la503040f_si_001.pdf (1.01 MB)
Impact of Electrostatics on the Adsorption of Microgels at the Interface of Pickering Emulsions
journal contribution
posted on 2014-12-16, 00:00 authored by Pascal Massé, Elisabeth Sellier, Véronique Schmitt, Valérie RavaineThe
importance of electrostatics on microgel adsorption at a liquid
interface is studied, as well as its consequence on emulsion stabilization.
In this work, poly(N-isopropylacrylamide) (pNIPAM)
microgels bearing different numbers of charges and various distribution
profiles are studied, both in solution and at the oil–water
interface of emulsion drops. Charged microgels are compared to neutral
ones, and electrostatic interactions are screened by adding salt to
the aqueous solution. In solution, electrostatics has a significant
impact on microgel swelling, as induced by the osmotic pressure exerted
by mobile counterions in the gel network. At the interface of drops,
microgels pack in a hexagonal array, whose lattice parameter is independent
of the number of charges and range of electrostatic interactions.
Microgel morphology and packing are ruled only by the adsorption of
the pNIPAM chain at the interface. Conversely, decreasing the charge
density of microgels by the protonation of the carboxylic groups leads
to unstable emulsions, possibly as a result of the impact of hydrogen
bonding on microgel deformability.