Research into nanoparticles
The field of nanoparticle research covers a wide range of interests in the fields of chemistry, physics and materials science. Control of the nanoscale morphology enables precise control of the properties of the end product.
Particle size, morphology and composition can be manipulated to produce materials of different properties. These novel substances have properties that differ from the bulk versions of the same materials. For example, nanoparticles can increase the strength and hardness of metals and ceramics and they can make protective coatings transparent. Some nanoparticle application areas include colloidal dispersions, metallic nanoparticles, biopolymers and nanostructured materials.
Dynamic Light Scattering (DLS)
The technique of DLS is ideally suited for the determination of the size of particles in the nanometer size range. The Malvern Zetasizer Nano S uses patented optics that provides exceptional levels of sensitivity and allows the determination of the size of samples that contain very small particles and/or particles that are present at very low concentrations.
In addition, the backscatter optics allows for the measurement of samples at much higher concentrations than is possible using conventional DLS instruments using a 90° detection angle
Determining particle interaction forces
If a nanoparticle sample contains aggregates, then an end product into which they are incorporated may end up containing defects. The stability of particle dispersion will depend upon 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 some instability mechanism will eventually take place e.g. flocculation, aggregation etc.
Malvern’s line of rheometers enable testing of a bulk sample, where the rheological properties help demonstrate whether a material is suitably stabilized or not.
Measurement of the Zeta Potential gives the degree of repulsion between particles, and hence the effects of changing the particle surface or the environment can be evaluated
The zeta potential of nanoparticles
The zeta potential of a particle is the overall charge that the particle acquires in a particular medium and can be measured on a Zetasizer Nano instrument.
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 the product. If all the particles in suspension have a large negative or positive zeta potential then they will tend to repel each other and there is no tendency for the particles to come together. However, if the particles have low zeta potential values then there is no force to prevent the particles coming together and flocculating.
The effect of the pH, concentration of an additive or the ionic strength of the medium on the zeta potential and rheological properties can give information in formulating the product to give maximum stability.
The effect of these parameters on the stability of particle dispersion can be automatically determined by using an autotitrator. The Malvern Multi Purpose Titrator (MPT-2) is a device capable of performing such titrations in conjunction with the Zetasizer Nano series. In addition, any one of the Malvern rheometer range can be used for providing complementary information.