| 1. |
- Rosén, Tomas, 1985-, et al.
(författare)
-
Cross-Sections of Nanocellulose from Wood Analyzed by Quantized Polydispersity of Elementary Microfibrils
- 2020
-
Ingår i: ACS Nano. - : American Chemical Society. - 1936-0851 .- 1936-086X. ; 14:12, s. 16743-16754
-
Tidskriftsartikel (refereegranskat)abstract
- Bio-based nanocellulose has been shown to possess impressive mechanical properties and simplicity for chemical modifications. The chemical properties are largely influenced by the surface area and functionality of the nanoscale materials. However, finding the typical cross-sections of nanocellulose, such as cellulose nanofibers (CNFs), has been a long-standing puzzle, where subtle changes in extraction methods seem to yield different shapes and dimensions. Here, we extracted CNFs from wood with two different oxidation methods and variations in degree of oxidation and high-pressure homogenization. The cross-sections of CNFs were characterized by small-angle X-ray scattering and wide-angle X-ray diffraction in dispersed and freeze-dried states, respectively, where the results were analyzed by assuming that the cross-sectional distribution was quantized with an 18-chain elementary microfibril, the building block of the cell wall. We find that the results agree well with a pseudosquare unit having a size of about 2.4 nm regardless of sample, while the aggregate level strongly depends on the extraction conditions. Furthermore, we find that aggregates have a preferred cohesion of phase boundaries parallel to the (110)-plane of the cellulose fibril, leading to a ribbon shape on average.
|
|
| 2. |
- Bagge, Joar, 1991-, et al.
(författare)
-
Parabolic velocity profile causes shape-selective drift of inertial ellipsoids
- 2021
-
Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 926
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding particle drift in suspension flows is of the highest importance in numerous engineering applications where particles need to be separated and filtered out from the suspending fluid. Commonly known drift mechanisms such as the Magnus force, Saffman force and Segre-Silberberg effect all arise only due to inertia of the fluid, with similar effects on all non-spherical particle shapes. In this work, we present a new shape-selective lateral drift mechanism, arising from particle inertia rather than fluid inertia, for ellipsoidal particles in a parabolic velocity profile. We show that the new drift is caused by an intermittent tumbling rotational motion in the local shear flow together with translational inertia of the particle, while rotational inertia is negligible. We find that the drift is maximal when particle inertial forces are of approximately the same order of magnitude as viscous forces, and that both extremely light and extremely heavy particles have negligible drift. Furthermore, since tumbling motion is not a stable rotational state for inertial oblate spheroids (nor for spheres), this new drift only applies to prolate spheroids or tri-axial ellipsoids. Finally, the drift is compared with the effect of gravity acting in the directions parallel and normal to the flow. The new drift mechanism is stronger than gravitational effects as long as gravity is less than a critical value. The critical gravity is highest (i.e. the new drift mechanism dominates over gravitationally induced drift mechanisms) when gravity acts parallel to the flow and the particles are small.
|
|
| 3. |
- Bragone, Federica, et al.
(författare)
-
Unsupervised Learning Analysis of Flow-Induced Birefringence in Nanocellulose: Differentiating Materials and Concentrations
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Cellulose nanofibrils (CNFs) can be used as building blocks for future sustainable materials including strong and stiff filaments. The goal of this paper is to introduce a data analysis of flow-induced birefringence experiments by means of unsupervised learning techniques. By reducing the dimensionality of the data with Principal Component Analysis (PCA) we are able to exploit information for the different cellulose materials at several concentrations and compare them to each other. Our approach aims at classifying the CNF materials at different concentrations by applying unsupervised machine learning algorithms, like k-means and Gaussian Mixture Models (GMMs). Finally, we analyze the autocorrelation function (ACF) and the partial autocorrelation function (PACF) of the first principal component, detecting seasonality in lower concentrations. The focus is given to the initial relaxation of birefringence after the flow is stopped to have a better understanding of the Brownian dynamics for the given materials and concentrations.Our method can be used to distinguish the different materials at specific concentrations and could help to identify possible advantages and drawbacks of one material over the other.
|
|
| 4. |
- Brouzet, Christophe, et al.
(författare)
-
Effect of Electric Field on the Hydrodynamic Assembly of Polydisperse and Entangled Fibrillar Suspensions
- 2021
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 37:27, s. 8339-8347
-
Tidskriftsartikel (refereegranskat)abstract
- Dynamics of colloidal particles can be controlled by the application of electric fields at micrometer-nanometer length scales. Here, an electric field-coupled microfluidic flow-focusing device is designed for investigating the effect of an externally applied alternating current (AC) electric field on the hydrodynamic assembly of cellulose nanofibrils (CNFs). We first discuss how the nanofibrils align parallel to the direction of the applied field without flow. Then, we apply an electric field during hydrodynamic assembly in the microfluidic channel and observe the effects on the mechanical properties of the assembled nanostructures. We further discuss the nanoscale orientational dynamics of the polydisperse and entangled fibrillar suspension of CNFs in the channel. It is shown that electric fields induced with the electrodes locally increase the degree of orientation. However, hydrodynamic alignment is demonstrated to be much more efficient than the electric field for aligning CNFs. The results are useful for understanding the development of the nanostructure when designing high-performance materials with microfluidics in the presence of external stimuli.
|
|
| 5. |
- Gowda, V. Krishne, et al.
(författare)
-
Effects of fluid properties, flow parameters and geometrical variations on viscous threads in microfluidic channels
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We report a combined experimental and numerical investigation to decipher and delineate the role of fluid properties, flow parameters, and geometries on the dynamics of viscous thread formation in microchannels with miscible solvents. A methodological analysis based on the evolution of viscous threads unveils the significance of effective interfacial tension (EIT) induced by the virtue of concentration gradients between the non-equilibrium miscible fluid pair colloidal dispersions and their own solvent. Functional scaling relationships developed with dimensionless capillary and Weber numbers, together with thread quantities thread detachment length, and thread width, shed light on the complex interplay of hydrodynamic effects and viscous microflow processes. The detachment of viscous threads inside microchannels is governed by the unified hydrodynamic effects of inertia, capillary, and viscous stresses in contrast to the natural phenomenon of self-lubrication, bringing new insights to the physical phenomena involved in the confined microsystems. Exploiting the experimentally measured thread quantities, the scaling laws are practically applied to estimate the inherent fluid properties such as EIT between two inhomogeneous miscible fluids, and the fluid viscosities. In addition, the cross-sectional aspect ratio of the channels is varied numerically in conjunction with the converging shaped sections. For specified flow rates and given rheologies of the fluids, a flow-focusing configuration producing the shortest thread detachment length, and a longer region of strain rate along the centreline is identified. Overall, this work provides a consolidated description of the effect of fluid properties, flow parameters, and geometry on the formation of miscible viscous threads in microchannel flows.
|
|
| 6. |
- Gowda, V. Krishne, et al.
(författare)
-
Nanofibril Alignment during Assembly Revealed by an X-ray Scattering-Based Digital Twin
- 2022
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 16:2, s. 2120-2132
-
Tidskriftsartikel (refereegranskat)abstract
- The nanostructure, primarily particle orientation, controls mechanical and functional (e.g., mouthfeel, cell compatibility, optical, morphing) properties when macroscopic materials are assembled from nanofibrils. Understanding and controlling the nanostructure is therefore an important key for the continued development of nanotechnology. We merge recent developments in the assembly of biological nanofibrils, X-ray diffraction orientation measurements, and computational fluid dynamics of complex flows. The result is a digital twin, which reveals the complete particle orientation in complex and transient flow situations, in particular the local alignment and spatial variation of the orientation distributions of different length fractions, both along the process and over a specific cross section. The methodology forms a necessary foundation for analysis and optimization of assembly involving anisotropic particles. Furthermore, it provides a bridge between advanced in operandi measurements of nanostructures and phenomena such as transitions between liquid crystal states and in silico studies of particle interactions and agglomeration.
|
|
| 7. |
|
|
| 8. |
- Motezakker, Ahmad Reza, et al.
(författare)
-
Effect of Stiffness on the Dynamics of Entangled Nanofiber Networks at Low Concentrations
- 2023
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 56:23, s. 9595-9603
-
Tidskriftsartikel (refereegranskat)abstract
- Biopolymer network dynamics play a significant role in both biological and materials science. This study focuses on the dynamics of cellulose nanofibers as a model system given their relevance to biology and nanotechnology applications. Using large-scale coarse-grained simulations with a lattice Boltzmann fluid coupling, we investigated the reptation behavior of individual nanofibers within entangled networks. Our analysis yields essential insights, proposing a scaling law for rotational diffusion, quantifying effective tube diameter, and revealing release mechanisms during reptation, spanning from rigid to semiflexible nanofibers. Additionally, we examine the onset of entanglement in relation to the nanofiber flexibility within the network. Microrheology analysis is conducted to assess macroscopic viscoelastic behavior. Importantly, our results align closely with previous experiments, validating the proposed scaling laws, effective tube diameters, and onset of entanglement. The findings provide an improved fundamental understanding of biopolymer network dynamics and guide the design of processes for advanced biobased materials.
|
|
| 9. |
|
|
| 10. |
- Nygård, K., et al.
(författare)
-
ForMAX – a beamline for multiscale and multimodal structural characterization of hierarchical materials
- 2024
-
Ingår i: Journal of Synchrotron Radiation. - : International Union of Crystallography (IUCr). - 0909-0495 .- 1600-5775. ; 31:Pt 2, s. 363-377
-
Tidskriftsartikel (refereegranskat)abstract
- The ForMAX beamline at the MAX IV Laboratory provides multiscale and multimodal structural characterization of hierarchical materials in the nanometre to millimetre range by combining small- and wide-angle X-ray scattering with full-field microtomography. The modular design of the beamline is optimized for easy switching between different experimental modalities. The beamline has a special focus on the development of novel fibrous materials from forest resources, but it is also well suited for studies within, for example, food science and biomedical research.
|
|
