# Poly(\(\varepsilon\)-caprolactone)-Ionic Liquid Composite as Piezoionic Mechanical Sensor
## 2 Materials and Methods
#### Characterization Methods  
The IL and silver-based varnish were determined by weight percentage content using an analytical balance. Thermogravimetric analyses (TGAs) have been carried out through a Shimadzu (Kyoto, Japan) model DTG-60 instrument. TGA curves have been recorded at a heating rate of 20 \({}^{\circ}\)C min\({}^{-1}\), under a nitrogen flux (20 mL min\({}^{-1}\)), and from 35 \({}^{\circ}\)C to 700 \({}^{\circ}\)C. Analyzed sample mass varied between 8.0 mg and 11.0 mg. Scanning electron microscopy (SEM) micrographs have been obtained using a SEM EVO (Zeiss, Cambridge, UK) instrument equipped with an energy dispersive X-ray microanalysis (EDX) facility. The analyses were performed by setting a high electron beam voltage (EHT) of 20 kV and using a LaB\({}_{6}\) (Lanthanum Exaboride) emitter as the electron source. To carry out the SEM analysis, the samples were gold-sputtered with a thin gold film deposited through a sputtering process that was carried out using an Agar Sputter Coater AGB7340 spray coating machine (Agar Scientific, Stansed UK). XPS spectra were recorded using a VG Microtech Ltd (Uckfield, UK) spectrometer with a CLAMII analyzer. The X-ray source (Mg K\(\alpha\), 1253.6 eV) worked at 200 kV and 10 mA at a pressure of <2 \(\times\) 10\({}^{-8}\) Torr, a pass energy of 100 eV, and a take-off angle 45\({}^{\circ}\). Binding energies were referenced according to the C-H level at 285.0 eV. Dynamical mechanical analysis (DMA) was carried out using a 2000 TA DMA produced by Triton Technology Ltd. (London, UK). The frequency dependence of the membrane modulus has been evaluated in single cantilever mode by applying a sinusoidal force to a rectangular sample in the range 0.1-50 Hz at the working temperature T = 25 \({}^{\circ}\)C.  
The investigation into the piezoelectric PCL sensor's response to mechanical vibrations was conducted on rectangular samples (1 cm \(\times\) 5 cm-170 \(\upmu\)m thick) with a suitable experimental setup. This setup comprised instruments to gauge the sensor's electrical signals under vibration and a shaker to apply controlled kinetic movement (Figure 1). To analyze the mechanoelectrical transduction behavior of the PCL-based device, the utilized configuration included the equipment as follows:  
* TIRA GmbH (Schalkau, Germany) S51110 Shaker: Used to impress motion in the sensor arranged as a cantilever beam.
* Agilent Infiniium MSO9064A Digital Oscilloscope (Agilent, Santa Clara, CA, USA): Equipped with an 8-bit resolution and a maximum input sensitivity of 5 V/div (with a 1 M\(\upmu\)d load). It was employed for signal visualization and acquisition.
* Keysight 33220A Signal Generator (Keysight Technologies Italy S.r.l., Milano, Italy): Used to drive the shaker, thereby enabling precise control over mechanical vibrations.
* Baumer 12U6460/S35A Laser Sensors (\(\times\)2) (Baumer Italia S.r.l. Assago, MI, Italy): These sensors, with a resolution of approximately 2 \(\upmu\)m and adjustable sensitivity, measured vibration at the anchor and monitored tip displacement.
* Accelerometer PCB333B40-SN51174 (PCB Piezotronics, Depew, NY, USA): Mounted on the shaker's moving plate, this accelerometer served as a reference with a resolution of a 0.0005 m/s\({}^{2}\) root mean squared value (RMS) and a sensitivity of about 51.0 mV/(m/s\({}^{2}\)).  
Figure 1: Photograph of the experimental setup.