Structure of hybrids based on TEOS-cyclic forms of siloxane system Marek Nocun * , Katarzyna Cholewa-Kowalska, Maria La ˛ czka Faculty of Materials Science and Ceramics, AGH-University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland article info Article history: Received 22 June 2009 Accepted 27 August 2009 Available online 2 September 2009 Keywords: Sol–gel Hybrid glasses Organic–inorganic Structure Optical properties abstract Hybrid glasses based on tetraethoxysilane (TEOS) modified by addition of selected cyclosiloxanes have been prepared by sol–gel method. Octamethylcyclotetrasiloxane (D4) and 2,4,6,8-tetramethyl-2,4,6,8- tetravinylsiloxane (VMC) have been chosen as an organic modifier of the silica matrix. Molar ratio of TEOS to cyclosiloxane varied from 1:0 to 1:0.5. Structure of prepared hybrids has been studied by infrared spec- troscopy (FTIR), photoelectron spectroscopy (XPS) and nuclear magnetic resonance spectroscopy (NMR). Optical properties of bulk glasses in the visible range have also been reported. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction Sol–gel technique gives the possibility to introduce organic mole- cules into the inorganic matrices. As the process is carried out in the solution the homogeneity can be obtained at the molecular level. Such hybrid materials comprise properties of inorganic materials such as high scratch resistance, hardness, high corrosion resistance and prop- erties of inorganic materials like high flexibility. Organic–inorganic hybrids create new class of materials with possible application in many fields like optoelectronics [1], hard optical coatings [2], and cor- rosion resistant coatings [3]. Hybrids are also starting materials for preparation many oxide and non-oxide ceramic powders and fibers like SiC [4], Si 3 N 4 [5,6] and others [7]. Two classes of hybrid materials are currently distinguished depending on whether the interaction be- tween organic and inorganic molecules are week and only hydrogen and van der Waals bonds are formed – class I or strong interactions lead to formation of strong covalent or ionic bonds – class II. Type of the structure has an implication on the physical and chemical proper- ties of the material. The main goal of this work was to prepare and study structure of the hybrids with silica matrices modified by addi- tion of selected cyclosiloxanes. Because of high resistance of cyclo- siloxanes to degradation by UV radiation [8] these hybrids can be considered as outer protective coatings. 2. Preparation procedure Pure reagents were used to synthesize samples of hybrid glasses. TEOS and VMC were purchased from Sigma–Aldrich, D4 from Degussa, ethyl alcohol (96%) and hydrochloric acid from Pol- ish Chemicals. Structure of D4 and VMC is shown in Fig. 1. D4 is build up with 4-member SiAO ring and contain eight methyl groups while VMC has four methyl groups and four vinyl groups. Molar ratio of TEOS:C 2 H 5 OH:H 2 O:HCl was kept 1:2:2.5:0.05 while TEOS:D4 ratio ranged from 0.1 to 0.5 and TEOS:VMC from 0.1 to 1 M. Preparation route of hybrids is shown in Fig. 2. FTIR analyses were carried out on BIO-RAD FTS-6000 spectrom- eter. Absorption spectra were measured from 400 to 4000 cm 1 using KBr pellet technique. The resolution was 1 cm 1 for all re- corded spectra. XPS spectra were recorded on VSW spectrometer equipped with hemispherical analyzer. Data were collected in the FAT 22 resolution mode. Mg Ka X-ray radiation with 200 W energy was used as the excitation source. Spectra were calibrated on a main carbon C1s peak at the 284.6 eV position. Transmittance spectra were recorded using Perkin–Elmer Lambda 19 double beam spectrometer in the range of 300 nm to 900 lm with a reso- lution 1 nm. The transmittance measurements were carried out on the samples ‘‘as received” without any preparation. 29 Si MAS NMR measurements were carried out using NMR spectrometer at the magnetic field of 7.05 T. 3. Results 3.1. FTIR Results of IR analysis of the gels from the TEOS-D4 system are shown in Fig. 3. Introduction of D4 into the TEOS gel leads to aris- ing absorption bands at 2965, 1264, 1030, 851 and 803 cm 1 and week band at 704 cm 1 . Bands at 949 and 459 cm 1 observed in pure TEOS gel vanished – Fig. 3a. Increasing amount of D4 leads 0022-2860/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.molstruc.2009.08.034 * Corresponding author. Tel.: +48 507787348. E-mail addresses: nocun@uci.agh.edu.pl, nocun@agh.edu.pl (M. Nocun). Journal of Molecular Structure 938 (2009) 24–28 Contents lists available at ScienceDirect Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc