Fabrication of colloidal doublets by a salting out-quenching-fusing technique

It is well-known that high ionic strength promotes colloid aggregation. Here we show that, by controlling this aggregation process, we can produce high yields of homodoublet and heterodoublet polymer colloids. The aggregation process is started by increasing the ionic strength to roughly 250 mM KCl. After approximately the rapid flocculation time, we quench the reaction by mixing in a large quantity of deionized water, which dilutes the ionic strength and prevents further aggregation. At this point, the suspension consists primarily of singlet and doublet particles. Through heating above the glass transition temperature of the polymers, the doublets are fused together and remain intact even after sonication. It is also shown that heterodoublets can include a silica particle together with a polymer colloid. The salting out-quenching-fusing technique is a rapid, easy-to-perform, repeatable process for fabricating colloidal doublets from polymers and other materials.