Thermal and dielectric studies of PEG/C/AST nanocomposites

Abstract

C/AST/PEG nanocomposites with fumed AST (89 wt % Al 2 O 3 , 10 wt % SiO 2 , 1 wt % TiO 2 ), activated carbon, and poly(ethylene glycol), PEG, were prepared in a wide range of PEG and C/AST (1 : 9) contents. Thermal transitions (mainly in a PEG phase) were investigated by differential scanning calorimetry. The dynamic behavior was investigated by thermally stimulated depolarization current and dielectric relaxation spectroscopy. The PEG crystallinity degree decreases in the nanocomposites, in particular at C PEG 40 wt %. A significant fraction of amorphous polymer is immobilized at a filler surface making no contribution to the glass transition, whereas the rest exhibits a lower glass transition temperature, when compared with bulk polymer, because of loosened molecular packing of the chains. Several relaxations arising from the polymer matrix, the filler, and their combination were identified and analyzed. The segmental a-relaxation of the PEG matrix was found to become faster in the nanocomposites.

Effects of Molecular Weight below the Entanglement Threshold on Interfacial Nanoparticles/Polymer Dynamics

“…As expected, the relaxation is significantly enhanced by the presence of interfacial water molecules (compare Figures SM.3a,c in Supporting Information) for dried and ambient neat silica A-300 samples. The S relaxation has been recorded previously also in other neat silica samples, ,, in different neat metal oxides, such as titania (TiO 2 ), , and in PNCs. ,, S , characterized by shape parameters α HN ∼ 0.4 and β HN = 1 (eq , average values), was recorded in neat oxides (Figure ) and in all PNCs (Figures and )­. Regarding its strength, S is dramatically suppressed in the PNCs by a factor of ∼20 (please compare Figures b and b, where Δε drops from 1.5 in neat oxides to 0.02–0.10 in PNCs) as a result of the disturbance in mobility of surface silanols due to their engagement by PDMS chains.…”

“…As expected, the relaxation is significantly enhanced by the presence of interfacial water molecules (compare Figures SM.3a,c in Supporting Information) for dried and ambient neat silica A-300 samples. The S relaxation has been recorded previously also in other neat silica samples, 9,77,78 in different neat metal oxides, such as titania (TiO 2 ), 30,79 and in PNCs. 5,9,30 S, characterized by shape parameters α HN ∼ 0.4 and β HN = 1 (eq 4, average values), was recorded in neat oxides (Figure 6) and in all PNCs (Figures 7 and 8).…”

Molecular dynamics and crystallization in polymers based on ethylene glycol methacrylates (EGMAs) with melt memory characteristics: from linear oligomers to comb-like polymers

“…S6, ESI †) the points of b for the POEGMAs are more close to each other, moreover, being separated (slower) from those of the OEGMAs (faster b therein). Comparing again with PEG we find slower b points for POEGMAs to coincide well with those for a relaxation of PEG assigned to hydrated local sites of the polymer chain (b PEG,JG ) 52,53 (and references therein). In Fig.…”

“…Compared with the structurally similar polymer, PEG, in Fig. S6 (ESI †) the corresponding process, g PEG , 52,53 fits quite well with g POEGMA here. g PEG has been attributed to the 'crankshaft motions' of methylene sequences.…”

“…The E act of b in PEG has been found to change at temperatures above T g and due to that it has been addressed also as a relaxation of the Johari-Goldstein (JG) 60 type. 52,53 Such a change in the time scale is recorded here for b in OEGMA-short (Fig. 8a, E act changes from 0.65 to B1.00 eV, Table 2).…”