Local Dynamics and Molecular Origin of Polymer Network−Water Interactions as Studied by Broadband Dielectric Relaxation Spectroscopy, FTIR, and Molecular Simulations

Abstract

An investigation was carried out of the molecular interactions and local relaxation dynamics in glassy polymer networks exposed to moisture. Stoichiometric and off-stoichiometric mixtures of the diglycidyl ether of bisphenol A (DGEBA) and diethylene triamine (DETA) were prepared, cured, and investigated. The physical and the chemical nature of the interactions between the network and the absorbed moisture were studied by broadband dielectric relaxation spectroscopy (DRS), Fourier transform near-infrared (FT-NIR) spectroscopy, and molecular simulations. Dry networks are characterized by two Arrhenius-like local relaxations: the β process, associated with hydroxyl groups, and the γ process, associated with primary and secondary amine, and glycidyl ether groups. Absorbed water interacts with the network and affects the dynamics of β and γ processes. FT-NIR spectra reveal the presence of three forms of water molecules, differing in the number of hydrogen atoms (0, 1, or 2) that participate in hydrogen bonds. The relative ratio of each form to the total absorbed water was calculated from the NIR data and from molecular simulations. An excellent agreement between those two techniques was observed.

In‐situ‐Synthetized Silver/Epoxy Nanocomposites: Electrical Characterization by Means of Dielectric Spectroscopy

“…Several authors have related the rapid climbing of those properties as indicative of percolation in nanocomposites based on polymer matrices and conductive fillers such as metallic NPs or carbon nanotubes. [35][36][37][38][39] …”

Change in dielectric relaxation with the presence of water in highly filled composites

“…6 The presence of water and its influence in the dielectric response were previously studied in various polymeric systems. [7][8][9][10][11] Here, we concentrate on the change in the dielectric properties of highly filled composites in the presence of water, and report on the dielectric relaxation of moisture-absorbed and dry samples.…”

“…The method has been applied to various different material systems. [7][8][9][10][11][20][21][22] Electrical properties of materials can be determined from the impedance measurements by performing current measurements with applied voltage and using the geometrical capacitance C 0 , the geometry of the sample. For example, for the complex permittivity, " Ã is estimated from the current measurement as a complex capacitance C Ã for a given geometrical shape of the measurement electrodes, which determine the geometrical capacitance C 0 , Here, the angular frequency, !, independent material properties are of relative permittivity at high frequencies, " 1 , and Ohmic (direct-current) conductivity, 0 ; ı ¼ ffiffiffiffiffiffi ffi À1 p .…”

Infrared Spectroscopy - Materials Science, Engineering and Technology

“…The band located at 5215 cm -1 can be used to quantify water, although it must be normalized for sample thickness. The band at higher wavenumbers is used to determine the kind of interactions between water and network (Mijovic & Zhang, 2003;Cabanelas et al, 2003), but not with quantitative purposes since it is superimposed on the O-H overtone of the resin (Musto et al, 2000). To overcome the thickness variation it is possible to normalize water signal with a reference band invariant against the presence of water (for example, the band at 4623 cm -1 , corresponding to aromatic rings of DGEBA).…”