Abstract: 

It is known that microgels can serve as soft, permeable and stimuli-responsive alternative of solid colloidal particles to stabilize oil-water emulsions. The driving force for the adsorption of the microgels on interface of two immiscible liquids is a shielding of unfavorable oil-water contacts by adsorbed subchains, i.e., the decrease of the surface tension between the liquids. Such phenomenon proceeds if volume fractions of the two liquids are comparable with each other and the microgel concentration is not high enough. The natural question arises: what is going on with the system in the opposite case of strongly asymmetric mixture (one of the liquids (oil) has a very small fraction) or high microgel concentration (the overall volume of the microgels exceeds the volume of the minor oil component)? We demonstrate that the microgels uptake the oil whose concentration within the microgels can be orders of magnitudes higher than outside leading to the additional microgel swelling (in comparison with the swelling in water). Thus, the microgels can serve as scavengers and concentrators of liquids dissolved in water. Such counterintuitive at the first glance effect has a clear physical reason related to incompatibility of oil and water. The microgels with up-taken oil are stable towards aggregation at very small oil concentration in the mixture. However, increase in the oil concentration can lead to aggregation of the microgels into dimers, trimers, etc. Oil in the aggregates is located in-between the microgels instead of their interior which is accompanied by the release of the elastic stress of the microgels. Further increase of oil concentration results in a growth of the size of the oil droplets between the microgels and of the number of the microgels at the droplet’s periphery, i.e., emulsion is formed.   

Acknowledgements. The financial support of the Russian Science Foundation, No.19-43-06306, is gratefully acknowledged.