"以鐵離子/雙氧水雙起始劑系統合成聚(3,4-乙烯二氧噻吩)導電乳膠顆粒及其可撓性透明導電複合材料之製備"

Abstract

在本研究中，我們合成了導電高分子聚(3,4-乙烯二氧噻吩) (PEDOT)奈米乳膠顆粒，並分析其性質。接著將PEDOT乳膠顆粒與高分子材料聚(苯乙烯-丙烯酸丁酯) P(St-BA)結合後，製作出具有可撓性之導電複合膜。另外，我們亦選擇了高導電度之聚(3,4-乙烯二氧噻吩)-聚(苯乙烯磺酸) (PEDOT:PSS)分散液作為導電材料，並與P(S St-BA)結合後，製作出具有可撓性之導電複合膜。 整個研究第一部分，我們使用Fe(OTs)3/H2O2雙起始劑系統進行PEDOT乳膠的化學氧化聚合，以獲得更好的乳液穩定性。整個反應過程隨著Fe(OTs)3與H2O2的先後添加方式，也分成前後兩個反應階段。在雙氧水的幫忙之下，反應後消耗的Fe3+，能夠藉由與雙氧水之間的氧化還原反應，重新被製造出來，持續地參與PEDOT的聚合反應，最後得到較高的單體轉化率。而這個鐵離子與雙氧水之間的反應，即為有名的Fenton反應。幾個實驗變因像是界面劑、鐵氧化劑、與雙氧水三者之間的比例和反應時的溫度都是我們討論的範圍。從粒徑分布的結果來看，室溫合成的PEDOT乳液其圓球顆粒粒徑能小於100奈米。另外，定量的三種不同親水性的溶劑(甲醇、丁醇與甲苯)在反應時跟單體EDOT一起被加到反應瓶中，以觀察溶劑對單體油滴成核之影響。由於單體與有機溶劑在水中溶解度的差異，造成了最後的乳膠顆粒隨著有機溶劑疏水性的增加，逐漸從實心結構轉為空心結構。接著，我們對乳化反應內EDOT單體轉化率進行進一步的鑑定。藉由分析各種反應物與產物的紫外光-可見光光譜，我們建立起一個簡單而且即時的轉化率鑑定方法，能隨時定量地掌握整個合成反應的轉化率隨反應時間而增加的過程。 第一階段合成好的PEDOT導電乳膠顆粒，首次被當成固體界面穩定劑使用在Pickering乳化聚合的過程裡，最後形成核殼型的PEDOT-P(St-BA)複合顆粒。 從穿透式電子顯微鏡與粒徑分析結果發現，隨著油滴內St/BA重量比例的增加，複合顆粒的粒徑從165奈米(St/BA = 1/0)，先增加到270奈米(St/BA = 3/1)，之後又再度變小(St/BA = 1/1)。經過改良合成配方與方法，我們成功地合成出高濃度且顆粒較均勻的PEDOT乳液(HC-PEDOT)，並且以之合成出高濃度(St固含量5 wt.%)的PEODT-PSt複合顆粒。高濃度的PEDOT乳膠顆粒表面的親疏水性質，能夠藉由調整環境pH值與添加電解質FeCl2加以控制，使其能更穩定地吸附在聚苯乙烯顆粒表面。從實驗中我們發現，鐵鹽的添加量與添加時機，對於最終複合顆粒的粒徑分布與外觀有影響。假如較多量的鐵鹽在均質後加入，可以獲得較大顆(7.1微米)與尺寸均一性較佳的複合顆粒。 除此之外，我們也研究並模擬了Pickering乳化聚合過程中，苯乙烯油滴彼此之間融合與分裂的情形。經由把油滴分布切成10種尺寸，我們推導出適合的微分方程式來描述各種尺寸的顆粒數目，隨著反應時間而消長的過程。模擬結果顯示，將每顆不同重量之粒子數目，隨時間變化的情形坐圖，發現粒子粒徑由初始之最小粒徑開始，隨著時間增加而長大，最後到達某時間後維持穩定大小。 在最後一部分，我們分別把PEDOT-PSt顆粒和PEDOT:PSS分散液與軟性P(St-BA)乳液做混合，製備了兩種可撓性透明導電膜。膜導電度的臨界PEDOT與PEDOT:PSS添加量因而獲得。我們另外將PEDOT:PSS導電液成膜於不織布基材，進行材料的可撓性測試。經過100次反覆地折曲後發現，添加軟性材料後的複合導電薄膜，其導電網路在經過撓曲後，尚能夠有效地被保留下來。另外，我們也選用了商用的PEDOT:PSS商品PH500作為界面穩定劑，直接以Pickering乳化聚合法與乳化聚合法合成PEDOT:PSS-PSt顆粒。因為使用了高導電性之PH500商品，配合上軟質材料P(St-BA)，製作出的可撓性PEDOT:PSS-PSt/P(St-BA)複合膜其導電度獲得了大幅度的提升。

In this study, conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) latex nanoparticles was synthesized and characterized, followed by combining it with polymer material poly(styrene-r-butyl acrylate) P(St-BA) to form a flexible conductive composite film.. Moreover, the highly conductive poly(3,4-ethylenedioxythiophene)- poly(styrenesulfonic acid) (PEDOT:PSS) dispersion had been chosen to fabricate the flexible conductive composite film as well. First, the chemical oxidative polymerization of PEDOT latex was carried out by using the Fe(OTs)3/H2O2 bi-oxidant system in the emulsion polymerization of PEDOT latex to obtain better colloidal stability. A two-stage polymerization profile was proposed. With the assistance of H2O2, the reactive Fe3+ ions could be continuously regenerated by via this cyclic oxidation-reduction, Fenton reaction, thus can polymerize the monomer to a very high extent even though the iron salt is deficient stoichiometrically. Several variables such as DBSA/Fe(OTs)3 ratio, Fe(OTs)3/H2O2 ratio, and reaction temperature were investigated. Latex synthesized at RT had smaller particle size than 100 nm was determined from DLS technique and particles with more spherical shape were seen. Three solvents with different hydrophilicity (methanol, butanol, and toluene) were introduced into EDOT oil phase. With increasing the hydrophobicity of solvent, the morphology of particles turned from solid to hollow structure. To determine the conversion of EDOT during the polymerization, we had developed a simple and quick UV-visible spectra method for calculating the conversion of EDOT monomer quantitatively. From the deconvolution of UV-visible spectra curves, the conversion of PEDOT latex could be calculated quantitatively with reaction time. The prepared stable PEDOT latex nanoparticles was then used as the stabilizer in the Pickering emulsion polymerization process to prepare core-shell-like PEDOT-P(St-BA) composite particles. From the TEM and DLS results, these composite particles size would increase from 165 nm (St/BA = 1/0 wt.) to 270 nm (St/BA = 3/1), and then decreased again when St/BA = 1/1. Moreover, PEDOT latex with higher concentration (HC-PEDOT, 1.97 wt.%) were prepared and its interfacial stability was controlled by adjusting the environmental pH value and adding electrolyte FeCl2 salt. Effects of ionic strength and adding timing of salt solution on the size distribution and morphology of oil droplets and HCPEDOT-PSt particles were investigated by the DLS method and SEM. Under the optimal conditions, larger-sized (7.1 μm) and more uniform PEDOT-PSt composite particles with styrene content up to 5 wt.% could be obtained. Besides, the coalescence and breakage of oil droplets in the Pickering emulsion polymerization was studied and simulated. By dividing the droplets size into discrete ten parts, the time evolution of particles number in each size was described by ODEs. Results showed that the major particle size grew from smallest one to larger size as time passed and then kept steadily until the end of simulation when the particle weight change of each particle were plotted with time. In the last part, we had prepared two kinds of flexible conductive films with transparency based on PEDOT-PSt particles, PEDOT:PSS dispersion, and soft P(St-BA) latex. The critical point of PEDOT and the percolation threshold of PEDOT:PSS content in the conductive composite films were obtained. For the PEDOT:PSS/P(St-BA) composite on nonwoven fabric substrate, the elasticity was evaluated by bending 100 times. After introducing the soft material, the formed composite film became more flexible and the conductive network could be preserved after bending. Furthermore, commercial product of PEDOT:PSS was used as stabilizer to synthesize core-shell conductive particles PEDOT:PSS-PSt by Pickering emulsion polymerization and emulsion polymerization. With using excellent conductive material PH500 and soft material P(St-BA), both the conductivity and flexibility of formed PEDOT:PSS-PSt/P(St-BA) composite films had great enhancement.