Thermotropic and Barotropic Phase Transitions of Dialkyldimethylammonium Bromide Bilayer Membranes: Effect of Chain Length

Abstract

The bilayer phase transitions of dialkyldimethylammonium bromides (2C(n)Br; n = 12, 14, 16) were observed by differential scanning calorimetry and high-pressure light-transmittance measurements. Under atmospheric pressure, the 2C(12)Br bilayer membrane underwent the stable transition from the lamellar crystal (L(c)) phase to the liquid crystalline (L(α)) phase. The 2C(14)Br bilayer underwent the main transition from the metastable lamellar gel (L(β)) phase to the metastable L(α) phase in addition to the stable L(c)/L(α) transition. For the 2C(16)Br bilayer, moreover, three kinds of phase transitions were observed: the metastable main transition, the metastable transition from the metastable lamellar crystal (L(c(2))) phase to the metastable L(α) phase, and the stable lamellar crystal (L(c(1)))/L(α) transition. The temperatures of all the phase transitions elevated almost linearly with increasing pressure. The temperature (T)-pressure (p) phase diagrams of the 2C(12)Br and 2C(14)Br bilayers were simple, but that of the 2C(16)Br bilayer was complex; that is, the T-p curves for the metastable main transition and the L(c(2))/L(α) transition intersect at ca. 25 MPa, which means the inversion of the relative phase stability between the metastable phases of L(β) and L(c(2)) above and below the pressure. Moreover, the T-p curve of the L(c(2))/L(α) transition was separated into two curves under high pressure, and as a result, the pressure-induced L(c(2P)) phase appeared in between. Thermodynamic quantities for phase transitions of the 2C(n)Br bilayers increased with an increase in alkyl-chain length. The chain-length dependence of the phase-transition temperature for all kinds of transitions observed suggests that the stable L(c(1))/L(α) transition incorporates the metastable L(c(2))/L(α) transition in the bilayers of 2C(n)Br with shorter alkyl chains, and the main-transition of the 2C(12)Br bilayer would occur at a temperature below 0 °C.

Thermal and phase behavior of didodecyldimethylammonium bromide aqueous dispersions

“…6), which display a sharp gel-to-liquid crystalline [3], or hydrated crystalline to the liquid crystalline [4], transition at T m ≈ 16 • C. The upper border of the Ves phase (at CVC 2 ≈ 0.7 mM) is the onset of the phase separation, with formation of a Lam top phase [9,11,12]. In the two-phase region of the phase diagram (Fig.…”

“…To the best of our knowledge the reverse liquid crystalline-to-gel transition temperature (T m ), has not been reported for DDAB so far because of its exceedingly slow kinetics [3,13]. We investigated the effect of the equilibrium (pre-scan) time on the heating DSC thermogram of DDAB dispersions, aiming to detect the characteristic thermogram with a single endotherm at T m [3][4][5]13]. Fig.…”

“…It has been reported that above the critical vesicle concentration (CVC) and above its gel-to-liquid crystalline [3], or hydrated crystalline-to-liquid crystalline [4], temperature (T m ≈ 16 • C), DDAB self-assembles in water as vesicles [3,5,6]. Even though the phase behavior of DDAB/water have already been reported [7][8][9][10], the effect of DDAB concentration on the bilayer structural organization, however, has been only poorly explored.…”

“…Unlike T m , the CVC of DDAB in aqueous solution is not uniquely determined. The CVC value depend on the technique used to determine it, while to our knowledge T m of DDAB has been determined only by DSC [3][4][5][6]. Then, what is the physical meaning of CVC values of DDAB?…”

Association Behavior of Double-Chain Ionic Surfactants: Elucidation of the Membrane States by High-Pressure Study

“…We could comprehensively interpret the complicated phase behavior of the 2C n Br bilayers, which has not been revealed by conventional experimental methods at ambient pressure. ［double-chain cationic surfactant, bilayer membrane, phase transition, high pressure］ [20,21]…”