經由原位溶膠-凝膠法製備 高分子/二氧化鈦混成材料與其特性分析

Abstract

摘 要

在本研究中，利用in-situ sol-gel的方式，合成不同功能性的有機高分子/無機奈米顆粒混成材料。如果所選用的有機高分子、無機金屬烷氧化合物，以及溶劑間有一定的作用力，再配合適當的反應劑量，則所合成之有機/無機混成材料將有最佳之混成效果。本研究所選用之有機高分子為poly acrylic acid (PAA)和 poly[2-methoxy-5-(2’-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV)，奈米無機顆粒為TiO2，溶劑則分別為丁醇與氯酚。依偱探討高分子與無機顆粒間的作用力，無機顆粒與溶劑間的作用力，以及三者之間的作用力，將本論文內容分為三個部份。 第一部份開始探討有機高分子與無機奈米顆粒間的作用力。在此部份選用PAA與TiO2作為研究有機高分子與無機顆粒間的作用力對合成穩定懸浮的混成材料之影響。分別以PAA比titanium isopropoxide先溶解或後溶解此兩種不同的合成方式來製備混成材料。此兩種不同的合成方式將會有先相分離或先凝膠化之不同現象，但最後均可得到穩定懸浮的混成溶液。另外再以不同的PAA/titanium isopropoxide(TIP)/H2O三者間的反應劑量為變因，來探討對於螫合效率、螫合程度以及TiO2顆粒形狀的影響。由FTIR中可得知PAA與TIP間有螫合鍵的產生。從TGA中可得知隨著PAA比上TIP的莫耳比增加，PAA與TiO2間的螫合程度也會隨著增加。從DSC中PAA的Tg點消失可得知PAA與TiO2間有強的作用力，因而限制了PAA的熱運動。最後從SEM中顯示PAA/titanium isopropoxide(TIP)/H2O三者間的莫耳比明顯的影響PAA-TiO2此聚集體(aggregate)的顆粒大小與形狀。如隨著PAA比上TIP的莫耳比增加，聚集的程度會下降，也就是聚集體會變小。而且在PAA比titanium isopropoxide後溶解的此合成方法中，如果額外加水，將可得到棒狀的聚集體。 接著則以SEM的實驗結果為基礎，嘗試利用理論來模擬TiO2在高分子螫合的情況下，所進行之顆粒的成長與凝聚的現象。由於鈦烷氧化合物的水解縮合速率太快，實驗中很難測得速率常數。因此以文獻中對SiO2所測得之水解與縮合速率常數為基礎，配合文獻中所查得之所有TiO2可能的化學反應式，再經過合理的假設與忽略，提出一系列完整的、適當的速率方程式與速率常數。根據此新提出的水解-縮合動力模型，H2O, Ti-OR, Ti-OH, Ti-O-Ti等反應物與產物的濃度對時間的變化將可計算得出。最後合理的提出顆粒數目與顆粒大小的成長方程式，由顆粒數目在不同螫合程度的變化情形顯示，隨著螫合程度的增加，顆粒數目亦增加，同時，隨著顆粒數目的增加，伴隨著顆粒大小的下降。由此新提出的動力模型所得之計算結果與從SEM中所得之實驗結果，相當的吻合。 在第二部份中，改為探討不同極性、不同內聚能的溶劑對TiO2的成長與穩定性的影響。這部份主要探討無機顆粒(TiO2)與溶劑間的作用力。首先嘗試純的TIP在不同溶劑中的水解縮合反應。結果在所選用的溶劑中，全部得到不穩定的、沉澱的TiO2顆粒。因此改由先經過acetyl acetone (acac)螫合過的TIP為反應起始物，溶在所選用的不同溶劑中後，再緩慢加水進行水解縮合反應。結果在不同化學特性的溶劑中得到不同穩定程度的TiO2懸浮液。從THF, acetone,與1-butanol等溶劑中可得到澄清的、穩定的TiO2懸浮液；從chloroform中得到混濁的、穩定的TiO2懸浮液；從toluene與hexane中得到沉澱的TiO2懸浮液。接著利用Hansen Solubility Papameter (HSP)來對此一結果作理論的解釋，並可估算出acetyl acetone modified TiO2的HSP。最後以此估算出的HSP可做出一關係圖來預測其他的溶劑是否適合用作合成穩定懸浮的TiO2溶液。 第三部份結合第一部份與第二部份的結果，既希望有機高分子與無機TiO2顆粒間有作用力，而且要降低TiO2的反應速率。因此選用具有多餘電子對的MEH-PPV(氧原子)來與具有空電子軌域的鈦烷氧化合物(d orbital of Ti)產生作用力。同時選用2-chlorophenol(2-CP)來與TIP進行錯合物反應以降低其反應速率。而且因為2-CP是一種芳香族溶劑(aromatic solvent)，又同時可以幫助MEH-PPV在成膜時的排列有較好的電子特性。在此部份，將針對三個主題進行討論。在第一和第二的主題中，探討在不同的MEH-PPV/TIP/H2O/2-chlorophenol之間的重量比以及不同的MEH-PPV分子量的情況之下，對於MEH-PPV/titania(TIP)混成材料的光學與物理性質的影響。從MEH-PPV的凝膠化、FTIR、以及XPS的量測結果得知，MEH-PPV與TIP之間確有作用力的存在。從UV-vis吸收光譜的結果得知，TIP的添加會降低MEH-PPV的共軛長度。從溶液態的PL的結果顯示幾乎所有的混成材料都會因為聚集而有紅位移的現象。但是經過旋轉塗佈後，MEH-PPV的聚集會因為離心力的破壞或者TiO2(TIP)的打散而降低。所以在固態的PL結果顯示混成材料反而都有藍位移的現象。從XRD的結果得到，如果TIP轉換成TiO2的效率愈高，晶形會愈明顯。從MEH-PPV/titania(TIP)混成材料的熱裂解行為變成單一曲線得知，titania(TIP)與MEH-PPV之間有好的相容性。從SEM的結果顯示不同重量比的MEH-PPV/TIP/H2O/2-CP與不同分子量的MEH-PPV對MEH-PPV/titania(TIP)混成溶液的顆粒分佈及穩定與否有明顯的影響。經一系列的實驗結果得知，如果反應條件在4當量莫耳的水量與5 mg/ml的濃度之下，MEH-PPV的分子量在600,000與50,000之間，TIP的重量百分比可高達89%，仍可得到均勻、穩定的MEH-PPV/titania(TIP)混成溶液。 第三個主題則針對混成材料的後處理來討論。我們選用退火處理(annealing)來作為我們材料的後處理。除了調整適當的組成比例來合成穩定的MEH-PPV/titania(TIP)混成溶液之外，亦可利用退火程序來使均勻分佈的MEH-PPV/TIP薄膜轉化成有用的MEH-PPV/titania薄膜。從UV-vis吸收光譜的藍移得知，在2300C、 1小時的退火處理下，可能導致MEH-PPV的部份斷鏈及鏈的捲曲，使得共軛長度被降低。但同時，此退火處理也促進MEH-PPV鏈的運動而增加一些比較低能階的鏈結構產生。此低能階的產生促使吸光的能量從高能階轉移到此低能階，接著放出紅光，所以導致PL的紅移。

Abstract In this research, various functional organic polymer/nano-sized inorganic particle hybrids were prepared via in-situ sol-gel reaction. The hybrid would have best mutuality, and then optimal performance, if the synthesis was operated in a suitable recipe and there were interactions among organic, inorganic and solvent. In this study, poly [2-methoxy-5-(2’-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) and poly(acrylic acid) (PAA) were chosen as organic polymer components, TiO2 was chosen as inorganic component, and 2-chlorophenol and 1-butanol were utilized as solvent for the MEH-PPV and PAA system, respectively. There are three major parts in this dissertation. In the first part, nanosize-hybrid colloids of poly(acrylic acid) (PAA)-titania (TiO2) were synthesized based on an in-situ sol-gel technique using titanium isopropoxide (TIP) as precursor in the butanol solution of PAA. Two synthetic pathways to the fabrication of hybrids were utilized, involving adding titanium precursor after or before the PAA was fully dissolved. Different phenomena of phase separation and gelation were observed in these two synthetic pathways, but both yielded stable colloidal solutions after further heating. Various molar ratios of PAA/titanium isopropoxide/water and synthetic routes were employed to examine the interaction between PAA and titania. The hybrid materials were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electronic microscopy (SEM). The FTIR results verified the successful formation of the chelation bond between PAA and titania. TGA demonstrated that the thermal stability of pure PAA was improved by chelating with titania. DSC showed that the PAA strongly interacted with titania, leading to the confinement of the thermal motion of PAA chains. The SEM results revealed that the preparation method and the molar ratios of PAA/titanium precursor/water considerably affected the size and shape of PAA-titania hybrid aggregates, and the extent of aggregation. As the molar ratio of PAA to TIP increased, the extent of aggregation would decrease. Moreover, if the preparation method was carried out under the adding of TIP before the PAA was fully dissolved, and then nanorod-like titania could be synthesized by adding additional water. According to the result of SEM photographs, the size of hybrid aggregates would be smaller as increasing the molar ratio of PAA to titania because the higher amount of PAA would decrease the extent of aggregation and inhibit the growth of titania. A new sol-gel kinetic model for partially chelated titanium alkoxide by PAA was proposed. Since the reaction rate of hydrolysis and condensation of titanium alkoxide was too fast to get the rate constant from experimental measurement, the proposed rate equations and rate constants in this part were based on the rate constants of silica and all discussed chemical reaction of titanium alkoxide from literatures, and then some reasonable assumptions and neglects were made to obtain the complete and appropriate rate equations and rate constants. Based on this sol-gel kinetic model that considered the effect of chelation, the concentration of water, Ti-OR, Ti-OH, and (Ti-O)-Ti bonds during sol-gel reaction could be calculated. The variation of number of particles at different degree of chelation showed that the particle number increased with increasing the degree of chelation. Finally, the size of hybrid aggregates at different degrees of chelation could be qualitatively described; thus, higher degree of chelation resulted in lower size of hybrid aggregates. The simulated results from this model were in agreement with the observation from SEM photographs. In the second part, the influence of polarity and cohesive energy of solvents on the interaction between inorganic particles and solvents in the synthesis of stable TiO2 colloid was investigated. Because TIP must be chelated before sol-gel reaction to obtain a stable TiO2 colloid for all selected solvents, the starting material of TIP was choosen to be acetyl acetone (acac) chelated; then, the sol-gel reaction proceeded in different selected solvents after slowly adding water. In this part, the selected solvents were tetrahydrofuran (THF), acetone, 1-butanol, chloroform, toluene and hexane. A clear and stable TiO2 colloid could be obtained from THF, acetone and 1-butanol; turbid but stable from chloroform; precipitated from toluene and hexane. The solvent effect on the colloidal particle size and stability were explained according to Hansen Solubility Parameters (HSP). Finally, the Hansen Solubility Parameters of acetyl acetone modified TiO2 were estimated and a useful correlation chart could be plotted to predict the other suitable solvents for the synthesis of stable TiO2 colloid. In the third part, homogenous organic (MEH-PPV)/inorganic (nanosized titania) hybrids were successfully synthesized via a one-step in-situ sol-gel technique using TIP as precursor. Interactions among titanium isopropoxide, 2-chlorophenol and MEH-PPV were identified to be one of the key points for decreasing the degree of aggregation and phase separation in hybrids. Moreover, the solvent, 2-chlorophenol, was benefit for the electrical property of MEH-PPV film because it was an aromatic solvent. In this part, three subjects were in discussion. First and second, various weight ratios of MEH-PPV/TIP/H2O/2-chlorophenol with different molecular weight of MEH-PPV were employed to examine the optical and physical properties of MEH-PPV/TIP(titania) hybrid. The observation of MEH-PPV gelation, FTIR and XPS results verified that the interaction existed in MEH-PPV and TIP. UV-vis absorption showed that the addition of TIP would decrease the conjugation length of MEH-PPV. Photoluminescence (PL) revealed that almost all hybrids had red-shift in solution state owing to the aggregation of MEH-PPV. But after spinning, the aggregation of MEH-PPV would be destroyed and separated by the centrifugal force. The XRD measurement exhibited that if the conversion efficiency of TIP to titania was higher, the crystal patterns were clearer. The TGA results indicated that the TIP(titania) had well mutuality with MEH-PPV from the thermal degradation behavior of hybrids became a single characteristic curve. The SEM results revealed that the weight ratios of MEH-PPV/TIP/H2O/2-chlorophenol and molecular weight of MEH-PPV considerably affected the morphology of MEH-PPV/TIP(titania) hybrid aggregates. In the condition of 4 equivalent moles ratio of water and 5 mg/ml concentration, the amount of TIP could be as higher as 89 wt% and still had homogenous MEH-PPV/TIP(titania) hybrid, whatever molecular weight of MEH-PPV was 600,000 or 50,000. Except for the adjustment of composition, the annealing treatment could be also helpful for the preparation of a homogenous MEH-PPV/titania film by the conversion of MEH-PPV/TIP film to MEH-PPV/titania film. So, in the third subject, the effects of annealing treatment on the optical properties and morphology of synthesized hybrid film were also investigated. Blue shift in UV-vis absorption was observed after annealing treatment at 2300C for 1 hr. It was because higher temperature and time of annealing treatment would give rise to the thermal decomposition and a coil-like structure of MEH-PPV chain. In contrast, the annealing treatment would promote the movement and migration of MEH-PPV chains and induce the chains to pack into a low-energy structure, thus lowering the energy band-gap and red-shifting the PL emission of hybrids after annealing treatment.