Top five reasons to replace a viscometer with a rheometer

Introduction

Is your viscometer approaching the end of its life?

Are you starting to feel that your trial and error, ‘rheology-light’ approach to formulation is becoming dated?

Or are there longstanding product performance issues that you’re failing to gain traction with, where you suspect rheology may hold the answer?

If the answer to any of these questions is yes, then it may be time to assess just what a modern rheometer can do, most especially relative to a cheaper viscometer. Rheometer design and functionality has advanced considerably over the course of the last decade and today’s instruments offer an extremely broad range of test capabilities, wrapped in software that makes them accessible to less expert users. Such systems support the industrial adoption of rheology and deliver cost benefits far beyond those returned by viscometers, from R&D, through formulation and into manufacture. Here we look at the top five measurements offered by rheometers that enhance their value relative to viscometers and provide some example studies to illustrate the potential benefits.

Reasons

1. A broader measurement range – extend your viscosity flow curve
2. Relevant yield stress measurement – generate accurate data for every sample type 
3. Oscillatory testing – characterize microstructure and control solid-liquid transitions
4. Axial testing – quantify tackiness and extend viscosity measurement capabilities
5. Sophisticated test sequences - delve deeper into process and product performance

Examples

Eye surgery Opthalmic Viscosurgical Devices (OVDs) are viscoelastic solutions or gels used during eye surgery, and are typically aqueous polymeric solutions containing one or more of the following constituents: hyaluronic acid; chondroitin sulfate and/or methyl cellulose. The International Standard (ISO 15798:2013) covering OVDs directly specifies rheological measurement because of the impact of product rheology on in-use performance. Carrying out steady state testing at shear rates in the range 0.001 to 100 s^-1 determines how a fluid will behave within the anterior chamber and when injected into the eye through a cannula, respectively. The lower end of this range is inaccessible to a typical rotational viscometer. Thixotropy of nasal sprays Thixotropy can be assessed using viscometry testing by monitoring the time evolution of viscosity on stepping from one shear rate to another, as shown in figure 16. For example with paint, a high shear rate is used to replicate brushing and a low shear rate to represent the film rebuild on the wall. Viscometry is very useful for assessing thixotropy but it is not capable of monitoring the full recovery of a gel structure since the application of a shear rate will continually break the reforming gel structure down. This is where oscillation testing is useful as it is possible to apply a constant shear rate to break the structure down then follow the recovery process in oscillatory mode allowing both pre-gelation and post-gelation processes to be followed through the evolution of G’ and G”.  >> Download the full Application Note as PDF

Malvern Instruments provides the materials and biophysical characterization technology and expertise that enable scientists and engineers to understand and control the properties of dispersed systems. These systems range from proteins and polymers in solution, particle and nanoparticle suspensions and emulsions, through to sprays and aerosols, industrial bulk powders and high concentration slurries. Used at all stages of research, development and manufacturing, Malvern’s materials characterization instruments provide critical information that helps accelerate research and product development, enhance and maintain product quality and optimize process efficiency. Our products reflect Malvern’s drive to exploit the latest technological innovations and our commitment to maximizing the potential of established techniques. They are used by both industry and academia, in sectors ranging from pharmaceuticals and biopharmaceuticals to bulk chemicals, cement, plastics and polymers, energy and the environment. Malvern systems are used to measure particle size, particle shape, zeta potential, protein charge, molecular weight, mass, size and conformation, rheological properties and for chemical identification, advancing the understanding of dispersed systems across many different industries and applications. Headquartered in Malvern, UK, Malvern Instruments has subsidiary organizations in all major European markets, North America, Mexico, China, Japan and Korea, a joint venture in India, a global distributor network and applications laboratories around the world. www.malvern.com severine.michel@malvern.com

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