The rheo-Raman microscope: Simultaneous chemical, conformational, mechanical, and microstructural measures of soft materials
Anthony P. Kotula, Matthew Meyer, Francesca De Vito, Jan Plog, Angela R. Hight Walker, Kalman D. Migler
We describe the design and demonstrate performance of an instrument capable of simultaneous Raman spectroscopy, rheology, and optical microscopy of materials. The instrument couples a Raman microscope with a rotational rheometer through an optically transparent base to collect Raman scattering at a user-defined radial position within the shearing geometry. We demonstrate the instrument performance in two material that show thermal transitions. First, in a cosmetic emulsion, we perform steady state viscometry, Raman scattering, and polarized imaging during a melting transition. Second, in a high density polyethylene, we perform small amplitude oscillatory shear modulus measurements along with Raman and imaging during crystallization. The instrument is advantageous in situations where rheology is closely coupled to either chemical or conformational changes in molecular structure as in crystallization, melting, gelation, or curing.