芴系硬桿及溫感性軟鏈之嵌段式共聚物 (PF-b-PNIPAAm) 高分子刷表面結構之研究

Abstract

本研究利用理論預測及實驗操作交互驗證的方式來研究共軛性硬桿-溫感性柔軟嵌段共聚高分子刷之表面結構。根據以耗散粒子動力學為基礎的模擬結果，我們發現這類溫度敏感性的高分子刷表面結構會受溫度刺激、高分子刷表面接枝密度與硬桿/柔軟嵌段長度比例的影響而有所改變。在溫度低時，會出現由硬桿所聚集而成的半圓球形聚集結構。隨著溫度的提高，這些聚集結構會轉換成島狀、蟲狀甚至是連結網狀的型態，其型態變化與高分子刷表面接枝密度相關。同時，這些由硬桿所組成的聚集體在溫度低時會受軟鏈保護而沉入軟鏈中，但隨著溫度的提升又會暴露於表面，聚集體受保護的程度則會受軟鏈長度的不同而改變。 爲了驗證此理論模擬的準確性，本研究合成了兩種不同硬桿/柔軟嵌段長度比例的聚芴-聚(氮-異丙基丙烯醯胺)嵌段共聚高分子，並利用物理吸附方法製備這兩種嵌段共聚高分子的高分子刷表面。藉由原子力顯微鏡的鑑定，吾人發現此高分子刷的表面結構會隨著溫度呈現可逆性變化。同時，接觸角測試結果顯示表面在升溫處理後變的稍加疏水，此即驗證了硬桿聚集體暴露於表面的現象。對應於光電性質，吾人發現因芴系分子聚集所產生之額外螢光放光峰確實存在，同時其波峰強度會隨溫度的變化而有所增強或削減。本研究顯示吾人可利用溫度來調控高分子刷的表面結構及其對應的光電性質，而這些結果皆與理論模擬相互呼應。

A combined theoretical and experimental investigation is performed to study the surface morphology of conjugated rod-coil block copolymer brushes. Based on dissipative particle dynamics, the surface structures of thermoresponsive polymer brushes are found to alter significantly in response to the effects of thermal stimuli, grafting density, and rod-coil block ratio of the polymer brushes. Small, hemispherical domains of the aggregation of rod-blocks are formed at low temperature. As the temperature increases, the conformations transform to isolated islands, worm-like structures, or even network-like morphologies depending on the grafting density. Furthermore, the aggregations tend to submerge into coil block at first and float on the top as the temperature increases. The degree of submergence depends on rod-coil block ratio of the polymer brushes. In the experimental part, two Poly[2,7-(9,9-dihexylfluorene)]-b-poly[N-isopropylacrylamide] (PF-b-PNIPAAm) rod-coil block copolymer with different block ratios are synthesized and used to prepare corresponding polymer brushes on the quartz glass by physisorption. The morphology on the top of the surface is characterized by atomic force microscopy image. The results show a thermoresponsive transformation via temperature variation and are consistent with theoretical predictions. In addition, the surface is verified to be more hydrophobic after temperature treatment by contact angle measurements, suggesting the flotation of the rod aggregative domain on the top. The photophysical properties of PF-b-PNIPAAm polymer brushes are also found to vary by thermal stimuli. The PL spectra reveals that emission peaks originated from the aggregation and/or excimer formation of PF blocks and the intensity slightly changes through temperature variation. Our study demonstrates that the surface morphology of polymer brush and its corresponding photophysical property can be tuned by thermal stimuli.