Interfacial Activity of Star Polymers at Fluid Interfaces

This dissertation investigates the effect of composition and architecture of star polymers on their fundamental interfacial behavior at fluid interfaces and determines the contributions of important interfacial activity to the high foaming and emulsifying efficiency of star polymers. Star polymers are a novel class of surface active materials with a dense polymeric core and emanating polymer arms. Star polymers developed in this work are synthesized via atom transfer radical polymerization (ATRP) and are shown to be efficient foam and emulsion stabilizers. Three important dynamic interfacial processes: interfacial tension reduction, dynamic dilatational modulus and extent of adsorption are examined for star polymers with various structures and chemistries at air/water, xylene/water and cyclohexane/water interfaces. Adsorption on planar interfaces was monitored by ellipsometry, while interfacial tension and dilatational elasticity were measured separately by pendant drop tensiometry. Star polymers strongly reduce the interfacial tension, produce significant dynamic dilatational modulus and extent of adsorption due to the compact structure of star polymers compared to their linear counterparts. More mass is introduced per unit area of interface, and more interfacial penetration is achieved, upon their adsorption than for adsorption of linear polymers that adopt the conformation of loops, trains and tails. Star polymers with polyelectrolyte arms show pH-responsive interfacial behavior. The lateral electrostatic repulsions between the charged star polymers decrease the surface coverage but also enhance emulsion stability. Dynamic dilatational modulus and the ability of the star polymer adsorbed layer to resist ejection from the interface are identified to be correlated with high foaming and emulsifying efficiency. Finally, factors affecting the formation and stability of nanoemulsions stabilized by star polymers are examined.