Manufacturing thin ionic polymer metal composite for sensing at the microscale

Abstract

Ionic polymer metal composites (IPMCs) are a class of materials with a rising appeal in biological micro-electromechanical systems (bio-MEMS) due to their unique properties (low voltage output, bio-compatibility, affinity with ionic medium). While tailoring and improving actuation capabilities of IPMCs is a key motivator in almost all IPMC manufacturing reports, very little efforts have been dedicated to sensing using IPMC thinner than 100 μm. Most reports on IPMC manufacturing and utilization rely on 180μm-thick Nafion with platinum electrodes, too stiff for bio-MEMS applications. The same fabrication process on thinner membranes does yield in very poor electrodes and performance, and needs to be studied to increase flexibility and sensitivity in the microscale range. This study demonstrates an electroless Pt deposition method for fabricating bio-MEMS-suitable 50 μm-thick IPMC samples. First, we perform a comparative study on the platinum distribution within the Nafion backbone as well as on the surface for the standard electroless deposition recipe for thin (50 μm) and thick (180 μm) Nafion. We report strong differences in platinum distribution for thick and thin IPMC that experienced the same manufacturing process. By varying chemical concentrations from the standard recipe we obtain convenient platinum distribution on thin Nafion, with platinum mainly localized in proximity of surface, as well as electrodes with lower sheet resistance. We could measure the flexural rigidity as 3.43 10−8 N.m2, 46 times lower than standard 180 μm thick IPMC. The calculated sensitivity is 0.476 ± 0.02 mV/mm and the limit of detection for our sensor is 500 ± 20 μm. This procedure sets a milestone for manufacturing 50 μm-thick IPMC for transducers and sensors in bio-MEMS applications.

Gold nanowire mesh electrode for electromechanical device

“…110 nm, respectively ( d in Table 1 ). Compared to the thickness of the electrode prepared by electroless plating (1–10 μm) 3 , 7 , 12 , the Au-NW mesh electrode was much thinner. The surface resistivities of Au-NW mesh electrodes ( R s in Table 1 ) were lower than that of Au-NW mesh film (1.23 ± 0.24 Ω sq −1 ) because of the improved connectivity between the Au-NWs by hot-pressing.…”

“…Ionic polymer-metal composite (IPMC) actuator, which consists of an ionic polymer sandwiched by the metal electrodes, is one of the most popular actuators in the fields of biomedical devices, flexible robots and microelectromechanical systems because of some advantages, light-weight, simple configuration, low operation voltage (< 5 V) and silent bending motion etc 1 – 5 . The typical combination of ionic polymer and electrode is a sulfonated tetrafluoroethylene polymer called “Nafion” and a noble metal electrode such as gold or platinum, respectively 6 , 7 . In most cases, the noble metal electrodes have been prepared on the Nafion surface by electroless plating 2 , 4 , 8 .…”

Gold Nanowire Mesh Electrode for Electromechanical Device

“…110 nm, respectively (d in Table 1). Compared to the thickness of the electrode prepared by electroless plating (1-10 µm), 3,7,13 the Au-NW mesh electrode was much thinner. The surface resistivities of Au-NW mesh electrodes (R s in Table 1) were lower than that of Au-NW lm (1.23 ± 0.24 Ω sq − 1 , see above) because of the improved connectivity between the Au-NWs by hotpressing.…”

“…It should be noted that the surface resistivity of Au-NW mesh electrode is much lower than that of the electrode prepared by electroless plating (1-10 Ω sq − 1 ) despite of its smaller thickness. 7,13,28 The mesh structure of the Au-NWs resulted in lower resistivity. The surface resistivity of the Au-foil was lower than that of the Au-NW mesh electrode.…”

“…[1][2][3][4][5] The typical combination of ionic polymer and electrode is a sulfonated tetra uoroethylene polymer called "Na on" and a noble metal electrode such as gold or platinum. 6,7 In most cases, the noble metal electrodes are prepared on the Na on surface by electroless plating. 2,4,8 The electroless plating requires to repeat the following two processes.…”