Infrared study on annealing effect on conformation of zinc stearate

Abstract

The molecular conformation and thermal transition behavior of two zinc stearate specimens, unannealed one and annealed one, were compared. The unannealed specimen has one thermal transition at 134 °C. Annealing was made by increasing temperature to 150 °C and cooling to room temperature slowly. This annealed specimen has an exothermic peak at 103 °C, and endothermic shoulders and a peak at 118, 124 and 131 °C, respectively. The observed frequencies of all bands of the unannealed specimen at room temperature are assigned to the all-trans conformation. We found new bands at 858, 823, 793, 766, 688, and 604 cm −1 for the annealed specimen. Based on the normal mode analyses, these bands are assigned to the TGT conformation at the COO end, where T means trans and G means gauche. The annealed specimen consists of almost all-trans molecule but partial molecules have the TGT conformation.