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DS: Fachverband Dünne Schichten
DS 1: Optical Analysis of Thin Films I (Reflection, Ellipsometry, Raman, IR-DUV Spectroscopy, ...
DS 1.5: Vortrag
Montag, 1. April 2019, 11:00–11:15, H32
Temperature induced changes in monolayers observed by sum frequency generation spectroscopy — •Damian Firla, Robert Rameker, Joshua Multhaup, and Eckart Hasselbrink — Universität Duisburg-Essen, Universitätsstr. 5, 45141 Essen, Germany
A major component in cell membranes are phospholipids which form bilayers. The amphiphilic character of phospholipids was exploited to spread a solution on water in a Langmuir trough. This monolayer was compressed, transfered on a substrate and studied by sum frequency generatation spectroscopy. The main goal was to observe changes upon raising the temperature. Typically conformational changes of alkyl chains from all-trans to a conformation with gauche defects were observed as recognized by the change of the intensities of the CH3 and CH2 vibrational modes. Different types of phospholipids and mixtures of phospholipids with varying chain lengts were studied. Investigations of single phospholipid species showed that the intensity of CH3 vibrational modes decreased with rising the temperature whereas the intensity of the CH2 symmetrical stretching mode was not increasing. This was attributed to the high density of such monolayers, in which conformational changes were not possible because of strong van der Waals interactions. Further on mixtures of phospholipids with different chain lenghs were used. In these studies the symmetrical stretching mode of CH2 was observed as well, consistent with the larger space for conformational changes. The thermal stability of phopholipid monolayers was also probed. Results showed that monolayers of single phospholipid species were more stable than monolayers of phospholipid mixtures.