(450b) Tuning the Wettability of Halloysite Clay Nanotubes By Surface Carbonization for Optimal Particle Stabilization of Emulsions
The attachment of particles to the oil-water interface with energies that are several orders of magnitude higher than the thermal energy provides a large steric hindrance to droplet coalescence and is the underlying concept behind particle-stabilization of emulsions. The partial wetting of particles by both the oil and aqueous phases drives the location of the particles at the oil-water interface. Here we advance the new concept of carbonizing the surface of anisotropic hydrophilic particles as an effective route for tuning particle wettability in the preparation of particle-stabilized emulsions. The wettability of anisotropic, naturally occurring halloysite clay nanotubes (HNT) are successfully tuned across a range of wettability’s by selective carbonization of the negatively charged external HNT surface. The positively charge chitosan biopolymer binds to the negatively charged external HNT surface by electrostatic attraction and hydrogen bonding, yielding carbonized halloysite nanotubes (CHNT) on pyrolysis in an inert atmosphere. Relative to the native HNT, the oil emulsification ability of the CHNT at intermediate levels of carbonization is significantly enhanced due to the thermodynamically more favorable attachment of the particles at the oil-water interface. Cryo-SEM imaging reveals that networks of CHNT attach to the oil-water interface with the particles in a side on-orientation. The concepts advanced here can be extended to other inorganic solids and carbon sources for the optimal design of particle-stabilized emulsions.