nonflowing

Nonflowing is an adjective used to describe substances or materials that do not flow under specified conditions, typically due to high viscosity, a yield stress, or a solid-like internal structure. In rheology, flow refers to the movement of material when subjected to shear; nonflowing materials resist such movement and may behave as a solid until a sufficient stress is applied, after which they begin to flow. Some materials are nonflowing at ambient temperatures but become flowable when heated or under high pressure, indicating a dependence on temperature or stress.

Causes of nonflowing behavior include strong interparticle cohesion, gelation, crosslinking, and the presence of a network structure that supports itself against deformation. Conversely, materials that are nonflowing at rest can still flow when subjected to adequate force, illustrating concepts such as yield stress and viscoelasticity. The relationship between shear stress and shear rate for nonflowing materials is often described using models like Bingham plastic or Herschel-Bulkley, which characterize the threshold stress required for flow and how flow rate changes with applied stress.

Applications and examples of nonflowing materials appear across industries. They include gels, pastes, putties, sealants, and certain high-viscosity liquids or powders designed to stay in place in a given setting. Nonflowing materials are important in applications where shape stability and local containment are critical, such as vertical joints, coatings, and precise bonding. They may also be formulated to transition to a flowing state under specific conditions to enable processing.

Not all uses of the term are scientifically precise; in practice, nonflowing is often a descriptive label for materials with low flowability, and detailed characterization relies on rheological measurements of viscosity, yield stress, and flow behavior. See also viscosity, yield stress, rheology, non-Newtonian fluids, and thixotropy.