• Korea-Australia Rheology Journal
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• v.20 no.3
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• pp.109-116
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• 2008

The effect of intermolecular aggregation induced by hydrophobic and electrostatic interactions on shear and elongational flow properties of aqueous acrylic thickener solutions is discussed. Complex shear modulus is determined at frequencies up to $10^4$ rad/s employing oscillatory squeeze flow. Extensional flow behavior is characterized using Capillary Break-up Extensional Rheometry. Aqueous solutions of poly(acrylic acid)(PAA)/poly(vinylpyrrolidone-co-vinylimidazole) (PVP-VI) mixtures exhibit unusual rheological properties described here for the first time. Zero-shear viscosity of the mixtures increases with decreasing pH and can exceed that of the pure polymers in solution by more than two orders of magnitude. This is attributed to the formation of complexes induced by electrostatic interactions in the pH range, where both polymers are oppositely charged. PAA/PVP-VI mixtures are compared to the commercial thickener Sterocoll FD (BASF SE), which is a statistical co-polymer including (meth) acrylic acid and ethylacrylate (EA) forming aggregates in solution due to "sticky" contacts among hydrophobic EA-sequences. PAA/PVP-VI complexes are less compact and more deformable than the hydrophobic Sterocoll FD aggregates. Solutions of PAA/PVP-VI exhibit a higher zero-shear viscosity even at lower molecular weight of the aggregates, but are strongly shear-thinning in contrast to the weakly shear-thinning solutions of Sterocoll FD. The higher ratio of characteristic relaxation times in shear and elongation determined for PAA/PVP-VI compared to Sterocoll FD solutions reflects, that the charge-induced complexes provide a much stronger resistance to extensional flow than the aggregates formed by hydrophobic interactions. This is most likely due to a break-up of the latter in extensional flow, while there is no evidence for a break-up of complexes for PAA/PVP-VI mixtures. These flexible aggregates are more suitable for the stabilization of thin filaments in extensional flows.

• Applied Microscopy
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• v.36 no.2
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• pp.131-140
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• 2006

Neurofascin, one of the members of L1CAM, has been known to have some important roles during the development of nerve fibers. In order to investigate the role of neurofascin associated with the myelination of peripheral nerves, the localization of neurofascin in myelinated rat sciatic nerve fibers was studied with the immuno-fluorescence and immune-electron microscopy and the results are as follows; 1. According to the myelination is going on, neurofascin localization was dramatically changed in the sciatic nerve fibers. 2. In the myelinated fibers, neurofascin was weakly localized along the axolemma at the node of Ranvier. 3. Neurofascin was also apparantly localized at the non-compact area of Schwann cell membrane such as paranodal loop, Schmidt-Lantermann incisure, inner & outer mesaxons in the myelinated fibers. From the above results, neurofascin is likely to have a role to sustain the ideal gap of apposing membranes of Schwann cell, so it may enable to materials transport in the myelin sheath.