Sökresultat

The interactions involved in aqueous mixtures of polyethyleneimine (PEI) and cetyltrimethylammonium bromide (CTAB) were studied under dilute conditions. The phase diagram of this polyelectrolyte-surfactant system of similar charge was constructed by determining the CAC and CMC* values at different PEI concentrations, using surface-tension and conductivity measurements, respectively. Formation of t

The formation of solid films at the air-solution interface is a common phenomenon, however, these films have largely not been explored from a materials point of view. In solutions containing inorganic species with surfactants these films, which can be several microns thick, have a highly organised nanoscale structure aligned with respect to the interface. More recently similar polyelectrolyte-surf

Growth of a mesostructured silica thin film at the air/water interface was observed in situ using Brewster angle microscopy and surface pressure measurements allowing real time observation of nucleation of the film and its rapid growth to full surface coverage at the end of the induction period.

Polymer/silica composite films, stable to calcination, were produced using catanionic surfactant mixtures (hexadecyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS)) and polymers (polyethylenimine (PEI) or polyacrylamide (PAAm)) at the air/water interface. Film formation processes were probed by time-resolved neutron reflectivity measurements. Grazing incidence X-ray diffraction (

Spontaneous growth of non-ionic surfactant-templated thin films at the air-water interface was investigated using three techniques: Brewster angle microscopy (BAM), time-resolved off-specular X-ray reflectivity and grazing incidence X-ray diffraction (GIXD). Experiments were also carried out to study the evolution of micelles in the subphase solution using small-angle neutron scattering (SANS). Fi

The accepted picture of the structure of a micelle in solution arises from the idea that the surfactant molecules self-assemble into a spherical aggregate, driven by the conflicting affinity of their head and tail groups with the solvent. It is also assumed that the micelles size and shape can be explained by simple arguments involving volumetric packing parameters and electrostatic interactions.

We describe a detailed synthesis of a silicified inorgaric/organic nanoporous monolithic composite conforming to the lyotropic liquid crystalline L3 phase. The pore dimensions of the silicified L3 phase scale with the solvent volume fraction in the synthesis reaction mixture. Changing the solvent fraction in the initial solution changes the ultimate pore diameter in the silicate, providing a simpl

The formation of a dense monolayer of methanol treated Silicate-1 nanocrystals on Si wafer was demonstrated using the Langmuir-Blodgett (LB) technique and its successful use as a seed layer for preparing a continuous zeolite film by subsequent secondary growth was presented. SEM results proved that a well developed dense Silicate-1 film was obtained, which demonstrated that the LB monolayers are i

Gold nanorods have been prepared in aqueous solution using a seed-mediated growth approach in the presence of surfactant. We observe the formation of liquid crystalline phases in concentrated solutions of high aspect ratio (13-18) gold nanorods by polarizing microscopy, transmission electron microscopy, and small angle x-ray scattering. These phases, which are stable up to 200°C, exhibit concentra

The validity of the fractal versions of the FHH and BET theories for describing the adsorption of butane and nitrogen on a variety of partially dehydroxylated silica surfaces has been tested. The fractal dimensions obtained from adsorption data have been compared with those obtained completely independently using SAXS. It was found that the fractal dimensions obtained from butane adsorption isothe

X-ray and neutron scattering from macroscopically rough surfaces and interfaces is considered and a new method of analysis based on the variation of the shape of the total reflection edge in the reflectivity profile is proposed. It was shown that in the limit that the correlation length and the height of the surface roughness are larger than the wavelength (at least 100 times bigger) of the incomi

Polyaniline of low molecular weight (ca. 10 kDa) is combined with cellulose nanofibrils (sisal, 4-5 nm average cross-sectional edge length, with surface sulphate ester groups) in an electrostatic layer-by-layer deposition process to form thin nano-composite films on tin-doped indium oxide (ITO) substrates. AFM analysis suggests a growth in thickness of ca. 4 nm per layer. Stable and strongly adher

A pure silica MCM-41 preparation with high crystalline order perpendicular to the channels has been examined using small-angle neutron scattering and the contrast variation method in both the calcined and template-containing forms. This defines various structural features such as template and water distributions and content, local silica density, and surface properties. Adsorption isotherm data, N

We have previously reported that robust mesostructured films will grow at the surface of alkaline solutions containing cetyltrimethylammonium bromide (CTAB), polyethylenimine (PEI), and silica precursors. Here we have used time-resolved small-angle X-ray scattering to investigate the structural evolution of the micellar solution from which the films form, at several different CTAB-PEI concentratio

Dilute mixtures of the water soluble polymer polyethyleneimine (PEI) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) form mesostructured thin films at the air/solution interface. In this paper we show that these films form spontaneously, reaching an equilibrium composition. When the film is removed, a new solid film rapidly reforms, with a similar morphology when inspected by Bre

Nanoparticle film voltammetry is employed to explore the presence and reactivity of surface-stabilised iron redox centers at the interface of immobilised Fe2O3 nanoparticles of ca. 4 nm diameter and aqueous buffer media. Mesoporous films of Fe2O3 nanoparticles on tin-doped indium oxide (ITO) substrates are formed in a layer-by-layer deposition process from aqueous colloidal Fe2O3 and aqueous cyclo

In order to rationally design polymer vehicles for controlled drug delivery it is important to completely understand the nature and mechanisms of the structural evolution of the polymer matrix that ultimately controls drug release kinetics. NMR cryoporometry has been used previously to study drug release from polymer vehicles. However, no previous studies have employed the integrated cryoporometry

We have prepared and analyzed thin film structures formed by polyethylenimine and alkyltrimethylammonium bromide (CnTAB) surfactants at the air/water interface, using both surface and bulk sensitive techniques. In initial experiments it was observed that hexagonal arrays of rodlike micelles surrounded by the polymer were formed at the solution surface, with the principal axis of the micelles runni

Cellulose nanofibrils from sisal of typically 4-5 nm diameter and ca. 250 ± 100 nm length are reconstituted into thin films of ca. 6 m thickness (or thicker freestanding films). Pure cellulose and cellulose composite films are obtained in a solvent evaporation process. A boronic acid appended dendrimer is embedded as a receptor in the nanofibrillar cellulose membrane. The number of boronic acid bi