(169k) Computational Modeling and Design of Self-Stratifying Colloidal Materials

Mixtures of colloidal particles suspended in a solvent can spontaneously form layered structures during fast solvent drying. This process, called self-stratification, can be leveraged to fabricate multilayered coatings (or supraparticles) from films (or droplets) in a single processing step. Such materials have applications in pressure-sensitive adhesives, abrasion-resistant coatings, drug encapsulation, and catalysis. The occurrence and extent of self-stratification are experimentally known to be sensitive to numerous physicochemical properties of the colloidal suspension and the processing conditions, but the process is poorly understood theoretically, and so is difficult to engineer. I am using computational modeling to understand the physics of self-stratification and then to design self-stratifying materials with targeted composition gradients.

Existing models for simulating self-stratification are computationally expensive or inaccurate. I have developed a better model for simulating the phenomena using dynamic density functional theory (DDFT). DDFT is a continuum model that is systematically formulated from particle-level interactions and dynamics. As such, it incorporates physics that would be present in particle-based simulations but can access much larger length scales and longer time scales. DDFT has two key inputs: a thermodynamic model (free-energy functional) and a dynamics model (mobility tensor). Different approximations of these inputs can be made, and the model can be made faster using the simplest models that give the desired accuracy. I systematically investigated approximations of both inputs to develop an accurate, efficient DDFT model for drying suspensions. I then coupled this model to an optimization strategy based on surrogate modeling to “inverse design” self-stratified coatings with targeted thickness and particle distribution. My work has the potential to reduce the time and resources required to create these novel materials in the laboratory.