Enthalpy Relaxation of Layered Silicate‐Epoxy Nanocomposites

Abstract

Using standard and temperature‐modulated differential scanning calorimetry, we have studied the segmental relaxation behavior of montmorillonite‐epoxy nanocomposites. The experimental results showed that the incorporation of clay particles caused the epoxy network to exhibit slower relaxation dynamics compared with the neat epoxy resin. Analysis based on the Tool‐Narayanaswamy‐Moynihan (TNM) model indicated that the nanocomposite systems had greater nonlinearity, higher apparent activation energy, and broader relaxation time distribution than the neat epoxy resin. Further analysis based on the Adam‐Gibbs model indicated that the presence of clay nanoparticles decreased the macroscopic configurational entropy of the epoxy network, and increased the size of the cooperative rearrangement region as well as the fundamental energy barrier. The peculiar relaxation behavior observed in the present experiments was attributed to the confinement effect of nanoparticles on molecular entities during the segmental relaxation. This confinement effect led to a stronger temperature dependence of the relaxation behavior near the glass transition temperature, or greater fragility. An inverse correlation between nonexponentiality and fragility was also observed, which is consistent with the results reported in the literature.

Structural relaxation of stacked ultrathin polystyrene films

“…Unlike ultrathin films, the physical aging of nanocomposites, especially for thermosetting resins, has been more extensively investigated. [34][35][36][37][38] The studies of physical aging of nanocomposites have focused on the type of nanofiller, such as silica nanoparticle, graphitic nanofiber, and polyhedral oligosilsesquioxane (POSS), because strong interactions between nanofiller and the thermosetting resin appear to restrict physical aging. 34 Similarly, in the case of ultrathin films, interfacial interactions may be an important factor for their physical aging behavior.…”

Miscibility and Properties of Acid-Treated Multi-Walled Carbon Nanotubes/Polyurethane Nanocomposites

“…Similarly, reported 2D layered (hydrogen bonding with polymer and clay) silicates (such as clay) can effectively reinforce the polymer matrix, 26 in which the polymer chains are considerably constricted by their confinement within 2D nanoclay platelets, increasing the T g of the nanocomposites. 27,28 In the system herein, the strong interaction (hydrogen bonding) between the urethane group (-OOCNH-) of PU and the carbonyl acid (-COOH) group in A-MWNTs also constrains the motion of the PU molecules. Therefore, the series of PU/A-MWNTs nanocomposites had higher T gh than the neat MWNT system.…”

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

“…Results of Lu and Nutt regarding physical ageing on montmorilloniteepoxy nanocomposites yielded to a slowdown of the main relaxation when compared with the neat polymer [136]. Besides, Priestley et al lately related the fall of the secondary relaxation on silica-filled PMMA nanocomposites with the hindered PMMA molecules at the filler surface making use of the enthalpy recovery decay on physical ageing assays [115].…”

“…Silicate-layered nanocomposites show two opposite tendencies which rule the occurrence and broadening of the cooperative main relaxation phenomenon: the existence of a less constrained phase than that of the bulk which includes molecules within galleries (spaces left between neighbour silicate layers); and hindered molecules at the interface between the organic and inorganic phases. This balance establishes the widening of the glass transition as well as the shift of T g [39,136].…”

“…In an elastic body the stiffness (S) can be related to the elastic modulus (Eq. 1.14) and the hardness [76,81,120,122,123,136], but for assessing the co-continuity of both phases an analysis of the stiffness itself throughout the nanocomposite surface suffices (to compute the sample Young modulus through a reduced modulus (E r ) is necessary to know the Poisson ratio of the sample). Therefore, we will be only able to map relative material property differences for our set of nanocomposites.…”