Morphology and phase transitions of n-alkyl alcohol microcrystals

Phase transition behaviors and morphology of thin crystals of 1-heptadecanol and 1-octadecanol with sample masses from 3 μg to 1 mg were investigated by the high-sensitive DSC and AFM. The solid transition and the melting temperatures depressed with the decrease in sample mass. The phase transition behaviors were divided into three groups, the transitions were same to the bulk (more than 0.1 mg), the solid-state transition temperature depressed (from 0.1 to 0.03 mg), both the melting and the solid-state transition temperature depressed (<0.03 mg). The crystal morphologies of 0.1, 0.01, 0.005 mg sample were observed by AFM for the representative of each groups. The morphologies of crystals were classified into three groups, the large droplets with the curved shape, the middle droplets with flat and round shape and the polygonal shape. The crystal morphologies correlated with the phase transition behaviors.