The drying and application times of a coating have always been crucial for paint sales, but now it seems, the way that a coating dries is set to revolutionise the specialty coatings industry. This is because researchers at the University of Surrey in Guildford, UK, have discovered that as coatings dry the molecules separate into layers based on their size (smaller on top of larger).
The APS Physics website reports the discovery as follows, “As the liquid in a drying colloid evaporates, particles below the surface are forced closer together. At the same time, Brownian motion results in the particles jostling about randomly. Brownian motion is faster for smaller particles, so they can more easily redistribute themselves as the colloid volume decreases. Larger particles cannot move away so quickly and accumulate at the surface-air interface. Researchers who have studied colloids containing particles of different sizes have found that for certain evaporation rates, larger particles concentrated at the top of a drying film while smaller particles were more evenly distributed throughout”
The discovery was a considerable shock to the researchers, with Richard Sear and fellow team member Andrea Fortini declaring, “The stratification that we found was neither predicted nor expected, and we spent a few months verifying the results.”
Unfortunately, the way that coatings dry is not entirely uniform and has proportional limitations, which may hamper some more technical applications of the discovery. However, at least the researchers have found a value for improving stratification, as explained, “The [layering] effect occurred for particle-size ratios ranging from 2:1 to 14:1, but only when the number of small particles exceeded the number of large ones by a factor of 200 or more. Even when stratification occurred, it was not perfect: some large particles remained trapped near the interface by surface tension.”
The United Press International news agency is speculating that, the discovery may, “… have implications for a variety of coatings and industries, from beauty products to pharmaceuticals.” Whilst Fortini himself has suggested on the University of Surrey website that, “This type of ‘self-layering’ in a coating could be very useful. For example, in a sun screen, most of the sunlight-blocking particles could be designed to push their way to the top, leaving particles that can adhere to the skin near the bottom of the coating.”
Whilst the research was EU funded with “aims at the reduction of environmentally damaging volatile organic compounds in paints.” The importance of the discovery may now be applied to any number of “industrial products such as paints, inks, and adhesives”.
Other coatings industry executives are still waiting for feedback from their own research communities, but it seems that the impact will be far reaching. Already paint and coating industry specialists are now considering how this improved understanding can be used in developing new coatings or improving current products. Others question whether the slight randomness of how the molecules separate will prevent the technology being applied to high-tech coatings, whilst more generic paints require lower technical specifications.
Only time will tell is this discovery will revolutionise the coatings industry, or is the research really just as interesting as watching paint dry?