Within the pages of the blog, the principles are explained, background information is supplied and guidance is given on how to select the most appropriate equipment for each application.
Sometimes referred to as photon correlation spectroscopy, dynamic light scattering can be used to measure the size, and the size distribution, of small particles held in suspension or of polymers held in solution. It is also widely used for investigating the behaviour of concentrated polymer solutions and other complex fluids.
A related method, electrophoretic light scattering, is also explored by the blog. In this case the parameter calculated is zeta potential, which can be seen as an indicator of the effective charge in solution.
Beckman Coulter® – one of many leading instrumentation manufacturers represented by Meritics – has developed a range of dynamic light scattering products, some of which combine both methods in the same instrument. The ability to obtain quick and accurate information on particle size and, at the same time, zeta potential makes this equipment very attractive in terms of cost efficiency.
Nanoparticles, polymers, carbohydrates, proteins, liposomes and micelles are just a few of the types of dissolved or suspended particle that can be characterised in this way.
Essentially, as the dynamic light scattering blog explains, photon correlation spectroscopy works by shining a light on a sample of liquid. As it hits the small particles, the light scatters in all directions. Brownian motion, which constantly changes the distance between the particles, results in time-dependent fluctuation in the scattering intensity. By analysing that fluctuation, particle size can be computed.
In electrophoretic light scattering, it is an oscillating electric field that causes the particles to move. This method measures electrophoretic mobility, from which zeta potential can then be calculated. Zeta potential is sometimes described as the potential difference between a dispersion medium and the stationary layer of fluid attached to a dispersed particle.
Knowledge of particle size is a fundamental requirement in many fields, while zeta potential, with its direct relation to solution stability, chemical modification and even biocompatibility, is an important factor in many nanoparticle synthesis and application studies.
For photon correlation spectroscopy, a submicron particle size analyser is used to measure items anywhere in the range from 0.6 nm to 7 µm. Electrophoretic light scattering requires a zeta potential analyser, for calculation of zeta potential in particles ranging from 0.6 nm to 30 μm. Both aqueous and non-aqueous samples can be handled, with particle concentrations ranging from 1 ppm to 40% (w/v).
Beckman Coulter instruments offer a variety of standard and optional cells, along with the extra option of an auto-titrator that allows determination of the isoelectric point by measuring zeta potential over a range of pH values. Other specialised choices include instruments with cells specially designed for measuring zeta potential of solvents, flat surfaces and films.
Meritics will be happy to guide users through the products and options available, to identify the right combination for any particular application. As well as online information, its advisory resources include a telephone hotline and a team of field-based engineers.
For further information on dynamic light scattering and electrophoretic light scattering visit http://www.dynamiclightscattering.co.uk.
To find out more about products and services available from Meritics, go to http://www.meritics.com.