Freitag vormittags Vorträge - Bunsentagung - Technische Universität ...

Freitag 21.05.2004, 17:30 Uhr
Vortrag - Grenzflächen
Spectroscopic Studies on Interphases:
Conformational Order and Dynamics
Gokulakrishnan Srinivasan , , Klaus Müller
Institut für Physikalische Chemie, Universität Stuttgart,
Pfaffenwaldring 55, D-70569 Stuttgart,
k.mueller@ipc.uni-stuttgart.de, 0711-6854470
D
37
Chemically modified inorganic metal oxides are widely used
stationary phase materials in gas and reverse-phase liquid chromatography
for well over a decade. The conformational features
and dynamics of the tethered n-alkyl chain segments
(CnH2n+1, n= 9 to 30) play an important role in determining
the efficiency and selectivity of separations. In order to enhance
the retention mechanisms for the chromatographic separations,
the understanding of the stationary phase behaviour on a molecular
level under various conditions is crucial.
The conformational order of the different stationary phase materials
is examined by variable temperature FTIR spectroscopy,
where several conformation sensitive vibration bands can
be analysed. In the present work, the CH2, CD2 symmetric and
anti-symmetric stretching modes, CH2 wagging bands as well
as CD2 rocking bands are analysed. Solid-state 2 H NMR and
13 C CP/MAS methods are used for the investigation of the dynamical
processes and conformational order in the specifically
deuterated and non-deuterated samples, respectively.
The impact of the sample preparation method, i.e., drop-cast
films (method I) and KBr pellets (method II), on the alkyl chain
properties is investigated. It is found that the systems prepared
by the method I have more conformational disorder as compared
to those from method II where the samples were prepared
with high external pressure. 1 The effect of different solid supports
(silica, zirconia and titania) bearing C30 self-assembled
monolayers (SAMs) on the conformational order of the alkyl
chains is examined, and the results showed that the solid substrate
plays a vital role for the actual conformational state of
the attached alkyl chains. 2 Recent results from FTIR and solid
state 2 H NMR investigations on the effect of the bonding
density on C30 alkyl modified silica gels and the influence of
solvents on the specifically deuterated n-alkyl modified silica
gels of various lengths are investigated as well.
References
1] G. Srinivasan, S. Neumann-Singh and K. Müller, manuscript
submitted. 2] G. Srinivasan, M. Pursch, L. C. Sander and K.
Müller, Langmuir, in press.