Ice Nucleation in the Presence of Nucleation Promoters Dispersed in Tetrabutylammonium Bromide (TBAB) Solutions

Ice nucleation is the initial step of ice formation that has significant impact on global climate, several engineering and structural surfaces and other systems like clathrate hydrates. The nucleation promoters for ice have been studied for decades but some problems or mechanisms remain unclear. In our earlier study [1], Snomax was found to be the most effective promoter among the common ice nucleation promoters we had tested and it was postulated that the efficacy of Snomax might be aided by its larger interfacial area available for heterogeneous nucleation because it could be easily dispersed in water. Here we attempted to disperse the three ice nucleation promoters which we had previously found to be effective - AgI, kaolinite and cholesterol - into liquid water to increase the interfacial area with water and the heterogeneous nucleation rate of ice. We found dispersion of these promoters into water to be difficult and required addition of Tetrabutylammonium bromide (TBAB) to the aqueous phase before they could be dispersed. We then investigated the nucleation rates of ice in the dispersed nucleation promoter suspensions. We found (1) addition of TBAB alone unexpectedly promoted the nucleation of ice, (2) dispersing AgI into 1 mM TBAB solutions further promoted ice nucleation, (3) dispersing kaolinite or cholesterol in TBAB solutions did not promote ice nucleation more so than the TBAB solutions without kaolinite or cholesterol.