Reversible Tenso‐Resistance and Piezo‐Resistance Effects in Conductive Polymer‐Carbon Nanocomposites

Abstract

Transmission Electron Microscopy (TEM): HITACHI H-600 electron microscope operating at an accelerating voltage of 100 kV was used. The samples were prepared according to the ASTM procedure. [17] Mechanical properties: Tensile specimens were punched out from the molded sheets using ASTM Die -C. The tests were carried out as per the ASTM D 412± 98 method in a Universal Testing Machine (Zwick 1445) at a crosshead speed of 500 mm/min at 25 C. The average of three tests and their standard deviations are reported here.Detection of dangerous deformations and vibrations of vehicle parts is important prior to exploitation under extreme conditions. Large-size flexible pressure or stretch sensors might be appropriate for this purpose. So far available reports [1,2] refer to electro-conductive carbon-polymer microcomposites exhibiting irreversible change of resistance under mechanical strain or pressure. We have succeeded to obtain electro-conductive polymer nanocomposites exhibiting a giant reversible change of resistance dependent on stretch and pressure. Electrically conductive polymer composites (ECPC) are obtained when particles of good conductors (carbon black, graphite powder, carbon fibre, micro-particles of metals) are implanted into an insulating polymer matrix. Most often such polymer composites are used as the so-called thermodynamic inactive materials in electric heating elements and resistors. Recently efforts have been made [1±8] to obtain active ECPC the conductivity of which would be strongly dependent on external thermodynamic parameters Ð pressure, temperature, and other. A new generation of cheap large-size sensors might be developed on the basis of such materials. Irreversible change of electrical resistance at stretch or pressure has been observed in case of micro-size particles. [1,2] New interesting properties are expected in case the composite contains dispersed nano-size conducting particles. [3±8] In our earlier studies of composites containing conductive carbon black nano-particles in polyisoprene matrix [5] reversible change of conductivity by several orders of magnitude has been revealed at stretch deformation. In other words, a giant and reversible tensoresistive effect is observed in the 742 2004

Epoxy based photoresist/carbon nanoparticle composites

“…for macro-size structures [17]. We thus verify that a similar behavior is found for microstructures.…”

Piezoresistive polymer composites based on EPDM and MWNTs for strain sensing applications

“…The decrease of conductivity with increasing strain is similar to the trend shown by carbon black filled elastomers [11][12][13][14][15][16][17][18][19]. In that case, the change in conductivity upon straining is generally explained in terms of two simultaneous processes that operate on a continuous conductive network of secondary aggregates in an insulating matrix.…”

“…For CPCs with a certain filler loading, any parameter that can alter the interparticle distance will affect the conductivity. Several groups have investigated the change of conductivity of CPCs as a function of temperature [3,4], solvent vapors [5][6][7][8][9], pressure [10] or mechanical stretching [11][12][13][14][15][16][17][18][19][20][21]. Such materials have the potential to become a new generation of sensors if the dependence is reversible.…”

Dielectric properties of exfoliated graphite reinforced flouroelastomer composites

“…Hence conductivity increases with filler loading. 38 Modeling of conductivity According to Jonscher 39 the electrical conductivity of many disordered solids (including polymer composites) was found to be sum of DC conductivity (independent of frequency) and AC conductivity (strongly frequency dependent). It was noted that the overall frequency dependence of r (so called 'universal dynamic response' of electron conductivity) could be approximated by the following simple relation: r ¼ r ac þ r a:c: or r ¼ r ac þ Ax s (14) where x ¼ 2pf is the angular frequency, A is constant and s are exponential parameter.…”