| Abstract
| - The phase properties of 14 tetra-n-alkylammonium and -phosphonium salts with chloride,bromide, iodide, and perchlorate as anions and alkyl chain lengths from heptyl to octadecylhave been examined as neat solids and as gelators in thermally reversible organogels. Thesegelator structures are among the simplest investigated to date. The salts with the longestalkyl chains and a nitrogen cationic center produce the most stable gels based upontemperatures at which gels form on cooling from sols, periods of stability at room temperature, and minimum concentrations of gelator necessary to effect gelation of a liquid at roomtemperature. Specific gel properties are dependent upon the rate at which their (precursor)sol phases are cooled. Generally, gels with ammonium salts persist for longer periods, requireless gelator, and exhibit higher gelation temperatures than those with the correspondingphosphonium salts. Typically, <2 wt % of a gelator is necessary to effect gelation. Severalof the gels have persisted without visible change for years when kept at room temperaturein sealed containers. The superiority of the tetra-n-octadecylammonium salts is attributedto greater dispersive (van der Waals) interactions among alkyl chains and stronger ionicinteractions between charged centers. However, since the phosphonium salts are moreresistant to thermal decomposition, their liquid mixtures can be cycled between the gel andsol states more times than those with ammonium salts.
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