A novel viscoelastic system from a cationic surfactant and a hydrophobic counterion

doi:10.1016/j.jcis.2005.03.040

Journal of Colloid and Interface Science

Volume 288, Issue 2, 15 August 2005, Pages 570-582

https://doi.org/10.1016/j.jcis.2005.03.040 Get rights and content

Abstract

The phase behavior of 2-hydroxy-1-naphthoic acid (2,1-HNC) mixed with cetyltrimethylammonium hydroxide (CTAOH) is reported. This novel system is compared with the published one of 3-hydroxy-2-naphthoic acid (3,2-HNC) mixed with CTAOH. We investigated the phase behavior and properties of the phases in aqueous solutions of 100 mM CTAOH with 2,1-HNC. In both systems a multilamellar vesicle phase is formed when the naphthoate/surfactant ratio (r) reaches unity. When an increasing amount of 2,1-HNC is mixed with a micellar solution of 100 mM CTAOH, an isotropic low-viscous micellar solution, a viscoelastic gel (consisting of rodlike micelles), a turbid region (two-phase region), and a viscoelastic liquid crystalline gel (consisting of multilamellar vesicles, MLV) were formed. The vesicular phase is highly viscoelastic and has a yield stress value. The transition from the micellar to the vesicle phase occurs for CTAOH/2,1-HNC over a two-phase region, where micelles and vesicles coexist. Also it was noticed that 2,1-HNC is dissolved in 100 mM CTAOH until the naphthoate/surfactant ratio reaches ∼1.5, and the liquid crystalline phases were found to change their color systematically when they were viewed between two crossed polarizers. The vesicles have been characterized by differential interference contrast microscopy, freeze-fracture electron microscopy, and cryo-electron microscopy (cryo-TEM). The vesicles were polydisperse and their diameter ranged from 100 to 1000 nm. The interlamellar spacing between the bilayers was determined with small angle neutron scattering and agrees with the results from different microscopical methods. The complex viscosity rises by six orders of magnitude when rodlike micelles are formed. The complex viscosity decreases again in the turbid region, and then rises approximately six orders of magnitude above the water viscosity. This second rising is due to the formation of the liquid crystalline MLV phase.

Introduction

Anionic hydrophobic counterions are negatively charged organic ions that result from the dissociation of organic acids or salts. Due to their organic nature they have a hydrophobic character. If a polar solvent contains anionic hydrophobic counterions and positively charged surfactant in the micellar form, the hydrophobic counterions bind on the micelle surface, so they can avoid interaction with the solvent. This process of adsorption has consequences for the micelle morphology and structure. First, the net charge on the micelle surface will be reduced by the strongly adsorbed counterion, and second, the organic part of the hydrophobic counterion may interact with surfactant tails and lead to a new packing of the surfactant–counterion mixed system. This will spontaneously drive the micelle to change its microstructure. From this point of view, hydrophobic counterions may also be defined as cosurfactants, since both influence the micelle microstructure.

Many investigations on hydrophobic counterions such as sodium salicylate (SS), sodium p-toluenesulfonate (NapTS), sodium 3-hydroxy-2-naphthoate (3,2-SHNC), and 3-hydroxy-2-naphthoic acid (3,2-HNC) mixed with cetylpyridinium chloride, CPC, cetyltrimethyammonium bromide, CTAB, or cetyltrimethylammonium hydroxide, CTAOH, have been reported [1], [2], [3], [4], [5], [6], [7], [8], [9].

3,2-SHNC hydrophobic counterion mixed with CTAB, was first investigated by Manohar et al. [10], [11], [12], [13], [14], [15], [16]. The 3,2-SHNC, which is structurally comparable to SS is strongly adsorbed on the micellar surface with the carboxylate and hydroxyl group protruding out of the micelle. The presence of a naphthalene ring in HNC⁻ was expected to confer more hydrophobicity on the molecule as compared to SS. It was also proven from surface tension measurements that SHNC is a weak surface-active agent and in view of the concentrations, it could be regarded as a hydrotope. ¹H NMR spectra of SHNC showed penetration of SHNC into CTAB micelles. The protons at the 4, 5, 6, and 7 positions are present in a nonpolar environment inside the micelles of CTAB.

Horbaschek et al. [17] have studied the system 3,2-HNC/CTAOH and they reported a single phase in the mixed system of 3,2-HNC/CTAOH up to mole ratio ∼0.92. This phase was followed by a two phase region from mole ratio 0.92 to 0.96. With further increase the r-value (0.96–1.1), a vesicle phase was found at 40 °C. However, addition of excess 3,2-HNC was found to remain in an unsolubilized form. Manohar and co-workers prepared CTAHNC by mixing equimolar solutions of SHNC (prepared from 3,2-HNC) and CTAB. Then the resulting CTAHNC was extracted using methyl isobutyl ketone as extracting solvent [16]. The authors noticed that the addition of ionic surfactants such as CTAB induces a transition from vesicles to rodlike micelles, probably by charging CTAHNC.

Vesicle phases are formed only in mixtures of cationic surfactant and hydrophobic counterion (at equal molar ratio) when the hydrophobicity of the counterion is high enough (e.g., 3,2-HNC forms vesicles, while SS does not).

Vesicles have been found to be useful agents in many practical applications and also as a model for several theoretical investigations. They are model systems for biological membranes in order to study the permeability as a function of various additives, for studying shape fluctuations and formation of biological cells, and for prevention of photooxidation of metal ions by inserting them into vesicles [18]. Vesicles can be utilized as vehicles for drug delivery, cosmetics, immunoagents, herbicides, pesticides, and imaging agents [19], [20]. They play an important role in polymerization processes to control the architecture of the resulting polymers that are based on vesicles as a matrix [21]. Vesicles were also tested for enzyme encapsulation [22], or as components of artificial photosynthesis, metallic, magnetic, and semiconducting nanoparticles [20].

The formation of vesicles from binary systems or more-component systems was observed for nonionic surfactants with hydrophobic chain or sugar surfactants with a small head group, nonionic surfactants with two hydrophobic chains, cationic or anionic surfactants with two long alkyl chains, mixtures of cationic and anionic single-chain surfactants, mixtures of amino acid surfactants or amino acid surfactants at intermediate pH values, perfluoro surfactants with two hydrophobic chains, mixtures of cationic perfluoro and anionic hydrocarbon surfactants, mixtures of cationic/anionic and zwittterionic perflouro surfactants or nonionic perfluoro surfactants, mixtures of surfactants with cosurfactants, and mixtures of perfluoro surfactants with cosurfactants or with perfluoro cosurfactants [23], [24], [25], [26], [27], [28], [29]. Unilamellar vesicles can be prepared also from the lamellar phase by shear [30], [31], [32], [33].

In the present study, phase transitions by varying the 2,1-HNC/CTAOH ratio are followed up. The multilamellar vesicles phase is formed in this new system of 2,1-HNC/CTAOH when the ratio of naphthoate/surfactant reaches values of one or higher. The resulting microstructures have been characterized by using different microscopical methods as well as small angle neutron scattering. Rheological measurements were made to illustrate the correlation between the microstructure and rheological behavior.

Section snippets

Materials

Cetyltrimethylammonium bromide, CTAB, was purchased from Fluka with purity >99%. CTAOH stock solutions were prepared from CTAB solutions by ion-exchange at 35 °C. The ion exchanger was from Merck (strongly basic anion exchanger with ion exchanging capacity $> 0.9 mmol / ml$ ). The concentration of the CTAOH was determined by pH titration against 100 mM HCl. 2-Hydroxy-1-naphthoic acid was from Fluka with purity $> 97 %$ . The solutions were prepared by adding an increasing amount of the acids to 100 mM of

Phase behavior of the system 2,1-HNC/CTAOH/water

The solutions with different mixtures containing a fixed amount 100 mM CTAOH (prepared via an ion-exchange process from CTAB) and varying concentrations of 2,1-HNC (0–150 mM) were prepared. The appearance of the phases when the solutions were placed between two crossed polarizers in all the solutions at 25 °C is displayed in Fig. 1. The initial pH of 100 mM CTAOH is 12 and not 13 as one calculates for 0.1 M basic solution. Some of the hydroxide ions are adsorbed into the cationic micellar

Conclusions

It has been shown that the system CTAOH/2,1-HNC forms a multilamellar vesicle phase. With increasing amounts of 2,1-HNC or 3,2-HNC [17] introduced into a micellar solution of 100 mM CTAOH, the microstructure of the this system undergo transformations from an isotropic low-viscosity and high-viscosity two-phase region and then into a liquid crystal phase consists of multilamellar vesicles. For the system of 3,2-HNC/CTAOH further increase in the naphthoate/surfactant ratio (0.95–1.1), the authors

Acknowledgments

The authors would like to acknowledge Dr. Thomas Dürrschmidt and Christne Thunig for rheological and DICM measurements. Prof. Dr. Volker Abetz is also acknowledged for cryo-TEM measurements.

References (46)

K. Horbaschek et al.
J. Colloid Interface Sci.
(1998)
M. Valiente et al.
J. Colloid Interface Sci.
(1993)
Z. Németh et al.
Colloids Surf. Physicochem. Eng. Aspects
(1998)
H. Rehage et al.
J. Phys. Chem.
(1988)
V. Aswal et al.
J. Phys. Chem. B
(1998)
Y. Sakaiguchi et al.
Colloid Polym. Sci.
(1987)
J. Narayanan et al.
Int. J. Mod. Phys. B
(2002)
T. Shikata et al.
J. Colloid Interface Sci.
(2001)
T. Shikata et al.
Langmuir
(1998)
T. Shikata et al.
Langmuir
(1994)

T. Shikata et al.

J. Phys. Chem. B

(1990)

T. Shikata et al.

J. Phys. Chem.

(1990)

E. Mendes et al.

J. Phys. Chem. B

(1998)

S. Mishra et al.

Langmuir

(1993)

R. Oda et al.

Langmuir

(1998)

P. Hassan et al.

Langmuir

(1998)

F. Lequeux

Europhys. Lett.

(1992)

B. Mishra et al.

Langmuir

(1993)

P. Hassan et al.

Langmuir

(1996)

S. Lukac et al.

Can. J. Chem. Soc.

(1982)

M. Wrence

Eur. J. Drug Metab. Pharmacokinet.

(1994)

M. Jung, Ph.D. Thesis, Technische Universiteit Eindhoven,...

Cited by (52)

Drug-induced transitions from micelles to vesicles in ionic surfactant solutions
2024, Colloids and Surfaces A: Physicochemical and Engineering Aspects
Surfactant solutions play key roles in scientific research and technological applications. Here we investigated solutions that combined an ionic surfactant, Cetylpyridinium Chloride (CPyCl), with a non-steroidal, anti-inflammatory drug, Sodium Diclofenac (Diclo). The study covered a wide range of compositions and utilized both rheology and cryogenic-Electron Microscopy (cryo-EM). The solutions were prepared at three different concentrations of CPyCl: 5.0 mM, 16.7 mM and 33.0 mM, and we maintained the ratio of surfactant to salt, R=CPyCl/Diclo, within the range of 0.24<R<1.2. Linear viscoelasticity was measured at 25°C. The use of dilute solutions allowed for detailed cryo-EM imaging. By tracking the evolution of the zero-frequency viscosity as a function of Diclo concentration, we identified distinct regions of different rheological responses. The correlation between frequency sweep data and cryo-EM images enabled us to link these regions to specific morphological transitions ranging from spherical micelles to long and entangled wormlike micelles, to branched networks and, eventually, to perforated vesicles. For some systems, we were able to measure the complete spectrum of relaxation times, including the shortest characteristic Rouse time at high frequencies, previously only achieved by Diffusive Wave Spectroscopy. The use of existing models to evaluate the relevant important microstructural parameters such as entanglement, contour, and persistence lengths allowed us to establish a clear correlation between the microstructural parameters derived through rheology and the insights from the cryo-EM analysis.
A dilute nematic gel produced by intramicellar segregation of two polyoxyethylene alkyl ether carboxylic acids
2024, Journal of Colloid and Interface Science
Surfactants like C₈E₈CH₂COOH have such bulky headgroups that they cannot show the common sphere-to-cylinder transition, while surfactants like C_18:1E₂CH₂COOH are mimicking lipids and form only bilayers. Mixing these two types of surfactants allows one to investigate the competition between intramicellar segregation leading to disc-like bicelles and the temperature dependent curvature constraints imposed by the mismatch between heads and tails.
We establish phase diagrams as a function of temperature, surfactant mole ratio, and active matter content. We locate the isotropic liquid-isotropic liquid phase separation common to all nonionic surfactant systems, as well as nematic and lamellar phases. The stability and rheology of the nematic phase is investigated. Texture determination by polarizing microscopy allows us to distinguish between the different phases. Finally, SANS and SAXS give intermicellar distances as well as micellar sizes and shapes present for different compositions in the phase diagrams.
In a defined mole ratio between the two components, intramicellar segregation wins and a viscoelastic discotic nematic phase is present at low temperature. Partial intramicellar mixing upon heating leads to disc growth and eventually to a pseudo-lamellar phase. Further heating leads to complete random mixing and an isotropic phase, showing the common liquid–liquid miscibility gap. This uncommon phase sequence, bicelles, lamellar phase, micelles, and water-poor packed micelles, is due to temperature induced mixing combined with dehydration of the headgroups. This general molecular mechanism explains also why a metastable water-poor lamellar phase quenched by cooling can be easily and reproducibly transformed into a nematic phase by gentle hand shaking at room temperature, as well as the entrapment of air bubbles of any size without encapsulation by bilayers or polymers.
Fluid state transition mechanism of a ternary component aqueous solution based on dynamic covalent bond
2021, Journal of Molecular Liquids
Dynamic covalent bonds are reversible and responsive, the external environment can cause change of molecular configuration of the compound system, leading to changes in the microscopic morphology of the micelles, thereby achieving intelligent control of the fluid state. Therefore, this work used cationic surfactant cetyltrimethylammonium bromide (CTAB), 4-carboxybenzaldehyde (CB) and aniline (NA) to develop a ternary composite fluid state transition system with a molar ratio of 60:40:40 (CTAB/CB/NA). The bottle test method, rheology, ¹H NMR, infrared spectroscopy, and Cryo-TEM were used to test and analyze the prepared ternary composite system to explore the effects of different dosages, temperatures and pH values on the rheological behavior of the system. The results show that when the pH increased from 3.13 to 7.25, the CTAB/CB/NA solution changed from a low-viscosity fluid to a transparent gel-like fluid, and the viscosity increased from 1 to 4.6 × 10⁴ mPa·s, and the viscosity recovered when the pH decreased again. Therefore, the reversible changes in the viscoelasticity of the system can be triggered by changing the pH of the CTAB/CB/NA solution. This drastic change in rheological properties is attributable to the pH dependent ionization and formation of dynamic covalent bond CBNA, which is shown microscopically as the morphology of the system micelles changing from spherical micelles to worm-like micelles. The viscosity of the system decreases when the temperature increases, and the viscosity is almost zero when it reaches 50 °C. In addition, by adjusting the pH value, the CTAB/CB/NA solution can obtain more than 3 cycles of morphological changes from spherical micelles to worm-like micelles. This pH-responsive fluid state transition system can meet the viscosity requirements of the oil-displacing agent, and can also reduce the adsorption loss in the formation, and has more valuable research in the field of enhanced oil recovery.
New insight into the transition mechanism of pH-tunable wormlike micelles based on experiments and DPD simulation
2019, Colloids and Surfaces A: Physicochemical and Engineering Aspects
A new gemimi-like surfactant (named C₁₄-N₆-C₁₄) formed by a mixed system of itaconic acid tetradecyl ester (C₁₄) and 1,6-hexamethylenediamine (N₆) at a molar ratio of 2:1 was developed to investigate the transition mechanism of pH-tunable wormlike micelles. pH-tunable properties of gemini-like surfactant were characterized by macroscopic observation, rheology, and ¹H NMR measurements. The experimental results indicated that the pH-tunable properties could be ascribed to different protonation degrees and noncovalent interactions of the diamine to carboxyl groups of C₁₄ at different pH values. The gemini-like surfactant C₁₄-N₆-C₁₄ could be changed into itaconic acid monosodium salt surfactant (C₁₄-ONa) when the pH was high enough. The formation of wormlike micelles was a result from the synergy between "gemini" and "unimer". In addition, the pH-tunable mechanism of the C₁₄-N₆-C₁₄ system was proposed and further confirmed by mesoscopic morphological simulations using the dissipative particle dynamics (DPD) modul. The simulation and experimental results showed a good consistency, revealing the formation and destruction processes of wormlike micelles in the long chain acids and short amines mixed system. Our studies have lighted new views on understanding of the noncovalent interactions behind the structural changes by experiments and DPD simulation.
Phase equilibria of mixtures of surfactants and viscoelastic properties of the liquid crystal phases
2016, Fluid Phase Equilibria
Mixtures of surfactants are widely used in many industrial and pharmaceutical products. Whereas diluted mixtures of surfactants have been studied in deep, much lesser studies at high surfactant concentrations have been made. A comparative study among the different systems of tetraoxyethylene dodecyl ether (C₁₂E₄) with different nonionic and anionic surfactants has been carried out. Four phase diagrams of C₁₂E₄/C₁₂E₁₀/water, C₁₂E₄/S40P/water, C₁₂E₄/SDS/water and C₁₂E₁₀/SDS/water systems at 30 °C are reported. In all of them, mixed micelles in water and reverse micelles have been found. Lamellar and hexagonal are the liquid crystals which appear in these ternary systems. Liquid crystals have been characterized by polarized light microscopy and rheology. Viscoelastic properties of the liquid crystals have been determined. Lamellar phase behaves like a gel with both mechanical moduli (G′ and G″) independent on frequency. The elastic properties of the lamellar phase are strongly dependent of the presence of ionic charges. Lamellar liquid crystals for the mixture with the anionic surfactant (SDS) have the higher elastic modulus. For hexagonal phase, elastic and viscous moduli increase with increasing frequency but with different slopes. Its elastic properties are strongly dependent of critical packing parameter of surfactants. Hexagonal liquid crystals for the mixtures with C₁₂E₄ (surfactant with the smaller area of the head group) show the more important elastic properties.
The effect of functional groups on the sphere-to-wormlike micellar transition in quaternary ammonium surfactant solutions
2016, Colloids and Surfaces A: Physicochemical and Engineering Aspects
Citation Excerpt :
This morphology is analogous to that of crosslinked polymer gel. Organic salts and cosurfactants can interact strongly with cationic surfactants in aqueous solutions due to intermolecular interaction, such as electrostatic attraction, hydrophobic effect and hydrogen bonding, thereby promoting the formation of wormlike micelles [41,44,45]. As shown in Fig. 1, the differences in the chemical structure among organic salts (NaSal, NaLau and NaBen) may cause difference in rheological behaviors and aggregate morphology.
To investigate the effects of functional groups on the formation of wormlike micelles, a cationic surfactant, N-tetradecyl-N-(2-hydroxyethyl)dimethylammonium bromide (DM), was synthesized in this work. The viscoelastic behaviors of DM aqueous solution mixed with sodium salicylate (NaSal), sodium benzoate (NaBen) and sodium laurate (NaLau), respectively, have been studied with rheological measurements. Cryogenic transmission electron microscopy (cryo-TEM) and ¹H NMR technology have been employed to investigate the morphology and arrangement of wormlike micelles. The results show that the effects of NaSal and NaLau on wormlike micellar growth are significantly higher than that of NaBen. Superficially, such a great difference in the rheology properties arises from the effect of hydroxyl group in NaSal because this is the sole difference between the NaSal and NaBen. By comparing with NaBen in DM solution, the long hydrocarbon chain of NaLau induces greater hydrophobic interactions between Lau⁻ anions and DM surfactants than aromatic phenyl group of NaBen, and hydrophobic interactions play an important role in the growth of micelles.

View all citing articles on Scopus

View full text

A novel viscoelastic system from a cationic surfactant and a hydrophobic counterion

Abstract

Introduction

Section snippets

Materials

Phase behavior of the system 2,1-HNC/CTAOH/water

Conclusions

Acknowledgments

J. Colloid Interface Sci.

J. Colloid Interface Sci.

Colloids Surf. Physicochem. Eng. Aspects

J. Phys. Chem.

J. Phys. Chem. B

Colloid Polym. Sci.

Int. J. Mod. Phys. B

J. Colloid Interface Sci.

Langmuir

Langmuir

J. Phys. Chem. B

J. Phys. Chem.

J. Phys. Chem. B

Langmuir

Langmuir

Langmuir

Europhys. Lett.

Langmuir

Langmuir

Can. J. Chem. Soc.

Eur. J. Drug Metab. Pharmacokinet.