Final Report Summary - PHOTOPATTTOCELL (Photopatterning of Cellulose Films for Creation of 2- and 3-Dimensional Nanostructures)
Three major scientific achievements have been made in the field of cellulose nanomaterials, namely the realization of photoregeneration, the establishment of a simple procedure to make 2-D structures vie photolithography and the first report on 3-D structures using 2-photon absorption lithography. Photoregeneration was investigated using acid labile cellulose derivatives, namely trimethylsilyl cellulose, (TMSC), which are dissolved in the presence of a photo acid generator. Such photo acid generators produce an acid when exposed to light of certain wavelengths. After making thin films (ca 100 nm) by spin coating, the films were illuminated and for some photo acid generators such as N-Hydroxyphtalimide triflate excellent results were obtained for the regeneration to cellulose. The morphology of the films was not affected by the photoregeneration step as proven by atomic force microscopy and nearly the same rms roughness was observed. Additionally, the resulting photoregenerated films show excellent degradability with cellulases. The next step was to create patterned films to create positive and negative type resists. For this purpose, the illumination step was performed on a mask aligner. For the realization of a negative type resist, the films were rinsed with the solvent used for film preparation and feature sizes down to 800 nm resolution were obtained. For the creation of positive type resists, the films were subjected to a cellulase solution directly after the illumination step. The cellulases digest the cellulose but do not attack the remaining TMSC film. In a subsequent step, the TMSC is converted to cellulose by illumination and a positive-type resist is obtained. The third major achievement was the realization of three-dimensional structures by two photon absorption lithography. The same compound as for the photolithography was used, namely N-Hydroxynaphtalimide triflate, which is also TPA active. This means that in the focus of a laser the compound is able to produce two photons which excite to molecule finally leading to the creation of an acid. Since the laser can be controlled with high precision, high three dimensional resolution were realized (ca 600 nm). Smaller feature sizes can be manufactured using phase separation of polymers. Such examples have been realized in the case of lignin palmitate/cellulose and PHB/cellulose films. Depending on the ratio of the two polymers, features as small as 50 nm can be realized. While the PHB/cellulose blend system is an enzymatically developed resist material, the lignin palmitate/cellulose blend can be exploited to minimize nonspecific protein adsorption.