| Conductive polymer composites(CPCs),which are prepared by incorporating conductive fillers into polymer matrix,have been investigated widely owing to their sensitive ability to external stimuli including thermal field,humidity,chemicalvapors,and external stress field,etc.In this paper,the strain-sensing behaviors of reduced graphene oxide(RGO)/polylactic acid(PLA)with good dispersionwere investigated profoundly,andthe strain-sensing behaviors of RGO/PLA and carbon nanotubes(CNTs)/PLA nanocomposites were compared detailedly.Thethermal stimuli-responsive behaviors of RGO/PLA nanocomposites were studied.Firstly,RGO/PLAand CNTs/PLA nanocomposites were prepared by ultrasound-assisted dispersion and hot-pressing method.The RGO and CNTs nanofillers,which had a hydrogen-bonding interaction with PLA matrix,were uniformly dispersed in the PLA matrix and a low percolation threshold(0.11 wt% for RGO/PLA and 0.80 wt% for CNTs/PLA CPCs)was observed in PLA nanocomposites.A comparative study of the thermal properties for RGO/PLA and CNTs/PLA nanocomposites suggested thatthe addition of RGO to PLA matrix showed weak crystallization ability and significant enhancement in thermal stability compared with CNTs/PLA nanocomposites(Xc is 49.82% for 0.8 wt% CNTs and 9.21% for 0.8 wt% RGO,respectively).Secondly,the microstructure evolution of conductive network constructed by different geometric nanofillers was investigated minutely.The microstructure of conductive network constructed by two-dimensional RGOwas obviously different to that formed by one-dimensional CNTs.During ten extension-retraction cycles,the values of the max and min ΔR/R0(R0 is the originalresistance and ΔR is the instantaneous change in resistance)for RGO/PLA CPCs shift upwards gradually with the increase of cycle number resulting from the breakdown of conductive networks caused by the slippage of overlapped RGO layers;while the values of the max and min ΔR/R0 for CNTs/PLA CPCs decrease gradually owing to the formation of better conductive network caused by the rearrangement of CNTs.Finally,the negative temperature coefficient(NTC)effecthas been observed in the RGO/PLA CPCs in the range of 20oCto 200 oC.The thermal-stimuli response mechanism of RGO/PLA CPCs to temperature was attributed to the change of intrinsic resistance of RGO and the morphology development of RGO.The stability and reproducibility of RGO/PLA CPCs to thermal-stimuli can be tuned by controlling the heat-treatment process of nanocomposites,the samples size of nanocomposites and the filler content of nanocomposites.The RGO/PLA CPCs are capable of detecting an extremely small temperature change as small as 0.1 °C and rapid responsive(< 10s)to temperature stimulation.This study indicated that the RGO/PLACPCsholds promise in practical applications as NTC materials with high sensitive and rapid responsivetowards temperature variation. |
