Dynamic and Static Assembly of Sulfated Cellulose Nanocrystals with Alkali Metal Counter Cations

Patrick Petschacher; Reza Ghanbari; Carina Sampl; Helmar Wiltsche; Roland Kádár; Stefan Spirk; Tiina Nypelö

doi:10.3390/nano12183131

Dynamic and Static Assembly of Sulfated Cellulose Nanocrystals with Alkali Metal Counter Cations

Nanomaterials (Basel). 2022 Sep 9;12(18):3131. doi: 10.3390/nano12183131.

Authors

Patrick Petschacher¹, Reza Ghanbari², Carina Sampl¹, Helmar Wiltsche³, Roland Kádár^{2

4}, Stefan Spirk¹, Tiina Nypelö^{4

5}

Affiliations

¹ Institute of Bioproducts and Paper Technology, Graz University of Technology, Inffeldgasse 23, 8010 Graz, Austria.
² Department of Industrial Materials Science, Chalmers University of Technology, 41296 Gothenburg, Sweden.
³ Institute of Analytical Chemistry and Food Chemistry, Graz University of Technology, 8010 Graz, Austria.
⁴ Department of Chemistry and Chemical Engineering, Chalmers University of Technology, 41296 Gothenburg, Sweden.
⁵ Wallenberg Wood Science Center, Chalmers University of Technology, 41296 Gothenburg, Sweden.

Abstract

Sulfate groups on cellulose particles such as cellulose nanocrystals (CNCs) provide colloidal stability credit to electrostatic repulsion between the like-charged particles. The introduction of sodium counter cations on the sulfate groups enables drying of the CNC suspensions without irreversible aggregation. Less is known about the effect of other counter cations than sodium on extending the properties of the CNC particles. Here, we introduce the alkali metal counter cations, Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺, on sulfated CNCs without an ion exchange resin, which, so far, has been a common practice. We demonstrate that the facile ion exchange is an efficient method to exchange to any alkali metal cation of sulfate half esters, with exchange rates between 76 and 89%. The ability to form liquid crystalline order in rest was observed by the presence of birefringence patterns and followed the Hofmeister series prediction of a decreasing ability to form anisotropy with an increasing element number. However, we observed the K-CNC rheology and birefringence as a stand-out case within the series of alkali metal modifications, with dynamic moduli and loss tangent indicating a network disruptive effect compared to the other counter cations, whereas observation of the development of birefringence patterns in flow showed the absence of self- or dynamically-assembled liquid crystalline order.

Keywords: birefringence; cellulose nanocrystals; ion exchange; ion pairs; rheo-PLI; rheology.

Grants and funding

Wallenberg Wood Science Center, Chalmers Excellent Initiative Nano, and Area of Advance Materials Chalmers are acknowledged for financial support. Erasmus+ is acknowledged for facilitating the training exchange between Graz University of Technology and Chalmers University of Technology. R.K. and R.G. are grateful for the financial support of the Chalmers Foundation though the project Chalmers Center for Advanced Neutron and X-ray scattering techniques. We acknowledge the Open Access Funding by the Graz University of Technology.