Stretchable Array of Highly Sensitive Pressure Sensors Consisting of ...
Supporting Information
Stretchable Array of Highly Sensitive Pressure Sensors Consisting of Polyaniline Nanofibers and Au-Coated Polydimethylsiloxane Micropillars
Heun Park 1, Yu Ra Jeong 1, Junyeong Yun 1, Soo Yeong Hong 1, Sangwoo Jin 2, Seung-Jung Lee3, Goangseup Zi4, and Jeong Sook Ha 1,2,* 1
Department of Chemical and Biological Engineering, Korea University, Seoul 136-
701, Korea 2
KU-KIST Graduate School of Converging Science and Technology, Korea University,
Seoul 136-701, Korea 3
New Transportation Systems Research Center, Korea Railroad Research Institute, Uiwang-
City, Gyeonggi-do 437-757, Republic of Korea 4
School of Civil, Environmental and Architectural Engineering, Korea University, Seoul 136-
701, Republic of Korea
1
Figure S1. Cross-sectional SEM images of the pressure sensor (a) before and (b) after applying a compressive force to the sensor, respectively. (c) and (d) Enlarged view of the PDMS micropillars that are in contact with polyaniline nanofiber surface.
2
Figure S2. (a) Schematic illustration showing the fabrication of three-component film layers of the deformable substrate. (b) Assembly of the fabricated three-film layers. Blue and red dots indicate via holes for liquid metal interconnections. (c) (Left) Top and (top right) crosssectional schemes of the deformable substrate with marked dimensions. (Bottom right) Crosssectional optical image of deformable substrate with embedded Galinstan interconnections.
3
Figure S3. Optical microscope images of dot patterns fabricated using the photolithography technique with an SU-8 3050 photoresist. (a) – (c) Dot patterns with the same unit cell size (160 × 160 µm2), but with different dot diameters of 50, 70, and 120 µm, respectively. (d) Dot pattern with a diameter of 50 µm and unit cell area of 240 × 240 µm2. Scale bar is 100 µm.
4
Figure S4. (Left and middle) 45° tilted and (right) cross-sectional SEM images of PDMS micropillars with different diameters and unit cell sizes. (a) Diameter of 50 µm and unit cell size of 160 × 160 µm2, (b) Diameter of 70 µm and unit cell size of 160 × 160 µm2, (c) Diameter of 120 µm and unit cell size of 160 × 160 µm2, (d) Diameter of 50 µm and unit cell size of 240 × 240 µm2.
5
Figure S5. (a) CV curve of polyaniline nanofiber film with 100 deposition cycle at a constant scan rate of 100 mV/s.
The potentiodynamic deposition was repeated from 0 V to 0.85 V and from 0.85 V to 0 V at a scan rate of 100 mV/s. In the CV curve obtained during polyaniline deposition cycle, three redox peaks a1/c1, a2/c2, and a3/c3 are observed. Peaks a1/c1 indicate the redox transition of polyaniline between a leucoemeraldine form (semi-conductive state) and an emeraldine form (conducting state). Peaks a2/c2 indicate the formation of other structures (e.g. the pbenzoquinone/hydroquinone couple). Peaks a3/c3 indicate the formation/reduction of bipolaronic pernigraniline and its resonance form, protonated quinonediimine.1,2 In Supplementary Figure S5, we observed those three peaks clearly. All deposition cycles of the polyaniline were finished at 0 V to form the oxidation state of polyaniline in leucoemeraldine form which is semiconducting so that we could control the optimized conductivity by increasing the film thickness.
6
Figure S6. (a) ATR-FTIR and (b) Raman spectra of electrodeposited polyaniline nanofiber film, respectively. (c) CV curves of polyaniline nanofiber film with different deposition cycles at a constant scan rate of 100 mV/s. (d) Molecular structure of polyaniline nanofiber.
7
Figure S7. Current response to pressure in the range of (a) 0.22-1.0 kPa and (b) 1.0-3.5 kPa, respectively.
8
Figure S8. Relative current change versus pressure with variation of (a) pillar diameter (50, 70, and 120 µm) under fixed unit cell size of 160 × 160 µm2 and (b) unit cell size (80 × 80, 160 × 160, and 240 × 240 µm2) under fixed pillar diameter of 50 µm, respectively.
9
Figure S9. Relative change in resistance vs. total contact area between PDMS micropillars and polyaniline nanofiber film at various applied pressures.
10
Figure S10. Dimensions of a grain of rice compared with a one-cent coin (U.S.) The contact area of the rice was estimated by assuming an elliptical shape with major and minor axis lengths of 5 and 3 mm, respectively, i.e., area of rice = (0.5/2) cm × (0.3/2) cm × π = ~ 0.118 cm2.
11
Figure S11. (a) Pressure-response curves of the pressure sensor measured on different substrates: rigid (red), PDMS (blue), and mixed film of PDMS and Ecoflex (green). The slope of the relative current change in the 1.0 kPa range is 1.12 (red), 0.78 (blue), and 0.37 (green) kPa-1, respectively. (b) Schematic illustration of the pressure sensors and measured substrates.
12
Figure S12. (a) Spatial mapping of current changes and (b) corresponding pressure on each pixel with loading of doughnut- shaped aluminum (220 Pa).
13
Figure S13. Relative current change on pixel (3, 3) under loading of various pressures on neighboring pixels of 5 × 5 pressure sensor array.
14
Figure S14. (a) Schematic illustration showing the fabrication of PDMS micropillars using the SU-8 mold. (b) (Top) Schematics showing the growth of polyaniline nanofiber layer on a PET film and (bottom) corresponding optical images. (c) Fabrication of the silver nanowire sticker as an electrode of the pressure sensor.
15
Table S1. Sensitivity of fabricated pressure sensor according to different pillar diameters and unit cell sizes.
16
Table S2. Comparison of the performance of pressure sensors. Types of device
Materials
Sensitivity (kPa-1)
Limit of detection (Pa)
Response time (ms)
Operating voltage (V)
Reference
Pentacene
0.05
-
30
20
3
Pil2TSi
8.4
-
10
100
4
PVDF
0.02
-
< 0.1
15
5
ZnO nanowires
0.131
-
150
1
6
PDMS/Rubrene
0.55
3
Stretchable Array of Highly Sensitive Pressure Sensors Consisting of Polyaniline Nanofibers and Au-Coated Polydimethylsiloxane Micropillars
Heun Park 1, Yu Ra Jeong 1, Junyeong Yun 1, Soo Yeong Hong 1, Sangwoo Jin 2, Seung-Jung Lee3, Goangseup Zi4, and Jeong Sook Ha 1,2,* 1
Department of Chemical and Biological Engineering, Korea University, Seoul 136-
701, Korea 2
KU-KIST Graduate School of Converging Science and Technology, Korea University,
Seoul 136-701, Korea 3
New Transportation Systems Research Center, Korea Railroad Research Institute, Uiwang-
City, Gyeonggi-do 437-757, Republic of Korea 4
School of Civil, Environmental and Architectural Engineering, Korea University, Seoul 136-
701, Republic of Korea
1
Figure S1. Cross-sectional SEM images of the pressure sensor (a) before and (b) after applying a compressive force to the sensor, respectively. (c) and (d) Enlarged view of the PDMS micropillars that are in contact with polyaniline nanofiber surface.
2
Figure S2. (a) Schematic illustration showing the fabrication of three-component film layers of the deformable substrate. (b) Assembly of the fabricated three-film layers. Blue and red dots indicate via holes for liquid metal interconnections. (c) (Left) Top and (top right) crosssectional schemes of the deformable substrate with marked dimensions. (Bottom right) Crosssectional optical image of deformable substrate with embedded Galinstan interconnections.
3
Figure S3. Optical microscope images of dot patterns fabricated using the photolithography technique with an SU-8 3050 photoresist. (a) – (c) Dot patterns with the same unit cell size (160 × 160 µm2), but with different dot diameters of 50, 70, and 120 µm, respectively. (d) Dot pattern with a diameter of 50 µm and unit cell area of 240 × 240 µm2. Scale bar is 100 µm.
4
Figure S4. (Left and middle) 45° tilted and (right) cross-sectional SEM images of PDMS micropillars with different diameters and unit cell sizes. (a) Diameter of 50 µm and unit cell size of 160 × 160 µm2, (b) Diameter of 70 µm and unit cell size of 160 × 160 µm2, (c) Diameter of 120 µm and unit cell size of 160 × 160 µm2, (d) Diameter of 50 µm and unit cell size of 240 × 240 µm2.
5
Figure S5. (a) CV curve of polyaniline nanofiber film with 100 deposition cycle at a constant scan rate of 100 mV/s.
The potentiodynamic deposition was repeated from 0 V to 0.85 V and from 0.85 V to 0 V at a scan rate of 100 mV/s. In the CV curve obtained during polyaniline deposition cycle, three redox peaks a1/c1, a2/c2, and a3/c3 are observed. Peaks a1/c1 indicate the redox transition of polyaniline between a leucoemeraldine form (semi-conductive state) and an emeraldine form (conducting state). Peaks a2/c2 indicate the formation of other structures (e.g. the pbenzoquinone/hydroquinone couple). Peaks a3/c3 indicate the formation/reduction of bipolaronic pernigraniline and its resonance form, protonated quinonediimine.1,2 In Supplementary Figure S5, we observed those three peaks clearly. All deposition cycles of the polyaniline were finished at 0 V to form the oxidation state of polyaniline in leucoemeraldine form which is semiconducting so that we could control the optimized conductivity by increasing the film thickness.
6
Figure S6. (a) ATR-FTIR and (b) Raman spectra of electrodeposited polyaniline nanofiber film, respectively. (c) CV curves of polyaniline nanofiber film with different deposition cycles at a constant scan rate of 100 mV/s. (d) Molecular structure of polyaniline nanofiber.
7
Figure S7. Current response to pressure in the range of (a) 0.22-1.0 kPa and (b) 1.0-3.5 kPa, respectively.
8
Figure S8. Relative current change versus pressure with variation of (a) pillar diameter (50, 70, and 120 µm) under fixed unit cell size of 160 × 160 µm2 and (b) unit cell size (80 × 80, 160 × 160, and 240 × 240 µm2) under fixed pillar diameter of 50 µm, respectively.
9
Figure S9. Relative change in resistance vs. total contact area between PDMS micropillars and polyaniline nanofiber film at various applied pressures.
10
Figure S10. Dimensions of a grain of rice compared with a one-cent coin (U.S.) The contact area of the rice was estimated by assuming an elliptical shape with major and minor axis lengths of 5 and 3 mm, respectively, i.e., area of rice = (0.5/2) cm × (0.3/2) cm × π = ~ 0.118 cm2.
11
Figure S11. (a) Pressure-response curves of the pressure sensor measured on different substrates: rigid (red), PDMS (blue), and mixed film of PDMS and Ecoflex (green). The slope of the relative current change in the 1.0 kPa range is 1.12 (red), 0.78 (blue), and 0.37 (green) kPa-1, respectively. (b) Schematic illustration of the pressure sensors and measured substrates.
12
Figure S12. (a) Spatial mapping of current changes and (b) corresponding pressure on each pixel with loading of doughnut- shaped aluminum (220 Pa).
13
Figure S13. Relative current change on pixel (3, 3) under loading of various pressures on neighboring pixels of 5 × 5 pressure sensor array.
14
Figure S14. (a) Schematic illustration showing the fabrication of PDMS micropillars using the SU-8 mold. (b) (Top) Schematics showing the growth of polyaniline nanofiber layer on a PET film and (bottom) corresponding optical images. (c) Fabrication of the silver nanowire sticker as an electrode of the pressure sensor.
15
Table S1. Sensitivity of fabricated pressure sensor according to different pillar diameters and unit cell sizes.
16
Table S2. Comparison of the performance of pressure sensors. Types of device
Materials
Sensitivity (kPa-1)
Limit of detection (Pa)
Response time (ms)
Operating voltage (V)
Reference
Pentacene
0.05
-
30
20
3
Pil2TSi
8.4
-
10
100
4
PVDF
0.02
-
< 0.1
15
5
ZnO nanowires
0.131
-
150
1
6
PDMS/Rubrene
0.55
3
