Leonard W. Reeves

New Lyotropic nematic phases with unusual anisotropies of magnetic susceptibility: Type I DM and type II CM

Abstract Two lyotropic mesophases of opposite signs of susceptibility anisotropy have been found, one a quaternary and the other a ternary phase. Conclusive evidence is presented that the disk-micelle mesophase has positive diamagnetic anisotropy and the rod-like micelle phase has negative anisotropy. These have been named type I DM and type II CM mesophases respectively to conform with the notation previously introduced for mesophases based on aliphatic chain surfactants.

Studies of Specific Adsorption Sites for Sodium Ion and Water on the Interface of Mixed Micelles of Novel Type II Lyomesophases

Abstract Novel aqueous type II lyotropic mesophases that align in magnetic fields have been synthesized for binary and ternary mixtures of amphiphiles. A system in which major components of the micelle bilayer are decyltrimethylammonium and dodecanoate ions is an aligning mesophase from 100% to 35% dodecanoate, but replacement of the cationic amphiphile with hexadecyltrimethylammonium facilitates the extension to aligning mesophases up to 100% replacement of the dodecanoate ions. A study of sodium and deuterium quadrupole splittings observed in their nuclear magnetic resonance spectra, confirms and extends a three site adsorption theory for sodium ion in the mixed head group interface. The first site is associated with more strongly hydrated ions and head groups and involves adjacent dodecanoate head groups, the second is not so strongly hydrated and involves one dodecanoate group while the third is a weakly bound water at - N(CH3)+ groups and a sodium remote from the interface layer in close to average i...

Studies in membrane processes X: A deuterium magnetic resonance study of dipalmitoyl lecithin and palmitic acid guests in magnetically-oriented hexadecyltrimethyl-ammonium bromide liquid crystalline system

Abstract The membrane phospholipid, dipalmitoyl lecithin, deuterium labelled in its fatty acyl chains, and palmitic acid-d31 have been incorporated into the same bilayer model membrane, a lyotropic liquid crystalline hexadecyltrimethylammonium bromide mesophase which spontaneously orients in an applied magnetic field. The order parameter profiles for the lecithin and palmitic acid, and that of the host detergent are quite different indicating that the ordering of the incorporated lipids is not dictated by surrounding detergent molecules, but rather the order imposed is a function of the nature of chemical anchoring of the hydrophilic headgroups of the individual molecules at the bilayer interface. Dissimilarities in the order profiles are interpreted in terms of variations in the case of formation of random gauche conformers along the length of the acyl chains. In addition, the validity of the use of perdeuterated fatty acids as probes of the order of other membrane components is questioned. For the host detergent the relaxation rate ‘ 1 T′ 2 obtained from the line width is directly proportional to the deuterium quadrupole splitting of the —CD2 — segments for that flexible part of the chain beyond the plateau region of constant degree of order. This indicates that for an aligned chain, the increasing motional freedom for each successive segment toward the chain end, which is linked with the increasing probability of single gauche rotations, is the motion responsible for both the decrease in degree of order and thus the increase in line width.

The Aqueous Lyotropic Analogues of Thermotropic Nematics and Cholesterics

Abstract The motional non-equivalence in a deuteriated -CD2-segment of a hydrocarbon chain near a chiral carbon atom has been investigated in a series of nematic and cholesteric phases. The deuterium nuclear magnetic resonance signals show the number of non-equivalent motions as equal to the number of different quadrupole doublet splittings. It is shown that a necessary but not sufficient condition for motional non-equivalence is the presence of a chiral carbon. The chiral carbon is not sufficient because in some cases the two quadrupole doublets may accidentally overlap. The composition of a number of nematic and cholesteric meso-phases has been located and recorded.The non-equivalence is affected to a large extent by the protonation of the chiral head group, showing that head group anchoring is changed in this chemical modification.

N.m.r. line shape-relaxation correlation analysis of bitumen and oil sands☆

Abstract The first results of the analysis of bitumen and oil sands using the recently developed n.m.r. spingrouping technique are presented. The n.m.r. relaxation experiments were carried out on bitumen, and on natural and dried oil sands samples. The results indicate that the spin-grouping can resolve and quantify several components of the samples studied. The bitumen and bitumen fraction of the oil sands are resolved according to their spin-spin relaxation times into three major groups: solid-like (rigid), solid-like (mobile) and semi-liquid. The water in the oil sands exists in two different environments. Tentatively one environment is assigned to be the bridges between the sand grains, while the other is assigned to be the clay surface. One can conclude that with spin grouping of complex mixtures the decomposition (in which components are resolved according to their dynamic state) is possible. The accuracy of such resolution is of the order of a few per cent.

Conformational Studies of a Carboxylic Acid Incorporated into Lyotropic Liquid Crystalline Systems. A Deuterium Nuclear Magnetic Resonance Investigation

Abstract Butanoic acid-d7 and its corresponding anion have been incorporated into two Type II disc micelle lyotropic liquid crystalline systems based on hexadecyltrimethylammonium bromide, and on sodium decylsulfate. The order parameter profiles for the perdeuteriated guests have been determined. Calculations based on these order profiles have been performed in order to describe the conformation of the guest carboxylic acid present in the bilayer micelle. These calculations indicate that two conformations predominate, one an all trans arrangement (63%), and the second possessing a single gauche rotation about the α-β C—C bond (37%). The model used was based on two possible methods of anchoring the polar group at the aqueous interface.

Pulsed Gradient NMR Diffusion Study in Lyotropic Nematics

Abstract The translational diffusion of amphiphile molecules in lyotropic nematic phases has been studied for different orientations of the pulsed magnetic field gradient using the magic angle NMR spin-echo technique. Unrestricted diffusion was observed along the long axis of the cylindrical micelles and in the plane of the discotic micelles whereas in directions perpendicular to the above orientations diffusion was too small to be detectable. The observed magnitude of the diffusion coefficients as well as their anisotropy are characteristic for lamellar and hexagonal phases but the finite alignment times favour the view that the two mesophases are composed of finite micelles.

ESR studies of magnetically aligned lyotropic liquid crystals

Abstract A type I lyotropic liquid crystalline system based on the amphiphile potassium laurate, and possessing positive diamagnetic anisotropy has been investigated using electron spin resonance (ESR) spectroscopy of spin labeled laurate molecules. A comparison has been made of the ESR order parameters and those derived from deuterium nuclear magnetic resonance (NMR). It is proposed that oscillation of the finite micelles produces additional averaging of the NMR spectra, while this motion is slow on the ESR time scale. Although the perturbation of the bulky spin label precludes a quantitative description of the motion of the hydrocarbon chains, the ESR spectra are entirely consistent with a cylindrical structure for these mesophases, and inconsistent with those of lamellar type structures. It is concluded that these type I lyotropic liquid crystals are indeed composed of cylindrical micelles of finite length.

Proton Spin Relaxation in the Rod Micelles of Type I CM Mesophases

Abstract The dynamics of the hydrocarbon chains in lyotropic nematic type I cylindrical micellar liquid crystals prepared with D2O has been selectively studied by Zeeman and rotating frame nuclear spin-lattice relaxation. The measurements of the proton spin-lattice relaxation time T 1 as a function of frequency and temperature demonstrate that relatively fast local fluctuations of individual amphiphilic chains relax the proton spins at high magnetic fields. This process is facilitated also by the rapid diffusive motion of the chains within the micellar units. The rotating frame Zeeman relaxation time T 1x, is associated at room temperature with a long correlation time of ~11 μs. Slow micellar orientational fluctuations have been assigned to this characteristic time.

Motion Profiles of Deuteriocarbon Chains in Lamellar and Type II DM Nematic Phases

Abstract A binary system decylammonium—d-21 chloride water and a ternary system with a small amount of ammonium chloride have been studied over a wide range of water content by deuterium magnetic resonance. For the binary system a lamellar phase is formed, which on dilution becomes a two phase system lamellar/type II DM nematic. There is a large isotope effect in the composition, at which the two phase region occurs. The ternary system passes directly from the lamellar phase to a nematic system at a phase transition. The segmental motions in the deuteriocarbon chains are independent of the mesophase formed and of the electrolyte content. Large contributions to the degree of order of segments arise from co-operative motions of the whole bilayer and these are significantly different in the lamellar and type II DM, with and without electrolyte.