Properties of ABA and BA polysiloxane amphiphiles modified by polyether

To investigate the effect of content of polyether (F400) grafted on the properties of polysiloxane amphiphiles, polyether was grafted on the polysiloxane by hydrosilylation reaction with H₂PtCl₆ catalyst. The modified polysiloxanes were divided into two types; moreover, the ratio of polyether and polysiloxane was 1:1 or 1:2. The first one was similar to the conventional surfactant structure that is BA polysiloxane amphiphile, which own one hydrophobic chain and one hydrophilic group. Another one was ABA polysiloxane amphiphile, which possess one hydrophobic chain and two hydrophilic groups at the terminal. In our work, we compared the property of modified polysiloxanes with various contents of polyether in aqueous solution at room temperature to analyze the impact of polyether content on siloxane surfactants. The conclusion was that siloxane amphiphiles possess good solubility, high surface activity, and excellent spreading property.     

Synthesis,physicochemical characterization,and self‐assembly of linear,dibranched, and miktoarm semifluorinated triphilic polymers

Linear, dibranched, and miktoarm amphiphiles containing both hydrophobic and fluorophilic moieties were synthesized and characterized in an attempt to elucidate the relationship between semifluorinated amphiphile structure and aggregate behavior in aqueous solution. For the linear and dibranched amphiphiles, there was an exponential decrease in critical aggregation concentration (CMC) and a logarithmic increase in core microviscosity with increasing length of the fluorocarbon segments; while the miktoarm architecture produced no notable trend in microviscosity or CMC. Furthermore, the linear and dibranched surfactants showed enhanced kinetic stability, dissociating more slowly in the presence of human serum than did either the dibranched or miktoarm amphiphiles. Finally, encapsulation studies with the hydrophobic drug paclitaxel (PTX) showed that the ability to solubilize and retain PTX increased with the presence and with the increasing size of the fluorocarbon moiety for both the linear and dibranched amphiphiles, while no such trend was observed for the miktoarm amphiphiles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3324–3336     

Lyotropic smectic layering of side-on polysoaps in water

 The synthesis and characterization of lyotropic smectic amphiphilic side-on polymers are described. The amphiphile consists of a rigid, aromatic core with two terminal ethyleneoxide chains of various lengths and is laterally attached to a polysiloxane backbone; the length of the spacer has also been varied. The phase behavior of the monomeric amphiphiles and side-on polymers are determined by polarizing microscopy and ²H-NMR measurements. In water, most of the low molecular weight surfactants show restricted lyotropic properties, namely lyotropic smectic phases. The packing restriction of the amphiphiles is due to their geometric anisometry. All side-on polymers exhibit only lyotropic smectic phases. The phase regime of the polymer mesophase with respect to the monomers depends on the spacer length. In contrast to surfactants having a flexible hydrophobic group, these amphiphiles align spontaneously parallel to an external magnetic field, leading to perfect lyotropic smectic monodomains. Received: 21 May 2001 Accepted: 27 August 2001     

Recent advances in assemblies of cyclodextrins and amphiphiles: construction and regulation

Cyclodextrins (CDs) had been regarded as destructors in molecular assembly systems for a long time until CD/surfactants were found to assemble into high order structure driven by hydrogen bonding between CDs. Thereafter, intensive researches have been conducted on construction and regulation of CD–amphiphile systems. Here, we summarized the recent progress on construction and regulation of CDs and amphiphiles assembly. The scope of amphiphiles have been extended from surfactants (ionic surfactants, zwitterion surfactants, nonionic surfactants, gemini surfactant, and so on), to nontypical amphiphiles (amines, aromatic molecules, alkanes, and so on). Owing to the abundant choices of guest amphiphiles and dynamic nature of host–guest inclusive interaction, numerous regulation methods (such as enzyme, light, pH, concentration, temperature, and so on) have been used in CD–amphiphile systems. Moreover, remarks and future perspectives are also discussed at the end of this review, which is expected to stimulate progress on both mechanism and application level.     

Studies on an ester-modified cationic amphiphile in aqueous systems: behavior of binary solutions and ternary mixtures with conventional surfactants

The aqueous behavior of an ester-modified cationic amphiphile with the molecular structure CH3CH2O(C=O)(CH2)6(C=O)O(CH2)8N+(CH3)3Br-, in the following referred to as A, has been investigated. Systems with A as the only solute, as well as different aqueous mixtures with conventional cationic surfactants, primarily dodecyltrimethylammonium bromide (DTAB), were included in the study. Isotropic solution samples were characterized using 1H NMR, 13C NMR, NMR diffusometry, and conductivity measurements, whereas liquid crystalline samples were investigated by optical polarization microscopy and small-angle X-ray diffraction. The results are compared to the behavior of the binary system of DTAB and water. A does not exhibit a typical surfactant behavior. When it is present as the only solute in a binary aqueous system, it forms neither conventional micelles nor liquid crystalline phases. However, there is clear evidence that it assembles with lower cooperativity into loose clusters at concentrations above 25-30 mM. When A is mixed with DTAB in solution, the two amphiphiles form mixed assemblies, the structure of which varies with the total amphiphile concentration. In concentrated mixtures with alkyltrimethylammonium surfactants, A can participate in hexagonal liquid crystalline phases even when it constitutes a significant fraction of the total amphiphile content.     

Simulations of a lattice model of two-headed linear amphiphiles: influence of amphiphile asymmetry

Using a 2D lattice model, we conduct Monte Carlo simulations of micellar aggregation of linear-chain amphiphiles having two solvophilic head groups. In the context of this simple model, we quantify how the amphiphile architecture influences the critical micelle concentration (CMC), with a particular focus on the role of the asymmetry of the amphiphile structure. Accordingly, we study all possible arrangements of the head groups along amphiphile chains of fixed length N = 12 and 16 molecular units. This set of idealized amphiphile architectures approximates many cases of symmetric and asymmetric gemini surfactants, double-headed surfactants, and boloform surfactants. Consistent with earlier results, we find that the number of spacer units s separating the heads has a significant influence on the CMC, with the CMC increasing with s for s < N/2. In comparison, the influence of the asymmetry of the chain architecture on the CMC is much weaker, as is also found experimentally.     

A Polyaromatic Gemini Amphiphile That Assembles into a Well‐Defined Aromatic Micelle with Higher Stability and Host Functions

A gemini‐type amphiphilic molecule, constituted of two V‐shaped polyaromatic amphiphiles linked by a linear acetylene spacer, was synthesized. The gemini amphiphile assembles into a well‐defined aromatic micelle (ca. 2 nm in core diameter), providing higher stability in water even at low concentration (0.09 mm ) and high temperature (>130 °C). Unlike common gemini amphiphiles with aliphatic chains, the present amphiphile and its micellar assembly emit green and orange fluorescence (Φ_F=33 and 9 %), respectively. Despite strong and multiple π‐stacks of the polyaromatic panels of the amphiphiles, the water‐soluble gemini aromatic micelle incorporates medium‐size to large hydrophobic compounds into the frameworks. Interestingly, the guest binding capability toward large planar molecules was enhanced by more than two times through the pre‐encapsulation of spherical molecules in the cavity.     

Mixed fluorinated-hydrogenated surfactant-based system: preparation of ordered mesoporous materials

We have investigated a mixed fluorinated-hydrogenated surfactant-based system [C8F17C2H4(OC2H4)9-C12H25(OC2H4)8] in water. The phase diagram exhibits that the micellar domain can be divided into three parts: above 80 wt% of water both hydrogenated and fluorinated surfactants are completely miscible and they formed mixed micelles in all proportion. When the water concentration is decreased from 80 to 60 wt% a gap of miscibility appears and two micellar zones, one fluorocarbon-rich micelles and one hydrocarbon-rich micelles are observed. The liquid crystal domain is composed of one fluorocarbon-rich (H(F)(1)) and one hydrocarbon-rich (H(H)(1)) hexagonal phase. The hydrophobic radius and the cross-sectional area remain constant in the H(H)(1) and in the H(F)(1) domains. Moreover, SAXS measurements proved that the hydrophobic chains in the liquid crystal phases adopt rather an extended conformation. Then the mixture of surfactants was used as template for the preparation of mesoporous materials. Mesostructured silicas with a well hexagonal array of their channels were prepared via a cooperative templating mechanism (CTM), if the loading of fluorinated surfactant is larger than 50%. Decreasing the proportion of the fluorinated amphiphile in the mixture leads to the formation of mesoporous silica with a disordered structure. In this case the channel arrangement is no longer governed by the fluorinated surfactant but by the hydrogenated one.     

Supra-molecular association and polymorphic behaviour in systems containing bile acid salts

A wide number of supra-molecular association modes are observed in mixtures containing water and bile salts, BS, (with, eventually, other components). Molecular or micellar solutions transform into hydrated solids, fibres, lyotropic liquid crystals and/or gels by raising the concentration, the temperature, adding electrolytes, surfactants, lipids and proteins. Amorphous or ordered phases may be formed accordingly. The forces responsible for this very rich polymorphism presumably arise from the unusual combination of electrostatic, hydrophobic and hydrogen-bond contributions to the system stability, with subsequent control of the supra-molecular organisation modes. The stabilising effect due to hydrogen bonds does not occur in almost all surfactants or lipids and is peculiar to bile acids and salts. Some supra-molecular organisation modes, supposed to be related to malfunctions and dis-metabolic diseases in vivo, are briefly reported and discussed.     

Preparation and characterization of new micelle-forming cholesterol amphiphiles

New sulfated and sulfonated cholesterol amphiphiles were synthesized and characterized by dynamic light scattering and electron microscopy. The surfactants form micelles with diameters up to 30 nm. Their critical micelle concentration values were determined by conductometry and photometric measurements. Use of the new amphiphiles enables the transfer of an asymmetric hydrogenation reaction into aqueous solution by keeping the activity and increasing the enantioselectivity. Interesting liquid-crystalline behaviour was observed. Received: 7 July 1999 /Accepted in revised form: 5 November 1999     

Synthesis and properties of cationic surfactants with tuned hydrophylicity

A series of pyridinium-based cationic surfactants has been synthesised and their amphiphilic properties have been studied by conductivity and surface tension measurements. The modification of the substitution pattern on the pyridinium ring by hydrophobic moieties (methyl vs. hydrogen and presence or not of condensed benzene ring) gave the opportunity to investigate structure–activity relationships. Characterization by conductivity and surface tension measurements shed light on the behaviour at the air/water interface and in the micellar environment. In particular, the tendency to form ion pairs at very low concentration was evidenced for all the surfactants substituted on the ring, but not for the simple pyridinium ones. The formation of ion pairs affects both the conductivity and the surface tension plots, showing that a series of steps is involved during the adsorption to the air/water surface. An attempt was made to qualify the single steps in the adsorption at the surface layer. Those steps were attributed to different chemical species (free surfactant ions or ion pairs) and to different arrangements of the surfactant. This work also represents a contribution of investigation at very low surfactant concentrations and high surface tension values.     

A Viscometric and Conductometric Investigation of the Micellar and Solution Properties of Two-Headed Surfactant Systems, the Disodium 4-Alkyl-3-sulfonatosuccinates

A family of two-headed surfactants, the disodium 4-alkyl-3-sulfonatosuccinates, has been prepared by reacting maleic anhydride with the appropriate chain-length alcohol and subsequent addition of sodium bisulfite to the corresponding monoester. The properties of the micelles formed by these compounds in aqueous solution (aggregation numbers, degrees of counterion binding, and the cmc values) have been investigated as a function of temperature and surfactant chain length using viscosity, density, and conductance measurements. The critical micelle concentrations (cmc's) and the aggregation numbers appear to indicate that, in agreement with the earlier literature on other two-headed surfactants systems, these amphiphiles have higher cmc and lower aggregation numbers when compared to single-headed surfactants of comparable chain length. In addition, viscosity B coefficients and the thermodynamic parameters of activation of viscous flow have been determined. These results are interpreted in terms of the structure-making or -breaking properties of the surfactant amphiphiles below the cmc region. Finally, the thermodynamic properties of micelle formation have been estimated from the dependence of the cmc on the absolute temperature according to the charged pseudo-phase separation model of micelle formation. All these results are discussed in terms of how the addition of the second charged surfactant headgroup alters the micellar and solution properties of two-headed surfactants vs. their single-headed counterparts.     

Preparation of substituted ionic carbohydrate polymers and their interactions with ionic surfactants

The formation of micelles of hexadecyltrimethylammonium chloride (CTAC) and sodium dodecylsulfate (SDS) in aqueous solutions containing charged polysaccharides was studied by steady-state and time-resolved fluorescence measurements using pyrene as a photophysical probe. Micropolarity studies using the I₁/I₃ ratio of the vibronic emission bands of pyrene and the behaviour of the I_E/I_M ratio between the excimer and monomer emissions show the formation of hydrophobic domains. The interactions between the polyelectrolytes and surfactants of opposite charge lead to the formation of induced pre-micelles at surfactant concentrations lower than the critical micellar concentration (cmc) of the surfactants. At similar concentrations, the I_E/I_M ratio shows a peak. This aggregation process is assumed to be due to electrostatic attractions. At higher surfactant concentrations, near the critical micellar concentration, micelles with the same properties as those found in pure aqueous solution are formed. On the other hand, systems containing polyelectrolytes and surfactants of the same charge do not show this behaviour at low concentrations. The presence of long alkyl chains bound to the polyelectrolytes also induces the formation of free micelles at concentrations somewhat below the aqueous cmc.     

Chelating DTPA amphiphiles: ion-tunable self-assembly structures and gadolinium complexes

A series of chelating amphiphiles and their gadolinium (Gd(iii)) metal complexes have been synthesized and studied with respect to their neat and lyotropic liquid crystalline phase behavior. These amphiphiles have the ability to form ion-tunable self-assembly nanostructures and their associated Gd(III) complexes have potential as magnetic resonance imaging (MRI) contrast enhancement agents. The amphiphiles are composed of diethylenetriaminepentaacetic acid (DTPA) chelates conjugated to one or two oleyl chain(s) (DTPA-MO and DTPA-BO), or isoprenoid-type chain(s) of phytanyl (DTPA-MP and DTPA-BP). The thermal phase behavior of the neat amphiphiles was examined by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and cross polarizing optical microscopy (POM). Self-assembly of neat amphiphiles and their associated Gd complexes, as well as their lyotropic phase behavior in water and sodium acetate solutions of different ionic strengths, were examined by POM and small and wide angle X-ray scattering (SWAXS). All neat amphiphiles exhibited lamellar structures. The non-complexed amphiphiles showed a variety of lyotropic phases depending on the number and nature of the hydrophobic chain in addition to the ionic state of the hydration. Upon hydration with increased Na-acetate concentration and the subtle changes in the effective headgroup size, the interfacial curvature of the amphiphile increased, altering the lyotropic liquid crystalline structures towards higher order mesophases such as the gyroid (Ia3d) bicontinuous cubic phase. The chelation of Gd with the DTPA amphiphiles resulted in lamellar crystalline structures for all the neat amphiphiles. Upon hydration with water, the Gd-complexed mono-conjugates formed micellar or vesicular self-assemblies, whilst the bis-conjugates transformed only partially into lyotropic liquid crystalline mesophases.     

Self-organization of double-chained and pseudodouble-chained surfactants: counterion and geometry effects

Self-organization in aqueous systems based on ionic surfactants, and their mixtures, can be broadly understood by a balance between the packing properties of the surfactants and double-layer electrostatic interactions. While the equilibrium properties of micellar systems have been extensively studied and are understood, those of bilayer systems are less well characterized. Double-chained and pseudodouble-chained (or catanionic) surfactants are among the amphiphiles which typically form bilayer structures, such as lamellar liquid–crystalline phases and vesicles. In the past 10–15 years, an experimental effort has been made to get deeper insight into their aggregation patterns. With the double-chained amphiphiles, by changing counterion, adding salt or adding anionic surfactant, there are possibilities to depart from the bilayer aggregate in a controlled manner. This is demonstrated by several studies on the didodecyldimethylammonium bromide surfactant. Mixtures of cationic and anionic surfactants yield the catanionics, surfactants of the swelling type, and also show a rich phase behavior per se. A variety of liquid–crystalline phases and, in dilute regimes, equilibrium vesicles and different micellar shapes are often encountered. Phase diagrams and detailed structural studies, based on several techniques (NMR, microscopy and scattering methods), have been reported, as well as theoretical studies. The main features and conclusions emerging from such investigations are presented.     

DNA condensation induced by cationic surfactant: a viscosimetry and dynamic light scattering study

The compaction of DNA induced by two simple amphiphiles, cetyltrimethylammonium bromide [CTAB] and dodecyldimethylamine oxide [DDAO], has been investigated by means of combined viscosity and dynamic light scattering measurements, to demonstrate the formation of soluble DNA/surfactant complexes, undergoing a coil-globule transition, upon the increase of the amphiphile concentration. In both of the two systems investigated, the complexation process reaches a maximum for a value of the surfactant to DNA phosphate groups molar ratio of about X = 1. Below this critical concentration, the coil and the globule state coexist in the solution, as clearly shown by the bimodal size distribution obtained from the light scattering intensity correlation functions. Some suggestions are given to support a molecular mechanism responsible for the complex formation, both in the case of a cationic surfactant (CTAB) and of a pH-dependent neutral or cationic amphiphile (DDAO), where the hydrophobic interactions play an important role.     

Organization of amphiphiles: XII. Evidence in favor of formation of hydrophobic complexes in aqueous solution

The effects of nonionic surfactants OP-10 and OP-30 (polyoxyethylated octyl phenols with 10 and 30 oxyethylene groups, respectively) in surfactant mixtures with ionic surfactants hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) have been investigated by a conductometric method in conjunction with fluorescence, surface tension, zeta potential, and DLS measurements. The interactions are found to be antagonistic in nature for each of the systems; i.e., micellization of CTAB as well as SDS is hindered on addition of the nonionic surfactants. The antagonism is found to be more prominent in the presence of OP-10 compared to that of OP-30. Two types of mechanistic paths, path A operating below the critical micellar concentration and path B operating beyond the critical micellar concentration of nonionic surfactants, have been suggested. In path A, the retardation in micellization has been attributed to a decrease in monomeric concentration of the ionic surfactants from solution as a result of the formation of a hydrophobic complex between nonionic and ionic surfactants. In path B, the decrease in monomer concentration is due to the solubilization of the ionic surfactant in micelles of the nonionic surfactants in a 1:1 stoichiometric ratio. A theoretical treatment to the interaction in each ionic-nonionic pair yields a positive value of the interaction parameter supporting the concept of antagonism. The formation of the hydrophobic complex is supported by fluorescence and surface tension measurements. A schematic representation of the stabilization of these hydrophobic complexes has been suggested. The association of ionic surfactants by nonionic micelles is suggested by zeta potential and DLS studies.     

Rheological study of the pH-dependence of interactions between gelatin and anionic surfactants: flow behaviour and gelation

The interactions between gelatin and two anionic surfactants (sodium di-sec-butylnaphthalenesulfonate and sodium dodecylbenzenesulfonate, respectively) were investigated using rheological methods, charge and surface tension measurements. Upon the addition of surfactants, the viscosity of aqueous gelatin solutions increases at pH values higher than the isoelectric point (IEP) of the gelatin, provided that a distinct surfactant concentration is exceeded. The increase in viscosity depends on the structure of the hydrophobic moiety of the surfactant. Surface tension measurements suggest the formation of gelatin-surfactant-complexes. If the surfactant is added in high concentration, the viscosity does not further increase, and free micelles are formed in the solution. Directly at the IEP and at pH values below, the addition of surfactants leads to flocculation because of electrostatic interactions. At all surfactant concentrations, the flow behaviour was strictly Newtonian. As a model of the structure of the complex, a modified bead and necklace-model is suggested. This model proposes the nucleation of micelles at the hydrophobic gelatin regions (micellar surfactant-gelatin complexes). The number of micelle moieties per gelatin chain could be estimated to be about three. The complex stability is dependent on the extent of hydrophobic interaction.The gelation behaviour of gelatin is strongly affected by the addition of the surfactant. The ratio between the attainable linear storage and loss moduli,G andG, decreases strongly. Gelation is generally hindered, but the effect is stronger at pH values below the IEP than above.     

Effect of the headgroup structure on the aggregation behavior and stability of self-assemblies of sodium N-[4-(n-dodecyloxy)benzoyl]-l-aminoacidates in water

Three amino acid-derived chiral surfactants, sodium N-[4-(n-dodecyloxy)benzoyl]-L-leucinate (SDBL), sodium N-[4-(n-dodecyloxy)benzoyl]-L-isoleucinate (SDBIL), and sodium N-[4-(n-dodecyloxy)benzoyl]-L-threoninate (SDBT), were synthesized, and their aggregation behavior was studied in aqueous solution. Surface tension, fluorescence probe, dynamic light scattering, nuclear magnetic resonance (NMR), gel permeation chromatography, circular dichroism, and optical as well as transmission electron microscopic techniques were utilized to characterize the self-assemblies formed by the amphiphiles. Results of these studies reveal that the surfactants have a very low critical aggregation concentration (cac) and they form spherical vesicles spontaneously in dilute aqueous solution. The mean diameters of the vesicles were measured to be in the range of 130-190 nm. 1H NMR spectra indicated hydrogen bonding between the amide groups near the surfactant headgroup, which is one of the driving forces for vesicle formation. The vesicle formation is more favored at a pH of about 7.0. The amphiphiles also form chiral helical aggregates at relatively higher concentrations as indicated by circular dichroism spectra. The stability of the vesicles was also evaluated with respect to the surfactant concentration, pH, temperature, and aging. The vesicles have a tendency to transform into elongated vesicles (closed tubules) or rodlike micelles with an increase of the surfactant concentration and/or pH. On the basis of the results obtained from different studies, phase diagrams for all three water/amphiphile systems have been constructed. The studies have further shown that the stereogenic center at the amino acid side chain has a significant effect on the aggregation properties of the amphiphiles and on the stability of the self-assemblies.     

Fluorocarbon polymerizable surfactants: viscometric behavior, micellar polymerization and interactions with associating polymers

 The micellar aggregation of two fluorocarbon surfactants bearing a polymerizable acrylamido group and differing only in the degree of amido substitution (CONH or CONC₂H₅) has been investigated by viscometry. The two surfactants exhibit distinct solution properties with a micellar growth occurring at a much lower concentration for the N-monosubstituted sample which shows in addition a shear thickening and rheopectic behavior. The ability of the latter surfactant to form hydrogen bonding is responsible for this difference in behavior. Micellar copolymerization of acrylamide with these surfactants or with a hydrocarbon analogue gives copolymers with a polysoap-like behavior. The copolymers in aqueous solution show a pronounced intramolecular hydrophobic aggregation expressed by relatively low-viscosity values when compared with those of other hydrophobically modified water-soluble polymers reported in the literature. Surfactant–polymer mixed systems do not show a strong incompatibility between fluorocarbon and hydrocarbon moieties. Received: 24 March 1998 Accepted: 30 June 1998