Colloid suspensions, liquids with microscopic particles dispersed throughout, play a big part in everyday life, with ink, milk, blood and paint all falling into this category.
Despite their prevalence, some basic properties of colloid suspensions are still being discovered, including one recently found by Jacinta Conrad, assistant professor of chemical and biomolecular engineering with the University of Houston Cullen College of Engineering.
Conrad, along with Melissa Spannuth, a former post-doctoral researcher, recently discovered that a model colloid-polymer suspension will turn from liquid to gel when placed in a confined space. They published a paper on their findings in the July 13 issue of Physical Review Letters.
Conrad conducted this work with a model suspension of solid particles and polymer chains – a simple system used to conduct basic research in this area. In such systems, each sphere has an area surrounding it that excludes other particles. Thanks to entropy, though, the polymer chains force these spheres together into take on a crystalline structure, giving the polymers as much room as possible to move within the crystals themselves.
Covering the suspension with a glass plate placed at an angle changes these interactions. Just as each sphere has an area of exclusion, the glass plate itself has a zone where neither the spheres nor the polymer chains can enter. This forces the spheres together more quickly, resulting not in a crystal, but a disordered gel.
Conrad noted that more study of this phenomenon is needed, especially on colloid systems consisting of different materials. If this property transfers, though, it could be used to create novel glues and adhesives, or in any situation where turning a liquid into a solid would be valuable, such as in wellbores. “One function of a drilling fluid is to lubricate a well bore, but also to seal any fissures. That’s precisely how this material behaves,” she said. “It behaves like a like a liquid when it’s not confined, but it behaves like a solid when it enters very small areas. The idea is that we make a fluid suspension that turns sticky and solidifies in a crack.”