| 1. |
- Abreu, Barbara, et al.
(författare)
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Gemini surfactants as efficient dispersants of multiwalled carbon nanotubes : Interplay of molecular parameters on nanotube dispersibility and debundling
- 2019
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Ingår i: Journal of Colloid and Interface Science. - : ACADEMIC PRESS INC ELSEVIER SCIENCE. - 0021-9797 .- 1095-7103. ; 547, s. 69-77
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Tidskriftsartikel (refereegranskat)abstract
- Surfactants have been widely employed to debundle, disperse and stabilize carbon nanotubes in aqueous solvents. Yet, a thorough understanding of the dispersing mechanisms at molecular level is still warranted. Herein, we investigated the influence of the molecular structure of gemini surfactants on the dispersibility of multiwalled carbon nanotubes (MWNTs). We used dicationic n-s-n gemini surfactants, varying n and s, the number of alkyl tail and alkyl spacer carbons, respectively; for comparisons, single-tailed surfactant homologues were also studied. Detailed curves of dispersed MWNT concentration vs. surfactant concentration were obtained through a stringently controlled experimental procedure, allowing for molecular insight. The gemini are found to be much more efficient dispersants than their single-tailed homologues, i.e. lower surfactant concentration is needed to attain the maximum dispersed MWNT concentration. In general, the spacer length has a comparatively higher influence on the dispersing efficiency than the tail length. Further, scanning electron microscopy imaging shows a sizeable degree of MWNT debundling by the gemini surfactants in the obtained dispersions. Our observations also point to an adsorption process that does not entail the formation of micelle-like aggregates on the nanotube surface, but rather coverage by individual molecules, among which the ones that seem to be able to adapt best to the nanotube surface provide the highest efficiency. These studies are relevant for the rational design and choice of optimal dispersants for carbon nanomaterials and other similarly water-insoluble materials.
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| 2. |
- Adolfsson, Karin
(författare)
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Hydrothermal recycling of natural and synthetic polymers to functional carbon materials
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Utilizing renewable recourses and waste recycling are necessary for reaching a circular resource society. The concept of this thesis was to set up a sustainable recycling route, suitable even for low quality biopolymer and plastic waste for production of functional carbon materials. Carbonaceous materials were prepared by mild hydrothermal carbonizations of cellulose and polypropylene (PP) under acidic conditions. The carbonization of cellulose resulted mainly in micro-/nanometer sized carbon spheres (CS) with polar functionalities. After carbonization of PP, products were found in solid and liquid phase. Completely carbonized solid carbons products were obtained from PP at 250 °C after 60 min. The liquid products from the same process displayed aromatics and exhibited fluorescence properties. In addition, new carbon materials were prepared by acid, base and thermal treatments of the carbonized products at low temperatures. Thermally resistant carbon products and antibacterial CS towards both Staphylococcus aureus and Pseudomonas aeruginosa were demonstrated as possible applications for these products. The minimum inhibitory concentrations of CS were 200-400 µg mL-1 depending on the bacteria strain and reached after only 3 h. Furthermore, nanometer sized carbon nanodots with high oxygenation degree and fluorescence properties were derived together with carbon flakes (CF) from the carbonized products. The CF with flat and micrometer sized morphology and polar groups were utilized for coating of cationized cellulose filters, applied as adsorbents and then subsequently as surfaces for SALDI-MS analysis of environmental contaminants. This work contributes with new routes to and applications for functional carbon materials.
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| 3. |
- Ansari, Farhan, et al.
(författare)
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Interface tailoring through covalent hydroxyl-epoxy bonds improves hygromechanical stability in nanocellulose materials
- 2016
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Ingår i: Composites Science And Technology. - : Elsevier BV. - 0266-3538 .- 1879-1050. ; 134, s. 175-183
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Tidskriftsartikel (refereegranskat)abstract
- Wide-spread use of cellulose nanofibril (CNF) biocomposites and nanomaterials is limited by CNF moisture sensitivity due to surface hydration. We report on a versatile and scalable interface tailoring route for CNF to address this, based on technically important epoxide chemistry. Bulk impregnation of epoxide-amine containing liquids is used to show that CNF hydroxyls can react with epoxides at high rates and high degree of conversion to form covalent bonds. Reactions take place inside nanostructured CNF networks under benign conditions, and are verified by solid state NMR. Epoxide modified CNF nanopaper shows significantly improved mechanical properties under moist and wet conditions. High resolution microscopy is used in fractography studies to relate the property differences to structural change. The cellulose-epoxide interface tailoring concept is versatile in that the functionality of molecules with epoxide end-groups can be varied over a wide range. Furthermore, epoxide reactions with nanocellulose can be readily implemented for processing of moisture-stable, tailored interface biocomposites in the form of coatings, adhesives and molded composites.
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| 4. |
- Ansari, Farhan, et al.
(författare)
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Interface tailoring through covalent hydroxyl-epoxy bonds improves hygromechanical stability in nanocellulose materials
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Wide-spread use of cellulose nanofibril (CNF) biocomposites and nanomaterials is limited by CNF moisture sensitivity due to surface hydration. We report on a versatile and scalable interface tailoring route for CNF to address this, based on technically important epoxide chemistry. Bulk impregnation of epoxide-amine containing liquids is used to show that CNF hydroxyls can react with epoxides at high rates and high degree of conversion to form covalent bonds. Reactions take place inside nanostructured CNF networks under benign conditions, and are verified by solid state NMR. Epoxide modified CNF nanopaper shows significantly improved mechanical properties under moist and wet conditions. High resolution microscopy is used in fractography studies to relate the property differences to structural change. The cellulose-epoxide interface tailoring concept is versatile in that the functionality of molecules with epoxide end-groups can be varied over a wide range. Furthermore, epoxide reactions with nanocellulose can be readily implemented for processing of moisture-stable, tailored interface biocomposites in the form of coatings, adhesives and molded composites.
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| 5. |
- Bastardo Zambrano, Luis Alejandro, et al.
(författare)
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Soluble complexes in aqueous mixtures of low charge density comb polyelectrolyte and oppositely charged surfactant probed by scattering and NMR
- 2007
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 312, s. 21-33
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Tidskriftsartikel (refereegranskat)abstract
- A low charge density polyelectrolyte with a high graft density of 45 units long poly(ethylene oxide) side-chains has been synthesized. In this comb polymer, denoted PEO45 MEMA:METAC-2, 2 mol% of the repeating methacrylate units in the polymer backbone carry a permanent positive charge and the remaining 98 mol% a 45 unit long PEO side-chain. Here we describe the solution conformation of this polymer and its association with an anionic surfactant, sodium dodecylsulfate, SDS. It will be shown that the polymer can be viewed as a stiff rod with a cross-section radius of gyration of 29 Å. The cross section of the rod contracts with increasing temperature due to decreased solvency of the PEO side-chains. The anionic surfactant associates to a significant degree with PEO45 MEMA:METAC-2 to form soluble complexes at all stoichiometries. A cooperative association is observed as the free SDS concentration approaches 7 mM. At saturation the number of SDS molecules associated with the polymer amounts to 10 for each PEO side-chain. Two distinct populations of associated surfactants are observed, one is suggested to be molecularly distributed over the comb polymer and the other constitutes small micellar-like structures at the periphery of the aggregate. These conclusions are reached based on results from small-angle neutron scattering, static light scattering, NMR, and surface tension measurements.
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| 6. |
- Bernin, Diana, et al.
(författare)
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On the ionization of cellulose in aqueous alkali
- 2017
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Ingår i: Abstracts of Papers of the American Chemical Society. - : AMER CHEMICAL SOC. - 0065-7727. ; 253
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 7. |
- Bialik, Erik, et al.
(författare)
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Ionization of Cellobiose in Aqueous Alkali and the Mechanism of Cellulose Dissolution
- 2016
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Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society. - 1948-7185. ; 7:24, s. 5044-5048
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Tidskriftsartikel (refereegranskat)abstract
- Cellulose, one of the most abundant renewable resources, is insoluble in most common solvents but dissolves in aqueous alkali under a narrow range of conditions. To elucidate the solubilization mechanism, we performed electrophoretic NMR on cellobiose, a subunit of cellulose, showing that cellobiose acts as an acid with two dissociation steps at pH 12 and 13.5. Chemical shift differences between cellobiose in NaOH and NaCl were estimated using 2D NMR and compared to DFT shift differences upon deprotonation. The dissociation steps are the deprotonation of the hemiacetal OH group and the deprotonation of one of four OH groups on the nonreducing anhydroglucose unit. MD simulations reveal that aggregation is suppressed upon charging cellulose chains in solution. Our findings strongly suggest that cellulose is to a large extent charged in concentrated aqueous alkali, a seemingly crucial factor for solubilization. This insight, overlooked in the current literature, is important for understanding cellulose dissolution and for synthesis of new sustainable materials.
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| 8. |
- Bielejewski, Michal, et al.
(författare)
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On electrophoretic NMR. Exploring high conductivity samples
- 2014
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Ingår i: Journal of magnetic resonance. - : Elsevier BV. - 1090-7807 .- 1096-0856. ; 243, s. 17-24
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Tidskriftsartikel (refereegranskat)abstract
- The performance of a new electrophoretic NMR (eNMR) method that uses a Carr-Purcell-Meiboom-Gill echo train with repeated electric field reversal is investigated. We show that this pulse sequence, with acronym CPMGER, yields strongly reduced artifacts from convective flow effects caused by the simultaneous presence of electroosmotic and thermal driving forces. We demonstrate the achieved improvements in various aqueous solutions. Ultimately, the method can be used for obtaining electrophoretic mobilities by eNMR without relying on uncharged reference molecules, otherwise a significant limitation for electrophoretic experiments performed with nuclei other than 1H.
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| 9. |
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| 10. |
- Callaghan, P. T., et al.
(författare)
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Diffusion-diffusion correlation and exchange as a signature for local order and dynamics
- 2004
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 120:8, s. 4032-4038
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the use of new two-dimensional nuclear magnetic resonance experiments in the examination of local diffusional anisotropy under conditions of global isotropy. The methods, known as diffusion-diffusion correlation spectroscopy and diffusion exchange spectroscopy, employ successive pairs of magnetic field gradient pulses, with signal analysis using two-dimensional inverse Laplace transformation. Diffusional anisotropy is measured for water molecules in a polydomain lamellar phase lyotropic liquid crystal, 40 wt % nonionic surfactant C10E3 (C10H21O(CH2CH2O)(6)H) in H2O.
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