Abstract
Polymeric composites of linear triblock copolymer poly(styrene-co- ethylene/butylene-co-styrene) with a maleic anhydride unit (SEBS-MA) modified by hydrophilic polyethylene glycol (PEG) with various amounts of conducting filler - carbon nanotubes (CNT) - were prepared by solvent casting. The CNT surface was modified by a noncovalent approach with a pyrene-based surfactant to achieve a homogeneous dispersion of the conducting filler within the polymeric matrix. The dispersion of the unmodified and surfactant-modified CNT within the elastomeric SEBS-MA and SEBS-MA-PEG matrices was characterized by studying the morphology (SEM, TEM). A dynamical mechanical analysis was used to evaluate the interaction between the CNT and copolymer matrix. The electrical conductivity of the prepared composites was measured by dielectric relaxation spectroscopy, and the percolation threshold was calculated. The prepared elastomeric composites were characterized and studied as humidity sensor. Our results demonstrated that an MWCNT concentration slightly above the percolation threshold could result in large signal changes. In our system, good results were obtained for an MWCNT loading of 2 wt. % and an ~ 0.1 mm thin composite film. The thickness of the tested elastomeric composites and the source current appear to be very important factors that influence the sensing performance.
Highlights
Polymer composite materials are cost-effective and consist of two or more components with significantly different physical or chemical properties, and when combined, the final material might possess superior characteristics when compared to the individual components
The data show a saturation of the dc conductivity at a higher filler concentration, which enables the estimation of the critical Multiwall carbon nanotubes (MWCNTs) concentration for the formation of the percolating conducting network
The critical concentration of the percolation threshold significantly dictates the filler concentration range for the composites that may be suitable for vapor sensing applications (The dc conductivity data for the SEBS-MA/MWCNT composites are not included in Figure 1D because their filler concentration dependence was almost linear in the range studied here and, no percolation threshold could be determined for these composites)
Summary
Polymer composite materials are cost-effective and consist of two or more components with significantly different physical or chemical properties, and when combined, the final material might possess superior characteristics when compared to the individual components. The composite materials are suitable for gas-sensing as chemical sensors, vapor detectors, and “electronic noses” because their electrical resistance can provide a reversible change upon attack by solvent vapor. Dong et al (2008) proved that the grafting of PEG to PMMA resulted in a lower resistance due to different filler dispersion status compared to composites prepared without PEG Another observation proved that PEG can influence the sensing rate by softening the polymeric matrix (Zhao et al, 2006). Extensive work has been carried out to enhance the water sorption mechanism by sulfonation and the introduction of polar groups into the non-polar material (Butkewitsch and Scheinbeim, 2006; Li et al, 2018) In this case, the introduction of PEG and CNTs in a hydrophobic dielectric SEBS matrix results in a hydrophilic and highly conductive material, which may be suitable for relative humidity (R.H.) sensing applications. Where S0 is the initial resistance or voltage recorded after the sensor equilibration under N2 flow, and S(t) is the resistance or voltage at any given time
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