| Abstract: | Some rather unusual optical morphologies in thin films of poly(hydroxybutyrate) in which a temperature gradient is imposed across the thickness of the film are reported. Spherulites in which the Maltese cross degenerates into a continuous spiral grow under these conditions, and the direction of the rotation of the spirals depends on the direction of heating. These morphologies are explained with the existing understanding of spherulite optics. The helicoidally twisting crystallites are modeled as twisting around an axis at a fixed angle to the radius of the spherulite (and the plane of the film). The possible implications for future, inclusive models of banding in spherulites are discussed. Further observations on the temperature dependence of the optical banding pattern in poly(hydroxybutyrate) are also reported, and an unexpected minimum in band spacing and fine optically visible fibrillar texture is discussed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1575–1583, 2000 |
