# Viscosity and Intrinsic Viscosity: What are the Key Differences?

Fluid dynamics is the branch of physics concerning fluid flow. It is distinguishable from other disciplines in fluid mechanics as it deals with fluids in motion. In physics, a fluid is a substance with zero resistance to shear force, meaning any applied stress causes persistent deformation.

Underlying this behavior are two connected concepts: viscosity and intrinsic viscosity. Whilst viscosity is a measure of a fluid's resistance to flow, intrinsic viscosity is a specialized measure that provides insight into the flow behavior of polymer solutions, offering valuable information on the molecular weight and size of the polymer chains.

This article aims to elucidate the nuances distinguishing these two concepts with precision and authority.

## Understanding Viscosity

Viscosity stands as a critical metric of a fluid's resistance to flow - denoted by "η," it quantifies the internal friction within a fluid which is recognized as its "stickiness" or "thickness."

This property is integral in understanding fluid flow behavior, with factors including pressure, temperature, and molecular structure each contributing to its value, given in units of pascal-seconds (Pa·s) or poise (P).

## The Concept of Intrinsic Viscosity

Intrinsic viscosity is a highly valuable measure in polymer and protein studies. Related to the flow behavior of colloidal suspensions, intrinsic viscosity refers to the amount of liquid a material can hold per unit weight and the contribution of that material to the viscosity of the overall solution.

This is a measure of the internal friction within a polymer molecule and is measured in units of deciliters per gram (dL/g) or milliliters per gram (mL/g). Intrinsic viscosity can help reveal the molecular weight and size - as well as the branching of - branching of polymer chains.

## Key Distinctions Between Viscosity and Intrinsic Viscosity

1. Definition: Viscosity quantifies a fluid's resistance to flow, while intrinsic viscosity measures the flow behavior of polymer solutions.
2. Scope: Viscosity is applicable to any fluid, Newtonian and non-Newtonian alike. Intrinsic viscosity specifically relates to polymer solutions.
3. Units: The units of viscosity are pascal-seconds (Pa·s) or poise (P), while intrinsic viscosity is measured in deciliters per gram (dL/g) or milliliters per gram (mL/g).
4. Information Provided: The viscosity is indicative of a fluid's behavior, influenced by factors such as pressure and temperature. Intrinsic viscosity provides information about the molecular weight and size of polymer chains in a solution.

Researchers and scientists working with polymers and fluids must have a strong understanding of the distinction between viscosity and intrinsic. Decisions and predictions regarding polymer processing, fluid behavior and material properties can be informed by viscosity and intrinsic viscosity.

## Viscosity and Intrinsic Viscosity: Why Are They Important?

Viscosity and intrinsic viscosity, though related, are distinct measures. Viscosity characterizes a fluid's resistance to flow, with the latter providing insights into the flow behavior of polymers in solutions.

Both are foundational to polymer science and fluid dynamics. Studying each of these properties can provide a great depth of insight into various fields of science and engineering.

Dynisco has been developing high-quality and innovative solutions for plastic extrusion processing for more than 60 years. Its controls, sensors, and analytical instruments offer improved control, less downtime, minimum scrap, and unmatched reliability and working life.

Dynisco is dedicated to collaborating with clients to help measure, analyze, and outfit extrusion control systems catering to specific needs.

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

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