Nucleation and crystal growth in sheared poly(1‐butene) melts

The nucleation and growth behavior of a poly(1‐butene) melt has been measured as a function of undercooling and shear rate. Experiments were conducted using a parallel‐plate rotary shearing device with polarized light microscopy as the measuring technique. An exponential increase of nuclei with time at constant undercooling and shear rate was found. Growth rates of the crystalline bodies showed no significant change in a shear field. Nucleation and growth rate data were analyzed using expressions of the form I = I 0 exp [‐ΔE/RT ‐ UT m / T Δ T ] G = G 0 exp [‐ΔE/RT ‐ UT m /TΔT] where Δ T is the undercooling, T m is the equilibrium melting temperature, and U contains lateral s̀ and end‐surface s̀ e free energies. The value of s̀s̀ e calculated from U for crystallization under shear differed from that calculated for the quiescent case by a factor of two. This difference is tentatively explained in terms of an entropy loss in the sheared system.