"Small plastic particles are usually obtained as spherical objects," says Miriam Unterlass from the Institute of Materials Chemistry at TU Wien. However, roundish particles are poorly suited for many applications. "Particle-containing liquids are extensively used as paints and protective coatings," says Unterlass. "The geometric shape of the particles then determines how the particles are arranged and move within the liquid." Many such dispersions do not dry uniformly, because an unfavourable current is produced during evaporation which transports the particles in a particular direction. Clearly, one would prefer paints to dry homogeneously.
There have been repeated attempts to give polyimide particles or similar materials an angular shape, but until now there has been little success. Miriam Unterlass’ team at TU Wien has now tried a completely new approach. At first, two different molecules, which usually combine in a rather disorganised manner, are used to produce an angular salt crystal. The salt crystal is formed by conducting the reaction in a gel. The viscous gel slows down the speed of the molecules, which decelerates the reaction, producing well-ordered, high-quality crystals with a diameter of hundreds of micrometres – these are visible to the naked eye.