ABSTRACT
Crystalline monolayers prevalent in nature and technology possess elusive elastic properties with important implications in fundamental physics, biology, and nanotechnology. Leveraging the recently discovered shape transitions of oil-in-water emulsion droplets, upon which these droplets adopt cylindrical shapes and elongate, we investigate the elastic characteristics of the crystalline monolayers covering their interfaces. To unravel the conditions governing Euler buckling and Brazier kink formation in these cylindrical tubular interfacial crystals, we strain the elongating cylindrical droplets within confining microfluidic wells. Our experiments unveil a nonclassical relation between the Young's modulus and the bending modulus of these crystals. Intriguingly, this relation varies with the radius of the cylindrical crystal, presenting a nonclassical mechanism for tuning of elasticity in nanotechnology applications.
ABSTRACT
Tailoring the microstructure of magnetic microparticles is of vital importance for their applications. Spiky magnetic particles, such as those made from sunflower pollens, have shown promise in single cell treatment and biofilm removal. Synthetic methods that can replicate or extend the functionality of such spiky particles would be advantageous for their widespread utilization. In this work, a wet-chemical method is introduced for spiky magnetic particles that are templated from microrod-stabilized Pickering emulsions. The spiky morphology is generated by the upright attachment of silica microrods at the oil-water interface of oil droplets. Spiky magnetic microparticles with control over the length of the spikes are obtained by dispersing hydrophobic magnetic nanoparticles in the oil phase and photopolymerizing the monomer. The spiky morphology dramatically enhances colloidal stability of these particles in high ionic strength solutions and physiologic media such as human saliva and saline-based biofilm suspension. To demonstrate their utility, the spiky magnetic particles are applied for magnetically controlled removal of oral biofilms and retrieval of bacteria for diagnostic sampling. This method expands the toolbox for engineering microparticle morphology and could promote the fabrication of functional magnetic microrobots.