Macro-scale phase separation morphology

Matyjaszewski et al. [2] patented a novel and flexible method for the preparation of CNTs with predetermined morphology. Phase-separated copolymers/stabilized blends of polymers can be pyrolyzed to form the carbon tubular morphology. These materials are referred to as precursor materials. One of the comonomers that form the copolymers can be acrylonitrile, for example. Another material added along with the precursor material is called the sacrificial material. The sacrificial material is used to control the morphology, self-assembly, and distribution of the precursor phase. The primary source of carbon in the product is the precursor. The polymer blocks in the copolymers are immiscible at the micro scale. Free energy and entropic considerations can be used to derive the conditions for phase separation. Lower critical solution temperatures and upper critical solution temperatures (LCST and UCST) are also important considerations in the phase separation of polymers. But the polymers are covalently attached, thus preventing separation at the macro scale. Phase separation is limited to the nanoscale. The nanoscale dimensions typical of these structures range from 5-100 nm. The precursor phase pyrolyzes to form carbon nanostructures. The sacrificial phase is removed after pyrolysis. 

Based on various experimental studies, one can schematically represent the morphology of segmented polyurethane (elastomer or flexible foam polymer) on the nano- and micro-scale as shown in Figm-e 2.1. For the range of hard segments volume fraction less than 50%, much of the space is occupied by the soft phase matrix. Microphase-separated nano-domains of the hard phase are dispersed in this matrix they can be individual islands or can form percolated networks. Finally, there could also be some larger (micron-sized) macrophase-separated domains of hard phase, where hard phase domains are ordered at the macro-scale (this is especially true in the case of flexible foams). The relative amounts of all these elements depend on the formulation and processing history. 

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