Decylammonium Chloride Research Articles

Phase diagrams of the decylammonium chloride/ammonium chloride/water system in the nematic micellar region

Phase diagrams were obtained as a function of temperature and surfactant concentration for the decylammonium chloride (DACl)-water binary system and for ternary systems containing 1:1627, 1:20, and 1:10 weight ratios of NH 4Cl:DACl. The binary system presents the usual hexagonal (middle soap), lamellar (neat soap), isotropic, and “coagel” phases as well as a micellar nematic of the disk type. The addition of NH 4Cl greatly inhibits the formation of the hexagonal phase, and increases the size of the nematic and lamellar regions while shifting them toward higher temperatures. As the concentration of NH 4Cl to DACl passes 7 wt% (for 45 wt% DACl), the nematic is replaced by a lamellar-isotropic two-phase region.

Diffusion Measurements in Aligned Nematic and Smectic Amphiphilic Liquid Crystalline Decylammonium Chloride and Ammonium Chloride Water Mixtures

Abstract The micellar diffusion constants have been measured perpendicular to the optic axis in an aligned aqueous solution of decylammonium chloride and ammonium chloride, 10:1 by weight. The diffusion constants were calculated by measuring the evolution of the dye concentration along a microslide (.2 or .3 mm thick and 10 cm long) which had initially been half filled with solution containing a dye soluble only in the micelle. the other half being pure solution. Measurements were made in the isotropic phase for solutions containing 64 wt% water; in the nematic and smectic (neat soap) phases in solutions of 54 wt% water; and in the smectic phase of a 52 wt% water solution. The measured diffusion ranges from 4 × 10−7 cm2/sec to 7 × 10−7 cm2/sec. Taking into account the temperature dependence of the viscosity of water. we find Diw D<1Nm = D1 Sm.

Nematic States in Micellar Systems of Mixed Composition

Abstract The correlation between the molecular composition of micelles and the temperature stability of micellar nematic states is investigated on mixtures of cetyltrimethylammonium bromide (CTAB) or decyltrimethylammonium bromide (DTAB) with decylammoniumchloride (DACl) or potassium laurate (KL), 1-decanol, and NaBr. The phases were identified using a polarizing microscope. Replacing, in a CTAB/l-decanol system with a nematic phase, CTAB mole by mole with KL increases the temperature stability of the lamellar smectic state but the width of the nematic range is reduced. Similarly, replacing CTAB with decanol increases the stability of the smectic state and reduces the width of the nematic range. In contrast, replacement of CTAB by DACl has little effect on the width of the nematic range up to 35% replacement and no enhancement of the temperature stability of a latent smectic state is observed. The results are qualitatively interpreted in terms of the electrostatic interactions of the ionic surfactants and...

Density and Susceptibility Measurements on a Micellar Nematic System

Abstract The densities and diamagnetic susceptibilities in the nematic and isotropic ranges of two mixtures of decylammonium chloride, ammonium chloride, and water are reported. The mixtures have a lamellar smectic phase, a nematic phase, and an isotropic micellar solution. The smectic-nematic transition is second order, the nematic-isotropic transition first order. The density does not show a discontinuous change at the nematicisotropic transition, and the expansion coefficients of the nematic and isotropic regions are the same within error limits. The diamagnetic susceptibility in the isotropic range and the susceptibility perpendicular to the optical axis in the nematic range were determined using the Gouy method. The diamagnetic anisotropy of the nematic range was derived. It varies from 2 X10−9 near the nematic-isotropic transition to 5 × 10−9 cgs near the nematic-smectic transition.

Optical Sign Determinations on Cholesteric Lyotropic Mesophases

Abstract Optical signs of type I and II micellar cholesteric lyotropic mesophases were for the first time determined. Lyomesophases were prepared from the following amphiphiles: potassium l-N-lauroyl-serinate, potassium laurate, sodium decylsulfate, cesium decylsulfate and decyl-ammonium chloride. Cholesterol was added to all mesophases in order to obtain the chevron pattern for magnetically oriented samples. The method involves the direct observation of the textures at the polarizing microscope. Using a quartz-wedge retardation plate the directions of the slow and fast light vibration components are determined. This method is simpler than the usual observation, under conoscopic illumination, of the basal interference figure which is hardly obtained in micellar lyotropic cholesteric mesophases. All type I cholesteric lyotropic mesophases here investigated exhibited a positive optical sign, whereas all type II cholesteric lyomesophases showed a negative birefringence.

Mixed Adsorbed Film of 2-(Octylsulfinyl)ethanol with Decylammonium Chloride at Water/Air Interface

Abstract The surface tension of the aqueous solution of 2-(octylsulfinyl)ethanol and decylammonium chloride mixture has been measured by changing the total molality and composition of surfactants at 298.15 K under atmospheric pressure. It has been observed that the surface tension decreases with increasing the total molality at a constant composition and with decreasing the composition of decylammonium chloride at a constant total molality. Further the surface tension vs. total molality curve has been found to have a break point at a relatively low concentration. The thermodynamic equations have been developed so as to be applicable to the adsorption of nonionic–ionic mixture and used to calculate the surface density and the surface composition. It has been shown that the surface density vs. molality curve has the discontinuous change caused by the transition from a gaseous to an expanded film. By drawing the two-dimensional phase diagram and comparing it with the diagrams of the ionic–ionic surfactant mixtures, it has been proved that the shape of the phase diagram is affected greatly by the difference in the surface activity between the two surfactants.

Adsorption of Dodecyltrimethylammonium Chloride-Decylammonium Chloride Mixtures at Water/Air Interface

Abstract The surface tension of the aqueous solution of dodecyltrimethylammonium chloride and decylammonium chloride mixture has been measured as a function of the total concentration and composition of the surfactants at 298.15 K under atmospheric pressure. It has been observed that the surface tension decreases with an increase in the composition of dodecyltrimethylammonium chloride at a fixed total concentration. A break point has been observed on the surface tension vs. total concentration curve. By applying the thermodynamic relations, the surface densities of surfactants have been evaluated numerically. It has been proved that the phase transition of the mixed adsorbed film takes place from a gaseous to an expanded state at the break point. By comparing the composition in the adsorbed film with that in the bulk phase, the difference between the compositions has been found to diminish as the surface tension decreases. It has been shown that the mutual relation between the compositions of the gaseous and expanded films at the transition point is described by the two-dimensional phase diagram.

Mixed adsorbed film of dodecylammonium chloride with decylammonium chloride at water/air interface

The surface tension of the aqueous solution containing dodecylammonium chloride and decylammonium chloride has been measured as a function of total concentration at 298.15°K under atmospheric pressure. It has been observed that the surface tension decreases with increasing the composition of dodecylammonium chloride at a fixed total concentration and the surface tension vs concentration curve has a distinct break point. By applying the thermodynamic relations developed, the surface densities of surfactants have been evaluated numerically. Examining the relation of the composition in the bulk phase to the one in the adsorbed film at constant surface tension, the difference in the surface activities of surfactants has been found to be pronounced at high surface tension. It has been proved that the break point corresponds to the phase transformation of the adsorbed film from a gaseous to an expanded state. It has been shown that the phase transition is expressed by a two-dimensional phase diagram.

Effects of Salt on the Orientational Order in Decylammonium Chloride/Ammonium Chloride/Water Systems

Abstract The effect of NH4Cl on the temperature dependence of deuterium oxide splitting (water order) and proton line width (surfactant order) in decylammonium chloride (DACl), D2O systems is reported. The molar ratio of DACl to D2O was held constant at .085 and the molar ratio of NH4Cl to D2O was varied from .012 to .029. We find for the above concentration ranges that in the nematic range the relative temperature dependence of the D2O splitting is little affected by changes on salt concentration. The slopes of the proton line widths as a function of temperature decrease with increasing salt concentration. The results are compared with earlier data on salt effects on order obtained with the disodium cromoglycate system.

Bend and splay elastic constants and the rotational viscosity of nematic decylammonium chloride and ammonium chloride water mixtures

Elastic and dynamic properties of two amphiphilic nematic mixtures consisting of decylammonium chloride and NH4Cl, molar ratio 2.76:1, and water, 90.5 and 89.7 mole %, respectively, were studied on thin surface aligned films. The data can be successfully analyzed on the basis of the Frank–Oseen and Leslie–Erickson theory. The magnitude of the curvature elastic constants is comparable to that of typical thermotropic nematics. The mixtures have a nematic range of 20 °C and transform in cooling to neat soap. The bend elastic constant and the rotational viscosity diverge at this transition while the splay elastic constant shows no critical behavior.

An investigation of the dilute solutions of lauric acid and laurate ion in cationic and anionic bilayers of disc micelles

Type II DM mesophases with disc-shaped micelles have been synthesized from decylammonium chloride and sodium decylsulphate – decanol amphiphiles with added water and electrolyte. Small amounts of guest amphiphiles have been added in the form of lauric acid or laurate ion. Specific and perdeuterated amphiphiles have been prepared and included in small quantifies in the mesophases. The deuterium magnetic resonance spectra of the magnetically aligned phases has been studied and quadrupole splitting doublets assigned to all segments of both host and guest hydrocarbon chains. The mesophases have been diluted with water over the stable range of type II DM behaviour at 34 ± 0.2 °C.The quadrupole splittings of all hydrocarbon chain segments, which reflect the degrees of order along C—D bonds in these segments, are accurately reproduced at all water contents by a knowledge of one quadrupole splitting in the chain and a simple proportionality constant which is derived for each segment of the chain. This further extends the previous results for host chains to those of guest chains studied here. The absolute degrees of order of chain segments are greatly influenced by water content because motion of the constituent disc micelles depends on the volume of interstitial water and they also vary in size as water is added. The packing in the bilayer solution of the disc micelles of the amphiphiles is therefore not a function of the interstitial water content in so far as the detailed trans/gauche motions of the hydrocarbon chains are not affected by changes in water content.The lauric acid-d23 chain in the decylammonium chloride bilayer has the same degree of order along the D—D axis and the C—D bond, confirming that the motion of the pseudo rigid chain in the bilayer is cylindrically symmetric. The degree of order profiles of hosts and guests are all quite distinct indicating that chemical identity of the head group and its anchoring in the interface is the main determinant of the motion profiles.

Analysis of carbon-13 longitudinal relaxation times and nuclear overhauser enhancements in alkyl chains

A simple procedure is proposed which yields, from carbon-13 longitudinal relaxation times and nuclear Overhauser enhancements, information concerning the local mobility of a given CH vector in an alkyi chain. This method is based on the definition of an effective rotation axis related to internal motions and makes use of Woessner's equations. It yields a correlation time τ R characteristic of the overall reorientation. In addition, for each carbon C i a correlation time τ G i , associated with the fast motion of the C i H vector, and an angle θ i , between C i H and an effective rotation axis, are determined. The effect of cross-correlation spectral densities is discussed. This model is used for analysing relaxation data of decylammonium chloride micelles. It is further checked by interpreting experimental results at two different observation frequencies.

Structural changes at hydrophobic/hydrophilic interfaces induced by thermal changes and isotopic composition of the water

A lyomesophase prepared from decylammorium tetrafluoroborate, ammonium tetrafluoroborate, and water, which orients in a magnetic field perpendicular to the directors (type II), has been investigated with respect to the isotopic composition, H2O/D2O of the aqueous compartment at constant overall chemical composition. An effect of the isotopic composition of the water has been discovered, which influences the packing of the water and tetrafluoroborate ions at the interface. An interface structure transition occurs at ∼ 14 mol% D2O in H2O. The ammonium ions, which do not form part of the first bound layer at the interface, are affected to a much smaller degree and the sudden changes in the direction of variation of nmr parameters are not observed for this ion. The interface structure at &gt; 14 mol% D2O evidently does include more remote participation of NH4+ ions.Recent low angle X-ray diffraction studies, available to us, indicate that the mesophases which orient in magnetic fields have two levels of structure, the packing of amphiphiles in discrete anisotropic micelles and the super-packing of the micelles themselves. These studies now enable us to reinterpret other similar thermally induced structural changes in the interface, from results previously encountered, in the decylammonium chloride system. It is possible to have changes in the packing of water, amphiphiles, and ions at the interface without changes in the superstructure. Such changes in interface packing might well go undetected in a measurement of bulk properties but are revealed by measurement of nmr parameters for the oriented mesophase of different species involved in the interface structure. The isotope effect on structural packing at the interface is absent in two other mesophases investigated.

Conformational Transition of Poly(l-glutamic acid) in Aqueous Decylammonium Chloride Solution

Abstract The cooperative binding of decylammonium chloride to poly(l-glutamic acid) (PLG) was studied by the potentiometric measurement of the binding isotherm at pH 7.9. Circular dichroism spectra were also measured as a function of the degree of binding of surfactant ion (x). It was shown that the coil to α-helix transition of PLG-surfactant complex takes place with a change in x. PLG did not undergo an appreciable conformational change in the range of x below 0.55. But the helical content increased suddenly with further increase in x. An abrupt increase in the helical content of PLG-surfactant complex can be well interpreted in terms of the hydrophobic interaction among bound surfactant ions. On the basis of the theoretical analysis of the cooperative binding isotherm, it was concluded that the formation of a micelle-like cluster consisting of at least eight surfactant ions is required for the stabilization of a surfactant induced helical structure.

Cholesteric states of micellar solutions

The effects of optically active compounds on amphiphilic nematics are reported. The following systems have been studied : (1) caesium decylsulphate, decanol, water plus tartaric acid ; (2) ammonium decylsulphate, ammonium sulphate, decanol, water plus brucine sulphate ; and (3) decylammonium chloride, water plus cholesterol. Phase transitions to cholesteric states are induced by the optically active compounds in all systems. Brucine sulphate has the highest twisting power ; tartaric acid the lowest. The results are analysed on the basis of intermolecular interactions and an explanation is proposed for the observed differences in twisting power.

Studies of the behavior in magnetic fields of some lyomesophase systems with respect to electrolyte additions

A systematic investigation has been made of some lyotropic mesophases (lyomesophases) which macroscopically orient in magnetic fields. These mesophases have been classified into type I which have a positive diamagnetic anisotropy (Δχ &gt; 0) and type II with Δχ &lt; 0. The mesophase behavior has been observed as a function mainly of electrolyte additions to binary and ternary systems. The electrolyte has a profound effect on the mesophase behavior at extremely low concentrations. It has the effect in the ternary system, sodium decylsulphate/decanol/water, of converting a type I to a type II mesophase with less than 1 wt.% electrolyte. The addition of electrolytes to binary surfactant/water systems had the effect of increasing the mesomorphic region to higher water concentrations. In the case of sodium and cesium decylsulphate, and potassium laurate, these ternary mesophases were of type I and for decylammonium chloride of type II. The method used to distinguish mesophases and determine the degrees of order of water and some hydrocarbon chain segments has been deuterium magnetic resonance.

The orientations of molecules dissolved in lyotropic surfactant solutions

Nematic lyotropic liquid crystals prepared from sodium decylsulphate and from decylammonium chloride have been used as solvents for benzene and its monohalogenated derivatives. The results of an N.M.R. investigation of these compounds indicate that vibrational corrections to the ortho dipolar couplings are about 1·5 per cent and that the structure of fluorobenzene in lyotropic solution is different from the microwave structure. It was found that iodine had the major influence on the alignments of the molecules. Fluorine tended to align the C 2 axis of the fluorobenzene molecule at 90° to that preferred by iodobenzene. This effect of substituent on the rotation by 90° decreased in the order I>Br>Cl>F. The preferential orientations were discussed in relation to the orientation of the superstructure of the nematic material. Only fluorobenzene orders, so that the carbon halogen bond is preferentially directed into the hydrocarbon water interface area and this significantly so only in the decylammonium phase.

A surface equation of state for mixed surfactant monolayers

The surface equation of state valid for a single, pure surfactant at the water/air interface has been extended to cover systems containing two different surfactants. Nonideality of each single surfactant at the water surface is fully accounted for, but specific interaction between the surfactants is neglected. This enables the surface tension, as a function of the concentrations for mixed surfactant solutions, to be predicted if the behavior of the separate constituents is known. Systems containing dodecyl ammonium chloride and either decylammonium chloride or octanoic acid show fair to excellent agreement with this theory, indicating that in these systems specific surface interactions have a negligible effect on the surface tension. Systems containing lauric acid and sodium laurate show wide deviations from the theory. These deviations may be used to assess specific interaction.