| 1. |
- Thuresson, Krister, et al.
(författare)
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Binding of SDS to Ethyl(hydroxyethyl)cellulose. Effect of Hydrophobic Modification of the Polymer
- 1996
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Ingår i: Journal of Physical Chemistry. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 100:12, s. 4909-4918
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Tidskriftsartikel (refereegranskat)abstract
- The binding of SDS to cellulose polymers in the semidilute concentration regime has been studied by means of NMR, ion-selective electrode, and a time-resolved fluorescence technique. Two polymers have been used, differing only in a low degree of hydrophobic modification of one of them. NMR self-diffusion and activity measurements show that the binding of SDS to the nonmodified polymer has a fairly pronounced critical aggregation concentration (cac), while binding to the hydrophobically modified polymer is less cooperative up to a concentration of about the cac in the nonmodified polymer/SDS system. NMR T-2 relaxation and fluorescence studies indicate that surfactants bound to the hydrophobically modified polymers in the noncooperative regime have slow dynamics compared to micellized surfactants, to surfactants bound to the unmodified polymer, and to surfactants bound to the hydrophobically modified polymer in the cooperative regime. Furthermore, in the non-cooperative regime the fluorescence studies imply that the SDS aggregation number of the mixed micelles is low and that the number of hydrophobic zones is invariant with respect to the surfactant concentration.
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| 2. |
- Thuresson, Krister, et al.
(författare)
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Effect of Hydrophobic Modification of a Nonionic Cellulose Derivative on the Interaction with Surfactants. Phase Behaviour and Association.K. Thuresson, B. Lindman,The Journal of Physical Chemistry, submitted.
- 1997
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 101:33, s. 6460-6468
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Tidskriftsartikel (refereegranskat)abstract
- Phase separation studies have been carried out concerning the addition of different surfactants to systems containing either ethyl(hydroxyethyl)cellulose (EHEC) or the hydrophobically modified analogue (HM-EHEC). The polymer concentration was kept constant at 1 g polymer/100 g of water (1 w/w%), while the surfactant concentration was varied. In the polymer/sodium dodecyl sulfate (SDS) systems, which were studied in more detail, phase diagrams were obtained in the presence of various concentrations of inert salt. Moreover, the phase behavior of the HM-EHEC/SDS system showed no marked changes by purification of the surfactant or by contamination with decanol. It was shown that the SDS binding to EHEC was cooperative and could be described in the framework of a closed association model, while for HM-EHEC a two-step binding model had to be used to get a proper description of the binding. In the noncooperative part of the HM-EHEC binding isotherm, the binding showed similarities to the adsorption of SDS on a hydrophobic surface and could be described by a Langmuir adsorption model. From the binding isotherms for SDS, binding isotherms for ionic surfactants with varying chain length could be calculated from simple assumptions. These isotherms give a basis for the interpretation of the phase diagrams. For the ionic surfactants, the phase behavior could be rationalized by considering the polymer/surfactant complex to possess polyelectrolyte characteristics. The observations were discussed in terms of an attractive hydrophobic interaction and a repulsive electrostatic force. Addition of nonionic surfactants was discussed by observing that generally a pair of a nonionic polymer and a nonionic surfactant segregates. However, with HM-EHEC there is an extra attractive hydrophobic interaction due to the presence of polymer hydrophobic tails which can serve as nucleation sites for the surfactants.
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| 3. |
- Thuresson, Krister, et al.
(författare)
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Effect of Hydrophobic Modification on Phase Behaviour and Rheology in Mixtures of Oppositely Charged Polyelectrolytes
- 1996
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Ingår i: Langmuir. - 0743-7463. ; 12:2, s. 530-537
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Tidskriftsartikel (refereegranskat)abstract
- Phase behavior and rheology of polymer mixtures comprising aqueous solutions of oppositely charged polyelectrolytes are investigated. Emphasis is put on the effects of hydrophobic modification of the polymers and addition of salt. The associative phase separation usually observed when mixing oppositely charged polyelectrolytes is effectively prevented over a large miscibility region for the hydrophobically modified polymers. Also, in the extended one-phase region, the viscosity is 3-4 orders of magnitude higher for mixed polyelectrolyte systems compared to that observed for either one of the polymers. Addition of ordinary electrolytes to the mixture decreases the viscosity strongly, and at higher electrolyte contents a phase separation is induced. A mechanism explaining the observations is proposed.
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| 4. |
- Thuresson, Krister, et al.
(författare)
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Effect of Surfactant on Structural and Thermodynamic Properties of Aqueous Solutions of Hydrophobically Modified Ethyl(hydroxyethyl)cellulose
- 1995
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 11:10, s. 3730-3736
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Tidskriftsartikel (refereegranskat)abstract
- Solution properties of ethyl(hydroxyethyl)cellulose (EHEC) and a hydrophobically modified analogue (HM-EHEC) in water in the presence of various amounts of sodium dodecyl sulfate (SDS) have been investigated by cloud point (CP) measurements, titration microcalorimetry, and static light scattering. The CP experiments revealed that the hydrophobically modified polymer is less soluble than the unmodified EHEC at low concentrations of SDS, while at higher surfactant concentrations the solubility properties of the two polymers are practically the same. The resulting enthalpic titration curves from the calorimetric measurements on 0.25% polymer solutions at 25 degrees C consist of a pronounced endothermic peak (moderate SDS concentration) followed by a shallow exothermic one at higher surfactant concentrations. The prominent endothermic peak observed for both systems indicates a strong polymer-surfactant interaction. From the shape of the curves, the onset of the saturation stage of the binding process was estimated to be 20 mm for both polymers. The degree of surfactant binding to the polymer was found, at moderate SDS concentrations, to be the same for EHEC and HM-EHEC. The light-scattering results for both the EHEC/ SDS and HM-EHEC/SDS systems revealed a decreasing angular dependence of the reduced inverse scattered intensity function S(0)S(q) (q is the wave vector) with increasing surfactant concentration. It is observed at moderate levels of surfactant addition that the correlation length xi decreases more strongly for the EHEC/SDS system than for the HM-EHEC/SDS system. By plotting the static light scattering data in the form S(xi)/S(0) versus the dimensionless parameter q xi a universal picture emerged. In the regime q xi > 1, the power law S(q) similar to q(-1.6) was observed for both systems.
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| 5. |
- Thuresson, Krister
(författare)
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Solution properties of a hydrophobically modified polymer
- 1996
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The influence of hydrophobic modification on solution properties of water-soluble polymers in the semi-dilute regime have been studied. The nonionic ethyl(hydroxyethyl)cellulose (EHEC) and its hydrophobically modified analogue (HM-EHEC) are used as model substances. Interactions between the polymer molecules in solution and a third component are investigated, and in particular the influence of the surfactant sodium dodecylsulfate (SDS). The polymer/SDS complex formation is investigated by using several techniques (phase behaviour, rheology, calorimetry, DS- sensitive electrode, NMR, and light scattering and fluorescence techniques). This combination of methods gives thermodynamic information on the complex formation, as well as information about the dynamics of the polymer/surfactant complex. In a binary, semi-dilute, HM-EHEC solution the hydrophobic tails associate in clusters with an average of ten tails. These 'pre-formed' micelles act as nucleation sites for other molecules that contain hydrophobic moieties. The number of mixed micelles, and the strengths of the inter polymeric bonds which they give rise to, control both microscopic properties (as chain motions) and macroscopic behaviour (as rheology and phase behaviour). Experimental phase studies with hexanol as a third component were compared with model calculations in a modified Flory-Huggins approach. By assuming that hydrophobic modification causes enhanced association with the polymer semi-quantitative agreement was found. The associative phase separation that is usually observed in mixtures of two oppositely charged polyelectrolytes is effectively prevented by hydrophobic modification of both polyelectrolytes; a highly viscous phase is formed.
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