| 1. |
- Ullah Khan, Zia, et al.
(author)
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Thermoelectric Polymers and their Elastic Aerogels
- 2016
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In: Advanced Materials. - : John Wiley & Sons. - 0935-9648 .- 1521-4095.
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Journal article (peer-reviewed)abstract
- Electronically conducting polymers constitute an emerging class of materials for novel electronics, such as printed electronics and flexible electronics. Their properties have been further diversified to introduce elasticity, which has opened new possibility for "stretchable" electronics. Recent discoveries demonstrate that conducting polymers have thermoelectric properties with a low thermal conductivity, as well as tunable Seebeck coefficients - which is achieved by modulating their electrical conductivity via simple redox reactions. Using these thermoelectric properties, all-organic flexible thermoelectric devices, such as temperature sensors, heat flux sensors, and thermoelectric generators, are being developed. In this article we discuss the combination of the two emerging fields: stretchable electronics and polymer thermoelectrics. The combination of elastic and thermoelectric properties seems to be unique for conducting polymers, and difficult to achieve with inorganic thermoelectric materials. We introduce the basic concepts, and state of the art knowledge, about the thermoelectric properties of conducting polymers, and illustrate the use of elastic thermoelectric conducting polymer aerogels that could be employed as temperature and pressure sensors in an electronic-skin.
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| 2. |
- Östmans, Rebecca, et al.
(author)
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Solidified water at room temperature hosting tailored fluidic channels by using highly anisotropic cellulose nanofibrils
- 2024
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In: Materials Today Nano. - : Elsevier BV. - 2588-8420. ; 26
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Journal article (peer-reviewed)abstract
- Highly anisotropic cellulose nanofibrils can solidify liquid water, creating self-supporting structures by incorporating a tiny number of fibrils. These fibrillar hydrogels can contain as much as 99.99 wt% water. The structure and mechanical properties of fibrillar networks have so far not been completely understood, nor how they solidify the bulk water at such low particle concentrations. In this work, the mechanical properties of cellulose fibrillar hydrogels in the dilute regime from a wt% perspective have been studied, and an elastoplastic model describing the network structure and its mechanics is presented. A significant insight from this work is that the ability of the fibrils to solidify water is very dependent on particle stiffness and the number of contact points it can form in the network structure. The comparison between the experimental results and the theoretical model shows that the fibrillar networks in the dilute regime form via a non-stochastic process since the fibrils have the time and freedom to find contact points during network formation by translational and rotational diffusion. The formed, dilute fibrillar network deforms by sliding fibril contacts upon straining the network beyond its elastic limit. Our results also show that before macroscopic failure, the fibril contacts are restored once the load is released. The exceptional properties of this solidified water are exploited to host fluidic channels, allowing directed fluid transportation in water. Finally, the microfluidic channels formed in the hydrogels are tailored by the layer-by-layer technique to be interactive against external stimuli, a characteristic envisioned to be useful in biomedical applications.
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| 3. |
- Andersson, Linnéa, et al.
(author)
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Evaluating pore space in macroporous ceramics with water-based porosimetry
- 2013
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In: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 96:6, s. 1916-1922
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Journal article (peer-reviewed)abstract
- We show that water-based porosimetry (WBP), a facile, simple, and nondestructive porosimetry technique, accurately evaluates both the pore size distribution and throat size distribution of sacrificially templated macroporous alumina. The pore size distribution and throat size distribution derived from the WBP evaluation in uptake (imbibition) and release (drainage) mode, respectively, were corroborated by mercury porosimetry and X-ray micro-computed tomography (μ-CT). In contrast with mercury porosimetry, the WBP also provided information on the presence of “dead-end pores” in the macroporous alumina.
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| 4. |
- Aulin, Christian, et al.
(author)
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Design of highly oleophobic cellulose surfaces from structured silicon templates
- 2009
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In: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 1:11, s. 2443-2452
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Journal article (peer-reviewed)abstract
- Structured silicon surfaces, possessing hierarchical porous characteristics consisting of micrometer-sized cavities superimposed upon a network of nanometer-sized pillars or wires, have been fabricated by a plasma-etching process. These surfaces have superoleophobic properties, after being coated with fluorinated organic trichlorosilanes, on intrinsically oleophilic surfaces. By comparison with flat silicon surfaces, which are oleophilic, it has been demonstrated that a combination of low surface energy and the structured features of the plasma-etched surface is essential to prevent oil from penetrating the surface cavities and thus induce the observed macroscopic superoleophobic phenomena with very low contact-angle hysteresis and low roll-off angles. The structured silicon surfaces were coated with cellulose nanocrystals using the polyelectrolyte multilayer technique. The cellulose surfaces prepared in this way were then coated with a monolayer of fluorinated trichlorosilanes. These porous cellulose films displayed highly nonwetting properties against a number of liquids with low surface tension, including alkanes such as hexadecane and decane. The wettability and chemical composition of the cellulose/silicon surfaces were characterized with contact-angle goniometry and X-ray photoelectron spectroscopy, respectively. The nano/microtexture features of the cellulose/silicon surfaces were also studied with field-emission scanning electron microscopy. The highly oleophobic structured cellulose surfaces are very interesting model surfaces for the development of biomimetic self-cleaning surfaces in a vast array of products, including green constructions, packaging materials, protection against environmental fouling, sports, and outdoor clothing, and microfluidic systems.
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| 5. |
- Aulin, Christian, 1980-, et al.
(author)
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Wetting kinetics of oil mixtures on fluorinated model cellulose surfaces
- 2008
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In: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 317:2, s. 556-567
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Journal article (peer-reviewed)abstract
- The wetting of two different model cellulose surfaces has been studied; a regenerated cellulose (RG) surface prepared by spin-coating, and a novel multilayer film of poly(ethyleneimine) and a carboxymethylated microfibrillated cellulose (MFC). The cellulose films were characterized in detail using atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). AFM indicates smooth and continuous films on a nanometer scale and the RMS roughness of the RG cellulose and MFC surfaces was determined to be 3 and 6 nm, respectively. The cellulose films were modified by coating with various amounts of an anionic fluorosurfactant, perfluorooctadecanoic acid, or covalently modified with pentadecafluorooctanyl chloride. The fluorinated cellulose films were used to follow the spreading mechanisms of three different oil mixtures. The viscosity and surface tension of the oils were found to be essential parameters governing the spreading kinetics on these surfaces. XPS and dispersive surface energy measurements were made on the cellulose films coated with perfluorooctadecanoic acid. A strong correlation was found between the surface concentration of fluorine, the dispersive surface energy and the contact angle of castor oil on the surface. A dispersive surface energy less than 18 mN/m was required in order for the cellulose surface to be non-wetting (Ξe > 90 °) by castor oil.
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| 6. |
- Fall, Andreas, et al.
(author)
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Colloidal Stability of Aqueous Nanofibrillated Cellulose Dispersions
- 2011
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:18, s. 11332-11338
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Journal article (peer-reviewed)abstract
- Cellulose nanofibrils constitute an attractive raw material for carbon-neutral, biodegradable, nanostructured materials. Aqueous suspensions of these nanofibrils are stabilized by electrostatic repulsion arising from deprotonated carboxyl groups at the fibril surface. In the present work, a new model is developed for predicting colloidal stability by considering deprotonation and electrostatic screening. This model predicts the fibril-fibril interaction potential at a given pH in a given ionic strength environment. Experiments support the model predictions that aggregation is induced by decreasing the pH, thus reducing the surface charge, or by increasing the salt concentration. It is shown that the primary mechanism for aggregation upon the addition of salt is the surface charge reduction through specific interactions of counterions with the deprotonated carboxyl groups, and the screening effect of the salt is of secondary importance.
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| 7. |
- Fält, Susanna, et al.
(author)
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Model films of cellulose II - improved preparation method and characterization of the cellulose film
- 2004
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In: Cellulose. - 0969-0239 .- 1572-882X. ; 11:2, s. 151-162
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Journal article (peer-reviewed)abstract
- An optimization study of the preparation of spin-coated cellulose model films from the NMMO/DMSO system on silicon wafers has been made. The study shows that the cellulose concentration in the solution determines the cellulose film thickness and that the temperature of the solution affects the surface roughness. A lower solution temperature results in a lower surface roughness at cellulose concentrations below 0.8%. Using the described method, it is possible to prepare films with thicknesses of 30-90 nm with a constant surface roughness by changing the cellulose concentration, i.e. by dilution with DMSO. On these films, water has a contact angle less than 20degrees and about 50% of the material can, according to CP/MAS C-13-NMR spectroscopy on corresponding fibrous material, be considered to consist of crystalline cellulose II type material. It has further been shown that AFM can be used to determine the thickness of cellulose films, in both dry and wet states. In this method, the difference in height between the top surface and the underlying wafer has been measured at an incision made into the cellulose film. The cellulose films have also been spin-coated with the same technique as on the silicon oxide wafer onto the crystal in a quartz crystal microbalance (QCM). These model films were found to be suitable for swelling measurements with the QCM. The films were very stable during this type of measurement and films with different amounts of charges gave different swelling responses depending on their charges. As expected, films with a higher charge showed a higher swelling.
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| 8. |
- Gustafsson, Emil, et al.
(author)
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Treatment of cellulose fibres with polyelectrolytes and wax colloids to create tailored highly hydrophobic fibrous networks
- 2012
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In: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 414, s. 415-421
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Journal article (peer-reviewed)abstract
- Paper is a versatile material with obvious advantages in being both inexpensive and environment friendly. However, a major drawback compared with many other materials, such as plastics, is that it is sensitive to both liquid water and moist air. Traditionally paper is protected from liquid water by sizing. The present work presents a new way to make paper water resistant by combining the layer-by-layer (LbL) technique with the adsorption of a colloidal wax onto the multilayer structure. After the adsorption of five layers of poly(allylamine hydrochloride) and poly(acrylic acid) followed by the adsorption of 8. mg paraffin wax per gram fibre, the contact angle measured 60. s after a drop of water was applied to the sheet was about 138°. If the sheets were cured for 30. min at 160. °C after sheet making, the contact angle was ca. 150°. The heat treatment of sheets prepared from LbL-modified fibres without the addition of wax gave a contact angle of about 113°. To decouple structural effects from changes in surface energy upon heat treatment of PAH/PAA LbL films, model experiments were carried out where LbL assemblies were prepared on silicon oxide and cellulose model surfaces. The contact angle increased when these films were heat treated but it did not exceed 90°. The reason for this is due to the lack of structure of the model surfaces on a micrometre scale. The adsorption of wax impaired the mechanical properties of paper sheets made from modified fibres compared to sheets from the LbL-modified fibres. However, at an adsorption of 8. mg paraffin wax per gram fibre there was still an increase by 37 ± 1% in tensile strength index compared to the untreated reference pulp (33.8 ± 0.7 and 24.7 ± 0.6. kNm/kg respectively).
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| 9. |
- Görür, Yunus Can
(author)
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Design of Cellulose-Based Materials via Sustainable and Scalable Processes
- 2022
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Doctoral thesis (other academic/artistic)abstract
- Plastic pollution is one of the most pressing environmental issues in today’s world. Addressing this problem calls for the development of environmentally friendly alternatives that would reduce the amount of persistent plastic waste. Wood-based cellulose is an excellent candidate as a renewable and biodegradable alternative to oil-based plastics in a variety of applications. However, for their widespread adoption, cellulosic materials need to perform comparably to their oil-based counterparts, while simultaneously attaining similarly high processing efficiencies. A major challenge today is to produce high-performance cellulosic materials at industrially feasible rates using scalable methods. This thesis demonstrates that with a fundamental understanding of fiber chemistry and behavior, cellulose fibers can be tuned to develop sustainable material streams and advanced functional materials at high process rates. First, a new stimuli-responsive cellulosic fiber material called self-fibrillating fibers (SFFs) was developed, where the mechanisms governing the swelling of the fiber wall were thoroughly investigated. The knowledge and understanding obtained from these fundamental studies were utilized to prepare pH-responsive filters. Secondly, the preparation of SFF papers and nanopapers using conventional papermaking methods and equipment was demonstrated within the context of rapid transparent paper preparation. It was shown that SFFs can be rapidly dewatered to obtain papers, where the constituting fibers can be nanofibrillated in situ, resulting in strong, transparent and gas barrier nanopapers without sacrificing processing speed. Thirdly, the use of SFFs was extended to functional nanocomposites. A new and scalable materials processing platform for the rapid preparation of functional cellulose hybrids was developed. The stimuli-responsive self-assembly of chemically nanofibrillated SFFs was studied and utilized to prepare nanopapers and hybrid materials. Finally, SFFs were used as bio-based binders in the fabrication of graphitic Li-ion battery electrodes with improved processing and electrochemistry. Taking advantage of their facile nanofibrillation and favorable chemistry, SFFs were nanofibrillated during slurry mixing then blade-coated on copper supports to create strong electrodes with excellent performance.The novel materials and methodologies presented herein combine an aqueous fiber modification strategy with excellent processing properties for the preparation of high-performance cellulosic materials that can compete with oil-based plastics in various applications.
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| 10. |
- Horvath, Andrew T., et al.
(author)
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Adsorption of highly charged polyelectrolytes onto an oppositely charged porous substrate
- 2008
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In: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:15, s. 7857-7866
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Journal article (peer-reviewed)abstract
- The adsorption behavior of highly charged cationic polyelectrolytes onto porous substrates is electrostatic in nature and has been shown to be highly dependent on the poly electrolyte properties. Copolymers of acrylamide (AM) and diallyldimethylammonium chloride (DADMAC) were synthesized to have a range of macromolecular properties (i.e., charge density and molecular mass). Traditional titration methods have been complemented by fluorescence labeling techniques that were developed to directly observe the extent that fluorescently labeled poly(AM-co-DADMAC) adsorbs into the pore structure of a cellulosic substrate. Although contributing to the electrostatic driving force, the charge density acts to limit adsorption to the outermost surface under electrolyte-free conditions. However, adsorption into the pores can occur if both the molecular mass and charge density of poly(AM-co-DADMAC) are sufficiently low. Adsorption initially increases as the electrolyte concentration is increased. However, the electrostatic persistence length of poly(AM-co-DADMAC) restricts the polyelectrolyte from entering the pores. Therefore, changes in the adsorption behavior at moderate electrolyte concentrations have been attributed to swelling of the polyelectrolyte layer at the fiber exterior. The adsorption behavior changes again at high electrolyte concentrations such that poly(AMco-DADMAC) could adsorb into the pore structure. This occurred when the electrolyte concentration was sufficient to screen the electrostatic persistence length of poly(AM-co-DADMAC), provided that the entropie driving force for adsorption still existed. It is suggested that adsorption into the pore structure is a kinetic process that is governed by localized electrostatic interactions between poly(AM-co-DADMAC) and the charges located within the pores.
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