| 1. |
- Ghanbari, Reza, 1984, et al.
(author)
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Painting Taylor vortices with cellulose nanocrystals: supercritical spectral dynamics
- 2023
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Journal article (other academic/artistic)abstract
- We study the flow stability and spatio-temporal spectral dynamics of cellulose nanocrystal (CNC) suspensions in a custom Taylor-Couette flow cell using the intrinsic shear induced birefringence and liquid crystalline properties of CNC suspensions for flow visualizations for the first time. The analysis is performed at constant ramped speed inputs of the independently rotating cylinders for several cases ranging from only inner or outer rotating cylinders to three counter-rotation cases. All CNC suspensions have measurable elastic and shear thinning, both increasing with CNC concentration. We show that the flow patterns recorded are essentially Newtonian-like, with non-Newtonian effects ranging from a decrease in wavenumbers to altering the critical parameters for the onset of instability modes. Outer cylinder rotation flow cases are stable for all concentrations whereas inner cylinder rotation flow cases transition to axisymmetric and azimuthally periodic secondary flows. However, unstable counter-rotation cases become unstable to asymmetric spiral modes. With increasing CNC concentration a counter-rotation case was found where azimuthally periodic wavy patterns transition to asymmetric spiral modes. In contrast to polymeric solutions of similar low to moderate elasticity and shear thinning, the shear-thinning region of CNC suspensions is expected to lead to the breakdown of the chiral nematic phase, whose elastic constants constitute the dominant structural elasticity mechanism. Thus, we interpret the Taylor-Couette stability of the CNC suspensions as dominated by their shear-thinning character due to the expected loss of elasticity in nonlinear flow conditions.
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| 2. |
- Ghanbari, Reza, 1984, et al.
(author)
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Painting Taylor vortices with cellulose nanocrystals: Suspension flow supercritical spectral dynamics
- 2024
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In: Physics of Fluids. - 1089-7666 .- 1070-6631. ; 36:4
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Journal article (peer-reviewed)abstract
- We study the flow stability and spatiotemporal spectral dynamics of cellulose nanocrystal (CNC) suspensions in a custom Taylor-Couette flow cell using the intrinsic shear induced birefringence and liquid crystalline properties of CNC suspensions for flow visualizations, for the first time. The analysis is performed at constant ramped speed inputs of the independently rotating cylinders for several cases ranging from only inner or outer rotating cylinders to three counter-rotation cases. All CNC suspensions have measurable elasticity and shear thinning, both increasing with CNC concentration. We show that the flow patterns recorded are essentially Newtonian-like, with non-Newtonian effects ranging from a decrease in wavenumbers to altering the critical parameters for the onset of instability modes. Outer cylinder rotation flow cases are stable for all concentrations whereas inner cylinder rotation flow cases transition to axisymmetric and azimuthally periodic secondary flows. However, counter-rotation cases become unstable to asymmetric spiral modes. With increasing CNC concentration, a counter-rotation case was found where azimuthally periodic wavy patterns transition to asymmetric spiral modes. Based on rheo-SAXS measurements, the shear-thinning region of CNC suspensions is expected to lead to the breakdown of the chiral nematic phase, whose elastic constants constitute the dominant structural elasticity mechanism. Thus, we interpret the Taylor-Couette stability of the CNC suspensions as dominated by their shear-thinning character due to the expected loss of elasticity in nonlinear flow conditions.
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| 3. |
- Kádár, Roland, 1982, et al.
(author)
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Challenges in nano-structured fluid flows for assembly into hierarchical biomaterials
- 2023
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In: AIP Conference Proceedings. - 0094-243X .- 1551-7616. - 9780735445475 ; 2997
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Conference paper (peer-reviewed)abstract
- Hierarchical biomaterials have their place in the context of developing novel material systems particularly in the framework of sustainability. The key to their development is in controlling their assembly into hierarchical orders at various lengthscales. Thus, flow can be an asset in e.g. controlling orientation, however, resolving the hierarchical orientation dynamics of such systems remains a challenge. We focus here mainly on cellulose nanocrystals water-based suspensions, however, the outline is representative of numerous nanostructured fluids.
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| 4. |
- Pashazadehgaznagh, Sajjad, 1994, et al.
(author)
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Mapping surface defects in highly-filled wood fiber polymer composite extrusion from inline spectral analysis
- 2023
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In: Composites Science and Technology. - 0266-3538. ; 242
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Journal article (peer-reviewed)abstract
- Surface defects in highly-filled wood polymer composites (WPCs) are mapped in single-screw extrusion via inline optical spectral analysis for the first time. The effects of wood fiber content and drying on the dynamics of surface defects are spatio-temporally resolved via space–time inline optical imaging. Surface tearing appeared from the lowest shear rates investigated followed by a gradual decay in spectral intensity with increasing shear rates/slip velocities. This is accompanied by broadening of the surface tearing characteristic frequency while the average wavelength is estimated to remain constant within the experimental conditions. Increasing shear rates, drying and increasing wood fiber content showed mitigating effects on surface tearing. However, surface tearing in undried samples was still present even at the highest shear rates and high wall slip velocities. A regime where the extrudate surface is dominated by bubbles at high shear rates and low wood fiber contents in undried WPCs was identified.
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| 5. |
- Petschacher, P., et al.
(author)
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Dynamic and Static Assembly of Sulfated Cellulose Nanocrystals with Alkali Metal Counter Cations
- 2022
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In: Nanomaterials. - : MDPI AG. - 2079-4991. ; 12
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Journal article (peer-reviewed)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.
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| 6. |
- Spiliopoulos, Panagiotis, 1987, et al.
(author)
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Cellulose modified to host functionalities via facile cation exchange approach
- 2024
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In: Carbohydrate Polymers. - 0144-8617. ; 332
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Journal article (peer-reviewed)abstract
- Properties of cellulose are typically functionalized by organic chemistry means. We progress an alternative facile way to functionalize cellulose by functional group counter-cation exchange. While ion-exchange is established for cellulose, it is far from exploited and understood beyond the most common cation, sodium. We build on our work that established the cation exchange for go-to alkali metal cations. We expand and further demonstrate the introduction of functional cations, namely, lanthanides. We show that cellulose nanocrystals (CNCs) carrying sulfate-half ester groups can acquire properties through the counter-cation exchange. Trivalent lanthanide cations europium (Eu3+), dysprosium (Dy3+) and gadolinium (Gd3+) were employed. The respective ions showed distinct differences in their ability of being coordinated by the sulfate groups; with Eu3+fully saturating the sulfate groups while for Gd3+ and Dy3+, values of 82 and 41 % were determined by compositional analysis. CNCs functionalized with Eu3+ displayed red emission, those containing Dy3+ exhibited no optical functionality, while those with Gd3+revealed significantly altered magnetic relaxation times. Using cation exchange to alter cellulose properties in various ways is a tremendous opportunity for modification of the abundant cellulose raw materials for a renewable future.
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