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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 running parallel to the surface. In the studies reported here, the formation of these ordered mesostructured films was identified as being kinetically but not thermodynamically favored, with some of the systems examined showing a loss of structure from their neutron reflectometry profiles with time. The polymer was used in both an as-diluted state (with a small net positive charge) and a neutral state, through the addition of sodium hydroxide to the solution. The primary interaction in these systems was found to be that of a neutral polymer with a cationic surfactant; however, by modifying the charge on the polymer it is possible to alter the distance between micelles by up to 6 Å without destroying the structure of the films. Analysis of the bulk solution with small-angle neutron scattering showed that the micelles in solution are elliptical rather than rod-shaped, and so the assembly of the hexagonal mesostructure occurs at the air/water interface rather than adsorbing to the interface from the bulk.

A fragment-based docking procedure followed by substructure search were used to identify active-site β-secretase inhibitors from a composite set of about 300 000 and a library of nearly 180 000 small molecules, respectively. EC50 values less than 10 μM were measured in at least one of two different mammalian cell-based assays for 12 of the 72 purchased compounds. In particular, the phenylureathiadiazole 2 and the diphenylurea derivative 3 are promising lead compounds for β-secretase inhibition.

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 isotherms, using both the fractal FHH and fractal BET theories, agreed well with the corresponding values obtained from SAXS over overlapping length scales. However, in general, a systematic deviation between the fractal dimension obtained from nitrogen adsorption and that obtained from SAXS was observed. The fractal dimensions obtained from nitrogen adsorption were consistently larger than those obtained from SAXS, which is the opposite of what has often been found in the literature. It has been suggested that the differences in the suitability of the adsorption theories tested to describe butane and nitrogen adsorption is due to the significant difference between the interaction strengths of these two different molecules with silica surfaces. A modified theory that can account for the discrepancy between the fractal dimensions obtained from nitrogen adsorption and SAXS has been proposed. The implications of the new theory for the accuracy of nitrogen adsorption BET surface areas for silicas are discussed.

Off-specular X-ray reflectivity measurements were carried out to follow the in situ development of surfactant-templated silica thin films at the air−water interface under conditions of controlled relative humidity and temperature, using an enclosed sample cell designed for this purpose. The results suggest a strong dependence of formation time and growth mechanism on ambient conditions. Thin films were synthesized at the air−water interface using cetyltrimethylammonium bromide (CTAB, 0.075 M) and a silica precursor, tetramethoxysilane (TMOS, 0.29−0.80 M) in an acidic medium. The studied humidity range was from 50 to 100%, the temperature was between 25 and 40 °C, and the TMOS/CTAB molar ratio was between 3.3 and 10.7. We observed that high humidity slows down the growth process due to lack of evaporation. However, increasing the temperature results in a decrease in the film-formation time. We proposed a formation mechanism for film growth as a consequence of phase separation, organic array assembly, and silica polymerization.

Grazing incidence X-ray diffraction (GIXD) and X-ray reflectivity have been used in situ to study the structure of surfactant-templated silica films grown at the air/water interface at different depths in the film. The results confirm that cylindrical silica-encased surfactant micelles are predominantly organized into a two-dimensional hexagonal structure, with the long axis parallel to the surface of the film. The arrangement of the micelles is well orientated near to the air/film interface but becomes disordered deeper into the sample. GIXD also reveals the existence of vertical channels extending down from the bottom of the film. This suggests a transition from in-plane to unconstrained growth.

The development of surfactant-templated mesoporous films grown at the air/water interface was investigated using specular and off-specular X-ray reflectivity techniques. The samples were prepared in acidic conditions using cetyltrimethylammonium bromide (CTABr, 0.075 M) and different concentrations (0.27−0.88 M) of tetramethyloxysilane (TMOS). At CTABr/TMOS molar ratio between 0.277 and 0.093, the final films exhibited at least three orders of diffraction, corresponding to a real space repeat distance of 46 Å. This long-range order was not observed when the TMOS content was increased to 0.88 M at constant CTABr concentration. In each case, the induction period prior to film formation was monitored using diffuse X-ray scattering. The intensity of the specular reflectivity peak, first and second-order diffraction peaks, and Yoneda wing were recorded as a function of time. The reflected intensity of the specular peak oscillated during the lengthy induction period, indicating that at some concentrations the films nucleate at the surface through a phase separation mechanism followed by growth of ordered arrays. This oscillation has been modeled as a surface layer having increasing thickness and roughness with time. The evolution of the first-order diffraction peak displays different characteristics depending on the TMOS content. For the shortest induction times (corresponding to a molar ratio of 0.139) the film formation mechanism appears to be bulk driven, but for longer development periods the film forms through assembly of ordered arrays at the surface.

Time-resolved small-angle neutron scattering has been used to investigate the evolution of micelles in the subphase of surfactant-templated silica film-forming solutions. Two samples have been prepared using cetyltrimethylammonium bromide (CTABr), as the structure-directing agent, and different amounts of tetramethoxysilane (TMOS) (CTABr/TMOS molar ratio 0.093, 0.139). The solutions have been reproduced at three different H2O/D2O contrasts and allowed to develop until a precipitate formed in the bulk. The surfactant initially forms micelles in solution while the hydrolyzed TMOS is dispersed uniformly through the aqueous phase. The micelles appear to have an ellipsoidal structure immediately after mixing, composed of a surfactant core surrounded by a thin, low-density silica film. The ellipsoidal micelles are typically 32 Å in length and with time elongate and become “rodlike” silica-coated cylinders with length in excess of 150 Å. This value is significantly larger in the composition containing more TMOS (≈1100 Å). In contrast, the radius of the core exhibits limited growth, swelling from 15.6 to ≈19 Å during the induction period. At long times the CTABr/TMOS = 0.139 sample exhibits a first-order diffraction peak at Q = 0.133 Å^-1, corresponding to cooperative scattering from an ordered mesostructure. An analogous peak is not observed in the CTABr/TMOS = 0.093 solution. This is discussed in terms of different film formation mechanisms and compared with previous data measured by X-ray reflection techniques at the air/water interface.

We describe a detailed synthesis of a silicified inorganic/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 simple method for tuning the diameter of the pores in the matrix. The resulting monolith is optically isotropic and transparent with a nonperiodic network. Accessible pores (which permeate the entire structure) in the silicified materials correlate with the solvent domain of the original liquid crystalline phase and therefore negate the need to remove the surfactant in order to gain access to the pore network. Measured characteristic dimensions are from 6 to well over 35 nm. X-ray scattering studies indicate a low polydispersity in the pore diameters for a given solvent fraction. Transmission electron and atomic force microscope images are consistent with a random morphology and measured surface areas exceed 960 m² g^-1 in extracted materials.

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, NMR, previous neutron scattering data, and the SANS data allow a choice between proposed models for the channel structure of MCM-41, in terms of the straightness of the channels and their surface roughness.