Electret Stability Related to the Crystallinity in Polypropylene Anders Thyssen, Kristoffer Almdal, Erik Vilain Thomsen 04/10/2015Anders Thyssen2DTU Nanotech, Technical University of Denmark Outline What is an electret? Why are we doing this? Experimental setup Results Decay Theory Thermal Stimulated Current Conclusion 04/10/2015Anders Thyssen3DTU Nanotech, Technical University of Denmark What is an electret? Electret. Electrical charges ++ ++ ++ ++ Electrical field Dielectrically material V Working with non-polar polymer PP Polypropylen Dipoles 04/10/2015Anders Thyssen4DTU Nanotech, Technical University of Denmark Why are we doing this? Polypropylene as a model system Correlation between polymer structure and electret properties Modelling: Activations energies Life time prediction Transfer gained knowledge to other electret polymers. 04/10/2015Anders Thyssen5DTU Nanotech, Technical University of Denmark Controlling the crystallinity Isotactic- Polypropylene Atactic- Polypropylene Sample Crystallinity SamplesCrystallinity 100 % i-PP37 % 67 % i-PP & 33 % a-PP31 % 33 % i-PP & 67 % a-PP17 % 100 % a-PP5 % Polypropylene solution Spin coating 04/10/2015Anders Thyssen6DTU Nanotech, Technical University of Denmark Corona charging 04/10/2015Anders Thyssen7DTU Nanotech, Technical University of Denmark Isothermal Potential Decay High crystallinity Better electret Room temperature Room temperature 04/10/2015Anders Thyssen8DTU Nanotech, Technical University of Denmark Humidity Induced Potential Decay High crystallinity More humid tolerant electret Room temperature 04/10/2015Anders Thyssen9DTU Nanotech, Technical University of Denmark Stability related to the crystallinity Sample Crystallinity SamplesCrystallinity 100 % i-PP37 % 67 % i-PP & 33 % a-PP31 % 33 % i-PP & 67 % a-PP17 % 100 % a-PP5 % High crystallinity High charge retention 04/10/2015Anders Thyssen10DTU Nanotech, Technical University of Denmark Energy Dimension Decay Theory - release current Energetic traps Retrapped charge Discharged charge Charges are bound to traps, which have an activation energy Charge 04/10/2015Anders Thyssen11DTU Nanotech, Technical University of Denmark Thermal Stimulated Current Heating rate 7.5 K/min Each current peak One type of trap 04/10/2015Anders Thyssen12DTU Nanotech, Technical University of Denmark Thermal Stimulated Current Heating rate 7.5 K/min 04/10/2015Anders Thyssen13DTU Nanotech, Technical University of Denmark Thermal Stimulated Current Heating rate 7.5 K/min 04/10/2015Anders Thyssen14DTU Nanotech, Technical University of Denmark Thermal Stimulated Current Heating rate 7.5 K/min Each current peak One type of trap 04/10/2015Anders Thyssen15DTU Nanotech, Technical University of Denmark Conclusion Samples with crystallinity of 37 %, 31 %, 17 % and 5 %. High crystallinity 75% of the charges remain on high crystalline samples corresponding to 0% for the low crystalline sample at 90 o C for 24 hours Charges are bound to traps, with have an activation energy Activations energies prediction of charges life time on an electret material Each current peak One type of trap Better electret More humid tolerant electret High charge retention Questions 04/10/2015Anders Thyssen17DTU Nanotech, Technical University of Denmark 04/10/2015Anders Thyssen18DTU Nanotech, Technical University of Denmark Decay Theory - release current 1. Order - No retrapping 2. Order - Pronounced retrapping E a =activation energy =attempt-to-escape-frequency n=charges N=number of traps A n /A h =ratio between re-trap/re-combine T=Temperature k b =Boltzmann constant 04/10/2015Anders Thyssen19DTU Nanotech, Technical University of Denmark SEM images of spherulites