Coincidence Doppler Broadening Spectroscopy in Polyvinyl Chloride after Doping with Al 2 O 3 Hamdy F. M. Mohamed Physics Department, Faculty of Science, Minia University, 61519 Minia, Egypt Received 14 April 2007; accepted 26 November 2007 DOI 10.1002/app.27835 Published online 23 January 2008 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: Coincidence Doppler broadening of annihi- lation radiation (CDBAR) and Vickers hardness techniques were performed to study pure Al 2 O 3 , pure polyvinyl chlo- ride (PVC), and doped PVC with different concentrations of Al 2 O 3 (10–50%). The CDBAR ratio curves with respect to pure PVC were presented and reflect the momentum distribution of all the samples. The peak around 14.5 3 10 23 m o C in the CDBAR ratio curves suggests a large contribution of positron annihilation with the Al 2 O 3 . There is a linear correlation between the height of this peak and the Al 2 O 3 concentration. The S- and W-parameters were extracted from the CDBAR spectra and increase with increasing the Al 2 O 3 concentration showing discontinuity at 30% of Al 2 O 3 concentration on PVC. The present data confirmed that there is no positronium formation in pure Al 2 O 3 as a result of smaller S-parameter. The Vickers hard- ness increases with increasing the Al 2 O 3 concentration in PVC showing a linear dependence with two different slopes depend on the Al 2 O 3 concentration range. A corre- lation between the Vickers hardness (macroscopic data) and the W-parameter (microscopic data) was observ- ed. Ó 2008 Wiley Periodicals, Inc. J Appl Polym Sci 108: 1307– 1313, 2008 Key words: coincidence Doppler broadening; Vickers hardness; polyvinyl chloride; Al 2 O 3 INTRODUCTION Polymeric materials have been widely used in our daily life and industrial areas not only as an efficient alternative to the traditional materials such as wood, stone, glass, natural fabrics, and metals, but they also become indispensable factor to a break through in up-to-date-technologies. 1 The needs for more so- phisticated polymeric materials whose functions and properties are precisely tuned for the intended appli- cations drive many researches to enhance the macro- scopic properties of polymer products. Polymers in their pure state are excellent electrical insulators, but they can be modified to be relatively semiconductors or good electrical conductors. 2,3 Electrical conductiv- ity in polymers can be improved by adding conduc- tive materials such as metals, metal oxides, and metal salts 4–8 to form a conductive polymer. The conductive polymers are presently of great interest because they offer the promise of combining metallic and semiconducting characteristics with the plastic and elastic properties of organic polymers. They offer many advantages compared with metals. The study on the relationship between the macroscopic and microscopic structure is one of the main research streams for the polymer field. The positron annihilation spectroscopy has found increasing interest and growing application for studying polymeric materials. 9–12 The reason for this is that it provides a unique probe for subnanometer local free volumes in polymers that arise from their structural disorder. Such free volume holes play a crucial role in determining a variety of properties of polymers. 13,14 By using positron annihilation spec- troscopy, many studies indicate that the macroscopic properties of conducting polymers are related to the positron annihilation properties. AL-Qaradawi and Abdel-Hady 15 applied the positron annihilation life- time (PAL) technique to investigate the behavior of the free volume in pure and doped polyvinyl chlo- ride (PVC) as a function of lead concentration and temperature. The influence of the plasticization pro- cess on free volume in PVC using PAL measurement was investigated by Borek and Osoba. 16 The electri- cal properties of flame retardant PVC were studied by Mostafa et al. 17 In our previous work, the correla- tion between the dielectric data and the positron annihilation data was established 18 on PVC doped with different concentrations of Al 2 O 3 . In the present work, taking into account for the chemical sensitivity of the coincidence Doppler broadening of annihilation radiation (CDBAR) in polymers, the CDBAR technique has been applied to study pure Al 2 O 3 , pure PVC, and PVC doped with different concentrations of Al 2 O 3 . In addition, the Vickers hardness of the samples has been measured to investigate a quantitative relationship between the Correspondence to: H. F. M. Mohamed (hamdyfm@link. net). Journal of Applied Polymer Science, Vol. 108, 1307–1313 (2008) V V C 2008 Wiley Periodicals, Inc.