Synthesis and characterization of hierarchical porous structure of polydimethylsiloxane (PDMS) sheets via two-step phase separation method

[Display omitted] •The porous PDMS sheets were fabricated using a two-step phase separation method.•Pores with 509 µm and 28 µm sizes were formed by THF and Toluene evaporation.•The density of large and small pores can be tuned by adjusting the THF/solvent ratio.•The modulus of the porous structure can be adjusted by controlling the solvent ratio.•The highest flexibility was observed when 50% THF and 50% Toluene were employed. This paper reports the synthesis and characterization of the hierarchical porous structure of polydimethylsiloxane (PDMS) sheets. A two-step phase separation synthesis protocol is designed based on a ternary solution of PDMS that contains both a nonsolvent and solvent. Tetrahydrofuran (THF) and Toluene with various mixing ratios are utilized as a solvent phase for inducing two-step phase separation. Two distinct pore size distributions are observed in the cast PDMS sheets. The large pores with an average of 509 µm are formed during the first-step phase separation due to evaporation of THF. The second-step phase separation occurs later at higher temperatures due to evaporation of Toluene, resulting in much smaller pores with an average size of 28 µm. The experimental results reveal that increasing the THF/solvent ratio increases the concentration of large pores and decreases small pore density. Tensile testing of dog bone-shaped porous PDMS sheets shows that the modulus varies between 0.64 and 0.95 MPa, indicating that the synthesis protocol can control the porous structure with a wide range of flexibility while keeping the density constant. An empirical relationship between elastic modulus and pore size is developed, promising in designing the PDMS porous structures for various engineering applications.