Material characterization data such as size distribution, particle shape, zeta potential, molecular weight, and bulk material properties, can be accurately and reproducibly measured using instruments from the Malvern range. Technologies used include laser diffraction, image analysis, laser Doppler electrophoresis, static and dynamic light scattering, capillary rheometry and strain controlled and stress controlled rheometry.

Operating from headquarters in the UK, Malvern has an established network of subsidiary organisations, local offices and distributors worldwide and provides the highest level of applications and technical support to its customers wherever they are located.

A highly developed and continually expanding programme of web-based information, education, training and support now plays a fundamental role in delivering on Malvern’s commitment to share its expertise and experience with customers worldwide, and to ensure that they realize the maximum value from their instruments. An extensive library of technical documents, application notes, white papers and articles is available for download from Malvern’s website; live, web-based particle characterization and rheology seminars allow interaction with experts in these fields; and on-demand multimedia presentations can be downloaded and experienced at the viewer’s convenience.

Characterizing nanoparticles
Since the physical and optical properties of nano-sized particles are related strongly to their size, there is a growing need for a reliable, accurate and rapid means of particle size measurement and materials characterization in the nanometer size range. The diversity of nanoparticles and their applications means that they are likely to be presented in a variety of formats and in concentrations ranging from the very dilute through to highly concentrated suspensions or emulsions. Being able to measure these particles in their native formats may be important. Dilution, for example, can disrupt finely balanced systems and give a misleading picture of the true particle size.

The technique of dynamic light scattering (DLS) is ideally suited to the determination of the size of particles in the nanometer range. The Malvern Zetasizer Nano series uses patented optics that provide exceptional levels of sensitivity and enable the determination of particle size in samples that contain very small particles and/or particles that are present at very low concentrations. In addition, the Zetasizer Nano’s novel backscatter optics allow the measurement of samples at much higher concentrations than is possible using conventional DLS instruments where a 90° detection angle is the norm. The Zetasizer Nano series also offers combined size and zeta potential measurement in a single system allowing the generation of information important in determining dispersion stability and understanding and controlling the behavior of nanoparticles in dispersion. Malvern rheometers have applications in testing the bulk properties of materials, for example to demonstrate whether or not materials are suitably stabilized.

Particle size
If a nanoparticle sample contains aggregates, then these may generate defects in the end product into which they are incorporated. The Zetasizer Nano series of particle characterization systems can measure particle size in the range from 0.6 nm to 6 µm.

Dispersion stability
The stability of a particle dispersion depends on the balance of the repulsive and attractive forces that exist between particles as they approach one another. If all the particles have a mutual repulsion then the dispersion will remain stable. However, if the particles have little or no repulsive force then eventually there will be some manifestation of this instability, for example flocculation or aggregation. Measuring the bulk rheological properties of a sample using a Malvern Series Rotational Rheometer will be strongly influenced by subtle changes in its microstructural properties, i.e. stability. The system's particle size, shape, distribution, and zeta potential, which can be directly measured by Malvern Instruments' other product lines, will generate a complete understanding to how the rheological information will be related to the dispersion stability of the sample.

Zeta potential
The zeta potential of a particle is the overall charge that the particle acquires in a particular medium and can be measured using the Zetasizer Nano series. The magnitude of the measured zeta potential is an indication of the repulsive force that is present and can be used to predict the long-term stability of a product. If all the particles in suspension have a large negative or positive zeta potential then they will tend to repel one another and there is no tendency for the particles to come together. However, where particles have low zeta potential values there is no force to prevent the particles coming together and flocculating. The effects of pH, concentration of an additive, or the ionic strength of the medium on the zeta potential and rheological properties can give information that helps in formulating the product for maximum stability. The effects of these parameters on the stability of a particle dispersion can be determined automatically using an autotitrator. The Malvern Multi Purpose Titrator (MPT-2) can perform such titrations in conjunction with the Zetasizer Nano series. In addition, any one of the Malvern rheometer range can be used to generate complementary information.

Rheological parameters
The measurement of rheological properties can contribute to the development of an improved product, predict a product’s end use performance, and anticipate the physical properties of a product during and after processing.

Rheology is defined as the flow and deformation of materials, from fluids through to solids. A material’s rheological properties are measured by a rheometer, and Malvern’s versatile instrument range includes systems for all application requirements, from simple viscometers to measure viscosity as a function of shear rate for assessing non-Newtonian behaviour, to high precision, multi-functional rheometers for characterisation of complex viscoelastic properties. Malvern provides both controlled stress and strain rotational rheometers and capillary rheometers, providing complete measurement solutions over ten decades of deformation rate.

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