(546a) Investigation and Analysis of the Particle-Boundary Interaction of Synthesized Soft Microcapsules Via Total Internal Reflection Microscopy

Understanding the adhesion and deformation of soft particles, such as red blood cells (RBCs), when interacting with a boundary is essential for diagnosing and treating diseases like a sickle-cell disease. Not only in the blood system, but it is also important in general when soft and hard surfaces come into contact. To investigate this phenomenon, the strategy herein is to utilize synthetic microcapsules with an enclosed oil core and a solid polymer shell that interacts with a boundary as the analog to investigate the adhesion and deformation of red blood cells.

Oil-in-water Pickering emulsions as a forerunner are synthesized from cinnamon leaf oil stabilized by calcium carbonate nanoparticles. Microcapsules are then synthesized via forming the shell through the ion exchange and cross-linking reactions by sodium alginate and calcium ions. Size and surface charge characterizations are measured. The size distributes from 4.3 to 5.3 μm depending on the fabrication time, and the zeta potential is around −20 mV regardless of the fabrication time. Scattering Morphology Resolved Total Internal Refraction Microscopy (SMR-TIRM) is utilized to study microcapsules' adhesion and deformation properties due to its high energy and spatial sensitivity. Our observations showed tethered-like interaction and hindered mobility under TIRM, which led us to hypothesize that tether potential contributes to the microcapsule system. Brownian Dynamics is studied and the relative diffusion coefficient is analyzed to support our hypothesis as the fluctuations in total scattered light intensity directly result from the fluctuations in separation distance. The deformation of a colloidal particle was further explored by first attaching soft gel particles to a microscopic slide and then systematically measuring, via SMR-TIRM, geometry changes in response to a changing shear force.