Observation of G−LE and LE−LC Phase Transitions of Adsorbed 1-Dodecanol Monolayer from Dynamic Surface-Tension Profiles

Abstract

Two phase transitions, G−LE and LE−LC, of the adsorbed monolayer of the soluble surfactant 1-dodecanol at the air−water interface were observed from the dynamic surface tension measurement by using a pendant bubble tensiometer. Two constant surface-tension (γ) regions were detected in the dynamic surface-tension γ(t) profiles of different surfactant concentrations at 20 °C. They are at π = 0.75 and 17.9 mN/m. A constant γ region in dynamic γ(t) profiles indicates the existence of a 2D phase transition. These 2D phase transitions of adsorbed layer are presumed to be the coexistence of the gas (G) and liquid-expanded (LE) phases and that of the LE and liquid-condensed (LC) phases. A new phase-transition isotherm, which is possible to describe the 1-dodecanol adsorbed monolayer, is also proposed.

Equilibrium and dynamic surface properties of trisiloxane aqueous solutions. Part 2. Theory and comparison with experiment

“…Note, that experimental dependences do not show a presence of levelling off or an inflection point at Π=22-25 mN/m, that is, in a region where aggregation starts in the adsorbed layer. The latter has previously been observed in other systems [16,25]. It is possible to assume, that the absence of inflection points on γ vs t dependences for Т8 is determined by a relatively low surface concentration of aggregates as deduced from Fig.…”

“…(5) and (9) that at such surface pressures Γ 1 >>Γ 2 . Hence, in this range we can neglect the adsorption in the state 2 and investigate adsorption behaviour of trisiloxanes using already know earlier theoretical models of aggregation processes [10][11][12][13][14][15][16][17][18][19][20][21][22][23].…”

“…If the dynamic surface tension of a surfactant aggregating in the surface layer is studied, then above the critical adsorption of aggregates formation one should expect retardation of the surface pressure dependence on time expressed by the dynamic curve [16,21]. The dynamic curves calculated assuming the aggregation in the monolayer exhibit (for the not too large values of Π)…”

Surface rheology and interface stability.

“…Recently, work by Alvarez, et al elucidated the limiting factors and applicable ranges for both the pendant-drop tensiometer and microtensiometer, concluding that in some cases surfactant dynamics can be diffusion-limited or kinetically limited, depending partially on the size of the drop [Alvarez et al 2010]. For this work, a diffusion-limited model coupled with convection should adequately describe behavior at the air-liquid interface, and presumably deviations from this model would be the result of intermolecular interactions or rearrangements Surface elasticity, or the response of a surface tension to deformation, can be determined using a pendant-drop setup in conjunction that allows for an oscillating drop size , Tsay et al 2004, Hsu et al 2000]. This elasticity is called the Gibbs elasticity, and is defined as:…”

Phase transition phenomena of the adsorbed 1-dodecanol monolayer at the air–water interface

“…So far, studies for the phase transition of 1-dodecanol were mostly limited to a few selected bulk concentrations. Equilibrium surface-tension data, reported by Tsay et al (2004), were the first to try to identify the phase transitions of a 1-dodecanol monolayer directly from the adsorption isotherms. In this work, two-phase transitions, that occurred at bulk concentrations of 1.3 Â 10 À9 and 3.7 Â 10 À9 mol/mL for the G-LE and LE-LC phase transitions, were identified.…”