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 onthe nano- and micro-scale. Already during the spreading process, aggregates formed, leading to acoexistence of randomly organized domains, consisting of preferentially oriented fibers, embedded in aless 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.