3 research outputs found
Dielectric relaxation dynamics of high-temperature piezoelectric polyimide copolymers
Polyimide co-polymers have been prepared based on different diamines as co-monomers:
a diamine without CN groups and a novel synthesized diamine with two CN groups
prepared by polycondensation reaction followed by thermal cyclodehydration. Dielectric
spectroscopy measurements were performed and the dielectric complex function, ac
conductivity and electric modulus of the co-polymers were investigated as a function of
CN group content in the frequency range from 0.1 Hz to 107
Hz at temperatures from 25
to 260 °C.
For all samples and temperatures above 150ÂşC, the dielectric constant increases with
increasing temperature due to increaseing conductivity. The α-relaxation is just detected
for the sample without CN groups, being this relaxation overlapped by the electrical
conductivity contributions in the remaining samples. For the copolymer samples and the
polymer with CN groups an important Maxwell-Wagner-Sillars contribution is detected.
The mechanisms responsible for the dielectric relaxation, conduction process and electric
modulus response have been discussed as a function of the CN groups content present in
the samples.This work was supported by FEDER through the COMPETE Program and by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Project PESTC/FIS/UI607/2011 and grants SFRH/BD/ 62507/2009 (A.C.L.) SFRH/BD/68499/2010 (C.M.C.). The authors also thank funding from “Matepro – Optimizing Materials and Processes”, ref. NORTE-07-0124-FEDER-000037”, co-funded by the “Programa Operacional Regional do Norte” (ON.2 – O Novo Norte), under the “Quadro de Referência Estratégico Nacional” (QREN), through the “Fundo Europeu de Desenvolvimento Regional” (FEDER). RSS acknowledge the support of the Spanish Ministry of Economy and Competitiveness through the project MAT2012-38359-C03-01 (including the FEDER financial support). Authors also thank the Basque Country Government for financial support (ACTIMAT project, ETORTEK Program, IE13-380, and Ayudas para Grupos de Investigación del Sistema Universitario Vasco Program, IT718-13)