Synthesis and properties of photosensitive polyimide–nanocrystalline titania optical thin films

Modification of TiO2 Nanoparticles with Oleyl Phosphate via Phase Transfer in the Toluene-Water System and Application of Modified Nanoparticles to Cyclo-Olefin-Polymer-Based Organic-Inorganic Hybrid Films Exhibiting High Refractive Indices

Oleyl-phosphate-modified TiO₂ nanoparticles (OP_TiO₂) were prepared via phase transfer from an aqueous phase containing dispersed TiO₂ nanoparticles to a toluene phase containing oleyl phosphate (OP, a mixture of monoester and diester), and employed for the preparation of OP_TiO₂/cyclo-olefin polymer (COP) hybrid films with high-refractive indices. The modification of TiO₂ by OP was essentially completed by reaction at room temperature for 8 h, and essentially all the TiO₂ nanoparticles in the aqueous phase were transferred to the toluene phase. The infrared and solid-state ¹³C cross-polarization and magic-angle spinning (CP/MAS) NMR spectrum of OP_TiO₂ showed the presence of oleyl groups originating from oleyl phosphate. The solid-state ³¹P MAS NMR spectrum of OP_TiO₂ exhibited new signals at -1.4, 2.1, and 4.8 ppm, indicating the formation of Ti-O-P bonds. CHN and inductively coupled plasma analyses revealed that the major species bound to the TiO₂ surface was tridentate CH₃(CH₂)₇CH═CH(CH₂)₈P(OTi)₃. These results clearly indicate that the surfaces of the TiO₂ nanoparticles were modified by OP moieties via phase transfer. OP_TiO₂/COP hybrid films exhibited excellent optical transparency up to 19.1 vol % TiO₂ loading, and the light transmittance of the hybrid films with 19.1 vol % TiO₂ loading was 99.8% at 633 nm. The refractive index of these hybrid films rose to 1.83.

Pore orientation effects on the kinetics of mesostructure loss in surfactant templated titania thin films

The mesostructure loss kinetics are measured as a function of the orientation of micelles in 2D hexagonal close packed (HCP) columnar mesostructured titania thin films using in situ grazing incidence small angle X-ray scattering (GISAXS). Complementary supporting information is provided by ex situ scanning electron microscopy. Pluronic surfactant P123 acts as the template to synthesize HCP structured titania thin films. When the glass substrates are modified with crosslinked P123, the micelles of the HCP mesophase align orthogonal to the films, whereas a mix of parallel and orthogonal alignment is found on unmodified glass. The rate of mesostructure loss of orthogonally oriented (o-HCP) thin films (∼60 nm thickness) prepared on modified substrate is consistently found to be less by a factor of 2.5 ± 0.35 than that measured for mixed orientation HCP films on unmodified substrates. The activation energy for mesostructure loss is only slightly greater for films on modified glass (155 ± 25 kJ mol(-1)) than on unmodified (128 kJ mol(-1)), which implies that the rate difference stems from a greater activation entropy for mesostructure loss in o-HCP titania films. Nearly perfect orthogonal orientation of micelles on modified surfaces contributes to the lower rate of mesostructure loss by supporting the anisotropic stresses that develop within the films during annealing due to continuous curing, sintering and crystallization into the anatase phase during high temperature calcination (>450 °C). Because the film thickness dictates the propagation of orientation throughout the films and the degree of confinement, thicker (∼250 nm) films cast onto P123-modified substrates have a much lower activation energy for mesostructure loss (89 ± 27 kJ mol(-1)) due to the mix of orientations found in the films. Thus, this kinetic study shows that thin P123-templated o-HCP titania films are not only better able to achieve good orthogonal alignment of the mesophase relative to thicker films or films on unmodified substrates, but that alignment of the mesophase in the films stabilizes the mesophase against thermally-induced mesostructure loss.

L-cysteine-induced fabrication of spherical titania nanoparticles within poly(ether-imide) matrix

In the presented study, a new L-cysteine-containing diamine is synthesized and fully characterized and its application for the in situ sol-gel fabrication of poly(ether-imide)/titania nano hybrid materials is investigated. The electron microscopic photographs (TEM, FE-SEM and AFM) of the resulted materials confirm the production of spherical nanoparticles with well dispersion and narrow particle size distribution which is a usual challenge in the sol-gel methods. In addition to the positive effects on the particles morphology, the existence of amino acid containing pendant groups in the structure of polymer chains led to the comprehensive interaction with titania phase. As a result, the improvement in the flexibility of polymer backbone (as one of the most serious difficulties in polyimides processing) is obtained while its thermal stability dose is not sacrificed (confirmed by TGA and DSC techniques).

Refractive index investigation of poly(vinyl alcohol) films with TiO2 nanoparticle inclusions

The refractive index (RI) of polymer nanocomposite of poly(vinyl alcohol) films with TiO(2) nanoparticle inclusions with low concentration up to 1.2 wt. % was investigated. Accurate refractometric measurements, by a specially designed laser microrefractometer, were performed at wavelengths 532 and 632.8 nm. The influence of TiO(2) concentration on the RI dispersion curves was predicted based on the well-known Sellmeier model. The theoretical analysis, in a small filling factor approximation, was performed, and a relation between the effective RI of the nanocomposite and weight concentrations of the TiO(2) nanofiller was derived. The experimental values were approximated by two different functions (linear and a quadratic polynom). The polynomial approximation yields better result, where R(2)=0.90.