Macro- and Nano-Rheological Properties of Carboxymethylcellulose – Water – Ethanol Ternary Mixtures
Restricted (Penn State Only)
- Author:
- Camacho, Gillian
- Area of Honors:
- Chemistry
- Degree:
- Bachelor of Science
- Document Type:
- Thesis
- Thesis Supervisors:
- Bratoljub Milosavljevic, Thesis Supervisor
Benjamin James Lear, Thesis Honors Advisor - Keywords:
- nano-viscosity
macro-viscosity
Smoluchowski-Stokes-Einstein equation
carboxymethylcellulose - Abstract:
- All tissues and organs are made up of cells that are held within an extracellular matrix, which is composed of a variety of proteins (collagens, fibronectin, glycoproteins, etc.) that interact to form a scaffolding that is filled by a polysaccharide gel. Cells also contain an intracellular matrix composed of the cytoskeleton and cytoplasm, which is 80% water and has a jelly-like consistency, so it is more viscous than water. This means that in tissues, gas exchange involving small molecules (oxygen, carbon dioxide, ethylene, etc.) happens within a complex network of macromolecules rather than in a pure solvent. Therefore, one would presume that all diffusion-controlled cellular reactions are slow; however, that contradicts the experimental observations. This seemingly counterintuitive result can be attributed to the phenomenon known as the nano- or micro-viscosity. Our project deals with experiments that are designed to (quantitatively) demonstrate the difference between the nano- and macro-viscosity of aqueous polymeric solutions. More specifically, the Smoluchowski-Stokes-Einstein (SSE) equation states that for a diffusion-controlled reaction carried out in two different media, the ratio of the corresponding rate constants will be equal to the inverse of the ratio of the media’s dynamic viscosities, provided that the reaction temperatures are the same. The dynamic viscosities of solutions containing carboxymethylcellulose (CMC), the dynamic viscosity of the solvent alone (5 wt% ethanol – water), and the rate constant of 1-pyrenemethanol fluorescence quenching by iodide anion in the solvent alone were input into this equation to predict the rate constant of the reaction in the presence of CMC. Comparing the measured rate constants to those predicted by the SSE equation revealed a significant disparity. As the CMC concentration increased, the quenching rate constant only slightly decreased despite SSE predictions exponentially decreasing, and in 2 wt% CMC the prediction was over two orders of magnitude slower than measured. These seemingly contradictory data can be rationalized in the following way: the ternary mixture containing CMC can be understood as a dynamic system consisting of interconnected solvent pools located between solvated CMC molecules. While the solubilized CMC impacts the macro-viscosity of the aqueous ethanol solution, it does not impact the nano-viscosity, as iodide anion and 1-pyrenemethanol molecules move through the solvent pools in the CMC-containing solution as freely as in a 5 wt% ethanol – water solution.