Hydrocarbon polymers, foams and nanocomposites are increasingly being subjected to extreme environments. Molecular scale modeling of these materials offers insight into failure mechanisms and complex response. Classical molecular dynamics (MD) simulations of the principal shock Hugoniot were conducted for two hydrocarbon polymers, polyethylene (PE) and poly(4-methyl-1-pentene) (PMP). We compare these results with recent density functional theory (DFT) calculations and experiments conducted at Sandia National Laboratories. Here, we extend these results to include low-density polymer foams using nonequilibrium MD techniques. We find good quantitative agreement with experiment. Further, we have measured local temperatures to investigate the formation of hot spots and polymer dissociation near foam voids.
Large-scale, high-throughput production of nano-structured materials (i.e. nanomanufacturing) is a strategic area in manufacturing, with markets projected to exceed $1T by 2015. Nanomanufacturing is still in its infancy; process/product developments are costly and only touch on potential opportunities enabled by growing nanoscience discoveries. The greatest promise for high-volume manufacturing lies in age-old coating and imprinting operations. For materials with tailored nm-scale structure, imprinting/embossing must be achieved at high speeds (roll-to-roll) and/or over large areas (batch operation) with feature sizes less than 100 nm. Dispersion coatings with nanoparticles can also tailor structure through self- or directed-assembly. Layering films structured with these processes have tremendous potential for efficient manufacturing of microelectronics, photovoltaics and other topical nano-structured devices. This project is designed to perform the requisite R and D to bring Sandia's technology base in computational mechanics to bear on this scale-up problem. Project focus is enforced by addressing a promising imprinting process currently being commercialized.
The most feasible way to disperse particles in a bulk material or control their packing at a substrate is through fluidization in a carrier that can be processed with well-known techniques such as spin, drip and spray coating, fiber drawing, and casting. The next stage in the processing is often solidification involving drying by solvent evaporation. While there has been significant progress in the past few years in developing discrete element numerical methods to model dense nanoparticle dispersion/suspension rheology which properly treat the hydrodynamic interactions of the solvent, these methods cannot at present account for the volume reduction of the suspension due to solvent evaporation. As part of LDRD project FY-101285 we have developed and implemented methods in the current suite of discrete element methods to remove solvent particles and volume, and hence solvent mass from the liquid/vapor interface of a suspension to account for volume reduction (solvent drying) effects. To validate the methods large scale molecular dynamics simulations have been carried out to follow the evaporation process at the microscopic scale.
This report summarizes the work completed under the Laboratory Directed Research and Development (LDRD) project 10-0973 of the same title. Understanding the molecular origin of the no-slip boundary condition remains vitally important for understanding molecular transport in biological, environmental and energy-related processes, with broad technological implications. Moreover, the viscoelastic properties of fluids in nanoconfinement or near surfaces are not well-understood. We have critically reviewed progress in this area, evaluated key experimental and theoretical methods, and made unique and important discoveries addressing these and related scientific questions. Thematically, the discoveries include insight into the orientation of water molecules on metal surfaces, the premelting of ice, the nucleation of water and alcohol vapors between surface asperities and the lubricity of these molecules when confined inside nanopores, the influence of water nucleation on adhesion to salts and silicates, and the growth and superplasticity of NaCl nanowires.