Organogels

Organogels are semisolid systems in which an organic liquid is immobilized within a three-dimensional network formed by gelators. Unlike hydrogels, which entrap water, organogels immobilize organic solvents or oils through a solid-like matrix.

The gel network can be built from low molecular weight organogelators or from polymeric gelators. Gelation can be physical, driven by noncovalent interactions such as hydrogen bonding, π–π stacking, and van der Waals forces, or chemical, through covalent crosslinks. Physical organogels are often thermo-reversible and may respond to temperature, shear, or solvents.

Preparation typically involves dissolving the gelator in the chosen organic solvent at elevated temperature and then cooling to form the gel; alternative routes include solvent exchange, ultrasound, or enzymatic crosslinking.

Organogels exhibit viscoelastic behavior, with a storage modulus generally exceeding the loss modulus in the gel state. They can be opaque or translucent, and their mechanical strength, transparency, and release characteristics depend on gelator concentration, solvent polarity, and temperature. They may show thixotropy and selective solvent retention.

Solvent scope includes many nonpolar to moderately polar organic liquids, such as alkanes, aromatics, esters, ketones, and oils; water is generally not the solvent.

Applications span cosmetics and dermatology for topical formulations, pharmaceutical delivery of lipophilic drugs, fragrance and flavor encapsulation, and use in materials science as templates for porous structures or self-healing gels. Limitations include mechanical fragility, solvent loss during handling, sensitivity to impurities, and potential toxicity of gelators, necessitating appropriate safety and regulatory evaluation. Characterization commonly uses rheology, microscopy (SEM/TEM), DSC, and spectroscopy to study network structure and interactions.