Colloidal clusters and chains of amphiphilic particles at air-water interface during drying

Vaibhav Raj Singh Parmar*, Sayantan Chanda, Ranjini Bandyopadhyay

The drying droplets of colloidal suspensions are ubiquitous. The kinetics of the drying drop and its final deposition pattern are of great industrial interest. When an aqueous drop of pNIPAM suspension is allowed to dry, the particles migrate to the air-water interface from the bulk due to their amphiphilic nature. We observe a transition from an ordered cluster of particles at the air-water interface to the formation of colloidal chains when the stiffness of pNIPAM particles is increased. The transition is controlled by the competition between the steric stabilization of pNIPAM particles and their deformability at the air-water interface. When a stiff particle moves to the interface, it changes the air-water interface curvature locally, giving rise to surface tension-originated stress on the particle. As time progresses, these particles experience an attraction toward each other, resulting in the formation of clusters at the air-water interface.