Mesoscale Simulations of Complex Liquids

North Dakota State University Fargo, Fargo ND

Investigators

Abstract

0706017 Ihle TECHNICAL SUMMARY: The project supports research end education in theoretical and computational modeling of complex fluids. Such fluids are common, including surfactants, to soap, emulsifies and are ubiquitous in biological systems. The fluids have resisted quantitative modeling because they spontaneously develop nanoscale and micronscale structures, e.g. micelles and lamellar structures, caused by properties of the constituent molecules which are two to four orders of magnitude smaller than the resulting mesoscale structures. The dynamic behavior of complex liquids and soft materials is studied through a combined effort of theoretical research and computational simulations. The studies expand on current capabilities in order to address the presence of disparate length and energy scales and the complicated coupling between the shape of embedded objects and the hydrodynamic flow field. In addition, the proper treatment of many of these phenomena requires a consistent description of thermal fluctuations. The project contributes to the understanding of these systems through the development and application of robust, quantitative mesoscale simulation techniques which incorporate both hydrodynamic interactions and thermal fluctuations. This project involves the development of a specific mesoscale computational and theoretical algorithm?stochastic rotation dynamics (SRD). One enhancement permits modeling multi-component amphiphilic mixtures. A second add a constrained dynamics algorithm for modeling the dynamical behavior of worm-like chains embedded in an SRD solvent. This project will achieve the goals of mesoscale modeling through two or three orders-of-magnitude enhancement of efficiency of computational algorithms by rigorously enforcing bond-length constraints permits the use of longer time steps which also eliminates high frequency degrees of freedom which often complicate comparison with theory and experiment. The the application of these algorithmic and analytic advances includes the study the dynamics of amphiphilic mixtures and non-equilibrium stress relaxation in worm-like chains. For amphiphilic mixtures, problems of interest include spontaneous emulsification and mesophase dynamics and rheology. For worm-like chains such as DNA and actin, the study addresses tension propagation and relaxation, and the influence of confinement. Broader impacts: The project has impact within the field of complex fluids by providing substantial enhancements other research may apply to efficiently model other complex forms of soft matter. These techniques are relevant to materials used in a large range of industrial applications and the research extends these to biological systems. The engagement of students, graduate and undergraduate, in the theoretical physics behind such leading edge technology is both enlightening for undergraduates and an excellent career starting point for dissertation student. NON-TECHNICAL SUMMARY: The project supports research and education in theoretical and computational modeling of complex fluids. Such fluids are common, including surfactants, soaps, emulsifiers and are ubiquitous in biological systems. The fluids have resisted quantitative modeling because they spontaneously develop nano-scale and micron-scale structures, e.g. micelles and lamellar structures, caused by properties of the constituent molecules which are two to four orders of magnitude smaller than the resulting mesoscale structures. Theoretical models will be constructed and computer simulations implemented to make predictions of the structures, their thermodynamic properties and the dynamical evolution in time as they are created and change under external influences. Success in this research will have direct implications to the understanding of materials as diverse as ice cream and living cells. The engagement of students, graduate and undergraduate, in the theoretical physics behind such leading edge technology is both enlightening for undergraduates and an excellent career starting point for dissertation student.