Synthesis of amphiphilic dendrons and their interactions in aqueous solutions with cetyltrimethylammonium p-toluenesulfonate (CTAT (original) (raw)
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Hydrophobic dendrons based on different branching patterns, viz. 3,5-di-and 3,4,5-trisub-stituted phenyl rings, consist of the same backbone but exhibit different sizes, shapes, and hydrophobic densities. These dendrons are attached to poly(ethylene glycol) and the core properties of the copolymer micelles are investigated in tetrahydrofuran (THF)/water mixtures by neutron scattering. Two polymers with intermediate hydrophobicity are studied further with variations in the solvent composition and the temperature. The aggregation numbers for 3,4,5-based dendron copolymers are lower, with more THF molecules of solvation compared with the 3,5-based dendron copolymer, the difference being greater at higher generations due to different molecular shapes. The micellar core size increases in small steps with dendron size so that dye encapsulation is tuned.
Journal of Colloid and Interface Science, 2007
Formation of wormlike micelles in mixed anionic/cationic system without the addition of any salt has been studied. Amino-acid based anionic surfactant N-dodecylglutamic acid (LAD), which is practically immiscible with water at 25 • C upon neutralization by 2,2 ,2 -nitrilotriethanol (TEA) forms small micellar aggregates and the solution behaves like a Newtonian fluid. The rheological behavior of LAD/water/hexadecyltrimethylammonium bromide (CTAB) and LAD/water/dodecyltrimethylammonium bromide (DTAB) systems were investigated at different degrees of neutralization of the LAD depending on the concentration of the cationic surfactants and on temperature. Addition of CTAB to the dilute aqueous solution of the LAD-TEA-x (the neutralized product, where x represents the mole ratio of TEA) causes one dimensional micellar growth. After certain concentration the elongated micelles entangle forming a rigid network of viscoelastic wormlike micelles. Thus formed viscoelastic solutions follow Maxwellian behavior over a wide range of frequency and thus are considered to consist of transient network of wormlike micelles. By varying the degree of neutralization from 1:1 via 1:1.5 to 1:2 (molar ratio) phase and rheological behavior were modified in that the highly viscous region of viscoelastic wormlike micelles shifted to higher CTAB concentrations and no maxima in the zero-shear viscosity could be observed for the higher degree of neutralization of the LAD (1:1.5 and 1:2). However, the obtained rheological parameters showed scaling relationships that were consistent with the living polymer model. The zero-shear viscosity decays exponentially with temperature following Arrhenius behavior. The flow activation energy calculated from the Arrhenius plot is very close to the value reported for the typical wormlike micellar solution. In contrast to CTAB no formation of viscoelastic wormlike micelles could be observed with DTAB, although, the solution viscosity increases. The elongated micelles could not entangle to form a rigid network of wormlike micelles in this system. For the first time viscoelastic wormlike micelles could be obtained in salt-free mixed anionic/cationic surfactant systems. (K. Aramaki).
Wormlike micelles in mixed amino acid-based anionic/nonionic surfactant systems
Journal of Colloid and Interface Science, 2008
We present the formation of viscoelastic wormlike micelles in mixed amino acid-based anionic and nonionic surfactants in aqueous systems in the absence of salt. N-Dodecylglutamic acid (designated as LAD) has a higher Krafft temperature; however, on neutralization with alkaline amino acid L-lysine, it forms micelles and the solution behaves like a Newtonian fluid at 25 • C. Addition of tri(oxyethylene) monododecyl ether (C 12 EO 3 ) and tri(oxyethylene) monotetradecyl ether (C 14 EO 3 ) to the dilute aqueous solution of the LAD-lysine induces one-dimensional micellar growth. With increasing C 12 EO 3 or C 14 EO 3 concentration, the solution viscosity increases gradually, but after a certain concentration, the elongated micelles entangle forming a rigid network of wormlike micelles and the solution viscosity increases tremendously. Thus formed wormlike micelles show a viscoelastic character and follow the Maxwell model. Tri(oxyethylene) monohexadecyl ether (C 16 EO 3 ), on the other hand, could not form wormlike micelles, although the solution viscosity increases too. The micelles become elongated; however, they do not appear to form a rigid network of wormlike micelles in the case of C 16 EO 3 . Rheological measurements have shown that zero shear viscosity (η 0 ) increases with the C 12 EO 3 concentration gradually at first and then sharply, and finally decreases before phase separation. However, no such maximum in the η 0 plot is observed with the C 14 EO 3 . The η 0 increases monotonously with the C 14 EO 3 concentration till phase separation. In studies of the effect of temperature on the wormlike micellar behavior it has been found that the η 0 decays exponentially with temperature, following an Arrehenius behavior and at sufficiently higher temperatures the solutions follow a Newtonian behavior. The flow activation energy calculated from the slope of log η 0 versus 1/T plot is very close to the value reported for typical wormlike micelles. Finally, we also present the effect of neutralization degree of lysine on the rheology and phase behavior. The formation of wormlike micelles is confirmed by the Maxwell model fit to the experimental rheological data and by Cole-Cole plots. (K. Aramaki). all these applications, knowledge of structure and dynamics of the wormlike micelles is of the essence for the optimization of the process. In the charged micelles, there are two contributions to the energy: the end-cap energy that promotes micellar growth and a repulsive contribution due to charges along the micelle that favors the breaking of micelles . Hence, micellar growth occurs as a consequence of the reduction of the repulsion between the surfactant head groups, which can be induced by adding salts, strongly binding counterions, or cosurfactants .
Colloid and Polymer Science, 2009
Amino acid-based anionic surfactant, N-dodecanoylglutamic acid, after neutralizing by 2, 2′, 2″-nitrilotriethanol forms micellar solution at 25°C. Addition of cationic cosurfactants hexadecyltrimethylammonium chloride (CTAC), hexadecylpyridinium chloride (CPC), and hexadecylpyridinium bromide (CPB) to the semi-dilute solution of anionic surfactant micellar solutions favor the micellar growth and after a certain concentration, entangled rigid network of wormlike micelles are formed. Viscosity increases enormously ∼4th order of magnitude compared with water. With further addition of the cosurfactants, viscosity declines and phase separation to liquid crystal occurs. The wormlike micelles showed a viscoelastic behavior and described by Maxwell model with a single stress-relaxation mode. The position of viscosity maximum in the zero-shear viscosity curve shifts towards lower concentration upon changing cosurfactant from CPB to CTAC via CPC; however, the maximum viscosity is highest in the CPB system showing the formation of highly rigid network structure of wormlike micelles. In all the systems, viscosity decays exponentially with temperature following Arrhenius type behavior.
Journal of Colloid and Interface Science, 2008
Viscoelastic micellar solutions are formed in poly(oxyethylene) cholesteryl ether (ChEO m , m = 15, 30) aqueous solutions on addition of tri(ethyleneglycol) mono n-dodecyl ether (C 12 EO 3). The steady-shear and dynamic rheological behavior of the systems is characteristic of wormlike micellar solution. In either system, the plateau modulus (G 0) and relaxation time (τ) are found to increase with increasing cosurfactant mixing fractions. The plateau modulus of the ChEO 30-C 12 EO 3 system at the maximum viscosity region is found to be higher than that in the ChEO 15-C 12 EO 3 system at the maximum viscosity region, whereas for the relaxation time the opposite relation is found. The maximum viscosities obtained in the two systems are of the same order of magnitude. In the ChEO 30-C 12 EO 3 system, the maximum viscosity is obtained at a higher cosurfactant mixing fraction than that in the ChEO 15-C 12 EO 3 system. It is concluded that decreasing the head-group size of the hydrophilic surfactant favors micellar growth. Monolaurin, another hydrophobic surfactant known to induce growth in some systems, is found to cause phase separation before significant micellar growth occurs in ChEO m solutions, although the effect of head-group size of ChEO m is found to be similar to the ChEO m-C 12 EO 3 systems.
European Physical Journal E, 2003
The mixed micellization between the cationic gemini surfactant [C12H25(CH3)2N + (C2H4) N + (CH3)2C12H25 • 2Br − ] and the cationic cetyltrimethylammonium bromide (CTAB) in 150 mM KBr solutions has been investigated. The variation of the cmc of the mixtures, measured by surface tension experiments, with composition revealed synergism in micelle formation. T-Jump and light scattering experiments performed in the vicinity of the crossover volume fraction showed the existence of two micellar populations, possibly linear and toroidal micelles. Rheological and dynamic light scattering experiments allowed to fully characterize the linear viscoelasticity of the mixtures. These measurements revealed synergistic gains in viscoelastic properties with a maximum of the stress-relaxation time around the equimolar composition. These effects are ascribed to a progressive intermicellar crosslinking resulting from a continuous increase of the end-cap energy with the 12-2-12 content in the mixture.
JOURNAL OF CHEMICAL ENGINEERING OF JAPAN, 2004
The phase behavior, microstructure and rheological properties of mixtures of polyoxyethylene type nonionic surfactants (C 12 EO n , n = 0-4) and alkyltrimethylammonium bromide cationic surfactants in water were investigated. Upon addition of C 12 EO 3 to the aqueous cationic system at high surfactant concentration, both the interfacial curvature of aggregates and the effective cross-sectional area per surfactant molecule, a S , decrease, resulting in a hexagonal-lamellar liquid crystal phase transition. This effect becomes more pronounced as the alkyl chain-length of the cationic surfactant increases. At low surfactant concentration, addition of nonionic amphiphile to micellar solution above a particular concentration, C * , induces a rapid unidimensional micellar growth, and particularly in CTAB systems viscoelastic micellar solutions of entangled wormlike micelles are formed. With successive addition of the nonionic amphiphile ultimately a micellar to lamellar phase transformation occurs. Rheological measurements within the W m-phase show that with decreasing EO chain-length, C * also decreases and viscosity increases more swiftly with increasing concentration of nonionic amphiphile, suggesting a rapid micellar growth. This is attributed to the decrease in a S , as predicted by a simple geometrical model.
Viscoelastic wormlike micelles and their applications
Viscoelastic wormlike micelles are important microstructures that relate to rhelogical properties of fluid in different applications. Recently, studies of structure and dynamic properties of wormlike micelle have extended to different surfactant type such as anionic, zwitterionic and polymeric surfactants. Applications have been found in oil fields, drag-reducing agents for district heating and cooling and thickeners for personal and home care products.