Kinetics of Surfactant Desorption at an Air–Solution Interface

Abstract

The kinetics of re-equilibration of the anionic surfactant sodium dodecylbenzene sulfonate at the air-solution interface have been studied using neutron reflectivity. The experimental arrangement incorporates a novel flow cell in which the subphase can be exchanged (diluted) using a laminar flow while the surface region remains unaltered. The rate of the re-equilibration is relatively slow and occurs over many tens of minutes, which is comparable with the dilution time scale of approximately 10-30 min. A detailed mathematical model, in which the rate of the desorption is determined by transport through a near-surface diffusion layer into a diluted bulk solution below, is developed and provides a good description of the time-dependent adsorption data. A key parameter of the model is the ratio of the depth of the diffusion layer, H(c), to the depth of the fluid, H(f), and we find that this is related to the reduced Péclet number, Pe*, for the system, via H(c)/H(f) = C/Pe*(1/2). Although from a highly idealized experimental arrangement, the results provide an important insight into the "rinse mechanism", which is applicable to a wide variety of domestic and industrial circumstances.

Protein crystallisation with air bubble templates: case of gas–liquid–solid interfaces

“…The air bubble surface, adsorbing the proteins, had a multilayer structure, contributing to a slower desorption and, therefore, it was more difficult to achieve new dynamic equilibrium on the surface of the bubbles during the shrinking [45]. The desorption rate may also be limited by the diffusion process [46]. The lysozyme surface concentration was estimated to be 7.0 mg/m 2 for 50 mg/mL starting lysozyme concentration, according to the literature [26].…”

Nonlinear dynamics of two-layer channel flow with soluble surfactant below or above the critical micelle concentration

“…Typical values of the physical parameters describing the geometrical specifications, properties of the fluids and the surfactants. Key to references: SH, Shen et al (2002); BA, Barthelet, Charru & Fabre (1995); PK, Pereira & Kalliadasis (2008); SO, Song et al (2006); MO, Morgan et al (2012); CL, Chen & Lee (2000); CF, Chang & Franses (1995); PH, Phan, Nguyen & Evans (2005); DA, Danov et al (1996); ED, Edmonstone, Craster & Matar (2006); MA, Mavromoustaki, Matar & Craster (2012a).…”

Effective osmotic cohesion due to the solvent molecules in a delocalized adsorbed monolayer

“…The Langmuir model and its derivatives still dominate the adsorption literature [9][10][11][12][13][14][15]. Significantly, Parsons himself was not persistent in pursuing a delocalized description of the adsorbed layer and, in his later works, he worked on localized models for liquid interfaces, e.g., [16].…”

“…Above this point, w decreases exponentially with s; this case (corresponding to series with respect to small w) is analysed in S3. By substitution of Eq (15) into the LHP EoS (9) and expansion in series with respect to s (an approximation corresponding to a dilute 2D solution of surfactant), one obtains the following 2D osmotic virial expansion [29] of the EoS of the monolayer at fixed chemical potential of the solvent:…”