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| 2. |
- Plunkett, M. A., et al.
(författare)
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Adsorption of a cationic polyelectrolyte followed by surfactant-induced swelling, studied with a quartz crystal microbalance
- 2002
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 18:4, s. 1274-1280
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption and subsequent surfactant-induced swelling of a 10% charged cationic polyelectrolyte (AM-MAPTAC-10), on a gold surface, was monitored by means of a quartz crystal microbalance with dissipation (QCM-D). This instrument gives information on the total adsorbed amount including any adsorbed solvent and on the manner of adsorption. In this case the total adsorbed amount from a 20 ppm AM-MAPTAC-10 solution registered by the QCM-D device was approximately 0.6 mug cm(-2). X-ray photoelectron spectroscopy results showed that the polyelectrolyte adsorbed mass was 0.16 mug cm(-2); thus the water trapped within the polyelectrolyte layer constitutes about 70% of the mass measured by the quartz crystal microbalance. The adsorption process was found to be rather complex, though the time evolution of the adsorbed mass indicated that the majority of the process was diffusion controlled, Toward the end of the adsorption process, the rate of adsorption drops off and the dissipation rate increases, indicating that as the surface becomes crowded the layer extends further in the direction normal to the surface. The effect of addition of sodium dodecyl sulfate (SIDS) to a preadsorped AM-MAPTAC-10 layer was also investigated. It was found that some swelling of the preadsorbed layer occurred once the bulk surfactant concentration reached 20% of the critical micelle concentration (cmc). Between 60% of the cmc and twice the cmc, the adsorbed layer swelled significantly and desorption started to occur. Rinsing the surface with the surfactant-free electrolyte solution results in a rapid decrease in dissipation and adsorbed mass indicating the removal of the surfactant but not the polyelectrolyte.
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| 3. |
- Plunkett, M. A., et al.
(författare)
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Comparison of the adsorption of different charge density polyelectrolytes : A quartz crystal microbalance and X-ray photoelectron spectroscopy study
- 2003
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 19:11, s. 4673-4681
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Tidskriftsartikel (refereegranskat)abstract
- The adsorption of a series of six cationic polyelectrolytes onto a gold surface was monitored via a quartz crystal microbalance with dissipation (QCM-D). The series of polyelectrolytes were chemically similar but differing in the ratio of two randomly ordered constituent monomers, one of which was charged, the other neutral. Thus the series of polyelectrolytes differed systematically in their charge densities, ranging from a high charge density (100% of monomers charged) to a low charge density (1% charged). It was determined that high charge density polyelectrolytes adsorbed in a relatively flat and rigid layer, while the low charge density polyelectrolyte, as expected, adsorbed in a much more extended structure that coupled strongly to the bulk solvent. By comparison to X-ray photoelectron spectroscopy results, we have also calculated the relative solvent mass hydrodynamically coupled to the adsorbed polymer, which ranges from almost 80% solvent for the 1% charged case down to close to zero for the 100% charged case. Since the QCM-D results are measured relative to uncoated gold in aqueous solution, the latter results should be interpreted as showing that the amount of water hydrodynamically coupled to gold and that coupled to gold coated with the 100% charged polyelectrolyte is very similar. It is believed that this systematic study on the effect of polyelectrolyte structure on the measured dissipation change in the QCM-D may serve as a first guide when inferring structural and viscoelastic information based solely on the QCM-D technique for other similar systems. In addition, a preliminary study on the ability of one polymer to replace another preadsorbed polymer layer was conducted that showed that a steric layer was able to prevent the adsorption of a thermodynamically more favorable polymer. In the reverse case, greater exchange was possible.
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| 4. |
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| 5. |
- Abraham, T., et al.
(författare)
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Polyelectrolyte-mediated interaction between similarly charged surfaces : Role of divalent counter ions in tuning surface forces
- 2001
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 17:26, s. 8321-8327
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Tidskriftsartikel (refereegranskat)abstract
- The effects of divalent salts (CaCl2, MgCl2 and BaCl2) in promoting the adsorption of weakly charged polyelectrolyte (polyacrylic acid), PAA, Mw similar to 250000 g/mol) on mica surfaces and their role in tuning the nature of interactions between such adsorbed polyelectrolyte layers were studied using the interferometric surface forces apparatus. With mica surfaces in 3 mM MgCl2 solutions at pH similar to8.0-9.0, the addition of 10 ppm PAA resulted in a long-range attractive bridging force and a short-range repulsive steric force. This force profile indicates a low surface coverage and weak adsorption. The range of the force can be related to the characteristic length scale R-G of polyelectrolyte chains using a scaling description. An increase of the PAA concentration to 50 ppm changed the attractive force profile to a monotonic, long-range repulsive interaction extending up to 600 Angstrom due to the increased surface coverage of polyelectrolyte chains on the mica surfaces. Comparison of the measured forces with a scaling mean field model suggests that the adsorbed polyelectrolyte chains are stretched, which eventually give rise to the polyelectrolyte brush like structure. When the mica surfaces were preincubated in 3 mM CaCl2 at pH similar to8.0-9.0, in contrast to the case of 3 MM MgCl2, the addition of 10 ppm PAA resulted in a more complex force profile: long-range repulsive forces extending up to 800 Angstrom followed by an attractive force regime and a second repulsive force regime at shorter separations. The long-range electrosteric forces can be attributed to strong adsorption of polyelectrolyte chains on mica surfaces (high surface coverage) which is facilitated by the presence of Ca2+ ions, while the intermediate range attractive forces can be ascribed to Ca2+ assisted bridging between adsorbed polyelectrolyte chains. Also interesting is to note various relaxation processes present in this system. In contrast to both MgCl2 and CaCl2 systems, with mica surfaces in 3 mM BaCl2 solution at pH similar to8.0-9.0, the addition of 10 ppm PAA resulted in precipitation of polyelectrolyte chains on mica surfaces, resulting in an extremely long-range monotonic repulsive force profile. In summary, our study showed that divalent counterions (Mg2+, Ca2+, and Ba2+) exhibit significantly different behavior in promoting PAA adsorption on mica surfaces, modifying and controlling various surface interactions.
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| 6. |
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| 7. |
- Arnebrant, Thomas, et al.
(författare)
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Lubricating Properties of the Initial Salivary Pellicle
- 2003
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Ingår i: Biofouling (Print). - : Harwood Academic Publishers. - 0892-7014 .- 1029-2454. ; 19:6, s. 365-369
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Tidskriftsartikel (refereegranskat)abstract
- The role of saliva in the oral cavity is manifold; an important function is to serve as lubricant between hard (enamel) and soft (mucosal) tissues. Intraoral lubrication is of crucial importance in order to maintain functions such as deglutition, mastication and the faculty of speech. A large number of people suffer from impaired salivary functions, displaying symptoms such as 'dry mouth'. This results in a need for methods to assess the lubricating properties of both native saliva and potential artificial saliva formulations. Here, normal as well as lateral forces, acting between adsorbed salivary films, have been measured for the first time by means of colloidal probe atomic force microscopy (AFM). It was found that the presence of salivary pellicles between hard surfaces reduces the friction coefficient by a factor of 20. This reduction of friction is consistent with the long-range purely repulsive nature of the normal forces acting between the salivary films. The lubricating mechanism is presumably based on a full separation of the sliding surfaces by the salivary films. The friction between salivary films has been investigated at normal loads that cover the clinical jaw closing forces, and it can be concluded that the lubricating properties are maintained within this load interval. The present study indicates the usefulness of colloidal probe AFM, which offers a direct and quantitative measure of lubrication at a molecular level, in the study of biotribological phenomena. In particular, the results obtained here may have implications for the development of saliva substitutes.
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| 8. |
- Arvidsson, M., et al.
(författare)
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Feeling fine - the effect of topography and friction on perceived roughness and slipperiness
- 2017
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Ingår i: Biotribology. - : Elsevier Ltd. - 2352-5738. ; 11, s. 92-101
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Tidskriftsartikel (refereegranskat)abstract
- (1) Background. To design materials with specific haptic qualities, it is important to understand both the contribution of physical attributes from the surfaces of the materials and the perceptions that are involved in the haptic interaction. (2) Methods. A series of 16 wrinkled surfaces consisting of two similar materials of different elastic modulus and 8 different wrinkle wavelengths were characterized in terms of surface roughness and tactile friction coefficient. Sixteen participants scaled the perceived Roughness and Slipperiness of the surfaces using free magnitude estimation. Friction experiments were performed both by participants and by a trained experimenter with higher control. (3) Results and discussion. The trends in friction properties were similar for the group of participants performing the friction measurements in an uncontrolled way and the experiments performed under well-defined conditions, showing that the latter type of measurements represent the general friction properties well. The results point to slipperiness as the key perception dimension for textures below 100 μm and roughness above 100 μm. Furthermore, it is apparent that roughness and slipperiness perception of these types of structures are not independent. The friction is related to contact area between finger and material. Somewhat surprising was that the material with the higher elastic modulus was perceived as more slippery. A concluding finding was that the flat (high friction) reference surfaces were scaled as rough, supporting the theory that perceived roughness itself is a multidimensional construct with both surface roughness and friction components.
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| 9. |
- Badal Tejedor, Maria, et al.
(författare)
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Tablet mechanics depend on nano and micro scale adhesion, lubrication and structure
- 2015
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Ingår i: International Journal of Pharmaceutics. - : Elsevier. - 0378-5173 .- 1873-3476. ; 486:1-2, s. 315-323
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Tidskriftsartikel (refereegranskat)abstract
- Tablets are the most convenient form for drug administration. However, despite the ease of manufacturing problems such as powder adhesion occur during the production process. This study presents surface and structural characterization of tablets formulated with commonly used excipients (microcrystalline cellulose (MCC), lactose, mannitol, magnesium (Mg) stearate) pressed under different compaction conditions. Tablet surface analyses were performed with scanning electron microscopy (SEM), profilometry and atomic force microscopy (AFM). The mechanical properties of the tablets were evaluated with a tablet hardness test. Local adhesion detected by AFM decreased when Mg stearate was present in the formulation. Moreover, the tablet strength of plastically deformable excipients such as MCC was significantly decreased after addition of Mg stearate. Combined these facts indicate that Mg stearate affects the particle-particle bonding and thus elastic recovery. The MCC excipient also displayed the highest hardness which is characteristic for a highly cohesive material. This is discussed in the view of the relatively high adhesion found between MCC and a hydrophilic probe at the nanoscale using AFM. In contrast, the tablet strength of brittle materials like lactose and mannitol is unaffected by Mg stearate. Thus fracture occurs within the excipient particles and not at particle boundaries, creating new surfaces not previously exposed to Mg stearate. Such uncoated surfaces may well promote adhesive interactions with tools during manufacture.
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| 10. |
- Claesson, Per M, et al.
(författare)
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Measuring interactions between surfaces
- 2002
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Ingår i: Handbook of Applied Colloid and Surface Chemistry. - Chichester, Weinheim : Wiley. - 0471490830 ; , s. 383-414
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