Thursday 11 July 2013, Sidlaw Room, 14:30-16:30
Surfactant phases
Structure and dynamics of microemulsions with polymer additives adjacent to planar walls
H Frielinghaus, F Lipfert, O Holderer, S Mattauch and D Richter
Forschungszentrum Jülich GmbH, Germany
Microemulsions display a higher degree of order at planar hydrophilic walls. The oriented lamellae, furthermore,
have three times faster relaxations compared to the bicontinuous bulk structure. Grazing incidence neutron
scattering techniques were employed to observe the structure and dynamics (PRE 83, 030401 (2011) & PRE 85,
041408 (2012)). By staying below the critical angle of total reflection an evanescent (tunneling) wave allowed for
highlighting near surface layers of varying depth. Especially, the depth resolved dynamics using neutron spin echo
spectroscopy have been obtained for the first time in this way. Amphiphilic polymers are the most promising
additives in microemulsions since a dramatic increase of the surfactant efficiency usually is obtained. For many
applications, the impact of the polymer on the near surface functionality of the microemulsion is highly important.
The materials to be cleaned usually appear as huge interfaces, for instance in the soil cleaning. The considered
diblock copolymer showed enrichment in the near surface region and the dynamics are slowed down. So the
viscosity effect of the polymer is increased at the surface. We speculate that the exposure time of the fluid is
increased in a rinsing process. The attraction of larger molecules by the confinement could also explain better
binding of receptors of immune cells at hard vessel walls.
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
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.
ICNS 2013 International Conference on Neutron Scattering
Molecular exchange in block copolymer micelles
S-H Choi1, F Bates2 and T Lodge2
1
Hongik University, Korea, 2University of Minnesota, USA
Block copolymers can self-assemble into micelles when dispersed in a selective solvent. Compared to
thermodynamic structure, much less attention has been paid to the dynamics of molecular exchange in block
copolymer micelles, which underlies the attainment of thermodynamically equilibrated structures. Single molecule
exchange between spherical micelles was investigated using time-resolved small-angle neutron scattering (TRSANS). Two pairs of structurally matched poly(styrene-b-ethylene-alt-propylene) (PS-PEP) compounds were
dispersed in an isotopic squalane mixture, which is highly selective towards the PEP blocks. Each pair includes
polymers with fully deuterated (dPS-PEP) and protonated (hPS-PEP) PS blocks. SANS intensity is directly related to
the concentration of protonated chains in the micelle cores. Therefore, a reduction in the measured scattering
intensity can be quantitatively correlated with the exchange of chains. The temperature dependence of the chain
exchange rate R(t) can be explained based on the core block dynamics, while the documented quasi-logarithmic
decay of R(t) is shown to be consistent with single chain exchange that is hypersensitive to the core degree of
polymerization and therefore polydispersity. Complementary measurements were also conducted with concentrated
solutions where the micelles pack onto a body-centered cubic lattice. Based on a first-principles model, the
exchange kinetics are expected to be independent of micelle concentration. However, slower dynamics in ordered
micelles were observed. These results suggest that contributions from factors other than core block dynamics can
come into play in the exchange kinetics for ordered micelles.
Controlling the morphology of surfactant aggregates in cylindrical nanopores
D Müter1, B Bharti2, H Bock1 and G H Findenegg3
1
Heriot-Watt University, UK, 2North Carolina State University, USA, 3Technical University of Berlin, Germany
Controlling surfactant self-assembly in confinement has implications for a range of technical applications, such as
micellar-enhanced ultrafiltration and surfactant-modulated switching of molecular transport in nanopores, but is
also of fundamental scientific interest.
We study the self-assembly of the non-ionic surfactant C12E5 in the cylindrical nanopores of SBA-15 ordered
mesoporous silica, using small-angle neutron scattering under silica contrast-match conditions. Co-adsorption of
lysine allows us to tune the hydrophilicity of the pore surface and determine the impact on the morphology of
surfactant aggregates.
Complementary to the experiments we present mesoscale molecular dynamics simulation results for a single
cylindrical pore connected to a bulk region that allow us to examine the subtle interplay between aggregation and
adsorption on the pore surface in detail.
As a main result, we conclude that changing the hydrophilicity of the pore wall directly determines the average
aggregation number. Thus, when lowering the hydrophilicity fewer head groups attach to the surface which allows
the aggregates to grow and eventually detach from the surface.
ICNS 2013 International Conference on Neutron Scattering
(invited) SANS and Surfactants for CO2
S Rogers1, J Eastoe2, R Heenan1, C James2 and S Alexander2
1
ISIS, UK, 2University of Bristol, UK
Due to the environmental drive to cut emissions, developing approaches for the use of carbon dioxide (CO 2) in
commercial applications as a replacement for Volatile Organic Compounds (VOCs) is a key challenge for
researchers. Potentially, super-critical CO2 (sc-CO2) is an excellent green solvent due to the ease of solvent removal,
recyclability and tuneability of solvent quality by temperature and pressure, the easily accessible critical point
(72.8bar, 31.1°C), it is non-flammable, non-toxic, environmentally benign, biocompatible, cheap and abundant.
Unfortunately, CO2 is generally a poor solvent (particularly for polar and high molecular weight solutes) so
enhancement of the solubility is needed. A method of achieving this is by the incorporation of water nano-droplets
in the CO2 as water-in-CO2 (w/CO2) microemulsions stabilized by compatible surfactants. It is well documented that
Small-Angle Neutron Scattering (SANS) is a key technique in understanding the structure of microemulsions. In the
case of w/CO2 microemulsions the use of heavy water (D2O) gives a clear contrast between the internal droplet and
the continuous phase giving direct structural evidence for the formation of ‘nano-pools’ of water in the CO2. This
invaluable information cannot be obtained by any other method and so SANS has become a crucial tool in this area
of research. The work presented here will show the advances that have been made by the collaborative effort of the
Eastoe Group in Bristol and the SANS Team at ISIS over the last fifteen years in the study of CO 2 compatible
systems via SANS, alongside the current breakthroughs in CO2-active surfactant design and the future developments
in surfactant and pressure cell design.
Self-assembly of amphiphilic molecules by controlling the external conditions in aqueous solution: A SANS study
T-H Kim, Y-S Han, J-D Jang and B-S Seong
Korea Atomic Energy Research Institute, Korea
Amphiphilic molecules such as surfactants, and block copolymerscan self-assemble into various micellar structures
and represent excellent phase behaviors depending on the geometrical molecular shape in aqueous solution.The
self-assembled structure of amphiphilic molecules easily transforms into other structure by controlling the external
conditions (temperature, additives, and so on) which can make a different geometrical molecular shape. Therefore,
the amphiphilic molecules have been of great interests in a broad spectrum of potential applications such as
nanotemplates, nanobuilding blocks or drug delivery in nano- or bio-science.However, for practical use of
amphiphilic molecules, it is essential to know the information for the phase behavior of amphiphilic molecules
under various external conditions. Here, the phase behavior of amphiphilic molecules including surfactants and
block copolymers under the additives and temperature change using the small angle neutron scattering (SANS) has
been investigated. The SANS intensity showed that the surfactants formed cylindrical micelle induced by the
additiveseven below CMC and transformed into unilamellar vesicles by further increasing the additives. Furthermore,
the surfactant vesicles transformed into cylindrical micelles by temperature elevation [1]. For the block copolymers,
the SANS intensity revealed that theyinitiallyself-assembled into spheres, and then transformed into cylinders or
large-sized spheres depending on the temperature and additives [2].
[1] Kim, T.-H., Han, Y.-S. Seong, B.-S. and Hong, K.-P. Soft Matter, 7, 2011, 10070-10075
[2] Kim, T.-H., Han, Y.-S., Jang, J.-D. and Seong, B.-S. Submitted (2013)
ICNS 2013 International Conference on Neutron Scattering