Traditional conductive polymer nanocomposite (CPN) liquid sensors have been studied for many years. However, they suffer from low sensitivity due to insufficient surface area and access points to the solvent. With increasing demand for highperformance smart sensors, the traditionally fabricated liquid sensors need major improvements in their performance. By introducing fused filament fabrication (FFF) smarter and environmentally friendlier parts can be made. The integration of FFF and CPN can provide increased degrees of freedom in the design and fabrication of liquid sensors.

In this work, design, 3D printing, and characterization of thermoplastic polyurethane/carbon nanotube (TPU/CNT) nanocomposites in response to acetone, toluene, and ethanol as solvents were conducted using a central composite design (CCD). CNT content, infill density, printing pattern, and solvent type were chosen as input factors and the sensor sensitivity was considered as the dependent response.

Response surface methodology (RSM) was employed to systematically assess the main effects and their quadratic terms and the two-way interactions of input parameters and identify the significant factors. The results showed that the solvent type, infill density, and CNT content are very significant factors while the infill pattern does not have a significant effect on the sensor sensitivity. The two-way interactions between the infill*solvent and CNT*solvent were found to have a P-value in the range of 0.05 and 0.1. A reduced model which offers a significant level of simplicity can be used to statistically describe the response behavior for further studying, design, and optimization of the sensors.

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