Title: Structure and Dynamics of Confined Liquids: Challenges and Perspectives for the X-ray Surface Forces Apparatus
Authors: Weiss, Henning 
Cheng, Hsiu-Wei 
Mars, Julian 
Li, Hailong 
Merola, Claudia 
Renner, Frank Uwe 
Honkimäki, Veijo  
Valtiner, Markus 
Mezger, Markus  
Issue Date: 2-May-2019
Weiss, H., Cheng, H.-W., Mars, J., Li, H., Merola, C., Renner, F. U., Honkimäki, V., Valtiner, M., & Mezger, M. (2019). Structure and Dynamics of Confined Liquids: Challenges and Perspectives for the X-ray Surface Forces Apparatus. https://doi.org/10.34726/1486
The molecular-scale structure and dynamics of confined liquids has increasingly gained relevance for applications in nanotechnology. 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 forces 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 analyzing 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-cyano-biphenyl (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 nonequilibrium conditions.
Keywords: SFA; synchrotron radiation; confinement; X-SFA
DOI: 10.34726/1486
URI: http://hdl.handle.net/20.500.12708/18450
Organisation: E134-02 - Forschungsbereich Applied Interface Physics 
License: CC BY-NC-ND 4.0 CC BY-NC-ND 4.0
Publication Type: Preprint
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