Adhesion of Capsules to Surfaces

Capsules are particles consisting of a liquid core enclosed within a thin elastic membrane. Such particles are widely used in personal care and pharmaceutical products. They are often designed to deliver active ingredients to target surfaces. Therefore, adhesion and retention of a capsule to a surface in flow are crucial to product effectiveness. In many applications, soft particles are being pushed towards a target surface by an external flow. Once the two surfaces get close enough, attractive surface forces pull the particle into an energy well. The membrane spreads along the adhesive surface until it reaches an equilibrium value that minimizes the sum of the elastic energy and surface interaction energy. The flow could then change direction and attempt to detach the adhered particle by peeling the contact area. We have developed scaling theories to predict the adhesive contact radius, the minimum force required to detach the adhered particle, and the peeling velocity. Boundary integral simulations and flow and pipette experiments are carried out to verify the theories.