Study of host–guest interaction between ß-cyclodextrin and alkyltrimethylammonium bromides in water

Cyclodextrins were found to play important roles in self-assembly systems of surfactants. The interactions between host molecule ß-cyclodextrin (CD) and model cationic surfactants, alkyltrimethylammonium bromides with different alkyl chain length: dodecyl-(C₁₂TAB), tetradecyl-(C₁₄TAB) and hexadecyl-(C₁₆TAB) are studied by means of conductivity measurements at 313.2 K. The data obtained indicate that inclusion complexes (CD:S⁺) had formed, and apparent critical micelle concentration (CMC*) is equivalent to the combined concentrations of surfactant monomers complexed with the CD and that of a free dissolved monomer in equilibrium with the micellized surfactant without CD. Inclusion complexes were characterized by an equilibrium binding constant K ₁₁, which value increases as the length of alkyl chains, and consequently the hydrophobicity, increases. From mathematical model the concentrations of the uncomplexed cyclodextrin, uncomplexed surfactant ion, and inclusion complex in the submicellar, as well as in the micellar range were calculated. The competition between the micellization and complexation processes leads to the existence of a significant concentration of free CD in equilibrium with the micellar aggregates. The percentage of uncomplexed cyclodextrin in equilibrium with the micelles is independent on cyclodextrin concentration for a particular ternary system and is 31, 37, and 34 % for C₁₂TAB/water/ß-CD, C₁₄TAB/water/ß-CD and C₁₆TAB/water/ß-CD, respectively. By using standard Gibbs free energy for micellization and surfactant complexation by CD, we can explain the observed behavior.     

Investigation on the interaction between C16TAB and NaCMC in semidilute aqueous solution based on rheological measurement

The rheological behavior of unentangled and entangled semidilute solution of anionic polyelectrolyte sodium carboxymethyl cellulose (NaCMC) containing cationic surfactant cetyltrimethylammonium bromide (C₁₆TAB) was investigated. The results reveal that the rheological properties of these semidilute NaCMC solutions depend on the amount of C₁₆TAB added. In the unentangled semidilute NaCMC solution (0.5 g/L), the viscosity decreases with the increase of C₁₆TAB amount in the low surfactant concentration region (below the critical aggregation concentration, CAC). However, in high surfactant concentrations (above CAC), the viscosity decreases sharply with the increase in C₁₆TAB amount. It is found that viscosity change of NaCMC solution could be described using Colby’s model when surfactant concentrations are between CAC and saturated concentration (C_s), suggesting that no inter-polymer interaction exists between C₁₆TAB and NaCMC in the unentangled semidilute solution. However, for the entangled semidilute NaCMC solution (5 g/L), the addition of C₁₆TAB leads to an increase in viscosity. Meanwhile, the solution exhibits an enhanced shear thinning behavior due to adding more C₁₆TAB than 1 mM. The viscosity increase is ascribed to the physical cross linking of surfactant micelles with NaCMC chains. Furthermore, it is suggested that the enhanced shear thinning behavior results from weak interaction between NaCMC chains and C₁₆TAB micelles.     

Rheological behavior of PAA–C n TAB complex: influence of PAA charge density and surfactant tail length in PAA semidilute aqueous solution

Interactions between anionic polyelectrolyte, poly(acrylic acid) (PAA), and cationic surfactant, alkyltrimethylammonium bromide (C _n TAB), were investigated by rheological measurements in semidilute PAA solution. The dependences of the rheological behavior on the chain length of the surfactant, PAA neutralization degree, and temperature were discussed. The results revealed that both dodecyl and cetyltrimethylammonium bromides (C₁₂TAB and C₁₆TAB) could increase the viscosity of PAA solution when the surfactant amounts surpassed a critical surfactant concentration (C _c), and C _c of C₁₆TAB was lower than that of C₁₂TAB at same PAA neutralization degree. The increase of viscosity is attributed to the surfactant micelles bridging of the polymer chains and confine the mobility PAA chain. On the other hand, it is found that the hydrogen bonding also played an important role in the PAA–C _n TAB system, especially in lower neutralization degree PAA solution, which results in the viscosity increase rapidly with the added surfactant into lower neutralization degree PAA solution.     

BINDING OF IONIC SURFACTANTS ON OPPOSITELY CHARGED POLYELECTROLYTES OBSERVED BY FLUORESCENCE METHODS

Our recent studies concerning the binding of ionic surfactants on oppositely charged polyelectrolytes observedwith fluorescence techniques are reviewed. The cationic surfactants cetyltrimethylammonium bromide (CTAB),dodecyltrimethylammonium chloride (DTAC), and nonionic surfactant octaethylene glycol monododecyl ether (C_(12)E_8) wereallowed to bind on anionic poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) and its pyrene and/or naphthalenelabeled copolymers. The relative excimer emission intensity I_E/I_M of a cationic probe l-pyrenemethylamine hydrochloride(PyMeA·HCl) and the non-radiative energy transfer (NRET) I_(Py)/I_(Np) of naphthalene to pyrene for labeled polyelectrolyteswere chosen to monitor the binding process and the conformation change of surfactant-bound polyelectrolytes. The 1:1aggregation of polyelectrolyte-CTAB with respect to the charge was found as long as the CTAB concentration was slightlyhigher than its critical aggregation concentration (CAC). The intermolecular NRET indicated that the CTAB-boundpolyelectrolytes aggregated together through the hydrophobic interaction between the CTAB tails. However, neither 1:1polyelectrolyte-DTAC aggregation nor intermolecular aggregation of DTAC-bound polyelectrolyte was observed owing to itsweaker hydrophobicity of 12 carbon atoms in the tail, which is shorter than that of CTAB. As known from the fluorescenceresults, nonionic surfactant C_(12)E_8 did not bind on the anionic polyelectrolytes, but the presence of PAMPS promoted themicelle formation for C_(12)E_8 at the CAC slightly below its critical micelle concentration (CMC). The solid complex of dansyllabeled AMPS copolymer-surfactant exhibited a decrease in local polarity with increasing charge density of thepolyelectrolyte or with alkane tail length of the surfactant. SAXS suggested a lamella structure for the AMPS copolymer-surfactant solid complexes with a long period of 3.87 nm for CTAB and 3.04 nm for DTAC, respectively.     

Interaction Between 1-Dodecyl-3-Methylimidazolium Bromide and Sodium Carboxymethylcellulose in Aqueous Solution: Effect of Polymer Concentration

Effect of the concentration of water-soluble polyanion (sodium carboxymethylcellulose, NaCMC) on the interaction between a cationic surfactant (1-dodecyl-3-methylimidazolium bromide, C₁₂mimBr) and NaCMC in aqueous solution has been studied by isothermal titration microcalorimetry (ITC), conductivity, surface tension, and rheological measurements. From the surfactant/polymer interacting enthalpy, it can be deduced that the electrostatic attraction between the cationic surfactant and anionic polyelectrolyte causes an endothermic process, and the C₁₂mimBr monomers binding to the NaCMC chains to form micelle-like aggregates through hydrophobic interaction is an exothermic process. Increasing the NaCMC concentration causes the interaction between C₁₂mimBr and NaCMC to decrease, and the characteristic surfactant concentrations, including the critical aggregation surfactant concentration (CAC), the surfactant concentration to form free micelles (C_m), and the saturation concentration of surfactant on the NaCMC chains (C_S) to increase. Because of the strong electrostatic interaction between C₁₂mimBr and NaCMC, the formation of C₁₂mimBr/NaCMC complexes can lead to precipitation or redissolution depending on solution composition, so the critical precipitation concentration (C_P) and the onset of a redissolution concentration (C_R) has been determined by the electrical conductivity. The rheological results reveal a dramatic increase in solution viscosity around the CAC, attributed to interpolymer cross-linking through the formation of mixed micelles involving the carboxylic acid groups of NaCMC and the surfactant.     

Adsorption of DNA and dodecyl trimethylammonium bromide mixtures at the air/water interface: a neutron reflectometry study

The interactions between dodecyl trimethylammonium bromide (C12TAB) and two samples of DNA with widely differing molecular weights have been studied using surface tension and neutron reflectometry. Neutron reflection data show that the surfactant and polymer are adsorbed together in a highly cooperative fashion over a 1000-fold change in surfactant concentration. Furthermore, the shorter DNA fragments adsorb with C12TAB as trilayers at higher surfactant concentrations, with overall layer thicknesses of 65-70 A. The high molecular weight DNA, however, shows only approximate monolayer adsorption with thicknesses varying from 19 to 26 A over the entire range of C12TAB concentrations. The difference in behavior between the different samples is believed to be a result of the rigid double helical structure of DNA which makes the formation of bulk phase polymer/micelle aggregates much less favorable for the short fragments. The resulting increase in the critical aggregation concentration (CAC) then leads to the adsorption of additional surfactant/polymer complex to the underside of the initial stable surface active DNA/C12TAB complex. Comparison with previous results obtained for synthetic polyelectrolytes shows that DNA/C12TAB complexes are not capable of reducing the surface tensions to the extent that other mixtures such as the poly(styrene sulfonate)/C12TAB mixtures do. A possible reason for this is the high rigidity of DNA combined with the fact that its hydrophobic moieties are positioned within the double helix so that the external molecule is largely hydrophilic.     

The influence of mixed cationic–anionic surfactants on the three-phase contact parameters in silica–solution systems

The formation of thin wetting films on silica surface from aqueous solution of (a) tetradecyltrimetilammonium bromide (C₁₄TAB) and (b) surfactant mixture of the cationic C₁₄TAB with the anionic sodium alkyl- (straight chain C₁₂–, C₁₄– and C₁₆–) sulfonates, was studied using the microscopic thin wetting film method developed by Platikanov. Film lifetimes, three-phase contact (TPC) expansion rates, receding contact angles and surface tension were measured. It was found that the mixed surfactants caused lower contact angles, lower rates of the thin aqueous film rupture and longer film lifetimes, as compared to the pure C₁₄TAB. This behavior was explained by the strong initial adsorption of interfacial complexes from the mixed surfactant system at the air/solution interface, followed by adsorption at the silica interface. The formation of the interfacial complexes at the air/solution interface was proved by means of the surface tension data. It was also shown, that the chain length compatibility between the anionic and cationic surfactants controls the strength of the interfacial complex and causes synergistic lowering in the surface tension. The film rupture mechanism was explained by the heterocoagulation mechanism between the positively charged air/solution interface and the solution/silica interface, which remained negatively charged.     

Characterization of Surfactant-Diblock Copolymer Interactions and Its Thermodynamic Studies

The interaction of nonionic diblock copolymer poly(ethylene oxide butylene oxide) (E₆₂B₂₂) with a cationic surfactant cetyl trimethyl ammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulphate (SDS) were studied using surface tension, conductivity, and dynamic laser light scattering techniques. Surface tension measurements were used to determine critical micelle concentration and thereby its free energy of adsorption (ΔG_ads), free energy of micellization (ΔG_m), surface excess concentration (Γ), and minimum area per molecule (A). Conductivity measurements were used to determine critical micelle concentration (CMC) critical aggregation concentration (CAC) at different temperatures, enthalpy of micellization (ΔH_m), free energy of micellization and entropy of micellization (ΔS_m). Changes in physicochemical properties of the micellized block copolymer were studied by using dynamic laser light scattering. The effect of surfactant on the size and properties of block copolymer has also been discussed.     

Interactions of monomeric and dimeric cationic surfactants with anionic polyelectrolytes: a fluorescence study

The interactions of conventional cationic, i.e. dodecyl-(DTAB), tetradecyl-(TTAB), and hexadecyltrimethylammonium bromides (HTAB), and dimeric cationic surfactants, i.e. dimethylene bis decyl-(10-2-10), and dodecyldimethylammonium bromides (12-2-12) with anionic polyelectrolytes, were studied by fluorescence measurements. The variation of I₁/I₃ ratio of the fluorescence of pyrene in aqueous solutions of polyelectrolytes was measured as a function of surfactant concentration. A three-step aggregation process involving the critical aggregation concentration (cac) and critical micelle concentration (cmc) was observed in each case. The cationic surfactants with lower hydrophobicity demonstrated higher degree of binding and vice versa.     

Interaction between two homologues of cationic surface active ionic liquids and the PEO-PPO-PEO triblock copolymers in aqueous solutions

The interaction of nonionic triblock copolymers of poly(ethyleneoxide) (PEO) and poly(propyleneoxide) (PPO) (PEO_nPPO_mPEO_n) with a series of cationic surface-active ionic liquids in aqueous solutions have been investigated. The cationic surface-active ionic liquids include 1-alkyl-3-methylimidazolium bromide (C_nmimBr, n?=?8, 10, 12, 14, 16) and N-alkyl-N-methylpyrrolidinium bromide (C_nMPB, n?=?12, 14, 16). For different polymer-surfactant systems, the critical aggregation surfactant concentration (cac), the surfactant concentration to form free micelles (C _m), and the saturation concentration of surfactant on the polymer chains (C ₂) were determined using isothermal titration microcalorimetry (ITC) and conductivity measurements. The structure of the formed aggregates depended strongly on the hydrophobicity of the surfactant and the ratio of polymer/surfactant concentration. For C₈mimBr, there were not any micelle-like surfactant?Cpolymer clusters detected in the solution, and only micelles appeared. For other surfactants, the polymer?Csurfactant aggregates were formed in the solution, which was verified by the appearance of a broad endothermic peak in the ITC thermograms. The intensity of polymer?Csurfactant interaction increased with the hydrophobicity of the surfactants and the polymers but was not affected by the surfactant headgroups.     

Self-association of n -hexyltrimethyl-ammonium bromide in aqueous electrolyte solution

 The self-association of n-hexyltrimethylammonium bromide (C₆TAB) in aqueous solution has been studied by static and dynamic light scattering and NMR spectroscopy at 25 °C in the presence of added electrolyte, and critical aggregation concentrations, aggregation numbers and the degree of ionization have been calculated. Aggregation numbers determined from light scattering and from the application of mass-action theory to the concentration dependence of ¹H NMR chemical shifts of four protons along the alkyl chain of C₆TAB, were between three and four over the range of electrolyte concentration studied (0.2–0.7  molkg⁻¹ NaBr). A structure for the small aggregates has been proposed from the NMR chemical shift data. Received: 4 June 2001 Accepted: 17 September 2001     

Dynamic Surface Elasticity of Polyelectrolyte/Surfactant Adsorption Films at the Air/Water Interface: Carboxylmethylchitosan and Cetyltrimethylammonium Bromide

The dynamic surface elasticity of the solution of carboxymethylchitosan (CMCH) and cetyltrimethylammonium bromide (C₁₆TAB) was measured as a function of the surfactant concentration and the surface age by the oscillating drop method. The results showed that the surface layer of the CMCH/C₁₆TAB solution transformed from loose to structured with the increase in the surfactant concentration. The surface elasticity versus the surface pressure curve during the adsorption showed different features at different surfactant concentration ranges, which was connected with the structural transformation of the surface layer. Our results show that the measurement of dynamic surface dilational properties is a powerful tool for studying the surface kinetics, which is helpful for dealing non-equilibrium systems in industry.     

Aggregation behavior of naphthalimide fluorescent surfactants in aqueous solution

A group of novel fluorescent surfactants, N-n-alkyl-4-(1-methylpiperazine)-1,8-naphthalimide iodine [C_nndi]I (n?=?8, 10, and 12), have been synthesized and their aggregation behavior in aqueous solution have been explored by surface tension, electric conductivity, hydrogen-1 NMR spectra, absorption, and fluorescence spectra. Compared with traditional cationic surfactants, the [C_nndi]I have a rather lower critical micelle concentration and higher surface activity. Absorption and fluorescence spectra were proved to be facile method to monitor directly the aggregation states of fluorescent surfactant molecules in solution and revealed clearly the formation of face-to-face stacked structure of the [C_nndi]I molecules driven by the π–π interactions. The micelle formation process for [C_nndi]I was demonstrated to be enthalpy-driven in the temperature range investigated. Possible aggregation process was given based on the experimental results. The combination of dye and surfactant provides a way for monitoring the formation process of micelle directly by fluorescence spectra.     

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.     

长链烷基季铵盐插层氧化石墨的结构变化

基于改进的Hummers法制备氧化石墨(GO),并以长链烷基季铵盐(CnTAB)对其进行插层处理;通过改变CnTAB的链长、浓度,得到系列CnTAB/GO插层复合物。采用XRD和元素分析对产物的最大底面间距及CnTAB插入量进行表征。结果表明,随着Cn TAB链长的增长、CnTAB浓度的增大,CnTAB/GO插层复合物的最大底面间距逐渐增大。CnTAB通过离子键作用和疏水键作用插入到GO层间,在GO片层上的吸附规律符合修正型(Modified)Langmuir模型,即CnTAB以单分子层吸附在GO片层上。根据CnTAB/GO插层复合物最大底面间距及CnTAB插入量的变化规律分析,得出CnTAB在GO层间的排布模式有单层平躺模式、类双层平躺模式、单层倾斜模式和单层直立模式。     

Rheological and microcalorimetric studies of a model alkali‐soluble associative polymer (HASE) in nonionic surfactant solutions

Rheological experiments were carried out on a 1 wt % hydrophobically modified alkali‐soluble emulsion (HASE) solutions at pH ∼ 9 in the presence of nonionic polyoxyethylene ether type surfactant (C₁₂EO₂₃). The low shear viscosity and dynamic moduli increases at c > cmc until they reach a maximum at a critical concentration, c^m of approximately 1 mM (∼17 times the cmc of free surfactant) and then decrease. The dominant mechanism at cmc < c < c^m is an increase in the number of intermolecular hydrophobic junctions and a strengthening of the overall associative network structure. Above c^m, the disruption of the associative network causes a reduction in the number of junctions and strength of the overall network structure. The influence of C₁₂EO₂₃ on HASE before cmc could not be detected macroscopically by the rheological technique. However, isothermal titration calorimetry enables the determination of complex binding of surfactant to the polymer. Isothermal titration of C₁₂EO₂₃ into 0.1 wt % HASE indicates that the C₁₂EO₂₃ aggregation in water and 0.1 wt % HASE polymer solutions is entropically driven. A reduction in the critical aggregation concentration (cac) confirms the existence of polymer–surfactant interactions. The hydrophobic micellar junctions cause a decrease in the ΔH and ΔS of aggregation of the nonionic surfactant. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2019–2032, 2000     

长链烷基季铵盐插层氧化石墨的结构变化

基于改进的Hummers法制备氧化石墨(GO),并以长链烷基季铵盐(C_nTAB)对其进行插层处理;通过改变C_nTAB的链长、浓度,得到系列C_nTAB/GO插层复合物。采用XRD和元素分析对产物的最大底面间距及C_nTAB插入量进行表征。结果表明,随着C_nTAB链长的增长、C_nTAB浓度的增大,C_nTAB/GO插层复合物的最大底面间距逐渐增大。C_nTAB通过离子键作用和疏水键作用插入到GO层间,在GO片层上的吸附规律符合修正型(Modified)Langmuir模型,即C_nTAB以单分子层吸附在GO片层上。根据C_nTAB/GO插层复合物最大底面间距及C_nTAB插入量的变化规律分析,得出C_nTAB在GO层间的排布模式有单层平躺模式、类双层平躺模式、单层倾斜模式和单层直立模式。     

Liquid—liquid distribution in reversed micellar systems

The equilibrium distribution of a hydrophilic solute (M^z+ between an aqueous phase and a reversed micellar organic phase (consisting of a surfactant HA with aggregation number x, and dissolved in a hydrocarbon diluent) is analyzed quantitatively by treating the reversed micelles as a pseudophase. It is shown that when the M—A complex is strongly solubilized by the micellar pseudophase, the distribution coefficient (D) has a first-order dependence on the concentration of micellized surfactant (C_s). On the other hand, when the M—A complex is not solubilized by the reversed micelles, a plot of log D versus log C_s has a slope of (z/x); in this case the monomeric species HA is the active extractant and any effect that decreases surfactant aggregation (e.g. low aggregation number, small aggregation equilibrium constant) leads to an increase in the distribution coefficient.     

Solubilization and Transfer Free Energy of Some Organic Compounds from Bulk Aqueous Phase to Micelle of a New Type of Surfactant

A new type of surfactant, 3‐alkoxyl‐2‐hydroxylpropyltrimethyl ammonium bromide (C_nH_2n+1OCH₂CH(OH)CH₂N(CH₃)₃ ⁺Br^?, abbreviated as R_nTAB, n=8, 12, 14, 16) was synthesized. The solubilization of n‐pentanol, n‐hexanol, n‐heptanol, benzyl alcohol, n‐hexane, benzene, toluene, heptane, and carbon tetrachloride in aqueous solutions of R_nTAB, sodium dodecyl sulfonic(R₁₂SO₃N_a), and in the mixed solution of R₁₆TAB/R₁₂SO₃N_a have been studied by the microtitration method. The experimental results show that the solubilized amounts of the organic compounds increase with the growing of the hydrocarbon chain of R_nTAB, and the solubilizing ability of the binary system is lower for polar substances than for a mono‐surfactant aqueous solution. “V” isothermal curves of the solubilized amount of polar substances have been observed, and the minimum solubilized amount is at the molar ratio 1∶1 of R₁₆TAB/R₁₂SO₃N_a. However, the solubilizing ability of mixed surfactants for non polar substances is higher than that for a mono‐surfactant solution, the solubilizing isotherm curves present a “saddle” shape, and the maximum solubilized amount is at the molar ratio 1∶1 of R₁₆TAB/R₁₂SO₃N_a too. The length of hydrophobic chains of surfactant and the polarity of the organic compound affect the transfer free energy from aqueous to micelle phase. The longer the hydrophobic chain of R_nTAB and the lower the polarity of the organic compound, the more easily will the compound transfer from aqueous phase to micelle phase.     

Aqueous films on silica in the presence of cationic surfactants

Summary The existence of thick, stable water films on silica as described byDerjaguin and Kussakov (1939) has been confirmed in several laboratories. There is much evidence showing that their thicknesses can be substantially accounted for by electrical double layer theory. Such wetting films can be influenced by a third component. For example, they are thinned in the presence of inorganic electrolytes or rendered unstable (or metastable) by prior methylation of the silica surface.Here, we consider the influence of alkyltrimethyl ammonium bromides on the stability of aqueous films on polished fused silica. In particular, the thickness and stability of aqueous films of C₅, C₈, C₁₀ and C₁₆ trimethyl ammonium bromides were studied over a range of surfactant concentrations. Contact angles of the TAB solutions on silica were also measured.The concentration of each cationic surfactant proved important in determining film stability. In dilute solution (well below the bulk CMC) uniform films could be formed only below a critical concentration which varied with the chainlength of the surfactant. The longer the chainlength, the lower was the critical concentration. In this regime, the film thickness decreased significantly with increasing surfactant concentration. This decrease was greater than that found for a simple 1:1 electrolyte such as KCl at the same concentration. As the surfactant concentration increased towards the critical value, the uniform films became increasingly more prone to rupture.Once the critical concentration of each surfactant was exceeded, uniform wetting films on silica could not be formed. The films ruptured immediately regardless of their initial diameter. In this regime, the contact angles, measured through the aqueous phase, increased with TAB concentration up to a maximum value which occurred near the CMC.For C₈, C₁₀ and C₁₆ trimethyl ammonium bromides, wetting films were again formed at concentrations above the CMC. At these concentrations, films were studied in detail only for the C_l6 surfactant. In this case, the wetting films were found to be somewhat thicker than free aqueous films of anionic surfactants formed at similar concentrations and hydrostatic pressures.

---

Zusammenfassung Die Existenz dicker stabiler Wasserfrlme auf SiO₂ (Derjaguin undKussakov (1939)) ist in verschiedenen Laboratorien bestätigt worden. Es gibt zahlreiche Hinweise, nach denen die Dicke durch die elektrische Doppelschichttheorie gedeutet werden kann. Solche benetzenden Filme können durch eine dritte Komponente beeinflußt werden; in Gegenwart anorganischer Elektrolyte werden sie dünner, durch vorhergehende Methylierung der SiO₂-Oberfläche instabil oder metastabil.In der Arbeit wird der Einfluß von Alkyltrimethylammoniumbromiden (C₅, C₈, C₁₀ und C₁₆ auf die Stabilität von Wasserfilmen auf polierten Quarzglasoberflächen untersucht. Die Konzentration der kationischen Tenside auf die Filmstabilität erwies sich als wichtig. In verdünnten Lösungen bilden sich einheitliche Filme nur unter einer kritischen Konzentration, die von der Kettenlänge des Tensids abhängt. Über der kritischen Konzentration bilden sich keine einheitlich benetzenden Filme; sie reißen sofort unabhängig von ihrem ursprünglichen Durchmesser. Es wird versucht, die Ergebnisse auf der Basis einer Doppelschichttheorie zu deuten.

---

---

With 7 figures and 2 tables