We have prepared and analyzed thin film structures formed by polyethylenimine and alkyltrimethylammonium bromide (C n TAB) 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.

Mesostructured films of alkyltrimethylammonium bromides or cetylpyridinium bromide and polyethylenimines that spontaneously self-assemble at the air/water interface have been examined using a range of surface sensitive techniques. These films are unusual in that they can be micrometers thick and are relatively robust. Here we show that the films can be cross-linked and thus removed from the liquid surface where they form, as solid, mesostructured polymer-surfactant membranes. Cross-linking causes little change in the structure of the films but freezes in the metastable mesostructures, enhancing the potential of these films for future applications. Cross-linked films, dried after removal from the solution surface, retain the ordered nanoscale structure within the film. We also report grazing incidence X-ray diffraction (GID), which shows that most films display scattering consistent with 2D-hexagonal phase crystallites of rodlike surfactant micelles encased in polymer. Polymer branching makes little difference to the film structures; however, polymer molecular weight has a significant effect. Films with lower polymer MW are generally thinner and more ordered, while higher polymer MW films were thicker and less ordered. Increased pH causes formation of thicker films and improves the ordering in low MW films, while high MW films lose order. To rationalize these results, we propose a model for the film formation process that relates the kinetic and thermodynamic limits of phase separation and mesophase ordering to the structures observed.

Lipid cubic phases are complex nanostructures that form naturally in a variety of biological systems, with applications including drug delivery and nanotemplating. Most X-ray scattering studies on lipid cubic phases have used unoriented polydomain samples as either bulk gels or suspensions of micrometer-sized cubosomes. We present a method of investigating cubic phases in a new form, as supported thin films that can be analyzed using grazing incidence small-angle X-ray scattering (GISAXS). We present GISAXS data on three lipid systems: phytantriol and two grades of monoolein (research and industrial). The use of thin films brings a number of advantages. First, the samples exhibit a high degree of uniaxial orientation about the substrate normal. Second, the new morphology allows precise control of the substrate mesophase geometry and lattice parameter using a controlled temperature and humidity environment, and we demonstrate the controllable formation of oriented diamond and gyroid inverse bicontinuous cubic along with lamellar phases. Finally, the thin film morphology allows the induction of reversible phase transitions between these mesophase structures by changes in humidity on subminute time scales, and we present time-resolved GISAXS data monitoring these transformations.

Tethered films of polystyrene-block-poly(methyl methacrylate) copolymers of varying composition and molecular weight were investigated using atomic force microscopy and the observed structures compared with theoretical predictions. Although the experimental results were in qualitative agreement with the theory, there was significant quantitative variation. This was attributed to the presence of solvent in the films prior to and during annealing, a hypothesis supported by new preliminary calculations reported here. Solvent exchange experiments (where a good solvent for both polymer blocks was gradually replaced by a selective solvent), were also performed on the films. This procedure generated textured films in which the structure was defined by miscibility of the polymer blocks with the second solvent.

Block copolymers (BCPs) are seen as a possible cost effective complementary technique to traditional lithography currently used in the semiconductor industry. This unconventional approach has received increased attention in recent years as a process capable of facilitating the ever decreasing device size demanded. Control over microdomain orientation and enhancing long range order are key aspects for the utility of BCPs for future lithographic purposes. This paper provides an efficient route for the fabrication of highly ordered nanostructures suitable for such application. We investigate the significant effect of surface treatment regarding the self-assembly process of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) by employing an ethylene glycol layer, producing well defined perpendicular P4VP cylinders with long range order over large surface areas. Nanopores are generated through surface reconstruction using a preferential solvent, which allows for the incorporation of an inorganic moiety. Treatment of this pattern with UV/Ozone leads to formation of well-ordered iron oxide nanodots with a pitch of $26 nm. Furthermore, high aspect ratio silicon nanopillars result following pattern transfer (using Ar/O 2).