Molecular Engineering of Triacylglycerols
Mary Biddy, University of Wisconsin
Rising concerns over the availability of petroleum-based products have generated considerable interest in finding alternative, renewable sources. In the particular case of industrial lubricants, vegetable oils provide one possible and promising alternative to petroleum-based products. Vegetable oils are environmentally benign, since they are naturally occurring and renewable, and they exhibit a number of physical attributes, including viscosity indices and pour point temperatures, which are superior to those of lubricants made from petroleum products. In order to formulate vegetable oils with optimal lubrication properties, the influence of the individual molecular components on the oil properties must be understood. Vegetable oils are essentially mixtures of triacylglycerols. Although triacylglycerols are naturally abundant, very little is known about them. Furthermore, most of the available physical properties are for pure, simple triacylglycerols, and the effect of molecular structure on physical properties is not understood. Computer simulations can directly relate molecular architecture to physical properties; they offer a valuable tool to improve our understanding of this important class of materials. We present our findings on the computational prediction of the transport coefficients, including viscosity, of triacylglycerols and vegetable oil mixtures. By using quantum chemistry we have developed an accurate force field to describe both intra- and inter- molecular potentials for these systems. By applying this force field in equilibrium molecular dynamics simulations, we have obtained viscosities and densities that agree well with experimentally observed values. The effect of molecular structure on physical properties is explored for triacylglycerols that are hard to isolate in vegetable oils and that are chemically modified. Novel algorithms have also been developed to decrease the amount of computational time required for viscosity calculations, including the use of multiple time step algorithms coupled to momentum-impulse relaxation methods.
Abstract Author(s): Mary J. Biddy<br />Amadeu K. Sum<br />Juan J. de Pablo