New theoretical and simulation approach for understanding packing structures of soft self-adjusting objects

Rensselaer Polytechnic Institute, Troy NY

Investigators

Abstract

When designing new solid materials, it is important to manipulate how a material’s constituent objects pack together to tailor the properties to an application. Using heat treatment or applying an external force can change this packing, thereby modifying the material’s structure to fit the developer’s need. For example, this type of manipulation is used to control properties of glass, steel, and plastics. Many conventional computer simulation methods used to predict these packing arrangements assume that the objects are hard spheres. But often real materials are made of soft objects. These will pack differently, like how balloons pack differently from bowling balls. This award uses a new computer model to understand how to control the packing of squishy polymeric objects. Connecting the polymer stiffness and processing conditions with the overall material properties will enable new opportunities for faster development of designer materials. This award aims to test the hypothesis that the packing structures observed for a material have less to do with the volume fraction of particles (the current common interpretation) and more to do with the surface area of the deformable particles. The simulations are based on a vertex model in which the geometry of contact between surfaces determines the physical interactions. The first objective is to quantify the roles of thermal fluctuations, particle surface tension, and exchange of material between particles in determining the equilibrium preferences for structures. The second objective is to understand the dynamic evolution in time. This includes the formation of ordered states upon quenching a disordered state, as well as transitions between ordered states. 2D simulations represent thin films while 3D simulations represent bulk materials. The coarse-grained nature of the model enables large assemblies including the effects of crystal grain size and grain boundaries. The award will train undergraduate and graduate students as well as a postdoctoral researcher in the application of computer simulations to materials. It will also create an interactive online tool to help motivate students to pursue STEM careers via learning about material properties and design. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.