Tandem Webinar April 11

Tandem Webinar – Perspectives on cellulose nanocrystals

It’s time for this year's first Tandem Webinar held by Chalmers Area of Advance Materials Science. 
When: 11th April 2022, at 1 pm. Place: Online.
In this webinar we will have two presentations dedicated to Cellulose nanocrystals. Two hot topics will be covered, one on Cellulose nanocrystals in simple and not so simple flows and one on Using liquid crystal phase separation to fractionate cellulose nanocrystals.

The webinar is held on the platform zoom. To login and participate, click on the following link: 
Password: 722177

Program:
  • 1 PM, The webinar starts. Moderator: Leif Asp, Co-Director Chalmers Area of Advance Materials Science
  • Cellulose nanocrystals in simple and not so simple flows, Roland Kádár, Associate Professor, Chalmers University of Technology.
  • Using liquid crystal phase separation to fractionate cellulose nanocrystals. Jan Lagerwall, Professor at the Physics & Materials Science Research Unit in the University of Luxembourg.


Roland KádárRoland Kádár:
Cellulose nanocrystals in simple and not so simple flows
Cellulose nanocrystals (CNCs) are 1D nanoparticles and part of the rodlike family of lyotropic materials. CNCs self-assemble and can be flow-assembled into liquid crystalline orders in a water suspension. The orders range from nano- to macroscale with contributions of individual crystals, their micron clusters, and macroscopic assemblies influencing their rheological properties and flow behavior. The resulting hierarchies are optically active materials that exhibit iridescence, reflectance, and lighttransmission. This has inspired several applications in the fields of optics and electronics among others. Although these assemblies have the potential for futurere newable materials, details about structures on different hierarchical levels that span from the nano- to the macroscale and the influence of flow thereon are still not unraveled. In this seminar several aspects of CNCs and their assembly in flow from our recent and ongoing work will be presented. This will be centered mainly in relation to their orientation, thixotropy, nonlinear material response, phase behavior and flow stability, including elastically driven instabilities. The experiments comprise mainly rheometric flows often coupled to polarized light imaging. The studies include commercial CNCs as well as surface treated variants.


Jan LagerwallJan Lagerwall:
Using liquid crystal phase separation to fractionate cellulose nanocrystals
Cellulose nanocrystals (CNCs) constitute a highly promising sustainably produced nanomaterial, with attractive physical and chemical properties and multiple application opportunities. The rod-like shape of CNCs has the interesting consequence that CNC suspensions undergo a transition from isotropic to liquid crystalline (LC) order at mass fractions on the order of a few percent.
Unfortunately, CNCs are inherently disperse in dimension, the rod length within a single batch typically varying from below 100 to several hundreds of nanometers, while the lateral dimension is about 3–5 nm. This causes multiple problems, e.g., expanding the isotropic–LC phase coexistence range to much greater width than expected from the classic Onsager theory, and requiring so high CNC content to achieve LC order that the suspension gets kinetically arrested in a non-equilibrium state with poor control of order.
Interestingly, because the stability limits of the isotropic and LC phases depend sensitively on the rod aspect ratio, the initially separating LC phase of an isotropic starting suspension in which the CNC content is gradually raised contains only the longest CNCs, while the final remaining isotropic phase contains only the shortest CNCs. By separating the LC fraction from the isotropic one, we can thus very easily and effectively extract the longest rods from the suspensions.
The resulting low-dispersity suspension exhibits greatly enhanced properties compared to the pristine CNC suspension, in particular an LC phase with so low viscosity that an equilibrium arrangement is reached almost instantaneously. This dramatically improves our ability to control materials produced using CNCs, for instance well-defined structurally colored films that selectively reflect only one circular polarization within a narrow wavelength band of light.

Category Seminar; Public lecture
Location: Online
Starts: 11 April, 2022, 13:00
Ends: 11 April, 2022, 14:00

Page manager Published: Sat 09 Apr 2022.