G. Schottner

Confocal Micro-Raman Spectroscopy: Theory and Application to a Hybrid Polymer Coating

Confocal micro-Raman spectroscopy has been applied for vibrational investigations on a sol-gel derived hybrid polymer coating. In order to characterize the dimensions of the focus inside the coating, the substrate, and the coating/substrate, a model that considers both the refraction and diffraction effects has been developed. A coating of ∼20.2 μm thickness applied to polycarbonate substrate has been investigated. The spatial distribution of the Raman intensity in the focal volume was studied at different depths within the sample and the Raman response at the corresponding levels has been calculated. The selection in depth of the Raman response, given by the confocal pinhole, was also taken into account. In comparing the prediction of this theoretical model to the empirical results, a good agreement has been observed.

Confocal Raman investigations on hybrid polymer coatings

Abstract Confocal Raman spectroscopy has been applied to investigate polycarbonate substrates equipped with sol–gel derived hybrid polymer films 20.2 and 6.2xa0μm in thickness. The spatial intensity distribution of the Raman bands by varying the focal position within the sample has been studied by means of confocal Raman spectroscopy. The dimensions of the focus within the different sample regions have been characterized by a modified theoretical model that considers not only the refraction effect, but also diffraction effect. The interfacial coating/substrate region has been experimentally and theoretically studied.

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.

Polarized Raman Spectra from Some Sol-Gel Precursors and Micro-Raman Study of One Selected Copolymer

The polarized Raman spectra of γ-substituted propyl-trialkoxysilanes have been recorded, and an assignment is proposed. The spectra are briefly discussed with emphasis on the glycidoxy compound (IV). Micro-Raman data are also given for the co-condensation product of a 5:95 mixture of III and IV. The copolymer spectrum is compared to the precursor spectrum to show the effect of condensation on some selected vibrational bands. No bands for residual, noncondensed Si-OH groups are found in the polymer spectrum from which condensation to a three-dimensional network can be assumed to a high degree. The epoxy ring-breathing vibrational band indicates the ring to be cleaved only to a minor extent by reaction with the base catalyst.

Electrochromic devices based on in situ polymerised EDOT and Prussian Blue: influence of transparent conducting oxide and electrolyte composition—towards up-scaling

Inorganic/organic (hybrid) complementary electrochromic devices (ECDs) of the type [transparent conducting oxide (TCO)//inorganic counter electrode/hydrophobic electrolytic membrane/polymeric working electrode//TCO] were assembled. The working electrodes consisted of spin-coated polymer films prepared by moderator-controlled in situ oxidative chemical polymerisation of 3,4-ethylene dioxythiophene (EDOT). Thin, galvanostatically deposited Prussian Blue (PB) films were employed as counter electrodes. Besides Fu2006:u2006SnO2 (FTO)/glass and Snu2006:u2006In2O3 (ITO)/glass, a flexible ITO/PET film was alternatively used for materials deposition. In order to attain the maximum device performance, the PB charge capacity was monitored and adapted to the capacity of the EDOT polymer films. The two electrochromic electrodes were separated by a novel hydrophobic polymer electrolyte based on a gel of 1-butyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide (BMI-TFSI) and poly(methylmethacrylate) (PMMA), with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the salt. The influence of two parameters—ITO sheet resistance and the PMMA content in the electrolyte—on the final device properties was investigated. The ITO sheet resistance value proved to be crucial for the switching kinetics. The variation of the weight ratio of PMMA in the electrolyte showed that the effect on the kinetics is small whereas the change in absorbance is highly affected. The properties of the complementary glass-based devices were eventually compared to the corresponding plastic-based electrochromic elements. First attempts to scale up the technology were made for flexible 12 × 15 cm2 (active area) devices.

Comparison of PEDOT Films Obtained via Three Different Routes through Spectroelectrochemistry and the Differential Cyclic Voltabsorptometry Method (DCVA)

The performance of different poly(3,4-ethylenedioxythiophene) (PEDOT) films was compared by electrochemical, spectroelectrochemical, and time-derivative measurements of absorbance versus potential (linear potential-scan voltabsorptometry) for an overall spectroelectrochemical characterization of the electrochromic properties in ionic liquids such as 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMITFSI). The time-derivative signals were monitored at different wavelengths, and information obtained therefrom was complementary to that obtained from conventional cyclic voltammetry. PEDOT films prepared via in situ chemical oxidative polymerization appeared to be much more efficient than electropolymerized and PEDOT-poly(styrenesulfonate) (PSS) reference films, in terms of both contrast ratio and coloration efficiency, which was the case even for PEDOT films deposited on less conductive flexible plastic substrates.

FT-Raman spectroscopic investigations on the organic crosslinking in hybrid polymers. Part II: Reactions of epoxy silanes

FT-Raman spectroscopy was used together with supplementary 13C-NMR measurements to analyze the reaction of the epoxy moieties of 3-glycidoxypropyltrimethoxysilane and 5,6-epoxyhexyltrimethoxysilane during sol-gel processing. Based on the results for simple epoxides reported in Riegel, Kiefer, Hofacker and Schottner (Appl. Spec. 54, 1384 (2000)) the formation of β-hydroxy methyl ethers can be derived. An additional condensation of the epoxy rings yielding a mixture of oligo ethers is considered very probable from the Raman measurements. Raman and NMR assignments are proposed for 5,6-epoxyhexyltrimethoxysilane.

FT-Raman Spectroscopic Study of the Structural Evolution in Binary UV-Curable Vinyltriethoxysilane/Tetraethoxysilane Mixtures from the Sol to the Xerogel State:

Fourier transform Raman spectroscopy was used in order to study acid catalyzed hydrolysis and polycondensation processes from the sol via the gel until the xerogel state in binary mixtures of vinyltriethoxysilane (ViTEOS) and tetraethoxysilane (TEOS). Supplementary 29Si-, 13C-MAS-NMR, and FT-IR data were considered. Intermediate hydrolysates, oligomers, and polycondensates were detected independently of the samples physical state. Vibrational assignments are given for pure ViTEOS and its partially hydrolyzed intermediates. The corresponding mono-, di-, and tri-hydroxylated species are found to exhibit characteristic νsym(CSiO3) vibrational modes in the 650–672 cm−1 region. Subsequent oligomerization results in a progressive shift of the νsym(CSiO3) bands towards lower wavenumbers. Condensation proceeds faster in ViTEOS–TEOS mixtures than in pure ViTEOS. Assignments for some early oligomeric species and some network connectivity are given. The Raman spectra suggest that the main building blocks of the evolving network are already present in the wet gels. Moreover, it is shown that residual ethoxy groups attached to the siloxane network are still present in xerogels, whereas no silanol groups are detected. The spectra demonstrate that the vinyl groups did not react under the applied conditions. This system has potential for the preparation of UV-curable abrasion-resistant coatings for plastic substrates.