Adsorption of the Neutral Macromonomeric Surfactant Tween-80 at the Mercury/Electrolyte Solution Interface as a Function of Electrode Potential and Time

Abstract

The adsorption of the neutral macromonomeric surfactant Tween-80 from electrolyte solutions on a polarized mercury electrode was studied by means of differential capacitance measurements of the electrode double layer. Its variation with potential and time can provide qualitative information on the state of the Tween-80 adsorbate. The time evolution of the phenomenon is followed by sampling the capacitive current at different time periods after stepping the electrode potential at given values, and the steady-state differential capacitance (C) vs electrode potential (E) curve is obtained from long-duration data. Features associated with surface aggregation processes, such as capacitance plateaus, deformed peaks, and increase in capacitance with increasing time or surfactant concentration, start to appear even at concentrations below the bulk critical micelle concentration (cmc). The type of surface aggregates (surface micelles) formed depends on surface coverage and orientation which vary with time and surfactant bulk activity up to the cmc value. This continuous change of the surface state with bulk concentration gives rise to a rather continuous change of the corresponding C vs E characteristics. Two distinct capacitance plateaus are observed for the higher concentrations studied and are attributed to two-dimensional surface micelles of different monomer-unit orientations, but (unlike the charged micelles studied previously) these surface micelles do not collapse at extreme potentials into condensed polylayers. The very slow attainment of a steady state even at high concentrations is indicative of a surfactant surface concentration and orientation (and, hence, state too) which are dependent on the slow three-dimensional interaction of the first adsorption layer with outer adsorbed layers.

Poly(glutaraldehyde)‐stabilized fish scale fibrillar collagen–some features of a new material for heavy metal sorption

“…The use of most kinetic models is usually been associated with the surface‐reaction kinetic step as controlling the sorption rate 47, 48. However, this frequently is not the case.…”

“…So, an intraparticle diffusion model was also used here to check Cr(VI) diffusion into GA‐scale, using eq. (12):47 where k dif is the intraparticle diffusion rate constant and I is the intercept.…”

“…The parameters of the Intraparticle diffusion kinetic model are presented in Table IV. If the intraparticle diffusion is involved in the sorption process, then a plot of t 1/2 vs q t would result in a linear relationship and the particle diffusion would be the controlling step if this line passed through the origin 47. When the plots do not pass through the origin, this is indicative of some degree of boundary layer control and this further show that the intraparticle diffusion is not the only rate‐controlling step, but also other processes may control the rate of sorption, all of which may be operating simultaneously.…”

Oil Detachment from Solid Surfaces in Aqueous Surfactant Solutions as a Function of pH

“…21 However, Rosen has reported that the oxygen of polyoxyethylene chains interacts electrostatically with protonated surfaces at low pH. 22 Avranas et al observed the adsorption of nonionic surfactants to mercury-water interfaces as functions of potential, 23 which supports the premise that adsorption is affected by surface charge and that nonionic surfactants are not affected to the same degree as ionic surfactants or mixtures of nonionic and ionic surfactants. Goloub et al found that the adsorption of cationic surfactants onto a silica surface increases as the pH increases because the silica surface develops a greater negative charge.…”

Polysorbate 80 UV/vis spectral and chromatographic characteristics – defining boundary conditions for use of the surfactant in dissolution analysis

“…Polysorbate 80, a polymeric non-ionic surfactant, is commonly used for applications in the chemical, cosmetic, food, environmental, and pharmaceutical industries [1][2][3][4][5][6][7][8][9][10][11][12][13]. These uses typically involve the ability of the surfactant to stabilize emulsions or to increase the aqueous solubility of hydrophobic compounds.…”