Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/3517
標題: 結晶誘導PCL-PLLA團聯共聚合物之奈米微結構的形態分析與探討
Crystal Morphology and Nanostructure of crystallization-induced PCL-PLLA diblock copolymers
作者: 謝秉諺
Hsieh, Ping-Yen
關鍵字: crystallization-induced;結晶誘導;block copolymer;高分子團聯共聚合物
出版社: 化學工程學系
摘要: 
本研究首先嘗試利用結晶誘導(crystallization-induced)的方式,針對特殊之雙結晶性團聯共聚合物(crystalline-crystalline block copolymer)聚己內酯-左旋乳酸(poly(-caprolactone)-poly(L-lactide), PCL-PLLA)系統,製備成大範圍且有序之奈米微結構薄膜。利用磊晶基材與結晶性團聯鏈段之晶格具有晶格吻合(lattice matching)效應,將原本無序之球晶結構,誘導形成大範圍且有規則性的結晶層板排整。針對此一特殊的結晶誘導形態,本實驗利用原子力顯微鏡(atomic force microscopy, AFM)結合穿透式電子顯微鏡(transmission electron microscopy, TEM)之形態觀察與電子繞射圖譜(electron diffraction pattern, ED)進行其結晶形態與結構的分析和探討。為了進一步釐清經由結晶誘導後形態之結晶結構及成長模式,本實驗亦利用poly(ethylene)裝飾法(PE decoration),分析其結晶成長方向(crystal growth direction)與結晶分子鏈折疊方向(chain folding direction)於空間中對應的方向與位置。對於不同的磊晶基材,與結晶團聯鏈段並不具有晶格吻合現象,卻仍然具有相同的誘導效果,本實驗亦針對此一問題探討其驅動力與所造成之特殊形態的分子鏈構形。結果顯示,於形態上所形成大範圍且有序之PLLA結晶層板可能與磊晶誘導基材於共晶點(eutectic point)時所發生的Directional crystallization行為有關。本實驗進一步建立符合PCL-PLLA系統之假設性相圖(hypothetical phase diagram),並提出本系統所形成之奈米微觀結構為結晶區域與非結晶區域所組成,和一般高分子團聯共聚合物利用不同物種間的排斥力與化學鍵結的相互影響,所形成熱力學上穩定的微觀相分離結構不同。
同時,本實驗嘗試利用不同的磊晶基材,對於不同體積分率組成之PCL-PLLA高分子團聯共聚合物薄膜進行結晶誘導實驗。實驗結果發現,不同於一般文獻針對均聚合物或是高分子團聯共聚合物所形成之結晶分子鏈構形,經由結晶誘導後之薄膜形態,其結晶分子鏈為平行於基板方向排列,即所謂edge-on 的形態,本實驗之材料PCL-PLLA系統經由結晶誘導後所形成之結晶分子鏈構形對應基材則呈現flat-on的形態。且隨著PCL團聯鏈段體積分率(volume fraction)的增加,原本受到PLLA結晶層板空間所侷限而不會結晶或結晶度很低之PCL團聯鏈段亦開始結晶,且由TEM可以觀察到特殊的波浪形態,即所謂的調節形態(modulated morphology),對應於其電子繞射圖譜,則可以明顯發現PCL結晶團聯鏈段之特徵電子繞射點,此現象顯示這個特殊之調節形態與PCL團聯鏈段之組成比例有著密切的相關性。
本研究進一步針對結晶誘導形成大範圍且有序之奈米微結構薄膜。並利用水解(hydrolytic degradation)或酵素劣解(enzymatic degradation)的方式,製備奈米鑄型模板(nanopatterned template)。如利用酵素劣解的方式,將對於不同物種之團聯鏈段或不同分子構形(crystalline or amorphous)作高選擇性的腐蝕; 若採用水解的方式,則可利用NaOH(0.5M)水溶液及NaOH(0.5M) :CH3OH =3:2(v/v)的溶液對結晶區域與非結晶區域作為水解效率之區別以進行劣解。換言之,利用分解腐蝕的選擇性,因而可以有效的製備具有蝕刻效果的奈米鑄型模板。

Crystallization-induced orientation was carried out to control over molecular chain orientation and phase-separated microdomain of crystalline-crystalline diblock copolymer, poly (-caprolactone) -poly (L-lactide) (PCL-PLLA). Well-aligned lamellar monodomain over hundreds m2 area was thus obtained by surface interaction due to crystallographic matching of unit cells between crystallizable block and benzoic acid (BA) crystalline substrate. Interestingly, a flat-on crystalline morphology (i.e., the molecular chain of crystallites is perpendicular to the substrate surface) corresponding with well-aligned crystalline lamellar microstructure was obtained as evidenced by the results of a single-crystal-like [001] zonal electron diffraction (ED). So far, only edge-on crystalline morphology (i.e., the molecular chain of crystallites is parallel to the substrate surface) was observed for the epitaxy-induced monodomain of crystallizable block copolymers. To understand the correlation between chain folding direction and crystal growth direction, polyethylene (PE) decoration method was used so as to build up the molecular dispositions for the final morphology.
In contrast to BA substrate, the formation of large size monodomain can also be obtained by using hexamethylbenzene (HMB) crystalline substrate where lattice matching between crystalline PLLA and substrate cannot be identified. This indicates that lattice matching for the induction of large scale orientation is not a dominant factor. Nevertheless, the formation of large scale monodomain is in accordance with the crystallization event (i.e., crystallization-induced orientation).
The essential aspects of the overall phase transformation can be understood by dividing the processes into different stages using a hypothetical solvent-polymer phase diagram. An important feature of the phase diagram is the absence of microphase separation for PCL-PLLA system. The well-aligned lamellar monodomain obtained in our experiment was consited of alternated crystalline and amorphous domains. By contrast to microphase-separated morphology generated by the interplay of repulsive force and chemical linkage between constituted blocks.
For PCL-PLLA with lower content of PCL (i.e., fPCL=0.29), the crystallinity of PCL blocks is very low due to the confined effect of PLLA crystalline lamellae. However, PCL [00l] zonal ED pattern was observed with increasing the volume fraction of PCL (say fPCL=0.44) and modulated morphology was observed by TEM.
Hydrolytic or enzymatic degradation for PCL-PLLA was used to create nanopatterned templates from crystallization-induced monodomain of thin film samples. Block copolymers consist of distinct components (e.g., PCL or PLLA) or molecular chain conformation (e.g., crystalline or amorphous) could be selectively degraded by different enzymes. Solution of NaOH (0.5M) or NaOH (0.5M):CH3OH = 3:2(v/v) solution can also be used to degrade the crystalline and amorphous domains due to different degradation rate during hydrolytic treatment. Owing to the high selectivity of degradation, nanopatterned template can be successfully prepared from the biodegradable thin-film samples.
URI: http://hdl.handle.net/11455/3517
Appears in Collections:化學工程學系所

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