Stress Development and Cracking During Drying of Latex films

This project proposes an experimental and theoretical examination of how drying bodies crack. This entails following the stresses developing in a body of particles as water is removed and the particles deform to fill all space. Starting with a stable colloidal dispersion, the particles pack and deform in a manner determined mainly by temperature. The stress, pulling the film apart, follows from the van der Waals attraction between particles being hindered by the substrate restricting lateral contraction. The material response is a result of the energy consumed by propagating a crack a unit length through a body of randomly aligned deforming particles. This project will model stresses and material fracture toughness to allow prediction of film cracking during drying. Experimentally, a systematic mapping of parameter space will be carried out and the model tested. The packing of particles is intuitively thought to be crucial in both stress generation and fracture toughness development. This can be controlled by manipulation of floc structures in aggregating dispersions, with subsequent drying. This presents the possibility of systematically controlling cracking of thin films.This work will enable coatings formulations to improve, with a reduction in volatile organic components, a major source of air pollution. Academically this is a major colloidal problem, with the coupling between stress generation and material property development making a challanging yet important area for study.