Dynamics of soft materials probed by local viscosity sensors

In this thesis, we aim to bridge the gap between macroscopic rheological properties and the underlying microscopic behavior of soft materials. We use environmentally sensitive molecular rotors to probe the local viscosity of various systems, ranging from viscous fluids like glycerol and viscoelastic solutions such as dextran polymer solutions to methyltriethoxysilane (MTEOS) gels and polyvinyl acetate (PVAc) polymer glasses. Through confocal laser scanning microscopy, we measure both fluorescence intensity and lifetime, providing high-resolution, three-dimensional images with notable temporal precision. Moreover, we employ the simultaneous use of a rheometer and confocal microscopy to establish direct correlations between the microscopic fluorescence properties of the fluorescent dye and their equivalent macroscopic rheological characteristics, such as the elastic and viscous moduli. These measurements enable us to investigate local dynamics in soft materials under conditions where access to macrorheology and other microrheology techniques is limited such as confinement or samples with relatively small volumes.