Fabrication and mechanical characterization of liquid-in-solid elastomeric soft composites

As one of the emerging new composite materials, liquid-in-solid elastomer soft composites are of the current research interest for their enhanced mechanical properties and high biological application potentials. Despite established microscopic models for describing elastic behaviors of the two-phase material incorporating liquid-solid interfacial energy, how multiple liquid inclusions would affect the macroscopic mechanical properties of composites are not yet fully understood. In this thesis research, by selecting polydimethylsiloxane (PDMS) as the matrix material and glycerol as the liquid material, liquid-in-solid composites with polydisperse and monodisperse inclusion sizes are fabricated by using the simple mixing method and the coaxial microfluidic device (CMD), respectively. The stiffness and toughness of composites are characterized by using adapted basic testing methods. The effects of the volume fraction, size, size polydispersity, and interactions of liquid inclusions on the elastic modulus, general toughness, and fracture energy of composites are evaluated and quantified by relating experimental measurements with theoretical predictions. From the results, macroscopic softening of stiff-matrix composites (E ≥ ~150 kPa) with an increasing inclusion volume fraction, macroscopic stiffening of polydisperse composites with a decreasing average inclusion size, and macroscopic toughening of composites with dilute liquid inclusions (3- 15% volume fraction ) are observed. Furthermore, counter-predictive stiffening in monodisperse composites is found; the effect of inclusion interactions is investigated as an additional stiffening contributor other than liquid surface tension. In general, this thesis research provides theoretical and experimental bases for designing composite-like bio-materials, along with insights into the mechanics of composites