Grant: Predictive formulation of high-solid-content complex dispersions
PIs: Dr Jin Sun, University of Edinburgh & Dr Mark Haw, University of Strathclyde
Presentation: Establishing principles for formulation and processing of high-solid-content dispersions of complex compositions in complex flows - pdf
Dr Jin Sun, School of Engineering & Dr John Royer, School of Physics and Astronomy, University of Edinburgh
Abstract: High-solid-content dispersions of solid particles of size about 1-50 microns in a liquid phase (HSCDs) occur ubiquitously in industrial applications, from cement and ceramic pastes to catalyst washcoats, paints, foods and drilling fluids. The reliable and efficient processing and manufacture of these diverse products presents 'grand challenges' to formulation technology because at high solids volume fraction process flow and product behaviour become increasingly unstable and unpredictable.
In this project, using both experimental and computational studies, we have been making advances in understanding the rheology of HSCDs with industry-relevant particle properties and compositions, linking rheology to flows in non-rheometric geometries and using flow to control the dispersion rheology. Specifically, we identified the roles of particle repulsive and attractive forces, and variable particle friction in shear thickening and thinning; enhanced the understanding and the predictability of the unstable flow behaviour through analytical models and statistical analysis of oscillations in shear rates and fluctuations of local probes; tested and extended a theoretical model for shear thickening in bi-dispersed mixtures of different particle sizes or friction; established a constraint-based model that predicts all known classes of experimental flow curve; linked shear thickening rheology to liquid migration in extrusion flows and to thickening in squeezing flows; and finally were able to tune the suspension viscosity by imposing oscillatory shear onto the main flows.
Overall, the progress provides new methodology of characterization, measurement, prediction and control of HSCD flows. The outcomes will enable manufacturers to formulate their products according to rational design principles, using parameters deduced from well-characterised reproducible flow measurements.
Q&A
Question (Tim Akerman): Did you explore the relationship between particle size distribution, in particular bimodal particle sizes, and shear thickening behaviour? When I was Albright and Wilson we had a rule of thumb that dispersions with a p/s relationship of 10% of particles at 1/10 of the bulk p/s tended to give dilatant behaviour. The effect was far more noticeable as the %solids rose above 40%. It's fantastic to see this observation starting to be quantified.
Answer (Jin Sun): The new framework of shear thickening due to frictional contacts has been more and more accepted in academic community; the industry seems to have known this better from experience…
Follow-up comment (Tim Akerman): Hi Jin, I was always frustrated that we didn't get the time or resources to investigate these effects in more detail. We had empirical observations and some measurements. I'm delighted to see these effects investigated academically. Data backed models are always preferable to empirical 'rules'. Even better when the models seem to provide some support for the 'rules'!
Follow-up (Jin Sun): Hi Tim, thanks. It would be great to talk with you about your data… and compare to our models/simulations.
Follow-up (Tim Akerman): HI Jin, I would be happy to have a discussion. The data sits in a company I worked for 23 years ago, so hard to access!
Question (Simon Gibbon): Thank you John and Jin - really nice to see the progress made over the course of the grant and how the complexity of the systems you are able to study / predict behaviour of has increased over the course of the problem. Impact in industrial applications is obvious - building on Tim's industrial rule questions - how accepting are industry of your learning when it conflicts with "what is industrially known"?
Answer (Jin Sun): We found that our industrial partners are very receptive when our model predict the behaviour they see in practice, even if sometimes the new model may be from a different angle from their empirical ones.
Response (Simon Gibbon): Jin certainly in the past with the ICI Slurries Processing handbook written by Buscall et al while there was some great science, they had also collected a lot of industrial experience which would be explained by your work, great.
Question (David Goodall): As someone working with high concentration antibody formulations (50 - 200 mg/mL protein in aqueous base formulations), does your generic model which you have exemplified for micron-sized particles scale to nanometre size, and can the adhesion / friction concepts be used in the same way?
Answer (Jin Sun): The model meant to be generic, agnostic of microphysics. But the nano-scale tribology is a very much unexplored area for combining to rheology. A lot to understand the specific details!
Follow-up question (David Goodall): On rheology of biopharma formulations, as a follow up from Jin's message to me |(David Goodall) about nano-scale tribology, it will be very interesting to get inputs from Robin Curtis and Paul Dalby on this, since these are the formulations they are working on as well.
Response (Robin Curtis): Following on from David Goodall’s comments on biopharma formulations, we are quite interested in applying colloidal approaches to describe what happens to concentrated antibody formulations, the key questions to address are the causes of shear thinning behaviour which are observed only under conditions where there are attractive inter-particle interactions. In addition, there has been a lot of work done in trying to understand the relationship between zero-shear viscosity and formation of transient structures between proteins (colloids) at moderate packing fractions.
Response (Jin Sun): @Robin, great to know. We are also doing simulations to characterise the structures during shear thinning etc. of adhesive particles.
Poster: Tuning the interactions in non-model suspensions - pdf
Lewis McHale, University of Edinburgh
Granular suspensions are widespread in multiple industries however the unification of multiple non-Newtonian affects such as shear thickening and shear thinning is not well understood. Here we use the mean field constraint theory to understand non-model silica which can be tuned between multiple rheologies using surfactant. Novel techniques allow us find that heterogeneous surface chemistry leads to unexpected rheologies and so a produced an understanding of this system from the atomic, particle and macroscopic scales.
RSC FST Future Formulation IV - The Conference
Grant Page: Predictive formulation of high-solid-content complex dispersions
PIs: Dr Jin Sun, University of Edinburgh & Dr Mark Haw, University of Strathclyde
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