Surfactant infrared measurements

Infrared measurements have been conducted with sulphonyl chlorides obtained from, in determination of, sulphonate surfactants (see Section I.B.2.b above)161-163. IR measurements at 1212cm-1 were employed to determine p-chlorosulphonyl chloride as impurity in iV,iV-di-n-butyl-p-chlorobenzenesulphonamide2 81. 

Hetsroni G, Gurevich M, Mosyak A, Rozenblit R (2003) Surface temperature measurement of a heated capillary tube by means of an infrared technique. Meas Sci Technol 14 807-814 Hetsroni G, Gurevich M, Mosyak A, RozenbUt R (2004) Drag reduction and heat transfer of surfactants flowing in a capillary tube. Int J Heat Mass Transfer 47 3797-3809 Hetsroni G, Mosyak A, Pogrebnyak E, Yaiin LP (2005) Eluid flow in micro-channels Int J Heat Mass Transfer 48 1982-1998... 

TGA measurements showed that 90-95w% of the surfactant is extracted by this procedure. Elemental analysis, X-Ray diffraction and infrared analysis proved that the recrystallized extracted surfactant is identical to the original one, and we have re-used it several times without any decrease in the quality of the obtained MCM materials. 

The surface forces technique measures the force between molecules (eg. surfactants, polymers) adsorbed on mica sheets. In the case of large molecules such as polymers, the measurement is most sensitive to the regions closest to the solution and provides little direct information about the region adjacent to the surface. As it is a measurement between macroscopic surfaces, it is unable to provide information on microscopic chemical differences at the interface. Infrared spectroscopy could provide additional information about the quantity of adsorbed material on the mica surface, the identity and orientation of the adsorbed species, and possibly the nature of the surface linkage. 

The foam bilayer is the main model system used to obtain experimental results for the stability of bilayers. The proof that the studied foam films are bilayers is based on the experimentally measured h(Cei) dependences and I"I(/i) isotherms. In both cases films with the same thickness are obtained, which corresponds to that of bilayers and does not change with further increase in Cei or IT (e.g. Figs. 3.44, 3.57, 3.62). This leads to the conclusion that the NB foam films do not contain a free aqueous core between its two monolayer of surfactant molecules. A similar conclusion is drawn from the investigatigations of NB foam films by infrared spectra [320,417] and by measuring longitudinal electric conductivity of CB and NB foam films [328,333,418]. 

For colloids with a physically adsorbed surfactant or cca, the adsorption isotherm is important. The adsorbant concentration on the particle surface can be measured by infrared spectroscopy using diffuse reflectance and by ESCA. Absolute concentrations are difficult to determine with ESCA on "rough" surfaces, and a calibration point is required with other techniques. The change of the concentration of adsorbant in solution after adsorption on the colloid surfaces can be detected by elemental analysis of supernatant with plasma emission or atomic absorption if adsorbant contains specific element(s). When colloids are sterically stabilized, the effectiveness of the stabilization can be evaluated with solvent-nonsolvent techniques and with temperature studies ( 25,26). 

Infrared observations of the effects of surface films on heat and gas transfer have been made in situ (Frew et al. 2004). Figure 10 (upper) shows the instrumented air-sea interaction catamaran LADAS operating within a banded surface slick during the CoOP97 study. Simultaneous infrared imaging and measurements of wave slope and surfactants outside and inside of the slick determined that, when the slick was entered, the surface temperature distribution shifted toward lower temperatures and the spatial scales of the temperature fluctuations at the sea surface increased (Fig. 10, lower), characteristic of reduced surface renewal and an attenuation of mixing in the aqueous boundary layer. The estimated temperature gradient increased from 0.13 Kelvin to 0.24 Kelvin and the net heat flux dropped from 77.2 Watt m 2 to 36.5 Watt m"2. The 80% increase in AT and a 50% decrease in the heat flux lead to a decrease in the estimated heat transfer velocity from 49.7 cm h"1 to 13.1 cm h"1. 

Understanding of the structure of the adsorbed surfactant and polymer layers at a molecular level is helpful for improving various interfacial processes by manipulating the adsorbed layers for optimum configurational characteristics. Until recently, methods of surface characterization were limited to the measurement of macroscopic properties like adsorption density, zeta-potential and wettability. Such studies, while being helpful to provide an insight into the mechanisms, could not yield any direct information on the nanoscopic characteristics of the adsorbed species. Recently, a number of spectroscopic techniques such as fluorescence, electron spin resonance, infrared and Raman have been successfully applied to probe the microstructure of the adsorbed layers of surfactants and polymers at mineral-solution interfaces. 

Spectroscopic methods are also commonly used for the analysis of surfactants. Among these methods ultraviolet/visible spectrophotometry and infrared/near-infrared spectroscopy are used for the measurement of surfactant concentration, while such techniques as nuclear magnetic resonance (NMR) and mass-spectroscopy (MS) are extensively used for... 

Several different experimental techniques, such as fluorescence decay, electron spin resonance (ESR) spectroscopy, Raman spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, neutron reflectome-try, calorimetry, Fourier-transform infrared (FT-IR) adsorption spectroscopy, small-angle neutron scattering (SANS), ellipsometry and surface force measurements, have been used to study self-assembled surfactant structures at the solid-liquid interface (11). These measurements, although providing insight into the hemimicellization process, critical aggregation numbers... 

More recently, an interesting technique has been used by Clark and Ducker [70] to measure kinetics, in the form of attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. They found that total surface exchange of a cationic ammonium bromide surfactant on a silica surface occurred in slightly less than 10 s (fig. 19.6). This technique had been used previously by Couzis and Gulari [71, 72] to look at the adsorption kinetics of anionic surfactants at the alumina-water interface with apparent timescales in the region of tens of hours. 

Recently, the same behavior was demonstrated for the system water (NaCl 8%) + decane 1 1-butanol-A-octylribonamide (CsNg), by using H chemical shift and relaxation time data. At saturation, the molar ratio of bound water to OH groups is again about 1 [135]. This is somewhat surprising, as usually the water solubilization behavior revealed by spectroscopic techniques is entirely different. Thus, NMR [14] (Fig. 17), time domain dielectric spectroscopy (TDS) [136], ESR [137], and Fourier transform infrared (FTIR) [15] measurements indicate that upon the addition of even a small amount of water, an equilibrium between free and bound water is established. This apparent discrepancy is readily understood because the spectroscopic techniques sense the water molecules most near the surfactant. 

Raynor et al separated additives in complex mixtures by capillery supercritical flow chromatography and deposited the separated products in potassium bromide discs prior to measurement of their infrared spectra by FTIR spectroscopy. Supercritical flow chromatography coupled with F.T. infrared spectroscopy (SFC-FTIR) has been used to provide quantitative information on and characterization of a range of polymeric surfactants. Bartle et al and Chester also investigated this technique. 

UHV is normally required when studying low-area flat surfaces (exceptionally this would not be a requirement if the adsorbate, such as a surfactant, is capable of displacing surface impurities) and this requires sophisticated equipment. Also, the high sensitivity needed for the measurement of spectra from single monolayers requires the use of FT-IR spectrometers with selective photoconductive infrared detectors the mercury/cadmium telluride detector which covers the major range of the spectrum down... 

While infrared spectrophotometry is most useful for the qualitative analysis of surfactants, various quantitative methods have been developed for well-characterized systems. For example, an attenuated total reflectance cell with a ZnSe crystal is useful for direct analysis of aqueous anionic surfactant solutions by FTIR, while avoiding the deleterious effects of water on the usual transmission cells. In this case, the sulfonate absorbance at 1175 cm" , or the sulfate absorbance at 1206-1215 cm , is used for quantification (10,26). In another application, the weak absorption bands in the 1429-1333 cm" region are used to measure the relative amounts of linear and branched chain alkylbenzene sulfonates extracted from environmental waters (27). This is the one advantage of the infrared technique over those that have supplanted it for wastewater analysis its ability to differentiate the straight and branched chain compounds (28). No procedure will be given here, since the cleanup prior to IR analysis can be handled adequately by the method for LAS analysis by desulfona-tion/gas chromatography, described in Chapter 8. 

PFPE-based surfactants have been studied extensively by Johnston and coworkers [26-29], Fourier transform infrared (FTIR) measurements on a w = 10 microemulsion based on ammonium carboxylate PFPE [CF30(CF2CF(CF3)0) CF2C00NH4] (MW = 740) indicated the presence of bulk water domains. Water solubility up to w = 14 was reported at 55°C and around 177 bar for 1.4wt% surfactant [26]. Time-resolved fluorescence and electron paramagnetic resonance (EPR) studies suggested the presence of anisotropic or nonspherical micelles. Zielinski et al. [30] studied the phase stability of this system at 35°C, as shown in Fig. 2 SANS was then employed to study droplet structure. Observations with PFPE were similar to the earlier study in H7E7 [11] discrete water droplets of around 25 A radius were found to be present, and as indicated in Fig. 3 the droplet size increased with added water. 

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