Microrheology of Bacterial Films At Oil-Water Interfaces

Bacterial films play key roles in emerging petroleum technologies such as enhanced oil recovery and oil remediation. In these applications, bacteria assemble at interfaces between the oil and water to form dense films that can strongly affect the interfacial properties of the oil, including its mechanical behavior. Despite this significance, limited previous research has sought to characterize systematically the mechanical properties of these films. The microstructure of the films, which can include not only dense packings of bacteria but macromolecular surfactants secreted by the bacteria and the remains of dead bacteria, resemble from a physical perspective a disordered colloidal suspension in a polymer solution. In this work, we employ passive and active microrheology and more traditional active rheometry to characterize the shear response of bacteria films during formation. We measure a dramatic evolution in film rheology, studied both from a fundamental perspective, as a quasi-two-dimensional, active, glassy system, and in the context of the application of the films to petroleum technologies.