@article{AntonSteyrleuthnerKossacketal.2015, author = {Anton, Arthur Markus and Steyrleuthner, Robert and Kossack, Wilhelm and Neher, Dieter and Kremer, Friedrich}, title = {Infrared Transition Moment Orientational Analysis on the Structural Organization of the Distinct Molecular Subunits in Thin Layers of a High Mobility n-Type Copolymer}, series = {Journal of the American Chemical Society}, volume = {137}, journal = {Journal of the American Chemical Society}, number = {18}, publisher = {American Chemical Society}, address = {Washington}, issn = {0002-7863}, doi = {10.1021/jacs.5b01755}, pages = {6034 -- 6043}, year = {2015}, abstract = {The IR-based method of infrared transition moment orientational analysis (IR-TMOA) is employed to unravel molecular order in thin layers of the semiconducting polymer poly[N,N'-bis(2-octyldodecyl),-1,4,5,8-naphthalene-diimide-2,6-diyl]-alt-5-5'-(2,2'-bithiophene) (P(NDI2OD-T2)). Structure-specific vibrational bands are analyzed in dependence On polarization and inclination of the sample-With respect to the optical axis. By that the molecular Order parameter tensor for the respective molecular moieties with regard to the sample: coordinate system is deduced. Making use of the specificity of the IR spectral range, we are able to determine separately the orientation of atomistic planes defined through the naphthalenediimide (NDI) and bithiophene (T2) units relative to the substrate, and hence, relative to each other. A pronounced solvent effect is observed While chlorobenzene causes the T2 planes to align preferentially parallel to the substrate at an angle of 29 degrees, using a 1:1 chloronaphthalene:xylene mixture results in a reorientation of the T2 units from a face on into an edge on arrangement. In contrast the NDI unit remains unaffected. Additionally, for both solvents evidence is observed for the aggregation of chains in accord With recently published results obtained by UV-vis absorption spectroscopy.}, language = {en} } @article{HollaenderKossackKolloscheetal.2016, author = {Holl{\"a}nder, Lars and Kossack, Wilhelm and Kollosche, Matthias and Wirges, Werner and Kremer, Friedrich and Gerhard, Reimund}, title = {Influence of the remanent polarisation on the liquid crystal alignment in composite films of ferroelectric poly(vinylidene fluoride-trifluoroethylene) and a cyanobiphenyl-based liquid crystal}, series = {Liquid crystals : an international journal of science and technology}, volume = {43}, journal = {Liquid crystals : an international journal of science and technology}, publisher = {Editions Rodopi BV}, address = {Abingdon}, issn = {0267-8292}, doi = {10.1080/02678292.2016.1185174}, pages = {1514 -- 1521}, year = {2016}, abstract = {Polymer-dispersed liquid crystals (PDLCs) of ferroelectric poly(vinylidene fluoride-trifluoroethylene) and nematic 4-cyano-4\&\#697;-n-hexylbiphenyl (6CB) or 4-cyano-4\&\#697;-n-pentylbiphenyl (5CB) were prepared to study the effect of the remanent polarisation of the polymer on the liquid crystal alignment. We measured the macroscopic alignment of the liquid crystal molecules in the thickness direction by means of Infrared Transition-Moment Orientational Analysis. Electrical poling at 100 V/µm caused an increased order parameter up to 0.15. After subsequent annealing above the nematic-to-isotropic phase-transition temperature, the order parameter was reduced to 0.02. Nevertheless, the order parameter was still higher than for non-poled film indicating a slight orientation in thickness direction. Both values are lower than those expected from model calculations. In agreement with dielectric measurements, we attribute this result to the shielding effect of mobile charge carriers within the liquid crystal inclusions.}, language = {en} } @article{KathreinKipnusuKremeretal.2015, author = {Kathrein, Christine C. and Kipnusu, Wycliffe K. and Kremer, Friedrich and B{\"o}ker, Alexander}, title = {Birefringence Analysis of the Effect of Electric Fields on the Order-Disorder Transition Temperature of Lamellae Forming Block Copolymers}, series = {Macromolecules : a publication of the American Chemical Society}, volume = {48}, journal = {Macromolecules : a publication of the American Chemical Society}, number = {10}, publisher = {American Chemical Society}, address = {Washington}, issn = {0024-9297}, doi = {10.1021/acs.macromol.5b00512}, pages = {3354 -- 3359}, year = {2015}, abstract = {A detailed birefringence analysis of the effect of strong dc electric fields on the order-disorder transition temperature (T-ODT) of lamella forming block copolymers is reported. The setup presented here enabled the measurement of the T-ODT with high temperature resolution while the birefringence measurements were nondestructive and straightforward compared to alternative methods. A downward shift in the transition temperature was found for all samples upon application of the electric field. The data indicate that the dominating parameter that evokes the mixing of block copolymers when exposed to electric fields is the difference in dielectric permittivity Delta epsilon between the block copolymer constituents. The extent to which the T-ODT is shifted is furthermore influenced by the degree of polymerization N. Shifts in the transition temperature of up to 7 degrees C were found upon application of an electric field of 5 kV/mm.}, language = {en} } @article{MeierStumpeFischeretal.1998, author = {Meier, Johann Georg and Stumpe, Joachim and Fischer, Birgit and Thieme, Cathrin and Fischer, Thomas M. and Kremer, Friedrich and {\"O}ge, Tanja and Zentel, Rudolf}, title = {Optical suppression of Ferroelectricity in polysiloxane copolymers with chiral an potochromic side groups}, year = {1998}, language = {en} }