| 1. |
- Rosén, Tomas, 1985-, et al.
(författare)
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Cross-Sections of Nanocellulose from Wood Analyzed by Quantized Polydispersity of Elementary Microfibrils
- 2020
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Ingår i: ACS Nano. - : American Chemical Society. - 1936-0851 .- 1936-086X. ; 14:12, s. 16743-16754
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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.
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| 2. |
- Rosén, Tomas, 1985-, et al.
(författare)
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Cellulose nanofibrils and nanocrystals in confined flow : Single-particle dynamics to collective alignment revealed through scanning small-angle x-ray scattering and numerical simulations
- 2020
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Ingår i: Physical review. E. - : AMER PHYSICAL SOC. - 2470-0045 .- 2470-0053. ; 101:3
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructured materials made through flow-assisted assembly of proteinaceous or polymeric nanosized fibrillar building blocks are promising contenders for a family of high-performance biocompatible materials in a wide variety of applications. Optimization of these processes relies on improving our knowledge of the physical mechanisms from nano- to macroscale and especially understanding the alignment of elongated nanoparticles in flows. Here, we study the full projected orientation distributions of cellulose nanocrystals (CNCs) and nanofibrils (CNFs) in confined flow using scanning microbeam SAXS. For CNCs, we further compare with a simulated system of dilute Brownian ellipsoids, which agrees well at dilute concentrations. However, increasing CNC concentration to a semidilute regime results in locally arranged domains called tactoids, which aid in aligning the CNC at low shear rates, but limit alignment at higher rates Similarly, shear alignment of CNF at semidilute conditions is also limited owing to probable bundle or flock formation of the highly entangled nanofibrils. This work provides a quantitative comparison of full projected orientation distributions of elongated nanoparticles in confined flow and provides an important stepping stone towards predicting and controlling processes to create nanostructured materials on an industrial scale.
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| 3. |
- Rosén, Tomas, 1985-, et al.
(författare)
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Flow fields control nanostructural organization in semiflexible networks
- 2020
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Ingår i: Soft Matter. - : Royal Society of Chemistry. - 1744-683X .- 1744-6848. ; 16:23, s. 5439-5449
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Tidskriftsartikel (refereegranskat)abstract
- Hydrodynamic alignment of proteinaceous or polymeric nanofibrillar building blocks can be utilized for subsequent assembly into intricate three-dimensional macrostructures. The non-equilibrium structure of flowing nanofibrils relies on a complex balance between the imposed flow-field, colloidal interactions and Brownian motion. The understanding of the impact of non-equilibrium dynamics is not only weak, but is also required for structural control. Investigation of underlying dynamics imposed by the flow requiresin situdynamic characterization and is limited by the time-resolution of existing characterization methods, specifically on the nanoscale. Here, we present and demonstrate a flow-stop technique, using polarized optical microscopy (POM) to quantify the anisotropic orientation and diffusivity of nanofibrils in shear and extensional flows. Microscopy results are combined with small-angle X-ray scattering (SAXS) measurements to estimate the orientation of nanofibrils in motion and simultaneous structural changes in a loose network. Diffusivity of polydisperse systems is observed to act on multiple timescales, which is interpreted as an effect of apparent fibril lengths that also include nanoscale entanglements. The origin of the fastest diffusivity is correlated to the strength of velocity gradients, independent of type of deformation (shear or extension). Fibrils in extensional flow results in highly anisotropic systems enhancing interfibrillar contacts, which is evident through a slowing down of diffusive timescales. Our results strongly emphasize the need for careful design of fluidic microsystems for assembling fibrillar building blocks into high-performance macrostructures relying on improved understanding of nanoscale physics.
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