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Date

2021 Aug 27
Expired!

Time

13:00

Location

Online

Presenter

Sylwia Wojno
Sylwia Wojno
Website
https://treesearch.se/researchers/sylwia-wojno/

More Info

To Chalmers.se

Licentiate seminar: Sylwia Wojno – Nonlinear rheological characterization of cellulose nanocrystals based systems

Chalmers

Supervisor: Roland Kadár, Chalmers
Opponent: Dr Tiffany Abitbol, Senior Researcher at RISE Bioeconomy

The defense will be held via Zoom.

Password: 075968

Abstract:

In this thesis, cellulose nanocrystals based systems were investigated using advanced rheological characterization techniques, with a particular focus on nonlinear material response functions and Rheo-PLI (Polarized Light Imaging). Cellulose nanocrystals (CNCs) show enormous potential for many applications, either as material on its own or as renewable reinforcement in polymers. In addition, nanocellulose systems have significant potential as sustainable rheology modifiers for e.g. cosmetics, paints, foods, etc, where rheological properties are essential from designing shelf life, avoid splattering and processing/transport efficiency. In this context, surface modification of CNC is essential to enhance properties and seek new applications. Flow structuring of suspensions, multiphase systems and composites also typically require fast and large deformations. Therefore, it is highly relevant to implement proper and precise analyzing methods sufficiently sensitive to flow-induced structuring.
In this framework, the PhD project focuses on investigating the relevance of nonlinear material rheological parameters on flow-field CNC interactions. Two water based CNC systems were characterized in this licentiate.
The first was CNCs with a lower ionic strength able to self-assemble from an isotropic phase with increasing CNC concentration into biphasic and liquid crystalline phases. The second one, CNCs with higher ionic strength, did not self-assemble. Instead, CNC suspensions with a higher sulfate content agglomerate into isotropic and isotropic gel phases. As nonlinear rheological characterization methods Fourier-Transform Rheology (FT-Rheology) and stress decomposition analysis were performed, to our knowledge, for the first time on the CNC systems analyzed. To investigate the dependence of concentration on self-assembled phase transitions in CNC suspensions, the rheological analysis was complemented by Rheo-PLI.