Understanding liquid formulated products
Implementing a new technique that can provide insights on the dynamics and local environments of liquid formulations.
A wide range of liquid products – including adhesives, inks, coatings, paints, and sealants – are formulated via a trial-and-error approach rather than an informed, science-based process.
This approach is ineffective for various reasons. It is time and resource consuming, hinders the development of sustainable formulations, and does not facilitate a fast response to external factors.
Therefore, developing new approaches to unveiling physicochemical interactions and local environments within these formulations is vital.
Methodology
We chose a type of polymer, a hydrophobically modified ethoxylated urethane (HEUR), as our model ingredient because it is ubiquitous in liquid formulations. It also provides the rheological properties that products need. For example, making a paint thick in the can so is stable during storage, but easy to spread on a surface when the shear of a brush is applied.
We then introduced a dye – whose lifetime is sensitive to the nanoviscosity of its local environment – to various dispersions of HEUR in water.
Next, we implemented a recently developed technique, shrinking gate fluorescence correlation spectroscopy (sgFCS) to study the self-assembly and dynamics of our model polymer accurately. It is known to form networks, but other techniques – such as shear rheology – do not provide a clear onset for the appearance of this network.
Findings
The application of sgFCS allowed the signal from the dye bound to the polymer to be isolated to that of the free dye in the dispersion. This greatly increased the sensitivity when compared with standard FCS and rheology measurements and revealed the appearance of small aggregates around 0.2–0.3 wt% HEUR.
The apparent size of the aggregates increased steeply above 1 wt% HEUR, suggesting the formation of a percolated network. No significant change in size was observed for PEG10k that has the same backbone as the HEUR but it is not expected to form networks.
Therefore, we proved that sgFCS can detect more accurately than current techniques the onset of polymer network formation and also provide information on the dynamics of the constituents using very small sample volumes (~ 50μL). This sgFCS approach, which we apply for the first time to polymers in this work, is readily extendable to any dye that changes lifetime on binding.
Impact
We believe this technique has the potential to serve as a screening tool to reformulate liquid products efficiently to make them more sustainable.
References
- Schroder et al. PNAS (2023), Vol. 120, No. 4, e2211896120.
- Murdoch et al. Understanding associative polymer self-assembly with shrinking gate fluorescence correlation spectroscopy, Nanoscale (2024), 16, 12660.
Meet our experts
- Dr Tim Murdoch
- Dr Nacho Martin-Fabiani