Surfactants sampling

Figure 12.18 LC-SFC analysis of mono- and di-laurates of poly (ethylene glycol) ( = 10) in a surfactant sample (a) normal phase HPLC trace (b) chromatogram obtained without prior fractionation (c) chromatogram of fraction 1 (FI) (d) chromatogram of fraction 2 (F2). LC conditions column (20 cm X 0.25 cm i.d.) packed with Shimpak diol mobile phase, w-hexane/methylene chloride/ethanol (75/25/1) flow rate, 4 p.L/min UV detection at 220 nm. SFC conditions fused-silica capillary column (15 m X 0.1 mm i.d.) with OV-17 (0.25 p.m film thickness) Pressure-programmed at a rate of 10 atm/min from 80 atm to 150 atm, and then at arate of 5 atm/min FID detection. Reprinted with permission from Ref. (23).

Indicator solution (5 cm ) (J5) and chloroform (10 cm3) were placed in the titration beaker together with the aqueous surfactant sample and water (30 cm3 less the volume of the surfactant sample). The titration was then carried out with hyamine solution (4.0 mmol dm""3) added in 0.05 cm3 increments after the addition of an initial single aliquot. 

EFFECT OF OIL. Titrations were performed in which small amounts of decane were added with the surfactant sample. The results were found to be insensitive to the presence of up to 2 cm3 of the decane. This allows the application of the method to both simple aqueous solutions and microemulsions containing significant quantities of decane. 

Phase Inversion Temperature The carboxymethylate surfactant sample available for test purposes exhibited excellent salinity tolerance, in fact too high for practical sea water flooding... 

The reason for these differences is not well known but it is interesting to speculate. The lower HLB surfactants tested are also those with the shortest hydrophilic chains, and so the smallest molecular areas (10). They should therefore have the highest concentrations at the LDL2 surface at saturation causing disruption and solubilization. The slow action of 012 23 could be due to slow replacement of 0 2 23 molecules by lower HLB impurities in the surfactant samples. 

Table VII Nonionic Surfactant Samples Used in the River Die-away Test (11)...

Phthalic anhydride 225 has been used in the environmental analysis of alcohol ethoxylates, which are widely found surfactants. Samples are derivatized with phthalic anhydride converting the ethoxylates into phthalate half-esters. Under analysis by electrospray LCMS, the derivatized alcohols gave stronger signals with less background in the negative ion spectra <2005JCH39>. 

The mass spectral data selected for multivariate analysis represented a suite of 30 microlayer and bulk surface seawater surfactant samples (fraction FI Frew et al. (2006)) including seven from waters off Monterey and Santa Barbara, California and 23 collected along a transect from Delaware Bay on the U. S. east coast to the Sargasso Sea. Sample extracts were analysed in triplicate by desorption-electron ionisation (DEI) mass spectrometry (Boon 1992 Frew et al. 2006). Individual DEI mass scans were summed over the full desorption/pyrolysis interval, reduced to integer masses, and averaged for processing by multivariate analysis. Elasticities were estimated quasi-statically from surface pressure-area (El A) isotherm measurements in a KSV 2200 Langmuir film balance (Frew et al. 2006). The elasticity data were subsampled at fixed surface pressure intervals (0.5 mN m"1) for comparison with the results of the multivariate analysis. 

Surfactant samples. Fifteen surfactants (a-o) used in this study were commercially available and involved anion-, cation-, zwitterionic- and non-ionic types. Each of surfactant samples at 0.5 or 2 % (w/v) prepared in water or methanol was used. The surfactants examined in this study are listed in Table 1. 

Table 1. Surfactant samples examined in this study...

Figure 5. Isotachopnerograms of CMC with different DS for evaluation of zone-length dependence on DS. conditions same as in Figure 3 except leading electrolyte pH 7.5 imidazole buffer, 0.5% Triton X-100 surfactant sample 20 Ml of CMC at 0.005 ag/t carboxyl group. Reproduced with permission from Ref. 11. Copyright 1986, Elsevier.

The purity of solvents, especially in studies at liquid-liquid interfaces, is as important as the purity of the surfactant sample. The proven absence of any surface active contamination, both in the surfactant sample and in the solvents, is a necessary prerequisite for interfacial studies. The picture shown in Fig. 5.6 demonstrates the situation. 

Fig. 5.6 Adsorption at a liquid-liquid interface, taking into account impurities from the surfactant sample and the organic solvent...

There is one striking difference between the two sources of impurities. The contamination present in the surfactant sample appears as a minor component in the solution bulk with a concentration proportional to that of the main surfactant. If the origin of the impurity is the organic phase, its concentration is constant and independent of the surfactant concentration. Therefore, the effects of these two types of impurities on the adsorption kinetics and adsorption equilibrium are different. 

When we use the reorientation isotherm as obtained on the basis of the above described algorithm (surface tension values at times corresponding to the adsorption times), we get the picture shown in Fig. 32. The experimental points are well described at all shown concentrations, up to a certain time moment, where the experimental data deviate from the theoretical curve, obviously due to an impurity component. This effect depends on the surfactant sample and was not observed by Lee et al. (2003). Note, however, that these authors did not measure the surface tensions for times larger than 1 hour so that the deviation was maybe not remarkable enough to be detected. 

Alkyl Aromatics. Related to the alkyl benzenes discussed above are materials based on the so-called polynuclear aromatics such as naphthalene and anthracene. Of this class, the primary surfactant samples prepared and used industrially are the alkylnaphthalene sulfonates. They usually consist of mixtures of mono-, di-, and trialkyl naphthalene sulfonates with the alkyl group usually being in the C2-C4 range. 

The analysis of solvent and perfumes in formulations is performed by GC. For solvent analysis in surfactants sample pretreatment with organic solvent is used for the separation of inorganic impurities. Regarding surfactants and complementary compounds, applications may be mentioned such as the separation of a hardness agent (sodium laurate) in liquid laundry detergent by GC and the Hofmann degradation and analyses of cationic surfactant of the alkyltrimethyl- and dialkyldimethylammonium type in fabric softener and hair rinse. 

In making that calculation, we assume that essentially all of the surfactant is in one phase. That assumption becomes less valid, and sometimes has to be rejected, for the last one or two (most dilute in surfactant) sample tubes. Some surfactant must always be present in excess oil and excess brine phases in equilibrium with a surfactant-rich microemulsion phase. At higher total surfactant concentrations, say the first seven of the tubes in the above set, the amount of surfactant in the excess phases is small relative to the total. At lower surfactant concentrations the amount of surfactant in the excess phases becomes a more significant fraction of the total. 

In Fig. 10 (A) the concentration profile is depicted for a surfactant sample solution which is to be analyzed by chromatography. 

Fig. 5. Variation of peel strength with exposure time after bonding for the cross-linked copolymer C (NCO = 0.2eq.) comprising 0.04 of surfactant. Samples were aged at 60 C under applying pressure of 0.2kg/cm after bonding. Peeling speed, 3 x lO mm/min.

In the metal oxide polycation / anionic surfactant system the use of iron and lead polycations proved to be successful in the formation of mesostructured materials. Fig. 5 shows three XRD patterns of Fe-oxide surfactant samples synthesized with different Fe-precursors FeCl (A), FeS04 (B) and Fe(N03>3 (C). 

Na MAS NMR spectra of NZ and AZ samples exhibit only one resonance line at <5 s 24 ppm - Fig. 24E,F [03R1]. The intensity of sodium lines, after acid treatment, decreased as a result of the loss of sodium cations. The CP-MAS NMR spectra of NZ-surfactant samples were assigned to the corresponding dmgs. These data... 

The surface purity of the surfactant solutions is an important question in connection with the reliability of the experimental surface tension data [13, 14, 15, 16], though its importance has still not received enough attention. Surfactant solutions always contain impurities, mainly alcohol and longer-chain homologues, with surface activities significantly higher than that of the surfactants investigated. Purification of the surfactant samples by physical methods (extraction, recrystallization) does not provide substances sufficiently pure from a surface chemical point of view. 

The hydrocarbon chain melting transition is facilitated by factors that reduce the polar headgroup network cohesion. The addition of water to cetyltrimethylam-monium tosylate produces a peak at 23°C, which is related to the melting of CTAT crystals (embedded in saturated aqueous solution below 23 C) to produce a liquid crystalline phase (in highly concentrated CTAT systems) or micellar solutions (in dilute systems). The peak is broad, probably due to the existence of a biphase transition zone. No melting peak related to the polar network was detected, probably because of the relatively weak cohesive forces in this particular polar network. The second peak detected in concentrated water-surfactant samples was due to the hexagonal mesophase-isotropic liquid transition [53]. 

In this section, we will focus on the solubilization of a substance in water-oil-surfactant samples containing initially three components. These ternary systems include microemulsions (w/o, o/w and bicontinous), lamellar phases and other liquid crystal mesophases. On a microscopic scale, oil microdomains are separated from water microdomains by a surfactant interface. A microdomain is here understood to be an aggregate of at least the order of a hundred self-assembled molecules, although being too small to be considered as a microphase-separated sample. A sample contains separated microphases when domains of micron size of two thermodynamically stable different phases co-exist and do not de-mix even after centrifugation, due to kinetic stability. The solute can then be located at the interface or in the oil or water microdomain (cf. Figure 9.9). Since three environments are available in ternary systems, the interface can be considered as a pseudo-phase or as a surfactant monolayer (37). 

Measuring surfactant concentration by using surface tension suffers from the same drawback as the potentiometric measurements, i.e. the change in surface tension varies with the logarithm of the surfactant concentration, rendering a low accuracy in the calculated adsorbed amount. Another drawback is due to the fact that the method is very sensitive to the most surface-active species in the measured sample. In the adsorption of a polydispersed surfactant sample on a hydrophobic surface, the most hydrophobic surfactant species will adsorb and the more hydrophilic species will remain in the solution. In the calibration, however, the original sample is used and hence the calibration curve reflects a more hydrophobic system than is used... 

Figure 22.3. Due to the fractionation of a polydispersed surfactant sample, the measured adsorption is larger than the real adsorption if the surfactant concentration is determined by surface tension...

Figure 22.7. Schematic chromatograms of three surfactant sample concentrations showing the tailing of the peaks (see text for details)...

Considerable batch variation in the solubilizing properties of polysorbate 80, and a correlation between the assay for ethylene oxide content and solubilizing capacity has been found [183]. This emphasizes the need for careful analytical control of materials when experimental work is in progress. The areas of the phase diagram which gave clear solutions with all the surfactant samples represent about half the area shown in Fig. 6.24 obtained with one sample. 

Surfactant Sample Solubility at 20% (w/v) pH Acidity (mEqg- ) Peroxide number (mEqkg- ) Cloud Point yi% (mNm )... 

Figure 3 Suspensions prepared using different surfactants sampled after 4 hours...

In many cases, a surfactant sample is found to exhibit particular phenomena only over specific concentration ranges. This type of concentration dependence generally reflects the presence of impurities, which can have both a qualitative and a quantitative effect on the behavior of the... 

This general expression for the mole fraction of the i-mer in a surfactant sample follows the Poisson distribution. 

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