Wetting and adsorption: I. The structure of adsorbed layer of nonionic surfactants at SiO2/water and SiO2/cyclohexane interface

Abstract

Based on the adsorption of Triton X‐100 on silica/water and silica/cyclohexane interfaces and the adsorption of Triton X‐305 on silica/water interface, two adsorption models have been proposed. On silica/cyclohexane interface, the adsorption of Triton X‐100 is monomolecular layer. The molecules in the monolayer are presumed to be attached to the silica surface by their EO chain such that their hydrocarbon chain are exposed to the cyclohexane phase. On silica/water interface, the adsorption of Triton X‐100 or Triton X‐305 is bimolecular layer. The surfactant molecules orientated in the first layer are similar with that on the silica/cyclohexane interface. The molecules in the second layer are postulated to adsorb on those of the first in the opposite orientation, with EO chain directed toward the adsorption medium. The contact angle of quartz‐water‐cyclohexane (θW) as a function of the concentration of Triton X‐100 and Triton X‐305 in water has been measured with quartz plate employing the captive drop (cyclohexane) technique. The observed θW (measured through water) rose from < 10° to a maximum of about 120° for Triton X‐100 and of about 40° for Triton X‐305 as the concentration of surfactant in water increased, and then fell, as the concentration increased further. The results are consistent with the proposed adsorption models.

General isotherm equation for adsorption of surfactants at solid/liquid interfaces. Part 1. Theoretical

“…12313 Thereafter, based on the mass-action model of surfactant adsorption, a theoretical approach was developed which also allows the calculation of the hemimicelle aggregation number (n), equilibrium constant ( K ) and the standard free energy of hemimicellization (AGE,) from the experimental data. l 8 The results show that the n values obtained by the mass-action model are in good agreement with those obtained by the empirical approach proposed earlier. Very recently, based on the mass-action model of one-step formation of hemimicelles, an isotherm equation was derived which explains the S-type adsorption isotherm and allows us to calculate n, K and AGim, and fits the experimental adsorption isotherms of non-ionic surfactants on silica gel very well.…”

“…We have been engaged for years in trying to elucidate the phenomena of surfactant adsorption at solid/liquid interfaces. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] Adsorption isotherms of various types, including Langmuir-type (L), S-type (S) and two plateaux-type (LS) have been reported. 6-8~10-17319920…”

Adsorption of organic molecules on silica surface

“…Gu et al and others [120][121][122][123][124][125][126][127] studied the adsorption of various types of surfactants on silica gel and generalized the followings. The adsorption isotherm of cationic surfactants on silica exhibits two plateaus.…”

On the Behavior of Nonionic Surfactants at the N-Heptane/Silica Gel Interface: Influence of the Presence of Interfacial Water Inferred from Adsorption Isotherms and Calorimetric Data

“…The present study was undertaken in an attempt to fill this gap. To our knowledge the only reported studies have essentially shown that the adsorption of poly(oxyethylene) glycol alkylphenyl ether onto solid surfaces has a strong solvent polarity dependence (38)(39)(40)(41)(42)(43). Adsorption depends not only on the solvent polarity but also on the difference in polarity between the solvent and the adsorbent.…”