Dipeptide hydrogel film deformation in response to extensional flow.

An emulsion is a nonequilibrium system, where a liquid is dispersed in another immiscible liquid in the form of fine droplets. Although it is easy to make droplets, it is more difficult to make them small enough (submicrometer) to be stable against creaming and coalescence. To break the initial droplets into very fine droplets they have to be deformed using large energy density flow. The deformation is inflicted on both the droplet and any material being used to stabilize the resulting interfaces. Here we stretch dipeptide hydrogels prepared with different salts and concentrations and study the mechanical properties of the resultant films. Surprisingly we find different collapse scenarios for each salt used (MgSO4, CaCl2 and NaCl) and observe a non-monotonic effect dependence of film strength on salt. Finally, we compare our results to those of films made of soap solutions from the literature.