Fabrication of solid-liquid composites with desired droplet size and volume fraction by adopting thermoreversible phase transition

Solid-liquid composites (SLCs) have recently attracted many researchers as a way to overcome soft polymer material's limitations, realize new properties, and fabricate the porous structure. Here, we develop a new fabrication method for SLCs, where thermoreversible hydrogel droplets with the desired size are uniformly distributed in the silicone matrix. Using a three-dimensional axisymmetric flow-focusing device, we successfully generate uniform size droplets and control the volume fraction of droplets with a highly viscous continuous phase. Since the continuous phase is a mixture of PDMS base and catalyst, adding a crosslinker to the continuous phase causes the PDMS to be cured and become a silicone matrix. As droplets distributed in silicone matrix go through sol-gel transitions, the SLCs sensitively change mechanical properties according to temperature. In addition, since the developed method can be used in fabricating designable porous structures by evaporating liquid droplets in SLCs, it has potential applications in diverse fields ranging from gas separation systems to tissue engineering.