Refine
Has Fulltext
- no (55)
Year of publication
Document Type
- Article (55) (remove)
Language
- English (55)
Is part of the Bibliography
- yes (55)
Atomic force microscopy inspection of the early state of formation of polymer surface relief grating
(2001)
Dielectric loss spectroscopy (DLS) was performed at compact samples and lamellary organized Langmuir-Blodgett (LB) films from various fatty acid salts. Previous thermoanalytical measurements at compact samples revealed the appearance of two different phase transition temperatures; the lower one is related to the acid the second one to the acid salt molecules. In spite of ill defined electrical contacts with the film the characteristic DLS frequencies obtained from about 100nm thick multilayer films are similar to those recorded from bulk samples. No significant variations of frequencies were found changing the counter ions. Besides conductivity influence at low frequncies we found two relaxations related to the mobility of the dipolar carboxylat-metal group at about 100 and 10000Hz. One of these frequencies is related to the rotation around the chain axis. The strength of this relaxation increases significantly with increasing the sample temperature above 105°C. This temperature is connected with a structural phase transition observed by X-ray reflectometry. In case of Pb-stearate the results of the dielectric measurements help to interprete this structural change as a transition from an orthorhombic into a free-rotator phase. The uncorrelated rotation of molecules around their molecular axes initiates a much increased relaxation strength at the carboxylat-metal sites.
Formation of a buried density grating on thermal erasure of azobenzene polymer surface gratings
(2002)
The glass transition process gets affected in ultrathin films having thickness comparable to the size of the molecules. We observe systematic broadening of the glass transition temperature (T-g) as the thickness of an ultrathin polymer film reduces below the radius of gyration but the change in the average T-g was found to be very small. The existence of reversible negative and positive thermal expansion below and above T-g increased the sensitivity of our thickness measurements performed using energy-dispersive x-ray reflectivity. A simple model of the T-g variation as a function of depth expected from sliding motion could explain the results
Grazing incidence x-ray diffraction (GIXD) measurements of uranyl arachidate (UO2A2) LB films
(1998)
In situ and ex situ SAXS investigation of colloidal sedimentation onto laterally patterned support
(2009)
We report on in situ investigations of colloidal ordering during gravity sedimentation from a colloidal suspension onto a prepatterned support using a polymeric surface relief grating (SRG) as the support. The ordering of colloids with a diameter of 420 nm was investigated by means of grazing-incidence small-angle X-ray scattering (GISAXS) and transmission SAXS using a preparation cell guaranteeing stable temperature and humidity. GISAXS was used for in situ monitoring of the time evolution of colloidal ordering within the whole illuminated sample area. The onset of ordering was indicated by the increase of integrated intensity within a small time frame shortly before complete evaporation of the dispersant. Single domains of coated samples were investigated ex situ by SAXS in transmission geometry where the irradiated sample area was 200 x 200 mu m(2) only. Domains with the typical size of a few millimeters were observed varying in orientation and crystallographic structure for various positions at the sample. They were mainly oriented along the grooves of the grating, confirming the influence of the underlying grating on colloidal ordering.