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

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.