This means that the nanoparticles replace a certain percentage of {HEAD ~ the microparticles}, which causes {TAIL ~ a reduction} of the viscosity  
causes
This means that the nanoparticles replace a certain percentage of { HEAD ~ the microparticles } , which causes { TAIL ~ a reduction } of the viscosity
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH