Microgel stabilized emulsions: Breaking on demand

Abstract

Here, we report on how to stabilize and break emulsions that are compatible with enzymatic reaction conditions. Many substrates of enzymatic reactions are soluble in unpolar organic solvents whereas the enzymes themselves often need an aqueous environment. We use a buffer solution (triethanolamine hydrochloride) as aqueous and MtBE (tert-butyl methyl ether) as organic phase which provide good enzyme compatibility. We are able to break emulsions in a desired temperature range by using NiPAM–NiPMAM microgels with different monomer compositions and architecture, respectively. Our microgels need to deswell to about 55% of its swollen size at room temperature to let the emulsion break. Emulsions can be broken such that the microgels are either colloidally stable in the aqueous phase or flocculated. The temperature interval in which the microgels stay colloidally stable while the emulsion is broken is broader for the core–shell microgel than for the copolymer microgel. The behavior of the microgels in aqueous solution allows predicting: (i) the temperature at which the emulsion breaks and (ii) whether microgels flocculate or not during breaking the emulsion. However, the partial miscibility of the organic phase with the aqueous phase has to be taken into account. Thus, we are able to stabilize and break emulsions by employing microgels as responsive emulsifiers and to adapt the microgels to the requirements of biocatalytic processes.