Effects of Metal Ions on the Equilibrium Thicknesses of Foam Films Stabilized by Lysophosphatidylcholine As Studied by FT-IR Spectroscopy

Abstract

The core thicknesses of macroscopic, vertical foam films have been measured by FT-IR technique for the equilibrium films formed from palmitoyllysophosphatidylcholine (lysoPC) solutions in varying concentrations of NaCl and CaCl2. The addition of NaCl exhibits no effect on the core thicknesses of equilibrium films; Newton black films (NBF) with constant core thickness of 2.5 nm are observed in the range of the measured concentrations up to 1M NaCl. Whereas, in CaCl2 the core thicknesses in equilibrium state strongly depend on CaCl2 concentrations. Consequently, the equilibrium films are NBF at below about 1.1 X KH M, silver films (SF) at about 1-4 X 1(H M, common black films (CBF) at about 5 X 1CH to 0.2 M and again NBF at higher concentrations than about 0.2 M. These transitions of film thickness are thought to be due to specific adsorption of Ca2+ on the zwitterionic head group. So, using the measured thickness of the film core and the Lifshitz theory applied for a triple-layer model, van der Waals dispersion forces ( ) were calculated and from the the effective Hamaker constants, A (h, 298 K), for a foam water film were simultaneously calculated. The values obtained vary from 2 X KH°J to 4.5 X Kb20 J in the range 5nm -30nm of film thicknesses. Next, for the equilibrium SF and CBF, surface potential^), surface charge density (a), and the binding constant (K) of Ca2+ to the equilibrium foam films were evaluated using the charge-regulation model taking account of the DLVO theory of colloid stability. At the thickness-transition concentration of 1.1 X 1(H M CaCl2 0 and are 11 mV and 1.3 X 1(H C nr* 12 345, respectively. Further, K is almost independent of the CaCl2 concentration in the range 3 X 1(H M to 0.1 M, i.e., the binding constant of Ca2+ to the lysoPC foam film is given as 15 ± 5 M-1 assuming a 2:1 stoichiometry for the PC/Ca2+.

Influence of Surfactant Structure on the Drainage of Nonionic Surfactant Foam Films

“…Fourier transform infrared (FT-IR) spectrometer, System 2000 FT-IR (Perkin Elmer Co.) was used to determine the thickness of the foam films according to previous papers (7,17,19). A measuring cell having two CaF 2 windows and a frame was used for measurements in the cell.…”

Clearning performance and foaming properties of lauroylamidopropylbetaine/nonionics mixed systems

“…FT-IR measurements were done as previously described using a System 2000 FT-IR (Perkin-Elmer Co., Ltd., Tokyo, Japan) to determine the aqueous core thickness (d2) of vertical foam films (12). A rectangular frame 18 mm wide and 15 mm high, which was hollowed out of a G4 sintered glass plate (32 mm wide, 30 mm high, and 2 mm thick), was used to support the foam films.…”

Unusual buffer action of free-standing nanoscopically confined water

“…Interestingly, the aqueous cores of the BSFs had a buffer action at least resistant to acidic/alkaline solutions in the neutral and basic conditions. FTIR spectroscopy is used to monitor aqueous core thickness of the soap films by measuring absorbances of the OH stretching bands (3400 cm À1 ) of water confined in the films [21,26]. The molar absorption coefficient of 150 L mol À1 cm À1 was used to convert IR absorbances in 3400 cm À1 into equivalent thicknesses of the aqueous cores by using the Lambert-Beer law [26].…”