TY  - JOUR
A1  - Bekir, Marek
A1  - Sharma, Anjali
A1  - Umlandt, Maren
A1  - Lomadze, Nino
A1  - Santer, Svetlana
T1  - How to make a surface act as a micropump
JF  - Advanced materials interfaces
N2  - In this paper, the phenomenon of light-driven diffusioosmotic (DO) long-range attractive and repulsive interactions between micro-sized objects trapped near a solid wall is investigated. The range of the DO flow extends several times the size of microparticles and can be adjusted to point towards or away from the particle by varying irradiation parameters such as intensity or wavelength of light. The "fuel" of the light-driven DO flow is a photosensitive surfactant which can be photo-isomerized between trans and cis-states. The trans-isomer tends to accumulate at the interface, while the cis-isomer prefers to stay in solution. In combination with a dissimilar photo-isomerization rate at the interface and in bulk, this yields a concentration gradient of the isomers around single particles resulting in local light-driven diffusioosmotic (l-LDDO) flow. Here, the extended analysis of the l-LDDO flow as a function of irradiation parameters by introducing time-dependent development of the concentration excess of isomers near the particle surface is presented. It is also demonstrated that the l-LDDO can be generated at any solid/liquid interface being more pronounced in the case of strongly absorbing material. This phenomenon has plenty of potential applications since it makes any type of surface act as a micropump.
KW  - azobenzene containing surfactant
KW  - light-driven diffusioosmosis
KW  - rate of
KW  - photo-isomerization
Y1  - 2022
U6  - https://doi.org/10.1002/admi.202102395
SN  - 2196-7350
VL  - 9
IS  - 12
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Umlandt, Maren
A1  - Feldmann, David
A1  - Schneck, Emanuel
A1  - Santer, Svetlana
A1  - Bekir, Marek
T1  - Adsorption of photoresponsive surfactants at solid-liquid interfaces
JF  - Langmuir
N2  - We report on the adsorption kinetics of azoben-zene-containing surfactants on solid surfaces of different hydrophobicity. The understanding of this processes is of great importance for many interfacial phenomena that can be actuated and triggered by light, since the surfactant molecules contain a photoresponsive azobenzene group in their hydrophobic tail. Three surfactant types are studied, differing in the spacer connecting the headgroup and the azobenzene unit by between 6 and 10 CH2 groups. Under irradiation with light of a suitable wavelength, the azobenzene undergoes reversible photoisomerization between two states, a nonpolar trans-state and a highly polar cis-state. Consequently, the surfactant molecule changes its hydrophobicity and thus affinity to a surface depending on the photoisomerization state of the azobenzene. The adsorption behavior on hydrophilic (glass) and hydrophobic (TeflonAF) surfaces is analyzed using quartz crystal microbalance with dissipation (QCM-D) and zeta-potential measurements. At equilibrium, the adsorbed surfactant amount is almost twice as large on glass compared to TeflonAF for both isomers. The adsorption rate for the trans-isomers on both surfaces is similar, but the desorption rate of the trans-isomers is faster at the glass-water interface than at the Teflon-water interface. This result demonstrates that the trans-isomers have higher affinity for the glass surface, so the trans-to-cis ratios on glass and TeflonAF are 80/1 and 2/1, respectively, with similar trends for all three surfactant types.
Y1  - 2020
U6  - https://doi.org/10.1021/acs.langmuir.0c02545
SN  - 0743-7463
SN  - 1520-5827
VL  - 36
IS  - 46
SP  - 14009
EP  - 14018
PB  - American Chemical Society
CY  - Washington
ER  -