semiliquid

Semiliquid describes materials whose mechanical behavior lies between that of a solid and a liquid. Such substances resist deformation like a solid to a degree, but will flow given sufficient stress and time, and often show viscoelasticity, combining elastic storage with viscous dissipation. Many semiliquids have a yield stress: they behave as a solid until the applied stress exceeds a threshold, after which flow commences. Their viscosity is typically non-Newtonian and can depend on shear rate, temperature, and history (for example, how long the material has rested).

Common examples include gels, pastes, creams, ointments, batters, and certain clays or putties. Foods like custards and mayonnaise, cosmetics such as hand creams, and pharmaceutical semisolids like topical gels illustrate how semiliquids combine spreadability with transient structure. Their microstructure—dispersions, networks, or packed particles—governs how they deform and relax after stress.

Rheological characterization uses instruments called rheometers to measure quantities such as the storage modulus G' and the loss modulus G'', as well as yield stress and thixotropy. Understanding semiliquids is important in formulation, processing, packaging, and application because flow behavior affects texture, stability, delivery, and user experience. Handling requires temperature control and appropriate mixing to avoid phase separation or segregation.