The Latest Developments in Dynamic Vapour Sorption (DVS)

Interview conducted by Jake WilkinsonJul 28 2016

Dynamic Vapor Sorption (DVS) is a gravimetric technique that measures the uptake and loss of vapour by a sample, enabling its physico-chemical & sorption behaviour to be accurately determined. The technique has developed significantly since it was created over 20 years ago by Daryl Williams, Director of Discovery Space in the Department of Chemical Engineering at Imperial College and founder of Surface Measurement Systems.

AZoM spoke to Daryl about the new developments Surface Measurement Systems are working on that will open up the field of DVS to new frontiers of science.

Please could you give our readers a brief overview of the science behind Dynamic Vapor Sorption (DVS)?

Dynamic Vapor Sorption (DVS) is a gravimetric method, i.e. a technique which involves measuring the change in mass of a sample. The DVS method involves exposing the sample of interest (a solid, a powder, fiber, or film) to known conditions of temperature & relative humidity while recording how the sample mass changes over time. The closest analytical technique to DVS is TGA (thermo gravimetric analysis) in which changes in sample mass as a function of temperature are observed and measured.

The water vapor present in our natural air is strongly attracted to almost all materials and we observe changes in a sample’s mass as it is adsorbed by solid materials. Water vapor shows a strong attraction towards solid materials because, as a condensable vapor, it prefers to be in a liquid (condensable) form. This means that water vapor will effectively interact with any solid materials whether they are organic, inorganic or biological.

DVS measures the change in the mass of a sample upon exposure to a known humidity of vapour. Image Credits: Vagengeim/shutterstock.com

What physical and chemical properties of a sample can be determined using techniques such as DVS?

When we carry out a DVS experiment we discover whether the water vapor can be adsorbed on to the surface of a sample, absorbed into the sample’s bulk or condensed inside the sample pores. These three distinct locations are where we can usually find water molecules in most materials.

Because there are three different environments on a material for water to adsorb, DVS can be used to determine three different material properties. DVS can be used to obtain details about the surface of a material, such as the surface area, the porosity of a material, such as the pore size distributions, and solubility of the material, i.e. the extent by which water dissolves inside the solid-state materials.

Simultaneous measurement of these three different information sets are often unique to the DVS method making it a very powerful tool for researchers.

How does the DVS method compare to other approaches available in the modern laboratory?

If we look at a modern analytical laboratory, you would find very few (if any) instruments that look at how a material behaves as a function of humidity. So DVS in many ways has a unique role in laboratories.

Other techniques you may find in laboratories that are relevant are the loss on drying and Karl Fisher titration methods. However, both of these techniques are relatively artificial because they expose samples to either a very strong chemical environment or heat. These two techniques will tell you how much moisture you have in your material but, unlike DVS, not as a function of humidity. It is this behaviour that makes DVS a unique technique in research laboratories.

Schematic of the DVS Adventure from Surface Measurement Systems. The sample is exposed to dry nitrogen gas carrying a solvent vapour. Changes in the mass of the sample following exposure to the vapour is recorded by the microbalance.

The technique of DVS is over 20 years old, what have Surface Measurement Systems done to improve this, now established, technique?

Although the technique of DVS is now over 20 years old it continues to advance, becoming more sophisticated and providing richer sets of data for the characterization of materials. SMS have developed the use of organic vapors, and have also introduced the use of Raman and NIR, whilst continuing to expand the scope of new DVS methods.

Some of the new developments we have been working on includes the use of gas adsorption rather than vapor sorption, the use of more than one gas or vapor molecule in one experiment and also the ability to process multiple samples at the same time, i.e. simultaneous DVS experiments. These are all new advances in DVS and they will create even more opportunities for researchers that use DVS in their everyday research work.

What drives Surface Measurement Systems to continue developing DVS?  As the inventor of the of the DVS method do you have a vision of where this technique will go in the next 5-10 years?

The most surprising development for users of DVS is the increasing number of new applications and scientific areas which benefit from the data that DVS produces. So, every year we discover many, many more application areas, more problems that DVS can be used to help us solve. And that is the most exciting thing about being involved in the field of DVS.

For example we've noticed an increasing use of DVS in materials research, including lots of research involving nanomaterials, such as graphene and carbon nanotubes, which are becoming increasingly important in both academic and industrial laboratories.

DVS is being used to analyse nanomaterials such as graphene and nanotubes. Image Credits: ktsdesign/shutterstock.com

What industries see the most benefit from using these techniques as part of their analytical or R&D processes?

Historically we work very closely with the pharmaceutical industry and they are certainly one of the major users of DVS technology. However, in the future we expect to see increasing interest in other sectors such as the nanomaterials, plastic electronics, biopharmaceuticals, biomaterials, polymers and food spaces.

Often the insight you obtain from DVS experiments is complimentary to other techniques such as DSC (differential scanning calorimetry), TGA (thermogravimetric analysis) and DMA (dynamic mechanical analysis). DVS provides unique information which can help us understand the complex behaviour of materials.

Analysis using DVS is common in the pharmaceutical industry, where control over product quality is of high importance. Image Credits: Yoottana Tiyaworanan/shutterstock.com  

Why is determining properties such as the water activity or the water sorption isotherms of a sample important for quality control?

I think one of the most important things that DVS has allowed us to learn is that water sorption behaviour varies in ways that people don’t expect. We've found that water sorption is very sensitive to the surface area, structure and morphology of a material and these are properties that can be difficult to measure using traditional analytical techniques.

It is not uncommon for companies to make products and discover that the current techniques that they use for quality control aren’t actually sensitive enough to measure these subtle changes in material behaviour. DVS is a very powerful technique for observing subtle changes in the material, particularly hydrophilic or amorphous materials.

What’s new in the world of DVS?

We are coming into a particular exciting time because this summer we are releasing a number of new DVS products.

These are products that we have been working on for the last 4 years. These new products represent a major development in the instrumentation used for DVS. We are looking into increasing the performance in terms of water sorption, and also in terms of vapor sorption science. The new instruments will have larger temperature ranges, more options, more facilities and allow researchers and investigators to undertake a wider range of DVS experiments.

Our DVS instruments are state-of-the-art. For example, the new DVS Adventure is specifically designed to study water sorption and operate at a wide temperature range from 5 to 85 ºC It. will also offer a wide-range of options, as we have in our previous products, including high resolution video (5 megapixels) and Raman amongst other features.

The DVS Adventure from Surface Measurement Systems

Where can our readers find out more about DVS, IGC and Surface Measurement Systems

If you are interested in DVS and IGC please visit our website where we often post information on new scientific breakthroughs in the fields and the latest DVS products.

About Dr. Daryl Williams

Dr. Daryl R. Williams graduated with a B.Sc. (Hons) in Physical Chemistry from University of Melbourne, Australia and a M.Sc. in Polymer Science from Lehigh University, USA before coming to Imperial College London complete his PhD.  He is currently the Director of the Discovery Space and a Reader in Particle Science in the Department of Chemical Engineering.

Daryl Williams has published over 80 papers in refereed journals and been granted international 5 patents. His research interests include the surface and bulk characterisation of complex organic solids, including especially biopharmaceutics, foods, pharmaceuticals and polymers as well as their manufacture using spray drying, crystallisation, freeze drying, milling and granulation.