| 1. |
- Berglund, Lars A., et al.
(author)
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Bioinspired clay nanocomposites of very high clay content
- 2012
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In: ECCM 2012 - Composites at Venice, Proceedings of the 15th European Conference on Composite Materials. - : European Conference on Composite Materials, ECCM. - 9788888785332
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Conference paper (peer-reviewed)abstract
- It is difficult to prepare clay nanocomposites of high volume fraction clay. Layer-by-layer methods have been successful, but are difficult to use in large-scale production. In the present study, papermaking techniques are used for fabrication of oriented clay platelet nanocomposites. Materials are characterized by TEM, SEM, XRD and mechanical and barrier properties are measured and fire retardance performance is demonstrated. High strength and stiffness is demonstrated and the potential for bionanocomposites is discussed, in particular with moisture durability in mind.
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| 2. |
- Ikkala, O., et al.
(author)
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Solid state nanofibers based on self-assemblies : From cleaving from self-assemblies to multilevel hierarchical constructs
- 2009
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In: Faraday discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 143, s. 95-107
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Journal article (peer-reviewed)abstract
- Self-assemblies and their hierarchies are useful to construct soft materials with structures at different length scales and to tune the materials properties for various functions. Here we address routes for solid nanofibers based on different forms of self-assemblies. On the other hand, we discuss rational "bottom-up" routes for multi-level hierarchical self-assembled constructs, with the aim of learning more about design principles for competing interactions and packing frustrations. Here we use the triblock copolypeptide poly(l-lysine)-b-poly(γ-benzyl-l-glutamate)-b-poly(l-lysine) complexed with 2′-deoxyguanosine 5′-monophosphate. Supramolecular disks (G-quartets) stabilized by metal cations are formed and their columnar assembly leads to a packing frustration with the cylindrical packing of helical poly(γ-benzyl-l-glutamate), which we suggest is important in controlling the lateral dimensions of the nanofibers. We foresee routes for functionalities by selecting different metal cations within the G-quartets. On the other hand, we discuss nanofibers that are cleaved from bulk self-assemblies in a "top-down" manner. After a short introduction based on cleaving nanofibers from diblock copolymeric self-assemblies, we focus on native cellulose nanofibers, as cleaved from plant cell wall fibers, which are expected to have feasible mechanical properties and to be templates for functional nanomaterials. Long nanofibers with 5-20 nm lateral dimensions can be cleaved within an aqueous medium to allow hydrogels and water can be removed to allow highly porous, lightweight, and flexible aerogels. We further describe inorganic/organic hybrids as prepared by chemical vapour deposition and atomic layer deposition of the different nanofibers. We foresee functional materials by selecting inorganic coatings. Finally we briefly discuss how the organic template can be removed e.g., by thermal treatments to allow completely inorganic hollow nanofibrillar structures.
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| 3. |
- Jin, H., et al.
(author)
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Effects of different drying methods on textural properties of nanocellulose aerogels
- 2009
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In: ICCM International Conferences on Composite Materials.
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Conference paper (peer-reviewed)abstract
- There is increasing research interest in nanocellulose aerogels because they have low density, hierarchical structure and they are biodegradable and biocompatible. Typically, aerogels are made by supercritical drying, freeze drying and vacuum drying. This work will report the effects that different drying methods have on textural properties of aerogels.
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| 4. |
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| 5. |
- Olsson, Richard T., et al.
(author)
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Making flexible magnetic aerogels and stiff magnetic nanopaper using cellulose nanofibrils as templates
- 2010
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In: Nature Nanotechnology. - 1748-3387. ; 5:8, s. 584-588
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Journal article (peer-reviewed)abstract
- Nanostructured biological materials inspire the creation of materials with tunable mechanical properties(1-3). Strong cellulose nanofibrils derived from bacteria(4) or wood(5,6) can form ductile or tough networks(7,8) that are suitable as functional materials(9,10). Here, we show that freeze-dried bacterial cellulose nanofibril aerogels can be used as templates for making lightweight porous magnetic aerogels, which can be compacted into a stiff magnetic nanopaper. The 20-70-nm-thick cellulose nanofibrils act as templates for the non-agglomerated growth of ferromagnetic cobalt ferrite nanoparticles(11) (diameter, 40-120 nm). Unlike solvent-swollen gels(12) and ferrogels(13-15), our magnetic aerogel is dry, lightweight, porous (98%), flexible, and can be actuated by a small household magnet. Moreover, it can absorb water and release it upon compression. Owing to their flexibility, high porosity and surface area, these aerogels are expected to be useful in microfluidics devices and as electronic actuators.
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| 6. |
- Olsson, R T, et al.
(author)
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Making flexible magnetic aerogels and stiff magnetic nanopaper using cellulose nanofibrils as templates
- 2010
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In: Nature Nanotechnology. - : Springer Science and Business Media LLC. - 1748-3387 .- 1748-3395. ; 5, s. 584-588
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Journal article (peer-reviewed)abstract
- Nanostructured biological materials inspire the creation of materials with tunable mechanical properties. Strong cellulose nanofibrils derived from bacteria or wood can form ductile or tough networks that are suitable as functional materials. Here, we show that freeze-dried bacterial cellulose nanofibril aerogels can be used as templates for making lightweight porous magnetic aerogels, which can be compacted into a stiff magnetic nanopaper. The 20-70-nm-thick cellulose nanofibrils act as templates for the non-agglomerated growth of ferromagnetic cobalt ferrite nanoparticles (diameter, 40-120 nm). Unlike solvent-swollen gels and ferrogels, our magnetic aerogel is dry, lightweight, porous (98%), flexible, and can be actuated by a small household magnet. Moreover, it can absorb water and release it upon compression. Owing to their flexibility, high porosity and surface area, these aerogels are expected to be useful in microfluidics devices and as electronic actuators.
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| 7. |
- Pääkkö, M., et al.
(author)
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Enzymatic hydrolysis combined with mechanical shearing and high-pressure homogenization for nanoscale cellulose fibrils and strong gels
- 2007
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In: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 8:6, s. 1934-1941
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Journal article (peer-reviewed)abstract
- Toward exploiting the attractive mechanical properties of cellulose I nanoelements, a novel route is demonstrated, which combines enzymatic hydrolysis and mechanical shearing. Previously, an aggressive acid hydrolysis and sonication of cellulose I containing fibers was shown to lead to a network of weakly hydrogen-bonded rodlike cellulose elements typically with a low aspect ratio. On the other hand, high mechanical shearing resulted in longer and entangled nanoscale cellulose elements leading to stronger networks and gels. Nevertheless, a widespread use of the latter concept has been hindered because of lack of feasible methods of preparation, suggesting a combination of mild hydrolysis and shearing to disintegrate cellulose I containing fibers into high aspect ratio cellulose I nanoscale elements. In this work, mild enzymatic hydrolysis has been introduced and combined with mechanical shearing and a high-pressure homogenization, leading to a controlled fibrillation down to nanoscale and a network of long and highly entangled cellulose I elements. The resulting strong aqueous gels exhibit more than 5 orders of magnitude tunable storage modulus G' upon changing the concentration. Cryotransmission electron microscopy, atomic force microscopy, and cross-polarization/magic-angle spinning (CP/MAS) C-13 NMR suggest that the cellulose I structural elements obtained are dominated by two fractions, one with lateral dimension of 5-6 nm and one with lateral dimensions of about 10-20 nm. The thicker diameter regions may act as the junction zones for the networks. The resulting material will herein be referred to as MFC (microfibrillated cellulose). Dynamical rheology showed that the aqueous suspensions behaved as gels in the whole investigated concentration range 0.125-5.9% w/w, G' ranging from 1.5 Pa to 10(5) Pa. The maximum G' was high, about 2 orders of magnitude larger than typically observed for the corresponding nonentangled low aspect ratio cellulose I gels, and G' scales with concentration with the power of approximately three. The described preparation method of MFC allows control over the final properties that opens novel applications in materials science, for example, as reinforcement in composites and as templates for surface modification.
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| 8. |
- Pääkkö, M., et al.
(author)
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Long and entangled native cellulose i nanofibers allow flexible aerogels and hierarchically porous templates for functionalities
- 2008
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In: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 4:12, s. 2492-2499
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Journal article (peer-reviewed)abstract
- Recently it was shown that enzymatic and mechanical processing of macroscopic cellulose fibers lead to disintegration of long and entangled native cellulose I nanofibers in order to form mechanically strong aqueous gels (Pääkkö¶ et al., Biomacromolecules, 2007, 8, 1934). Here we demonstrate that (1) such aqueous nanofibrillar gels are unexpectedly robust to allow formation of highly porous aerogels by direct water removal by freeze-drying, (2) they are flexible, unlike most aerogels that suffer from brittleness, and (3) they allow flexible hierarchically porous templates for functionalities, e.g. for electrical conductivity. No crosslinking, solvent exchange nor supercritical drying are required to suppress the collapse during the aerogel preparation, unlike in typical aerogel preparations. The aerogels show a high porosity of ˜98% and a very low density of ca. 0.02 g cm -3. The flexibility of the aerogels manifests as a particularly high compressive strain of ca. 70%. In addition, the structure of the aerogels can be tuned from nanofibrillar to sheet-like skeletons with hierarchical micro- and nanoscale morphology and porosity by modifying the freeze-drying conditions. The porous flexible aerogel scaffold opens new possibilities for templating organic and inorganic matter for various functionalities. This is demonstrated here by dipping the aerogels in an electrically conducting polyaniline-surfactant solution which after rinsing off the unbound conducting polymer and drying leads to electrically conducting flexible aerogels with relatively high conductivity of around 1 ×— 10-2 S cm-1. More generally, we foresee a wide variety of functional applications for highly porous flexible biomatter aerogels, such as for selective delivery/separation, tissue-engineering, nanocomposites upon impregnation by polymers, and other medical and pharmaceutical applications.
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