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| 3. |
- Kadi, M., et al.
(författare)
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Mixed micelles of fluorocarbon and hydrocarbon surfactants. A small angle neutron scattering study
- 2004
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:10, s. 3933-3939
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Tidskriftsartikel (refereegranskat)abstract
- Mixtures of the partly fluorinated cationic surfactant HFDePC (N-(1, 1,2,2-tetrahydroperfluorodecanyl)pyridinium chloride and deuterated headgroup) with C(16)TAC, hexadecyl-trimethylammonium chloride, have been investigated using small angle neutron scattering with contrast matching. Earlier results from this system suggested that a demixing occurred, into two coexisting populations of micelles, hydrocarbon-rich and fluorocarbon-rich, respectively. The present results could be explained by one type of mixed micelles with an inhomogeneous distribution of fluorinated and hydrogenated surfactants within the micelles although a demixing cannot be definitely excluded.
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| 4. |
- Nadutov, V. M., et al.
(författare)
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Anti-Invar properties and magnetic order in fcc Fe-Ni-C alloy
- 2011
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 323:22, s. 2786-2791
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Tidskriftsartikel (refereegranskat)abstract
- Anti-Invar effect was revealed in the fcc Fe-25.3%Ni-0.73%C (wt%) alloy, which demonstrates high values of thermal expansion coefficient (TEC) (15-21) x 10(-6) K(-1) accompanied by almost temperature-insensitive behavior in temperature range of 122-525 K. Alloying with carbon considerably expanded the low temperature range of anti-Invar behavior in fcc Fe-Ni-based alloy. The Curie temperature of the alloy T(C) = 195 K was determined on measurements of temperature dependences of magnetic susceptibility and saturation magnetization. The Mossbauer and small-angle neutron scattering (SANS) experiments on the fcc Fe-25.3%Ni-(0.73-0.78)%C alloys with the varying temperatures below and above the Curie point and in external magnetic field of 1.5-5 T were conducted. Low value of the Debye temperature Theta(D) = 180 K was estimated using the temperature dependence of the integral intensity of Mossbauer spectra for specified temperature range. The inequality B(eff) = (0.7-0.9)B(ext) was obtained in external field Mossbauer measurement that points to antiferromagnetically coupled Fe atoms, which have a tendency to align their spins perpendicular to B(ext). Nano length scale magnetic in homogeneities nearby and far above T(C) were revealed, which assumed that it is caused by mixed antiferromagnetically and ferromagnetically coupled Fe atom spins. The anti-Invar behavior of Fe-Ni-C alloy is explained in terms of evolution of magnetic order with changing temperature resulting from thermally varied interspin interaction and decreasing stiffness of interatomic bond.
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| 5. |
- Almgren, Mats, et al.
(författare)
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Nonideal Mixed Micelles of Fluorinated and Hydrogenous Surfactants in Aqueous Solution. NMR and SANS Studies of Anionic and Nonionic Systems
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 26:8, s. 5355-5363
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Tidskriftsartikel (refereegranskat)abstract
- Contrast variation SANS and F-19 chemical shifts were measured for three mixed equimolar micelle systems: sodium perfluorooctanoate (SPED) and sodiumdecylsulfate (SDeS) in 200 mM NaCl, lithium perlluorononanate LiPFN) and lithium dodecylsulfate (Li DS) in 200 mM LiCl, and a nonionic system C8F17C2H4(OC2H4)(9) and C12H25(OC2H4)(8) in water, all at 25 C. The chemical shift measurements allow the calculation of the average fraction of nearest neighbors of each kind around the reporter group (the trifluoromethyl group). A preference for like neighbors were found in all systems, smallest in the SDeS/SPFO system and largest in the nonionic system, but in all cases substantially smaller than expected at critical conditions. From the SANS measurements the width of the micelle composition distribution was obtained. For the ionic systems similar values were obtained, showing a broadening compared to ideal mixtures, but not broad enough for demixing or clearly bimodal distributions. In the nonionic system the width was estimated as sigma = 0.18 and 0.22 using two different evaluation methods. These values suggest that the system is close to critical conditions. The lower value refers to a direct modeling of the system, assuming an ellipsoidal shape and a Gaussian composition distribution. The modeling showed the nonionic mixed micelles to be prolate ellipsoids with axial ratio 2.2 and an aggregation number larger than 100. whereas the two ionic systems fitted best to oblate shapes (axial ratios 0.8 and 0.65 for SDeS/SPFO and LiDS/LiPFN. respectively) and aggregation numbers of 60 for both.
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| 6. |
- Bastardo Zambrano, Luis Alejandro, et al.
(författare)
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The structures of complexes between polyethylene imine and sodium dodecyl sulfate in D2O : a scattering study
- 2005
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 109:1, s. 167-174
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Tidskriftsartikel (refereegranskat)abstract
- The association between a highly branched polyelectrolyte with ionizable groups, polyethylene imine (PEI), and an anionic surfactant, sodium dodecyl sulfate (SDS), has been investigated at two pH values, using small-angle neutron and light scattering. The scattering data allow us to obtain a detailed picture of the association structures formed. Small-angle neutron scattering (SANS) measurements in solutions containing highly charged PEI at low pH and low SDS concentrations indicate the presence of disklike aggregates. The aggregates change to a more complex three-dimensional structure with increasing surfactant concentration. One pronounced feature in the scattering curves is the presence of a Bragg-like peak at high q-values observed at a surfactant concentration of 4.2 mM and above. This scattering feature is attributed to the formation of a common well-ordered PEI/SDS structure, in analogue to what has been reported for other polyelectrolyte-surfactant systems. Precipitation occurred at the charge neutralization point, and X-ray diffraction measurements on the precipitate confirmed the existence of an ordered structure within the PEI/SDS aggregates, which was identified as a lamellar internal organization. Polyethylene imine has a low charge density in alkaline solutions. At pH 10.1 and under conditions where the surfactant was contrast matched, the SANS scattering curves showed only small changes with increasing surfactant concentration. This suggests that the polymer acts as a template onto which the surfactant molecules aggregate. Data from both static light scattering and SANS recorded under conditions where SDS and to a lower degree PEI contribute to the scattering were found to be consistent with a structure of stacked elliptic bilayers. These structures increased in size and became more compact as the surfactant concentration was increased up to the charge neutralization point.
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| 7. |
- Bergström, L. M., et al.
(författare)
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A small-angle neutron and static light scattering study of micelles formed in aqueous mixtures of a nonionic alkylglucoside and an anionic surfactant
- 2005
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 109:25, s. 12387-12393
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Tidskriftsartikel (refereegranskat)abstract
- The size and shape of micelles formed in aqueous mixtures of the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic sugar-based surfactant n-decyl beta-D-glucopyranoside (C(10)G) at different concentrations of added salt have been investigated with small-angle neutron and static light scattering. Rather small prolate ellipsoidal micelles form in the absence of added salt and at [NaCl] = 10 mM in D2O. The micelles grow considerably in length to large rods as the electrolyte concentration is raised to [NaCl] = 0.1 M. In excess of nonionic surfactant ([SDS]/[C(10)G] = 1:3) at [NaCl] = 0.1 M in D2O, several thousands of Angstroms long wormlike micelles are observed. Most interestingly, a conspicuously large isotope solvent effect was observed from static light scattering data according to which micelles formed at [SDS]/[C(10)G] = 1:3 and [NaCl] = 0.1 M in H2O are at least five times smaller than micelles formed in the corresponding samples in D2O.
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| 8. |
- Knaapila, Matti, et al.
(författare)
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An effect of side chain length on the solution structure of poly(9,9-dialkylfluorene)s in toluene
- 2008
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 49:8, s. 2033-2038
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Tidskriftsartikel (refereegranskat)abstract
- The effect of side chain length of pi-conjugated poly(9,9-dialkylfluorene)s has been studied in semi-dilute (10 mg/mL) toluene solutions using small-angle neutron scattering (SANS) and H-1 and H-2 NMR spectroscopies. Under these conditions, SANS data indicate that poly(9,9-dinonylfluorene) and poly(9,9-dioctylfluorene) are dissolved down to the molecule level and appear as elongated one-dimensional chains (length >20-30 nm). In contrast, the shorter side chain polymers exhibit a self-association so that poly(9,9-diheptylfluorene) forms thin sheet-like (similar to 1 nm) and poly(9,9-dihexylfluorene) thin (similar to 1 nm) and thick sheet-like (>6 nm) aggregates. H-1 NMR data, together with the density functional theory (DFT) calculations, however, show that this occurs without changes in the conformation of the polymer backbone.
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| 9. |
- Knaapila, Matti, et al.
(författare)
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Control over phase behavior and solution structure of hairy-rod polyfluorene by means of side-chain length and branching
- 2008
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Ingår i: Physical Review E (Statistical, Nonlinear, and Soft Matter Physics). - 1539-3755. ; 77:5
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Tidskriftsartikel (refereegranskat)abstract
- We present guidelines on how the solution structure of pi-conjugated hairy-rod polyfluorenes is controlled by the side-chain length and branching. First, the semiquantitative mean-field theory is formulated to predict the phase behavior of the system as a function of side-chain beads (N). The phase transition at N=N* separates a lyotropic phase with solvent coexistence (N < N*) and a metastable membrane phase (N > N*). The membrane phase transforms into the isotropic phase of dissolved rodlike polymers at the temperature T-mem*(N), which decreases both with N and with the degree of side-chain branching. This picture is complemented by polymer demixing with the transition temperature T-IN*(N), which decreases with N. For N < N*, the lyotropic phase turns isotropic with increasing T at T-IN*. For N > N*, stable membranes are predicted for T-IN*< T < T-mem* and metastable membranes with nematic coexistence for T < T-IN*. Second, in experiment, samples of poly(9,9-dialkylfluorene) with N=6-10 were mixed in methylcyclohexane. For N=8 the side-chain branching was controlled by (9,9-dioctylfluorene)/(9,9-bis(2-ethylhexyl)fluorene) (F8/F2/6) random copolymers. The proportion of F8 to F2/6 repeat units was 100:0, 95:5, 90:10, 50:50, and 0:100. In accordance with the theory, lyotropic, membrane, and isotropic phases with the corresponding phase transitions were observed. For N < N*similar to 6 only the lyotropic phase is present for attainable temperatures. The membrane and isotropic phases are present for N > N*. T-mem*(N) decreases from 340 K to 280 K for N >= 8. For copolymers, the membrane phase is found when the fraction of F8 units is at least 90%, T-mem* decreasing with this fraction. The membrane phase contains three material types: loose sheets of two polymer layers, a better packed beta phase, and dissolved polymer. For N >= 7 and T < T-mem* the tendency for membrane formation becomes stronger with increasing temperature.
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| 10. |
- Knaapila, Matti, et al.
(författare)
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Influence of side chain length on the self-assembly of hairy-rod poly(9,9-dialkylfluorene)s in the poor solvent methylcyclohexane
- 2007
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:26, s. 9398-9405
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Tidskriftsartikel (refereegranskat)abstract
- We report on the phase behavior of poly(9,9-dihexylfluorene) (PF6), poly(9,9-diheptylfluorene) (PF7), poly(9,9-diocylfluorene) (PF8) poly(9,9-dinonylfluorene) (PF9), and poly(9,9-didecylfluorene) (PF10) in methylcyclohexane (MCH). After a heating-cooling cycle, in the 10-50 mg/mL. concentration range. PF6/ MCH. PF7/MCH. PF8/MCH, and PF9/MCH systems were found to be gel-like, while PF10/MCH appears less viscous. PF6/MCH, PF7/MCH, PF8/MCH, and PF9/MCH form large (10- 100 nm) sheetlike assemblies (thickness of 2-3 nm). The larger length scale Structures of these sheets show an odd-even dependence on the side chain (spacer) length: the PF6 and PF8 sheets are broader and thinner, whereas PF7 and PF9 sheets are thicker with a Putative double layer Structure. PF10 does not follow this sequence, and only part of the polymer is assembled into a sheetlike structure the rest remaining dissolved at the molecular level. PF8/MCH and PF9/MCH mixtures also have lower length scale crystalline structures with an internal period corresponding to the periodicity observed in the solid-state P phase of PF8. Vestiges of crystalline domains are found for PF6 and PF7 but not for PF10. PF7/MCH. PF8/MCH, and PF9/MCH systems contain the conformational isomer C, of those chains observed in the ss phase, while this is not observed with other polymer/MCH systems.
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