Dynamic Mechanical Relaxation of Poly(2‐Hydroxyethyl Acrylate)‐silica Nanocomposites Obtained by the Sol‐gel Method

Abstract

A series of poly(hydroxyethyl acrylate)-silica nanocomposites has been polymerized by the simultaneous sol-gel reaction of the organic monomer and the silica precursor tetraethyl orthosilicate (TEOS). Samples with different silica contents were prepared and their mechanical properties have been investigated by dynamic mechanical spectroscopy (DMS). The application of the time-temperature superposition principle to the isothermal DMS results in the main relaxation region permits to successfully construct master curves. The calorimetric properties of these hybrid materials have also been measured in order to compare the results of DMS and DSC. The presence of a polymer phase formed by polymer chains with reduced mobility has been proved by the DMS results. The main relaxation due to the segmental dynamics of these chains takes place at frequencies around seven decades smaller than in the bulk PHEA homopolymer.

Structure and Mobility of Lactose in Lactose/Sodium Montmorillonite Nanocomposites

“…Similar observations have been demonstrated in nanocomposites with silica or carbon nanotubes as fillers. 27,[58][59][60][61] Assuming that the intercalated lactose is the fraction that not contributes to the magnitude of expected from simple physical mixtures of the lactose and Na-MMT. Overall, the plot in Figure 7 follows the assumed phase behavior for the co-spray-dried nanocomposites with a decreasing non-intercalated lactose fraction at increasing Na-MMT content in the nanocomposites, and both methods confirm presence of non-intercalated lactose even at high Na-MMT content.…”

Acrylate-silica polymer nanocomposites obtained by sol-gel reactions. Structure, properties and scaffold preparation.

“…The results of the nanoindentation experiments ( Figure 3.21) are in good agreement with the mechanical properties of these nanocomposites as obtained by standard macroscopic methods along this work (Figure 3.14) and in previous studies [73,124]. The average stiffness as calculated from Eq.…”

“…This is in fact reflected in the dynamicmechanical loss tangent (Figure 3.23), whose dissipation maximum significantly decreases in intensity as the silica content of the sample increases. Other results on the same hybrid system also hinted to the existence of a more constrained PHEA phase within the nanocomposites whose dissipation maximum corresponding to the main mechanical relaxation takes place at lower frequencies in comparison with the less constrained PHEA rich-domains, which behaves as the pure homopolymer [73]. The presence of the silica phase has also an influence on the secondary dynamic-mechanical relaxation of the polymer.…”

“…In this second part of the thesis, the simultaneous polymerization of the organic and inorganic phases was carried inside a specially tailored porogenic template. The ensuing scaffolds thus resulted in organic-inorganic hybrid nanocomposite materials [29,59,73] with a well-ordered array of large interconnected orthogonal cylindrical pores.…”

“…This interlayer with special properties differing from the bulk polymer (which plays a key role in the performance of the hybrid system [40]) is identified as the interphase. It can be distinguished two main sorts of interphases: those composed by completely immobilized polymeric chains (they do not devitrify at any temperature) and interphases formed by partly hindered polymer chains, which relaxes at higher temperatures giving rise to a second glass transition temperature or, at least, a shoulder at the high energy side of the relaxation main transition [73,82].…”