Polymer phase separation, pattern

Pattern Formation by Polymer Phase Separation. Like the SAM technique, polymer phase separation plays an important role in fabrication of microstructures, as it provides the opportunity for nanoscale patterning which otherwise is difficult by lithographic techniques 278, 279). The conditions necessary for microphase separation in immiscible polymer mixtures depend on their molecular architectures, nature of monomers, compositions, and molecular weights 280). Briefly, for linear homopolymer mixtures of A and B, the free energy of mixing per unit volume is given by 280, 281) ... 

The numerical simulation was consistent with experimental data with regards to influences of substrate pattern width, polymer weight ratio and polymer molecular weight of PAA. Both, experimental and simulated results showed that the intrinsic characteristic length should be compatible with the substrate pattern size for a reflned phase separation pattern, according to the substrate pattern. Simulations also showed that the increase in polymer molecular weight can increase the speed of morphologic evolution. As the film thickness is very small the checkerboard structure of spinodal decomposition cannot be seen in these results, but they are present. 

The outlined problems correspond to the most typical system where three phases, e.g. liquid, gas and solid, are brought in contact. Additional wetting geometries can occur when the liquid phase consists of two subphases, e.g. mixture of incompatible polymer liquids, and/or the substrate surface exhibits variations in chemical composition. In these cases, the interfacial interactions will strongly interfere with the phase separation inside the film. Laterally ordered polymer films might be formed due to the preferential wetting of the patterned substrate by one of the liquid phases. 

Elsewhere in this book, Prof. Steiner describes the wealth of patterns arising from phase separation of polymer blends and different strategies to control this phase separation into... 

FIGURE 2.2. Phase separation of spincoated polymer blends on patterned surfaces. 

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