| 1. |
|
|
| 2. |
- Jansson, M, et al.
(författare)
-
Aggregation in tetraalkylammonium dodecanoate systems
- 1991
-
Ingår i: Colloids and Surfaces. - 0166-6622 .- 1873-4340. ; 59, s. 387-397
-
Tidskriftsartikel (refereegranskat)abstract
- Aggregation in some different tetraalkylammonium dodecanoate systems has been studied. The influence of counterions on the phase behaviour of both binary surfactant/water systems and more complicated, multi-component systems were investigated, by applying NMR self-diffusion and Langmuir Blodgett techniques. Increasing the size of the tetra_x001F__x001F_alkylammonium counterions was found to lead to a substantial reduction of the critical micelle concentration. This is due to increased ion-micelle interactions associated with the enhanced hydrophobicity of the larger counterions. Furthermore, the increase in the ion size was found to be correlated with a depression of the tendency of the surfactant to form aggregates with low surface curvature, such as liquid-crystalline phases and rod-like micelles. The importance of the counterion size with regard to the formation of microemulsions in surfactant/water/oil systems was also demonstrated.
|
|
| 3. |
- Li, P, et al.
(författare)
-
An investigation on the influence of intermolecular interactions on the dynamics and molecular order of micellized zwitterionic surfactants
- 1991
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 142, s. 593-595
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of intramolecular as well as intermolecular interactions on the dynamics of micellized mixtures of decyldimethylammoniopropanesulfonate, a zwitterionic surfactant with an anionic surfactant (lithium decyl sulfate) and a cationic surfactnat (decylammonium acetate), have been studied by 13C multifield NMR relaxation. The experimental results, as analyzed by a two-step spin relaxation model, suggest that, in contrast to liquid crystalline systems, intramolecular interactions alone determine the order parameter profile and the local chain dynamics.
|
|
| 4. |
- Abrahmsen-Alami, S, et al.
(författare)
-
Effect of temperature on NMR self-diffusion in aqueous associative polymer solutions
- 1996
-
Ingår i: Journal of Physical Chemistry. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 100:11, s. 4598-4605
-
Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence of polymer self-diffusion rates in aqueous solutions of C12EO200C12 (AP9, Mw = 9300) and C12EO90C12 (AP4, Mw = 4600) and nonmodified analogues PEO10 and PEO4 (Mw = 10 000 and 3400) has been studied. The effect of the hydrophobic end-groups on the self-diffusion of the associative polymer (AP) was found to be proportional to the polymer content and inversely related to the temperature. The variation of the AP self-diffusion coefficient follows an Arrhenius behavior. The resulting apparent activation energies, Ea, increase with polymer content from 15 to 55 kJ/mol in the range 0.5−50 wt % for AP9, whereas the parent PEO10 shows an almost constant Ea of about 25 kJ/mol in the same concentration range. Activation energies derived from self-diffusion and low shear viscosity measurements were found to be quite similar. The distribution of self-diffusion coefficients often observed in AP systems is discussed in terms of distribution of aggregate sizes at low AP content and homogeneity of the network at higher contents. The residence time of an AP monomer in a hydrophobic domain was estimated as 0.1 ms at 25 °C and decreases with temperature. Also included are turbidity measurements on the AP systems.
|
|
| 5. |
- Abrahmsén-Alami, S, et al.
(författare)
-
Water self-diffusion in aqueous associative polymer solutions
- 1996
-
Ingår i: JOURNAL OF PHYSICAL CHEMISTRY. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 100:16, s. 6691-6697
-
Tidskriftsartikel (refereegranskat)abstract
- Water self-diffusion in aqueous model associative polymer (AP) solutions, hydrophobically end-capped poly(ethylene oxide), C12EO200C12 (AP9,) and C12EO90C12 (AP4), has been studied with the NMR-PGSE method and compared to the diffusion in nonmodified poly(ethylene oxide) PEO. It was found that it decreases monotonically with increasing polymer concentration, giving Di/D0 ≈ 0.2 at 50 wt % (D0 being the water self-diffusion coefficient in the absence of polymer), independently of polymer molecular weight and modification. In further evaluation of the data, the cell-diffusion model was used. Such an analysis suggests that up to a polymer content of about 2 wt % AP9, water diffusion is not significantly affected by the polymer. Above this concentration, up to about 10 water molecules per EO group are affected in AP9 and AP4 solutions. On increasing the temperature, water self-diffusion increases, following an Arrhenius-like equation, with Ea equal to that of pure water at low polymer content (10 wt %). The activation energy increases with polymer content, and at 50 wt %, Ea is about 30 kJ/mol, independently of polymer type. A minor difference in Ea between AP4 and AP9 solutions at intermediate polymer content is likely to originate from the ability of AP4 to form well-developed cubic phase structures. An increase in temperature was found to lead to a slight dehydration of the associative polymer EO monomers closest to the hydrophobic core.
|
|
| 6. |
- Björling, Mikael, et al.
(författare)
-
An NMR Self-Diffusion Study of the Interaction between Sodium Hyaluronate and Tetradecyltrimethylammonium Bromide
- 1995
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 28:20, s. 6970-6975
-
Tidskriftsartikel (refereegranskat)abstract
- A decrease of the NMR self-diffusion coefficient of sodium hyaluronate (NaHy) upon increasing tetradecyltrimethylammonium bromide (TTAB) concentration in 202 mM NaCl (just enough to attain single phase conditions irrespective of the TTAB concentration) is interpreted in terms of the formation of NaHy–TTAB complexes containing several NaHy chains. The complexes are judged to be induced by multiple-site electrostatic condensation of TTAB micelles onto the Hy chains. Thus, the TTAB micelles may act as bridging points between, and within, the NaHy chains. For a 1% wt NaHy solution, at 202 mM NaCl, the fraction of adsorbed TTAB has a maximum at 10 mM TTAB where an estimated 54% of all the added TTAB is bound. At 70 mM TTAB, the fraction of bound TTAB has decreased to 42%. The decrease of the binding constant with increasing TTAB concentration is attributed to a more efficient electrostatic screening; i.e., the ionic strength (due to uncondensed species) increases. The observed NaHy–TTAB complexes are likely to be precursors of the precipitated phase formed at lower salt concentrations.
|
|
| 7. |
- Björling, Mikael, et al.
(författare)
-
Using end-confined chains to model end-absorbing, triblock copolymers : 2. Numerical approach
- 1998
-
Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 31:25, s. 9033-9043
-
Tidskriftsartikel (refereegranskat)abstract
- The bridging attraction mediated by end-absorbing, triblock copolymers in a good solvent is analyzed using numerical methods and compared to analytical results. Good agreement is found. The main deviations may be attributed to the neglect of thermal fluctuations in the extension of the loops at the brush edge in the analytical treatment. With a suitable choice of "natural" units, the numerical results for the bridging probability and the free energy of interaction per chain collapse onto universal master curves in the two arrangements considered: symmetric and asymmetric adsorption of associative polymers (APs) on the surfaces of a planar slit.
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
|
|
