Pyrophosphate-Based Gemini Surfactants

Abstract

Two series of pyrophosphate-based gemini surfactants [diimidazolium (<b>1</b>) and disodium <i>P,P</i><i>‘</i>-dialkyl\npyrophosphate (<b>2</b>) (<b>a</b>, R = 1-octyl; <b>b</b>, R = 1-dodecyl; <b>c</b>, R = 2-dodecyl)] were synthesized, along with a series\nof imidazolium monoalkyl phosphate surfactants (<b>3a</b>−<b>c</b>) for comparison. The surfactants were characterized\nby measurement of their Krafft temperatures (<i>T</i>_k) and critical aggregation concentrations (cac's). The <i>T</i>_k\nand cac values of the pyrophosphate surfactants are lower than those of their conventional phosphate\nsurfactant counterparts. Aggregated surfactants <b>1</b> and <b>3</b> in D₂O were characterized by ¹H and ³¹P NMR\nspectroscopy, and solutions of <b>1c</b> and <b>3c</b> in H₂O were characterized by phase-contrast optical microscopy\nand cryogenic high-resolution scanning electron microscopy (cryo-HRSEM). By optical microscopy, fiberlike\naggregates were observed for gemini surfactant <b>1c</b>, and both fibers and rod/tubule-like aggregates were\nobserved for its single-chain counterpart <b>3c</b>. By cryo-HRSEM, lamellar ice was observed for both <b>1c</b> and\n<b>3c</b>. Also, a single-crystal X-ray diffraction study of <b>1b</b> was performed, and its cleavable nature was\ndemonstrated.