Effects of polymers on the regulation of p-aminobenzoic acid crystal habit

This study focuses on how polymers regulate the crystal habit of p-aminobenzoic acid (PABA) from long rodlike to blocklike. To propose the regulation mechanism of polymers on the crystal habit of PABA, experiments include cooling crystallization and single crystal growth as well as molecular simulation have been carried out. Firstly, crystal form of PABA from cooling crystallization was determined as α form. Secondly, among four 1.0 wt% polymers, polyvinylpyrrolidone (PVP) played a more significant role in regulating crystal habit, which inhibited the growth of long axis resulting the growth rates of the long axis from 92.1 μm/h down to 6.7 μm/h. Furthermore, the effect of PVP chain length and concentration on crystal habit has also been studied, 0.2 wt% PVP-K17 regulated the crystal habit of PABA from long rodlike to blocklike but the effect of PVP was weakened with increasing chain length and decreasing concentration. Molecular simulation results show that the interaction between PVP-K17 and (1 1 0)/(0 1 1) face, which determines the axial growth rate, is stronger compared with other crystal faces. The mechanism of PVP-K17 regulating crystal habit was that it can be selectively adsorbed on (1 1 0) and (0 1 1) faces, hindering the diffusion and adsorption of solute molecules, inhibiting the growth of the long axis of PABA crystals, so the crystal habit of obtained crystal is blocklike.