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| 2. |
- Jansson, M, et al.
(författare)
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Aggregation in tetraalkylammonium dodecanoate systems
- 1991
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Ingår i: Colloids and Surfaces. - 0166-6622 .- 1873-4340. ; 59, s. 387-397
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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.
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| 3. |
- Li, P, et al.
(författare)
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An investigation on the influence of intermolecular interactions on the dynamics and molecular order of micellized zwitterionic surfactants
- 1991
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Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 142, s. 593-595
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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.
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| 4. |
- Baeckstroem, P., et al.
(författare)
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Convenient Method for the Synthesis of Lineatin, a Pheromone Component of Trypodendron-Lineatum
- 1991
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 56:10, s. 3358-3362
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Tidskriftsartikel (refereegranskat)abstract
- Synthesis of racemic lineatin (1), a pheromone component of Trypodendron lineatum, is described. Condensation of 5-methyl-5-hexen-2-one (2) and triethyl phosphonoacetate with LiN(SiMe3)2 gave esters 3, which upon hydrolysis gave acids 4a-f. The bicyclo[3.2.0] ring compounds 5 and 6 were obtained via an intramolecular [2 + 2] addition by refluxing underivatized carboxylic acids 4a-f with NaOAc and Ac2O. Compound 5 was isomerized to the thermodynamically more stable isomer 6 using a Pd/C catalyst activated with hydrogen. Reduction of 6 with LiAlH4 gave the endo and exo isomers 7a and 7b (4:1). Isolation of the alcohol 7a followed by acetylation gave 8. Subsequent oxidation with OsO4 and methylmorpholine N-oxide gave diol 9. Cleavage of 9 with H5IO6 in diethyl ether gave keto aldehyde 10, which was converted to keto acetal 11. Treatment of 11 with MeMgBr followed by acidic workup gave 1. The overall efficiency is approximately 20%.
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| 5. |
- Chachaty, C, et al.
(författare)
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Influence of the polar head size on the dynamics of micellized surfactants
- 1991
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Ingår i: Journal of Physical Chemistry A. - 1089-5639 .- 1520-5215. ; 95, s. 3830-3836
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of micellized quaternary ammonium surfactants has been investigated by means of the frequency dependence of the 13C longitudinal relaxation rates. Trimethyl-, triethyl-, and tributyldodecylammonium bromides were used to systematically vary the bulk of the polar head and examine its influence on the internal and overall motions of the surfactants. The relaxation data were analyzed by means of the two-step model and of a rotational jump model relevant to the trans-gauche isomerizations about the bonds. In the case of the trimethyldodecyl--ammonium bromide an excellent agreement is obtained by the two-step model as the vicinity of the nitrogen is well above the values expected for methylene groups. The jump model shows that this behavior results from a slowing of the internal motions beyond the domain of validity of the two-step model.
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| 6. |
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| 7. |
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| 8. |
- Ringer, S.P, et al.
(författare)
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Effect of particle pinning on recrystallization of a titanium-stabilized stainless steel
- 1990
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Ingår i: Recrystallization '90. - Warrendale, Pa : Minerals, Metals & Materials Society. - 0873391241 ; , s. 483-489
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Konferensbidrag (refereegranskat)abstract
- Recent work has shown that maintenance of coherency between stable particles and matrix after the bypassing of grain boundaries during grain growth can occur to reduce the energy of the particle /matrix interface, and that this occurs by a diffusion controlled bodily rotation of the particle. Since coherent particles, in general, offer more resistance to migrating boundaries than incoherent ones, a particle rotation, if it occurs, should tend to help refine grain size following recrystallization. The recrystallization and early stages of grain growth of a deformed Ti-stabilized austenitic stainless steel (321) containing coherent and semicoherent TiC precipitates has been studied by light optical and transmission electron microscopy. Evidence for a particle rotation following recrystallization of this alloy is presented. A model explaining this behaviour is developed and discussed in terms of the likely effects phenomena such as this and particle reversion will have on the recrystallization behaviour of these steels
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| 9. |
- Ringer, S.P., et al.
(författare)
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On the rotation of precipitate particles
- 1992
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Ingår i: Acta Metallurgica et Materialia. - 0956-7151. ; 40:2, s. 275-283
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Tidskriftsartikel (refereegranskat)abstract
- An energetically unfavourable situation can develop when coherent particles are bypassed by migrating grain boundaries. This is due to the precipitates being exposed to incoherent interfaces in the new matrix. In this work, the rotation of precipitate particles to low energy, coherent orientations in the new matrix is shown to be one of several possible responses to this situation. A physical and kinetic model for the rotation is put forward and the results of calculations of rotation rate presented. It is shown that particle rotation is controlled by interfacial diffusion and depends upon alloy composition, time, temperature and particle size and shape. The possibility of particle rotation occurring during particle/boundary contact is also discussed. This is shown to depend upon the nature of the boundary type. Generally, boundaries moving under large driving pressures with high velocities (e.g. phase transformation interfaces), are less likely to allow rotation during particle/boundary contact than less mobile boundaries such as those in grain growth and recrystallization. Experimental results, from SAD and TEM of a Ti stabilized austenitic stainless steel containing a dispersion of coherent TiC precipitates is also presented and supports the particle rotation model
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| 10. |
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