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