碳纤维和碳纳米管的一篇综述

Elastomeric transparent capacitive sensors based on an interpenetrating composite of silver nanowires and polyurethane

Weili Hu, Xiaofan Niu, Ran Zhao, and Qibing Pei

Citation: Appl. Phys. Lett. 102, 083303 (2013); doi: 10.1063/1.4794143

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Elastomeric transparent capacitive sensors based on an interpenetrating composite of silver nanowires and polyurethane

Weili Hu,1,2Xiaofan Niu,1Ran Zhao,1and Qibing Pei 1,a)

1

Department of Materials Science and Engineering,Henry Samueli School of Engineering and Applied Science,University of California,Los Angeles,California 90095,USA 2

State Key Laboratory for Modification of Chemical Fibers and Polymer Materials,

Department of Materials Science and Engineering,Donghua University,Shanghai 201620,China

(Received 12January 2013;accepted 18February 2013;published online 28February 2013)Highly flexible transparent capacitive sensors have been demonstrated for the detection of deformation and pressure.The elastomeric sensors employ a pair of compliant electrodes comprising silver nanowire networks embedded in the surface layer of polyurethane matrix,and a highly compliant dielectric spacer sandwiched between the electrodes.The capacitance of the sensor sheets increases linearly with strains up to 60%during uniaxial stretching,and linearly with externally applied transverse pressure from 1MPa down to 1kPa.Stretchable sensor arrays consisting of 10Â10pixels have also been fabricated by patterning the composite electrodes into X-Y addressable

passive matrix.V

C 2013American Institute of Physics .[/10.1063/1.4794143]Future electronics are expected to be flexible,conforma-ble,and can take various form factors in order to realize a

plethora of user-friendly applications such as expandable dis-plays,conformable photovoltaic sheets,and artificial skins.1–4Pressure sensors strategically placed on a flexible synthetic skin working in the pressure range of 1kPa to 1MPa would be able to detect fingertip texture,hand grip,and in-shoe pressures.5Future robots wearing such a flexible pressure-sensitive skin can “feel”a touch or pressure.An electronic skin could also be used for advanced prosthetic limbs or applied as surgical gloves to perform feel-real remote opera-tions.6Being stretchable and able to detect the pressure or de-formation at the same time would allow for feedback control.Patients with prosthetic hand or limbs equipped with such arti-ficial skins could completely regain dexterity and maneuver-ability.In consumer electronics,capacitive touch sensors found on most current smartphones and tablet computers do not differentiate pressure differences.The addition of pressure sensing could make the touch screen more intuitive for users.Replacing the touch screen with an electronic skin would sig-nificantly increase the amount of data input or the “livelihood”in each finger touch via pressure sensitivity.7High visual transparency is required for such applications.

In these device applications,stretchable transparent elec-trode is an indispensable element.A variable capacitor using a pair of compliant electrodes sandwiching an elastomeric spacer can detect pressure or deformation in the change of ca-pacitance.8–12The Bao’s group recently reported a skin-like capacitive sensor based on single-walled carbon nanotubes (SWNTs)with detectable pressure of 50kPa and strain up to 50%.13This sensor,though not as sensitive to low pressures as their previously reported microstructured sensors,which could detect pressures generated by a fly weighing about 20mg,is stretchable and transparent.The transparency could expand the application scope,such as touch screens and elec-tronic skins with various options of skin color.Cohen et al.reported elastic strain gauges based on percolation SWNT

coatings.10The high sheet resistance of the SWNT coatings could limit the data speed and active area of these devices.The challenge still remains unresolved in developing an elas-tomeric electrode with low surface resistance and high visual transparency.

Several methods have been reported in the literature for the preparation of stretchable electrodes.1,3,14–19However,none has simultaneously achieved high stretchability,high conductivity,high transparency,and a low-cost large-area fabrication.Here,we report the fabrication of a high-performance transparent electrode by embedding an ultrathin silver nanowire (AgNW)network in the surface layer of an elastomeric polyurethane (PU)matrix.The composite elec-trodes retain high surface conductance at tensile strains up to 60%,and can be stretched repeatedly with minimal loss of electrical conductivity under both slow and fast strain rates.High-performance stretchable transparent capacitors can be readily fabricated by sandwiching an acrylic elastomer layer between two AgNW-PU composite electrodes.The resulting variable capacitors can detect pressure and deformation in a wide range of stretching and pressure conditions.

The preparation of the elastomeric transparent electro-des started with the formation of a conductive AgNW coat-ing on glass.19AgNWs with an average diameter of 60nm and an average length of 10l m were employed.Its disper-sion obtained from Seashell Technologies was diluted with methanol to a concentration of 2mg/ml,drop-cast on a pre-cleaned glass substrate,dried and annealed on a hotplate for 30min at 190 C to form a conductive AgNW coating.AgNWs in the network are uniformly distributed and ran-domly oriented over the entire coating area as shown in Figure 1(a).For the fabrication of capacitive sensor arrays,patterned AgNW coatings were deposited by spray-coating through a contact mask.The patterned AgNW coatings were annealed under the same condition as the un-patterned AgNW coatings.

Urethane liquid rubber compounds (Clear Flex V R

95,Smooth-On USA LLC)were mixed,degassed,and then drop-cast over the AgNW coatings on glass substrate.A second

a)

Electronic mail:qpei@.

0003-6951/2013/102(8)/083303/5/$30.00V

C 2013American Institute of Physics 102,083303-1APPLIE

D PHYSICS LETTERS 102,083303

(2013)