Cracking in films of titanium dioxide nanoparticles with varying interaction strength

We present an experimental investigation into how altering the inter-particle potential between colloids affects the cracking of a ca. 100 μm film deposited on a hard substrate. The colloidal material used was titanium dioxide (r ≈ 30 nm) in an aqueous solvent with interaction strength being adjusted through alteration of the pH away from the isoelectric point. Stable suspensions were observed to form as surface charging increased. Drop casting was used to demonstrate the flow properties of the suspensions; doctor-bladed strips of suspension were subsequently imaged to capture the drying dynamics. Alteration of the pH between 3 and 4 resulted in significant changes in cracking patterns, with the normalised crack domain area α=√A/h increasing for unstable suspensions (pH 4) and the appearance of order in the initial crack pattern for stable suspensions (pH 3). These results can be unified in terms of the barrier to nucleate a new crack.