Scratch and Abrasion Resistant Coatings on Plastic Lenses—State of the Art,Current Developments and Perspectives

The manufacturing of ophthalmic lenses is one of the most important markets worldwide and, therefore, strong research efforts are undertaken to continuously improve the quality of the products, either silicate glasses or organic polymer lenses. Hybrid sol-gel based materials play a major role in this highly competitive field and have contributed significantly to the commercial success of the organic base materials. Recent developments concern fast curing and patternable coatings that might soon become part of this business. The compatibility of hybrid sol-gel materials either with organic dyes or with inorganic vacuum borne coatings offers further possibilities to develop highly sophisticated lenses meeting not only customer needs like perfect corrective function, high optical quality and protection, but also high durability as well as cosmetic and decorative aspects. An overview and a few recent developments are outlined below.     

Industrial Application of Hybrid Sol-Gel Coatings for the Decoration of Crystal Glassware

The coloration of glass via melting techniques presents some unique problems with respect to the reproducibility, toxicology and economics of certain colors, especially if the market demands are highly variable. This is also the case for consumer products such as crystal glass and tableware. Traditionally, the decoration of crystal glasses is performed by laborious manual techniques, which are costly and do not meet modern market requirements. Alternatively, spraying of colored lacquers is a highly flexible and valuable tool for the development of new products. Sol-gel type hybrid coatings provide several advantages compared to conventional organic systems like high abrasion resistance, almost perfect adhesion, refractive index matching and sufficient stability in dishwashing procedures. The solubility of organic dyes in the hybrid matrix is sufficient for intense colors even at rather low layer thicknesses, which on the other hand convey the high brilliance of the base material. The development of transparent, translucent and opaque hybrid coatings for crystal glass has been completed in the last few years and the production of partially coated articles has started recently. The synthesis and properties of the coating material are reviewed and the industrial process and first market results are also outlined.     

Inorganic-Organic Cross-Linking in UV Curable Hard Coats Based Upon Vinyltriethoxysilane-Tetraethoxysilane-Polyfunctional Acrylate Hybrid Polymers: A Raman Spectroscopic Study

Hydrolysis, polycondensation and UV-induced radical polymerization processes in binary and ternary mixtures of vinyltriethoxysilane (VTEOS), tetraethoxysilane (TEOS), and several polyfunctional acrylates as reactive diluents were studied by means of FT-Raman and confocal micro-Raman spectroscopy. The study comprises measurements on sols, gels, xerogels, and thin films applied on top of glass slides and polymeric substrates. Characteristic Raman bands are utilized to gain information about the structural evolution, inorganic network connectivity, and organic cross-linking reactions. Supplementary, ²⁹Si-NMR spectroscopic data are considered and correlated with Raman data. Structure-property correlations based on spectroscopic and mechanical data are outlined and discussed. It is demonstrated that thin hybrid polymer films may be studied in-situ by means of confocal micro-Raman spectroscopy.     

Zur Struktur der basischen Diquecksilber(I)-nitrate. I kristallstruktur des Hg2OH(NO3) · Hg2(NO3)2

The Crystal Structure of the Basic Dimercury (I) Nitrates. I. The Crystal Structure of Hg₂OH(NO₃) · Hg₂(NO₃)₂ The unit cell of Hg₂OH(NO₃) · Hg₂(NO₃)₂ is orthorhombic, space group Cc2a - standard setting Aba2 (C) — with a = 2017.1(5) pm, b = 935.8(3) pm, c = 1121.7(3) pm and contains 8 formula units. Characteristic are chains [Hg₂OH(Hg₂)_2/2]³⁺ parallel [001]. These are interconnected to a three-dimensional network by nitrate ions coordinated to mercury. The structure achieves additional stabilization through weak hydrogen bonds between oxygen atoms of the hydroxy groups and neighbouring nitrate ions. The bonding relationship of one hydrogen atom to four tetrahedrally correlated oxygen atoms is discussed.     

Zur Struktur der basischen Diquecksilber(I)-nitrate. II. Kristallstruktur des Hg10(OH)4(NO3)6

Crystal Structure of the Basic Dimercury(I) Nitrates. II. Crystal Structure of Hg₁₀(OH)₄(NO₃)₆ . The crystal structure of Hg₁₀(OH)₄(NO₃)₆ has been determined from single crystal x-ray diffraction data. The unit cell is triclinic, space group P1 , a = 999.4(5), b = 909.9(5), c = 765.9(2) pm, α = 85.98(4), β = 78.70(3), γ = 109.83(5)°; Z = 1, R = 6.2%, R_w = 8.2%. Finite cationic chains [(Hg₂)₅(OH)₄(NO₃)₂]⁴⁺ are joined together by weak van der Waals-type interactions between neighbouring Hg and O atoms, thus forming ribbons running along [100]. The coordination sphere of the Hg atoms is completed by further nitrate ions, which lead to the formation of a loose framework. Thereby the metal atoms are not surrounded by simple coordination polyhedra.     

Sol-gel derived hybrid polymers as alternative materials for optical data storage in the frequency domain

Sol-gel derived hybrid organic-inorganic materials show attractive properties as alternative media for optical data storage in the frequency domain. Doping of the matrix is easily achieved by dissolving different types of organic dyes in appropriate amounts in the clear sols, obtained via cohydrolysis and -condensation of 3-glycidoxypropyl-trimethoxysilane and aluminium-tri (secondary butylate).By evaporating volatile solvents and drying the resulting gel at room temperature, the dyes are trapped in the hybrid network. Surprisingly narrow spectral holes in the absorption bands of the dyes were generated by photophysical or photochemical hole-burning at very low temperatures. For dihydroxyanthraquinone/YbCl₃-complexes the measured holewidth of 2,1 GHz at 3,94 K is about 1/5 of that found for the same complex in an ethanol/methanol glass.     

Functional coatings on glass using ORMOCER®-systems

Sol-gel derived ORMOCER^® materials (organically modified ceramics) have been developed for the functionalization of glass. The adjusted coating systems can be applied in optical quality by conventional paint technologies. Good long-term adhesion, scratch and abrasion resistance, stability against weathering and resistance towards corrosive delamination are additional outstanding advantages of such coating systems. The ORMOCER^® coatings can also carry additional functions. For example, the surface polarity of glass can be modified. Hydrophilic as well as extremely hydrophobic surfaces can be attained. The contact angles measured with water range between 10° and 110°. Furthermore, colouring of glass articles is possible with coatings containing chromophores.     

Hybrid Pigments via Sol-Gel Processing

The incorporation of organic dyes into inorganic and hybrid sol-gel derived materials is a valuable method for the fabrication of colored layers for optical applications like filters, solar energy conversion, non-linear optical devices, and active laser media. There have been clear hints for photochemical stabilization of the organic dyes, therefore, our aim was to investigate the light stability of organic dyes within hybrid solids. Besides the traditional way of doping sol-gel coatings with dyestuffs, they were also covalently attached to the hybrid matrix and pigments were produced by spray-drying processes.The resulting spherical powders were investigated with respect to their morphological, structural and photochemical properties. The results show that uniformly shaped and colored hybrid pigments can be synthesized. The spectroscopic studies demonstrate the fixation of the dye to the matrix and the high degree of crosslinking achieved in the composite. Additionally, the hybrid pigments drastically improve the resistance of the dye against bleeding from thermoplastic polymers. Furthermore, a higher photochemical stability of the dye is observed within the hybrid matrix compared to a solution, and purely organic or inorganic solid hosts.     

FT-Raman-Spectroscopic Investigations of the System Glycidoxypropyltrimethoxysilane/Aminopropyltriethoxysilane

The base catalyzed sol-gel process in the system 3-glycidoxypropyltrimethoxysilane (GPTS)/3-aminopropyltriethoxysilane (APTS) is highly interesting for the synthesis of hybrid (inorganic-organic) polymers. FT-Raman spectroscopy with excitation in the near infrared as a versatile tool for in situ measurements was used to monitor the kinetic behavior of the hydrolysis reaction.An unexpected slow-down of the hydrolysis of GPTS recorded at higher temperatures can be attributed to a decrease of the pH-value during hydrolysis caused by silanol groups. After condensation has started, the pH-value reincreases and forces hydrolysis to reaccelerate. The results strongly suggest the existence of a pentacoordinated transition state with a negative charge at the silicon atom during base catalyzed hydrolysis.     

Zur Struktur der basischen Diquecksilber(I)-nitrate. III. Kristallstruktur des Hg4O2(NO3)2

Crystal Structure of the Basic Dimercury(I) Nitrates. III. Crystal Structure of Hg₄O₂(NO₃)₂ Hg₄O₂(NO₃)₂ crystallizes monoclinic, space group P2₁/a – standard setting P2₁/c (C) – with a = 1158.0(2), b = 666.4(1), c = 553.3(1) pm, β = 98.82(1)° and Z = 2. The structure determination from single crystal diffractometer data (AgKα, 1170 I₀(hkl), numerical absorption corrections applied) resulted in a final R = 0.0512 (R_w = 0.0685). The mixed valence compound is built up of puckered layers [(Hg^II)_2/2O(Hg)_1/2]⁺ parallel (201). Within the layers there are exclusively covalent Hg? Hg and Hg? O bonds; whereas the linkage between the layers is achieved by weak Hg^I? O contacts and by nitrate ions functioning as weak bridging ligands for mercury atoms. This layer structure explains the distinct cleavage of crystals of Hg₄O₂(NO₃)₂.