Academic Awards 2025 booklet

49 Multi-component polymer mixtures at an interface We live in a polymeric world: we find polymers - long, chain-like molecules - everywhere: from food and cosmetics to paints and medicines. In these applications polymers are often mixed together in liquids alongside alongside tiny particles called colloids. The interactions in such mixtures determine the stability. Sometimes polymers stick to particles; sometimes they avoid them. But what happens when multiple types of polymers are present, or when polymers with varying sizes are present? My thesis presents a new theoretical framework to make predictions about such complex polymer mixtures. Using analytical mean-field theory, the theory predicts how the polymer concentration changes in the vicinity of particles, and how surface tension and inter-particle forces evolve in these systems. It uncovers a subtle effect: when a weakly adsorbing polymer is mixed with one that tends to avoid the particles, the first polymer becomes much more strongly adsorbed—an effect we call “depletion-enhanced adsorption”. I also investigated what happens when polymers are trapped between two surfaces. Depending on whether the polymers are free to move or stuck in place, they may either pull the surfaces together or push them apart. These findings help to understand and design stable multi-component materials—vital for emulsions, coatings, and biotechnology—by revealing how molecular interactions dictate large-scale material behavior.

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