| 51. |
- Acciaro, Roberta, et al.
(författare)
-
Investigation of the formation, structure and release characteristics of self-assembled composite films of cellulose nanofibrils and temperature responsive microgels
- 2011
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 7:4, s. 1369-1377
-
Tidskriftsartikel (refereegranskat)abstract
- The possibility of forming self-organized films using charge-stabilized dispersions of cellulose I nanofibrils and microgel beads of poly-(N-isopropylacrylamide-co-acrylic acid) copolymer is presented. The build-up behavior and the properties of the layer-by-layer (LbL)-constructed films were studied using quartz crystal microbalance with dissipation (QCM-D) and ellipsometry. The morphology of the formed films was also characterized using atomic force microscopy (AFM) imaging. The applied methods clearly demonstrated the successful LbL-assembly of the monodisperse microgels and nanofibrils. The in situ QCM-D measurements also revealed that contrary to the polyelectrolyte bound microgel particles, the nanofibrils-bound gel beads preserve their highly swollen state and do not suffer a partial collapse due to the lack of interdigitation of the oppositely charged components. To probe the accessibility of the gel beads in the formed films, the room temperature (similar to 25 degrees C) loading and release of a fluorescent dye (FITC) was also investigated. The incorporation of the cellulose nanofibrils into the multilayer resulted in an open structure that was found easily penetrable for the dye molecules even at constant room temperature, which is in sharp contrast with previously reported systems based on synthetic polyelectrolytes. The amount of dye released from the multilayer films could be fine-tuned with the number of bilayers. Finally, the thermoresponsivity of the films was also shown by triggering the burst release of the loaded dye when the film was collapsed.
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| 52. |
- Ahrenstedt, Lage
(författare)
-
Surface modification of cellulose materials : from wood pulps to artificial blood vessels
- 2007
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes the improvement of two radically different cellulose materials, paper and artificial blood vessels, constructed from two diverse cellulose sources, wood pulp and Acetobacter xylinum. The improvement of both materials was possible due to the natural affinity of the hemicellulose xyloglucan for cellulose. Chemical and mechanical pulps were treated with xyloglucan in the wet-end prior to hand sheet formation or by spray application of dry hand sheets, loading a comparable amount of xyloglucan. The tensile strength increases for the wet-end treatment and spray application were 28% and 71% respectively for bleached soft wood, compared to untreated sheets (20.7 Nm/g). The corresponding strength increases for hand sheets made of thermo-mechanical pulp were 6% and 13% respectively compared to untreated sheets (42.4 Nm/g). The tendency for chemical pulp to be superior to mechanical pulp with respect to strength increase was valid even for tear strength and Scott-Bond. These results suggest, in agreement with other studies, that adhesion of xyloglucan to wood fibres is dependent on their degree of surface lignification. Also, a method was developed to increase the blood compatibility of artificial blood vessels constructed of bacterial cellulose. Xyloglucan was covalently linked to the endothelial cell adhesion motif (Arg-Gly-Asp). To obtain this, new solid-phase coupling chemistry was developed. Xyloglucan oligosaccharides (XGO) were transformed into XGO-succinamic acid via the corresponding XGO--NH2 derivative prior to coupling with the N-terminus of the solid-phase synthesised Gly-Arg-Gly-Asp-Ser peptide. The resin-bound glyco-peptide was then cleaved and enzymatically re-incorporated into high molecular weight xyloglucan. The glyco-peptide was further adsorbed onto bacterial cellulose scaffolds, increasing the adhesion and proliferation of endothelial cells and therefore blood compatibility.
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| 53. |
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| 54. |
- Alipoormazandarani, Niloofar, et al.
(författare)
-
Functional Lignin Nanoparticles with Tunable Size and Surface Properties : Fabrication, Characterization, and Use in Layer-by-Layer Assembly
- 2021
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:22, s. 26308-26317
-
Tidskriftsartikel (refereegranskat)abstract
- Lignin is the richest source of renewable aromatics and has immense potential for replacing synthetic chemicals. The limited functionality of lignin is, however, challenging for its potential use, which motivates research for creating advanced functional lignin-derived materials. Here, we present an aqueous-based acid precipitation method for preparing functional lignin nanoparticles (LNPs) from carboxy-methylated or carboxy-pentylated lignin. We observe that the longer grafted side chains of carboxy-pentylated lignin allow for the formation of larger LNPs. The functional nanoparticles have high tolerance against salt and aging time and well-controlled size distribution with R-h <= 60 nm over a pH range of 5-11. We further investigate the layer-by-layer (LbL) assembly of the LNPs and poly(allylamine hydrochloride) (PAH) using a stagnation point adsorption reflectometry (SPAR) and quartz crystal microbalance with dissipation (QCM-D). Results demonstrate that LNPs made of carboxypentylated lignin (i.e., PLNPs with the adsorbed mass of 3.02 mg/m(2)) form a more packed and thicker adlayer onto the PAH surface compared to those made of carboxymethylated lignin (i.e., CLNPs with the adsorbed mass of 2.51 mg/m(2)). The theoretical flux, J, and initial rate of adsorption, (d Gamma/dt)(0), analyses confirm that 22% of PLNPs and 20% of CLNPs arriving at the PAH surface are adsorbed. The present study provides a feasible platform for engineering LNPs with a tunable size and adsorption behavior, which can be adapted in hionanomaterial production.
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| 55. |
- Andersson, J, et al.
(författare)
-
Ageing of Flexographic Printed Model Cellulose Surfaces and Determination of the Mechanisms Behind Ageing
- 2009
-
Ingår i: Pulp & paper Canada. - 0316-4004. ; 110:6, s. 34-38
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of storage conditions on the ink detachment efficiency of water-based flexographic ink printed onto model cellulose surfaces and handsheets was investigated. It was shown that UV light, elevated temperatures, longer storage time, increasing surface roughness, and increasing surface hydrophobicity all had a negative effect on ink detachment. It was also shown that the ink's chemical and structural characteristics changed when stored at elevated temperatures. No chemical or structural changes could be observed for the ink when stored under UV light.
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| 56. |
- Andersson, Linnéa, et al.
(författare)
-
Evaluating pore space in macroporous ceramics with water-based porosimetry
- 2013
-
Ingår i: Journal of The American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 96:6, s. 1916-1922
-
Tidskriftsartikel (refereegranskat)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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| 57. |
- Andreasson, B., et al.
(författare)
-
Determination of fibre pore structure : influence of salt, pH and conventional wet strength resins
- 2005
-
Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 12:3, s. 253-265
-
Tidskriftsartikel (refereegranskat)abstract
- It has been shown, in the present investigation, that the two methods used to investigate the pore size distribution of unbleached chemical pulps, i.e. inverse size exclusion chromatography (ISEC) and nuclear magnetic resonance (NMR), give different average pore radius for the pores inside the fibre wall. This is due to the way in which these experiments are performed and the sensitivity of the methods to different types of pores in the cell wall. It was also shown that the two methods gave different results when changing the pH and the ionic strength of the pulp suspension. The pore radius, as detected with ISEC, decreased with both increasing ionic strength and decreasing pH, indicating a loose structure of the exterior of the fibrillar network. However, the pore radius as detected with NMR, was virtually unaffected when increasing the ionic strength, indicating a very rigid structure of the interior of the fibre wall. Decreasing pH though, lead to a decrease in pore radius indicating that upon protonation of the carboxylic groups in the fibre wall, the electrostatic repulsion is diminished and the average pore radius decreases. The NMR technique was also used to study wet strength aid penetration into the fibre wall. It was shown that wet strength aids with a small molecular weight, penetrated the fibre wall, as detected by a decrease in pore radius. It was also shown that addition of different wet strength aids increased the tensile index of the sheet and decreased the fibre strength, measured as zero span-strength of the sheets.
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| 58. |
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| 59. |
- Andreasson, B., et al.
(författare)
-
The porous structure of pulp fibres with different yields and its influence on paper strength
- 2003
-
Ingår i: Cellulose. - 0969-0239 .- 1572-882X. ; 10:2, s. 111-123
-
Tidskriftsartikel (refereegranskat)abstract
- The porous structure of the interior of papermaking fibres is a well-known important property of the fibres. Changes of this structure will influence tensile and burst strength of paper formed from the fibres and a change in pore size of the pores within the fibre wall is also important for the ability of molecules to diffuse in and out of the fibre wall. Relevant examples of this latter effect are the removal of lignin during cooking and the addition of performance chemicals during papermaking. In this paper, pore sizes and the pore size distribution of unbleached softwood fibres have been studied. A well-characterised fibre material consisting of laboratory cooked spruce and pine pulp of various lignin contents was used. Pore size and pore size distribution were measured by studies of the relaxation behaviour of H-2 in fibres saturated with (H2O)-H-2. Beside this the total and surface charge of the fibres were also measured together with strength properties of papers from unbeaten fibres. For both pulps, there is a maximum in pore radius at a yield around 46%. Calculations of fibre wall volume from water retention values and yield levels show that there is a discontinuity in pore radius as a function of the fibre wall volume around a yield of 51%. It is suggested that this discontinuity is caused by the breakdown of the hemicellulose/ lignin matrix within the fibre wall at this yield level. The strength of the papers formed from the fibres shows a correlation with the surface charge of the fibres. Based on the change in surface charge with yield and the change in total charge with yield, this correlation is suggested to be due to an opening up of the external part of the fibre wall. This stresses the importance of the chemical composition and physical structure of the outer layer of the fibre wall.
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| 60. |
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| 61. |
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| 62. |
- Ankerfors, Caroline, et al.
(författare)
-
AFM adhesion imaging for the comparison of polyelectrolyte complexes and polyelectrolyte multilayers
- 2012
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 8:32, s. 8298-8301
-
Tidskriftsartikel (refereegranskat)abstract
- The adhesion and topography of dry surfaces treated with polyelectrolyte complexes (PECs) and multilayers (PEMs) of PAH/PAA or CPAM/silica nanoparticles were studied using AFM adhesion mapping. PEMs gave higher adhesion than did PECs for the PAH/PAA system, but adhesion did not differ significantly between PEMs and PECs for the CPAM/silica system. The latter system displayed multiple release patterns, interpreted as disentanglements and tentatively ascribed to nanoparticle presence. AFM adhesion mapping is valuable for analysing PEC and PEM. The measurements should, however, be combined with separate force measurements for a more complete picture of the adhesion.
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| 63. |
- Ankerfors, Caroline, 1979-
(författare)
-
Polyelectrolyte complexes : Preparation, characterization, and use for control of wet and dry adhesion between surfaces
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis examines polyelectrolyte complex (PEC) preparation, adsorption behaviour, and potential use for control of wet and dry adhesion between surfaces. PEC formation was studied using a jet-mixing method not previously used for mixing polyelectrolytes. The PECs were formed using various mixing times, and the results were compared with those for PECs formed using the conventional polyelectrolyte titration method. The results indicated that using the jet mixer allowed the size of the formed PECs to be controlled, which was not the case with the polyelectrolyte titration method, and a two-step mechanism for PEC formation was suggested. Adsorption experiments comparing two types of PECs, both produced from PAA and PAH, but with different molecular weights, demonstrated that surface-induced aggregation occurred in the high-molecular-weight PECs, whereas the adsorption stopped at a low level in the low-molecular-weight PECs. It was suggested that the latter PECs consisted of two fractions of complexes and that the fraction with lower polymer density exerted a site-blocking effect, hindering further adsorption. It was also demonstrated that particle-PECs (PPECs), in which one polyion was replaced with a silica nanoparticle, could be prepared. The purpose of preparing PPECs was to create a PEC structure that could create a joint with a special failure pattern referred to as disentanglement behaviour. Using the colloidal probe AFM technique, the expected disentanglement could be detected in PPECs, though the joint strength was low. Adhesion experiments demonstrated significantly higher pull-off values with polymer–polymer complexes than with PPECs. However, there was large spread in the data, possibly due to the surface inhomogeneity. Experiments using low-molecular-weight PECs as a paper strength agent demonstrated that PECs can indeed increase paper strength. Comparing the PEC results with those for polyelectrolyte multilayers (PEMs) prepared from the same polyelectrolytes indicated that, since the PEM strategy enables higher adsorption levels than does the PEC strategy, greater absolute strength improvements could be achieved using PEMs. However, PEC treatment resulted in the greatest effect per adsorbed amount of polymer.
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| 64. |
- Ankerfors, Caroline
(författare)
-
Polyelectrolyte complexes : their preparation, adsorption behaviour and effect on paper properties
- 2008
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this work, the formation of polyelectrolyte complexes (PECs) has been studied using a jet mixing method not previously used for mixing polyelectrolytes. The PECs were formed from two weak polyelectrolytes, i.e., polyacrylic acid (PAA) and polyallylamine hydrochloride (PAH), with different mixing times, and the results were compared with those for PECs formed using the conventional polyelectrolyte titration method. The adsorption behaviour of the formed PECs on silicon oxide substrates and pulp fibres was analysed, and the results were compared with those for polyelectrolyte multilayers (PEMs) prepared from the same two polyelectrolytes. The results indicated that by using the jet mixer, the size of the formed PECs could be controlled, which was not the case with the polyelectrolyte titration method. The PECs produced by jet mixing were also found to be smaller than those produced by polyelectrolyte titration. From these results, a two-step mechanism for the formation of PECs was suggested: initial precomplex formation, which is a fast and diffusion-controlled process, followed by a reconformation process, during which the vigorous mixing in the jet mixer can partially limit secondary aggregation. When the complexes were adsorbed to silicon oxide or pulp fibre surfaces, adsorption studies indicated that it was impossible to reach the same adsorption levels for PECs as for PEMs. This was explained in terms of free energy, entropical, reasons rather than to any geometric limitation of the surface. Despite the smaller amount of polyelectrolyte adsorbed from the PEC treatment than from the PEM treatment of pulp fibres, the PEC treatment had the greatest effect on paper strength per adsorbed amount of polymer. This was thought to be because the three-dimensional structure of the PECs, versus the smoother structure of PEMs, allows for the formation of multiple contact points between the macroscopically rough fibres and increased molecular contact area. In the adsorption experiments, it was also found that net cationic complexes can adsorb to both anionic and cationic substrates. This phenomenon was explained by the occurrence of anionic patches on the surface of the net cationic PECs and the ability of the PECs, formed from weak polyelectrolytes, to partially change charge upon exposure to a surface of the same charge as the complex itself, due to a change of the degree of dissociation of the polyelectrolytes constituting the complex.
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| 65. |
- Ankerfors, Caroline, et al.
(författare)
-
Polyelectrolyte Complexes for Tailoring of Wood Fibre Surfaces
- 2014
-
Ingår i: Polyelectrolyte Complexes In The Dispersed And Solid State II. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 0065-3195 .- 1436-5030. - 9783642407468 - 9783642407451 ; , s. 1-24
-
Bokkapitel (refereegranskat)abstract
- The use of polyelectrolyte complexes (PECs) provides new opportunities for surface engineering of solid particles in aqueous environments to functionalize the solids either for use in interactive products or to tailor their adhesive interactions in the dry and/or wet state. This chapter describes the use of PECs in paper-making applications where the PECs are used for tailoring the surfaces of wood-based fibres. Initially a detailed description of the adsorption process is given, in more general terms, and in this respect both in situ formed and pre-formed complexes are considered. When using in situ formed complexes, which were intentionally formed by the addition of oppositely charged polymers, it was established that the order of addition of the two polyelectrolytes was important, and by adding the polycation first a more extensive fibre flocculation was found. PECs can also form in situ by the interaction between polyelectrolytes added and polyelectrolytes already present in the fibre suspension originating from the wood material, e. g. lignosulphonates or hemicelluloses. In this respect the complexation can be detrimental for process efficiency and/or product quality depending on the charge balance between the components, and when using the PECs for fibre engineering it is not recommended to rely on in situ PEC formation. Instead the PECs should be pre-formed before addition to the fibres. The use of pre-formed PECs in the paper-making process is described as three sub-processes: PEC formation, adsorption onto surfaces, and the effect on the adhesion between surfaces. The addition of PECs, and adsorption to the fibres, prior to formation of the paper network structure has shown to result in a significant increase in joint strength between the fibres and to an increased strength of the paper made from the fibres. The increased joint strength between the fibres is due to both an increased molecular contact area between the fibres and an increased molecular adhesion. The increased paper strength is also a result of an increased number of fibre/fibre contacts/unit volume of the paper network.
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| 66. |
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| 67. |
- Ankerfors, Caroline, et al.
(författare)
-
Use of polyelectrolyte complexes and multilayers from polymers and nanoparticles to create sacrificial bonds between surfaces
- 2013
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 391, s. 28-35
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, particle polyelectrolyte complexes (PPECs) were formed by mixing cationic polyacrylamide (CPAM) and silica nanoparticles using the jet mixing technique. Within certain limits, the size of the formed PPECs could be controlled. The aim was to prepare PPECs with embedded sacrificial bonds, similar to those found in bones. Examination of PPEC adsorption to silica model surfaces indicated that,smaller PPECs adsorbed to a higher level than larger ones, due to the higher diffusion speed of smaller complexes. Adsorption studies of the same components as in the PPECs, but arranged in multilayers, that is, particle polyelectrolyte multilayers (PPEMs), indicated a stable, gradual build-up of material on the surface with smaller nanoparticles, whereas PPEMs comprising elongated nanoparticles appeared to be more loosely adsorbed onto the surface when the nanoparticles were in the outer layer, due to repulsive forces within the adsorbed layer. The AFM colloidal probe technique was used to study the interaction between surfaces treated with PPECs, multilayers, or polyelectrolyte complexes (PECs). The results showed that the expected long-range disentanglement could be achieved with PPECs but that the pull-off forces were generally low. Treatment with PPEMs comprising the same polymer and nanoparticle components produced higher pull-off values, together with disentanglement behaviour, possibly due to better contact between the surfaces. Adhesion experiments with polymer PECs showed significantly higher pull-off values than with the PPECs, probably due to polymer interdiffusion across the surface boundary.
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| 68. |
- Ankerfors, Mikael
(författare)
-
Microfibrillated cellulose : Energy-efficient preparation techniques and key properties
- 2012
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work describes three alternative processes for producing microfibrillated cellulose (MFC) in which pulp fibres are first pre-treated and then homogenized using a high-pressure homogenizer. In one process, fibre cell wall delamination was facilitated with a combined enzymatic and mechanical pre-treatment. In the two other processes, cell wall delamination was facilitated by pre-treatments that introduced anionically charged groups into the fibre wall, by means of either a carboxymethylation reaction or irreversibly attaching carboxymethyl cellulose (CMC) onto the fibres. All three processes are industrially feasible and enable production with low energy consumption. Using these methods, MFC can be produced with an energy consumption of 500–2300 kWh/tonne, which corresponds to a 91–98% reduction in energy consumption from that presented in earlier studies. These materials have been characterized in various ways and it has been demonstrated that the produced MFCs are approximately 5–30 nm wide and up to several microns long.
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| 69. |
- Ankerfors, Mikael, 1978-
(författare)
-
Microfibrillated cellulose: Energy-efficient preparation techniques and applications in paper
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work describes three alternative processes for producing microfibrillated cellulose (MFC; also referred to as cellulose nanofibrils, CNF) in which bleached pulp fibres are first pretreated and then homogenized using a high-pressure homogenizer. In one process, fibre cell wall delamination was facilitated by a combined enzymatic and mechanical pretreatment. In the two other processes, cell wall delamination was facilitated by pretreatments that introduced anionically charged groups into the fibre wall, by means of either a carboxymethylation reaction or irreversibly attaching carboxymethylcellulose (CMC) to the fibres. All three processes are industrially feasible and enable energy-efficient production of MFC. Using these processes, MFC can be produced with an energy consumption of 500–2300 kWh/tonne. These materials have been characterized in various ways and it has been demonstrated that the produced MFCs are approximately 5–30 nm wide and up to several microns long.The MFCs were also evaluated in a number of applications in paper. The carboxymethylated MFC was used to prepare strong free-standing barrier films and to coat wood-containing papers to improve the surface strength and reduce the linting propensity of the papers. MFC, produced with an enzymatic pretreatment, was also produced at pilot scale and was studied in a pilot-scale paper making trial as a strength agent added at the wet-end for highly filled papers.
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| 70. |
- Ariza, David, et al.
(författare)
-
First Mode Negative Streamers along Mineral Oil-solid Interfaces
- 2017
-
Ingår i: IEEE transactions on dielectrics and electrical insulation. - : IEEE. - 1070-9878 .- 1558-4135. ; 24:4
-
Tidskriftsartikel (refereegranskat)abstract
- This document presents an experimental study on the propagation of first mode negative streamers along mineral oil-solid interfaces. Samples made of an oil impregnated kraft paper and a low-porosity paper made from cellulosic micro and nano fibrils, as well as different polymeric films (low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF)) are used as the solid. A comparison of the length, charge and velocity of streamers for all different mineral oil-solid interfaces is reported. It is shown that streamers propagate longer and faster along mineral oil-solid interfaces with low surface roughness, low porosity and higher electrical permittivity than mineral oil. Those streamers show a quasi-continuous injection of charge in the early stage of their propagation. This quasi-continuous charge injection consists of a sequence of small charge steps separated by few tens of nanoseconds in between. In comparison, the streamers that propagate along surfaces with similar permittivity to the mineral oil have lower injection of charge and higher stopping voltage conditions than streamers propagating free in the liquid without any solid barrier.
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| 71. |
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| 72. |
- Ariza, David, et al.
(författare)
-
Inception of first mode negative streamers at liquid/solid interfaces
-
Ingår i: Journal of Physics D: Applied Physics.
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents an experimental study on the inception of first mode negative streamers at different mineral-oil/solid interfaces. This study is performed with a point-plane configuration immersed in mineral oil (point cathode). The mineral-oil/solid interface is done by assembling a solid in an inclined position into the point-plane gap. The solid is in contact (or in the proximity) with the point electrode tip. The tested solids are a kraft paper, a paper made from cellulosic micro and nano fibrils and different polymeric films (low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF)). These solids have different relative permittivity and structural composition. It is found that the streamer inception voltage is statistically similar for the cases with solids with higher permittivity than mineral oil. The streamer inception voltage for the case without any solid barrier is also statistically similar to the cases with solids with higher permittivity than mineral oil. It is also found that the inception voltage is higher for streamers initiated at permittivity-matched interfaces (cases with LDPE and PTFE). Additionally, the influence of the spatial limitation with the solid surface to the volume where the streamer initiation process takes is performed with PTFE by varying the distance between the point electrode and the solid surface. It is shown that the streamer inception voltage depends on the distance between the point electrode and the solid surface. Furthermore, It is observed that the streamer inception voltage is also influenced when the distance between the point electrode and the surface of the PTFE is several micrometers (twenty times longer than the penetration depth of the avalanche responsible of streamer initiation). Additionally, it is also shown that a recently-proposed streamer inception criterion is unsuitable to predict the streamer inception conditions close to permittivity matched and mismatched liquid/solid interfaces.
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| 73. |
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| 74. |
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| 75. |
- Ariza, David, et al.
(författare)
-
Influence of Paper Properties on Streamers Creeping in Mineral Oil
- 2017
-
Ingår i: Proceedings of IEEE International Conference on Dielectric Liquids. - : IEEE. - 2153-3725 .- 2153-3733.
-
Tidskriftsartikel (refereegranskat)abstract
- This work presents an experimental study ofsecond mode positive streamers propagating along mineral oilpaperinterfaces. A point-plane arrangement immersed inmineral oil with the paper inclined 60 degrees to the planeelectrode is used to create the liquid-solid interface. Kraft paperand a kraft fibril paper, made from cellulosic micro and nanofibrils, with higher density and lower surface roughness are usedas the solid materials. High speed shadowgraphy and chargerecordings are used to compare the propagation of second modepositive streamers along the mineral oil-kraft paper and mineraloil-kraft fibril paper. Streamers creeping along the mineral oilkraftpaper interface propagate mainly into the liquid, with oneor two main filaments. In comparison, the streamers propagatingalong the kraft fibril paper show a strong reduction of thebranching; these streamers consist of a single filament thatpropagates exactly on the solid surface. Streamers along the kraftfibril paper also have longer propagation time than for the casewith kraft paper. Mutual electrostatic shielding betweenfilaments is observed for the streamers creeping on the kraftpaper. An electrostatic analysis of the influence of permittivity,density and surface roughness of the solid in the electricalproperties of the streamer filaments is also performed.
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| 76. |
- Ariza, David, et al.
(författare)
-
Second Mode Positive Streamers Propagating Along Mineral-oil/solid Interfaces
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents an experimental study on second mode positive streamers propagating along mineral-oil/solid interfaces. The inception and propagation of these streamers is investigated with different impregnated solids (low density polyethylene (LDPE), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE) polyvinylidene fluoride (PVDF), two papers referred to as kraft paper and a kraft fibril paper, made from cellulosic micro and nano fibrils, a lignin-free paper and a paper with high lignin content referred to as k107 kraft paper). Streamers are initiated in a point-plane configuration under step voltages with 35 ns rise time. The radius of the tip is 2.9 μm and the solid is installed in an inclined position in close contact to the point electrode. Shadowgraphs, charge and light recording of the streamers are reported for each case. Furthermore, estimations of the streamer stopping length, velocity, current and average charge are reported. It is found that the streamer inception is influenced by the solid interface indicating that the inception process is not only conditioned by the field at the tip but also by the interface. A time delay is observed before the initiation of the streamer and probably correlated with the initiation process and formation of the gaseous phase. Additionally, the threshold propagation voltage of the second mode streamers at mineral-oil/solid interfaces is shown to be independent of the interface. It is also shown that the different characteristics of streamers propagating along the tested interfaces cannot be fully explained by the capacitive coupling effect due to permittivity mismatch. Thus, it is suggested that the characteristics of streamers propagating near interfaces is affected by other properties of the solid such as chemical composition, wettability and surface roughness.
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| 77. |
- Arumughan, Vishnu, 1994, et al.
(författare)
-
Specific ion effects in the adsorption of carboxymethyl cellulose on cellulose: The influence of industrially relevant divalent cations
- 2021
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 1873-4359 .- 0927-7757. ; 626
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of carboxymethylcellulose (CMC) on cellulose surfaces is of relevance from both academic and industrial perspectives as it facilitates resource-efficient modification of cellulose fibres that allows them to carry negative charges. It is known that, compared to monovalent ions, Ca2+ ions are superior ions in facilitating CMC adsorption and the subsequent introduction of charge on cellulose fibres. However, the formation and deposition of calcium oxide involved in this process necessitates the search for alternative cations. Magnesium ions form one of the more promising candidates since they are already used in the pulping process to prevent cellulose degradation during peroxide bleaching. This work aims at elucidating the effects of the industrially relevant alkaline earth metal divalent cations Mg2+ and Ca2+ on the CMC adsorption process onto cellulose surfaces. Quartz Crystal Microbalance (QCM-D) technology was used to follow the adsorption in model systems in real time, whereas the adsorption of CMC on commercial fibres was studied using polyelectrolyte titrations, total organic carbon (TOC) analysis and conductometric titrations. This study shows that the presence of Ca2+ ions was more favourable for the adsorption of CMC to both types of cellulosic surfaces than Mg2+ ions. The distinction in the adsorption behaviour in the presence of Mg2+ and Ca2+ is suggested to be due to the differences in the polarizability of the ions. The findings are decisive in designing efficient industrial processes for the adsorption of polyelectrolytes to cellulose surfaces of similar charge.
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| 78. |
- Asta, Nadia
(författare)
-
Fundamentals of Interactions between Cellulose Materials and its Implications on Properties of Fibrous Networks
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fundamental research plays a pivotal role in the development of sustainable solutions that benefit both our environment and everyday lives. Cellulose, as an abundant and renewable resource, holds immense potential for sustainable applications. However, navigating the complexities of molecular and supramolecular structure of cellulose poses significant challenges in harnessing its full potential. By delving into fundamental research, we aim to uncover the underlying mechanisms governing cellulose interactions, paving the way for innovative advancements in sustainable material development.This thesis uncovers the intricate relationship between fundamental research and applied methodologies by showing how molecular contact and structure at the interface of cellulose-rich materials will control the development of the macroscopic mechanical properties of networks from cellulose-rich fibres. The study encompasses various facets, ranging from the development of model materials for studying interfacial interactions to the preparation of fibrous networks with tailored properties.In the initial part of the work the research delves into the development of model materials to investigate interactions at smooth interfaces of regenerated cellulose. The study reveals the crucial role of the making and breaking of cellulose interface, or sometimes interphase, in the development of adhesive joints. Experimental findings demonstrate how chemical additives influence the interactions between cellulose surfaces, thereby modulating the structural and adhesive properties at the interface. Furthermore, by utilizing model materials, insights are gained into fibre-fibre interactions and the influence of surface treatments on network formation and mechanical performance. Lastly, the research focused on investigating the preparation of fibrous networks at different densities and amount of adsorbed additives, providing a comprehensive understanding of how network density and composition affect mechanical properties of the networks.This work not only exemplifies a synergistic approach, where fundamental insights into molecular contacts and interface structures are translated into practical applications for enhancing macroscopic properties but also highlights the importance of integrating fundamental and applied methodologies in molecular engineering, offering novel strategies for advancing sustainable paper production practices and contributing to the attainment of sustainable development goals.
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| 79. |
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| 80. |
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| 81. |
- Asta, Nadia, et al.
(författare)
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The Use of Model Cellulose Materials for Studying Molecular Interactions at Cellulose Interfaces
- 2023
-
Ingår i: ACS Macro Letters. - : American Chemical Society (ACS). - 2161-1653. ; 12, s. 1530-1535
-
Tidskriftsartikel (refereegranskat)abstract
- Despite extensive research on biobased and fiber-based materials, fundamental questions regarding the molecular processes governing fiber-fiber interactions remain unanswered. In this study, we introduce a method to examine and clarify molecular interactions within fiber-fiber joints using precisely characterized model materials, i.e., regenerated cellulose gel beads with nanometer-smooth surfaces. By physically modifying these materials and drying them together to create model joints, we can investigate the mechanisms responsible for joining cellulose surfaces and how this affects adhesion in both dry and wet states through precise separation measurements. The findings reveal a subtle balance in the joint formation, influencing the development of nanometer-sized structures at the contact zone and likely inducing built-in stresses in the interphase. This research illustrates how model materials can be tailored to control interactions between cellulose-rich surfaces, laying the groundwork for future high-resolution studies aimed at creating stiff, ductile, and/or tough joints between cellulose surfaces and to allow for the design of high-performance biobased materials.
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| 82. |
- Atoufi Najafabadi, Zhaleh
(författare)
-
Development and Tailoring of Low‐Density Cellulose‐Based Structures for Water Treatment
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The challenges posed by our limited clean water sources and the well-known global water pollution demand more efficient water purification technologies. Additionally, the increasing environmental awareness has inspired a shift towards eco-friendly and renewable materials and technologies. This thesis is focused on developing effective adsorbent materials from renewable resources to eliminate organic solvents, dyes, and metal ions from water. Cellulose, the most abundant biopolymer in nature, is the main component used to develop new materials in the present study. Its distinctive physical and colloidal properties, in the form of nanocellulose, along with tunable surface chemistry, play key roles in enhancing the effectiveness of the developed materials.The primary focus of the first part of the thesis was to develop a molecular layer-by-layer modification technique to customize the surface functionality of cellulose aerogels in a uniform and controlled manner. Through the sequential deposition of diamine and triacid monomers, exceeding lythin polyamide coatings were formed on the cellulose aerogels, altering the surface properties from hydrophilic to hydrophobic. This transformation made them well-suited structures for oil-water separation.Following this, a biohybrid aerogel was developed based on cellulose nanofibrils (CNFs) and amyloid nanofibrils (ANFs), the latter derived by heat treatment of β-lactoglobulin proteins. The pH-tunable surface charge of the aerogel, controlled by the amphiphilicity of the protein, allowed for the adsorption of both cationic and anionic contaminants by adjusting the pH of the solutions. Furthermore, the aerogels exhibited remarkable selectivity for lead (II) ions and they could also be regenerated and reused after each adsorption cycle without a significant loss of their adsorption capacity. This was to a large extent possible due to the excellent wet stability of these aerogels, which was achieved by crosslinking the CNFs during freezing and ice templating, eliminating the need for freeze-drying. However, a solvent exchange to acetone after melting was still necessary to reduce the influence of the capillary forces during drying to avoid the collapse of the aerogels. In a consecutive study, the foaming characteristics of the heat-treated β-lactoglobulin system were exploited to create highly stable Pickering foams with the aid of using CNFs as stabilizers and to physically lock the system through a controlled pH reduction. Interestingly, these Pickering foams could be directly oven-dried without collapsing, yielding low-density foams. Furthermore, it was demonstrated that the foams can be chemically crosslinked by incorporating chemical crosslinkers in the formulation or by pre-functionalizing the CNFs with dialdehydes. This crosslinking naturally also provided wet stability to the oven-dried foams.Finally, an innovative and environmentally friendly method was introduced to increase the charge of cellulose fibers by radical polymerization of acrylic acid from the fibers, enabling the preparation of fibers with an exceptionally high charge of 6.7 mmol/g. The introduction of these charged groups significantly enhanced the interaction of the fibers with methylene blue as a model dye and lead (II), Copper (II), and Zinc (II) ions as model metal ions, showing the huge potential of these fibers as building blocks for a wide range of adsorbent applications. Overall, this thesis demonstrates the development and characterization of several bio-based adsorbents for water remediation.
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| 83. |
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| 84. |
- Atoufi, Zhaleh, et al.
(författare)
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Green Ambient-Dried Aerogels with a Facile pH-Tunable Surface Charge for Adsorption of Cationic and Anionic Contaminants with High Selectivity
- 2022
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 23:11, s. 4934-4947
-
Tidskriftsartikel (refereegranskat)abstract
- The fabrication of reusable, sustainable adsorbents from low-cost, renewable resources via energy efficient methods is challenging. This paper presents wet-stable, carboxymethylated cellulose nanofibril (CNF) and amyloid nanofibril (ANF) based aerogel-like adsorbents prepared through efficient and green processes for the removal of metal ions and dyes from water. The aerogels exhibit tunable densities (18-28 kg m-3), wet resilience, and an interconnected porous structure (99% porosity), with a pH controllable surface charge for adsorption of both cationic (methylene blue and Pb(II)) and anionic (brilliant blue, congo red, and Cr(VI)) model contaminants. The Langmuir saturation adsorption capacity of the aerogel was calculated to be 68, 79, and 42 mg g-1for brilliant blue, Pb(II), and Cr(VI), respectively. Adsorption kinetic studies for the adsorption of brilliant blue as a model contaminant demonstrated that a pseudo-second-order model best fitted the experimental data and that an intraparticle diffusion model suggests that there are three adsorption stages in the adsorption of brilliant blue on the aerogel. Following three cycles of adsorption and regeneration, the aerogels maintained nearly 97 and 96% of their adsorption capacity for methylene blue and Pb(II) as cationic contaminants and 89 and 80% for brilliant blue and Cr(VI) as anionic contaminants. Moreover, the aerogels showed remarkable selectivity for Pb(II) in the presence of calcium and magnesium as background ions, with a selectivity coefficient more than 2 orders of magnitude higher than calcium and magnesium. Overall, the energy-efficient and sustainable fabrication procedure, along with good structural stability, reusability, and selectivity, makes these aerogels very promising for water purification applications.
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| 85. |
- Atoufi, Zhaleh, et al.
(författare)
-
Surface tailoring of cellulose aerogel-like structures with ultrathin coatings using molecular layer-by-layer assembly
- 2022
-
Ingår i: Carbohydrate Polymers. - : Elsevier BV. - 0144-8617 .- 1879-1344. ; 282
-
Tidskriftsartikel (refereegranskat)abstract
- Cellulose nanofibril-based aerogels have promising applicability in various fields; however, developing an effi-cient technique to functionalize and tune their surface properties is challenging. In this study, physically and covalently crosslinked cellulose nanofibril-based aerogel-like structures were prepared and modified by a mo-lecular layer-by-layer (m-LBL) deposition method. Following three m-LBL depositions, an ultrathin polyamide layer was formed throughout the aerogel and its structure and chemical composition was studied in detail. Analysis of model cellulose surfaces showed that the thickness of the deposited layer after three m-LBLs was approximately 1 nm. Although the deposited layer was extremely thin, it led to a 2.6-fold increase in the wet specific modulus, improved the acid-base resistance, and changed the aerogels from hydrophilic to hydrophobic making them suitable materials for oil absorption with the absorption capacity of 16-36 g/g. Thus, demon-strating m-LBL assembly is a powerful technique for tailoring surface properties and functionality of cellulose substrates.
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| 86. |
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| 87. |
- Atoufi, Zhaleh, et al.
(författare)
-
Synergistically stabilized wet foams from heat treated β-lactoglobulin and cellulose nanofibrils and their application for green foam production
- 2024
-
Ingår i: Applied Materials Today. - : Elsevier BV. - 2352-9407. ; 39
-
Tidskriftsartikel (refereegranskat)abstract
- Achieving a sustainable foam production requires a complete substitution of synthetic components with natural and renewable alternatives, as well as development of an environment-friendly production process. This work demonstrates a synergetic combination of heat-treated beta-lactoglobulin proteins and cellulose nanofibrils (CNFs) to create fully bio-based and highly-stable wet foams. Furthermore, a gradual reduction in the pH, enabled oven-drying of the wet foams without any major structural collapse of the foam, resulting in the preparation of lightweight solid foams with the density of 10.2 kg.m(-3). First, the foaming behavior of heat-treated beta-lactoglobulin systems (HBSs) containing amyloid nanofibrils (ANFs) and non-converted peptides was investigated at different pHs. Subsequently, the HBS foams were stabilized using CNFs, followed by a gradual acidification of the system to a final pH of 4.5. To gain a deeper understanding of the stabilization mechanism of the foam, the interactions between the foam's components, their positioning in the foam structure, and the viscoelasticity of the fibrillar network were investigated using quartz crystal microgravimetry, confocal microscopy and rheology. The analysis of the obtained data suggests that the stability of the foams was associated with the accumulation of CNFs and ANFs at the air-water interface, and that the concomitant formation of an intertwined network surrounding the air bubbles. This together resulted in a significant decrease in drainage rate of the liquid in the foam lamellae, bubble coarsening and bubble coalescence within the foams. The results also show that the major surface-active component participating in the creation of the foam is the free peptide left in solution after the formation of the ANFs. A slow reduction in pH to 4.5 lead to further gelation of the fibrillar network and an improved storage modulus of the foam lamellae. This resulted in a strong coherent structure that could withstand oven-drying without collapse. The density, porosity, microstructure and compressive mechanical properties of such prepared dry foams were assessed. Overall, the results demonstrate the potential of HBSs to replace synthetic surfactants and outlines a sustainable preparation protocol for the preparation of light-weight porous composite structures of ANFs and CNFs.
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| 88. |
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| 89. |
|
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| 90. |
- Aulin, Christian, et al.
(författare)
-
Aerogels from nanofibrillated cellulose with tunable oleophobicity
- 2010
-
Ingår i: SOFT MATTER. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 6:14, s. 3298-3305
-
Tidskriftsartikel (refereegranskat)abstract
- The formation of structured porous aerogels of nanofibrillated cellulose (NFC) by freeze-drying has been demonstrated. The aerogels have a high porosity, as shown by FE-SEM and nitrogen adsorption/desorption measurements, and a very low density ( < 0.03 g cm(-3)). The density and surface texture of the aerogels can be tuned by selecting the concentration of the NFC dispersions before freeze-drying. Chemical vapor deposition (CVD) of 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane (PFOTS) was used to uniformly coat the aerogel to tune their wetting properties towards non-polar liquids. An XPS analysis of the chemical composition of the PFOTS-modified aerogels demonstrated the reproducibility of the PFOTS-coating and the high atomic fluorine concentration (ca. 51%) in the surfaces. The modified aerogels formed a robust composite interface with high apparent contact angles (theta* >> 90 degrees) for castor oil (gamma(1v) = 35.8 mN m(-1)) and hexadecane (gamma(1v) = 27.5 mN m(-1)).
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| 91. |
- Aulin, Christian, 1980-, et al.
(författare)
-
Buildup of polyelectrolyte multilayers of polyethyleneimine and microfibrillated cellulose studied by in situ dual-polarization interferometry and quartz crystal microbalance with dissipation
- 2008
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:6, s. 2509-2518
-
Tidskriftsartikel (refereegranskat)abstract
- Polyethyleneimine (PEI) and Microfibrillated cellulose (MFC) have been used to buildup polyelectrolyte multilayers (PEM) on silicone oxide and silicone oxynitride surfaces at different pH values and with different electrolyte and polyelectrolyte/colloid concentrations of the components. Consecutive adsorption on these surfaces was studied by in situ dual-polarization interferometry (DPI) and quartz crystal microbalance measurements. The adsorption data obtained from both the techniques showed a steady buildup of multilayers. High pH and electrolyte concentration of the PEI solution was found to be beneficial for achieving a high adsorbed amount of PEI, and hence of MFC, during the buildup of the multilayer. On the other hand, an increase in the electrolyte concentration of the MFC dispersion was found to inhibit the adsorption of MFC onto PEL The adsorbed amount of MFC was independent of the bulk MFC concentration in the investigated concentration range (15-250 mg/L). Atomic force microscopy measurements were used to image a MFC-treated silicone oxynitride chip from DPI measurements. The surface was found to be almost fully covered by randomly oriented microfibrils after the adsorption of only one bilayer of PEI/MFC. The surface roughness expressed as the rms-roughness over 1 ÎŒm2 was calculated to be 4.6 nm (1 bilayer). The adsorbed amount of PEI and MFC and the amount of water entrapped by the individual layers in the multilayer structures were estimated by combining results from the two analytical techniques using the de Feijter formula. These results indicate a total water content of ca. 41% in the PEM.
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| 92. |
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| 93. |
- Aulin, Christian, et al.
(författare)
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Design of highly oleophobic cellulose surfaces from structured silicon templates
- 2009
-
Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 1:11, s. 2443-2452
-
Tidskriftsartikel (refereegranskat)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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| 94. |
- Aulin, Christian, et al.
(författare)
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Nanoscale Cellulose Films with Different Crystallinities and Mesostructures : Their Surface Properties and Interaction with Water
- 2009
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:13, s. 7675-7685
-
Tidskriftsartikel (refereegranskat)abstract
- A systematic study of the degree of molecular ordering and swelling of different nanocellulose model films has been conducted. Crystalline cellulose II surfaces were prepared by spin-coating of the precursor cellulose solutions onto oxidized silicon wafers before regeneration in water or by using the Langmuir-Schaefer (LS) technique. Amorphous cellulose films were also prepared by spin-coating of a precursor cellulose solution onto oxidized silicon wafers. Crystalline cellulose I surfaces were prepared by spin-coating wafers with aqueous suspensions of sulfate-stabilized cellulose nanocrystals and low-charged microfibrillated cellulose (LC-MFC). In addition, a dispersion of high-charged MFC was used for the buildup of polyelectrolyte multilayers with polyetheyleneimine on silica with the aid of the layer-by-layer (LbL) technique. These preparation methods produced smooth thin films on the nanometer scale Suitable for X-ray diffraction and swelling measurements. The surface morphology and thickness of the cellulose films were characterized in detail by atomic force microscopy (AFM) and ellipsometry measurements, respectively. To determine the surface energy of the cellulose surfaces, that Is, their ability to engage in different interactions with different materials, they were characterized through contact angle measurements against water, glycerol, and methylene iodide. Small incidence angle X-ray diffraction revealed that the nanocrystal and MFC films exhibited a cellulose I crystal structure and that the films prepared from N-methylmorpholine-N-oxide (NMMO), LiCl/DMAc solutions, using the LS technique, possessed a cellulose II structure. The degree of crystalline ordering was highest in the nanocrystal films (similar to 87%), whereas the MFC, NMMO, and LS films exhibited a degree of crystallinity of about 60%. The N,N-dimethylacetamide(DMAc)/LiCl film possessed very low crystalline ordering (<15%). It was also established that the films ha different mesostructures, that is, structures around 10 nm, depending on the preparation conditions. The LS and LiCl/DMAc films are smooth without any clear mesostructure, whereas the other films have a clear mesostructure in which the dimensions are dependent oil the size of the nanocrystals, fibrillar cellulose, and electrostatic charge of the MFC. The swelling of the films was studied using a quartz crystal microbalance with dissipation. To understand the swelling properties of the films, it was necessary to consider both the difference in crystalline ordering and the difference in mesostructure of the films.
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| 95. |
- Aulin, Christian, 1980-
(författare)
-
Novel oil resistant cellulosic materials
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this study has been to prepare and characterise oil resistant cellulosic materials, ranging from model surfaces to papers and aerogels. The cellulosic materials were made oil resistant by chemical and topographic modifications, based on surface energy, surface roughness and barrier approaches. Detailed wetting studies of the prepared cellulosic materials were made using contact angle measurements and standardised penetration tests with different alkanes and oil mixtures. A significant part of the activities were devoted to the development of model cellulosic surfaces with different degrees of crystalline ordering for the wetting studies. Crystalline cellulose I, II and amorphous cellulose surfaces were prepared by spin-coating of cellulose nanocrystal or microfibrillated cellulose (MFC) dispersions, with Langmuir-Schaefer (LS) films or by a layer-by-layer (LbL) deposition technique. The formation of multilayers consisting of polyethyleneimine (PEI)/anionic MFC or cationic MFC/anionic MFC was further studied and optimized in terms of total layer thickness and adsorbed amount by combining Dual Polarization Interferometry (DPI) or Stagnation Point Adsorption Reflectrometry (SPAR) with a Quartz Crystal Microbalance with Dissipation (QCM-D). The smooth cellulosic surfaces prepared had different molecular and mesostructure properties and different surface energies as shown by X-ray diffraction, Atomic Force Microscopy (AFM) imaging, ellipsometry measurements and contact angle measurements. The cellulose model surfaces were found to be ideal for detailed wetting studies, and after the surface has been coated or covalently modified with various amounts of fluorosurfactants, the fluorinated cellulose films were used to follow the spreading mechanisms of different oil mixtures. The viscosity and surface tension of the oil mixtures, as well as the dispersive surface energy of the cellulose surfaces, were found to be essential parameters governing the spreading kinetics. A strong correlation was found between the surface concentration of fluorine, the dispersive surface energy and the measured contact angle of the oil mixtures. Silicon surfaces possessing structural porous characteristics were fabricated by a plasma etching process. The structured silicon surfaces were coated with sulfate-stabilized cellulose I nanocrystals using the LbL technique. These artificial intrinsically oleophilic cellulose surfaces were made highly oleophobic when coated with a thin layer of fluorinated silanes. By comparison with flat cellulose surfaces, which are oleophilic, it is demonstrated that the surface energy and the surface texture are essential factors preventing oil from spreading on the surface and, thus, inducing the observed macroscopic oleophobic properties. The use of the MFC for surface coating on base papers demonstrated very promising characteristics as packaging materials. Environmental-Scanning Electron Microscopy (E-SEM) micrographs indicated that the MFC layer reduced the sheet porosity, i.e. the dense structure formed by the nanofibers resulted in superior oil barrier properties. Attempts were made to link the procedure for preparation of the MFC dispersions to the resulting microstructure of the coatings, and film porosity and the film moisture content to the resulting permeability properties. Finally, MFC aerogels were successfully prepared by freeze-drying. The surface texture of the porous aerogels was carefully controlled by adjusting the concentration of the MFC dispersion used for the freeze-drying. The different scales of roughness of the MFC aerogels were utilised, together with the very low surface energy created by fluorination of the aerogel, to induce highly oleophobic properties.
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| 96. |
- Aulin, Christian
(författare)
-
Preparation, characterisation and wetting of fluorinated cellulose surfaces
- 2007
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the wetting by oil mixtures of two different model cellulose surfaces. The surfaces studied were a regenerated cellulose (RG) surface prepared by spin-coating, and a film consisting of polyelectrolyte multilayers (PEM) of Poly(ethyleneimine) (PEI) and a carboxymethylated Microfibrillated Cellulose (MFC). After coating or covalently modifying the cellulose surfaces with various amounts of fluorosurfactants, the fluorinated cellulose films were used to follow the spreading mechanisms of the different oil mixtures. The viscosity and surface tension of the oil, as well as the dispersive surface energy of the cellulose surface, are essential parameters governing the spreading kinetics. X-ray Photoelectron Spectroscopy (XPS) and dispersive surface energy measurements were made on the cellulose films treated with fluorosurfactants. A strong correlation between the surface coverage of fluorine, the dispersive surface energy and the measured contact angle of the oil mixtures was found. For example, a dispersive surface energy less than 18 mN/m was required in order for the cellulose surface to be non-wetting (θe > 90º) by castor oil. Significant parts of this work were devoted to the development of cellulose surfaces for the wetting studies. The formation of a PEM consisting of PEI and MFC was studied and the total layer thickness and adsorbed amount were optimized by combining Dual Polarization Interferometry (DPI) with a Quartz Crystal Microbalance with Dissipation (QCM-D). The adsorption behaviour as well as the influence of the charge density, pH and electrolyte concentration of PEI, and electrolyte concentration of the MFC dispersion on the adsorbed amount of MFC were investigated. Results indicate that a combination of a high pH, a fairly high electrolyte concentration for PEI solution together with low or zero electrolyte concentration for the MFC resulted in the largest possible adsorbed amounts of the individual PEI and MFC layers. The structures of the two cellulose surfaces were characterised with atomic force microscopy measurements and a difference in terms of surface structure and roughness were observed. Both surfaces were however very smooth with calculated RMS roughness values in the range of a few nanometers. The adsorption behaviour of water-dispersible fluorosurfactants physically adsorbed at various concentrations onto the two model cellulose surfaces was investigated using DPI. The aggregate structure of an anionic fluorosurfactant, perfluorooctadecanoic acid, dispersed in water was studied by Cryo Transmission Electron Microscopy (Cryo-TEM). The fluorosurfactants had an adsorption and desorption behaviour in water which was dependent on the fluorinated chain length and the aggregation form of the fluorosurfactant. Perfluorooctanoic acid and a commercial cationic fluorosurfactant with a formal composition of CF3 (CF2)nSO2NH(CH2)3-4N(CH3)3+I- was found to desorb from the MFC and RG surfaces upon rinsing with water, whereas perfluorooctadecanoic acid was strongly adsorbed to the surfaces. It is essential for a fluorosurfacatant to be strongly adsorbed to the cellulose surface even after rinsing to yield hydrophobic and lipophobic (oleophobic) properties with a large contact angle for oils and water.
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| 97. |
- Aulin, Christian, et al.
(författare)
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Self-Organized Films from Cellulose I Nanofibrils Using the Layer-by-Layer Technique
- 2010
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 11:4, s. 872-882
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of forming self-organized films using only charge-stabilized dispersions of cellulose I nanofibrils with opposite charges is presented, that is, the multilayers were composed solely of anionically and cationically modified microfibrillated cellulose (MFC) with a low degree of substitution. The build-up behavior and the properties of the layer-by-layer (LbL)-constructed films were studied using a quartz crystal microbalance with dissipation (QCM-D) and stagnation point adsorption reflectometry (SPAR). The adsorption behavior of cationic/anionic MFC was compared with that of polyethyleneimine (PEI)/anionic MFC. The water contents of five bilayers of cationic/anionic MFC and PEI/anionic MFC were approximately 70 and 50%, respectively. The MFC surface coverage was studied by atomic force microscopy (AFM) measurements, which clearly showed a more dense fibrillar structure in the five bilayer PEI/anionic MFC than in the five bilayer cationic/anionic MFC. The forces between the cellulose-based multilayers were examined using the AFM colloidal probe technique. The forces on approach were characterized by a combination of electrostatic and steric repulsion. The wet adhesive forces were very long-range and were characterized by multiple adhesive events. Surfaces covered by PEU/anionic MFC multilayers required more energy to be separated than surfaces covered by cationic/anionic MFC multilayers.
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| 98. |
- Aulin, Christian, et al.
(författare)
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Structure and Properties of Layer-by-Layer Films from Combinations of Cellulose Nanofibers, Polyelectrolytes and Colloids
- 2014
-
Ingår i: HANDBOOK OF GREEN MATERIALS, VOL 3. - : World Scientific. - 9789814566506 - 9789814566452 ; , s. 57-77
-
Bokkapitel (refereegranskat)abstract
- The formation of nanometer-thin films of cellulose nanofibers (CNFs), polyelectrolytes, and/or nanoparticles has opened up new possibilities of manufacturing interactive devices with controlled mechanical properties. By controlling the charge of the CNF and the charge and 3D structure of the polyelectrolytes, it is possible to control the buildup, i.e., the thickness, the adsorbed amount, and the immobilized water of layer-by-layer (LbL) films of these materials. The charge balance between the components is not the only factor controlling the LbL formation. The structure of these adsorbed layers in combination with the properties of the constituent components will in turn control how these layers interact with, for example moist air. The mechanical properties of the LbLs can be tuned by combining the high-modulus CNF with different components. This has been shown by using a microbuckling technique where the mechanical properties of ultra-thin films can be measured. In combination with, for example, moisture-sensitive poly(ethylene imine) (PEI), the Young's modulus of CNF/PEI films can be changed by one order of magnitude when the humidity is increased from 0% RH to 50% RH. The incorporation of high-modulus nanoparticles such as SiO2 particles can also be used to prepare LbLs with a higher modulus. Examples are also given where it is shown that the color of an LbL film can be used as a non-contact moisture sensor since the thickness is related to the amount of adsorbed moisture. By chemical modification of the CNF, it is also possible to tailor the interaction between the CNF and multivalent metal ions, enabling a specific interaction between multivalent for example metal surfaces in water and modified CNF.
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| 99. |
- Aulin, Christian, et al.
(författare)
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Transparent Nanocellulosic Multilayer Thin Films on Polylactic Acid with Tunable Gas Barrier Properties
- 2013
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 5:15, s. 7352-7359
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Tidskriftsartikel (refereegranskat)abstract
- The layer-by-layer (LbL) deposition method was used for the build-up of alternating layers of nanofibrillated cellulose (NFC) or carboxymethyl cellulose (CMC) with a branched, cationic polyelectrolyte, polyethyleneimine (PEI) on flexible poly (lactic acid) (PLA) substrates. With this procedure, optically transparent nanocellulosic films with tunable gas barrier properties were formed. 50 layer pairs of PEI/NFC and PEI/CMC deposited on PLA have oxygen permeabilities of 0.34 and 0.71 cm(3).mu m/m(2).day.kPa at 23 degrees C and 50% relative humidity, respectively, which is in the same range as polyvinyl alcohol and ethylene vinyl alcohol. The oxygen permeability of these multilayer nanocomposites outperforms those of pure NFC films prepared by solvent-casting. The nanocellulosic LbL assemblies on PLA substrates was in detailed characterized using a quartz crystal microbalance with dissipation (QCM-D). Atomic force microscopy (AFM) reveals large structural differences between the PEI/NFC and the PEI/CMC assemblies, with the PEI/NFC assembly showing a highly entangled network of nanofibrils, whereas the PEI/CMC surfaces lacked structural features. Scanning electron microscopy images showed a nearly perfect uniformity of the nanocellulosic coatings on PLA, and light transmittance results revealed remarkable transparency of the LbL-coated PLA films. The present work demonstrates the first ever LbL films based on high aspect ratio, water-dispersible nanofibrillated cellulose, and water-soluble carboxymethyl cellulose polymers that can be used as multifunctional films and coatings with tailorable properties, such as gas barriers and transparency. Owing to its flexibility, transparency and high-performance gas barrier properties, these thin film assemblies are promising candidates for several large-scale applications, including flexible electronics and renewable packaging.
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