- 學位論文
混合溶劑效應對MEH-PPV共軛高分子溶液之分子運動及凝膠機理的研究
Effects of the cosolvent on the molecules mobility and gelation mechanism of MEH-PPV conjugate polymer in solutions
摘要
本論文利用靜態光散射、動態光散射、UV-vis吸收光譜以及PL光激發光光譜進行一系列濃度效應、混合溶劑效應、老化時間及溫度效應對MEH-PPV/toluene/nonane溶液中的聚集行為及其光物理性質影響的研究，本研究結果獲得以下的結論： 由濃度效應得知MEH-PPV/Toluene/Nonane在不同混合溶劑條件下，散射光強度隨濃度增加而增加，並且發現當濃度小於0.016mg/mL時散射強度相當小並呈現MEH-PPV共軛高分子側鏈及MEH-PPV共軛高分子單一分子鏈的緩和運動時間，相對的當濃度高於0.16mg/mL時散射強度明顯增加並且形成MEH-PPV共軛高分子聚集結構的緩和運動行為。並由UV-vis吸收光譜以及PL光激發光光譜圖發現當溶液的濃度增加，在約480nm(UV-vis吸收光譜) 以及 550~570nm(PL光激發光光譜)之0-0單重態能量轉移光激發光峰呈現些微的往長波長方向偏移(紅移)。相對的隨不良溶劑(nonane)含量的增加，在PL光譜中580~610nm波長之0-1單重態能量轉移的光激發光強度明顯的增加，這可能是由於不良溶劑(nonane)的含量增加，促使MEH-PPV共軛高分子之間的接觸機率並誘導MEH-PPV共軛高分子間形成些微的π-π作用力的聚集結構所導致。 在靜態光散射實驗中得知當溫度在20±0.1oC條件下，MEH-PPV/Toluene/ nonane混合稀薄溶液的Zimm 圖在較高濃度有偏離直線現象意味溶液中有少量的聚集結構。另一方面，溫度在50±0.1oC條件下MEH-PPV/Toluene/nonane混合稀薄溶液的Zimm 圖則呈現一直線行為，且MEH-PPV共軛高分子在100/0vol%以及70/30vol%混合稀薄溶液A2 值分別為1.778×10-5以及1.113×10-5mol dm/g；相對的Rg 值分別為78.0以及65.8nm以及MEH-PPV共軛高分子的分子量分別為2.428×106以及1.344×106 g/mol。最後利用 Kratky-Perod 方程式推算出MEH-PPV共軛高分子的持續長度lps， MEH-PPV共軛高分子的單元分子量和單元長分別為260g/mol 和 0.67nm。因此根據Kratky-Perod 方程式MEH-PPV分子鏈在50±0.1oC以及 100/0vol%以及70/30vol%混合稀薄溶液的持續長度lps分別為5.24和3.68nm，相對的Kuhn鏈結長 lk (lk = 2lps) 分別為 10.48nm 及 7.36nm；以及Kuhn鏈結數分別為1329 及 1871。由實驗中得知在較高溫度及較優良溶液中，MEH-PPV共軛高分子的尺寸將會形成更伸展的形態。最後在20±0.1oC條件下，本實驗我們推算MEH-PPV共軛高分子在100/0vol%以及70/30vol% Toluene/nonane混合稀薄溶液中的重疊濃度分別為0.103和0.135mg/mL。 在老化時間效應中發現，在良溶劑條件下條件下(100/0及90/10vol%)，可清楚發現MEH-PPV/Toluene/nonane 溶液之散射強度隨老化時間之增加幾乎不變。相對的，在較不良溶劑條件下(80/20及70/30vol%)，MEH-PPV/Toluene/nonane 溶液之散射強度隨老化時間之增加呈現些微的增加。這是因為不良溶劑含量的增加，將會導致MEH-PPV共軛高分子鏈與甲苯之間的溶解力逐漸下降，相對的促進MEH-PPV共軛高分子鏈之間的結合因此形成較明顯的聚集結構。並促使MEH-PPV共軛高分子鏈之間的聚集結合而形成三次元的網狀結構的凝膠。 最後在溫度效應中得知在良溶劑性質中隨著溫度的增加，聚集結構有慢慢的瓦解的趨勢，但當溫度高達90oC時MEH-PPV/Toluene/nonane 混合溶液中的聚集結構也尚未完全的瓦解，意味MEH-PPV/Toluene/nonane 混合溶液中的聚集結構內部也具有兩種聚集作用力；其中不可被溫度所瓦解的作用力可能是共軛高分子側鏈之間利用-O-R或-O-CH3之間的偶極作用力結合所形成的聚集結構；相對的可被溫度所瓦解的的作用力可能是已經形成的共軛高分子鏈聚集結構進一步的結合，因此隨著溫度的升高則溶液的UV-vis吸收光譜突變窄以及PL光激發光光譜圖均呈現以0-0單重態能量轉移(在約550~570nm)的光激發光峰有些微的藍栘，其最強發光位置λmax由570nm下降至550nm。另一方面，在較不良溶劑條件下，當溫度增加溶液的slow model的聚集結構產生明顯的瓦解並且向較短緩和時間偏移形成較小的聚集結構。並且當溫度增加至90oC溶液中依然保持大量的聚集結構。因此隨著溫度的升高除了有最強發光峰的藍栘現象之外，相對的0-1單重態能量轉移和(在約580~610nm)光激發光峰也隨溫度的增加快速消失，當溫度為60oC以上時這光激發光峰則完全消失。
並列摘要
In this work, we provided insights into effect of the concentration, cosolvents, aging time and temperature on the aggregation behaviors and photophysical properties of poly(2-methoxy- 5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV), in, mixed solvents of toluene and nonane, solutions. The dynamic light scattering indicated that the scattering intensity of MEH-PPV/Toluene/Nonane solutions increased with increasing concentration, c. At c bellower than 0.016mg/mL, the DLS presented a very low intensity corresponded to combine the side chain motion and segments motion of MEH-PPV conjugated polymer in the dilute solutions. Whereas, at c higher than 0.16mg/mL, the DLS showed that increased in the scattering intensity with increasing c, it may imply the aggregated structures of MEH-PPV conjugated polymer in semidilute solutions. Therefore, photoluminescence (PL) of MEH-PPV/Toluene/Nonane solutions presented that the maximum excited luminescence attribute to 0-0 energy transformation in singlet state shift slightly to larger wavelength from 550 to 570nm (red-shift). However, the excited luminescence intensity at 580 to 610nm attribute to 0-1 energy transformation in singlet state from aggregated structure increased as poor solvent, Nonane, was added. The static light scattering indicated that the Zimm plot of MEH-PPV/Toluene/ Nonane dilute solutions exhibetd a cover-like, which imply the aggregated clusters in MEH-PPV/Toluene/Nonane dilute solutions at 20±0.1oC. Whereas, the Zimm plot of MEH-PPV/Toluene/Nonane dilute solutions presented an ideal straight line at 50±0.1oC. The values of A2 in 100/0 and 70/30% MEH-PPV/Toluene/nonane dilute solution is 1.778×10-5and1.113×10-5mol dm/g, respectively, and the values of Rg in 100/0 and 70/30% MEH-PPV/Toluene/nonane dilute solution is 78.0 and 65.8nm, respectively, the Mws of MEH-PPV in 100/0 and 70/30% MEH-PPV/Toluene/nonane dilute solution is a.c. 2.428×106 and 1.344×106 g/mol, respectively. However, the persistence length of lps of MEH-PPV polymer chain in dilute solution could be described by the Kratky-Porod equation with the monomer molecular weight and length were 260 g/mol and 0.67nm, respectively. The contour length of the MEH-PPV polymer chain was thus ca. 3500±200 nm, and the persistence lengths calculated from Kratky-Porod equation were 5.24 and 3.68nm nm at 100/0 and 70/30%, respectively, which again verified the promotion of the stiffness of MEH-PPV chain in Toluene/nonane dilute solution with increasing temperature and decreasing nonane content. The polymer assumed a more extended wormlike chain conformation in the former. The difference in the strength of interaction in the two mix-solvents gave rise to contrasting aggregation behavior of the MEH-PPV conjugated polymer in the semidilute regime. Therefore, in better cosolvent (100/0 and 90/10vol%), the scattering intensity of MEH-PPV/Toluene/nonane solutions maintained the same, while the scattering intensity of MEH-PPV/Toluene/nonane solutions increased in poorer cosolvent (80/20 and 70/30vol%) with increasing ageing time. It is maybe indicated that the interaction force between MEH-PPV conjugated polymer and toluene decreased, whereas that between MEH-PPV conjugated polymer chains increased to promote MEH-PPV conjugated polymer aggregated forming three-dimensional network-like gels with nonane was added. However, the interchain aggregation was never completely dissipated by the heating, suggesting the existence of two types of segmental association with distinct stability. The highly stable segmental association that could neither be disrupted thermally in better cosolvent was attributed to the interaction between –O-R or –O-CH3 groups in side chains of MEH-PPV in the MEH-PPV/Toluene/Nonane semidilute solutions. In the poorer cosolvent, further π-π interaction between MEH-PPV conjugate polymer chains took place within the preexisting aggregates, making the networks more compact. This type of π-π interaction could be disrupted by moderate heating, and the PL intensity at 580 to 610nm attribute to 0-1 energy transiformation in singlet state decreased as temperature was raised to over 60oC.