Effect of Processing Parameters on Electrophoretically Deposited ZnO Nanoparticles on Conductive Fabrics

Introduction

                Interest in controlling the assembly of the nanostructured materials has recently increased due to their great potential for a wide range of applications [1]. The processes of nanostructured materials require more complex methods. The electrophoretic deposition (EPD) of ceramic materials has become attractive not only because of its high versatility but also because of low cost equipment [2]. EPD process can be applied to various types of substrates such as fibers, cloths and complex shaped metals [3]. Development of composites with multi-scale reinforcements consisting of multi-walled carbon nanotubes or carbon nanofibers has also been explored [4]. Although coating metal oxide on various types of substrates by EPD has been well studied, few studies have been performed regarding the deposition on conductive fabrics such as metal plated fabrics or carbon fabrics. Such a flexible, soft and nonfragile substrate is being explored for flexible and wearable functional device, but the deposition behaviors and the properties of the deposits have not been thoroughly investigated.

In this study, ZnO nanoparticles and other nanostructures were coated by EPD on flexible fabrics and solid plate substrates. The effects of particle size, pH of suspension, applied voltage and substrate type on the EPD kinetics and morphological properties were investigated. The structural and optical properties of deposit ZnO layers by EPD were also examined by SEM, XRD and UV–Vis DRS.

Experimental

                Four different sizes (50, 100, 200, and 400 nm) of commercial ZnO powders were used. ZnO particles were mixed with ethanol. PEI was added as a dispersant and the pH levels of the suspensions were adjusted with NH₄OH. Other shapes of nanostructures were also synthesized for EPD. The deposition process was performed using two electrodes, fixed with distance of 10 mm, vertically immersed in prepared suspensions. Stainless steel plates, copper plates, copper coated fabrics, carbon fabrics were used as the working electrode and stainless steel plates were used as the counter electrode. The deposited area on the each substrate was 1 cm². The experiments were performed within 1-5 min under a constant voltage of 10-100 V. The structural and optical properties of deposit ZnO layers by EPD were analyzed by using SEM, XRD and UV–Vis DRS.

Results

                To study the effect of particle size and pH in suspension, EPD performed with 4 different sizes of ZnO nanoparticles. The suspension was prepared at different pH ranging from 8 to11, and a constant voltage of 50 V was applied for 5 min. For all suspension, deposition weights showed sharp decrease over pH 10 and increased with the decrease of the particle size, which may result from the change of zeta potential in the solution.

The effect of applied voltage was verified by EPD with 4 different size of ZnO powders at pH 9 for 1 min with the applied voltage of 10-100 V. The experimental results were compared with Zhang’s equation [5]. The deposition weight increase with the voltage increase, as expected.

ZnO nanoparticles were deposited on flexible fabrics and solid plates for comparison. The weight gain of the deposit on both substrates was measured as a function of applied voltage. The weight gain of ZnO deposits on both Cu coated fabric and Cu plate increased linearly with the applied voltage, but larger deposition weight on Cu coated fabric was observed. Larger surface area of woven fabric due to non-flat surface can be attributed to more deposition of ZnO nanoparticles.

XRD patterns show only peaks of ZnO and substrates. No preferred orientation of ZnO layers was observed. Morphologies of deposited layers show smaller particle size shows denser layer. In addition, higher electric field in EPD process promotes particles to be coated more quickly, but uniform and dense coating may be limited. The optical properties of dried ZnO layer prepared EPD show comparable results to reported bulk ZnO ceramic.

Conclusions

                Nanostructured ZnO was deposited on fabric substrates by EPD on fabric. Dominant parameters to determine EPD process on the fabric were investigated by comparing reported EPD empirical equations. Among the investigated parameters, particle size in suspension appears to play an important role in EPD kinetics. The characterization results of the nanostructured ZnO on fabrics could provide a path to promote the development of flexible or wearable devices.

Acknowledgements

This research was supported by Agency for Defense Development (ADD) as global corporative research for direct urine fuel cell.

References

1.             Corni, I., M.P. Ryan, and A.R. Boccaccini, J. Eur. Ceram. Soc., 28,  1353 (2008).

2.             Besra, L. and M. Liu, Prog. Mater Sci., 52,  1 (2007).

3.             Wang, Y.C., I.C. Leu, and M.H. Hon, J. Am. Ceram. Soc., 87,  84 (2004).

4.             Lee, S.-B., O. Choi, W. Lee, J.-W. Yi, B.-S. Kim, J.-H. Byun, M.-K. Yoon, H. Fong, E.T. Thostenson, and T.-W. Chou, Composites Part A: Applied Science and Manufacturing, 42,  337 (2011).

5.             Zhang, Z., Y. Huang, and Z. Jiang, J. Am. Ceram. Soc., 77,  1946 (1994).