Highly Oriented Electrospun P(VDF‐TrFE) Fibers via Mechanical Stretching for Wearable Motion Sensing

Abstract

materials, piezoelectric materials, which can convert mechanical shape changes into electric outputs, are particularly favorable to fabricate wearable devices for mechanicalrelated sensing and power generation. [15][16][17] According to material molecular compositions, piezoelectric materials are generally divided into ceramics and polymers. Indeed, even though inorganic piezoelectric materials offer high piezoelectric property, they are mechanically hard and brittle, which have difficulties to be directly applied to wearable devices. Besides, many piezoelectric ceramics contain heavy metal elements such as lead, that are harmful to human and environment. [18][19][20] On the other hand, piezoelectric polymers, represented by polyvinylidene fluoride (PVDF) and its copolymer poly[(vinylidenefluoride-cotrifluoroethylene] (P(VDF-TrFE)), are more preferable for wearable devices as they are lightweight, stretchable, environmentfriendly and chemically stable. [21,22] To construct piezoelectric polymer fibers, electrospinning, as a representative template-free method, [23,24] is a versatile technique to produce extended length of fiber-shaped structures with a number of advantages such as large surface area, tunable surface morphologies, and enhanced mechanical performance. [25][26][27][28] With electrospinning, when the droplet of polymer solution is charged by high applied voltage, the liquid droplet is pulled into a thin fiber and then collected by the grounded electrode. However, this liquid-to-solid transferring process normally results in randomly distributed fibers with poor electrical properties and limited response to mechanical stimuli. Therefore, to improve the performance of electrospun fibers, several methods have been demonstrated to obtain aligned electrospun fibers. [29][30][31][32][33] Two most frequently adopted methods are: 1) using a high-speed rotating collector with a very sharp edge, [34][35][36] and 2) using two separated parallel electrodes. [37,38] A very high rotating speed (>3000 rpm) is necessary for the rotating collector method, which brings high requirements to the fabrication facilities and increases electricity consumption. Also, the necessary role of sharp edge further restricts the amount of highly aligned electrospun fibers that can be collected. The parallel electrode method, on the other hand, can only fabricate aligned electrospun fibers in a very limited length, typically on millimeter scale.Advances in functional fabrics enable the realization of wearable devices in the form factor of fibers that can be seamlessly adapted in our daily lives. For mechanical-related sensing and power generation, piezoelectric materials are particularly favorable because they can convert mechanical shape changes into electric outputs. Electrospinning is a widely applied technique to produce extended length of fiber-shaped piezoelectric devices. However, this versatile process normally results in randomly distributed fibers with poor electrical properties and limited response to mechanical stimuli. H...

Ferroelectric P(VDF-TrFE)/POSS nanocomposite films: compatibility, piezoelectricity, energy harvesting performance, and mechanical and atomic oxygen erosion

“…Researches of P(VDF-TrFE) in hybrid composite used as touch sensors, energy storage devices, and eld-effect transistors have been widely studied in recent years. [27][28][29][30] Nah et al 31 fabricated and reported the ultrathin P(VDF-TrFE) nanober air lter that can be activated by the dipoles polarization to enhance the ltering efficiency. The electrically activated P(VDF-TrFE) lter demonstrates that the ltering efficiencies were over 88% aer polarization and 94% aer tribo-electrication.…”

Developable Rotationally Symmetric Kirigami‐Based Structures as Sensor Platforms

“…The ability to quantify movement of key joints during activity can dramatically improve outcomes for rehabilitation and boost athletic performance. [16][17][18][19][20][21] However, the sensing is based on stretching of the fibers, typically unidirectional and poorly suited for integration with substantially rigid electronic components that do not tolerate well to repeated mechanical deformation. [8][9][10] Currently, tracking motion or deducing impact stresses is performed using camera motion tracking systems [11,12] or inertial measurement units (IMUs) that consist of an accelerometer, gyroscope, and magnetometer, typically packaged in a rigid brace or integrated within a band or suit.…”

Epitaxy Enhancement of Piezoelectric Properties in P(VDF‐TrFE) Copolymer Films and Applications in Sensing and Energy Harvesting

“…For example, mapping of insole plantar pressure distribution [50] and detection of impact of water drops [51] were both designed according to longitudinal piezoelectric property. However, transverse piezoelectric property is of especial consideration in most of piezoelectric sensing and energy harvesting applications, including in situ measurement of stress intensity factors during fatigue crack growth, [52] detection of body gestures including angles of elbow bending and directions of a swinging arm, [19] stretchable micromotion sensors for voice recognition [53] and energy harvesting from one finger-striking motion. [54] So, it is required to further explore the contribution of epitaxy process on transverse piezoelectric property.…”