A longstanding roadblock in materials science lies in the controlled preparation of composite materials composed of more than two components and this holds especially true for nanoscale multi-composites. This is due to the fact that phase separation phenomena at the micro- and nanoscale frequently prevent to organize the individual components in a composite with precise distances between them. Over the last 25 years our team has focused on the development of one-dimensional multicomposites, so-called Layer-by-Layer (LbL) assembled films, in which the sequence of different materials and the distances between them are precisely controlled along the layer normal. An even greater challenge in materials science lies in the preparation of anisotropic materials which possess physical properties, for example optical, electronic or mechanical properties that differ in different directions of space. Particularly interesting components for the preparation of anisotropic multi-component materials are anisotropic nanoparticles, such as nanofibrils, nanowires or nanorods whose physical properties can often be tuned by varying their aspect ratio. While the physical properties of such nano-objects are usually highly anisotropic at the single particle level, their controlled integration into composites or multicomposites is even more difficult than the integration of their spherical counterparts. Macroscopic anisotropies are commonly induced by external electrical or magnetic fields, by surface templating or mechanical stretching, but all of these techniques impose severe restrictions with respect to the requirements for the size and the chemical nature of the materials onto which the composite films can be deposited. For keeping the alignment method as general as possible we have therefore recently developed grazing incidence spraying as a LbL-compatible technique for aligning anisotropic nanoparticles essentially by liquid shear with moderate to high aspect ratios in the form of LbL-films. Here we discuss the preparation and the anisotropic properties of thin films composed of cellulosic nanofibrils and of silver nanowires. The first materials we made have already shown highly interesting properties. Cellulose nanofibrils allow to prepare biodegradable transparent objects with the tensile strength of steel and silver nanowires allow to challenge some of the plasmonic properties of metallic nanostructures that could previously only be prepared by nanolithography.

Toward the self-assembly of layered multi-nano-composite films with complex anisotropies

253rd National Meeting (2017)

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