| 1. |
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| 2. |
- Enarsson, Lars-Erik, et al.
(författare)
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Adsorption Kinetics of cationic Polyelectrolytes studied with Stagnation Point Adsorption Reflectometry and Quartz Crystal Microgravimetry
- 2008
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:14, s. 7329-7337
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Tidskriftsartikel (refereegranskat)abstract
- The effects of charge density, pH, and salt concentration on polyelectrolyte adsorption onto the oxidized surface of silicon wafers were studied using stagnation point adsorption reflectometry and quartz crystal microgravimetry. Five different polyelectrolytes-cationic polyacrylamides of four charge densities and one cationic dextran-were examined. The adsorption kinetics was characterized using each technique, and the adsorption kinetics observed was in line with the impinging jet theory and the theory for one-dimensional diffusion, respectively. The polyelectrolyte adsorption increased with pH as an effect of the increased silica surface charge. A maximum in the saturation adsorption for both types of polyelectrolytes was found at 10 mM NaCl concentration. A significant adsorption also occurred at I M NaCl, which indicated a significant nonionic contribution to the adsorption mechanism. The fraction of solvent in the adsorbed layer was determined to be 70-80% by combining the two analysis techniques. This indicated a loose structure of the adsorbed layer and an extended conformation at the surface, favoring loops and tails. However, considering the solution structure with a hydrodynamic diameter larger than 100 nm for the CPAM and a thickness of the adsorbed layer on the order of 10 nm, the results showed that the adsorption is accompanied by a drastic change in polymer conformation. Furthermore, this conformation change takes place on a time scale far shorter than seconds.
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| 3. |
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| 4. |
- Enarsson, Lars-Erik, et al.
(författare)
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Conformation of preadsorbed Polyelectrolyte Layers on Silica studied by secondary Adsorption of Colloidal Silica
- 2008
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 325:1, s. 84-92
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Tidskriftsartikel (refereegranskat)abstract
- The conformation of cationic polyelectrolytes preadsorbed on macroscopic silica surfaces was studied before and after addition of colloidal silica (CS) and compared to the fixation capacity of CS. The Study included two polyelectrolytes of equal charge density, cationic polyacrylamide and cationic dextran. Adsorbed amounts were determined with stagnation point adsorption reflectometry (SPAR) and quartz crystal microgravimetry (QCM). Unsaturated layers of polyelectrolyte were formed in SPAR by stopping the adsorption at a fractional coverage relative to saturation adsorption. These layers were probed by secondary saturation adsorption of colloidal silica (CS). At low salt concentrations a high fractional coverage of polyelectrolyte was required to attain adsorption of CS, while significant adsorption of CS was found also for low fractional coverages of polyelectrolyte at salt concentrations above 10 mM NaCl. Saturation adsorption of cationic polyacrylamide (CPAM) and cationic dextran (Cdextran) onto the silica surface was found to be similar, while the secondary adsorption of CS was significantly higher onto preadsorbed CPAM compared with Cdextran. The QCM and SPAR data together indicated that the adsorbed layer of Cdextran was thinner than CPAM, and that a loose, expanded layer was formed after adsorption of CS on CPAM but not on Cdextran.
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| 5. |
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| 6. |
- Enarsson, Lars-Erik, et al.
(författare)
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Kinetics of sequential adsorption of polyelectrolyte multilayers on pulp fibres and their effect on paper strength
- 2007
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Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 22:2, s. 258-266
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Tidskriftsartikel (refereegranskat)abstract
- Conditions for sequential adsorption of polyelectrolyte multilayers (PEM) onto pulp fibres were investigated in terms of appropriate addition levels and adsorption times. The objective was a technical application for improved tensile strength of paper. Two common polyelectrolytes (PE) in papermaking, polyamideamine epichlorolrydrin (PAE) and carboxymethyl cellulose (CMC), were consecutively adsorbed onto long fibres from a bleached softwood kraft pulp, adding up to four PE layers on the fibre surfaces. Adsorption isotherms and adsorption kinetics were studied layer by layer, giving recommended addition levels and adsorption times for each layer. PAE adsorbed in larger amounts than CMC, 4 and 1 mg/g, respectively on fractionated pulp free of fines. For the kinetics, longer times were required to reach saturation adsorption for PAE compared to CMC, corresponding to three and two minutes, respectively. Tensile testing of handsheets based on both fractionated and beaten pulp showed that four PE layers increased the tensile index by about 50%, reaching levels of 34 (unbeaten) and 88 Nm/g (beaten), respectively. The effect of PEM on strain at break depended on the beating level as the fractionated pulp showed an improvement from 2.5 to 4.1% while beaten pulp showed a reduction from 6.1 to 4.5%.
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| 7. |
- Enarsson, Lars-Erik, 1976-
(författare)
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Polyelectrolyte adsorption on oppositely charged surfaces - Conformation and adsorption kinetics
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Denna avhandling presenterar experimentella studier av polyelektrolytadsorption på motsatt laddade ytor, där substrat av både kiseloxid och blekt barrsulfatmassa har använts. Ett huvudsakligt syfte med denna forskning var att karaktärisera konformationen hos adsorberade skikt av katjonisk polyakrylamid (CPAM) i jämförelse med katjonisk dextran (Cdextran) och relatera denna information till inbindningskapaciteten av kolloidal kiselsyra. Ett andra syfte i denna avhandling var att studera kinetiken för sekventiell adsorption av polyamidamin epiklorhydrin (PAE) och karboxymetyl cellulosa (CMC) på massafibrer och att bestämma adsorptionsisotermer för deponering av polyelektrolyter skikt för skikt på massafibrer. Adsorptionen av CPAM på kiseloxidytor studeras med stagnationspunkts-reflektometri och kvartskristalls-mikrogravimetri för att bestämma adsorptionskinetiken och mättnadsadsorptionens beroende av polyelektrolytens laddningstäthet, pH och NaCl koncentration. Konformationen hos adsorberade skikt av CPAM och Cdextran bestämdes både före och efter sekundär tillsats av kolloidal kiselsyra (CS) och adsorptionen av CS kvantifierades också som funktion av yttäckningen av polyelektrolyt. Resultaten indikerar att laddningstätheten hos CPAM kontrollerar den adsorberade mängden på kiseloxidytor vid låga NaCl koncentrationer. Både adsorptionen av CPAM och Cdextran på kiseloxid visades vara effektiv i NaCl koncentrationer upp till 1 M, vilket indikerar ett signifikant bidrag av icke-jonisk interaktion mellan polyelektrolyterna och kiseloxid. Adsorptionen av CS var högre på föradsorberad CPAM än Cdextran. Konformationen hos de adsorberade skikten efter tillsats av CS sågs expandera signifikant för skikt baserade på CPAM medan skikt av Cdextran vid låga salthalter verkade återta sin konformation efter en temporär expansion. I den andra delen av avhandlingen studerades sekventiell adsorption av PAE och CMC på massafibrer. Adsorptionsisotermer skikt för skikt på avkryllad massa visade att PAE adsorberade i större mängd än CMC, både i hänseende av massa och laddning. Adsorptionen av PAE var signifikant långsammare än CMC och adsorptionstiden till 90% av mättnadsadsorptionen bestämdes till 3 respektive 1 minut. Zetapotentialen för kryll bestämdes för adsorption av de två första polyelektrolytskikten och resultaten tydde på att kryllmaterialet omladdade inom en minut efter tillsatserna av polyelektrolyt. Reflektometriförsök inom sekventiell adsorption av PAE och CMC på kiseloxid antydde att den låga molekylviktsfraktionen av PAE störde uppbyggnaden av polyelektrolyt-multiskikten.
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| 8. |
- Enarsson, Lars-Erik, et al.
(författare)
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Polyelectrolyte Adsorption on Thin Cellulose Films Studied with Reflectometry and Quartz Crystal Microgravimetry with Dissipation
- 2009
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 10:1, s. 134-141
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Tidskriftsartikel (refereegranskat)abstract
- Thin cellulose films were prepared by dissolving carboxymethylated cellulose fibers in N-methyl morpholine oxide and forming thin films on silicon wafers by spin-coating. The adsorption of cationic polyacrylamides and polydiallyldimethylammonium chloride onto these films was studied by stagnation point adsorption reflectometry (SPAR) and by quartz crystal microgravimetry with dissipation (QCM-D). The polyelectrolyte adsorption was studied by SPAR as a function of salt concentration, and it was found that the adsorption maximum was located at 1 mM NaCl for polyelectrolytes of low charge density and at 10 mM NaCl for polyelectrolytes of high charge density. Electrostatic screening led to complete elimination of the polyelectrolyte adsorption at salt concentrations of 300 mM NaCl. According to the QCM-D analysis, the cellulose films showed a pronounced swelling in water that took several hours to complete. Subsequent adsorption of polyelectrolytes onto the cellulose films led to a release of water from the cellulose, an effect that was substantial for polyelectrolytes of high charge density at low salt concentrations. The total mass change including water could therefore show either an increase or a decrease during adsorption onto the cellulose films, depending on the experimental conditions.
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| 9. |
- Enarsson, Lars-Erik, et al.
(författare)
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Tailoring the chemistry of polyelectrolytes to control their adsorption on cellulosic surfaces
- 2009
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Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 340:1-3, s. 135-142
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of two types of cationic polyacrylamides in the presence of a background electrolyte was studied on substrates including silicon oxide, kraft pulp fibres and thin films of regenerated cellulose. One of the polyelectrolytes was a conventional cationic polyacrylamide (MeCPAM) and the other was a benzyl-containing derivative of cationic polyacrylamide (BzCPAM). It was found that the aromatic substituents of BzCPAM strongly enhanced the adsorption on substrates of hydrophobically modified silicon oxide when a background electrolyte was present. A similar effect was also seen in the case of BzCPAM adsorption on unbleached pulp fibres, but in this case MeCPAM also exhibited a strong adsorption at high background electrolyte concentrations. On bleached pulp fibres, BzCPAM maintained a high adsorption up to a concentration of 100 mM NaCl whereas MeCPAM adsorption showed a significant decrease at this salt concentration. On model cellulose films, the adsorption of BzCPAM was similar to that of MeCPAM and the non-ionic interactions with cellulose appeared weak, since there was no adsorption of either polyelectrolyte in 300 mM NaCl.
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| 10. |
- Illergård, Josefin, et al.
(författare)
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Interactions of Hydrophobically Modified Polyvinylamines : Adsorption Behavior at Charged Surfaces and the Formation of Polyelectrolyte Multilayers with Polyacrylic Acid
- 2010
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Ingår i: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 2:2, s. 425-433
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Tidskriftsartikel (refereegranskat)abstract
- The structure and adsorption behaviors of two types of hydrophobically modified polyvinylamines (PVAm) containing substituents of hexyl and octyl chains were compared to a native polyvinylamine sample. The conformation of dissolved polyvinylamines was studied in aqueous salt solutions using dynamic light scattering. Modified PVAm showed hydrodynamic diameters similar to native PVAm, which indicated that all PVAm polymers were present as single molecules in solution. The adsorption of the polyvinylamines, both native and hydrophobically modified, from aqueous solution onto negatively charged silica surfaces was studied in situ by reflectometry and quartz crystal microgravimetry with dissipation. Polyelectrolyte multilayers; (PEM) with up to nine individual layers were formed together with poly(acrylic acid). Obtained PEM structures were rigid and showed high adsorbed amounts combined with low dissipation, with similar results for both the modified and unmodified PVAm. This suggests that electrostatics dominated the PEM formation. At lower salt concentrations, the hydrophobically modified PVAm produced multilayers with low water contents, indicating that secondary interactions induced by the hydrophobic constituents can also have a significant influence on the properties of the formed layers. The surface structure of PEMs with nine individual layers was imaged in dry state using atomic force microscopy in a dynamic mode. Modified PVAm was found to induce a different structure of the PEM at 100 mM, with larger aggregates compared to those of native PVAm. From these results, it is proposed that modified PVAm can induce aggregation within the PEM, whereas PVAm remains as single molecules in solution.
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| 11. |
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| 12. |
- Marais, Andrew, et al.
(författare)
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Pilot-scale papermaking using Layer-by-Layer treated fibres; comparison between the effects of beating and of sequential addition of polymeric additives
- 2016
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 31:2, s. 308-314
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Tidskriftsartikel (refereegranskat)abstract
- The Layer-by-Layer (LbL) deposition technique was used to treat fibres before papermaking on a pilot scale. Following a laboratory pre-study performed earlier to determine the adsorption isotherms and the kinetics of formation of multilayers of polyamideamine epichlorydrine (PAE) and carboxymethylated cellulose (CMC) on unbeaten, bleached softwood fibres, online LbL treatment of the furnish was carried out on the EuroFEX pilot paper machine. Papers from fibres coated with up to four layers of polyelectrolytes were produced. Two different LbL systems were investigated, with anionic CMC in combination with either PAE or cationic starch (CS). The results showed that the mechanical strength of the paper significantly increased when the fibres were LbL-treated online. A comparison with conventional beating of the fibres revealed that the LbL treatment was a potential substitute to beating treatment, as the density of the LbL-treated papers remained constant while the mechanical properties were significantly improved. At the same time, the press solids content was significantly higher (2%) when using LbL-treated fibres than with beaten fibres.
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| 13. |
- Ondaral, Sedat, et al.
(författare)
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The adsorption of hyperbranched polymers on silicon oxide surfaces
- 2006
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 301:1, s. 32-39
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Tidskriftsartikel (refereegranskat)abstract
- The electrostatic interaction between quarternised hyperbranched polymers (polyesteramides) and a silicon oxide (SiO2) surface has been studied via adsorption studies with quartz crystal microbalance instrument with dissipation (QCM-D). Frequency shift (Delta f) results show that the increase in both pH and salt concentration positively affect the adsorbed amount of these polymers, calculated by Sauerbrey equation, on the QCM crystal. The adsorbed amount of HA1 (with lower molecular weight and higher charge density) was lower than that of HA2 (with higher molecular weight and lower charge density) in all experiments. It was also observed that there are no significant changes in the dissipation after adsorption of these polymers. This indicated that both hyperbranched polymers formed rigid adsorbed layers on the negative SiO2 surface. Additionally, the results were compared with adsorption of poly-DADMAC and the results showed that the hyperbranched polymers formed thicker and more rigid layers as compared with the poly-DADMAC.
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| 14. |
- Westman, Eva-Helena, et al.
(författare)
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Assessment of Antibacterial Properties of Polyvinylamine (PVAm) with Different Charge Densities and Hydrophobic Modifications
- 2009
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 10:6, s. 1478-1483
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Tidskriftsartikel (refereegranskat)abstract
- Hydrophobically modified and unmodified polyvinylamines (PVAm), including a total of five polymers, were tested against both gram-negative (Escherichia coli) and gram-positive (Bacillus subtilis) bacteria for antimicrobial activity. The assessment of PVAm in solution against bacteria is described, and the influence of the charge density and of the hydrophobic modification of the polyelectrolyte is discussed. The antimicrobial activity was found to depend upon the concentration of PVAm and also on the type of bacteria used. The results also indicated that no direct relationship exists between antimicrobial activity and charge density of the different PVAms. It was, however, observed that an alkyl chain length of six or eight alkane units had a substantial effect on the bacteria investigated. The best combined antibacterial activity for the two bacteria tested was achieved for PVAm with a C-6 alkane substituent (PVAm C-6). To evaluate the antimicrobial activity on a solid substrate, PVAm C-6 was further studied after being deposited onto a glass slide and the results show a large reduction in bacterial infection.
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| 15. |
- Wågberg, Lars, et al.
(författare)
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Hyperbranched polymers as a fixing agent for dissolved and colloidal substances on fiber and SIO2 surfaces
- 2007
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Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 0888-5885 .- 1520-5045. ; 46:7, s. 2212-2219
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Tidskriftsartikel (refereegranskat)abstract
- Hyperbranched polymers (polyesteramides) were used as a cationic fixing agent to remove dissolved and colloidal substances (DCS) from the water phase in a fiber suspension. The relative turbidity, electrophoretic mobility, and average diameter of the colloidal particles were determined as a function of polyelectrolyte concentration. The results indicated that maximum removal of DCS was achieved at about zero electrophoretic mobility of the suspension where the negative surface charges of particles were neutralized by the oppositely charged hyperbranched polymer. The amount of hyperbranched polymers needed to maximize DCS fixation on the fibers was higher than the amount of poly-DADMAC (diallyldimethylammonium chloride) needed to reach the same effect. This was found to be due to the lower molecular weight and lower charge density of hyperbranched polymers. The lower molecular mass allowed penetration of these polymers into pores of fibers that resulted in higher polymer consumption before removal of the dissolved and colloidal substances from the fiber suspensions. A lower charge density further resulted in a higher saturation adsorption of the hyperbranched polymer. Experiments with both DCS and model-latex particles showed that the initial increase in relative turbidity was due to the aggregation of particles before fixation to fibers. The results from quartz crystal microbalance with dissipation (QCM-D) experiments showed that the efficiency of hyperbranched polymer and poly-DADMAC was similar even if they had different structure. Therefore, this study highlights the importance of molecular mass and charge density of the polymers as well as the surface structure of polymer layers which in turn gives implications for development of new structures of fixing agents.
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