Yang-Yen Yu

Transparent organic-inorganic hybrid thin films prepared from acrylic polymer and aqueous monodispersed colloidal silica

Highly transparent hybrid films containing nano-sized silica domain were synthesized from acrylic polymer and aqueous monodispersed colloidal silica (CS) with a coupling agent, 3-(trimethoxysilyl)propyl methacrylate (MSMA). The silica content in the hybrid thin films was varied from 0 to 50 wt.%. The experimental results showed that the silica particle size in the precursor solution and the hybrid films was varied from 20 to 40 nm. It could be controlled by the mole ratio of MSMA to silica. The results of scanning electron microscope (SEM), transmission electron microscope (TEM), and elemental analysis support the above conclusion. The prepared hybrid films showed high film uniformity and optical transparence. The thermal stability of the prepared hybrid films increased with the increasing silica content. The refractive index decreased linearly with the increasing silica fraction in the hybrid films. The experimental results suggest that the hybrid thin films have potential applications as passive films for optical devices.

Highly flexible and optical transparent 6F-PI/TiO2 optical hybrid films with tunable refractive index and excellent thermal stability

In this study, a synthesis route was developed for preparing highly transparent novel polyimide-nanocrystalline-titania hybrid optical films with a relatively high titania content (up to 50 wt%) and thickness (20–30 μm) from a soluble polyimide 6F-poly(p-hydroxy-imide) (6FPI). It has been demonstrated that the introduction of bulky CF3 groups into polyimide backbones enhanced both solubility and optical transparency. Furthermore, the attachment of hydroxyl groups provided the organic–inorganic bonding and resulted in homogeneous hybrid solutions by controlling the mole ratio of titanium butoxide : hydroxyl groups. AFM, SEM, TEM, and XRD results indicated the formation of well-dispersed nanocrystalline-titania. The flexible hybrid films revealed excellent optical transparency in the visible range, good surface planarity, high thermally dimensional stability, and tunable refractive index. A three-layer anti-reflection coating based on the hybrid films was prepared and revealed a reflectance of less than 0.7% in the visible range, indicating its potential optical applications.

Tunable dielectric constant of polyimide–barium titanate nanocomposite materials as the gate dielectrics for organic thin film transistor applications

We report on a systematic study of hydroxyl-containing polyimide (PI)–BaTiO3 (BT) nanoparticle (NP) nanocomposite dielectric materials, to determine the effects of BT NPs loadings (X) for X = 0, 2, 5, 8, 10, and 12 wt%, on p-type pentacene organic thin film transistors (OTFTs). A condensation reaction to produce well-dispersed BT NPs within the PI matrix was followed by spin-coating to form a dielectric thin film directly on a silicon substrate. The thermal, optical, surface, dielectric, and electrical properties of the PI–BPX hybrid dielectric composite correlated to BT content for each sample. The hybrid dielectric composites exhibit tunable insulating properties, including high dielectric constant values in the range 5.2–11.3, high capacitances from 3.1 to 27.9 nF cm−2 for a film thickness of approximately 350 nm, and low leakage current densities in the range of 1.85 × 10−7 to 2.76 × 10−6 A cm−2 at 2 MV cm−1. Bottom-gate top-contact OTFTs fabricated using various PI–BTX hybrid dielectrics, exhibit low threshold voltages of −4.09–2.62 V, moderately high field-effect mobility rates of 3.36 × 10−2∼2.32 × 10−1 cm2 V−1 s−1, and high ON/OFF ratios of approximately 105. This study opens a route towards transparent and highly stable hybrid dielectric materials with tunable dielectric properties, by careful selection of NPs and polymer matrix combinations.

Synthesis and Morphological Transformation of Conjugated Amphiphilic Diblock Copolymers in Mixed Solvents

The synthesis, morphological transformation, and photophysical properties of a rod-coil block copolymer, poly[2,7-(9,9-dihexylfluorene)]-block-poly(2-vinylpyridine) (PF-b-P2VP), with P2VP coils of various lengths in a mixed methanol/tetrahydrofuran (MeOH/THF) solvent are reported. Various morphological structures of PF-b-P2VP aggregates, including spheres, short worm-like structures, long cylinders, and large compound micelles (LCMs), were observed after varying the coil length of PF-b-P2VP and the selectivity of mixed solvents. These aggregated structures demonstrated considerable variation with regard to optical absorption, fluorescence, and the PL quantum yield of rod-coil copolymers. The degree of hypsochromic spectral shift was enhanced as the length of P2VP coils and the content of poor solvent increased. This study reveals the influence of coil length and selectivity of solvents on the morphology and the optical characteristics of rod-coil amphiphilic copolymers.

Morphological Transformation and Photophysical Properties of Polyfluorene-Based Luminescent Rod-Coil Block Copolymers

The morphologies, synthesis, and photophysical characterizations of poly[2,7-9,9-dihexylfluorene]-block-poly2-diethylaminoethylmethacrylate using amphiphilic rod-coil PF-b-PDEAEMA were demonstrated. The aggregation morphologies of PF13-b-PDEAEMA100 were manipulated by tuning the selectivity of mixed THF/methanol solvents with methanol contents ranging from 0 to 90 vol%. The morphological transformation of PF13-b-PDEAEMA100 caused significant changes in its photophysical properties, including absorption, fluorescence spectra, and fluorescence quenching. Moreover, the thermal stability of PF13-b-PDEAEMA100 was investigated by varying the annealing temperature. The results of the present study suggest that the solvent selectivity influences the photophysical properties and aggregation morphologies of rod-coil block copolymers in solid and solution states.