Dielectric properties of ternary melt processed blends C.R. Martins a , C.P.L. Rubinger b, * , L.C. Costa b , R.M. Rubinger b,c a Departamento de Ciências Exatas e da Terra, Universidade Federal de São Paulo, 09972-270 Diadema, SP, Brazil b Physics Department, University of Aveiro, 3810-193 Aveiro, Portugal c Physics and Chemistry Department, Institute of Science, Federal University of Itajubá, CP 50, 37500-903 Itajubá, MG, Brazil article info Article history: Available online 20 October 2008 PACS: 77.84.Jd 77.22.d Keywords: Dielectric properties, relaxation, electric modulus Scanning electron microscopy Polymers and organics abstract Thermal, morphological and dielectric properties of conductive thermoplastic blends based on polysty- rene, styrene–butadiene–styrene block copolymer and doped polyaniline have been investigated with special emphasis on the effect of doped polyaniline concentration. Blends were prepared by melt blend- ing using an internal mixer. Morphological studies by scanning electron microscopy of cryofractured sur- faces indicated that thermoplastic matrix had a better miscibility with the presence of copolymer as compatibilizer and also good dispersability and structuring of doped polyaniline particles within polysty- rene. A reduction in impedance from 26 to 2 MX at 10 Hz, with the increasing polyaniline content is also observed. The blends can be used for antistatic applications. From the fit to the impedance spectroscopy data we obtained the relaxation strength, the depression angle and the relaxation. Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Polyaniline (PAni) has received attention due to low cost, simple polymerization and high yield of the polymerization [1]. Electrical, electrochemical and optical properties [2], coupled with good sta- bility, turn PAni into an attractive material for application such as electronic devices, antistatic coatings and anticorrosive protection [3]. However, besides its promising role for the manufacture of electronic devices, PAni processing remains a difficult task. Direct melt processing of PAni is not possible because it starts to degrade at temperatures close to its softening or melting points [4]. A dif- ferent approach consists of the use of a polymer acid [5] for PAni doping and also to improve processability. There are reports employing melt processing as a doping method to prepare blends with thermoplastic polymers [3,4,6]. The charge transport mechanism of polymers is investigated through dielectric relaxation [7–11]. The dielectric properties of polymers depend on chain structure, doping level [12] and synthe- sis [13]. In this work, we prepared PS/SBS/(doped PAni) (PS = polysty- rene, SBS = styrene–butadiene–styrene) blends in a double screw internal mixer and carried out thermal, dielectric and morpholog- ical characterization. SBS acts as plastic modifier allowing a disper- sion of PAni into the polymeric matrix by the melting process. 2. Experimental Blend preparation methods were described elsewhere [14,15]. Termogravimetry (TGA) was studied in a DuPont 951 thermal ana- lyzer, from 25 to 900 °C (rate 10 °C min 1 ) in argon atmosphere. For pure samples the higher temperature was 500 °C. All samples were pre-heated to 100 °C for 5 min to eliminate residual water. Dielectric measurements were carried out on a SR850 DSP Lock- in amplifier, Stanford Research. ‘In phase’ and ‘out of phase’ com- ponents of the output signal were used to obtain equivalent resis- tance R and capacitance C in parallel. The frequency range was 10 Hz–100 kHz, and sinusoidal voltage amplitude of 1.0 V rms . All measurements were carried out at 23 °C. Scanning electron microscopy (SEM) of gold-sputtered cryogenically fractured sur- faces was carried on a JEOL JSM-T300 with 20 kV accelerating voltage. 3. Results and discussion The composition of the blends was designed with three vari- ables as described on Table 1 [14]. TGA curves and first derivatives, Fig. 1, indicate for the blends initial thermodegradation temperature at 230 °C due to the ther- mal decomposition of dodecylbenzene sulfonic acid (DBSA) [14]. All blends present a sharp mass loss above 400 °C, corresponding to the degradation of PS. Blends also show a larger residue above 500 °C, which is proportional to the PAni content. The first deriva- tive of the TGA curves present a shift on dw/dT peak as a function 0022-3093/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2008.05.070 * Corresponding author. Tel.: +351 234 370 356; fax: +351 234 424 965. E-mail address: carlarubinger@yahoo.com.br (C.P.L. Rubinger). Journal of Non-Crystalline Solids 354 (2008) 5323–5325 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol