Probing concentration and time dependent conformational changes in poly acrylic acid stabilized magnetic nanoemulsion using magnetic chaining-based inter-droplet force measurement

Abstract

Emulsions are stabilized with surfactants, polymers, or polyelectrolytes to extend their shelf-life and colloidal stability. Electro-steric interaction in polyelectrolyte stabilized emulsions makes them ideal systems for probing the conformational dynamics. Here, magnetic chaining technique is exploited for inter-droplet force measurement in poly acrylic acid (PAA) stabilized magnetic nanoemulsions, and to probe the conformational changes of the stabilizing moieties as a function of time and PAA concentration. Force measurement studies indicate an increased inter-droplet spacing for higher concentration of PAA due to an increase in osmotic pressure with concentration. Further, for a fixed concentration, the inter-droplet spacing decreases with time due to the slow diffusion of the polymer chains resulting in conformational changes. This is the first experimental report on conformational dynamics of PAA stabilized oil-in-water magnetic nanoemulsions. The obtained results are beneficial for understanding the nature of colloidal interaction forces in polyelectrolyte stabilized nanoemulsions.