**4. Conclusions**

bigger size of the fillers but creates additional free volume probably at the interface. The results also indicate that the layers of oMMT will result in favorable interaction with the epoxy resins

The dielectric strength (DES) is the vital properties of dielectric insulators. With reference to the discussion in Section 2.4, the properties of epoxy nanocomposites are mainly explained by interfacial interaction of polymer and of nanofillers. This interfacial area is responsible for the interaction of the electric field between the base epoxy and nanofiller. The DES of the nanocomposites depends largely on nanofiller content and even a very less quantity of nanofiller can cause improvement. When nanofiller particles are incorporated into the epoxy matrix, there is a change in morphology of the epoxy due to the interfacial interaction of epoxy with

The **Figure 10** shows the variation of Dielectric strength, free volume with respect to nanofiller loading. With the addition of 2 wt.% oMMT into epoxy matrix, it is observed that T<sup>g</sup> increases due to increase in cross linking density and hence less free charge carriers are available leading to slightly higher value of DES than that of pure epoxy. A further increase in the filler loading up to 5 wt.% of oMMT shows an increase in the DES above that of

Here the effect of third interface layer also called loose layer comes into scenario. The loose polymer layers contain more traps or free volumes as discussed in Section 2.4. These charge carriers are easily and more frequently trapped in trap sites rather than in the base epoxy.

**Figure 10.** Plot of DES, Fv with respect to filler content (wt.%) of epoxy-oMMT nanocomposites.

is justified by the decrease in free volume content.

decreases, and hence more free charge carriers

percentage

and thereby the segmental motion is hindered. Hence, the significant increase in F<sup>v</sup>

is not observed. The decrease in Tg

152 Optimum Composite Structures

the oMMT nanofiller.

are available.

**3.6. Effect of interface on dielectric strength (DES)**

2 wt.% of nanocomposite. In this case the Tg

The following remarks are drawn:


**iv.** The characteristics of the interface region of the nanocomposite depend on the number of oMMT nanofiller particles included in the epoxy resin and how the oMMT nanoparticle loading affects the dielectric strength.

[9] Nelson JK, Utracki LA, Mac Crone RK, Reed CW. Role of the interface in determining the dielectric properties of nanocomposites. In: IEEE Conference on Electrical Insulation

Improved Dielectric Properties of Epoxy Nano Composites

http://dx.doi.org/10.5772/intechopen.78057

155

[10] Maity P, Kasiomayajula SV, Parameswaran V, Basu S, Gupta N. Improvement in surface degradation properties of polymer composites due to pre-processed nanometric alumina fillers. IEEE Transactions on Dielectrics and Electrical Insulation. 2008;**15**:63-73

[11] Nelson JK, Hu Y. Nanocomposite dielectric properties and implications. Journal of

[12] Zou C, Fothergill JC, Rowe SW. A water-shell model for the dielectric properties of hydrated silica filled epoxy nanocomposites. In: International Conference on Solid

[13] Costa LC, Devesa S, Andre P, Henry F. Microwave dielectric properties of polyethylene terephthalate (PBT) with carbon black particles. Microwave and Optical Technology

[14] Roberston J, Varlow BR. The AC non liner permittivity characteristics of barium titanate filled acrylic resin. In: Proceedings of the International Conference on Properties and Applications of Dielectric Materials (ICPADM), Nagoya, Japan. 2003. pp. 761-764 [15] Singha S, Thomas MJ. Dielectric properties of epoxy Nanocomposites. IEEE Transactions

[16] Ash BJ, Schadler LS, Siegel RW. Glass-transition temperature behavior of alumina/PMMA nanocomposites. Journal of Polymer Science Part B: Polymer Physics. 2004;**42**:4371-4383

[17] Sun YY, Zhang Z, Wong CP. Rheology study of wafer level underfill. Macromolecular

[18] Becker O, Cheng YB, Varley RJ, Simon GP. Layered silicate nanocomposites based on various high-functionality epoxy resins: The influence of cure temperature on morphology, mechanical properties, and free volume. Macromolecules. 2003;**36**:1616-1625 [19] Ambid M, Maryz D, Teyssedre G, Lauramt C, Maontanari GC, Kaempter D, Mulhaupt R. Effect of filler concentration on dielectric behavior and on charge trapping in PP/clay nanocomposites. In: IEEE Conference on Electrical Insulation and Dielectric Phenomena

[20] Roy M, Nelson JK, MacCrone RK, Schadler LS. Candidate mechanisms controlling the electrical characteristics of silica/XLPE nanodielectrics. Journal of Materials Science.

and Dielectric Phenomena (CEIDP). 2004. pp. 314-318

Dielectrics (ICSD), Winchester, UK. 2007. pp. 389-392

on Dielectrics and Electrical Insulation. 2008;**15**:12-23

Materials and Engineering. 2005;**290**:1204-1212

Physics D: Applied Physics. 2005;**38**:213-222

Letters. 2005;**46**:61-63

(CEIDP). 2004. pp. 389-392

2007;**42**:3789-3799
