Hydrophobic and stretchable Ag nanowire network electrode passivated by a sputtered PTFE layer for self-cleaning transparent thin film heaters.

Sang-Mok Lee,Sang-Jin Lee,Jae Heung Lee,Sung Hyun Kim,Han-Ki Kim

doi:10.1039/c8ra00880a

Abstract

We demonstrated hydrophobic, flexible/stretchable, and transparent electrodes made up of Ag nanowire (NW) networks passivated by a sputtered polytetrafluoroethylene (PTFE) layer to produce self-cleaning transparent thin film heaters (TFHs). Using carbon nanotubes and a PTFE mixed conducting target, we successfully sputtered a transparent PTFE layer on the Ag NW network using mid-frequency magnetron sputtering. The hydrophobic surface of the PTFE/Ag NW electrodes led to water-repelling and self-cleaning transparent Ag NW electrodes, which are beneficial for transparent TFH-based smart windows. Furthermore, hydrophobic PTFE/Ag NW electrodes coated on polyethylene terephthalate (PET) and polyurethane (PU) substrates showed outstanding flexibility and stretchability, respectively, due to the capping effect of the PTFE layer. Based on outer/inner bending and stretching test results, we demonstrated the superior mechanical properties of the PTFE/Ag NW electrode compared to a bare Ag NW electrode. Finally, we investigated the feasibility of the PTFE/Ag NW film coated on a PU substrate as a transparent and stretchable electrode for stretchable and self-cleaning transparent TFHs. The effective heat generation of the stretchable PTFE/Ag NW electrode indicates the potential for energy-efficient multi-functional PTFE/Ag NW-based TFHs attached to automobile windows.

Highlights

We report highly exible/stretchable, transparent, and superhydrophobic Ag NW network electrodes passivated by polytetra uoroethylene (PTFE) using a midfrequency (MF) magnetron sputtering to realize self-cleaning and transparent thin film heaters (TFHs)
The PTFE/Ag NW hybrid electrode represented by Fig. 1(b), the Ag NW percolating network acted as a exible or stretchable conduction path for current ow while the PTFE layer acted as a hydrophobic passivation layer to protect the Ag NW network and prevent heat loss from the TFHs
Radio frequency (RF) magnetron sputtering has been considered as a simple, largearea coating technique, and is a mature thin lm process compared to many physical vapor deposition (PVD) techniques, investigations of MF- or DC-sputtered PTFE layers is still lacking due to the absence of a conductive PTFE sputtering target

Summary

Introduction

Transparent thin lm heaters (TFHs) have attracted much interest for use in defogging/de-icing windows and as heating sources for automobiles, displays, sensors, reaction cells, microchips, and transparent vinyl-based greenhouses.[1,2,3] In particular, the demand for exible or stretchable TFHs that can be attached to curved windows or the human body has rapidly increased due to advances in smart windows and wearable electronics.[4,5] Among the several components which comprise transparent and stretchable TFHs, high-performance transparent electrodes with low resistivity, high transparency, and outstanding mechanical exibility/stretchability are very important because the power injection, heat generation properties, heating uniformity, and transparency of TFHs are critically affected by the electrical, optical, and mechanical properties of the electrodes.

Results

Conclusion