Soft condensates in hard confinement – Structure and molecular mobility

QUICK INFORMATION
Type
Seminar
Start Date
30-01-2020 13:00
End Date
30-01-2020 14:00
Location
Room 337, Central Building
Speaker's name
Mark BUSCH
Speaker's institute
Institute of Materials Physics and Technology at Hamburg University of Technology, Germany
Contact name
Claudine Roméro
Host name
Manfred Burghammer
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The overall topic is the influence of nanoscale spatial confinement on the properties of soft matter – especially on its structure and molecular mobility.

In the first part of the talk, the cation self-diffusion dynamics of the room-temperature ionic liquid 1-N-butylpyridinium bis((trifluoromethyl)sulfonyl)imide ([BuPy][Tf2N]) within the nanopores of carbide-derived carbons of different pore sizes are studied as a function of temperature using quasi-elastic neutron spectroscopy methods. It is shown that already the analysis of data from so-called fixed window scans, which allow a rapid investigation of a large temperature range, while acquiring one energy transfer value only, delivers a quite comprehensive picture of the confinement-induced changes of the cation's molecular dynamics. This is confirmed by the information gained from full spectroscopic data from two instruments with practically complementary dynamic range and resolution. These data reveal the existence of two translational diffusive processes, deviating by around one order of magnitude and obeying an Arrhenius temperature behaviour. Furthermore, the dynamics appear to slow down with decreasing confinement size. The ionic liquid confined in the nanoporous carbon is found to exhibit some molecular mobility already well below the melting point of the bulk liquid, but in contrast there is also a fraction of immobile cations at all investigated temperatures – even far above the bulk melting point.

In the second part, the structure of the chiral liquid crystal 2MBOCBC within the anodic aluminium oxide nanochannels (AAO) is investigated using neutron diffraction. On the transition from the smectic A* to the smectic C* phase the gradual formation of a rotational symmetric chevron-like smectic layer structure of the liquid crystal within these nanochannels is found. This process is fully reversible upon temperature cycling.

Finally, in the third part an outlook is given towards the investigation of the structure of soft matter within individual nanopores. Preliminary results of a respective X-ray diffraction experiment at a nanoprobe beamline are presented.

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