INVESTIGATION OF POLYMER DYNAMICS IN PVB-ATO NANOCOMPOSITES BY LOW-FIELD AND FAST FIELD-CYCLING 1H NMR RELAXOMETRY

Nanocomposites of polymers and inorganic fillers are materials of great interest for many practical applications. Polyvinylbutyral (PVB) is an amorphous polymer employed as an inter-layer film in laminated safety-glass manufacture industry thanks to its high optical clarity and good adhesion to glass. Additional interesting properties can be obtained by adding a filler to the PVB matrix. Indeed, PVB loaded with Antimony doped Tin Oxide (ATO) nanoparticles is able to filter out the near infrared waves of sunlight, while maintaining transmission in the visible region [1]. Given the worldwide energy saving and environmental preservation policies, this property seems promising for applications in building and vehicle glass construction. In view of the optimization of PVB-ATO nanocomposites for applicative purposes, a thorough characterization of its structural and dynamic microscopic properties is necessary. To this aim, we studied PVB films loaded with 0, 5 and 23 wt% of ATO nanoparticles across the polymer glass transition (Tg = 70 oC) by means of low-field (20 MHz) and fast field-cycling (FFC) 1H NMR relaxometry. Both uncoated and surface modified (with methacryloxypropyltrimethoxysilane) nanoparticles were dispersed in the polymer matrix. Analysis of the FIDs recorded in solid-echo experiments with different echo delays and of the dispersion curves obtained by measuring 1H longitudinal relaxation times by FFC in the 0.01 to 35 MHz frequency range allowed us to investigate the effects of the nanoparticles on the polymer dynamics and to quantitatively determine the fractions of polymer with different mobility. In particular, it was observed that the surface-modified particles do not affect the dynamics of the polymer matrix at any loading level in the whole temperature range investigated. On the contrary, the uncoated particles induce a slowing down of the polymer motions above the glass transition but do not significantly affect them below it. Our data demonstrate the crucial role played by the particle surface in influencing the polymer dynamics. References [1] G. Zhang, W. Yan, T. Jiang J. Wuhan University of Technology-Mater. Sci. Ed. 28, 912-915 (2013)