(2-vinylpyridine) (PVP) polymer blends. Their best polymer assembly occurred when the pattern periodicity and phase domain size were commensurate. Ginger and coworkers - ° generated uniformly spaced dot patterns with dip pen nanolithography (DPN). They demonstrated assembly for PS/poly-3-hexylthiophene (P3HT) in patterns as small as 150 nm. 

The outstanding behavior of multipolymer cdmbinations usually derives from the phase-separated nature of these materials. In fact, polymer blends, blocks, grafts, and IPNs are interesting because of their complex two-phased nature, certainly not in spite of it. Aspects of phase continuity, size of the domains, and molecular mixing at the phase boundaries as well as within the phase structures all contribute to the mechanical behavior patterns of these multicomponent polymer materials. 

We have recently shown that the presence of phase-separated structures in polymer-blend microparticles can be indicated qualitatively by a distortion in the two-dimensional diffraction pattern. The origin of fringe distortion from a multi-phase composite particle can be understood as a result of refraction at the boundary between domains of different polymers, which typically exhibit large differences in refractive index. Thus, the presence of separate sub-domains introduces optical phase shifts and refraction resulting in a randomization (distortion) in the internal electric field intensity distribution that is manifested as a distortion in the far-field diffraction pattern. 

The properties of the external surface can significantly alter phase separation in a thin polymer film. In extensive experimental investigations of the phase separation of polymer blends directed by patterned substrates [1,56,58,60,80-88] it was observed that the domain size evolved in a power law relation with time. The composition wave was normal to, and propagates inward from, the functionalized substrate. Likewise, processing parameters such as pattern size in the substrate were seen to affect refinement of the morphology. 

Subsequently, a numerical model was introduced to simulate self-assembly by the phase separation of polymer blends on a heterogeneously functionalized substrate patterns. From thermodynamic principles, when polymer blends are quenched into the spinodal region in the phase diagram, phase separation can be initiated from small composition fluctuations in the blend. The Cahn-Hilliard equation is used to describe the energy profile in the domain with varying... 

Films formed from blends can also produce hierarchical ordered materials. Raczkowska et al. [66] prepared films from blends of polar PMMA and nonpolar PS. Spin-coating of the blends under an appropriate relative humidity produced macrophase separated domains and simultaneously droplet-like patterns selectively in the domains rich in the polar polymer. Submicrometer pores decorated large PMMA-rich surface regions thus resulting in hierarchical film morphology. 

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