| 1. |
- Magnani, Chiara, et al.
(författare)
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Green Topochemical Esterification Effects on the Supramolecular Structure of Chitin Nanocrystals: Implications for Highly Stable Pickering Emulsions
- 2022
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Ingår i: ACS Applied Nano Materials. - : American Chemical Society (ACS). - 2574-0970. ; 5:4, s. 4731-4743
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Tidskriftsartikel (refereegranskat)abstract
- In nature, chitin is organized in hierarchical structures composed of nanoscale building blocks that show outstanding mechanical and optical properties attractive for nanomaterial design. For applications that benefit from a maximized interface such as nanocomposites and Pickering emulsions, individualized chitin nanocrystals (ChNCs) are of interest. However, when extracted in water suspension, their individualization is affected by ChNC self-assembly, requiring a large amount of water (above 90%) for ChNC transport and stock, which limits their widespread use. To master their individualization upon drying and after regeneration, we herein report a waterborne topochemical one-pot acid hydrolysis/Fischer esterification to extract ChNCs from chitin and simultaneously decorate their surface with lactate or butyrate moieties. Controlled reaction conditions were designed to obtain nanocrystals of a comparable aspect ratio of about 30 and a degree of modification of about 30% of the ChNC surface, under the rationale to assess the only effect of the topochemistry on ChNC supramolecular organization. The rheological analysis coupled with polarized light imaging shows how the nematic structuring is hindered by both surface ester moieties. The increased viscosity and elasticity of the modified ChNC colloids indicate a gel-like phase, where typical ChNC clusters of liquid crystalline phases are disrupted. Pickering emulsions have been prepared from lyophilized nanocrystals as a proof of concept. Our results demonstrate that only the emulsions stabilized by the modified ChNCs have excellent stability over time, highlighting that their individualization can be regenerated from the dry state.
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| 2. |
- Kádár, Roland, 1982, et al.
(författare)
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Challenges in nano-structured fluid flows for assembly into hierarchical biomaterials
- 2023
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Ingår i: AIP Conference Proceedings. - 0094-243X .- 1551-7616. - 9780735445475 ; 2997
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Konferensbidrag (refereegranskat)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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| 3. |
- Pandit, Santosh, 1987, et al.
(författare)
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The Exo-Polysaccharide Component of Extracellular Matrix is Essential for the Viscoelastic Properties of Bacillus subtilis Biofilms
- 2020
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Ingår i: International Journal of Molecular Sciences. - : MDPI AG. - 1661-6596 .- 1422-0067. ; 21:18, s. 1-17
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Tidskriftsartikel (refereegranskat)abstract
- Bacteria are known to form biofilms on various surfaces. Biofilms are multicellular aggregates, held together by an extracellular matrix, which is composed of biological polymers. Three principal components of the biofilm matrix are exopolysaccharides (EPS), proteins, and nucleic acids. The biofilm matrix is essential for biofilms to remain organized under mechanical stress. Thanks to their polymeric nature, biofilms exhibit both elastic and viscous mechanical characteristics; therefore, an accurate mechanical description needs to take into account their viscoelastic nature. Their viscoelastic properties, including during their growth dynamics, are crucial for biofilm survival in many environments, particularly during infection processes. How changes in the composition of the biofilm matrix affect viscoelasticity has not been thoroughly investigated. In this study, we used interfacial rheology to study the contribution of the EPS component of the matrix to viscoelasticity of Bacillus subtilis biofilms. Two strategies were used to specifically deplete the EPS component of the biofilm matrix, namely (i) treatment with sub-lethal doses of vitamin C and (ii) seamless inactivation of the eps operon responsible for biosynthesis of the EPS. In both cases, the obtained results suggest that the EPS component of the matrix is essential for maintaining the viscoelastic properties of bacterial biofilms during their growth. If the EPS component of the matrix is depleted, the mechanical stability of biofilms is compromised and the biofilms become more susceptible to eradication by mechanical stress.
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| 4. |
- Wojno, Sylwia, 1990, et al.
(författare)
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Phase transitions of cellulose nanocrystal suspensions from nonlinear oscillatory shear
- 2022
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 29:7, s. 3655-3673
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose nanocrystals (CNCs) self- assemble in water suspensions into liquid crystalline assemblies. Here, we elucidate the microstructural changes associated with nonlinear deformations in (2–9 wt%) CNC suspensions through nonlinear rheological analysis, that was performed in paral- lel with coupled rheology—polarized light imaging. We show that nonlinear material parameters from Fourier-transform rheology and stress decomposition are sensitive to all CNC phases investigated, i.e. iso- tropic, biphasic and liquid crystalline. This is in con- trast to steady shear and linear viscoelastic dynamic moduli where the three-region behavior and weak strain overshoot cannot distinguish between biphasic and liquid crystalline phases. Thus, the inter-cycle and intra-cycle nonlinear parameters investigated are a more sensitive approach to relate rheological meas- urements to CNC phase behavior.
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