Swift heavy ion induced structural and chemical changes in BOPP film S. Chawla a, * , A.K. Ghosh b , S. Ahmad c , D.K. Avasthi d a Amity School of Engineering and Technology, 580, Bijwasan, New Delhi 110 061, India b Centre for Polymer Science and Engineering, Indian Institute of Technology, New Delhi, India c Materials Research Laboratory, Department of Chemistry, Jamia Millia Islamia, New Delhi, India d Nuclear Science Centre, New Delhi, India Available online 20 January 2006 Abstract Swift heavy ions (SHIs), such as, 80 MeV Si 7+ and 120 MeV Ag 9+ ions were used to irradiate 15 lm bi-axially oriented polypropylene (BOPP) films. The fluence (U) dependence of the structural and chemical changes in BOPP was investigated. The irradiated BOPP films were analyzed ex situ by means of FTIR, UV and DSC. Due to SHI irradiation, the isotactic helical structure of polypropylene (PP) gets reduced. PP undergoes distortion of its crystal lattice in magnitude proportional to the fluence. The scission of C–H bonds and produc- tion of unsaturated groups like dienes and trienes occurred after irradiation with Si ions for U P 10 12 ions/cm 2 and Ag ions for U P 10 11 ions/cm 2 . It was found that Ag ions are better than Si ions for creation of free radical active sites on BOPP. The observed findings are very useful particularly in the selection of optimum experimental conditions for SHI induced graft copolymerization. Ó 2005 Elsevier B.V. All rights reserved. PACS: 61.41.+e; 61.80.Jh; 61.82.Pv; 68.55.Nq Keywords: Swift heavy ions; Modification; Scission; Polypropylene 1. Introduction Swift heavy ions (SHIs) have the ability to deposit extre- mely high energy per unit ion path length. They are there- fore, characterized by extremely high linear energy transfer (LET), and are used for the nanometer scale tailoring of surfaces in materials research [1]. They can also be used for grafting as they create highly reactive nuclear tracks on their way through the solid polymeric film. ‘‘Grafting’’ is a process whereby chemical groups are attached by cova- lent bonds to a polymer backbone usually via an aliphatic carbon atom. SHI grafting is unique in the respect that it can generate surfaces with microdomains of modified and unmodified polymer. If the ion incidence is normal to the surface, then circular islands corresponding to the grafted domains are seen [2]. Moreover, in response to a stimulus, the grafted domains are transformed from an expanded conformation to compact ball leading to an increase or decrease in the pore size and thus can be used for the production of permeability – adjustable membranes. These are also called as ‘‘intelligent’’ membranes. Their potential applications include the controlled release of drugs [3]. Apparently, SHI can be used to bring about new properties not accessible with conventional chemical, radiochemical or physical means [4]. Although much work has been con- ducted [5,6] the attained knowledge about track structures is still too much limited, especially from an experimental point of view. In the present work, an attempt has been made to study the structural and chemical changes in BOPP induced by swift Si 7+ and Ag 9+ ion irradiation. The structural changes observed are then co-related with the changes in crystalliza- tion behavior and melting characteristics with the help of DSC. The optimum experimental conditions for creating residual active sites on PP for its efficient graft copolymer synthesis has been presented. 0168-583X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.11.159 * Corresponding author. Tel.: +91 11 28062106/28061487; fax: +91 11 28062105. E-mail address: shashichawla10@rediffmail.com (S. Chawla). www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B 244 (2006) 248–251 NIM B Beam Interactions with Materials & Atoms