Precipitate Deposition around CMC and Vesicle-to-Micelle Transition of Monopotassium Monododecyl Phosphate in Water

Abstract

Monoalkyl phosphate (MAP) salts are a kind of bivalent anionic surfactants. The difference of properties between half-neutralized monosalt and completely neutralized disalt is very interesting. In this study, the aggregation behavior of monopotassium monododecyl phosphate (MAP-12K) in aqueous solution with an increase in concentration was investigated by surface tension (γ), elemental analysis, gas chromatography, differential scanning calorimetry, steady-state fluorescence, and negative strained transmission electron microscopy techniques. MAP-12K aqueous solution showed some characteristics: (I) Vesicle aggregates were formed at very dilute concentration (1.2 mM). (II) The precipitate of a highly hydrophobic dimer of MAP, which was quaternary neutralized by potassium, was generated only in a certain dilute concentration region (2.7-200 mM) around the critical micelle concentration (cmc = 20 mM). (III) Vesicles spontaneously translate into micelles at the cmc. (IV) In the higher concentration above 200 mM, the solution becomes homogeneous micellar solution. All of these uncommon characteristics are thought to be caused by the generation of the dimer, which is much more hydrophobic than dissolved MAP derivatives, in the complicated chemical equilibria based on the weakly acidic character of MAP. MAP-12K aqueous solution behaves as if it is a binary mixed surfactant solution of hydrophobic dialkyl surfactant and hydrophilic monoalkyl surfactant in spite of a single component solution.

Spontaneous Vesicle Formation of Monododecenyl Phosphonic Acid in Water

“…The results indicated the PC 12 vesicles transformed into plate-like crystals and micelles depending on the pH. The same behavior was also observed for dodecyl phosphate of mono and di-potassium salts 33 . The dodecyl phosphate of mono-potassium salt precipitated in water because of dimerization with that of non-ionic form as acid soap type complex.…”

Neutralisation rate controls the self-assembly of pH-sensitive surfactants

“…[7][8][9] The spontaneous formation of stable, or at least metastable, vesicles in single component surfactant solutions is uncommon and, for the most part, restricted to double-tailed molecules. [10][11][12] Recently, spontaneous vesicle formation has also been reported in single-chain surfactants with phosphate 13,14 or carboxylate headgroups. [15][16][17] In this case, it is thought that the vesicles are composed of acid-soap dimers, whereby surfactant molecules with protonated and monoanionic headgroups undergo hydrogen bonding to form dimers with a single negative charge.…”

“…[15][16][17] In this case, it is thought that the vesicles are composed of acid-soap dimers, whereby surfactant molecules with protonated and monoanionic headgroups undergo hydrogen bonding to form dimers with a single negative charge. Such systems are of interest, as the size and type of the aggregates depend both on the concentration of the surfactant 14,15 and the pH of the solution, 13,[16][17][18] and could therefore be tuned to suit particular formulations or applications.…”

Self-assembling systems based on quaternized derivatives of 1,4-diazabicyclo[2.2.2]octane in nutrient broth as antimicrobial agents and carriers for hydrophobic drugs

“…The vesicle-to-micelle transitions have been described previously [60,61]; however, to describe the type of structures formed in CMC range requires additional experimental verification. One of the methods successfully used to determine the morphology of aggregates makes use of DPH fluorescent probes [62][63][64].…”