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Crostack H.-A. Nellesen J. Fischer G. Hofmann M. Rademacher H.-G. Tillmann W. 《Experimental Mechanics》2012,52(7):917-932
The formation of crack patterns in drying starch-water slurries is studied by means of in-situ radiography (measuring of the crack front velocity) and X-ray microtomography as an example of crack patterns driven by inhomogeneous shrinkage. The tomograms show the 3D crack networks forming columns with polygonal cross-sections. After crack initiation, the average crack spacing increases with growing depth, even if the crack front velocity is constant. A constant velocity is obtained by maintaining a constant evaporation rate using a feedback control. When the crack front has propagated at a constant evaporation rate over a distance of some millimeters, the average crack spacing approaches a stable value which depends on crack front velocity according to a power law. This relationship is compared to corresponding results of other authors and model predictions. The increase of crack spacing before stable values are achieved, is interpreted as a result of successive crack front instabilities. 相似文献
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Klärner FG Kahlert B Nellesen A Zienau J Ochsenfeld C Schrader T 《Journal of the American Chemical Society》2006,128(14):4831-4841
The newly prepared water-soluble naphthalene tweezer 2a and anthracene clip 4a (substituted both with lithium methanephosphonate groups in the central spacer unit) undergo an unexpected self-assembly in aqueous solution. The highly ordered intertwined structures of the self-assembled dimers [2a]2 and [4a]2 were elucidated by quantum chemical 1H NMR shift calculations. 2a and 4a form extremely stable host-guest complexes with N-methylnicotinamide 8 in methanol and water as well. According to the thermodynamic parameters determined by 1H NMR titration experiments at various temperatures the self-assembly of 2a and 4a and their strong binding to NMNA 8 observed in aqueous solution are enthalpy driven (DeltaH < 0); the enthalpic driving force is partially compensated by an unfavorable entropy (TDeltaS < 0). Self-assembly and the host-guest binding are therefore beautiful examples of the nonclassical hydrophobic effect. 相似文献
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