The Microstructure Of Polymeric Nanocomposites Studied By Positrons

In this dissertation, the microstructure of Polymeric nanocomposites is systematically studied by several technologies (Positron Annihilation Lifetime Spectroscopy, XRD TEM and so on) for two kinds of polymeric nanocomposites (polymer/nanoparticle and polymer/clay nanocomposites). The distribution of the positron lifetime has been obtained by the new computer program-MELT. The main results are as follows.1. PALS measurements were performed for polymer/nanoparticle nanocomposites HDPE/nano-CaCO3 as a function of composition. It is observed that there is strong interaction between CaCO3 nanoparticles and HDPE matrix, which can restrict the main-chain segmental motion and reduce the mobilization of PE chains. The interfacial layers between CaCO3 and HDPE have be detected and play important role to affect the mechanical properties of materials. These results show that positron annihilation is an effective tool to probe the atomic-scale microstructure of polymeric nanocomposite.2. Two kinds of polymer/clay nanocomposites (Polystyrene/Rectorite and Epoxy/Rectorite nanocomposites) have been prepared successfully by dispersing organically modified rectorite. The results of X-ray diffraction and TEM show that the rectorite platelets become fully separated for the low rectorite content. The Epoxy/Rectorite nanocomposite with 0.5% rectorite content exhibits high mechanical performance and thermal stability.3. Positron lifetime spectra were measured for Polystyrene/Rectorite and Epoxy/Rectorite nanocomposites as a function of the rectorite content. We find that o-Ps can form and annihilate between the rectorite silicate layers. In the exfoliated nanocomposite, positronium is mainly formed and annihilate in polymer matrix, the free volume fraction decreases with the increasing rectorite content. The positron annihilation in the rectorite platelets and the interfaces between polymer and rectorite platelets makes the increase of I2.4. The structural transformation of Epoxy (cured by polyamide) and epoxy/Rectorite nanocomposite is studied by PALS as a function of temperaturefrom 30K to 490K. For Epoxy and Epoxy/Rectorite nanocomposite, the glass transition temperature (Tg) is observed to be 270K and 260K, the second transition temperature (Tr) is 160K and 100K, the exclude temperature (Te) is the same as 380K. The result shows that properties of the free-volume in nanocomposite have been changed by the rectorite platelets fully separated in material at low temperature. At the same time, we find that the intensity of o-Ps decreases with increase of the temperature at the softening temperature above the Te.5. The positron lifetime distribution in HDPE/CaCO3, Polystyrene/Rectorite and Epoxy/Rectorite nanocomposites has been obtained by the new computer program-MELT. The main results are as follows.a. The structure of interface between polymer and nanoparticles in the polymer/nanoparticle nanocomposite is more complicated than the interface between polymer and nano-scale platelets in the polymer/clay nanocomposite. It can be explained with that the average diameter of the nanoparticle has a distribution and every rectorite platelet is same as each other.b. The distribution of free-volume-hole size in epoxy and epoxy/rectorite nanocomposites is studied as a function of temperature. It observed that the distribution at low temperature is narrower than it at high temperature. The distribution becomes narrower because of the rectorite platelets separated in the nanocomposites. At the same time, at the Tg, the distribution of the free-volume-hole size has two peaks for the two materials. We consider it is caused by the firming agent-polyamide. The epoxy with different firming agent has been studied to improve our supposition.c. The effect of rectorite platelets to distribution of free-volume-hole size in epoxy and epoxy/rectorite naocomposites has been studied. It observed that the interaction between platelets and polymer matrix bl...