利用乳化聚合法合成導電奈米核殼乳膠顆粒及其性質研究

Abstract

聚(3,4-二氧乙基噻吩)：磺酸化之聚苯乙烯(PEDOT：PSS)為已商品化之導電高分子乳膠顆粒，此材料具有良好之加工性質，因此可製備成導電薄膜與添加劑。但由於PEDOT：PSS之薄膜導電度仍遠低於其純導電高分子PEDOT之導電度，因此開發同時具備塗佈加工性質與高導電度之PEDOT乳膠顆粒為本研究之目標。 本研究利用具備導電性質的側鏈磺酸化之聚噻吩(SPT) 水溶性導電高分子(導電度約10-2 S/cm)取代無導電性質的磺酸化之聚苯乙烯(PSS)，以乳化聚合方法來合成高導電度之PEDOT：SPT奈米乳膠顆粒。本研究中SPT具備有多重功能，第一可做乳化聚合之界面活性劑，第二作為增加PEDOT導電度之摻雜劑(dopant)，第三所合成出之PEDOT：SPT為核殼同時具備導電性質之乳膠顆粒。 本研究探討不同分子量之SPT，在不同添加量下對PEDOT奈米乳膠顆粒的形態、結構、導電性質與熱性質之影響。利用TEM觀察其形態，隨著SPT添加量的增加，PEDOT:SPT乳膠顆粒形態會逐漸成圓球形，而粒徑也隨之縮小，最後達到顆粒約為50 nm~100 nm。實驗發現，添加低分子量SPT對乳膠聚合具較佳界面活性劑效果，在添加少量時，乳膠顆粒已轉變為圓球狀且顆粒變小；而添加高分子量SPT，需添加較多量才顯現的出其形態轉變圓球形與較小顆粒之效果。利用XRD分析其結晶排列性與堆疊面間距之變化，無論添加高、低分子量SPT均會增進PEDOT結晶性，在添加某一定量時，高分子量SPT摻雜PEDOT，促使PEDOT結構產生較多共平面，結構有較多硬桿(rod)形態相對地減少柔曲(coil)的形態，(020)晶格間距因而縮短。添加低分子量之SPT使其乳膠顆粒最佳導電度比未添加任何界面劑所合成的PEDOT提高了約4倍，而添加高分子量之SPT則提高了約3倍。添加高、低分子量之SPT均會使乳膠顆粒的UV-Vis最大吸收有紅移之現象。利用TGA分析其熱性質，添加高、低分子量之SPT均會使聚合出較高分子量之PEDOT，隨著添加量的增加，其效果越明顯，耐熱性亦跟著提升，整體熱性質變佳。而添加低分子量之SPT所達到提升熱性質的效果較好。FT-IR觀察聚PEDOT的qunoid官能基之扭曲振動行為，添加高、低分子量之SPT均會影響PEDOT的qunoid官能基之扭曲振動，隨著添加量之增加，會增加其扭曲振動之困難度。而在少量之添加量時，高分子量之SPT所造成其振動之難度會較為顯著。XPS推測SPT摻雜PEDOT的程度，隨著添加量之增加，高、低分子量之SPT均會使其增加摻雜程度，SPT摻雜程度的增加對導電度會有提升之作用。

Poly(3,4-ethylenedioxythiophene) : polystyrene sulfonic acid (PEDOT:PSS) is a widely used conductive aqueous latex dispersion synthesized by using emulsion polymerization. In order to further enhance its conductivity we propose to replace the nonconductive PSS with conductive poly[2-(3thienyl)-ethoxy-4-butylsulfonate] (SPT) as the surfactant for the PEDOT emulsion polymerization. The effect of the molecular weight and the amount of SPT in PEDOT:SPT on the electrical property, thermal property, crystal structure and the morphology of the core-shell latex are thoroughly studied using the four-point probe measurement, XPS, TGA, XRD and TEM. Smaller and spherical core-shell PEDOT:SPT nanoparticles with diameter <100nm can be synthesized with increasing amount of SPT added during the emulsion polymerization. TGA measurement shows that the thermal degradation temperature of latex increases considerably with increasing amount of SPT which indicates an increase in the molecular weight of PEDOT synthesized. XPS and FTIR measurements show an increased level of doping on PEDOT with increasing amount of SPT. The substantial increase in the conductivity of PEDOT:SPT film is attributed mainly to the combined effect of higher molecular weight and the doping level of PEDOT synthesized. Lower molecular weight SPT is shown to synthesize higher molecular weight PEDOT of which a higher conductivity is measured.