Optical properties of a polyethylene dispersion with a luminescent silica prepared by surface grafting of a perylene derivative Angela Cardelli, Lucia Ricci ⇑ , Giacomo Ruggeri, Silvia Borsacchi, Marco Geppi Dipartimento di Chimica e Chimica Industriale, Università di Pisa, v. Risorgimento 35, 56126 Pisa, Italy article info Article history: Received 4 January 2011 Received in revised form 21 April 2011 Accepted 9 May 2011 Available online 13 May 2011 Keywords: 13 C- 29 Si- and 1 H-MAS Fluorescence spectroscopy Luminescent silica filler Perylene aggregation Solid state NMR abstract A micrometric silica modified with perylene derivative (SiO 2 –TES) has been prepared by hydrolysis–condensation reactions between silica and N,N’-bis-(3-triethoxysilylpropyl)- perylene-tetracarboxyldiimide (P-TES) and utilized as filler in LLDPE films together with a compatibilizer. Spectroscopic analyses on SiO 2 –TES confirmed the grafting of P-TES on silica, while its amount was determined by thermogravimetric analysis. Solid state NMR provided information about the structure of silicon atoms involved in the condensation of SiO 2 and P-TES that resulted mainly in silicon atoms grafted with bi-dentate anchorages. UV–Vis and fluorescence analyses carried out on P-TES showed the ability of the dye to generate J-type aggregates in apolar solvents. The same analyses on SiO 2 –TES revealed the presence of both isolated and aggregated dye molecules grafted on silica surface, while on polymeric dispersions of SiO 2 –TES, they have shown only the presence of P-TES aggregates grafted to silica. Thanks to the direct correlation between optical properties (obtained both by UV–Vis and by fluorescence analyses) and the chemical environment of composites, the lumines- cent silica SiO 2 –TES could be used to estimate the filler dispersion extent in different microcomposite polymer materials. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Over the last few years, nano-hybrid materials based on organic polymers and inorganic fillers represent one of the most attractive world in materials chemistry. The advan- tage of these systems consists in the great possibilities of combining different properties in one material. On the other hand, the basic science of these compounds is often not completely understood. Therefore, studies in this field (in particular to analyze the structure–property relation- ships) are crucial [1]. Both nano- and micro-composites are important classes of materials in which the properties of a polymer matrix can be dramatically improved even with small filler load- ings [2,3]. The composites exhibit improved modulus [4], heat resistance [5], gas permeability [6] and flame retar- dancy [7], with respect to the pristine polymers [8]. Among composites, those based on polyolefin matrices are of par- ticular interest because of the necessity to improve the performances in packaging and engineering applications [9]. Many methods to prepare composites can be adopted, but melt processing is the best one to produce composites for commercial uses [10,11]. However, polymers such as polyethylene, that is one of the most widely used, only weakly interact with mineral surfaces, making the synthe- sis of polyolefin composites by melt compounding consid- erably difficult [12,13]. To overcome this problem, the interfacial interaction between fillers and polyolefin has been improved by using polymer compatibilizers, such as maleic anhydride grafted polyethylene (PE-g-MAH) [14], or by grafting to the filler surface functional groups that can act as coupling agents [15–17]. Chemically modified silicas have been widely used for different purposes, for example as supports for biological 0014-3057/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2011.05.006 ⇑ Corresponding author. Tel.: +39 050 2219358; fax: +39 050 2219260. E-mail address: lucia.ricci@ns.dcci.unipi.it (L. Ricci). European Polymer Journal 47 (2011) 1589–1600 Contents lists available at ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj