無機材料/嵌段共聚合物P4VP-PCL之混成系統其相行為研究與應用

Phase Behavior of Inorganic/P4VP-PCL Hybrids and Its Applications

林濤(Lin, Tao)

指導教授 ： 何榮銘

國立清華大學/工學院/奈米工程與微系統研究所/博士(2009年)

https://doi.org/10.6843/NTHU.2009.00789

摘要

The hybrids comprising of inorganic and organic functional materials have attracted intensive attention in the past decade because of their tremendous potentials in applications by combining inorganic and organic characters for functions and complexity. In this study, a series of poly ((4-vinylpyridine)-block-ε-caprolactone) diblock copolymers (P4VP-PCL) have been synthesized for hybridization through sequential living ring-opening polymerization and atom transfer radical polymerization. Through the association, such as protonation and coordination, between the nitrogen lone-pair electron of pyridine and the inorganic species, the inorganic/P4VP-PCL hybrids can be simply created. We aim to examine the phase behavior of inorganic/P4VP-PCL hybrids by controlling the factors including the adding amounts of inorganic species, the kinds of inorganic species and the compositions of block copolymers.
Gold ions (Au3+)/P4VP-PCL hybrids were used as a model system for the study on the phase behavior of inorganic/P4VP-PCL hybrids. Consistent to theoretical prediction, phase transformation in the hybrids with PCL-rich P4VP-PCL could be induced by the introduction of the gold precursors. In particular, the phase transformation could be achieved by introducing very small amount of the Au3+ ions because of significant increase in the effective excluded volume of hybridized P4VP microdomain as identified by small angle X-ray scattering (SAXS) experiments through the analysis of one-dimensional correlation function. This morphological evolution is referred to the bridging mechanism, suggesting that the PCL block of the P4VP-PCL in the hybrids might play an important role to blocking the interconnection between hybridized P4VP microdomains. By contrast, disordered morphology was observed in the hybrids with the P4VP-rich P4VP-PCL because of the strong association between the Au3+ ions and the P4VP block that might demolish the ordered phase from microphase separation.
To extend the hybridization to other metal ions, various metal ions including Au3+, Cu2+,Cu+ and Ag+ ions were used. As demonstrated by transmission electron microscopy (TEM), the phase transformation of self-assembled nanostructures can be easily induced by adding small amount of metal ions due to the significant increase of effective excluded volume beside the Ag+ ions. The variation in the effective excluded volume (relevant to the degree of domain swelling as evidenced by the down shifting of small angle X-ray scattering reflections) is strongly dependent upon the association strength of the metal ions with the P4VP block, as determined by the degree of blue shift in the adsorption peak of Fourier transform infrared spectrum corresponding to the characteristic CN stretching vibration of pyridine (that is the increase of binding energy associated with in-plane CN stretching). As observed, the association strength for the formation of the hybrids follows the order of Au3+ > Cu2+ and Cu+ > Ag+. Accordingly, the degree of domain swelling in the hybrids increases with the enhancement of association strength following the order of Au3+ > Cu2+ and Cu+ > Ag+. Furthermore, as demonstrated in the hybrids of Au nanoparticles and P4VP-PCL, a dramatic decrease of the association strength can be found in the hybrids after the reduction of the metal ions. Consistent to the theoretical prediction, the reduction of metal ions lead the alleviation of the binding energy to the pyridine unit such that the association strength for the hybridization can be effectively reduced from ionic state to element state. The association effect is also dependent upon the particle size; the larger the particle size is, the weaker the association will be. Consequently, the accommodation of the metal nanoparticles (NPs) within the P4VP microdomains is justified by the size of the metal NPs.
To demonstrate the potential applications of the inorganic/organic hybrids, both Ag NPs/polymer and Ag nanorods/polymer hybrids were prepared to use as flexible electrodes. Notably, the mechanical properties of the hybrids would be dictated by the polymeric matrix whereas the metal materials could be responsible for the conductivity. The critical issue to achieve the synergetic characters from the metallic and polymeric materials, in particular for the application of flexible electrodes is to build up the interconnecting networks of the metallic materials for conductivity. Nevertheless, the hybridized morphologies indicate that the NPs are difficult to form the conducting paths within the polymer matrix so that no significant conductivity can be achieved. By contrast, conducting paths can be easily formed in the Ag nanorods/polymer hybrids due to the effective interconnection by the long axis of the Ag nanorods. As a result, the conductivity of hybrids may reach the ability of the commercial ITO glass. Although there are still problems with respect to the film formation and the reliability of such flexible electrode, the approach to prepare Ag nanorods/polymer hybrids can provide a convenient and promising way to create new materials by integrating the advanced characters of inorganic and organic materials so as to resolve the problems with respect to electrical failure in metal thin films with tensile deformation and low conductivity of organic conducting polymers. As a result, it is promising to exploit the synergetic properties of Ag NPs/block copolymer hybrids.

關鍵字

混成系統 ； 嵌段共聚合物 ； 相轉換

並列摘要

無資料

並列關鍵字

hybrid system ； block copolymer ； phase transformation

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