離子與共價鍵結改質操控片狀黏土之自我排列及熱穩定性與相變化之研究

Modification of Layered Silicate by Ionic and Covalent Bonding and their Self-Assembly, Thermal Stability, and Phase Transition Behaviors

陳育民(Yu-Min Chen)

指導教授 ： 林江珍教授

國立臺灣大學/工學院/高分子科學與工程學研究所/博士(2009年)

https://doi.org/10.6342/NTU.2009.03252

摘要

本論文中，利用離子交換與共價鍵結方法操控改質層狀黏土，其改質有機黏土性質表現出 (1) 雙性POP/Clays的自我排列行為；(2) HCP-POP400/Clays具有加乘效應之熱穩定特性與 (3) NSP-PNiPAAm的相變化與自我排列行為。其詳細探討可分為三個部份來描述，如下：
第一部分：利用掃描式、穿透式電子顯微鏡與原子力顯微鏡觀察，發現層狀黏土可以藉由自我排列行為形成獨特長柱狀(半徑寬度ca. 0.3 μm與長至40 μm )、分枝狀與叢束狀(半徑寬度ca. 3 μm)的型態。此乃利用聚丙烯醚胺(ploy(oxypropylene)-amine; POP-amine)以離子交換方方法改質層狀黏土，具有親油親水的雙性特質，經由一級結構的層狀有機無機黏土自我排列形成具結構性的微觀結構(Microstructure)。根據黏土的尺寸結構，高比表面積的合成雲母(片狀大小約300-500 nm)傾向形成長柱狀與叢束狀，相對於較低規整性之蒙托土(片狀大小約80-100 nm)則是以分枝狀型態呈現。其多變化的幾何微觀結構可藉由直接分散於水的介質中與在水/甲苯界面形成薄膜而將其溶劑蒸發的自我排列製程來調控。根據穿透式電子顯微鏡與原子力顯微鏡的分析，可以歸納其自我排列的機制可分為面與面的離子作用(ionic charge attraction)及邊對邊之疏水影響(hydrophobic POP-amine interaction)。
第二部分：以六氯環三磷腈(Hexachlorocyclotriphosphazene; HCP)與聚丙烯醚胺(ploy(oxypropylene)-amine; POP-amine)衍生物改質層狀黏土，進而掺混於環氧樹脂之奈米複合材料的熱性質探討。製備功能性有機黏土步驟中，先以聚丙烯醚胺(POP400與POP2000)與六氯環三磷腈進行取代反應形成衍生物 (HCP-POP adducts)，其衍伸物所含有的胺官能基可與黏土層間陽離子以離子交換方式改質之。利用HCP-POP polyamine salts改質層狀蒙托土可將層間從1.2 nm提升至2.4-5.1nm。經由穿透式電子顯微鏡(TEM)觀察，此有機黏土掺混至環氧樹脂系統中，可發現層狀黏土已脫層化並均勻分散。進一步從熱分析比較中，發現其奈米複合材料的熱性質可有效提升(T10wt% from 360 to 385 oC and T85wt% from 598 to 696 oC)。隨著不同有機黏土添加量，從裂解趨勢顯示出同時含有磷化合物與無機黏土具有加乘效應。同時，添加此有機黏土之複合材料之表面硬度(3H to 5H)與沾附性等物理特性均有效提升。
第三部分：以熱感應型聚異丙基丙烯醯胺高分子(poly(N-isopropylacrylamids; PNiPAAm)接枝於奈米矽片(Nano-Silicate Platelet; NSP)製備具有相變化與自我排列特性之新穎複合材料(NSP-PNiPAAm)。利用Esterfication與Michael addition合成雙活性基之連接劑(dibromo-organo-silane linker)，並以共價鍵方式改質奈米矽片。利用連接劑與矽片表面≡Si-OH官能基以溶凝膠方式進行水解縮合反應共價鍵結形成具有活性基之功能性，然後應用原子轉移活性自由基方法聚合出聚異丙基丙烯醯胺高分子。在奈米矽片表面進行接枝聚合反應可控制其鏈長(degree of polymerization = 350-1890)與分子量分布(1.21-1.50 polydispersity)。此外，此新穎複合物經由微差掃描式熱卡計可觀察發現NSP-PNiPAAm具有兩個不同的相轉變溫度，分別為26.6-29.4與27.2-36 oC，並且具有兩個相轉變構型的NSP-PNiPAAm會隨著增加鏈長而轉變成單一相轉變的構型。藉由穿透式電子顯微鏡的觀察，溫度感應型之NSP-PNiPAAm可因熱誘導相變化而產生自我排列的特性，其構型的相變化前後分別為均勻分布與立體網狀結構之差異。所以，利用溫度調控之相變化所產生的規則性尺寸之網狀結構(100-500 nm)，具有開發新穎奈米材料之應用。

關鍵字

自我排列 ； 層狀黏土 ； 疏水性 ； 幾何片狀 ； 聚丙烯醚胺 ； 環磷腈熱穩定性 ； 原子轉移自由基活性聚合 ； 溫度感應 ； 相變化

並列摘要

Layered silicates (clays) were modified through ionic exchange reaction and covalently surface-initiated polymerization to obtain the materials that possesses (1) self-assembling behavior of the amphiphilic POP2000/Clay; (2) synergistic thermal stability of HCP-POP400/Clay and (3) phase transition and self-aligning behavior of NSP-PNiPAAm hybrids. The thesis is divided into three parts:
Part 1. New self-assembled morphologies such as lengthy rods, dendrites and rod-bundles from the lamellar clays were discovered. Unique formation of lengthy rod (ca. 0.3 μm in diameter and up to 40 μm in length), hierarchical rod-bundle (ca. 3 μm in diameter) and dendrite-like arrays was observed by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). These microstructures were formed by self-piling the primary units of lamellar clay stacks that were intercalated with poly(oxypropylene)-amine salts (POP) within the interlayer spaces. Depending on the clay dimensions, the high-aspect-ratio mica (300-500 nm for plate dimension) tends to form lengthy rods and rod-bundles, while montmorillonite (80-100 nm for average plates) often leads to less orderly dendrites. The self-assemblies, elucidated by TEM and AFM micrograms, may involve two piling direction of the primary stack units by face-to-face alignment and edge-to-edge POP interaction. These hierarchical microstructures with different morphologies are controllable by selecting the self-assembling procedures such as direct water evaporation and toluene/water interfacial film formation.
Part 2. Amine substitution of hexachlorocyclophosphazene (HCP) with poly(oxypropylene)-diamines (POP) afforded the HCP-POP adducts which was subsequently intercalated into a layered silicate clay. Their relative thermal stabilities of the epoxies cured with the phosphazene-amines and the intercalated clays were studied. The organoclays, with the confined HCP-POP from 400 and 2000 g/mol Mw amines, are non-gelled products when using 1:6 molar ratio of HCP/POP starting materials in tetrahydrofuran solvent. The intercalation of HCP-POP polyamine-salts into sodium montmorillonite afforded the HCP-POP embedded organoclays with an expanded interlayer silicate spacing (2.4–5.1 nm) from the original 1.2 nm spacing (X-ray diffraction). The effect of silicate clays was evaluated by blending the HOP-POP/clay hybrids into a two-component epoxy system (diglycidyl ether of BPA and a diamine) and fully cured to form solid materials. The distribution of the exfoliated silicate platelets in the matrix was analyzed by transmission electronic microscopy (TEM). Thermal gravimetric analysis (TGA) indicated an enhanced thermal stability for the HCP/clay epoxy nanocomposites, with a delayed weight-loss pattern (T10wt.% from 360 to 385 °C and T85wt.% from 598 to 696 °C), as compared to the pristine epoxies. By comparing these epoxies with different amounts of phosphazene and/or silicates, the TGA revealed a synergistic effect for the presence of both phosphorous and silicate components. Furthermore, the epoxies had shown to have improved physical properties such as hardness (from 3H to 5H) and surface adhesion (observed by SEM on fracture surface).
Part 3. Thermoresponsive poly(N-isopropylacrylamide) (PNiPAAm) was covalently tethered to nanosilicate platelets (NSP) to generate a new class of organic–inorganic hybrid that exhibits self-assembly and phase transformation properties under applied stimuli. Hybrids of two grafting densities were prepared and the PNiPAAm length was precisely controlled to yield a degree of polymerization of 350–1890 and a narrow molecular weight distribution (1.21–1.50 polydispersity or Mw/Mn). Two distinctive second-order transitions were observed during differential scanning calorimetry analysis, indicating the existence of dual-segment density zones. The difference between the two transition temperatures gradually vanished with increasing chain length and a single endothermic first-order transition emerged. The hybrid also underwent a heat-induced phase transformation after treatment with several heating and cooling cycles. It is believed that fixation of PNiPAAm onto NSP greatly inhibited chain relaxation movements and hindered reversible coil–globule transitions. Furthermore, thermally induced self-assembly behavior was directly observed by transmission electronic microscopy of the hybrid coating as a thin film on a silicon wafer surface. The formation of a 3D network of nanostructures was directed by the platelet shape at temperatures higher than the critical solution temperature of the PNiPAAm brushes. The temperature-controllable phase separation for formation of an ordered domain network of 100–500 nm in dimension has potential for the fabrication of new smart nanomaterials.

並列關鍵字

self-assembly ； silicate clay ； hydrophobic ； plate directing ； poly(oxypropylene)-amines ； phosphazene ； thermal stability ； ATRP ； thermoresponsive ； phase transition

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