PolyU IR
 

PolyU Institutional Repository >
Applied Physics >
AP Theses >

Please use this identifier to cite or link to this item: http://hdl.handle.net/10397/3381

Title: Laser surface modifications of polymeric electrets for efficient charge trapping
Authors: Hui, Chi-yuen
Subjects: Hong Kong Polytechnic University -- Dissertations
Electrets
Polymers
Charge transfer
Lasers -- Industrial applications
Issue Date: 2006
Publisher: The Hong Kong Polytechnic University
Abstract: In this study, poly(ethylene terephthalate) (PET) films were irradiated by KrF pulsed excimer laser of wavelength 248 nm with different number of pulses at IHz. The PET samples were then electrified by the negative corona discharging method. The electret properties of the charged samples were studied by various techniques. A significant increase of surface potential was obtained for the PET films irradiated of more than 15 pulses with a laser fluence of 86 mJ/cm² . The surface potential of those films irradiated for more than 20 pulses did not increase further but dropped to the same level as untreated films. From the SEM pictures, melt ripple tips were observed in the laser irradiated area on the PET film surface and some of them were even fused together. This layer of melt polymer led to an increase of charge storage, which the surface potentials of the samples were enhanced. It suggested the possibility of enhancing the charge trapping capability of polymers by altering the surface morphology with the laser ablation process. On the other hand, the charge retention capabilities of the PET films electrified with different corona voltages were studied. The results showed that the surface potential of the electrets would decay and reach a steady value whatever the initial charging condition and the corona voltage were different. This steady value was depending on the sample thickness. Using the open-circuit Thermally Stimulated Depolarization Current (TSDC) with a Polytetrafluoroethylene (PTFE) spacer, the characteristics of the PET electrets obtained in various conditions were studied. The polarization and space charges peaks were distinguished clearly in the TSDC thermograms. TSDC with different heating rates were conducted. From the current magnitudes and peak positions obtained, the activation energy of the space charges in PET can be estimated. Finally, a prototype electret microphone was fabricated to examine the laser irradiated PET film with respect to its frequency responses and signal sensitivity as the microphone diaphragm. It can be seen that the performance of the laser irradiated PET film was better than the untreated film and was comparable to the commercial Teflon diaphragm and even better at frequencies over 5 kHz.
Degree: M.Phil., Dept. of Applied Physics, The Hong Kong Polytechnic University, 2006
Description: xii, 153 leaves : ill. (some col.) ; 30 cm.
PolyU Library Call No.: [THS] LG51 .H577M AP 2006 Hui
Rights: All rights reserved.
Type: Thesis
URI: http://hdl.handle.net/10397/3381
Appears in Collections:AP Theses
PolyU Electronic Theses

Files in This Item:

File Description SizeFormat
b19579391_ir.pdfFor All Users (Non-printable) 12.58 MBAdobe PDFView/Open
b19579391_link.htmFor PolyU Users 161 BHTMLView/Open



Facebook Facebook del.icio.us del.icio.us LinkedIn LinkedIn


All items in the PolyU Institutional Repository are protected by copyright, with all rights reserved, unless otherwise indicated.
No item in the PolyU IR may be reproduced for commercial or resale purposes.

 

© Pao Yue-kong Library, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
Powered by DSpace (Version 1.5.2)  © MIT and HP
Feedback | Privacy Policy Statement | Copyright & Restrictions - Feedback