fluidens

Fluidens are a class of responsive fluids in the field of soft matter science. They are defined by a dynamic internal order parameter that couples to the flow, producing fluid materials whose viscoelastic properties can be tuned by external conditions. Unlike simple Newtonian liquids, fluidens can exhibit both liquid- and solid-like behavior, depending on temperature, applied stress, or external fields such as electric or magnetic fields. When aligned by a field, their flow becomes anisotropic; their viscosity can change by several orders of magnitude. They may display shear-thinning, shear-thickening, or thixotropic behavior and can form transient structures under flow that alter rheology.

Fluidens can be synthesized in various ways, including colloidal systems with anisotropic inclusions, polymer networks swollen with responsive solvents, or active gels containing self-driven components. They are studied using rheometry, scattering techniques, and rheo-optical methods, and are modeled with theories that couple a viscoelastic constitutive relation to an order-parameter field.

Applications are mostly exploratory and include adaptive lubricants for machinery, rheology-modulated 3D printing inks, soft-robotic actuators, and medicated or cosmetic delivery matrices where flow can be controlled on demand. Challenges include achieving stable, repeatable responses, controlling aging and degradation, and scaling synthesis for practical use.

See also: non-Newtonian fluids, viscoelastic fluids, smart materials, active matter.