Suspensions and dispersions are encountered in a wide range of applications, from liquid abrasive cleaners, personal care products, ceramic slurries and medicines to paints and inks. In most cases it is necessary to keep the suspension stable for the product lifetime although, in others, destabilizing the suspension may be a requirement. An example of the latter would be for water treatment or de-aeration.

With this widespread, and ever broadening use of dispersions, the options for ‘product engineering’ to optimize stability is a question that Malvern is often asked due to the complementary nature of our instrumentation portfolio that is directly applicable to characterizing these materials.

Stabilizing a suspension

There are various routes that can be undertaken to improve suspension stability – for example, stabilization can be achieved by:

  • preventing coagulation through inter-particle repulsion
  • slowing down sedimentation by increasing the viscosity of the continuous phase
  • making the material solid-like by creating a network structure.

Which then poses the question what is the optimum mechanism for my material type and application?

Understanding suspension stability

This particular question was discussed recently in a presentation by Malvern Product Technical Specialists, Dr John Duffy and Dr Adrian Hill at the November 2011 SCI conference; ; ‘Innovation in Colloid Formulation: Secrets of Formulation III’, London.

The papers from that conference are now available on the Society of Chemical Industry (SCI) website: Innovation in Colloid Formulation conference papers.

The presentation Suspension stability: why particle size, zeta potential and rheology are important details the various approaches above, and explains why one mechanism may be more appropriate than another by considering the nature, influence and probably most importantly, the interaction of both particle properties (size and zeta potential) with the rheological characteristics of the material in question. Following his presentation at the SCI meeting, John Duffy commented that he ‘had several discussions with delegates on the importance of really understanding their material and the conditions it will be subjected to over the full product lifetime. Knowing what you need your product to do, and what it is within that product formulation that imparts such properties is key!

Anyone with further questions is invited to contact the authors via Malvern’s website. Alternatively, do feel free to comment below – are dispersion stability issues affecting your products?