Isothermal and Self-Seeding Crystallization from Polyethylene Solution*

We have applied time-resolved small angle neutron scattering (SANS) to studying self-seeding and isothermal crystallization kinetics of low molecular weight polyethylene in solution. In one example, SANS spectra of isothermal crystallization of 2.1 kg/mol PE at 78.8 $^{\circ}$C from a solution containing 4.3 {\%} PE by mass show both the characteristic form and structure factors of stacked lamellae. The intensity hump around 0.025 {\AA}$^{-1}$ indicates the correlation among lamellae. On the other hand, SANS from the same solution after quenched from melt to the room temperature, then stored at 90 $^{\circ}$C for 5 min, followed by quenching to 78.7 $^{\circ}$C are different from those of isothermal crystallization; the first correlation peak from the structure factor is not obvious, implying that crystals are dominantly in single or few lamellae forms. A morphological model that accommodates arbitrary distributions of structures from individual lamellae to infinite stacks has been used to analyze the SANS data. A possible lyotropic transition from isolated to stacked lamellae is suggested.