**1. Introduction**

The interface of surface functionalized nano-clay (oMMT) filler and polymer matrix (epoxy) of the polymer nanocomposites play a very important role in improving the electrical, thermal and mechanical properties. Therefore, detailed studies on the interfacial effects of filler-matrix on several properties have been investigated. The chemical bonding established

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between epoxy and oMMT nanofiller has been investigated using Fourier transform infrared spectroscopy (FTIR). The cross linking between polymer and nanofiller was measured to determine the glassy state of the nanocomposite called glass transition temperature (Tg ) by using differential scanning calorimetry (DSC). Further, the positron annihilation spectroscopy (PALS) has been utilized to determine free volume as outlined in the multi-core model [1]. Many researchers have theoretically estimated the free volume of nanocomposites and there is no experimental data on the evaluation of free volume. In the present work, PALS has been used in the accurate evaluation of free volume. A brief explanation of nanocomposite interface dynamics, free volume estimation and the effect of intermolecular interactions and hydrogen bonding are discussed. The effect of these results on electrical property such as dielectric strength (DES) at room temperature was studied.

strongly bound to the primary layer and outer surface of nanofiller. Thickness of the layer varies between 2 and 9 nm. This value mainly relies on the strength of interaction between organic polymer and nanofiller or nanoparticles. Stronger the interaction, the larger will be the bound polymer fraction. This may correspond to a stoichiometrically cross-linked layer.

Improved Dielectric Properties of Epoxy Nano Composites

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The loose layer is a region which is loosely coupled, at the same time interacts with the bound region. It is generally considered that the loose layer has different chain conformation, chain mobility, and even free volume in the polymer matrix. It may also consist of a less stoichiometrically cross-linked layer. In addition, interfacial structures obtained from chemistry, Columbic interaction is superimposed, when dielectric and electrical insulation properties are investigated [1]. The nanoparticle may be charged either positively or negatively. When a polymer has mobile charge carriers, they are distributed in the interface in such a manner that the charge carriers with the opposite polarity are diffused outward from the contact surface to the Debye shielding length that corresponds to the Gouy-Chapman diffuse layer in which charge decays exponentially with distance, in accordance with Born approximation [1].

The thickness of these layers may varies from 1 nm to, several tens nm for the bonded, bound and loose layers respectively. It is not clearly known whether the thickness of the loose layer is the same as that of the Gouy-Chapman diffuse layer. It may appear that the latter might extend over the former. Therefore, far-field effect must be involved in mesoscopic interactions in the loose layer or the diffuse Gouy-Chapman layer, and it is expected to cause some combined effect among neighboring nanoparticles. Macroscopic phenomena and parameters are different from polymer to polymer and polymer with filler particles due to the relative differences in its thickness and interaction strengths in the multi-core model with the far-field effect.

The Bisphenol A diglycidyl ether based Epon 828 epoxy resin (DGEBA) with epoxy equivalent weight (EEW) of 188 g/mol and curing agent such as Epikure W which is chemically called diethyl toluene diamine (DETDA) with an amine hydrogen equivalent weight of 45 g/ mol were used in the present work. These materials were supplied by M/s. Miller-Stephenson Chemical Company, USA. The nanoclay used in the present work is called as Nanomer 1.30E supplied by M/s. Nanocor, USA. This nanoclay was surface treated with surface functionalizer namely octadecylamine mainly used for uniform dispersion of nanoparticle epoxy resin polymer. This surface functionalized nanoclay is called organically modified montmorillonite

One of major challenges in the processing of nanocomposites is the non-uniform mixing of curing agent. Non uniform mixing of nanofiller, resin, and the curing agent or hardner may

Debye shielding length is calculated approximately as 30 nm [1].

**2. Experimental studies**

clay represented as oMMT.

**2.2. Fabrication process of nanocomposite**

**2.1. Matrix and fillers**

## **1.1. Multi-core interface model**

The interaction of nanoparticles with the surrounding polymer matrix by means of three layers is described by Multi-core model [1] as shown in **Figure 1**. It consists of (i) Primary layer also referred as bonded layer, (ii) Secondary layer as referred as called bound layer, (iii) tertiary layer also referred as called loose layer, and the next fourth layer which overlaps all the above three layers called electric double layer. Primary layer represents a type of transition layer which is firmly attached to the carbonless nanofiller or inorganic nanofiller and carbon based organic base matrix polymer by compatabilizer or hardner. Secondary or bound layer addressed as interfacial layer or region consists of a region or area of layer of polymer chains

**Figure 1.** Multi-core model for nano-particle-polymer interfaces (source: Toshikatsu Tanaka and co-authors [1]).

strongly bound to the primary layer and outer surface of nanofiller. Thickness of the layer varies between 2 and 9 nm. This value mainly relies on the strength of interaction between organic polymer and nanofiller or nanoparticles. Stronger the interaction, the larger will be the bound polymer fraction. This may correspond to a stoichiometrically cross-linked layer.

The loose layer is a region which is loosely coupled, at the same time interacts with the bound region. It is generally considered that the loose layer has different chain conformation, chain mobility, and even free volume in the polymer matrix. It may also consist of a less stoichiometrically cross-linked layer. In addition, interfacial structures obtained from chemistry, Columbic interaction is superimposed, when dielectric and electrical insulation properties are investigated [1]. The nanoparticle may be charged either positively or negatively. When a polymer has mobile charge carriers, they are distributed in the interface in such a manner that the charge carriers with the opposite polarity are diffused outward from the contact surface to the Debye shielding length that corresponds to the Gouy-Chapman diffuse layer in which charge decays exponentially with distance, in accordance with Born approximation [1]. Debye shielding length is calculated approximately as 30 nm [1].

The thickness of these layers may varies from 1 nm to, several tens nm for the bonded, bound and loose layers respectively. It is not clearly known whether the thickness of the loose layer is the same as that of the Gouy-Chapman diffuse layer. It may appear that the latter might extend over the former. Therefore, far-field effect must be involved in mesoscopic interactions in the loose layer or the diffuse Gouy-Chapman layer, and it is expected to cause some combined effect among neighboring nanoparticles. Macroscopic phenomena and parameters are different from polymer to polymer and polymer with filler particles due to the relative differences in its thickness and interaction strengths in the multi-core model with the far-field effect.
