Droplets fully covered by particles serve as models for biological containers. They are also extensively used to stabilize emulsions and enable encapsulation and controlled release of materials such as medicines and self-healing materials. For many container and delivery applications, especially involving rupture and release, an understanding and characterization of the mechanical properties of the particle shell is essential. There are various methods for probing the mechanical properties of shells, but few of them are non-contact or tested on particle-covered droplets. We utilize electric fields and droplets as a contactless method to both fabricate particle shells of tailored composition and to control their deformation. By deforming particle shells, crumpling of their particle layers is induced which can be measured and used to determine the elasticity of the shell.
We investigate droplets that are covered by nano – and micrometer sized particles, and suspended in another fluid. Subjected to electric field-induced stress, we observe that particle shells on silicone oil droplets fail in various crumpling instabilities, including wrinkling, ridge formation, buckling and folding. In this research, we demonstrated how the strength and type of electric field can be used to control the crumpling behavior of the particle shell, and found that the crumpling wavelength decreases with the size of the particles at the drop interface. Moreover, the method for forming particle shells and controlling crumpling dynamics by applying electric-fields can easily be extended to multiple particle shells. The utilization of electric fields for both fabrication of shells and probing of their mechanical properties make the approach attractive for development of advanced materials with properties tailored to specific applications.