A continuous mesoporous silica film with uniaxially aligned hexagonal mesochannels was formed on a silica glass substrate using a rubbing-treated thin polyimide coating on the substrate. Polyimide which has a hexamethylene group per the repeating unit as a part of the main chain was used. The mesostructured silica film was grown on the polyimide-coated substrate through the hydrolysis of tetraethoxysilane under acidic conditions in the presence of hexadecyltrimethylammonium chloride. X-ray diffraction experiments show that the hexagonal mesochannels in the film run parallel to the substrate surface and are aligned normal to the rubbing direction with a very narrow distribution of ±6°. The hexagonal arrangement of the mesochannels over the whole film thickness was proved by cross-sectional transmission electron microscopy. This highly preferred alignment of the mesochannels is caused by strong interactions between the surfactant tail groups and the polymer chains.

Mesoporous silica films with uniaxially aligned large-sized mesochannels were prepared using nonionic alkyl poly(ethylene oxide) surfactants and a rubbing-treated polyimide coating. Although the increment of the pore size was small as long as conventional alkylammonium surfactants were used, the use of nonionic surfactants with poly(ethylene oxide) headgroups led to successful enlargement of the mesochannels. The directional distribution of the mesochannels in the films, which is estimated by in-plane X-ray diffraction, was very narrow and was comparable with that in the oriented mesostructured silica films prepared using hexadecyltrimethylammonium chloride as a templating agent. The distribution of the alignment direction of the mesochannels is nearly independent of the nature of the hydrophilic headgroup, but is slightly affected by the alkyl-chain length of the surfactants used. These results indicate that the alignment of the mesochannels is determined by the hydrophobic interactions between the oriented polymer chains of the rubbed polyimide and the surfactant tail groups.

In this Communication, we show that nanometer scale control of semiconducting polymer chain conformation is possible using host/guest chemistry in highly ordered and macroscopically oriented thin films of mesoporous silica. This control leads to a thin film composite material that is optically transparent, densely filled with polymer, and has highly polarized optical properties. Calculations of absorption and emission anisotropies further indicate full incorporation of the polymer into the nanoscale pore spaces. Such materials could serve as a useful tool for further investigations of polymer photophysics, as well as for device applications.

It has been proved that surfactant−silicate supramolecular architecture formed on a silicon substrate is strongly affected by the crystal orientation of a silicon wafer, indicating the variation of the interactions between the surfactants and the silicon surfaces. The hexagonal mesoporous silica film with aligned mesochannels was grown on a (110) wafer, whereas the mesochannels were not aligned in the films grown on (100) and (111) wafers. The alignment direction of the mesochannels on the (110) wafer is parallel to the [001] direction. The Gaussian distribution of the alignment direction with a full width at half-maximum (fwhm) of 29° was shown by in-plane X-ray diffraction. The hexagonal packing of the mesochannels in the film is distorted. The strong anisotropy of the atomic arrangement of silicon on the (110) surface causes the preferential alignment of mesochannels.

Films of mesoporous materials attract broad interest because of their wide applicability in the fields of optics and electronics. Although many of these films have a regular local porous structure, the structural regularity has not been used practically yet because of difficulties in its control on macroscopic scales. Here, we demonstrate the preparation of mesoporous silica films whose porous structure can be described as a single crystal, that is, a long-range order of cage-like pores is maintained over centimetre scales. These films have a three-dimensional hexagonal (space group P6(3)/mmc) porous structure, and the in-plane arrangement of the pores is strictly controlled by a polymeric substrate surface that has been treated by rubbing. This new class of single-crystalline films with mesoscopic periodic structure is a significant breakthrough in bottom-up nanotechnology, and could lead to novel devices, for example, optics in a soft X-ray region, and quantum electronics.

A novel strategy for the preparation of a mesoporous silica film, in which the in-plane alignment of the honeycomb packed mesochannels is strictly controlled, is developed. The highly aligned porous structure is achieved by using a substrate with a rubbing-treated polyimide coating in the evaporation induced self-assembly process. It is shown that the controlled porous structure is formed over the entire thickness of the film and that the alignment distribution is much narrower than that in the films prepared by the conventional process based on a heterogeneous nucleation and growth mechanism. In the present process, the aligned porous structure would be formed through a directional lamellar-to-hexagonal phase transition from the substrate surface toward the air/film interface. The new formation mechanism as well as the lower process temperature enables the observed strict alignment control of the mesochannels.

Alignment of hexagonal mesoporous silica particles was achieved by a simple rubbing method used for the alignment of liquid crystals on a very thin polyimide film coated on a silica glass substrate. Mesoporous silica was synthesized through the hydrolysis of tetraethoxysilane under acidic conditions in the presence of hexadecyltrimethylammonium chloride. The arrangement of the elongated particles was observed with their long axes parallel to the rubbing direction. The maximum aspect ratio of the particles reached ∼100. Both the elongation and alignment of the particles were not observed on the same substrate without the rubbing treatment. The hexagonal channel orientation was confirmed using in-plane X-ray diffraction and high-resolution scanning electron microscopy. The hexagonal mesoporous structure was retained over calcination in air and the adhesion of the particles onto the substrate was greatly improved.

We control the chain conformation of a semiconducting polymer by encapsulating it within the aligned nanopores of a silica host. The confinement leads to polarized, low-threshold amplified spontaneous emission from the polymer chains. The polymer enters the porous silica film from only one face and the filling of the pores is therefore graded. As a result, the profile of the index of refraction in the film is also graded, in the direction normal to the pores, so that the composite film forms a low-loss, graded-index waveguide. The aligned polymer chains plus naturally formed waveguide are ideally configured for optical gain, with a threshold for amplified spontaneous emission that is twenty times lower than in comparable unoriented polymer films. Moreover, the optimal conditions for ASE are met in only one spatial orientation and with one polarization. The results show that nanometre-scale control of semiconducting polymer chain orientation and position leads to novel and desirable optical properties.