Herbert Krug

Fine patterning of thin sol-gel films

Abstract An embossing technique was used to fabricate surface reliefs in organically modified ceramics of the Ormocer type, synthesized via the sol-gel route. Embossing techniques for these materials are described and results of embossed grids and gratings with up to 2400 lines/mm and peak-to-trough values up to 3 μm are presented.

Tailoring of thermomechanical properties of thermoplastic nanocomposites by surface modification of nanoscale silica particles

Thermoplastic nanocomposites based on linear polymethacrylates as matrix materials and spherical silica particles as fillers have been synthesized using the in situ free radical polymerization technique of methacrylate monomers in presence of specially functionalized SiO{sub 2} nanoparticulate fillers. Uncoated monodisperse silica particles with particle sizes 100 nm and 10 nm were used as reference fillers. For surface modification, the alcoholic dispersions of the fillers were treated with appropriate amounts of methacryloxypropyltrimethoxysilane (MPTS) and acetoxypropyltrimethoxysilane (APTS). Transmission electron microscopy (TEM) was used to investigate dispersion behavior in dependence on surface modification. Dynamic mechanical properties were measured by dynamic mechanical thermal analysis (DMTA).

Organic-inorganic composite materials: optical properties of laser-patterned and protective-coated waveguides

A composite materials based on organically modified Si alkoxides and modified alkoxides from Zr were prepared. The index of refraction of the system was tailored by the variation of the modified Zr component. Channel waveguides were prepared by a laserwriting technique based on the ability to photopolymerize this material. To decrease optical loss caused by effects of the waveguide surface and to be independent of the used substrate, a buffer layer and a protective layer of the same material of lower index of refraction was combined with a waveguiding film and optical losses were determined.

The Sol-gel process for nano-technologies : new nanocomposites with interesting optical and mechanical properties

Various nanocomposite systems have been synthesized by sol-gel routes. For this reason, prefabricated nanoparticles (SiO2 sols or boehmite powder) have been dispersed after surface modification in sol-gel-derived organically modified or polymeric ligand matrices. In all cases, a significant effect on dispersibility by surface modification could be observed. After curing, the mechanical or optical properties depend strongly on the dispersion and surface modification. Using these results, composites to be used in chip coupling and as hard coatings on polycarbonate and CR 39 have been developed.

Characterization of Electrochromic WO3-Layers Prepared by Sol-Gel Nanotechnology

Stable tungsten oxide coating sols suitable for electrochromic applications were prepared by a modified peroxotungstic acid route. Layers up to 250 nm thickness could be deposited on ITO-coated and/or FTO-coated glass substrates in a single dip-coating process. Optoelectrochemical measurements were employed to determine the variation of the electrochromic properties (change in optical density (ΔOD) and switching times) of WO3-layers, investigated as a function of coating parameters, such as chamber humidity and the temperature of heat treatment. High resolution transmission electron microscopy (HR-TEM) has shown that the optimized layers possess a partially crystalline morphology with nanocrystalline regions 2–3 nm in size.

Synthesis and characterization of novel aramid-zirconium oxide micro-composites

Abstract New micro-composites containing different proportions of zirconium oxide in aromatic polyamide have been prepared via a sol-gel process. Poly(phenyleneterephthalamide) chains with carbonyl chloride end groups were synthesized by reacting a mixture of p- and m-phenylene diamines with terephthaloyl chloride. The chain ends were endcapped with aminophenyltrimethoxysilane. Appropriate amount of zirconium propoxide solution (82.3 wt.%) in propanol was mixed in the polymer solution and then a stoichiometric amount of water was added to the mixture to carry out the hydrolysis of methoxy and propxy groups. Hybrid materials using different proportions of zirconium propoxide in the organic polymer were thus prepared. Thin films cast from this material were transparent, yellow in color and tough. A gradual increase in the tensile strength was observed with increase in the zirconia content (up to 10%). The tensile modulus of the hybrid mixture was in the range of 2.7 to 4.0 GPa at 25°C. The values of the tensile strength varied from 163 to 203 MPa at 25°C. The maximum strain at the break point initially increased but then decreased with further addition of zirconia. The glass transition temperature determined from the maxima of the tan δ data using dynamic mechanical thermal analysis increased with increase in the zirconia content. The thermal decomposition temperature of the hybrid material measured through thermogravimeteric analysis was around 450°C.

Development of optical waveguides by sol-gel techniques for laser patterning

ORMOCERs with high optical performance and chemical stability are synthesized via the sol-gel process. Methacrylate group substituated silanes are copolymerized with methacrylic acid which acts as a chemical link between Zr as second inorganic network former. Chemical stable complex formation is proved by IR analysis and 13c NMR investigations. This material is laser patternable by the addition of a suitable photoinitiator and is characterized by high dielectric strength and low optical loss for applications in optics and non-linear optics.

Dynamics of the sol-gel transition in organic-inorganic nanocomposites

Abstract Two different techniques have been used to follow the gelation of photochromic organic—inorganic nanocomposites. The variations of molecular and macromolecular motions in these complex systems have been analyzed. Photo-correlation spectroscopy probes the formation of the gel network. Forced Rayleigh scattering experiences the microstructure of the mixtures via the measurement of the translational diffusion coefficient of entrapped photoreactive targets. In the different mixtures, a drop of the network mobility could be observed around the sol to gel conversion, while the entrapped molecules do not experience the macroscopic transition.

Generation of wet-chemical AR coatings on plastic substrates by the use of polymerizable nanoparticles

Multi-layer interference filters of surface modified SiO2- and TiO2-nanoparticles have been produced on polycarbonat (PC) and on scratch resistant film. AR-coatings (anti-reflex- coatings) were prepared from a dispersion of SiO2 and TiO2 colloidal nanoparticles in a hybrid inorganic organic matrix. The TiO2 particles have been synthesized by addition of HCl and H2O to a solution of titanium tetraisopropanolate in isopropanol. The SiO2 nanoparticles were synthesized by base catalyzed hydrolyses and condensation of tetraethoxysilane (TEOS) mixed with an aqueous solvent. The surface modification of the TiO2 and SiO2 nanoparticles with 3-glycidoxypropyltrimethoxysilane (GPTS) avoids the agglomeration of the nanoparticles and covalent bonds between the matrix and nanoparticles are formed during a photopolymerization step. The nanoparticles were dispersed in a hydrolyzed GPTS matrix and UVI Cygacure 6974 was added as a photoinitiator. The (lambda) /4 ((lambda) equals 550 nm) films of TiO2 and SiO2 sols were prepared on PC and on scratch resistant coated PC by spin-coating techniques. The refractive index of the SiO2/TiO2-coatings can be adjusted from 1.47 up to 1.94 depending on the SiO2 or TiO2 concentration. By the combination of index matching and photopolymerization, a low temperature interference filter can be realized for plastic substrates with reflection of 0.5% at 550 nm. The coatings show excellent adhesion to the substrates in the cross hatch test and promising mechanical properties.

All sol—gel electrochromic system for plate glass

Abstract The development on an all sol—gel electrochromic system for large area devices is described. Previously developed syntheses routes for tungsten oxide, WO3, coating sols and cerium oxide-titanium oxide sols, CeO2TiO2, were employed, which enabled large substrates (35 × 35 cm2) to be coated homogeneously and without visible cracking. Optoelectrochemical measurements were employed to determine the variation of the electrochromic properties (change in optical density, ΔOD, and switching times) of WO3 layers, investigated as a function of coating parameters, such as chamber humidity and the temperature of heat treatment. A novel composite electrolyte system, based on organically modified silanes, was developed, which has an ionic conductivity of ∼10−5 S cm−1 at 25°C. Cells were constructed in two formats: 10 × 15 cm2 and 35 × 35 cm2. Switching times less than one minute were achieved for the smaller format with a change in transmission from 75% to 20% (at λ = 0.633 μm).