Thursday 11 July 2013, Strathblane & Cromdale Halls, 16:30-18:30
Poster session C - Surfactant phases
P.196 Clouding and micellar growth in aqueous anionic surfactants: A SANS study
A Bhadouria1, S Kumar1, S Kumar2 and V Aswal2
1
The Maharaja Sayajirao University of Baroda, India, 2Bhabha Atomic Research Centre, India
The self-assembly of surfactant in aqueous solution exhibit anomalous temperature dependence [1]. Various
surfactants (ionic or non-ionic) exhibit clouding upon heating their aqueous solutions. This phenomenon is known
as clouding phenomenon and the temperature at which it occurs is known as cloud point (CP). However, the
phenomenon occurs rarely in ionic surfactant solutions. The present study includes the study of clouding
phenomenon in novel ionic surfactants having quaternary counter ions (tetra-n-butyl ammonium dodecylsulfate
(TBADS), tetra-n-butyl ammonium dodecylbenzene sulfonate (TBADBS) and tetra-n-butylammonium a-sulfonato
myristic acid methyl ester (TBAMES)). It has been observed that CP is dependent on the surfactant concentration
and nature of the alkyl head group. Further, inorganic salt addition shows an increase followed by decrease in CP on
continuous addition of salt to a fixed surfactant concentration. Small angle neutron scattering (SANS)
measurements have been performed to have an idea about the structural transitions when a system approaches the
CP. An anomalous micellar growth has been observed by SANS data (semi major axis, semi minor axis, aggregation
number and charge fraction (a)). The data further hint about the formation of cloud of micelles near CP. The study
allows concluding that pseudo non ionic micelles are formed on heating which coalesce near/at CP.
[1]
S.Kumar, A. Bhadoria, H. Patel and V.K. Aswal, J. Phys. Chem. B 2012, 116, 3699-3703.
P.197 SANS and SAXS investigation of hierarchical self assembly of functionalized single-walled carbon nanotubes
in surfactant system
S-H Lim1, H-S Jang2, T-H Kim3 and S-MChoi2
1
Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology,
Korea, 2Department of Nuclear and Quantum Engineering, Korea Advanced Institute of Science and Technology,
Korea, 3Neutron Science Division, Department of Reactor Utilization and Development, Korea Atomic Energy
Research Institute, Korea
Hierarchical self-assembly of single-walled carbon nanotubes (SWNTs) into highly ordered superstructures in
amphiphlic molecular systems has been of great interest as a route toward materials with new functionalities. The
rich phase behavior of amphiphilic molecules such as surfactants may provide a general and inexpensive way for
fabricating a large variety of highly ordered arrays of SWNTs without going through complicated preparative
procedures [1]. Here, we investigated cooperative self assemblies of hydrophilically functionalized SWNTs (p-SWNTs
[2]) and non-ionic surfactants (C12E5) in water using small angle neutron and x-ray scattering measurements.
Different amount ofp-SWNTs were mixed with a solution of 45 wt% C12E5 in water (which shows hexagonal,
isotropic cylindrical micellar, and lamellar phases as temperature increases from 10 ℃ to 65 ℃). When the
C12E5/water system is in the hexagonal phase, the p-SWNTs form hexagonal arrays interspaced by C12E5
cylinders. The transition temperatures from the hexagonal to the isotropic cylindrical micellar phases and from the
isotropic to the lamellar phases increased significantly with the concentration of p-SWNTs [3].
[1]
[2]
[3]
T.-H. Kim, C. Do, S.-H. Kang, M.-J. Lee, S.-H. Lim and S.-M. Choi, Soft Matter, 8, 9073 (2012)
T.-H. Kim, C. Doe, S. R. Kline and S.-M. Choi, Adv. Mater., 19, 929 (2007)
S.-H. Lim, H.-S. Jang, T.-H. Kim and S.-M. Choi (in preparation)
ICNS 2013 International Conference on Neutron Scattering
P.198 Structure of confined microemulsions in AAO nanopores
F Lipfert and H Frielinghaus
Jülich Centre for Neutron Science, Germany
Microemulsions are used in a variety of different applications such as detergence or oil recovery where they are
exposed to a variety of surfaces and confinements. We analyzed the structure of symmet- rical microemulsions with
different surfactant concentrations in two- dimensional confinement using cylindrical nano pores arranged
hexagonally on anodized aluminum oxide (AAO) membranes. The microemulsions we used have a water-oil domain
sizes in the range of 200Å while the pores we used have diameters of 180nm and 400nm. We found the
microemulsion exhibiting a lamellar, shell-like structure at the interface even tough their equilibrium state is
bicontinuous. We used small angle neutron scattering for the analysis because of the neutron wavelength being
comparable to the examined structures and the possibility of contrast matching the microemulsion to the AAO
membranes by partly replacing the H2O with D2O. This matching suppresses the scattering from the membrane
which would overshadow the scattering from the microemulsion and makes the microemulsion scattering
accessible. The scattering from the interface near lamellar structure is Bragg like while the scattering from the
bicontinuous microemulsion in the pore center is isotropic. Both structures have the same domain size so in order to
distinguish between both structures we set up the sample perpendicular to the incoming neutron beam then turned
it 15, effectively decoupling the recorded scattering.
P.199 The self-assembly of same-charge inorganic macroions: COSAN
S Prevost1, P Bauduin2, T Zemb2, O Diat2, F Teixidor3 and P Farràs3
1
TU Berlin, Germany, 2ICSM, 3ICMAB CSIC, Spain
Theta-shaped (θ) rigid surfactant molecules such as COSAN show complex multi-scale patterns in aqueous
solutions as seen by small angle neutron and X-ray scattering over large q-window (qmax/qmin>100). At wide
angles a correlation between COSAN (bis(1,2-dicarbollide) cobaltate) is seen, while oligomeric aggregates that
correspond to charged micelles scatter in the intermediate q-regime (~0.1nm-1). The low-q part finally exhibit a
scattering intensity that is modelled by vesicles made of one or several monolayers of adjacent COSAN. Vesicles
form at lower concentration than micelles (Angewandte Chemie 2011 vol 123 p5410). However, there is a
coexistence range of these two aggregates. Therefore, the scattering spectra can be modelled as the sum of two
intensities. Exploitation of absolute scale with and without salt allows determining the area per molecule in the two
pseudo-phases, as well as equilibrium shape of the aggregates. Thermodynamic reasons of coexistence of vesicles
and micelles are consistent with cryo-TEM and surface tension measurement. Entropic terms like required of
Onsager transition favour the enclosure of vesicles, as predicted by Ninham and Marcelja twenty years ago. Some
points of lateral equation of states involved can be derived from the quantitative exploitation of SANS patterns;
SAXS is less quantitative since contrast with water is very low. Last but not least, a new and direct method for
determining the free energy of transfer between micelles and vesicles seen as miscible pseudo-phases is proposed.
P.200 Structure of mixed micellar solutions study by small angle neutron scattering method
A Rajewska
National Center for Nuclear Research, Poland
The mixed systems of nonionic classic surfactant C14E7 (heptaethylene glycol monotetradecyl ether) and 3 anionic
surfactants SDS (sodium dodecyl sulfate), LiDS (lithium dodecyl sulfate) and CsDS (cesium dodecyl sulfate) in
heavy water solutions was investigated for concentration of nonionic surfactant c=0.17%, 0.5%, 1% for
concentrations of anionic surfactants:1. 0.216mmol/l,1.083mmol/l, 2.16mmol/l (0.17% C14E7), 2.0.372mmol/l,
ICNS 2013 International Conference on Neutron Scattering
1.860mmol/l, 3.720mmol/l (0.5% C14E7), 3. 0.573mmol/l, 2.866mmol/l, 5.733mmol/l (1% C14E7) at
temperature t= 25oC with two methods - tensiometric and small-angle neutron scattering (SANS) on SANS
spectrometer ("YuMO") of the IBR-2 on pulsed neutron source at FLNP, JINR in Dubna (Russia). Measurements
have covered Q range from 7x10-3 to 0.4 Å-1. The micellar solutions were prepared in D2O since the contrast between
the micelles and the solvent in neutron experiments is better with D2O than with H2O. It was obtained as the result
that the shape of micelles changes depending on surfactant concentration at temperature constant. At lower
concentrations micelles are spherical but at higher concentrations and are rather ellipsoidal. For calculation and
approximation results from SANS experiment was used program PCG 2.0 of Glatter O. and co-workers from
University of Graz (Austria).
P.201 Dynamics of ionic micelles: Effect of hydrotropic salt
V K Sharma1, S Mitra1, V Garcia Sakai2 and R Mukhopadhyay1
1
Bhabha Atomic Research Centre, India, 2ISIS Facility, UK
By tailoring the molecular architecture and the interaction between the surfactants, micellar structures of a specific
size, shape and order can be created. The addition of inorganic or organic salts to an ionic micellar solution
facilitates the transition from spherical to rodlike micelles by screening the repulsions between the charged head
groups. Organic counterions that bind strongly to the micellar surface are highly efficient in promoting micellar
growth and interact with the surfactants electrostatically as well as hydrophobically. The effect of addition of sodium
salicylate salt on the dynamics of DTAB and CTAB micelles is studied using Quasielastic Neutron Scattering (QENS)
technique. Data analysis indicates presence of two distinct motions: global motion of the whole micelles and
internal motion of the monomers in the micelle. Addition of sodium salicylate is found to affect both global as well
internal motions of the micelles vis-à-vis the micelles without salt. It is found that the global motion gets slower
which could directly be correlated with the change of shape and aggregation number. The internal motion is also
found to be restricted. Our experiment shows that the effect of the organic salt is much more comparative to the
inorganic one. This could be due to the fact that organic salt screens the repulsion between the head groups more
efficiently. Moreover, salicylate ion is strongly adsorbed to these micelles in a configuration that allows the
carboxylic and hydroxyl groups to protrude from the micelle. This may be the reason for the hindered internal motion
of the micelles in presence of sodium salicylate salts.
ICNS 2013 International Conference on Neutron Scattering