空間侷限環境中高分子晶體方向性的發展

Development of Polymer Crystal Orientation under Spatial Confinement

劉建良(Chien-Liang Liu)

指導教授 ： 陳信龍

國立清華大學/工學院/化學工程學系/博士(2016年)

摘要

準確的控制晶體方向性可以直接的影響結晶高分子的性質。利用奈米模版在空間上限制高分子結晶的過程，是有效創造大尺度高分子方向性的方法。這篇論文將系統性的研究高分子在共嵌段高分子和AAO(陽極氧化鋁)奈米通道的侷限空間下所形成的晶體方向性。論文將深入的探討兩個關鍵的問題：高分子在結晶初期晶體方向性的發展機制、高分子在AAO奈米通道所形成的二維侷限空間中多重晶體方向性的特性。
利用時間解析(time-resolved)的廣角度X-ray散射(WAXS)，我們分析PDLLA-b-PE和PE-b-PLLA共嵌段高分子所形成的層狀侷限空間下，高分子晶體方向性隨時間的演化。PE晶體的平行方向性(parallel orientation)和PLLA晶體的垂直方向性(perpendicular orientation)在結晶早期的變化將不間斷的被測量。結果顯示這兩種高分子晶體在剛形成時，方向性都是隨機分布。隨著結晶的進行，晶體的方向性慢慢的往傾向的方向性進行調整，而調整的速度和結晶的速度成正相關。藉由晶體方向性和結晶度的關係圖，我們證實PLLA晶體的垂直方向性源自於高分子傾向形成大尺度晶體的結晶成長，而PE晶體的平行方向性源自於PE高晶核密度所造成的晶體之間的排斥體積。
同時，論文中也研究了PEO在AAO奈米通道中晶體的方向性。PEO分別以溶液法(solution method)跟熔融法(melt method)滲入AAO奈米通道中，並且分別於AAO中形成管狀和棒狀結構。這裡將系統性的研究結晶溫度(Tc)、PEO的分子量(MnPEO)、還有AAO奈米通道的直徑(DAAO)對於晶體方向性的影響。藉由對於二維廣角度X-ray散射圖譜中，PEO晶體的(120)繞射峰進行azimuthal scan，我們成功的揭露PEO於AAO奈米通道中的晶體方向性。研究中發現到PEO晶體呈現兩種方向性：PEO晶體(120)晶面沿著通道軸(channel axis)方向成長的垂直方向性(perpendicular orientation)，和(120)晶面傾斜於通道軸45度角的傾斜方向性(tilt orientation)。對於管狀和棒狀的PEO，當結晶溫度下降時，晶體方向性會由垂直方向性轉變成傾斜方向性。而當PEO分子量、AAO奈米通道的直徑上升時，晶體的垂直方向性將受到壓抑。這裡我們對高分子在AAO中的方向性發展提出假設，我認為晶體方向性是由晶體成長受到的侷限強度所決定的。當結晶的過冷(supercooling)相當大時，晶核密度將會非常高，這時AAO奈米通道中的環境將變的非常壅擠，晶體沿著通道軸方向的成長也將受到限制。在這個情形下，PEO晶體將形成傾斜方向性，讓兩組(120)晶體成長面可以長的一樣而且最長。另一方面，當AAO奈米通道的直徑較小時(較薄的管柱厚度、較小的棒狀直徑、較大的取率)，晶體將會在結晶早期，也就是晶核密度比較低的時候，形成垂直方向性。在棒狀的PEO中，我們發現道垂直方向性出現的區間變得比較狹小，這是因為比起管狀，棒狀提供較弱的侷限強度，進而使得較多的晶體形成傾斜方向性。

關鍵字

空間侷限環境 ； 高分子 ； 結晶 ； 晶體方向性 ； 廣角度X-ray散射

並列摘要

The precise control of crystal orientation provides a methodology for directional manipulation of the properties of crystalline polymers. The use of nanoscale templates to spatially confine the crystallization process is an effective approach to create crystal orientation over a large length scale. This thesis presents the systematic studies of the preferred orientation of polymer crystallites developed in the confined spaces templated by block copolymer microdomains and anodic alumina oxide (AAO) nanochannels. Two critical problems were examined here, namely, the mechanism of the development of the crystal orientation from the early stage of crystallization and the variable orientational order of the crystallites developed in the 2-D confined space templated by AAO nanochannels.
Using time-resolved WAXS with synchrotron radiation, we explored the time evolution of the preferred crystal orientation within one-dimensionally confined space constructed by the lamellar microdomains of two crystalline block copolymers, PE-b-PDLLA and PLLA-b-PE, where the developments of the parallel and the perpendicular orientation of PE and PLLA crystallites, respectively, were monitored from the early stage of crystallization. Both types of crystallites were randomly oriented at the early stage of formation. As crystallization proceeded further, the ensemble-average orientation progressively improved toward the preferred orientation type and the rate of establishing the orientation exhibited the same dependence on crystallization temperature (Tc) as the crystallization kinetics. Further examination of the effectiveness of enhancing the average orientation with respect to the increase of crystallinity supported the postulate that the perpendicular orientation of PLLA crystallites arises from the tendency to attain long-range crystal growth, while the parallel crystal orientation of PE is driven by the excluded volume interaction between the crystallites as a result of the intrinsically high nucleating power of PE.
The orientation of PEO crystallites developed within the AAO nanochannels has been investigated. PEO was infiltrated into AAO nanochannels by solution and melt infiltration method to yield tubular and rod confinement space, respectively, for the crystallization. The effects of crystallization temperature (Tc), PEO molecular weight (MPEO) and AAO channel diameter (DAAO) on the crystal orientation attained have been systematically examined. The PEO crystal orientation was revealed from the azimuthal scan of the (120) diffraction arcs in 2-D WAXS patterns. Two modes of crystal orientation were identified here, namely, perpendicular orientation with the (120) plane aligning along the channel axis and tilt orientation with the (120) planes tilted 45o away from the channel axis. For both tube and rod geometry, decreasing Tc tended to transform the orientation from perpendicular type to tilt configuration with 45o of tilt angle, whereas increasing MPEO and DAAO suppressed the population of crystallites with perpendicular orientation. The crystal orientation was postulated to be governed by the strength of confinement to the crystal growth. Higher nucleation density at the larger degree of supercooling created a crowded environment where the growth along the channel axis was highly restricted; in this case, the crystallites tilted 45o from the channel axis to maximize the growth distance of the two (120) planes. On the other hand, the smaller tube thickness and rod diameter and larger curvature prescribed by smaller DAAO tended to force the crystallites to adopt perpendicular orientation at the early stage of crystallization at which the nucleation density was low. The window of pure perpendicular orientation was apparently narrower for the nanorods, since rod morphology created weaker confinement, and therefore increased the population of the tilt-oriented crystallites.

並列關鍵字

Spatial confinemnt ； Polymer ； Crystallization ； Crystal orinetation ； WAXS

參考文獻

Chapter 1

14. Maiz, J.; Martin, J.; Mijangos, C. Langmuir 2012, 28 (33), 12296-12303.

18. Lee, W.; Chen, H.-L.; Lin, T.-L. Journal of Polymer Science Part B: Polymer Physics 2002, 40 (6), 519-529.

21. Lin, M.-C.; Wang, Y.-C.; Chen, J.-H.; Chen, H.-L.; M Ller, A. J.; Su, C.-J.; Jeng, U.-S. Macromolecules 2011, 44 (17), 6875-6884.

26. Kofinas, P.; Cohen, R. E. Macromolecules 1994, 27 (11), 3002-3008.