Large-Scale Synthesis and Surface Modification of Silver Nanomaterials and Their Applications to Flexible and Stretchable Devices

Abstract

Metal nanomaterials have attracted tremendous attention because of their fascinating physicochemical properties, including their optical, electronic, magnetic, mechanical, and chemical properties. Metallic Ag nanomaterials have been especially intensely investigated for their applications in various fields because of their unique properties such as their excellent electrical conductivity, catalysis, plasmon light-scattering ability, and antibacterial activity. These properties are critically dependent on the size, size distribution, and shape of the nanoparticles (NPs). Thus, substantial efforts have been made in recent decades to develop synthetic methods with improved control over the size and shape of Ag nanomaterials. This dissertation describes the synthesis of uniform Ag nanomaterials using colloidal chemistry and their application as flexible and stretchable electrodes. First, I report the fabrication of uniform and ultra-small-sized Ag nanoparticles (AgNPs) by using a simple synthetic method with high productivity. The NP size was controlled by varying the heating rate. This method is easy to scale up to multigram quantity. The formation of the AgNPs through this synthetic reaction was investigated by ultraviolet (UV)-vis and fluorescence spectroscopy, transmission electron microscopy (TEM), and matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) mass spectrometry. The data show that kinetic control of the formation of Ag clusters enables the synthesis of ultra-small-sized AgNPs. Second, I describe a soft and stretchable electrode element that is lightweight and thin and is conformally integrated with various surfaces and the skin. The electrode is composed of a highly conductive Ag nanowire (AgNW)/elastomer nanocomposite. The ligand exchange (LE) of AgNWs allows the NWs to be homogeneously dispersed in the elastomeric medium. This excellent homogeneity leads to mechanically and electrically uniform characteristics and the processability of the composite into various patterns, thereby enabling the production of reliable, large-area conductive electrodes. The softness of the electrode provides maximum comfort, system robustness, and effective conduction, even under bending and stretching. Finally, I introduce electromechanical cardioplasty using an epicardial mesh made of an electrically conductive and mechanically elastic nanocomposite material designed according to two strategic approaches. i) I created an epicardium-like substrate that mechanically integrates with the heart and acts as a structural element in cardiac chambers. ii) I instilled the electrical function of a cardiac conduction system (His-bundles and Purkinje fiber network) into the mesh to deliver impulses from the elasto-conductive epicardial mesh device to the whole ventricular myocardium in concert. These design concepts could allow the recruitment of the entire surviving myocardium, including areas surrounded by fibrotic tissues, to participate in synchronous contraction, significantly improving systolic function while preserving diastolic function.