Surfactants, ionic

FIGURE 2-11 S-shaped adsorption isotherm for an ionic surfactant on an oppositely charged substrate. 

Adsorption from Aqueous Solution onto Adsorbents with Strongly Charged Sites 

The efficiency of adsorption due to nonelectrical interaction of an ionic surfactant onto an oppositely charged solid adsorbent can be measured by the log of the reciprocal, or negative log, of the equilibrium concentration of the surfactant in the liquid phase (log 1/Co or log Co) when the potential at the Stern layer becomes zero (point of zero charge, p.z.c.) This follows from the Stern-Grahame 

Z = the valence of the surfactant ion, including the sign, F = the Faraday constant, v /g = the potential in the Stem plane, 

4 = the nonelectrical free energy change upon adsorption. 

Another system showing an intermediate phase between the H, and phase is the caesium tetradecanoate-water [149]. The phase behavior between 24 and 80 °C was studied (Fig. 30). The H, phase is first seen in a two phase region with L( micellar phase 

One of the first major surveys into the phase behavior of cationic surfactants was done by Blackmore and Tiddy who did penetration scans on a variety of surfactants including the -NH, NMej, NEtj, NPr and NBu series [151]. Previous studies had mostly been limited to alkylammonium and alkylmethylammonium salts [152, 153]. These show a qualitatively similar behavior to that of the anionic systems, with the sequence H,/V,/Lo( for short chain derivatives being replaced by Hi/lnt/Lj, for long chain compounds. For the intermediate chain lengths, V, phases replace the intermediate structures as temperature increases. 

They also studied the ternary phase diagram of the divalent surfactant dipotassium dodecylphosphate (K2D0P), monovalent surfactant potassium tetradecanoate (KTD) and D2O [155]. At 25 °C K2D0P exhibits L, (0-37% surfactant), I, (37-67%), H, (67-75%) and two phase liquid crystal/ hydrated surfactant crystal (75-100%). In the ternary system I cubic is seen between 20 and 60% K2D0P. Up to 30% KTD ean be incorporated into the phase at lower eon- 

The second of the above compounds is an example of a so-called gemini surfactant. Recently there has been considerable interest in these surfactants which are doubleheaded cationic compounds in which two alkyl dimethyl quaternary ammonium groups per molecule are linked by a hydrocarbon spacer chain. (These are denoted as n-m-n 

In a second paper [158] Fuller et al. report the phase behavior of further m-n-m OCB surfactants and some straight chain 15-M-15 surfactants (n = 1,2,3,6). Note that these compounds have terminal hydrophobic chains of the same length as the oxycyanobiphenyl compounds. The m-n-m OCB surfactants all give just a lamellar phase from 18°- 100°C. Penetration scans on the 15-n-15 surfactants show that they all exhibit HI, V] and phases to 100 °C. Additionally, a nematic phase is seen for m = 1, 2 and intermediate phases for m = 1, 2, 3. 

The linear dependence of KP on the alkyl (linear) chain length is very clear. KP for C12 sulfate is 21°C, and it is 34°C for C14 sulfate. 

It may be concluded that KP increases by approximately 10°C per CH2 group. Since no micelles can be formed below the KP, it is important that one keeps this information in mind when using any 

FIGURE 1.24 Solubility (KP) of ionic (anionic or cationic) surfactants in water (as a function of temperature). 

FIGURE 1.25 Variation of KP with chain length of sodium alkyl sulfates. 

Alkyl chain length (KP increases with alkyl chain length). 

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If an ionic surfactant is present, the potentials should vary as shown in Fig. XIV-5c, or similarly to the case with nonsurfactant electrolytes. In addition, however, surfactant adsorption decreases the interfacial tension and thus contributes to the stability of the emulsion. As discussed in connection with charged monolayers (see Section XV-6), the mutual repulsion of the charged polar groups tends to make such films expanded and hence of relatively low rr value. Added electrolyte reduces such repulsion by increasing the counterion concentration the film becomes more condensed and its film pressure increases. It thus is possible to explain qualitatively the role of added electrolyte in reducing the interfacial tension and thereby stabilizing emulsions. 

The ernes of ionic surfactants are usually depressed by tire addition of inert salts. Electrostatic repulsion between headgroups is screened by tire added electrolyte. This screening effectively makes tire surfactants more hydrophobic and tliis increased hydrophobicity induces micellization at lower concentrations. A linear free energy relationship expressing such a salt effect is given by ... 

The Kraft point (T ) is the temperature at which the erne of a surfactant equals the solubility. This is an important point in a temperature-solubility phase diagram. Below the surfactant cannot fonn micelles. Above the solubility increases with increasing temperature due to micelle fonnation. has been shown to follow linear empirical relationships for ionic and nonionic surfactants. One found [25] to apply for various ionic surfactants is ... 

Manne S 1997 Visualizing self-assembly Force microscopy of ionic surfactant aggregates at solid-liquid interfaces Prog. Colloid Polym. Sol. 103 226-33... 

For nonionic amphiphiles, the effects of temperature on the phase behavior are large and the effects of inorganic electrolytes are very small. However, for ionic surfactants temperature effects are usually small, but effects of inorganic electrolytes are large. Most common electrolytes (eg, NaCl)... 

Vdl W (64XT P7V d) exp( — f) where y is a factor of order unity for highly dissociated ionic surfactants (4). In practice, the interaction strength may... 

Physical and ionic adsorption may be either monolayer or multilayer (12). Capillary stmctures in which the diameters of the capillaries are small, ie, one to two molecular diameters, exhibit a marked hysteresis effect on desorption. Sorbed surfactant solutes do not necessarily cover ah. of a sohd iaterface and their presence does not preclude adsorption of solvent molecules. The strength of surfactant sorption generally foUows the order cationic > anionic > nonionic. Surfaces to which this rule apphes include metals, glass, plastics, textiles (13), paper, and many minerals. The pH is an important modifying factor in the adsorption of all ionic surfactants but especially for amphoteric surfactants which are least soluble at their isoelectric point. The speed and degree of adsorption are increased by the presence of dissolved inorganic salts in surfactant solutions (14). 

Two kinds of barriers are important for two-phase emulsions the electric double layer and steric repulsion from adsorbed polymers. An ionic surfactant adsorbed at the interface of an oil droplet in water orients the polar group toward the water. The counterions of the surfactant form a diffuse cloud reaching out into the continuous phase, the electric double layer. When the counterions start overlapping at the approach of two droplets, a repulsion force is experienced. The repulsion from the electric double layer is famous because it played a decisive role in the theory for colloidal stabiUty that is called DLVO, after its originators Derjaguin, Landau, Vervey, and Overbeek (14,15). The theory provided substantial progress in the understanding of colloidal stabihty, and its treatment dominated the colloid science Hterature for several decades. 

The conditions for surfactants to be useful to form Hquid crystals exist when the cross-sectional areas of the polar group and the hydrocarbon chain are similar. This means that double-chain surfactants are eminently suited, and lecithin (qv) is a natural choice. Combiaations of a monochain ionic surfactant with a long-chain carboxyHc acid or alcohol yield lamellar Hquid crystals at low concentrations, but suffer the disadvantage of the alcohol being too soluble ia the oil phase. A combination of long-chain carboxyHc acid plus an amine of equal chain length suffers less from this problem because of extensive ionisa tion of both amphiphiles. 

One useful method of aqueous defoaming is to add a nonfoam sta-bihzing surfac tant which is more surface-active than the stabilizing substance in the foam. Thus a foam stabilized with an ionic surfactant can be broken by the addition of a very surface-active but nonstabihzing sihcone oil. The sihcone displaces the foam stabilizer from the interface by virtue of its insolubility. However, it does not stabilize the foam because its foam films have poor elasticity and rupture easily. 

Ionic surfactants adsorb at the foam interface and orient with the... 

C is the concentration in the bulk, and subscript s refers to the surfactant. Under some conditions, Eq. (22-43) may apply to an ionic surfactant as well (Lemlich, loc. cit.). 

Recent publications indicate the cloud-point extraction by phases of nonionic surfactant as an effective procedure for preconcentrating and separation of metal ions, organic pollutants and biologically active compounds. The effectiveness of the cloud-point extraction is due to its high selectivity and the possibility to obtain high coefficients of absolute preconcentrating while analyzing small volumes of the sample. Besides, the cloud-point extraction with non-ionic surfactants insures the low-cost, simple and accurate analytic procedures. 

CONCENTRATING OF THE MICRO-ADMIXTURES FROM AQUA SOLUTIONS OF THE NON-IONIC SURFACTANTS... 

METHODOLOGICAL ASPECTS OP CLOUD POINT PRECONCENTRATING OF MICRO-ADMIXTURES BY PHASES OF NON-IONIC SURFACTANTS Doroschuk V.O. 

The study of the mechanism of cloud point micellar extractions by phases of non-ionic surfactant (NS) is an aspect often disregarded in most literature reports and, thus, is of general interest. The effective application of the micellar extraction in the analysis is connected with the principled and the least studied problem about the influence of hydrophobicity, stmcture and substrate charge on the distribution between the water and non-ionic surfactant-rich phase. 

THE CLOUD-POINT EXTRACTION OF ALIPHATIC AMINES INTO THE NON-IONIC SURFACTANT-RICH PHASES... 

A new generation of mesoporous silica (SG) materials obtained by sol-gel technique where polymers and ionic or non-ionic surfactant act as stmcture - directed templates is widely developed during last year s. Final materials can be synthesized as thin films and used as sensitive elements of optical and electrochemical sensors. 

In the present work it was studied the dependence of analytical characteristics of the composite SG - polyelectrolyte films obtained by sol-gel technique on the content of non-ionic surfactant in initial sol. Triton X-100 and Tween 20 were examined as surfactants polystyrene sulfonate (PSS), polyvinyl-sulfonic acid (PVSA) or polydimethyl-ammonium chloride (PDMDA) were used as polyelectrolytes. The final films were applied as modificators of glass slides and pyrolytic graphite (PG) electrode surfaces. 

SILICA BASED THIN FILMS OBTAINED BY SOL-GEL TECHNOLOGY IN THE PRESENCE OF NON-IONIC SURFACTANTS AND MODIFIED WITH POLYELECTROLYTE... 

Low temperature sol-gel technology is promising approach for preparation of modified with organic molecules silica (SG) thin films. Such films are perspective as sensitive elements of optical sensors. Incorporation of polyelectrolytes into SG sol gives the possibility to obtain composite films with ion-exchange properties. The addition of non-ionic surfactants as template agents into SG sol results formation of ordered mechanically stable materials with tunable pore size. 

The aim of the present work was optimization of synthesis of SG -polymeric cation exchanger composite films by sol-gel technology in the presence of non-ionic surfactants and their application for detenuination of Zn (II) as phenanthrolinate (Phen) complex. 

SG sols were synthesized by hydrolysis of tetraethyloxysilane in the presence of polyelectrolyte and surfactant. Poly (vinylsulfonic acid) (PVSA) or poly (styrenesulfonic acid) (PSSA) were used as cation exchangers, Tween-20 or Triton X-100 were used as non- ionic surfactants. Obtained sol was dropped onto the surface of glass slide and dried over night. Template extraction from the composite film was performed in water- ethanol medium. The ion-exchange properties of the films were studied spectrophotometrically using adsorption of cationic dye Rhodamine 6G or Fe(Phen) and potentiometrically by sorption of protons. 

Non-ionic surfactants used in detergents, paints, herbicides, pesticides and plastics. Breakdown products, such as nonylphenol and octylphenol, are found in sewage and industrial efffuents Products of combustion of many materials Widely used as plasticisers for PVC. Common environmental pollutants... 

The substitution of water-borne versions of these primers is increasing as environmental restrictions on the use of organic solvents become stricter. These are generally aqueous emulsions of epoxy novolac or phenolic based resins stabilized by surfactants [34]. Non-ionic surfactants are preferred, as they are non-hygroscopic in the dried primer films. Hygroscopic ionic surfactants could result in excessive water absorption by the primer film in service. 

An application of an LC-SFC system has been demonstrated by the separation of non-ionic surfactants consisting of mono- and di-laurates of poly (ethyleneglycol) (23). Without fractionation in the precolumn by normal phase HPLC (Figure 12.18 (a)) and transfer of the whole sample into the SFC system, the different homologues coeluted with each other. (Figure 12.18(b)). In contrast with prior fractionation by HPLC into two fractions and consequent analysis by SFC, the homologues in the two fractions were well resolved (Figures 12.18(c) and 12.18(d)). 

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