FLASHCARDS-Rheological properties of materials (polymers)-

Rheology

The study of the deformation and flow of materials.

Viscosity

A measure of a fluid's resistance to flow, stemming from internal friction between adjacent layers.

Newtonian Fluid

A fluid whose viscosity remains constant regardless of the shear rate.

Pseudoplastic Fluid

A non-Newtonian fluid that exhibits shear-thinning behavior, where viscosity decreases with increasing shear rate.

Dilatant Fluid

A non-Newtonian fluid that exhibits shear-thickening behavior, where viscosity increases with increasing shear rate.

Shear Stress (τ)

The force per unit area applied parallel to the material under consideration.

Shear Strain Rate (dγ/dt)

The rate at which deformation occurs under shear stress.

Power Law Equation

A mathematical representation that relates shear stress and shear rate for non-Newtonian fluids, often in the form τ = k (dγ/dt)^n.

Viscoelasticity

The property of materials that exhibit both viscous and elastic characteristics when undergoing deformation.

Apparent Viscosity (ηa)

The viscosity of a fluid as determined under specific conditions and often depends on the shear rate.

Bingham Plastic Fluid

A fluid that behaves like a solid until a certain yield stress is applied, after which it flows like a viscous fluid.

Elongational Flow

A type of flow that occurs when a fluid is subjected to uniaxial or biaxial tension, significant in processes like film blowing.

WLF Equation

The Williams-Landel-Ferry equation used to describe the temperature dependence of viscosity in polymers.

Thixotropic Fluid

A type of fluid that decreases in viscosity over time when subjected to a constant shear rate.

Rheopectic Fluid

A type of fluid that increases in viscosity over time when subjected to a constant shear rate.

Yield Stress (τy)

The stress level at which a material begins to deform plastically.

Capillary Rheometer

A device used to measure the flow properties and apparent viscosity of fluids by forcing them through a capillary.

Cone and Plate Rheometer

A rheometer that uses a cone and flat plate configuration to measure shear stress and viscosity.

Normal Stress Difference

The generation of differing normal stresses in a material as it undergoes deformation.

Die Swell

The phenomenon where the extrudate swells after leaving a die due to elastic recovery.

Herschel-Bulkley Model

A model that describes the flow behavior of fluids that combine characteristics of Bingham plastics and power-law fluids.

Strain Hardening

An increase in viscosity with increasing strain, often observed in polymer melts during processing.

Elongational Viscosity

The viscosity experienced during elongational (tensile) flow, often greater than shear viscosity.

Processing Aids

Additives used to improve the processing characteristics of polymers, such as reducing melt viscosity or enhancing flow.