奈米矽片黏土其自組裝排列性質探討及應用

Abstract

本研究旨在探討具有高片徑比及高表面電荷之脫層型奈米矽片其自組裝排列特性。由於具不同金屬反離子 (metal counter-ion) 之奈米矽片具有其獨特的自我組裝排列特性，利用此特性可發展出特殊的功能性材料，如抗火焰性之黏土薄膜及超疏水薄膜。 第一部分為探討脫層型之奈米矽片與層狀型蒙脫土於自組裝排列成膜之差異性。奈米矽片之結構為單一片狀型態且均勻分散在水溶液中的無機黏土，具高長徑比及表面電荷性質，由 SEM 證實脫層型奈米矽片具有高度規整排列性，層狀型蒙脫土則無。此薄膜具有矽片/孔洞交錯之微結構，經由密度量測實驗證實薄膜孔洞含量可達 40 % 且具有低熱傳導係數 (0.17 W m-1 K-1)。此薄膜經由火焰燃燒測試，其表面不被火焰貫穿，未來可應用於防火材。 第二部份為將鈉型奈米矽片與一價的鋰和鉀、二價的鎂和鈣、及三價的鋁金屬離子進行離子交換反應，並透過界面電位及粒徑的量測，探討奈米黏土表面電荷之差異性對於溶液分散穩定性及自組裝排列特性之的影響。結果顯示，當金屬離子價數增加時，矽片界面電位之絕對值有顯著降低，粒徑增加及溶液穩定性低之趨勢。將溶液製備成膜後，由 SEM 證實三價型奈米矽片膜之微結構規整度最低，二價型奈米矽片次之，一價型奈米矽片排列最為規整，此結果顯示溶液分散狀態與黏土自我排列整齊度具有高度之正相關。 第三部份為超疏水複材的備製，將鋁離子型奈米矽片、聚烯基丁二酸酐 (poly(isobutylene)-g-succinic anhydride)及三胺基聚丙烯醚 (poly(oxypropylene)- triamine) 行縮合的聚異丁烯胺共聚物及雙酚 A 二縮水甘油醚型環氧樹脂 (diglycidyl ether of bisphenol-A) 混合液，經由塗佈與硬化反應可形成具有強度之薄膜。由 SEM 及親疏水角量測證實，藉由操控黏土表面粗糙度以及聚異丁烯胺與環氧樹脂之疏水特性，此系列超疏水複合薄膜表面具有微米及奈米級化微結構，且其接觸角高於 150o。

The research is mainly dedicated to the self-assembling behavior of the exfoliated nanosilicate platelets with various metal counter-ions (NSP-OM, where M = metal counter-ions). We were able to develop a variety of functional materials by manipulating the differences in the self-assembly of these NSP species. In the first part of the research, we reported an organic-free clay film capable of both flame- and heat-shielding. Traditionally, polymeric composite films with a high loading of nano-size silicates can hardly meet the increasingly stringent fireproof and smoke-free requirements during burning. Thus, it is desirable to prepare pure clay films that can block air, heat, and flame. Our clay film was prepared from the self-assembly of sodium form of nanosilicate platelets (NSP-ONa) derived from the exfoliation of natural sodium montmorillonite (Na+-MMT). The self-assembled film has a highly regular multilayered nanostructure over a large area and an appreciable volume of air entrapped in between. The combination of regular structure and substantial air volume (40 %) contributes to the low thermal conductivity (0.17 W m-1 K-1) and flame blocking property of the film. It was demonstrated that the film can shield flame over hour duration and prevent temperature rising on the backside of film. This remarkable clay film has a myriad of uses including gas barrier, heat insulator, and fireproof devices. In the second part, the sodium counter-ions of NSP-ONa were subsequently exchanged with various metal ions including lithium(I), potassium(I), magnesium(II), calcium(II), and aluminum(III) to afford the corresponding species of NSP-OM. In solution, their ionic properties were characterized by measuring zeta potentials over pH to reveal the electrokinetic shifting from -50 to -5 mV. As the valence of the metal counter-ion increases, the zeta potential (in absolute value) of the silicate surface is apparently lowered, indicating an increase in the particle size and a decrease in the solution stability. Under the process of solution coating and evaporating, the silicate platelets self-assembled into thin films of 20–100