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- 저자 : Dingenouts, N. (검색결과 2 건)
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New developments for the mechanical characterization of materials
N. Dingenouts,M. Wilhelm 한국유변학회 2010 Korea-Australia rheology journal Vol.22 No.4
Rheology as a science of flow of matter is highly influenced by the topology and morphology of the investigated materials, e.g. polymer molecules. Within this publication three current developments will be presented. In the first part, the direct influence of molecular structure on the non-linear mechanical properties and the processing will be presented. In a second part, rheological methods, e.g. elongation rheology or non-linear shear (especially FT-Rheology) are further developed. Finally the combination of rheological measurements with a second characterization method (NMR, X-ray, dielectric spectroscopy etc.) is described. These new combinations gain unique information about molecular dynamic and structure of time and shear dependant phenomena.
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Meins, T.,Hyun, K.,Dingenouts, N.,Fotouhi Ardakani, M.,Struth, B.,Wilhelm, M. American ChemicalSociety 2012 Macromolecules Vol.45 No.1
<P>In-situ flow alignment kinetics of a self-assembled lamellarphasepolystyrene-<I>block</I>-polyisoprene (PS-<I>b</I>-PI, <I>M</I><SUB>w</SUB> = 26 500 g/mol, <I>f</I><SUB>PS</SUB> = 51%) diblock copolymer melt has been investigatedin detail under mechanical large amplitude oscillatory shear (LAOS)utilizing a unique Rheo–SAXS combination developed in cooperationwith the German Electron Synchrotron (DESY) in Hamburg. This marksthe first time that the strain and time dependence of the shear-inducedmacroscopic perpendicular orientation of the lamellar microstructurecould be monitored with a time resolution of 10 s per frame. Two mechanicalparameters were used to compare the structural evolution and dynamicswith the mechanical response of the sample. The mechanical loss modulusG″, which was directly obtained from the in situ Rheo–SAXSexperiments performed with a stress controlled rheometer, and thenonlinear parameter <I>I</I><SUB>3/1</SUB>, which was calculatedby Fourier-transform-rheology (FT-rheology) from the raw stress dataobtained from a strain controlled rheometer. Significant correlationsbetween the mechanical response and the structural changes of thesample were detected. For example, the orientation times τ calculatedfrom both the X-ray and the mechanical measurements showed a powerlaw dependence with τ ∼ γ<SUB>0</SUB><SUP>–1.6</SUP> (in situ SAXS) and ∼ γ<SUB>0</SUB><SUP>–2</SUP> (FT-rheology). Furthermore, the quality of the macroscopic orientationat large shear amplitudes (γ<SUB>0</SUB> = 2 and γ<SUB>0</SUB> = 3) was found to be a function of the mechanical excitationtime. A better macroscopic orientation for shorter mechanical excitationtimes was achieved, while longer experimental times caused an unexpectedreduction in the degree of orientation. In these situations, ex-situSAXS and TEM studies indicated that a stable biaxial distributionof the lamellar microstructure that was preferentially orientatedboth parallel and perpendicular was formed, causing a drastic changein the response of both the mechanical quantities <I>G</I>″(<I>t</I>) and <I>I</I><SUB>3/1</SUB>(<I>t</I>).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2012/mamobx.2012.45.issue-1/ma201492n/production/images/medium/ma-2011-01492n_0020.gif'></P>
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