TY  - JOUR
A1  - Carl, Nico
A1  - Müller, Wenke
A1  - Schweins, Ralf
A1  - Huber, Klaus
T1  - Controlling self-assembly with light and temperature
JF  - Langmuir
N2  - Complexes between the anionic polyelectrolyte sodium polyacrylate (PA) and an oppositely charged divalent azobenzene dye are prepared in aqueous solution. Depending on the ratio between dye and polyelectrolyte stable aggregates with a well-defined spherical shape are observed. Upon exposure of these complexes to UV light, the trans -> cis transition of the azobenzene is excited resulting in a better solubility of the dye and a dissolution of the complexes. The PA chains reassemble into well-defined aggregates when the dye is allowed to relax back into the trans isomer. Varying the temperature during this reformation step has a direct influence on the final size of the aggregates rendering temperature in an efficient way to easily change the size of the self-assemblies. Application of time-resolved small-angle neutron scattering (SANS) to study the structure formation reveals that the cis -> trans isomerization is the rate-limiting step followed by a nucleation and growth process.
Y1  - 2020
U6  - https://doi.org/10.1021/acs.langmuir.9b03040
SN  - 0743-7463
VL  - 36
IS  - 1
SP  - 223
EP  - 231
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Bressel, Katharina
A1  - Müller, Wenke
A1  - Leser, Martin Erwin
A1  - Reich, Oliver
A1  - Hass, Roland
A1  - Wooster, Tim J.
T1  - Depletion-induced flocculation of concentrated emulsions probed by photon density wave spectroscopy
JF  - Langmuir
N2  - Stable, creaming-free oil in water emulsions with high volume fractions of oil (phi = 0.05-0.40, density matched to water) and polysorbate 80 as an emulsifier were characterized without dilution by Photon Density Wave spectroscopy measuring light absorption and scattering behavior, the latter serving as the basis for droplet size distribution analysis. The emulsion with phi = 0.10 was used to investigate flocculation processes induced by xanthan as a semi-flexible linear nonabsorbing polymer. Different time regimes in the development of the reduced scattering coefficient mu(s)' could be identified. First, a rapid, temperature-dependent change in mu(s)' during the depletion process was observed. Second, the further decrease of mu(s)' follows a power law in analogy to a spinodal demixing behavior, as described by the Cahn-Hilliard theory.
Y1  - 2020
U6  - https://doi.org/10.1021/acs.langmuir.9b03642
SN  - 0743-7463
VL  - 36
IS  - 13
SP  - 3504
EP  - 3513
PB  - American Chemical Society
CY  - Washington
ER  -