Wetting characteristics of cellulosic substrates designed by partially imitating sized paper surfaces were investigated with regard to the surface morphology by contact angle measurement, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy. The contact angles of water droplets on cellulose films decreased with increasing surface roughness at the nm level according to Wenzel's theory. Binary alkanethiolate self-assembled monolayer (SAM) prepared as a hydrophobic surface model of size components demonstrated the characteristic water repellency of Cassie's theory. These two surface-design methods were combined to control the surface morphology of sized cellulose imitations. Vaporized Au colloids were deposited on the cellulose film, and subsequently dodecanethiol (DT) self-assembled only at the Au positions. The AFM phase images confirmed that the total Au coverage was less than 20% of the substrate surface, but the water repellency of the model cellulosic surface attained ca. 103°, which is almost as high as that of the DT-SAM surface (ca. 112°). These results strongly suggest that the surface morphology involved both in substrate roughness and size distribution must be an important factor in the sizing enhancement, and a good sizing response appears without complete coverage of the hydrophilic substrates by the hydrophobic size components.
All Science Journal Classification (ASJC) codes
- Chemical Engineering (miscellaneous)
- Materials Science (miscellaneous)
- Polymers and Plastics
- Industrial and Manufacturing Engineering