Dynamics of Condensed Monolayer and Multilayer Formation of Hexadecylpyridinium Chloride–Sodium Dodecyl Sulfate Mixed Systems at the Air/Water Interface

Abstract

The adsorption dynamics of mixed adsorbed films of hexadecylpyridinium chloride (HPC) and sodium dodecyl sulfate (SDS) were investigated through external reflection absorption FTIR (ERA FTIR) and surface tension measurements, following two different experimental approaches. In the first approach (case 1), solutions of SDS and HPC, at the desired total concentration and composition, were first introduced into the measurement cell, and then, the measurement was started. In the second approach (case 2), the HPC solution, at a given concentration, was first introduced into the cell, and after adsorption equilibrium was reached, a certain volume of concentrated SDS solution (to attain the desired total concentration and composition) was added to the cell, and the measurement was continued. The experiments clearly showed that the adsorption rate, as well as the mechanism, differed significantly between the two approaches.There are many researches concerned with the adsorbed film of binary surfactant systems 1 from the thermodynamic 2,3 and spectroscopic 4,5 point of views, and the existence of the three distinguishable surface phases has been confirmed experimentally. The gaseous state is a 2D gas of adsorbed surfactant molecules. An increase in surface density often gives rise to a surface phase transition to the expanded (liquid-like) and the condensed (solid-like) state. These surface phase transitions and the properties of each surface state probably control the stability of colloidal dispersions such as foams and emulsions. Moreover, monolayer formation as well as multilayer formation have been reported in some systems. 6,7 Several anionic and cationic surfactant mixed systems form vesicles owing to ion pairing in aqueous solution.8 For the HPC SDS system, Kawai et al. reported multilayer formation at the air/water interface, 9 while our own studies using ERA FTIR measurements revealed that first the condensed monolayer with a hexagonally packed structure is formed, and then other layers accumulate beneath or over it to form the multilayer. 10 In the present study, we investigate the formation dynamics of both multilayers and condensed monolayers by measuring ERA FTIR and surface tension as a function of time, using two experimental approaches. In the first approach (case 1), mixed solutions of SDS and HPC were first introduced into the measurement cells, at the desired total concentration and composition, after which the measurement was started. In the second approach (case 2), the HPC solution at a given concentration was first introduced into the cell, and after the adsorption equilibrium was reached, the required volume of concentrated SDS solution was added to the cell to reach a certain total concentration and composition, and the measurement was continued.The surface tension was measured by the pendant bubble or drop method, at 298.15 K under atmospheric pressure. 11 The total molality and composition were fixed at the values where multilayer formation was reported, i.e.,X 2 ¼ 0:64 andm ¼ 1:9 and 1.4 mmol ...

Multilayering of Surfactant Systems at the Air–Dilute Aqueous Solution Interface

“…Nevertheless, ST itself remains an important thermodynamic measurement. Spectroscopic methods, although not generally effective for determining the surface excess in monolayers, can be useful in the multilayer situation as shown by Takumi et al, 13 who used the IR intensity to measure extra surfactant above a monolayer. Ellipsometry is sensitive to the surface excess and can detect anomalous excesses above a monolayer, 14 but it cannot resolve multilayer structure.…”

The Formation of Surface Multilayers at the Air–Water Interface from Sodium Polyethylene Glycol Monoalkyl Ether Sulfate/AlCl3 Solutions: The Role of the Size of the Polyethylene Oxide Group

“…The nonionic surfactant with a bulky headgroup (C 12 E 8 or C 12 E 12 ) introduces a steric hindrance which disrupts the complex formation, as originally proposed by Alargova et al 17 Although surface multilayer structures have been reported previously in concentrated surfactant systems, 24−26 in lung surfactants, 27,28 and in polyelectrolyte/surfactant mixtures, 29 there are relatively few observations reported for relatively dilute systems. 22,23,30,31 The surface multilayer structures induced by polyelectrolytes 29 and multivalent counterions 22,23 exhibit extreme and persistent wetting properties on hydrophobic surfaces and offer great potential for applications requiring enhanced adsorption, delivery and retention of benefit agents to interfaces, and in soft or biolubrication.…”

The Formation of Surface Multilayers at the Air–Water Interface from Sodium Diethylene Glycol Monoalkyl Ether Sulfate/AlCl3 Solutions: The Role of the Alkyl Chain Length

“…Surface multilayer formation or surface self-assembly from more concentrated surfactant solutions, − in lung surfactants, , layer-by-layer polyelectrolyte deposition , and in polyelectrolyte/surfactant mixtures have been extensively reported. In contrast, reports on surface self-assembly and surface multilayer formation from dilute surfactant solutions, in mixtures, , induced by multivalent counterions − or oligoions , are relatively sparse and recent. However their marked and persistant wetting properties, their enhanced adsorption and efficient delivery and retention of different benefit agents (such as perfumes) are potentially attractive for many applications.…”