Rhythmic Crystallization of Poly-L-alanine

Abstract

IN a recent morphological study of poly-L-alanine spherulites¹, ring and spiral structures observed under the polarizing microscope were ascribed to thickness variations. These spherulites were cast on a watchglass from 1 : 1 v/v mixtures of trifluoroacetic acid and trifluoro-ethanol, using concentrations from ∼0.1 to ∼2.0 weight per cent, evaporation rates varying between 0.13 and 0.042 ml./h (but usually 0.083 ml./h) and a casting temperature of 25° ± 2° C. The relative humidity in the vapour space above the crystallizing solution was varied from dry to saturated for the given conditions without apparent effect on the quality of the spherulites.