• Korea-Australia Rheology Journal
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• 제20권3호
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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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• 제36권2호
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• pp.131-140
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• 2006

Neurofascin은 L1CAM의 하나로 신경섬유의 발달과정에서 중요한 역할을 하는 것으로 알려져 있다. 말초신경의 수초형성과 관련된 neurofascin의 역할을 알아볼 목적으로 면역형광염색과 면역전자현미경기법을 이용하여 랫드의 수초좌골신경섬유에서 neurofascin의 분포를 추구하여 다음과 같은 결과를 얻었다. 1.수초형성이 진행됨에 따라 좌골신경섬유에서 neurofascin 분포는 매우 심하게 변화되었다. 2. 수초신경섬유에서 neurofascin은 Ranvier마디에서 약하게 국재하였다. 3. Neurofascin은 수초신경섬유의 paranodal loop, Schmidt-Lantermann incisure, 속축삭사이막, 바깥축삭사이막처럼 Schwann세포의 막이 밀착되지 않은 부위에서도 뚜렷하게 국재하였다. 이상의 연구결과로 neurofascin은 Schwann세포의 마주보는 막사이에 이상적인 간격을 유지하는데 어떤 역할을 하는 것으로 생각되며, 수초층에서 물질이동이 가능하게 하는 것으로 보인다.