Study of Organic Phase Mobility in Nanocomposite Organic‐Inorganic Coatings

Abstract

Summary: Organic‐inorganic hybrids synthesized by a dual photopolymerization and condensation process from (i) two organic precursors, either poly(ethylene glycol) α,ω diacrylate ($\overline M _{\rm w}$ = 600) (PEGDA) or bisphenol‐A‐ethoxylate(15EO/phenol)‐dimethacrylate (BEMA), (ii) the organic‐inorganic bridging monomer (methacryloyl‐oxypropyl‐trimethoxysilane, (MEMO)) and (iii) the inorganic precursor tetraethoxysilane (TEOS) were investigated by differential scanning calorimetry (DSC) and dynamic mechanical spectroscopy (DMTA). It is found that progressive formation of the crosslinked network during the different steps of hybrid production results in changes of molecular mobility that show up in changes of the glass transition of the organic phase. While moving from the organic precursor to the final hybrid through the subsequent photopolymerization and condensation reactions, the transition is seen to broaden, decrease in intensity and shift to higher temperature. Excellent agreement of DSC and DMTA results is obtained. Dynamic mechanical analysis of the hybrids coated on PET film (coating thickness 10 and 40 µm) show an additional up‐shift of Tg, more marked in the case of the thinner hybrid coating. This result is attributed to molecular interactions at the substrate‐coating interface that locally hinder molecular mobility. The consequent increase of Tg is more evident when the coating layer is thin. The results show the potential of the DMTA technique in coating‐polymer substrate adhesion studies. Finally, the relaxation spectrum of the hybrids is sensitive to humidity absorbed from the environment and reversibly changes in absorption‐desorption cycles.

Preparation and Characterization of Hybrid Nanocomposites Coated on LDPE

“…In order to perform the measurement in bending mode, both on the 'free' hybrid films and on LDPE coated with hybrids, rectangular aluminium plates (dimensions: 5 Â 40 Â 0.6 mm 3 ) were used to sandwich the film samples. [14] The sandwich contained one hybrid film between two aluminium plates in the case of the free-standing samples, while for the ceramers coated on LDPE the sandwich was prepared by alternating two films with three aluminium plates, in order to enhance the signals of the hybrid coating.…”

“…Both techniques were recently shown to be particularly suited to the investigation of changes of organic phase mobility in ceramers. [13,14] Here, we report results on the hybrid Hyb-24-30, obtained by photocuring and thermally treating 4 h at 75 8C a mixture of 70% BEMAM-HBP-24 with 30% TEOS. Additional samples, obtained by UV-curing individual hybrid components and some of their mixtures were also analyzed for the sake of comparison.…”

“…The same samples investigated by DSC were analyzed by DMTA using small aluminium plates to provide a convenient support for the measurement of films in bending mode, [14] and the loss factor curves are reported in Figure 8. The DMTA spectra of all analyzed samples show a main relaxation process (a) and a lower-temperature secondary dissipation region (b).…”

“…[10][11][12] In this context, we earlier reported the synthesis and characterization of new hybrid systems obtained through the mentioned dual-curing process, using an organic poly(ethylene oxide) (PEO)-based dimethacrylate oligomer precursor (BEMA 1400), tetraethoxysilane (TEOS) and methacryloyloxypropyltrimethoxysilane (MEMO) as the interphase agent. [13,14] The hybrids were nanostructured, transparent and thermally stable. [13] When coated on poly(ethylene terephthalate) (PET), they showed good adhesion to the substrate.…”

“…[13] When coated on poly(ethylene terephthalate) (PET), they showed good adhesion to the substrate. [14] The aim of this work is to extend the study of ceramer synthesis via double curing, by incorporating in the reaction mixture a hyperbranched polymer (HBP) bearing acrylic groups. It is well known that the use of HBPs with densely branched structures and a large number of reactive end-groups is very attractive, especially for coating and thermoset applications.…”