Interfacial Interactions and Segmental Dynamics of Poly(vinyl acetate)/Silica Nanocomposites

Abstract

We investigate the interfacial interactions and segmental dynamics of hydrophilic and hydrophobic (calcined) silica nanoparticle (NP) filled poly(vinyl acetate) (PVAc) composites via a combination of Fourier transform infrared spectroscopy (FTIR) and broadband dielectric spectroscopy measurements. For hydrophilic silica NP filled composites, an increase in the amount of bound carbonyl groups with increasing silica loading can be noted due to hydrogen bonding interactions with hydroxyls on the NP surfaces and carbonyl groups of PVAc. It is surprising that the apparent glass transition temperature (T g ) increases very slightly (∼1 K) compared to pure PVAc, but the glass transition process becomes much broader, indicating the existence of a slower relaxation mode. In addition to the bulklike α-relaxation assigned to polymer segments away from the NP surfaces, the nanocomposites also exhibit a slower interfacial α′-relaxation by 3−4 orders of magnitude compared to bulk polymers. However, in the case of hydrophobic (calcined) silica NP filled composites, T g shifts to higher temperatures by 4−5 K even if there is the absence of strong polymer-NP interfacial interactions confirmed by the FTIR results. Consequently, the overall α-relaxation dynamics are suppressed in the presence of silica NPs, which is attributed to an increase of steric hindrance and decrease of free volume. More importantly, in the nanocomposites with high NP loadings, it is worth noting a weak physical adsorption interfacial layer for which the segmental mobility is on average slower by 1−2 orders of magnitude relative to that for bulk polymers. However, the dielectric strength and interfacial bound fraction is much smaller than that of hydrophilic silica NP filled composites, indicating the fact that physical adsorption is much weaker compared to hydrogen bonding.

Facile and controllable synthesis of hybrid silica nanoparticles densely grafted with poly(ethylene glycol)

“…In recent years, polymer–nanoparticle (NP) composites have found applications in many fields due to their enhanced thermomechanical, electrical and mechanical properties . These properties are mainly exhibited in their dispersed state, which is a function of other chemical and physical properties . The properties of the polymer matrix and the processing technology also affect the dispersion of NPs .…”

Morphology, structure, and segmental dynamics in polyazomethine/hybrid carbon nanofillers composites

“…Furthermore, when MWCNTs are additionally introduced in the nanofller (rGO:MWCNTs = 75:25 wt%:wt%), extra π ‐ π interactions between MWCNTs, rGO, and PAZ arise, thus increasing T g 100 up to 326 K. Subsequent increase in the MWCNTs portion in the nanofiller, probably, does not enhance interactions since T g 100 , in fact, does not change. An increase in T g 100 attributed to attractive interactions between nanoparticles and polymer chains has previously been reported …”

“…We should emphasize an increase in τ max for all the nanocomposites as compared with τ max for PAZ, that is, retardation the α ‐process. This means attractive interaction between the nanofillers and the polymer chains . Meanwhile, it is not so easy to find a general trend in variation of τ max with variation of the nanofiller content.…”

“…Following refs. and using Figure , we estimated the so‐called “dielectric glass transition temperature” T g 100 as a temperature related to macroscopically observation time, τ max = 100 seconds. The T g 100 values for the PAZ/rGO:MWCNTs nanocomposites are indicated with the arrows in Figure and also are summarized in Table .…”

“…Furthermore, fragility depends on the nanoparticle‐polymer interaction and nanoparticles concentration. It is expected to increase for attractive interactions or decrease for repulsive interactions . Following just mentioned references, we estimated the polymer fragility m as a slope of the Arrhenius plot at τ max = 100 seconds divided by T g 100 . …”