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H. Weiss, H. Cheng, J. Mars, H. Li, C. Merola, F. Renner, V. Honkimaki, M. Valtiner, M. Mezger:
"Structure and Dynamics of Confined Liquids-Challenges and Perspectives for the X-Ray Surface Force Apparatus";
Langmuir, 35, 51 (2019), 16679 - 16692.

The molecular-scale structure and dynamics of confined liquids increasingly gains relevance
for applications in nano-technology. Thus, a detailed knowledge of the structure of confined liquids on
molecular length scales is of great interest for fundamental and applied sciences. To study confined structures
under dynamic conditions, we constructed an in-situ X-ray surface force apparatus (X-SFA). This novel
device can create a precisely controlled slit-pore confinement down to dimensions on the 10 nm scale by
using a cylinder-on-flat geometry for the first time. Complementary structural information can be obtained
by simultaneous force measurements and X-ray scattering experiments. The in-plane structure of liquids
parallel to the slit-pore and density profiles perpendicular to the confining interfaces are studied by X-ray
scattering and reflectivity. The normal load between the opposing interfaces can be modulated to study
the structural dynamics of confined liquids. The confinement gap distance is tracked simultaneously with
nanometer precision by analysing optical interference fringes of equal chromatic order. Relaxation processes
can be studied by driving the system out of equilibrium by shear stress or compression/decompression cycles
of the slit-pore. The capability of the new device is demonstrated on the liquid crystal 4`-octyl-4-cyanobiphenyl
(8CB) in its smectic A (SmA) mesophase. Its molecular-scale structure and orientation confined in
100 nm to 1.7 μm slit-pores was studied under static and dynamic non-equilibrium conditions.

http://dx.doi.org/10.1021/acs.langmuir.9b01215

https://doi.org/10.1021/acs.langmuir.9b01215