ARTICLES Electrical and mechanical properties of free-standing PMMA–MMT clay composites Syed Abusale Mhamad Nabirqudri Department of Materials Science, Gulbarga University, Gulbarga 585106, India; and Department of Mechanical, KBN College of Engineering, Gulbarga 585104, Karnataka, India Aashis S. Roy and M.V.N. Ambika Prasad a) Department of Materials Science, Gulbarga University, Gulbarga 585106, India (Received 9 June 2014; accepted 1 October 2014) Modified MMT clay-doped PMMA composites have been prepared by solvent casting method for different weight percentages. The prepared composite films were characterized by FTIR and SEM. Also, the DC conductivity was carried out for PMMA and PMMA composite films. Among all composites, it was found that 30 wt% shows highest conductivity of 1.59 Â 10 À3 S/cm. The negative thermal coefficient behavior of these polymer composite films confirms that the increase in conductivity is due to the elongation of polymer chain which helps in charge transport mechanism. Dielectric study also shows that 30 wt% has the lowest dielectric constant and dielectric loss of 2.5 and 3.3, respectively, resulting in an increase in conductivity of 5 Â 10 À3 S/cm. The isotropic nature of 30 wt% composite film shows a high quality factor of 0.005 because of overdamping of electron at 10 4 Hz. Cole–cole plots show that the semi arc originated from a single point and its area decreases with filler concentration up to 30 wt% due to drop in the electrical resistance. Tensile modulus increases because of high MMT aspect ratio and distribution ratio. The 30 wt% of the composite shows high tensile strength at 55 MPa which induces 8% of strain in the PMMA–MMT clay composite films. Therefore, these composite films can be used in many sensor and solar technologies as encapsulation materials. I. INTRODUCTION Polymer inorganic composites attracted the researchers in the past decade due to drastic changes in the mechanical properties, enhanced thermal stability, flame retardancy, better gas barrier properties, and corrosion resistance. 1 Moreover, small amounts of doping of clay result either in intercalation or exfoliation, and these changes of the composites can be detected by the x-ray diffraction method (XRD). Exfoliated composites show significant improvement in the physical and chemical properties due to the large aspect ratio as well as the surface area of the clay. 2,3 Since clay is naturally hydrophilic and inher- ently incompatible with most organic polymers, several methods have been developed to make clay more com- patible with organic polymers. 4–6 The interaction mech- anism of clay with polymer is well known, i.e., the metal cations on clay exchange with carbocations of surfactants to form long alkyl chains. 7 This process improves the interface of the polymer clay composites and hence the physical and chemical properties are enhanced. 8 Poly(methyl methacrylate) (PMMA) is a transparent, hard, and stiff material with excellent ultraviolet stability, low water absorption, and outstanding outdoor weathering properties. 9 PMMA/montmorillonite clay composites are of interest for improved electrical, thermal, and mechanical properties, reduced flammability, reduced gas permeability, as well as their good potential to retain excellent optical clarity. 10,11 These polymer com- posites have very low dielectric constant and tangent loss; hence, conductivity of these polymer composites is very low. 12 The conductivity of these composites depends on the filler concentration, distribution of filler, orientation, and method of preparation. 13,14 Various methods have been reported such as solvent casting, coprecipitation method, melt mixing, in situ polymerization, interfa- cial method etc. 15–18 Among all the techniques, in situ polymerization is one of the desirable methods because the fillers are homogeneously distributed throughout the polymer matrix and therefore isotropy is maintained. In the present work, the authors have made an attempt to improve the electrical and mechanical properties of PMMA/montmorillonite clay composites. Various pro- portions of clay were doped in to the PMMA and further characterized by XRD, FTIR, and SEM. The electrical property is studied by Kelvin two probe method using a Keithley source meter and the mechan- ical property was studied by using a micromechanical testing machine. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 a) Address all correspondence to this author. e-mail: prasad1_amb@rediffmail.com DOI: 10.1557/jmr.2014.301 J. Mater. Res., Vol. 29, No. 0, 2014 Ó Materials Research Society 2014 1