Learning from a dark brew: how traditional coffee-making can inspire the search for improved colloidal stability

Abstract

The recipe for making Turkish coffee in some parts of former Yugoslavia calls for the dilution of the turbid liquid with lukewarm water just before the boiling point is reached. The enigmatic gastronomic purpose of this step notwithstanding, here it is being used as an inspiration for deriving a simple stabilization step for protocols for the synthesis of fine particle colloids. The dilution step inspired by coffee-making was performed in a protocol for the synthesis of hydroxyapatite nanoparticles by their precipitation from supersaturated alkaline aqueous solutions. The implementation of this step in the post-precipitation stage, concurrently with boiling, evidently improved the stability of the nanoparticle colloids. The stabilization effect was limited to the suspensions where the parent solution was equilibrated with the fresh precipitate and was not reproduced in colloids comprising HAp nanoparticles redispersed in deionized water. The dilution step produced a mild and counterintuitive increase in crystallinity, suggesting complex recrystallization mechanisms driven by mutually antagonistic dissolution caused by the dilution and reprecipitation caused by the heating to be responsible for the observed increase in stability. Incongruent dissolution favoring a less entropic surface order and reduced charge screening entailing the expansion of the Debye lengths were suggested as complementary mechanisms explaining the improvements in stability caused by adding this simple and economical, yet very efficacious touch to the synthesis. It is concluded that unconventional protocols in spheres other than the scientific and heritages routinely discarded as disreputable could be sources of insight relevant to a plethora of distant domains and disciplines.