Compression Induced Syneresis and Yielding in Fibrous Oil-in-Hydrogel Emulsions

Emulsion gels stabilized by fibrous networks are found in cosmetic, pharmaceutical, and food industries where oil droplets are dispersed throughout a continuous water phase and fibers form a continuous network. While the droplets and fibrous network work together to impart unique mechanical properties, the release of water and subsequent collapse of the gel under compression is less understood. In this work, we probe the effects of emulsion droplets on hydrogel syneresis in a fibrous gel network to control and optimize water flow and retention within the gel. Sodium myristate surfactant, silicone oil, and water are mixed to form an emulsion that gels when cooled to room temperature. Compressing these oil-in-hydrogel structures causes the release of water from the highly permeable gel phase and eventually creates a reinforced compressed emulsion with a storage modulus that scales with the Laplace pressure. Further compression of the sample results in a buckling-like failure of the material as either the emulsion breaks due to increased droplet coalescence and the oil is released as a single phase, or the fibers fail, and the gel deforms plastically. The failure stress of the material depends on the radius of the emulsion droplets, and is greatest for oil volume fractions of around 40%. The results have implications for the understanding of complex gels such as those of food and tissue.