Effect of coexistent hydrocarbon phase on the volume behavior of adsorbed film and micelle of dodecyltrimethylammonium chloride

Interfacial tension () between aqueous dodecyltrimethylammonium chloride (DTAC) solution and benzene was measured as a function of pressure (p) and concentration. The/p was observed to change discontinuously at the critical micelle concentration; this indicates that the micelle formation of DTAC in the aqueous solution coexisting with benzene can be treated like the appearance of a macroscopic phase. It was shown by drawing the vs.A curves that hydrocarbon, such as benzene, cyclohexane, and hexane, make the adsorbed film of DTAC expand. The volume behavior of the micelle with benzene molecules solubilized was found to bear a strong resemblance to that of the adsorbed film at the water/benzene interface. The difference in the molar volume value of adsorbed DTAC among the coexistent hydrocarbon phases was attributed to the difference in the contribution of the hydrocarbon molecules to the interfacial excess volume; the number of the solubilized hydrocarbon molecules was evaluated to be one or two a micelle.     

Heat of micelle formation: Effect of counterions with concentrated,diffused, and separated electric charges

Heats of micelle formation were estimated from calorimetric measurements of anionic surfactants to see if there is any effect of the electrical charge of the counterion on micelle formation from the viewpoint of enthalpy change. The cationic counterions used are Na⁺ and Cu²⁺ for the concentrated electric charge, MV²⁺ for the diffused and 1,1-(1,)-alkanediyl)bispyridiniumions n=2, 4, 6, 8, 10, 12, 14 for the separated. The heat of micelle formation was obtained by subtracting an enthalpy change of dissolution of surfactant solid precipitated below the micelle temperature range (MTR or Krafft point) from a heat of complete dissolution of the precipitated surfactant solid around the MTR. The heats thus evaluated were found to be much more temperature-dependent than counterion-dependent. They were compared with the enthalpy change calculated from the CMC change with temperature, and the big difference between them was discussed from a thermodynamic point of view.     

Spontaneous film formation from a polymer solution

An unusual continuous film formation process of lateral pentyloxy substituted poly(p-phenylene terephthalate)s (s-PPPT) and poly(carbonate) (PC) is observed. A liquid film of polymer solution creeps over the surface of water dropped into the polymer solution. By vaporization of the solvent a solid polymer film is formed on the water surface and can be removed. The driving force for the film formation mechanism is assumed by the reduction of the surface tension of water. Experiments verify this mechanism by increasing the film formation speed using a gas stream, by reducing the formation speed through lowering the surface tension by rinsing agents, and by lowering the solubility of the polymer. As expected, no effects are found by variation of the pH-value of water. Necessary conditions for the film formation process are: good solubility of the polar polymers in organic solvents having a high vapor pressure, complete phase separation, solution density higher than water density, and a surrounding gas phase unsaturated with solvent vapor.The thickness of the mechanically stable films is less than 0.5 m. The films are amorphous by microscopical, FT-IR, x-ray, and DTA investigations.     

Effects of urea and a nonionic surfactant on the micellization and counterion binding properties of cetyltrimethyl ammonium bromide and sodium dodecyl sulfate

Micellization characteristics and counterion binding properties of cetyltrimethyl ammonium bromide (CTAB) in presence of urea and a nonionic surfactant polyoxyethylene sorbitan monolaurate (PSML), and of sodium dodecyl sulphate (SDS) in presence of urea as well as of several mixtures of CTAB with a bile salt, sodium cholate (NaC), and sodium chloride have been studied. Both urea and PSML have increased the critical micelle concentration (CMC) of the surfactants, the former being more effective than the latter. The analysis of the results supports the pseudophase micellar model to hold over the mass action model. Pure CTAB micelles bind more counterions (96 %) than pure SDS micelles (87 %), and the decreasing effect of urea on the binding is less in case of the former than the latter. A 41 mixture of CTAB and sodium cholate (NaC) can micellize and the micelles bind 87 % bromide ion, whereas 21 and 11 mixtures do not micellize. Micelles of 11 mixture of CTAB and NaCl can bind counter bromide ions to the extent of 92 %. The limiting concentrations of urea required to effect counterion binding by CTAB and SDS micelles are 0.15 mol dm^–3 and 0.25 mol dm^–3, respectively. Such effect is shown by PSML on CTAB at a ratio 0.281. The activation energy of conduction of SDS has increased in the presence of urea up to a concentration of 4 mol dm^–3, at higher concentrations the activation energy has decreased, the effect being more for surfactant concentration above CMC than below.     

Miscibility behavior of ternary lipidphospholipid/water systems

Differential-scanning-calorimetry was applied to study the lyotropic and thermotropic properties of the two ternary systems dimyristoylcephaline (di-(C14:0)-PE)/Palmitic acid (C₁₅COOH)/water (H₂O) and dimyristoylcephaline (di-(C14:0)-PE)/palmitic acid methyl ester (C₁₅COOMe)/water (H₂O) in dispersions with excess water (50 wt.%).The phase diagrams of both systems showed that the two systems differ in their miscibility behavior. The system di-(C14:0)-PE/C₁₅COOH/H₂O is completely miscible in its high-temperature phase. In the low-temperature phase the mixing gap was found within the concentration range of C₁₅COOH and was also indicated by a maximum value of the transition enthalpy of the pseudo-binary mixtures.In the pseudo-binary system di-(C14:0)-PC/C₁₅COOMe/H₂O, the tendency towards demixing is much more pronounced. It was observed that the incorporated C₁₅COOMe melted above its normal melting point, but below the transition temperature of di(C14:0)-PE/H₂O system; therefore, the phase transition started at lower temperature. In the low-temperature phase, both lipids are partially miscible. The demixing range of the phase diagram lies within the concentration region of C₁₅COOMe. Up to the mole fraction ofXC₁₅COOMe=0.43, C₁₅COOMe can be incorporated into theL-phase of the system di-(C14:0)-PE/H₂O.     

Mixed micelles of tetradecyltrimethylammonium bromide and chlorhexidine digluconate in aqueous solutions of isopropyl alcohol

The influence of isopropyl alcohol (IPA) on the size and composition of the mixed micelles in mixtures of tetradecyltrimethylammonium bromide (TTAB) and chlorhexidine digluconate (CG) has been determined as a function of the composition of the systems. The addition of 0.5 M and 1.0 M IPA had little significant effect on the composition of the mixed micelles as determined both by analysis of critical micelle concentration (CMC) data using a theoretical treatment based on excess thermodynamic quantities and by an empirical treatment of conductivity data. Static and quasielastic light scattering measurements showed a progressive decrease of the aggregation number and hydrodynamic radius of TTAB micelles on addition of IPA, but minimal changes in the properties of the small CG aggregates. The results show that the micellar weight in the TTAB/CG/IPA solutions is determined by the ratio of the surfactants in the system and for each TTAB/CG ratio decreases on addition of IPA.     

Evaluation of surfactant ion activity in micellar solutions of dodecylpyridinium chloride from partition data and counter ion activity measurements

The partition isotherm of dodecylpyridinium chloride in the water-1,2-dichloroethane system, measured over a broad concentration range, served for the evaluation of the critical micelle concentration and of the effective concentration and mean activity of the surfactant ions in the micellar concentration range. On the basis of the charged phase separation model for the micelles and EMF measurements of counter-ion activity, the surfactant cation activity and the apparent degree of counter ion association to the micelle () of 0.69 were estimated. The results indicate a gradual decrease of surfactant cation activity with increasing total concentration in the micellar range and support literature data derived from EMF measurements that apply surfactant selective plastic exchange membrane electrodes.     

Interface stabilization and micelle formation in blends with a block copolymer

The phase separation behavior of ternary blends of two homopolymers, PMMA and PS, and a block copolymer of styrene and methylmethacrylate, P(S-b-MMA), was studied. The homopolymers were of equal chain length and were kept at equal amounts. Two copolymers were used with blocks of equal length, which exceeded or equaled that of the homopolymer chains. Varied was the copolymer contentf. Films were cast from toluene, which is a nonselective solvent. The morphologies of the cast films were compared with the structure of the critical fluctuations in solution, which were calculated in mean field approximation. The axis of blend compositionsf can be divided into parts of dominating macrophase and microphase separation. Above a transition concentrationf _o, all copolymer chains are found in phase interfaces. Belowf _o, part of them form micelles within the homopolymer phases.     

Small angle X-ray scattering study of an extremely elongated micelle system of CTAB-p-toluidine solution

Whenp-toluidine is added to an aqueous solution of CTAB, a remarkable increase of viscosity is accompanied by a spectacular elasticity. We detected the existence of extremely elongated rod-like micelles in electron micrographs. SAXS measurements indicate a closely packed array of cylindrical rod-like micelles, brought about when solutions flow through a thin capillary. A scattering maximum ofd=160 Å almost corresponds to the distance between the nearest neighbours of the cylindrical rod-like micelles. This value agrees with the diameter measured on electron micrographs. The second broad peak (d=75 Å) is assigned to a subsidiary maximum of the shape function of the cylinder with infinite length.     

Behavior of pure and mixed DPPC liposomes spread or adsorbed at the air-water interface

Liposomes from pure dipalmitoylphosphatidylcholine (DPPC) and mixed DPPC: distearoylphosphatidylcholine (DSPC): soybean lecithin (SL) prepared by the Bangham method with sonication were dispersed into solution or spread at the interface and the kinetics of the surface film formation was studied by measuring and recording the evolution of superficial tension, surface potential, and superficial (¹⁴C labeled) DPPC density.A simple theoretical approach can describe these kinetics by two processes: irreversible diffusion of closed vesicles into or from the bulk phase, and irrevers ible transformation of closed spherical vesicles into destroyed ones which form the surface film. Diffusion controls the phenomenon for small initial amounts of liposomes.Transformation controls the phenomenon for important initial amounts of liposomes. The kinetic constant of the transformation,K, does not depend on the technique used to form the surface film (spreading or adsorption).The equilibrium and rheological properties of surface films formed after liposome spreading are compared to those of monolayers     

An absolute differential maximum bubble pressure surface tensiometer employing displaced capillaries

A modification of the differential maximum bubble pressure method for determining surface tensions is described. In this method, surface tension is calculated from the difference between maximum bubble pressures reached at capillaries of differing internal radii, vertically displaced by an amount calculated from the theory of Cuny and Wolf (1956) Ann Physik 17:57). The density dependence of the technique is eliminated and surface tension becomes a truly linear function of the differential maximum bubble pressure, which is easily measured. The absolute measuring technique is illustrated for equilibrium and dynamic surface tensions of a series of pure liquids and aqueous solutions.For dynamic measurements on surfactant solutions some important experimental considerations and limitations are described. In particular, a previously unrecognized source of error in estimating bubble surface ages is identified. It was found that the maximum bubble pressure for a large capillary does not immediately precede the detachment of the bubble, but occurs at one-third the overall bubble period. Thus, for large capillaries, subsequent to attaining the maximum bubble pressure, there exists a significant decay time in addition to the dead time. In general, surface ages corresponding to maximum pressure at small and large capillaries bubbling with the same period are not equal. This can lead to a large error in dynamic and equilibrium surface tensions of surfactant solutions. With suitable correction the technique is capable of measuring absolute surface tension, even for quite slowly equilibrating surfactant solutions.     

Determination of the surface free energy of modified carbon fibers and its relation to the work of adhesion

Surface free energy of various carbon fibers was determined by tensiometric method in three different procedures. The dispersive _s ^d and the nondispersive _s ^p components were separately determined by contact angle measurements in two-phase system, formamide-n-alkanes. The _s ^p increased by oxidation and decreased by hydrogen reduction, while the _s ^d remained almost constant.The _s ^p value determined from contact angle of water/ethyleneglycol solution tended to become higher. The critical surface free energy was in harmony with the total free energy determined from formamide-n-alkanes system as long as liquids were properly selected. The formation of oxygen-containing functional groups was evidenced by ESCA, and the surface [O]/[C] ratio was related linearly to the surface polarity defined by _s ^p [ _s ^d + _s ^p ] Oxidation in liquid phase resulted in the formation of both hydroxyls and carboxyls, while only hydroxyls were formed in gas phase. The interfacial shear strength of the fiber-epoxy resin could be closely correlated with thermodynamical work of adhesion calculated on the basis of surface free energy and its component.     

Preparation of asymmetric polymer film by emulsion blend technique

Two kinds of anionic polymer emulsions, of which particle sizes were greatly different, were blended and then cast on a release-paper at 30 °C. One was poly(butyl acrylate) emulsion, 0.46n in diameter, produced by emulsifier-free emulsion polymerization, and the other was ethyl acrylate-methyl methacrylate (1/1, mole ratio) copolymer emulsion, 0.02m in diameter, produced by emulsifier-containing emulsion polymerization. The film produced had asymmetric surface properties: the air-side surface was nontacky and the bottom-side surface was tacky. The forming mechanism is discussed.     

Determination of dispersive and nondispersive components of the surface free energy of glass fibers

The dispersive component _s ^d of the surface free energy of glass fibers and its interaction energy with alkanes, benzene, 1-nitropropane, ethyleneglycol, glycerol, formamide, and water were quantitatively determined by the tensiometric method within two liquids. The values of nondispersive interaction energy I _SL ^p were found to be a linear function of the square root of the nondispersive component of the surface free energy of liquids. This suggests that the nondispersive interaction energy may be represented by the geometric mean of the nondispersive component of the surface free energy of a solid and a liquid. The slope gave the nondispersive component _s ^p of the surface free energy. The _s ^p values are 33 and 14 mJ/m² for the untreated and aminosilane-treated fibers, respectively, suggesting that organophilic character has developed on the surface after aminosilane treatment. The _s ^p value was almost similar after the treatment, probably because of the polar characteristics of amino groups.     

Molecular properties of acetone and some of its chloroderivatives adsorbed at the surface of water

The relations between the electric surface potential (V) and the surface tension () of aqueous solutions of acetone, chloroacetone, 1,3-dichloroacetone, and their concentration were investigated. The vertical components of dipole moments of the above mentioned compounds were determined using the Helmholtz equation. The calculations were carried out on the basis of surface excess values, which were obtained from surface tension measurements and surface potential changes. Once the vertical component of dipole moments were found and the orientation of adsorbed molecules was assumed, the local dielectric permittivities of the surface monolayer were estimated.     

Lamellar phases in mixtures of low molecular weight alkanols and cetyltrimethylammonium bromide (CTAB)

Partial phase diagrams showing the domains of existence of a transparent, viscous, lamellar-structured (D)-phase that transforms reversibly into fluid single phase solutions at high temperature are presented for the system: cetyltrimethylammonium bromide (CTAB), two low molecular weight alcohols, and water with and without additives. At constant temperature and with a fixed amount of surfactant, the size and location of this phase in the phase diagram depends upon three composition variables: i) the ratio of concentrations of medium chain alcohol to long chain alcohol (R), ii) the ratio of concentrations of medium chain alcohol to surfactant (R), and iii) the concentrations of small amounts (up to 10 % by weight) of additives such as ethylene glycol, propylene glycol, and dimethylformamide, as well as NaBr. Small-angle x-ray scattering measurements of these mixtures reveal a lamellar structure. The observed lamellar repeat distances range from 60 A to 290 Å and depend upon the ratiosR andR and the concentration of the additives. The mechanical and structural properties of theseD-phases can be tuned by adjustingR andR. TheD-phase-to-isotropic transition temperature can be varied from near room temperature to above 80 °C by adjustingR andR.     

Estimation of the critical micelle concentrations and the aggregation numbers of sodium alkyl sulfates by capillary-type isotachophoresis

The analytical procedure for the separation and quantification of bulk and micellar phases for sodium alkyl sulfates has been investigated by a capillary-type isotachophoresis using a potential gradient detector. Monomer solutions were distinguished from micellar solutions at pH 5.5–6.0; hydrochloric acid — L-Histidine mixture was used as the leading electrolyte and 2-(N-Morpholino) ethanesulfonic acid as the terminating electrolyte.The potential unit value (PU value) due to the monomer solutions was larger than that due to the micellar solutions. The zone length due to monomer solutions increased with increasing concentration of surfactant until a given concentration (CMC); beyond this point the values became constant. On the other hand, the zone length due to micellar solutions increased from this point. We report an applicability of capillary-type isotachophoresis to determination of the CMC's and aggregation number for various sodium alkyl sulfates.     

The molecular weight dependence of intrinsic viscosity of rod-like micelles of dodecyldimethylammonium chloride

It is shown that the non-linear logarithmic dependence of the intrinsic viscosity on the molecular weight for rod-like micelles of dodecyldimethylammonium chloride (as reported by Ozeki and Ikeda [1]) can be interpreted in terms of the Yamakawa-Fujii theory of worm-like chains. Characteristic parameters of the micelles are estimated: persistence length (a=14 nm), linear mass density (M _L=4800 nm^–1), diameter (d=3 nm), molecular pitch (b=0.052), and the number of surfactant chains in a layer of rod-like micellen=12. The results are compared with those derived from light-scattering measurements.     

Interaction between amphiphiles and water molecules in concentrated bilayer aqueous colloids

Interaction between amphiphiles and water molecules in micelle or bilayer structure has been investigated using aqueous colloids of various amphiphiles through the rheological data and the spin-lattice relaxation timeT ₁ of the proton of water molecule.T ₁ of the water proton has been measured by the inversion recovery method and determined as a single exponential relaxation process.The chemical shift of the water proton is almost independent of the amphiphilic concentration; however, it shifts toward a higher magnetic field with increasing temperature in a way similar to that in pure water and in the amphiphilic aqueous systems. These facts mean that there is no significant difference in the magnetic field environment of the water protons in these systems.The water molecule is not necessarily bound in the fully developed micelle or bilayer (rod-like or lamella) structure which induces the high viscosity or high rigidity of the colloidal system. On the other hand, the water molecule is bound in the micelle colloids of amphoteric amphiphiles or amphiphiles whose molecular assembly creates a relatively strong electrostatic field. The activation entropy of the bound water is negative and this suggests that water molecules assume some ordered structure in the bound state.     

The structure of adsorbed films of some aliphatic compounds at the water/air interface

Electric surface potential (V) and surface tension measurements of aqueous solutions of some aliphatic compounds were used to determine the surface activity, orientation of molecules at the water/air interface, effective dipole moments (connected with water molecules, hydrophilic and hydrophobic groups), and local dielectric permittivities of the surface layer.