porogens

Porogens are materials incorporated into a precursor matrix to create pores after removal. They are used to tailor porosity, pore size, and interconnectivity in polymers, ceramics, and composite structures for filtration, catalysis, and biomedical applications.

Porogens can be soluble or dispersible in the processing medium, gas-evolving, or decomposable during curing. Common porogens include soluble salts (such as sodium chloride or ammonium chloride), sugars, waxes or paraffin, organic solvents, and gas-forming compounds like ammonium bicarbonate. Removal occurs via extraction or dissolution, leaching with water or solvent, sublimation, or gas evolution that leaves behind voids.

Processing methods include particulate leaching (salt or sugar particles dispersed in a polymer precursor and later dissolved), gas foaming (saturation with supercritical or high-pressure gas followed by depressurization), phase separation (thermally induced or solvent-induced), and freeze-drying or freeze casting (ice crystals act as porogens that sublimate). Pore size and porosity are controlled by porogen size, loading, and the processing parameters.

Properties relevant to porogen-based porous materials include total porosity, pore-size distribution, interconnectivity, and mechanical strength. Biocompatibility and residual porogen removal are important for biomedical uses; for filtration or catalysis, chemical compatibility and stability are also considered.

Applications span tissue engineering scaffolds, bone substitutes, drug-delivery matrices, filtration membranes, and catalyst supports. Porogen strategies enable tuning of structure to balance porosity with mechanical integrity for the intended function.