Processes of Ordered Structure Formation in Polypeptide Thin Film Solutions
An experimental study is presented on the hierarchical assembly of α-helical block copolymers polystyrene–poly(γ-benzyl-L-glutamate) into anisotropic ordered structures. We transformed thin solid films into solutions through exposure to solvent vapor and studied the nucleation and growth of ordered three- dimensional structures in such solutions, with emphasis on the dependence of these processes on supersaturation with respect to the solubility limit. Interestingly, polymer solubility could be significantly influenced via variation of humidity in the surrounding gas phase. It is concluded that the interfacial tension between the ordered structures and the solution increased with humidity. The same effect was observed for other protic non-solvents in the surrounding gas phase and is attributed to a complexation of poly(γ-benzyl-L-glutamate) by protic non-solvent molecules (via hydrogen-bonding interactions). This change of polymer solubility was demonstrated to be reversible by addition or removal of small amounts of protic non-solvent in the surrounding gas phase. At a constant polymer concentration, ordered ellipsoidal structures could be dissolved by removing water or methanol present in the solution. Such structures formed once again when water or methanol was reintroduced via the vapor phase.
KeywordsHumidity Hydrogen bonding Macromolecular self-assembly Nucleation Solvent effects Supersaturation
We are indebted and grateful to Hildegard Kukula for polymer synthesis. We acknowledge financial support provided through the European Community’s “Marie-Curie Actions” under contract MRTNCT- 2003-505027 [POLYAMPHI]. Use of the Center for Nanoscale Materials was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
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