Adsorption Kinetics of 1-Octanol at the Air−Water Interface

Abstract

The adsorption of 1-octanol at an air−water interface is studied theoretically and experimentally. A video-enhanced pendant bubble tensiometry is utilized for the measurement of relaxation of surface tension. Two types of processes were investigated: the adsorption onto an initially clean air−water interface and the desorption out of a suddenly compressed interface which is originally at equilibrium. A theoretical simulation using the equilibrium surface tension is performed and it is concluded that there is no shift in controlling mechanism for the adsorption of 1-octanol molecules from an aqueous phase onto an initially clean air−water surface. The adsorption of 1-octanol onto a clean air-water interface is verified experimentally to be a diffusion-controlled process. A diffusion coefficient was computed by comparing these adsorption profiles with numerical solutions of bulk surfactant diffusion equation and the generalized Frumkin adsorption model. The re-equilibration of a compressed interface agrees well with a diffusion-controlled process. Lower bounds on the kinetic constants for the sorption process are inferred for octanol by comparing numerical solutions of mixed diffusion and surface kinetic transfer with the desorption relaxation data.

Dynamic adsorption of octanols at air/water interface

“…Moreover, the best-fitted values of B also varied with 1-octanol concentration. The variation of kinetics constants was also observed in other investigations (Bleys, 1985;Lin and Lin, 1997). The variations indicated that the kinetic dependency on subsurface concentration is more complicated than the available models.…”

A Study on Surfactant Adsorption Kinetics: The Role of the Data of Equation of State γ(Γ) for C14E8

“…A similar result was also reported for other polyethylene surfactants C 10 E 8 , C 12 E 8 , C 12 E 6 , C 12 E 4 , and Triton X-100 (1, 3, 5, 6). A negative K was found for n-alcohols (10,13,14,18) and fatty acid (12,15).…”

Modeling of adsorption dynamics at air–liquid interfaces using statistical rate theory (SRT)

“…The geometry of the pendant drop is approximated as a sphere. The diffusion is assumed to be spherically symmetrical and is described by Fick's second law [14][15][16][17],…”

“…Although the rate constants can be calculated from the theory in principle, we estimated these rate constants using reported experimental data and related rate constants of the same system. Table 1 lists the physically realizable range of values for each of the parameters involved in the governing equations [2,[11][12][13][14][15][16][17]19,22,[25][26][27]. For example, the range of the bulk concentrations is considered from a very dilute concentration to the critical micelle concentration of common surfactants.…”

“…The adsorption kinetics is mixed diffusion and transfer controlled when steps (i) and (ii) are equally important. Currently, most of the theoretical models have been developed using the following two mechanisms: diffusion controlled [9][10][11][12] and mixed diffusion and transfer controlled [13][14][15][16][17]. Rearrangements at the surface may consist of reorientation, conformational changes, complex formation, chemical reactions, phase transitions, or formation of three-dimensional structures resembling liquid crystals.…”