As scientists and engineers, we want to optimize our formulation and quality control - time is money. The wishlist of improvements often contains objectives such as reducing the timeline from prototype to process scale-up, obtaining a better degree of certainty about product lifetime, and defining tolerances for the material’s use by the customer. As we seek solutions to these various problems, we need to maintain a realistic mindset. This is important because implementing new test methods requires us to fully understand what is going on as well as implement changes to both our SOPs and our way of thinking.
Rheology is a useful system for obtaining the information needed to resolve problems with soft material formulation and processing. The right test methods can yield various insights on the conditions for flow, sedimentation, hardening, aging, and much more. Along with these capabilities, using a shear rheometer also brings in a new responsibility for the staff involved with method development, formulation, and data analysis. Not only does the individual who runs the samples in the rheometer need to have a good understanding of rheology, but also the process engineer, chemist, and QC lab members who oversee all steps the product production, from raw material to post-use by the customer. Rheology data is only useful when implemented for making decisions about the product.
Rheology data do not necessarily have to turn your current lab life upside down, but can bring about incremental improvements to current procedures and inspire better designs for product preparation.
If one chemical composition is separating out much quicker than others, do not expect it to perform the same way during scale-up and application. You will need to adjust your development process accordingly. Probe the reasons for the abnormality: conduct more specialized rheometry tests and compare to the best performing specimens. Then investigate changing one characteristic at a time based on the results. Depending on the information revealed, some example changes include: adding a stabilizer, mixing at a faster rate during processing, or adjusting the sample pH. This process takes time but overall solves problems that would otherwise escelate into exasperating and expensive issues.
Rheology is indeed a science, not magic. I once spoke with a ceramics manufacturer regarding an issue they were seeing in a process for mixing a new slurry. After voicing their frustration with how their current mixing process produced unusable material, they inquired if any rheometry test methods may solve the issue. I proposed general methods for initially evaluating sedimentation and analyzing the structural recovery of slurries post-mixing. Then I asked which parameters they could change in the process to implement a solution based on the potential rheology results.
I inquired about the following: Mix at a faster speed? No way! Our mixers are one-speed. Change mixing equipment/procedure? Heck no, we don’t have that kind of money. Adjust the composition of the slurry by either reducing solids content or adding a stabilizer? No, the composition of the slurry cannot be adjusted! Any chance you can change the process temperature? No way!
I left the meeting puzzled about their unrealistic expectations, unable to find a way to contribute to the problem’s resolution. They could run a thousand samples and it wouldn’t be worthwhile to solve the issue. The solution that this client was looking for was a magic wand-waving solution that would not require any change. These senior engineers and scientists were expecting a magical Rheomancer, not a Rheologist.