Fabrication And Manipulation The Fluorescent Properties Of Ⅱ-Ⅵ Semiconductor Nanocrystals-Polymer Nanostructure

In recent years, fabrication of polymer-based nanocomposites through incorporating preformed nanoparticles (NPs) with polymers has attracted great interests owning to the excellent performances of these nanocomposites in a vast range of applications, for instance, optical displays, nonlinear optical devices, and biological encoding. In this regard, polymers play a key role to maintain the chemical and physical stability of NPs in the resulting nanocomposites, because of the relative inertness of polymer materials. Although a variety of techniques have been developed for embedding preformed NPs into polymer media to preserve the functionalities of NPs, the evolution of NP functionalities in the resulting nanocomposites was less investigated, which is important for the long term maintenance of the functionalities or an inverse functional modulation of nanocomposites. Here in my thesis, to solve the current problems of fabricating NP-polymer nanocomposites, the investigations were divided into two parts: on one hand, we developed a new method of constructing fluorescent NP-polymer rods; on the other hand, we analyzed the growth trends of semiconductor nanocrystals (NCs) under annealing in polymer media.In Chapter One, we introduced some basic information of semiconductor NCs. As nano-sized NPs, they processed distinct properties from bulk semiconductor. The most outstanding one is that as the band gap of NCs changes, the emitted fluorescent colors are varying correspondingly. At the beginning of this chapter, we explained the causes of such a magic phenomenon by specializing several models of quantum size effect. In the following parts, we introduced the progresses of synthesizing semiconductor NCs and fabricating NC based nanocomposites. At the end of Chapter One, we enumerated detailed problems we solved in this thesis. In Chapter Two, we fabricated fluorescent NP-polymer rods based on semiconductor NCs and PLA&PS mixture. Firstly, we conbined the solution of PLA, PS and NCs and developed them into fibers by electrospinning; secondly, we put these fibers into basic solutions for a period of time; finally, we obtained the ideal structures we desired. Moreover, to investigate the influences on these structures, we varied the etching time, the annealing temperatures of fibers, and the concetrations of the basic solutions.In Chapter Three, the growth of semiconductor NCs in polymer media was investigated. It was found that the growth trend was dependent on two aspects; OR growth and dynamic coalescence. By examining the growth of NCs in different polymer hosts, it could be concluded that the dynamic coalescence was significantly influenced by the annealing temperatures, the repeating units, and the molecular architectures of polymers. According to the free volume theories, a higher Tg, Mn, or crosslinking degree restrained the mobility of NCs and polymer chains, thus suppressing the dynamic coalescence of NCs. Meanwhile, the existence of interactions between NCs and polymer media greatly influenced the growth of NCs; a poor compatibility between NCs and polymers promoted the dynamic coalescence of NCs. These results revealed that the growth rate of NCs could be deliberately controlled by tuning the species of polymer media, thus provided a new protocol to prepare NCs and/or tune their functionalities in the preformed nanocomposites.