Time-Resolved WAXD and SAXS Investigations on Butyl Branched Alkane at Elevated Pressures

The crystallization behavior and the morphological aspect of the butyl branched alkane C96H193CH(C4H9)C94H189 have been investigated using time-resolved wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) at atmospheric and elevated pressures. The solution crystallized sample shows pronounced crystalline reflections in WAXD with a lamellar thickness of 127 Å, corresponding to a once-folded structure in SAXS at atmospheric pressure. Cooling the sample from the melt at 4 °C/min at atmospheric pressure results in a lamellar thickness of 104 Å with chains having a tilt angle of 35°. The crystallization of the branched alkane at pressures of ca. 4 kbar and the same cooling rate of 4 °C/min reveals a new crystal reflection emerging between the (100) monoclinic and the (110) orthorhombic reflections. Simultaneous to the appearance of the new reflection, a sudden shift in the Bragg d value of the (110) orthorhombic reflection occurs, indicating densification of the orthorhombic unit cell. The new reflection has been assigned as the pseudohexagonal phase attributed to the crystallization of the butyl branches at elevated pressures. The pseudohexagonal phase merged into the orthorhombic phase upon releasing pressure and reappeared on increasing pressure. Compared to lamellar thickness at atmospheric pressure, an increased lamellar thickness of 118 Å was observed at ca. 4 kbar with SAXS