Self-assembly behavior of a rod-like polypeptide at the air-water interface

We present a systematic study of morphological changes in monolayers of a rod-like polypeptide (poly-gamma-benzyl-L-glutamate (PBLG)) on a Langmuir trough as a function of increasing surface density. Through the combination of atomic force and Brewster angle microscopy, we accessed structural information on the nano-and micro-scale. Already during the spreading process, aggregates formed, leading to a coexistence of randomly organized domains, consisting of preferentially oriented fibers, embedded in a less ordered matrix of lower density. The resulting morphology after spreading resembles a structure of a 2D foam as observed for small amphiphilic molecules. With increasing surface density, we observed that the domains became larger with fibers showing a strong tendency to coarsen. Due to this coarsening process, the plateau region of the surface pressure isotherm exhibited a continuous increase in width of the fibers. In the region of highest surface density, solid-like films composed of compacted wide fibers were observed. These fibers, which were most likely in a glassy state, were fully oriented orthogonal to the compression direction. (C) 2016 Elsevier Ltd. All rights reserved.