Ethyl stearate: ethanol binary mixtures investigated by ultrafast OKE spectroscopy, optical microscopy, dynamic light scattering, and rheology

Abstract

We report an experimental study of ethyl stearate/ethanol binary mixtures employing optical microscopy, rheology, dynamic light scattering, and femtosecond optical Kerr effect spectroscopy. Optical microscopy images show that at 25 °C this mixture is homogeneous up to 10 wt% ethyl stearate mass fraction and it leads to crystallization of ethyl stearate from solution at higher mass fractions. Rheological measurements at 40 °C and 25 °C exhibited an increase in viscosity of the binary mixture with increasing ethyl stearate mass fraction, consistent with molar mass considerations. Moreover, closer inspection of the rheology data from 0 to 10 wt% ethyl stearate mass fraction indicate a plateau in the viscosity near 10%, thus indicating how crystallization affects the rheological properties of the solution, even at 40 °C. Dynamic light scattering data are consistent with two major components at all mass fractions investigated: a small ethyl stearate aggregate consisting of approximately seven monomers and a micron‐sized crystallite. Femtosecond time‐resolved optical Kerr effect indicates slower nuclear relaxation with increasing ethyl stearate mass fraction, thus suggesting that low‐frequency motions of the binary mixture are involved in the early events of crystal nucleation. Copyright © 2013 John Wiley & Sons, Ltd.