SANS studies of liquid crystalline microemulsion gels

We have investigated by small-angle neutron scattering (SANS) the ternary system containing water, alkane and the surfactant mixture benzyltetradecyldimethylammonium chloride and tetradecyltrimethylammonium bromide, which we have found to form a cubic liquid crystalline phase. A contrast variation experiment with equal volume fractions of water and oil showed three Bragg reflections varying in agreement with theoretically calculated scattering amplitudes for an infinite periodic minimal surface (IPMS) with cubic symmetry. We have, in addition, studied the “ringing” gel phases of the system water/octane/didodecyldimethylammonium bromide by SANS and electron microscopy

Reflection and transmission coefficients of nano-metamaterial antennas at microwave frequencies

The hypothesis of this paper is that when metallic nanoparticles are grouped together by suitable field coupling they can behave like larger objects which will resonate at microwave frequencies. This means that sheets of nanomaterials can be designed that are largely transparent at these spectra except where an antenna has been created from densely grouped clusters of metallic nanoparticles. Simulations, based on actual samples composed of nano-metamaterials, show the behaviour of the reflection and transmission coefficients of antennas. The resonant frequency can increase or decrease depending on the geometry

Metallic inclusions in a non-uniform lattice

This paper is part of a larger project which aims to investigate the fabricational and electromagnetic advantages of creating integrated antenna systems using emerging nanomanufacturing technology. It has been known for several decades that the effective permittivity of a mixture consisting of dielectric inclusions in a host dielectric can be controlled by varying the permittivity, size and spacing of the inclusions. Various authors have developed theoretical equations to analyse these structures but are typically limited to spherical inclusions in a uniform cubic lattice. This paper extends this work from spheres in a uniform mesh to investigate thin metallic inclusions in a dielectric host using a non-uniform lattice (spacing in x, y and z, not the same). Electromagnetic simulations of these structures have been compared to canonical equations of spheres in a cubic uniform lattice with the same volume ratio

SINGLE CRYSTALS OF CUBIC TERNARY PHASES IN THE DDDAB/D2O/OCTANE SYSTEM

La connaissance des structures cubiques qui apparaissent dans les systèmes ternaires tensioactif/eau/huile pourrait être bien plus précise si l'on disposait de monocristaux. La possibilité d'en croître est démontrée dans cet étude. On présente des résultats de diffraction de neutrons et de rayons X aux petits angles par les premiers monocristaux obtenus pour le système DDDAB/D2O/octane.Precise knowledge of the cubic structures appearing in ternary systems surfactant/water/oil can be achieved if single crystals of these phases can be grown. In this work this is shown to be possible. Small angle X-ray and neutron scattering results are presented for the first single crystals of this type, grown for the system DDDAB/D2O/octane

Symmetry transition in the cubic phase of a ternary surfactant system

We report a small-angle X-ray and neutron scattering investigation in the cubic phase of the ternary system water/didodecyldimethyl ammonium bromide (DDAB)/octane. We have observed a systematic variation in the lattice parameter as a function of water content, which can be related to the change in interfacial area per unit cell with the aqueous volume fraction. Our results are consistent with a bicontinuous periodic constant mean curvature structure, and show a transition from diamond to body-centred cubic symmetry on increasing the water content of the system

Analysis of structure and orientation of adsorbed polymers in solution subject to a dynamic shear stress

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Polymer-based separation techniques rely on the ability of a binding portion of the polymer to interact with a specific molecule in a solution flowing past the polymer. The location of the binding site within or out of the entangled polymer chains is thus crucial to the effectiveness of these methods. For this reason, the details of flow induced deformation of the polymer chains is important in such applications as exclusion chromatography, waste water treatment, ultrafiltration, enhanced oil recovery and microbial adhesion. Few techniques exist to examine the structure and orientation of polymeric materials, and even fewer to examine systems in a dynamic fluid flow. The goal of this project was to understand the molecular structure and orientation of adsorbed polymers with and without active binding ligands as a function of solvent shear rate, solvent power, polymer molecular weight, surface polymer coverage and heterogeneity of the surface polymer chains by neutron reflectometry in a newly designed shear cell. Geometrical effects on binding of molecules in the flow was also studied subject to the same parameters

CONFORMATIONAL TRANSITIONS OF END-ADSORBED COPOLYMER CHAINS AT THE LIQUID/SOLID INTERFACE

Using the surface force apparatus, the conformational rearrangements of end-adsorbed diblock and triblock copolymer chains at the liquid/solid interface have been investigated. While the end-adsorbed poly(ethylene oxide)-polystyrene, PEO-PS, diblock copolymer ''blushes'' at a toluene/mica interface were seen to collapse upon the replacement of toluene by cyclohexane, rapid conformational transitions between ''loops'' and ''tails'' were observed for the end-adsorbed poly(2-vinylpridine)-polystyrene-poly(2-vinylpridine), PVP-PS-PVP, triblock copolymer chains at the toluene/mica interface during compression- decompression cycles. It was demonstrated for the first time that the newly formed tail-like triblock copolymer chains could be mechanically stretched beyond their equilibrium dimensions, a process which to some extent can be described by Rabin and Alexander's scaling model. The dynamics of the conformational rearrangements was followed by surface force measurements at the molecular level