The Features of Percolation and Piezoresistive Effect in Polyisoprene – Nanostructured Carbon Composites
2011
Juris Zavickis

Defending
09.09.2011. 14:00, Materiālzinātnes un Lietišķās Ķīmijas fakultāte, Āzenes iela 14/24, 272. auditorija

Supervisor
Māris Knite

Reviewers
Mārtiņš Kalniņš, Jānis Kleperis, Oļesja Starkova

The dissertation is devoted to physical properties of pressure-sensitive polyisoprene – nanostructured carbon composites (PNCC) and designing of a completely flexible pressure sensing element prototype. Technology of producing PNCC by ultrasound dispersing of the electro-conductive filler in chloroform is developed and used in the study. Original techniques is devised and used for measuring electrical properties of PNCC in-situ during vulcanization. A Zwick/Roell z2.5 material testing device was optionally modified with instruments for automated wide-range measurements of electrical resistivity. By performing in-situ measurements of electrical resistivity during vulcanization, electrical conductivity of PNCC is proven to appear just at the beginning of vulcanization. To obtain additional information, the measurements of initial electrical resistivity, piezo-rezistivity and a SEM study of microstructure is performed with samples of different duration of vulcanization. Kinetic agglomeration of electro-conductive filler is found taking place and creating a complex electro-conductive network at the beginning of vulcanization, stimulated by increased temperature. By a detailed study of electrical percolation thresholds of PNCCs, made with different electro-conductive fillers and using different dispersing techniques, the ultrasound dispersing of carbon black is found to decrease the electrical percolation threshold by about 40 % and dramatically reduce the structure of carbon black to improve dispersion and to increase the relative intensity of tunneling currents. The theoretical model of the positive piezo-resistive effect proposed on the basis literature explains the increase of electrical resistivity of PNCC in the direction parallel to the applied compressive force by elongation of the matrix and subsequent increase of the tunneling junctions, and change of the number of electro-conductive channels in the transversal direction. The model is successfully used to explain the experimentally obtained data of the piezo-resistive effect in PNCC. A completely hyper-elastic pressure-sensing element made of PNCC only is designed, manufactured and tested within the framework of the study and is the subject of LV patent No. 14085 (registered 10.12.2009).


Keywords
polyisoprene, nanostructured, carbon, composite, percolation, piezoresistive, pressure sensing

Zavickis, Juris. The Features of Percolation and Piezoresistive Effect in Polyisoprene – Nanostructured Carbon Composites. PhD Thesis. Rīga: [RTU], 2011. 128 p.

Publication language
Latvian (lv)
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