AFM STUDY OF MORPHOLOGICAL DEVELOPMENT DURING THE MELT-CRYSTALLIZATION OF POLY(ETHYLENE OXIDE)

The atomic force microscope (AFM) has been used to investigate morphol ogical development during the crystallization of poly(ethylene oxide) (PEO) from the melt. PEOs with molecular weights of 1 x 10(5) and 7 x 10(6) were used. Height and amplitude images were recorded, using the tapping mode. For both polymers, the mode of spherulite development va ried with the velocity of the growth front. For slow growth velocities , the growth of the crystallites was linear, with growth initially occ urring by single lamellae, later developing into growth arms by screw dislocation spawning of crystallites. At intermediate growth velocitie s, stacks of lamellae develop rapidly. The splaying apart of adjacent crystals and growth arms is abundant. The operation of growth spirals was observed directly in this growth velocity range. The crystals form ed by the giant screw dislocations diverge immediately from the origin al growth direction, providing a source of interlamellar splaying. At low and intermediate velocities, the front propagates by the advance o f primary growth arms, with the regions between the arms filled in by arms growing behind the primary front. At the highest velocity observe d here, the formation of lamellar bundles and immediate splaying resul ts in recognizable spherulites developing at the earliest stages of cr ystallization. The change from linear growth to splaying and nonlinear growth are qualitatively explained in terms of driving force, elastic resistance and the presence of compositional and/or elastic fields in the melt. (C) 1998 John Wiley & Sons, Inc.