Ultrathin Flexible Strain Sensors Based On Polyurethane/Polyaniline Electrospinning Fibrous Mats

As a conducting polymer, polyaniline has amount of advantages in the application of sensors, including its low cost, easy accessibility, simple process, excellent physical and chemical properties, diversified structure, specific doping method and good environmental stability. Elastic polyurethane was chosen as the raw material because of its good performance, including good elasticity, oil resistance, ozone resistance, aging resitance, radiation resistance, low temperature resistance, strong cohesive force and good biocompatibility. Polyurethane/polyaniline nanofibers were prepared through in situ chemical polymerization of aniline monomers on the surface of the PU nanofibers. The ultrathin flexible strain sensor was made from polyurethane/polyaniline nanofibers. A series of performance of the strain sensor were evaluated, including mechanical properties, conductivity and the sensitivity of strain response. The main work of this paper as follows:Firstly, a suitable amount of polyurethane was dissolved in N, N-dimethylformamide with a concentration 20 wt. %. This solution was electrospun in electrostatic spinning device. The optimum parameters was obtained by three sets of single variable experiments, which the flow rate of the solution kept constant at 0.1 ml/h, a voltage of 20 k V was applied directly to the spinneret and the distance between the needle tip and the collector was maintained at 12.5cm.Secondly, Polyurethane(PU) nanofibers were prepared by electrospinning approach. And Polyaniline(PANI) was coated on the resulting nanofiber surface via in-situ polymerization to form flexible PU/PANI composite nanofibers with conductivity. The morphology and chemical composition of the as-obtained composite nanofibers were characterized by scanning electron microscopy(SEM) and fourier transform infrared spectroscopy(FTIR), respectively. The results showed polyaniline was successfully synthesized on the surface of PU nanofiber and PU/PANI composite nanofibers possessed skin-core structure. Furthermore, the experiments indicated the optimal technological parameters of the polymerization process were as follow: the concentration of aniline monomers was 1.3 mol/L, the polymerization time was 120 min. And the resultant nanofibers expressed high electrical conductivity(7.6×10-1S/cm).Thirdly, the as-spun polyurethane/polyaniline fiberous nanocomposites, which the thickness was about 10 micrometres, were glued on a flexible PVC plate to fabricate ultrathin flexible strain sensors based on polyurethane/polyaniline electrospinning fibrous nanocomposites. The sensitivity of the strain sensor was tested under bending strain and tensile strain, respectively. Normalized resistance- strain curves were drawn and the changing of the resistance was discussed. These experiments demonstrated that the strain sensor had good reversibility and sensitivity. It was expected to be applied in precision sensors, smart textiles and so on.