Fast, small and strong: Probing viscoelastic properties of binary colloidal networks with optically trapped nanoparticles.
Viscoelastic materials are all around us. From bulk materials as ketchup or paint to more delicate materials as hydrogels or the cytoplasm of living cells.
Hydrogels usually have poor mechanical stability. Recent discoveries on improvement of the mechanical stability by using binary polymer networks suggest a local yielding mechanism. This mechanism however lacks experimental evidence.
Traditionally viscoelastic properties are measured with bulk rheometers. This method however requires large sample volumes and only gives macroscopic information. By employing micrometer-sized colloidal particles as probes one can locally measure viscoelastic responses in microliter sample volumes. The inertia of these particles can be neglected up to 100 kHz. This allows for viscoelastic characterization far beyond the frequency range of classic rheometers. As driving forces one can use either Brownian motion or external forces exerted with, for example, optical tweezers.
The aim of this project is to characterize microscopic deformation and yielding of binary networks. For this binary colloidal networks will be made of micrometer-sized particles. This allows to visualize the microscopic structure and measure mechanical properties directly with optical methods such as high-speed confocal microscopy and optical tweezers. The direct visualization of all elements in these networks enables to observe and quantify local deformations and local yielding directly.