In situ X-ray characterization of mixing processes can pose some engineering challenges especially when the process leads to a dramatic change in viscoelasticity of the material. One notable challenge is to create a well-defined mixing system without the residual material sticking on walls, which often leads to unreliable measurements of the time-resolved data. Furthermore, in order to minimize radiation damage, it is desired to not irradiate the same material during the mixing process. In this work, we present a flow-focusing mixing system for in-situ structural characterization during mixing using a scanning SAXS technique. In this system, the focused core material detaches from the walls and forms a plug flow with no shear, allowing for easy conversion of spatial coordinates to mixing time. Additionally, radiation damage can be neglected as the material is continuously flowing through the beam. Using this system, we studied dispersed cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) mixed with a NaCl solution, which results in gel formation. The structural changes during this process reveals new information regarding how the positive ions screen the charges of CNC and result in the loss of structure through Brownian motion. For CNF, the structural changes can be attributed to the formation of a connected network with segmental aggregates, which in turn leads to reduced Brownian motion and a more oriented structure. This work not only captures the timescales of nanocellulose gelation, but also provides new insight into the development of new processes of making continuous nanostructured bio-based materials. The demonstrated technique can serve as a powerful tool for time-resolved investigation of any structural change occurring during mixing, especially relevant to soft matter.

Time-resolved structural transition during nanocellulose gel formation using an <i>in situ</i> SAXS/flow-focusing technique

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.

Time-resolved structural transition during nanocellulose gel formation using an in situ SAXS/flow-focusing technique