(435c) Liquid Coating Processes for Nanoparticle Films With Defined Microstructure

Particles with diameters below a micrometer are versatile building blocks for thin films applicable in electronics, photovoltaics, sensors, packaging, batteries, and many other fields. The arrangement of particles in the films affects its properties: percolating networks of metallic particles facilitate electric conductivity, alignment of nanorods yields polarizing films, for example. Conventional wet coating methods provide little control over the microstructure.

In this contribution, I will discuss how doctor blading and spray-coating of nanoparticles alone and in combination with polymers can be used to obtain layers with defined microstructures. Tuning liquid flows and colloidal interactions provides structural control without templates [1]. Doctor blading can be combined with template surfaces to create fully defined particle arrangements [2]. Emulsions direct the structure of spray-coated layers and enable aqueous processing on unpolar particles [3]. I will discuss which deposition rates can be achieved using different methods, the requirements on process control, and the degree of structural control achievable.

In-situ observation of the deposition provides direct feedback and simplifies the screening of the very large parameter spaces. I will present data from setups for wet deposition with microscopic online analysis of the process. Models are used to fit this data and make predictions on suitable ranges of process parameters to yield desirable film structures.

In summary, this contribution will present new processing routes for functional thin films based on nanoparticles. Different strategies that yield films with controllable microstructures using standard industrial coaters will be introduced and discussed.

[1] T. Geyer, P. Born and T. Kraus: Switching between crystallization and amorphous agglomeration of alkyl thiol-coated gold nanoparticles. Physical Review Letters 109 (2012) 128302  

[2] T. Kraus, L. Malaquin, H. Schmid, W. Riess, N. D. Spencer and H. Wolf: Nanoparticle printing with single particle resolution. Nature Nanotechnology 2 (2007) 570–576

[3] J. Lacava, P. Born and T. Kraus: Nanoparticle clusters with Lennard-Jones geometries. Nano Letters 12 (2012) 3279–3282