Roughening up polymer microspheres and their diffusion in a liquid
Spherical microparticles that are roughened up, so that their surfaces are no longer smooth, are intriguing. You can wonder that when we place a large number of these particles in a liquid, it may show interesting rheological behaviour. For example, would they behave like cornstarch in that when we apply a lot of shear it thickens? You can imagine that spiky spheres can interlock and jam. Biologists are interested in how microparticles interact with cells and organisms, and have started to show that the shape of the particle can play an important role. Similarly, these small particles of intricate shape may show fascinating behavior at deformable surfaces, for example is there a cheerio effect?, and may show unexpected motion. This sounds all fun, but how do we make rough microparticles, as for polymer ones this is not easy?
Fig. 1 Transmission electron microscopy (TEM) images of poly(styrene) microspheres deformed at 110 °C within a dried colloidal inorganic matrix for approximate time periods of 10, 30, 60 and 120 min (a–d), (e–h), (i–l). The inorganic particles utilized were cigar-shaped calcium carbonate (a–d), large, rod-shaped calcium carbonate (e–h) and small, spherical/oblong-shaped zinc oxide (i–l). Scale bars = 1.0 μm.
In our paper published in Soft Matter we report an easy and versatile method to morph spherical microparticles into their rough surface textured analogues. For this, we embed the particles into an inorganic matrix of intricate shape and heat them up above the temperature at which the particles become a polymer melt. Capillary imbibition imprints the inorganic texture into the particles, turning them rough. We also look at how the particles move through a liquid, by tracking their motional behavior. Rough particles appear bigger, than their smooth precursors.
You can read the paper here: DOI:10.1039/C7SM00589J