Poly phase-separated patterns

Self-assembled block copolymers are basically amphilic molecules which contain distinctively different polymers. This block copolymer contains two or more polymers quantitatively in the form of blocks. Some of the block copolymers are polyacrylic acid, polymethylacrylate, polystyrene polyethylene oxide, polybutadiene, polybutylene oxide, poly-2-methyloxazoline, polydimethyl sUoxane, poly-e-caprolactone, polypropylene sulfide, poly-A -isopropylacrylamide, poly-2-vinylpyridine, poly-2-diethylamino ethyl methacrylate, poly-2-(diisopropylamino) ethyl methacrylate, poly-2-(methacryloyloxy) ethyl phosphorylcholine, and polylactic acid. These copolymers contain more than polymers to form certain configurations like linear, branched, patterned. For example, if we take three polymers named A, B, and C, they can be combined to form arrangements AB, BA, AA, BAB, ABCAB, ABCABC, ABABAB, etc. in the form of branched configuration it forms (ABQa, (ABA)a, (AB)4, etc. Depending on the above-mentioned number of blocks, they are named as AB diblock copolymers, ABC triblock copolymers, ABC star block copolymers, etc. The covalent linkage between these different blocks of polymers makes macroscopic phase separation impossible, that is, in its place the phase separation... 

L. Cui, Y.C. Han, Honeycomb pattern formation via polystyrene/poly(2-vinylpyridine) phase separation, Langmuir 21 (2005) 11085-11091. 

There is current interest in the use of block copolymers to help create structures that have potential sensor applications, e.g. block copolymers of poly styrene-poly (methyl methacrylate) (PS-b-PMMA). The nature of the organization that is created in thin films is influenced by the factors influencing phase separation of the polymers and very importantly the surface energy of the substrate on which they are deposited (Figure 8.14). If a substrate is patterned and then certain areas chemically modified, a substrate is created with variation in the surface energy across the surface. This is discussed in more detail in Chapter 9. The differences in surface energy will influence the morphology created. 

Similarly, Guan et al. (2007) developed an elastomeric poly (ester urethane)-urea scaffold by a thermally induced phase separation method for the release of bFGF. The scaffold maintained bFGF bioactivity over a period of 21 days and showed a two-phase protein release pattern, characterized by a fast initial release of about 30% in the first 2 days, followed by a slow release over a period of 4 weeks. 

Phase separating polymer systems can exhibit both buoyancy-driven and Marangoni convection. Mitov and Kumacheva observed both in the polystyrene/poly(methyl methacrylate) system in which both were dissolved in toluene. The toluene was evaporated from layers of initial thickness of 0.12 - 3 mm (45). They were able to obtain ordered hexagonal patterns on the scale of 10 microns, which they ascribed to the ordering effects of buoyancy-driven and Marangoni convection. 

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