Vibrational Spectroscopy 68 (2013) 1–10 Contents lists available at SciVerse ScienceDirect Vibrational Spectroscopy jou r n al hom ep age: www.elsevier.com/locate/vibspec Vibrational spectroscopic study of poly(dimethylsiloxane)-ZnO nanocomposites L. Bistriˇ ci´ c a,∗ , V. Borjanovi ´ c a,b , L. Mikac c , V. Danani ´ c d a University of Zagreb, Faculty of Electrical Engineering and Computing, Unska 3, 10000 Zagreb, Croatia b International Technology Center, 8100-120 Brownleigh Drive, Raleigh, NC 27617, United States c Rud ¯er Boˇ skovi´ c Institute, Bijeniˇ cka 54, Zagreb, Croatia d University of Zagreb, Faculty of Chemical Engineering and Technology, Maruli´ cev trg 19, 10000 Zagreb, Croatia a r t i c l e i n f o Article history: Received 20 June 2012 Received in revised form 17 May 2013 Accepted 17 May 2013 Available online 27 May 2013 Keywords: Poly(dimethylsiloxane) ZnO nanoparticles Nanocomposite DFT Cross-linking a b s t r a c t A series of poly(dimethylsiloxane)-zinc oxide (PDMS-ZnO) nanocomposites having different concentra- tions of ZnO nanoparticles (0, 1, 5, 10 and 20 wt%) have been prepared. Raman and FTIR-ATR spectroscopic analysis was performed in order to determine the interaction between the ZnO nanoparticles and PDMS polymer matrix. Density functional theory (DFT) using the (B3-LYP)/6-311++G(2df,2p) method was used to investigate the vibrational spectra of PDMS. A complete vibrational assignment is supported by the normal coordinate analysis, calculated Raman activities as well as IR intensities. The presence of ZnO nanoparticles in PDMS gives rise to significant differences in relative intensities of the characteristic vibrational bands with respect to the cross-linked polymer. The changes in rela- tive intensities of Raman bands, as well as swelling measurements, were used to explain the effect of ZnO nanoparticles on the cross-linked structure of PDMS nanocomposites. It is established that ZnO nanoparticles influence the cross-linking density of the polymer matrix. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Polymer based nanocomposites have attracted increasing atten- tion because of their unique properties emerging from the combination of organic and inorganic materials. The incorporation of nanoparticles within a polymer matrix to create nanocompos- ites is a well-known technique to enhance material properties. Nanoparticles are able to intercalate and bond to the polymer chains, as a consequence of their high surface reactivity, which is attributed to the very large surface-to-volume ratio. The addition of inorganic nanoparticles to a polymer matrix improves or generates new physical properties such as thermal, mechanical, electrical, magnetic or optoelectronic properties. Therefore, nanocomposites offer significant potential in the development of advanced materi- als with potential applications in light emitting diodes, solar cells, optical sensors [1–3]. Zinc oxide (ZnO) is a direct band gap semiconductor with a room temperature wide band gap of 3.37 eV and a large exci- tonic (electron–hole) binding energy of 60 meV, larger than thermal energy at room temperature (26 meV). ZnO is also biocompati- ble and environmentally friendly. These properties make ZnO an interesting material with potential applications in optoelectronics, photovoltaics, lasers, photonics, biomaterial science, etc. [4]. ∗ Corresponding author. Tel.: +385 1 6129 670; fax: +385 1 6129 605. E-mail address: lahorija.bistricic@fer.hr (L. Bistriˇ ci´ c). The combination of ZnO nanostructures and polymers may achieve three specific goals: tailor or tune the properties of ZnO, tailor the properties of a polymer or/and create a hybrid nanocom- posite with unique or enhanced optical and electronic properties [2,5,6]. Poly(dimethylsiloxane) (PDMS) is the most commonly used silicone polymer [7]. Due to its good thermal stability, good biocom- patibility, low toxicity and high chemical resistance PDMS has great potential for applications in biomaterials science (implants, contact lenses, tissue engineering) [8–10]. It is also used in the aerospace as well as in the electronics and semiconductor industry. PDMS is a linear polymer that consists of an inorganic back- bone of alternating silicon and oxygen atoms. The repeating unit [ Si(CH 3 ) 2 O] consists of two methyl groups directly attached to the silicon atom. Linear PDMS polymer chains containing two vinyl end groups react with multifunctional cross-linker leading to a three-dimensional network. The properties of PDMS-based nanocomposite materials depend not only on the properties of their individual constituents, the volume fraction of filler, size and shape of nanofillers but also on their morphology, interfacial character- istics and the nature of the interphase that sometimes develops at the interface of the two components. The reinforcement of PDMS elastomers by fillers has been reported in several studies [Ref. [11] and ref. therein]. PDMS composites containing garnet parti- cles have been investigated for potential application in solid state lightning devices [12]. It has been shown that PDMS-ZnO nanocom- posites show laser-like emission behaviour at around 385 nm [13]. 0924-2031/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.vibspec.2013.05.005