A study of the formation of supermolecular order in polymeric solutions by means of low‐angle scattering of polarized light

Abstract

AbstractA relatively simple device is described for studies of phase transitions in polymer solutions and films by means of low‐angle scattering of polarized light. The device differs from that described by Stein. It functions as a horizontal polarizing microscope, as a photodiffractometer, and as a photometer. A study was carried out of the structure formation in concentrated solutions of poly‐γ‐benzyl‐L‐glutamate with Mw = 105 in dioxane. At room temperature and in the absence of external fields a successive development of several levels of supermolecular order is observed. The structure formation starts with the spherulitic phase characterized by a cross‐shaped diffraction pattern. During their progressive growth the spherulites fill the volume of the solution and finally begin to collapse. This changes the scattering pattern to a circular one. The mechanical instability of this phase and the thermodynamic advantage of a parallel packing of rodlike particles leads to the appearance of an orientational order in the system with a rhombic‐shaped scattering pattern. The structure formation is completed with the development of a highly ordered liquid crystalline (cholesteric) phase characterized by a specific pattern similar to the x‐ray diffraction patterns of oriented crystalline polymers. A detailed interpretation of rhombic scattering pattern is presented based on an analysis of polarized light scattering from a system of noncoherent scattering elements with the shape of a rectangular parallelepiped. Expressions are derived connecting the shape and the size of the scattering pattern with the dimensions of a single scattering element, and with the optical properties of this element and of the supporting medium. The spherulitic growth habit in isotactic polypropylene solutions when subjected to cooling also has been studied. At temperatures below 100°C. the spherulites appear and the rate of their growth is dependent on the thermal history of the solution. Kinetic curves are obtained showing the existence of a “kinetic memory” in the system which is manifested by a pronounced acceleration of growth of the structure when the fusioncrystallization cycles are repeated.