Labeled Surfactants

The FRRPP process has been proposed to generate unique materials with certain programmable structures. Some of the unique features involve polymeric surfactants that have the ability to be dispersed in water at relatively low concentrations, and to be environmentally responsible formulations which allow for wide area/volume delivery. They would also have the ability to penetrate low porosity solids, such as soil, cement, rock, masonry with modest pressure drop requirements. If labeled, these surfactants can be applied on various surfaces or within porous stmctures for subsequent detection of changes in surface/underground structures. These materials can also be transformed into a nonflowing gel, and finally into a hard rubber dry sealant material. Other transformations of interest could be investigated from various possible polymeric surfactants that can be synthesized using the FRRPP process. 

When the vinyl acetate segments were hydrolyzed, a gel material was formed from the surfactant, which was expanded in volume by a factor of about 5. Upon drying, the gel turned into a hard rabber sealant material (Fig. 6.1.2(a)), which has a closed structure (Fig. 6.1.2(b)) and a surface that is very adherent to glass. 

The hydrolysis of the vinyl acetate from the material (also called B6-1) was obtained when 0.5 wt% was dispersed in water at 80°C for less than 3 weeks. Acetic acid is a product of the reaction, which also results in the formation of vinyl alcohol 

Caneba, in Free-Radical Retrograde-Precipitation Polymerization (FRRPP), 

It should be noted that these VA/VOH/AA-based multipolymeric surfactants were developed as a displacement fluid for petroleum and tar sands (Caneba, 2007) thus, their permeability properties have been tested as well. If conditions are such that in time the material hydrolyzes to become a sealant in the rock formation, then it could also be investigated for its potential use in carbon sequestration operations. 

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The adsorption values calculated by the method of Motomura et at. differ appreciably from those calculated by the procedures of Pethica and of Alexander and Barnes. Discrimination between these theories should therefore be possible by measuring the adsorptions by an independent experimental method, such as through the use of radio-labelled surfactants (11-12). 

Adsorption can be measured by direct or indirect methods. Direct methods include surface microtome method [46], foam generation method [47] and radio-labelled surfactant adsorption method [48]. These direct methods have several disadvantages. Hence, the amount of surfactant adsorbed per unit area of interface (T) at surface saturation is mostly determined by indirect methods namely surface and interfacial tension measurements along with the application of Gibbs adsorption equations (see Section 2.2.3 and Figure 2.1). Surfactant structure, presence of electrolyte, nature of non-polar liquid and temperature significantly affect the T value. The T values and the area occupied per surfactant molecule at water-air and water-hydrocarbon interfaces for several anionic, cationic, non-ionic and amphoteric surfactants can be found in Chapter 2 of [2]. 

Work with labeled surfactants at Davis, Fort Detrick, and VPI by both authors has shown that with nonionic surfactants such as Tween 20 and Tween 80 very few of the tagged atoms are translocated away from the site of application (Figure 4). For Tween 20 less than 2-3% were found outside the treated leaf after 7 days (Table II). Even in cases where translocation of label had occurred such as with 35S-labeled sodium lauryl sulfate the label in remote parts of the plant was not in the form of the original surfactant molecule but was in other metabolites. 

The surfactant protein B was unspecifically labelled with/ac-[99mTc(CO)3]+. The highly lipophilic protein spread over a hydrophilic surface and could have potential in the diagnosis of acute respiratory disease syndrome. The spreading properties of the labelled and native surfactant protein B were in coincidence, making labelled surfactant protein B a potential diagnostic radiopharmaceutical [122]. 

An early indication that a widely used agricultural chemical might be metabolized to a nonpolar conjugate in plants came from an in vitro enzyme study with C-labeled surfactants of the Triton family. A crude particulate enzyme preparation from com shoots catalyzed the formation of fatty acid ester conjugates from the two 1"c-labeled polyethoxylated surfactants indicated below (Equation 32). The ester conjugates were formed primarily from palmitic and linoleic acids 0851). They were identified by mass spectrometry and by GLC analysis of hydrolysis products (J48). In vljro, rice and... 

We assume that conditions can be controlled to minimize additional relaxation effects such as magnetic dipole-dipole interactions. As the number of relaxation mechanisms decreases, the information necessary for a line shape analysis of the spectra also decreases. Thus, a poorer signal-to-noise ratio can be tolerated, and the signal can be smoothed by curve fitting techniques. Since little is known at the molecular level about two-dimensional transport coefficients, such as the surface viscosity, large uncertainties can be tolerated. In this sense, we believe that much can be learned from monolayer experiments using spin label surfactants. 

In this section we discuss a motional model [54-56] of aggregated surfactant molecules that involves a time scale separation of fast local and slow global motions. This model has been extensively applied to, and has been shown to rationalize, NMR relaxation data from aggregated surfactant systems. We discuss it in connection with H relaxation experiments, since the most extensive experimental studies have been performed on H-labeled surfactants. We begin by recalling that the longitudinal (R ) and transverse (R2) relaxation rates of an 7 = 1 nucleus due to a quadrupolar interaction in an isotropic solution are given... 

Initially, the decane and hexadecane microemulsion systems were studied at the emulsification boundary T m) to make an accurate comparison between the two systems. Deuterium-NMR relaxation using selectively deuterium-labeled surfactant is a useful method to detect variation of micelle size when changing composition and/or temperature. In a relaxation NMR experiment the combined motion of longitudinal (1/Ti) relaxation of the micelles and the transverse relaxation (I/T2) of the surfactants inside the film (internal diffusion) are measured. The measured parameters are therefore sensitive to the micellar size but essentially insensitive to intermicellar interaction. More information can be found in papers by Wennerstrom [133] and Halle [33]. At Tbpb the microemulsion droplets are generally spherical at infinite dilution [84]. The results from the relaxation measurements (expressed as l/r2-l/Ti) on the two systems are presented in Figure 3.3. 

Several techniques have been developed over the last 15 years to visually probe the morphology of surfactant monolayers at the air-water interface. In fluorescence microscopy, a small amount of fluorescently labeled surfactant molecules is added to a monolayer due to steric effects these tagged molecules tend to partition into less-ordered phases, which results in a visual contrast between coexisting phases [25-29]. Fluorescence microscopy has been used to determine domain sizes and shapes during phase transitions [25,28,30]. Polarized fluorescence microscopy (PFM) provides additional information on the lipid hydrocarbon chain ordering within condensed monolayers, especially in areas where the lipid hydrocarbon chains are tilted with respect to the surface normal [31,32]. The interaction of the electric field vector of the polarized light with the absorption dipole moment of the... 

The main technique used to look at exchange processes in equilibrium systems employs labeled surfactants, particularly with ESR spectroscopy. Fox s ESR study [92] of a paramagnetic surfactant in micellar solution was the first of its kind, and yielded a solution-micelle monomer exchange rate of 10 s" at room tanperature for 2,2,6,6-tetramethylpiperidine-oxidedodecyldimethylammonium bromide. These techniques, along with time-resolved luminescence quenching, have shown that the entry of surfactant molecules into micelles is near-diffusion controlled, whereas loss from micelles is rate limiting, and hence kinetically controlled [93]. A decade later (1981), Bolt and Turro [94] were able to find the separate exit and reentry rate constants for 10-(4-bromo-l-naphthoyl)decyltrimethylammonium bromide as 3.2 x 10 s and 5.7 x 10 mok s", respectively. 

Fig. 3. Structure of spin-labeled surfactants, (a) 5-DOXYL-stearate. b) Cat-16, (c) Tail-labeled n-aUcyltrimethylammonium surfactant.

Fig. 11. Site selection by different spin probes in an aqueous polymer dispersion (latex). Spin-labeled surfactants insert into the surfactant layer and may probe insertion of the surfactant tail into the polymer (16-DOXYL-stearate) or order of the surfactant layer (5-DOXYL-stearate). The weakly polar prohe TEMPO diffuses (dotted arrow) from the aqueous serum into the polymer sphere (gray). More polar prohes such as 4-hydroxy-TEMPO and TEMPO-4-carboxylate reside in the aqueous serum.

Just like NMR, ESR is sensitive to exchange phenomena. This also residts in a broadening and shift of the ESR lines. However, since electrons rather than nuclei are now involved, the time scale of processes that can be probed by ESR is shifted to much shorter values. Typically exchange processes with characteristic times between 10 ps and 1 ns can be probed by ESR. The main problem in using ESR is that it requires spin-labeled surfactants. The process investigated is then the exchange of the spin-labeled srufactant and not that of the surfactant of interest. 

Other methods than chemical relaxation methods have been used to determine the rate constants k+ and k". ESR (see Chapter 2, Section V) has been used to investigate the exchange of spin-labeled surfactants and lipids. The spin-labeled surfactant was formd to have values of the cmc and k that did not differ much from those for the corresponding unlabeled surfactant. The values of k+ for spin-labeled lecithins with decyl and dodecyl chains were formd to be 4.8 x 10 and 1.2 x 10 respec-... 

The uptake of " C-labeled surfactants (0.1% w/v) in the presence of difenzoquat indicated an intimate association between surfactant and chemical. In the presence of C12 E8, uptake of difenzoquat was increased fivefold, particularly during the first 48 h after treatment. There was evidence that surfactant and herbicide penetrated at similar rates, confirming the findings of Stevens and Bukovac. The interaction between OPE 9.5 and difenzoquat, however, was different. The overall rate of uptake was lower than that for the herbicide alone, though a greater proportion of the absorbed herbicide was translocated. 

Tanaka, F. S., R. G. Wien, Specific C-labeled surfactants addition of homogeneous polyoxyethylene glycols to p-(l,l,3,3-tetramethylbutyl)phenol, y. Labelled Compd. Radiopharm., 1976,72,97-105. 

Figure 18 Structural and semi-dynamical models of organically modified clay and polymer-clay nanocomposites. Brown discs correspond to silicate platelets, red balls to surfactant headgroups, yellow strings to surfactant alkyl chains, blue strings to polymer chains and the green wire frame to the nitroxide spin label, (a) Organically modified clay, doped with 1 % of spin-labeled surfactant, (b) Intercalated polymer-clay nanocomposite, (c) Exfoliated polymer-clay nanocomposite, (d) Visualization of the dynamics gradient along the surfactant alkyl chain.

A quantitative analysis of thermally activated surfactant dynamics was undertaken on organically modified magadiite with matching headgroups of the spin-labeled surfactants and majority surfactants. In organodays in the absence of the polymer and in microcomposites with PS and ammonium surfactants, bimodal dynamics was observed, which lead to instabilities in this analysis and difficulties in interpretation. In contrast, spectra of nanocomposites formed with poly (s-caprolactone) (PCL) and spectra of both PS and PCL composites with phosphonium surfactants could be analyzed to a good approximation in terms a single rotational correlation time. 

In a study focused on structure of the composites, DEER measurements on 7-SL-UTMA, 9-SL-UTMA, and 11-SMJTMA in organoclay, PS midocomposites, and PCL nanocomposites were performed to reveal the distribution of spin-labeled surfactants. No well-defined distances were found. The data could be fitted by a stretched exponential decay 7(t) =exp(-at° ), where D is the fradal dimension of the homogeneous distribution of spin labels and a is a generalized density parameter. 

Figure 21 Changes in surfactant layer structure observed with ENDOR on spin-labeled UTBP surfactants in composites prepared from hexadecyl-tributylphosphonium modified magadiite. For clarity the alkyl chain (yellow) is shown only for spin-labeled surfactants, (a) Organoday (top panel) and PS microcomposite (bottom panel) with an increase in the first mean distance q between spin label (green sphere) and phosphonium surfactant headgroup surface layer (red spheres) by 1 A. (b) Organoday (left panel) and PCL (blue) nanocomposite (right panel) with a widening Adooi of the basal spacing of 6 A and an increase in the second mean distance T2 between the spin label and phosphonium surfactant headgroup center layer by 1.4 A.

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