Vapour-assisted roll-to-roll nanoimprinting of micropillars on nanocellulose films

• Published in: Microelectronic engineering Vol. 225; p. 111258
• Main Authors: Mäkelä, Tapio, Hokkanen, Ari, Sneck, Asko, Ruotsalainen, Teemu, Khakalo, Alexey, Tammelin, Tekla
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.03.2020; Elsevier BV
• Subjects: Cellulose; Cellulose nanofibrils; Diffraction; Diffraction grating; Diffraction patterns; Gratings (spectra); Hot embossing; Laser beams; Microstructure; Nanoimprinting; Offset printing; Optical effect; Patterning; Production methods; R2RNIL; R2RVANIL; Replicating; Roll-to-roll; Softening; Surface modification; Surface properties; TEMPO CNF; Tensile strain; Tensile strength; Thin films; Water chemistry; Water vapor; Diffraction grating; Surface modification; Roll-to-roll; TEMPO CNF; Nanoimprinting; Cellulose nanofibrils; R2RNIL; R2RVANIL; Optical effect; Hot embossing
• ISSN: 0167-9317; 1873-5568
• DOI: 10.1016/j.mee.2020.111258

Here we demonstrate a straightforward vapour-assisted roll-to-roll nanoimprinting lithography (R2RVANIL) patterning method to biobased nanocellulosic films with the aim to fabricate microstructured films with diffraction effect. In the R2RVANIL technique a roll with pillar structures is softly pressed against nanocellulose film in the presence of hot water vapour replicating the pattern onto the film. The printed pillar structures are compared with the structures produced using traditional thermal R2RNIL. The manufacturing method is demonstrated using optically transparent TEMPO-oxidised cellulose nanofibrils (TEMPO CNF). TEMPO CNF films possess high tensile strength and modulus whereas the tensile strain is low, they are very hygroscopic - a property which improves material processing at elevated humidities, thus overcoming a lack of a clear softening point. In this context, the water molecules are acting as plasticising molecules thereby softening the relative brittle nanocellulose film structures. Patterned pillars were achieved due to the swelling and softening of the film which was contacted with moist air. R2RVANIL method appears to be more gentle and surface properties such as roughness are different from the ones achieved via conventional thermal NIL method. The diffraction grating is demonstrated using laser beam compared to calculated diffraction patterns. Water vapour assisted patterning methods are beneficial, for example, in the future optics and electronics where films cannot be processed under high pressure and, on the other hand, high production volumes are needed. Vapour-Assisted Roll-to-Roll Nanoimprinting on TEMPO-CNF. Diffraction pattern is demonstrated using transmitting laser beam through R2RVANIL patterned TEMPO CNF film. [Display omitted] •Vapour-assisted roll-to-roll imprinting method (R2RVANIL) to form structures on TEMPO CNF films was demonstrated•TEMPO CNF is not thermally modified but relies on swelling behaviour•Diffraction pattern is demonstrated for transparent TEMPO CNF film•R2RVANIL process for TEMPO-oxidised cellulose nanofibrils (TEMPO CNF) films show a huge potential for future applications in optics and electronics