ISSN:
1435-1536
Keywords:
n-hexadecylammonium hydrogensulphate
;
concentrated sulphuric acid as solvents
;
static light scattering
;
dynamic light scattering
;
micellar structures
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract A common cationic surfactant,n-hexadecylammonium hydrogensulphate, dissolved in concentrated sulphuric acid, has been studied by static and dynamic light scattering. Micelle formation has been observed even in this unusual solvent. An apparent molar mass of 45 500±4.5% was found for the aggregates. A translational diffusion coefficientD 0=5.5×10−9 cm2/s was measured which gave a hydrodynamically effective radius ofR h=17.7 nm. The geometric radius of gyration wasR g=76.2 nm. The ratioR g/R h=4.33 is indicative for rodlike structures. Assuming a polydispersity ofL w/L n=2 this corresponds to a cylinder ofL w=152 nm. An axial ratiop w=(L w/d)=60.4 nm was estimated which leads to a cylinder diameter of 2.53 nm. At surfactant concentrations higher than 5% (w/vol) the rod-like micelles aggregate to form more globular structures. The time correlation function, recorded by dynamic light scattering, exhibited a two-step decay which indicates a bimodal distribution of particle sizes. The fast motion coincides with that of the micelles at low concentrations while the other is slower than the fast one by three orders of magnitude and corresponds to the translational motion of large clusters.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00657636
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