Fundamental study of emulsions stabilized by soft and rigid particles

Two distinct uniform hybrid particles, with similar hydrodynamic diams. and comparable zeta potentials, were prepd. by copolymg. N-iso-Pr acrylamide (NIPAM) and styrene. These particles differed in their styrene to NIPAM (S/N) ratios of 1 and 8, and were referred to as S/N 1 and S/N 8. Particle S/N 1 exhibited typical behavior of soft particles, i.e., the particles shrank in bulk aq. solns. when the temp. was increased. As a result, S/N 1 particles were interfacially active. In contrast, particle S/N 8 appeared to be rigid in response to temp. changes. In this case, the particles showed negligible interfacial activity. Interfacial shear rheol. tests revealed the increased rigidity of the particle-stabilized film formed at the heptane-water interface by S/N 1 than S/N 8 particles. As a result, S/N 1 particles were shown to be better emulsion stabilizers and emulsify a larger amt. of heptane compared to S/N 8 particles. The current investigation confirmed a better performance of emulsion stabilization by soft particles (S/N 1) than by rigid particles (S/N 8), reinforcing the importance of controlling softness or deformability of particles for the purpose of stabilizing emulsions. [on SciFinder(R)]