| 1. |
|
|
| 2. |
- Enarsson, Lars-Erik, et al.
(författare)
-
Adsorption Kinetics of cationic Polyelectrolytes studied with Stagnation Point Adsorption Reflectometry and Quartz Crystal Microgravimetry
- 2008
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:14, s. 7329-7337
-
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.
|
|
| 3. |
|
|
| 4. |
- Enarsson, Lars-Erik, et al.
(författare)
-
Conformation of preadsorbed Polyelectrolyte Layers on Silica studied by secondary Adsorption of Colloidal Silica
- 2008
-
Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 325:1, s. 84-92
-
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.
|
|
| 5. |
|
|
| 6. |
- Enarsson, Lars-Erik, et al.
(författare)
-
Kinetics of sequential adsorption of polyelectrolyte multilayers on pulp fibres and their effect on paper strength
- 2007
-
Ingår i: Nordic Pulp & Paper Research Journal. - 0283-2631 .- 2000-0669. ; 22:2, s. 258-266
-
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%.
|
|
| 7. |
- Enarsson, Lars-Erik, 1976-
(författare)
-
Polyelectrolyte adsorption on oppositely charged surfaces - Conformation and adsorption kinetics
- 2006
-
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.
|
|
| 8. |
- Enarsson, Lars-Erik, et al.
(författare)
-
Polyelectrolyte Adsorption on Thin Cellulose Films Studied with Reflectometry and Quartz Crystal Microgravimetry with Dissipation
- 2009
-
Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1525-7797 .- 1526-4602. ; 10:1, s. 134-141
-
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.
|
|
| 9. |
- Enarsson, Lars-Erik, et al.
(författare)
-
Tailoring the chemistry of polyelectrolytes to control their adsorption on cellulosic surfaces
- 2009
-
Ingår i: Colloids and Surfaces A. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 340:1-3, s. 135-142
-
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.
|
|
| 10. |
- Illergård, Josefin, et al.
(författare)
-
Interactions of Hydrophobically Modified Polyvinylamines : Adsorption Behavior at Charged Surfaces and the Formation of Polyelectrolyte Multilayers with Polyacrylic Acid
- 2010
-
Ingår i: ACS Applied Materials & Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 2:2, s. 425-433
-
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.
|
|
