Influence of the Porosity of Polymer Foams on the Performances of Capacitive Flexible Pressure Sensors

• Published in: Sensors (Basel, Switzerland) Vol. 19; no. 9; p. 1968
• Main Authors: Bilent, Sylvie, Dinh, Thi Hong Nhung, Martincic, Emile, Joubert, Pierre-Yves
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 26-04-2019; MDPI
• Subjects: Curing; Deformation; Dielectric properties; Electrodes; electromechanical characterizations; Engineering Sciences; microporous PDMS foam; Plastic foam; Polydimethylsiloxane; polymer-based flexible pressure sensors; Polymers; Porosity; Pressure sensors; Sensitivity; sensor behavioral modeling; sensor sensitivity and measurement range; Sensors; Silicone resins; Wearable technology; sensor behavioral modeling; microporous PDMS foam; polymer-based flexible pressure sensors; sensor sensitivity and measurement range; electromechanical characterizations
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s19091968

This paper reports on the study of microporous polydimethylsiloxane (PDMS) foams as a highly deformable dielectric material used in the composition of flexible capacitive pressure sensors dedicated to wearable use. A fabrication process allowing the porosity of the foams to be adjusted was proposed and the fabricated foams were characterized. Then, elementary capacitive pressure sensors (15 × 15 mm
square shaped electrodes) were elaborated with fabricated foams (5 mm or 10 mm thick) and were electromechanically characterized. Since the sensor responses under load are strongly non-linear, a behavioral non-linear model (first order exponential) was proposed, adjusted to the experimental data, and used to objectively estimate the sensor performances in terms of sensitivity and measurement range. The main conclusions of this study are that the porosity of the PDMS foams can be adjusted through the sugar:PDMS volume ratio and the size of sugar crystals used to fabricate the foams. Additionally, the porosity of the foams significantly modified the sensor performances. Indeed, compared to bulk PDMS sensors of the same size, the sensitivity of porous PDMS sensors could be multiplied by a factor up to 100 (the sensitivity is 0.14 %.kPa
for a bulk PDMS sensor and up to 13.7 %.kPa
for a porous PDMS sensor of the same dimensions), while the measurement range was reduced from a factor of 2 to 3 (from 594 kPa for a bulk PDMS sensor down to between 255 and 177 kPa for a PDMS foam sensor of the same dimensions, according to the porosity). This study opens the way to the design and fabrication of wearable flexible pressure sensors with adjustable performances through the control of the porosity of the fabricated PDMS foams.