Investigating the adsorption of anisotropic diblock copolymer worms onto planar silica and nanocellulose surfaces using a quartz crystal microbalance†
Electrostatic adsorption of cationic polyelectrolytes onto anionic cellulosic substrates is an attractive route for facile surface modification of biorenewable materials. Recently, attention has focused on adsorbing cationic spherical diblock copolymer nanoparticles onto model cellulose and/or nanocellulosic substrates. Herein, we investigate physical adsorption of highly anisotropic copolymer worms bearing either anionic or cationic charge onto planar silica, cellulose nanocrystal (CNC) or cellulose nanofibril (CNF) surfaces using quartz crystal microbalance with dissipation monitoring. Electrostatic interactions dominate in the case of anionic silica and CNC surfaces because the adsorbed mass of cationic worms was greater than that of anionic worms. However, either anionic or cationic worms could be adsorbed onto in situ generated CNF substrates, suggesting that additional interactions were involved: hydrogen bonding, van der Waals forces, and possibly covalent bond formation. Scanning electron and atomic force microscopy studies of the dried planar substrates after adsorption experiments confirmed the presence of adsorbed copolymer worms. Finally, composite worm/CNF films exhibited restricted swelling behavior when immersed in water compared to reference CNF films, suggesting that the worms reinforce CNF films by acting as a physical crosslinker. This study is the first investigation of the physical adsorption of highly anisotropic diblock copolymer worms onto cellulosic surfaces.