Preparation of spherical, ordered colloidal aggregates using inkjet printing
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Preparation of spherical, ordered colloidal aggregates using inkjet printing Enrico Sowade1, Thomas Blaudeck1, 2, Reinhard R. Baumann1, 3 1 Institute for Print and Media Technology, Digital Printing and Imaging Technology, Chemnitz University of Technology, Chemnitz, Germany. 2 Center for Microtechnologies, Chemnitz University of Technology, Chemnitz, Germany. 3 Printed Functionalities, Fraunhofer Institute for Electronic Nanosystems (ENAS), Chemnitz, Germany. ABSTRACT In this paper we report about combining inkjet printing technology and self-assembly as a scalable manufacturing tool for spherical, well-ordered aggregates. The aggregates consist of a high number of ordered colloidal nanospheres arranged as ball-shaped structures. Applying inkjet printing based on the principle of droplet ejection the spherical aggregates can be deposited on various surfaces in dry environment and under ambient conditions. The aggregation of the nanospheres is independent of the surface energy of the substrate leading to the assumption that the main part of the assembly and aggregation process takes place in-flight [1]. By applying inkjet printing with an adapted control signal, small droplets of a water-based ink formulation containing monodisperse polystyrene nanoparticles are ejected out of the inkjet nozzles. The ejected droplets serve as a confined geometry for the nanospheres in the carrier liquid during evaporation. As a result, the particles form stable ball-shaped aggregates with hexagonal order. Due to the in-flight self-assembly of the nanospheres, our approach is suitable for any solid surface in dry environment and allows the deposition of the ball-shaped aggregates in appropriate patterns. INTRODUCTION Complex, ordered structures on nano- and micrometer scale are ubiquitous in nature and advanced science. Due to their promising properties and potential applications in numerous fields these sophisticated structures have been attracting more and more interest in recent years [2-6]. Examples of creatures and plants in nature that exhibit complex, ordered structures are beetles, butterflies, peacocks, lotus leafs, insect eyes, fishes and reptiles [2, 5, 6]. All the examples have extraordinary functionalities such as brilliant colors described as structural colors, special wettability (e.g. superhydrophobicity) or material absorbency. These functionalities are mainly related to the unique arrangement of the nano- and microstructure and not to the intrinsic property of the material they made of [5]. Mimicking such nano- and microstructures found in nature requires state-of-the-art nanofabrication procedures to make them utilizable for nanotechnology and exploit them to create structures, surfaces, devices or systems with novel functionalities and properties. Nano- and microstructures can be manufactured applying either top-down or bottom-up methods [7]. However, nanofabrication of very complex three dimensional and well-ordered structures is highly challenging for top-down methods without specialized and expensive equipment
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