Thermomechanical cubic closed-cell model of liquid-saturated soft composites with surface effects

• Established a micro-mechanical model of closed-cell liquid-saturated soft composites. • Investigated the effects of surface effects on thermo-mechanical behaviors of closed-cell composites. • Revealed the effects of porosity and liquid compressibility on thermo-mechanical behaviors of closed-cell composites. Many animal and plant tissues, such as adipose tissue and fruits, can be taken as liquid-saturated soft composites, which have densely packed pores that are filled with liquid. Typically, when the pore dimensions are sufficiently small (at the micro- or nanoscale), surface effects significantly influence the mechanical properties of the material. To characterize the thermomechanical properties critical for animals and plants, we propose an idealized cubic closed-cell model in which liquid compressibility and surface stress (i.e., surface moduli and residual surface stress) are considered. Analytical solutions of the model are then employed to quantify how the surface stress, porosity, and liquid bulk modulus affect the effective Young’s modulus, effective Poisson ratio, and effective coefficient of thermal expansion (CTE) of the liquid-saturated soft composite. An increase in residual surface stress reduces both the effective modulus and effective CTE, whereas increasing the surface moduli result in a greater effective modulus and reduced effective CTE. The results provide critical insights into how surface effects govern the macroscopic thermomechanical behavior of liquid-saturated soft composites with small pores.