Surfactant Adsorption Kinetics by Total Internal Reflection Raman Spectroscopy. 2. CTAB and Triton X-100 Mixtures on Silica

Abstract

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Surfactant adsorption by total internal reflection Raman spectroscopy. Part III: Adsorption onto cellulose

“…In a previous paper [5] we have studied the adsorption of mixtures of CTAB and TX-100 mixed systems onto silica, measuring the surface excesses for both surfactants at varying bulk composition with a constant 2 mM concentration.…”

“…One of the most striking features of adsorption onto silica is a two-fold increase in adsorbed amount caused by the presence of small (2%) mole fractions of CTAB. [5] The origin of this cooperative effect is likely to be the interaction between the positively charged CTAB and the negatively charged silica surface. On cellulose there is no such promotion of adsorption at low CTAB mole fractions.…”

“…TIR Raman spectroscopy was invented in the 1970s [1,2] but it is only recently that it has been developed into a powerful, surface-sensitive technique for quantitative studies of adsorption at the solid-liquid interface. [3][4][5][6][7] In Parts 1 and 2 of this series, [4,5] we demonstrated the use of TIR Raman spectroscopy in the study of the adsorption of pure and mixed surfactants on a silica substrate. While the technique is at its most straightforward when the substrate is transparent and has vibrational bands that do not overlap with those of the adsorbates, TIR-Raman spectroscopy can also be applied successfully to thin 2 films deposited on transparent substrates even when, as is the case with cellulose, the vibrational spectrum of the thin film strongly overlaps the spectra of the adsorbates of interest.…”

Total internal reflection Raman spectroscopy

“…The TIR Raman spectrometer at Durham University, 29,30 is illustrative of a design in which the beam is delivered externally to the collection optics in order to have a well-defined angle of incidence. The pump laser is a continuous-wave, frequency-doubled solid-state laser with a wavelength of 532 nm yielding between 0.1 and 1 W at the sample, depending on the application (and, in particular, on the damage threshold of the sample).…”

“…We have extended TIR Raman to look at adsorption and desorption kinetics of surfactants at solid-liquid interfaces, 30,56 with a sampling frequency of 0.5 Hz-sufficient to follow the kinetics in real time-with a standard deviation from point to point of 1-5% of a saturated layer. For measuring the adsorption kinetics of single-component systems, techniques such as ellipsometry, optical reflectometry and QCM offer higher sampling rates (up to 1 kHz) with little increase in noise, but for multi-component systems TIR Raman is one of the most useful techniques available.…”