Introduction to Measuring Viscosity

Viscosity can be defined as the resistance of a fluid to flow. This resistance is caused from the forces of attraction between the fluid molecules.

A fluid will only flow if sufficient energy is applied to overcome these resistive forces. For something to move through a fluid, the fluid has to flow across it or around it. Hence the energy needed for moving a body through a fluid is directly related to the degree to which that fluid resists flow.

Scientifically, viscosity is a liquid or gas’ tendency to resist by internal friction, the relative motion of its molecules and hence any change of shape, the magnitude of this, as measured by the force per unit, area resisting a flow in which parallel layers unit distance apart have unit speed relative to one another, also called absolute or dynamic viscosity.

Kinematic viscosity is the dynamic viscosity divided by the density of the fluid.

Definition of Viscosity

The Newtonian law derived a mathematical formula relating the viscosity to the resistive drag force experienced by a thin flat plate “cutting” its way “shearing” through the fluid.

The definition was based on two quantities that is the shear rate which is the speed of the thin plate divided by its distance from some reference surface, such as the wall of the container. Shear stress is the drag force experienced by the thin plate divided by its surface area. Viscosity is defined as the shear stress divided by the shear rate.

Why is Viscosity Measured?

There are a number of reasons for making rheology measurements. Mostly, rheology testing or viscosity testing objectives are to quantify and identify rheological properties that correlate to consumer perceived product attributes.

These attributes includes the following:

• How does it look in its container on the shelf?
• How easily does the product dispense (squeeze, pump or spray) from the container?
• Does the lotion easily spread on the face, hands or nails?
• How does it apply to a hard or soft surface, and remain on the surface?

One objective of the Rheology Central is to quantify customer perception of product attributes that are rheology driven. Comprehensive rheology studies of consumer properties are completed specifically for correlation to consumer sensory studies. Are the products pseudoplastic or viscoelastic? Do they exhibit time dependent shear effects such as thixotropy or rheopexy?

A large number of products are non-Newtonian pseudoplastic fluids. Emulsions and other complex dispersions are frequently viscoelastic.

Fungilab manufactures advanced and high quality rotational viscometers. Fungilab is a strong and solid brand, recognized around the world for its best practices in products and services in the viscosity market.

The values that Fungilab brand transmits to market for improving the client’s confidence are high quality equipment with an accurate, easy and evolved working system, featuring the latest advances in technology; specialized customer and technical service to differentiate fungilab from the rest of the brands in the viscosity market; pre-sales and post-sales support to end customers and dealers; and equipment repairs.

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This information has been sourced, reviewed and adapted from materials provided by Fungilab.