Nanocellulose based piezoelectric sensors

Transcription

1 Tampere University of Technology Nanocellulose based piezoelectric sensors Citation Tuukkanen, S., Viehrig, M., Rajala, S., & Kallio, P. (216). Nanocellulose based piezoelectric sensors Paper presented at Advances in Functional Materials (AFM 216), ICC, Korea, Republic of. Year 216 Link to publication TUTCRIS Portal ( Take down policy If you believe that this document breaches copyright, please contact and we will remove access to the work immediately and investigate your claim. Download date:

2 Nanocellulose based piezoelectric sensors Sampo Tuukkanen Assistant Professor (tenure track), BioMediTech, Department of Automation Science and Engineering, Tampere University of Technology (TUT) Tampere, FINLAND

3 Outline Nanocellulose fabrication Piezoelectricity of wood cellulose Nanocellulose film fabrication Piezoelectric sensitivity measurements Results and conclusions Sampo Tuukkanen

4 Nanocellulose fabrication Chemical structure of cellulose: [For more details see e.g.: Moon et al., Chemical Society Reviews 4(7) (27) 3941] Sampo Tuukkanen

5 Cellulose nanocrystal (CNC) AFM (atomic force microscope) image shows that CNCs are highly crystalline, rigid, rod-like nanoparticles (nanowhiskers) with a high aspect ratio Length of a few 1 nm Diameter of 5-2 nm CNC nanowhisker [AFM images by S. Tuukkanen, in 214 at Nanomicroscopy Center, Aalto University, Espoo, Finland] Sampo Tuukkanen, TUT, Tampere, Finland

6 Piezoelectricity of CNCs Piezoelectric effect = Electric charge separation by applied mechanical force The piezoelectric tensor d mn is determined by the symmetry of a crystal lattice [E. Fukada, J. Phys. Soc. Japan (1955)] The monoclinic C2 symmetry and the cancellation effects result into piezoelectric coefficient matrix: Chemical structure of cellulose: Cellulose crystal [[C 6 H 1 O 5 ] n ] unit cell: d mn d 14 d 25 [Zuluaga et al. (213)] Sampo Tuukkanen

7 Nanocellulose film fabrication Aqueous dispersion of CNF material (bleached birch cellulose mass) produced by a mechanical homogenizing process (6 passes through a microfibrillator) [Described in details in: M. Pääkkö et al. Biomacromolecules 8 (27) 1934] 1 cm CNF film was prepared by pressure filtering, followed by pressing and drying in hot-press (2 1 C), resulting a bendable CNF film containing amorphous areas and nonaligned CNC crystals areas [S. Rajala et al, ACS Applied Materials and Interfaces (216)] Amorphous nanocellulose Cellulose nanocrystals (CNC) Sampo Tuukkanen

8 Permittivity and hysteresis Relative permittivity and loss tangent were similar to typical dielectric polymers Polarization-voltage hysteresis curves for CNF film showed has some level of ferroelectric properties at high electric fields [S. Rajala et al, ACS Applied Materials and Interfaces (216)] Sampo Tuukkanen

9 CNF sensor assembly For piezoelectric sensitivity measurements, five nominally identical CNF sensors were assembled Pieces of CNF films assembled between two evaporated copper electrodes on polyethylene terephthalate (PET) substrate using adhesive film Crimp connectors (Nicomatic Crimpflex) were used for getting a reliable contacts to the copper electrode on flexible PET substrate PET Cu 125 µm 1 nm Nanocellulose film CNF: 45 µm Cu PET 1 nm 125 µm [S. Rajala et al, ACS Applied Materials and Interfaces (216)] Sampo Tuukkanen

10 Measurement setup Mini-Shaker (Brüel & Kjaer type 481) used for sensitivity measurements Reference sensors for dynamic and static forces (normal direction) DUT (device-under-test) placed horizontally on the metal plate The sensor sensitivity measure here is closely related to transverse piezoelectric coefficient d 33 (from piezoelectric tensor) [For details see: S. Tuukkanen et al., Synthetic Metals (212) or IEEE Sensors (215)] Sampo Tuukkanen

11 Sensitivity measurements Static force of ~3 N was used to keep sample steady Excitation with 2 Hz sinusoidal input signal of 1 V (peak to peak) results in a dynamic force of ~1.3 N Excitation by applying the force in the middle of the sensor; measurement repeated 3-9 times from both sides, resulting in a total of 6-18 excitations per sensor The sensor sensitivity by dividing the generated charge by the dynamic force Sensor sample The unit of sensitivity is pc/n Sampo Tuukkanen

12 Piezoelectric sensitivity Mean piezoelectric sensitivity ± standard deviation for excitations from each side of the CNF-sensors are shown in the Table 1 Sensitivity from different excitation positions for the CNF sensor and a polyvinylidene fluoride (PVDF) reference sensor shows only small variations The average sensitivity for the CNF sensor was 4.7 pc/n, while for the reference PVDF sensor was 27.5 pc/n [S. Rajala et al, ACS Applied Materials and Interfaces (216)] Sampo Tuukkanen

13 Sensor linearity and hysteresis Plots show (a) nonlinearity and (b) hysteresis curves for the CNF and the PVDF reference sensor Nonlinearity (charge vs. force curve by fitting a first degree polynomial via least-squares minimization) was found to be (.86 ±.48) pc for CNF and (6.47 ± 3.76) pc for PVDF Nonlinearity Sensor hysteresis (with increasing vs. descreasing force) was below 1 pc in maximum for both sensors Sensor hysteresis [S. Rajala et al, ACS Applied Materials and Interfaces (216)] Sampo Tuukkanen

14 Conclusions and summary Prepared self-standing 45-μm-thick cellulose nanofibrils (CNF) showed piezoelectric sensitivity of 4.7 ±.9 pc/n Not (intentionally) oriented/polarized, organization by fabrication process possible Sensitivity values align between quartz (2.3 pc/n) or PVDF (-3 pc/n) Nanocellulose is a promising solution-processable, renewable and disposable piezoelectric material!! [S. Rajala et al, ACS Applied Materials and Interfaces (216)] Ongoing work: Orientation/polarization & Flexibility by mixing with elastomer Sampo Tuukkanen

15 Funding from: Acknowledgements Nanocellulose and film preparation: Aalto University, Department of Forest Products Technology & Department of Materials Science and Engineering, Finland Maija Vuoriluoto, Dr. student: CNF-film preparation Orlando Rojas, Prof: Supervision Sami Franssila, Prof: Supervision Permittivity and hysteresis measurements: University of Oulu, Microelectronics Research Unit, Finland Tuomo Siponkoski, Dr. student: Hysteresis and permittivity Jari Juuti, D.Sc. (Tech.), Adj. Prof: Supervision Film characterisation and sensitivity measurements: Tampere University of Technology (TUT), Department of Automation Science and Engineering, Finland Satu Rajala, D.Sc. (Tech.): Sensitivity measurements Essi Sarlin, D.Sc. (Tech.): SEM imaging Marja Mettänen, D.Sc. (Tech.): Image based analysis Arno Pammo, B.Sc. (Tech.): Sensor assembly Sampo Tuukkanen, Ph.D., Asst. Prof: Supervision Sampo Tuukkanen