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Geometrical Shape of Micelles Formed by Cationic Dimeric Surfactants Determined with Small-Angle Neutron Scattering
KTH, Skolan för kemivetenskap (CHE), Kemi, Yt- och korrosionsvetenskap.
2012 (Engelska)Ingår i: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 28, nr 25, s. 9311-9321Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

The influence of spacer group on the geometrical shape of micelles formed by quaternary-bis dimeric (Gemini) surfactants C12H25N(CH3)(2)(CH2)(5)N(CH3)(2)C12H25 (12-s-12) has been investigated with small-angle neutron scattering (SANS). Dimeric surfactants with a short spacer unit (12-3-12 and 124-12) are observed to form elongated general ellipsoidal micelles with half axes a < b < c, whereas SANS data demonstrate that 12-s-12 surfactants with 6 <= s <= 12 form rather small spheroidal micelles rather than strictly spherical micelles. By means of comparing our present SANS results with previously determined growth rates using time-resolved fluorescence quenching, we are able to conclude that micelles formed by 12-6-12, 12-8-12, 12-10-12, and 12-12-12 are shaped as oblate rather than prolate spheroids. As a result, our present investigation suggests a never before reported structural behavior of Gemini surfactant micelles, according to which micelles transform from elongated ellipsoids to nonelongated oblate spheroids as the length of the spacer group is increased. The aggregation number of oblate micelles is observed to monotonously decrease with an increasing length of the surfactant spacer group, mainly as a result of a decreasing minor half axis (a), whereas the major half axis (b) is rather constant with respect to s. We argue that geometrically heterogeneous elongated micelles are formed by dimeric surfactants with a short spacer group mainly as a result of the surface charges becoming less uniformly distributed over the micelle interface. As the length of the spacer group increases, the distance between intramolecular charges become approximately equal to the average distance between charges on the micelle interface, and as a result, rather small oblate spheroidal micelles with a more uniform distribution of surface charges are formed by dimeric 12-s-12 surfactants with 6 <= s <= 12.

Ort, förlag, år, upplaga, sidor
2012. Vol. 28, nr 25, s. 9311-9321
Nyckelord [en]
Cationic surfactants, Neutron scattering
Nationell ämneskategori
Kemiteknik
Identifikatorer
URN: urn:nbn:se:kth:diva-99417DOI: 10.1021/la301190dISI: 000305661400018Scopus ID: 2-s2.0-84862905274OAI: oai:DiVA.org:kth-99417DiVA, id: diva2:542296
Forskningsfinansiär
VetenskapsrådetEU, Europeiska forskningsrådet, 226507-NMI3
Anmärkning
QC 20120731Tillgänglig från: 2012-07-31 Skapad: 2012-07-30 Senast uppdaterad: 2017-12-07Bibliografiskt granskad

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Bergström, L. Magnus
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