A Comparative Study on the Effects of Spray Coating Methods and Substrates on Polyurethane/Carbon Nanofiber Sensors

Abstract

Thermoplastic polyurethane (TPU) has been widely used as the elastic polymer substrate to be combined with conductive nanomaterials to develop stretchable strain sensors for a variety of applications such as health monitoring, smart robotics, and e-skins. However, little research has been reported on the effects of deposition methods and the form of TPU on their sensing performance. This study intends to design and fabricate a durable, stretchable sensor based on composites of thermoplastic polyurethane and carbon nanofibers (CNFs) by systematically investigating the influences of TPU substrates (i.e., either electrospun nanofibers or solid thin film) and spray coating methods (i.e., either air-spray or electro-spray). It is found that the sensors with electro-sprayed CNFs conductive sensing layers generally show a higher sensitivity, while the influence of the substrate is not significant and there is no clear and consistent trend. The sensor composed of a TPU solid thin film with electro-sprayed CNFs exhibits an optimal performance with a high sensitivity (gauge factor ~28.2) in a strain range of 0–80%, a high stretchability of up to 184%, and excellent durability. The potential application of these sensors in detecting body motions has been demonstrated, including finger and wrist-joint movements, by using a wooden hand.

Use of Electrospinning for Sustainable Production of Nanofibers: A Comparative Assessment of Smart Textiles-Related Applications

“…In general, a process sequence that is frequently employed for the fabrication of flexible configurations for body motion monitoring is the development of PU/TPU nanofiber mats through electrospinning and their coating through various techniques with conductive materials, such as conducting polymers [ 130 ], reduced-GO (RGO) [ 131 ], and carbon nanofibers (CNFs) [ 132 ] and nanotubes (NTs) [ 133 ]. PU and TPU electrospun substrates can offer not only an excellent flexibility, which is crucial where the attachment of the produced arrays on clothes and skin is concerned, but also a large specific surface area and high porosity.…”

“… Material Used for Electrospinning Optimum Electrospinning Conditions Process Steps for the Preparation of Smart Textile Type of Smart Textile Potential Application Reference TPU (matrix), DMF (solvent) 15 kV voltage, 0.8 mL/h feed rate, 30 cm tip-to-collector distance, ∼50 rpm rotating speed of drum Preparation of PU fibrous non-woven via electrospinning Dip coating of the electrospun PU nonwoven with the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) Mechanically stretchable and electrically conductive textile Wearable electronics [ 130 ] TPU (matrix), DMF:THF (1:1) (solvent) 20 kV voltage, 3 mL/h feed rate, 15 cm tip-to-collector distance Fabrication of PU fibrous mat via electrospinning Ultrasonication of reduced graphene oxide (RGO) Fabrication of RGO/PU composite by immersion of PU fibers into RGO solution and ultrasonication Flexible resistive-type strain sensors Smart wearable device [ 131 ] TPU (matrix), DMF:THF (1:3) (solvent) 8 wt%. TPU in DMF:THF, 23 kV voltage, 2.5 mL/h feed rate, 10 cm tip-to-collector distance Preparation TPU substrate by electrospinning Deposition of carbon nanofibers (CNFs) on TPU by spray coating Durable, stretchable piezoresistive strain sensor E-skin for detecting body motions [ 132 ] TPU (matrix), DMF:THF (1:1) (solvent) 15 wt%. TPU in DMF:THF, 30 kV voltage, 5 mL/h feed rate, 16 cm tip-to-collector distance Preparation of the TPU fibrous film by electrospinning Fabrication of TPU/carbon nanotu...…”

The technology of wearable flexible textile-based strain sensors for monitoring multiple human motions: construction, patterning and performance

“…Additionally, the sensitivity of the sensors was found to increase with higher concentrations of carbon nanofibers in the composite. 52…”

“…Additionally, the sensitivity of the sensors was found to increase with higher concentrations of carbon nanofibers in the composite. 52 2.5 Overview of optical-based strain sensor with performance An optical sensor refers to a type of sensor that uses optical fibres to detect changes in strain or deformation in a material or structure. The sensor works by transmitting light through the fibre, which is sensitive to changes in the material or structure's deformation.…”

Enhanced Piezoelectricity of PVDF-TrFE Nanofibers by Intercalating with Electrosprayed BaTiO3

“…Novel flexible polymer nanocomposites and microstructures have recently been widely utilized to develop flexible and stretchable sensors and energy harvesters. − Piezoelectric materials are of particular interest due to their capability of transducing mechanical stress to electrical signals and vice versa. Some examples of common piezoelectric materials include barium titanate (BaTiO 3 or BTO), , lead zirconate titanate , with a high piezoelectric coefficient, and flexible piezoelectric polymers, e.g., polyvinylidene fluoride (PVDF) , and its copolymers (e.g., poly­(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE)). − …”