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《高分子凝聚态结构与性能》作业。请阅读以下一段话，分析纳米粒子填充高分子黏度降低的原因。撰写500字以内的报告。

VISCOSITY REDUCTION OF NANOPARTICLE FILLED POLYMERS  It is a common observation that particle addition produces an increase in viscosity in many systems having particle sizes much larger than molecular size of suspending fluids. Nanoparticles well dispersed in polymer melts have also been shown to anomalously decrease bulk viscosity of entangled polymer, which contradicts to the well-known Einstein theory but is understandable in systems with repulsive particle-polymer interactions [1]. However, the aggregated nanoparticles do not contribute to the viscosity decrease [2]. [3] found that nanoparticles of intramolecular crosslinking of single PS chains reduce the viscosity of high molecular weight linear PS when the interparticle gap is smaller than the linear polymer size and the viscosity reduction scales with the change in free volume.  

[1]          Smith GD, Bedrov D, Li L, Byutner O. J Chem Phys 2002;117:9478-9489.

[2]          Nusser K, Schneider GJ, Pyckhout-Hintzen W, Richter D. Macromolecules 2011;44:7820-7830.

[3]          Mackay ME, Dao TT, Tuteja A, Ho DL, Van Horn B, Kim H-C, Hawker CJ. Nat Mater 2003;2:762-766.