溶劑蒸氣對超分子薄膜奈米結構之影響

Abstract

近年來嵌段共聚物在高分子基礎科學及應用領域均為熱門題材，其可調控形態的特殊性質尤其受到廣泛研究，包括外加電場、光感應、熱退火以及溶劑退火等，均為改變嵌段共聚物奈米微結構的常見方法。本研究使用嵌段共聚物及PDP小分子組成超分子，探討溶劑蒸氣對於嵌段共聚物及超分子薄膜微結構形態之影響。在嵌段共聚物中添加小分子形成超分子之後，可以使溶劑蒸氣對超分子微結構發揮調控方向性的作用。透過PS與P4VP一系列溶解度測試，在低溶解度參數的溶劑中，4VP與PDP的氫鍵可以穩定存在；在高溶解度參數的溶劑中，4VP與PDP的氫鍵比例大幅降低。 透過AFM、GISAXS、橫截面TEM等影像分析，均可以證實本系統選用的超分子薄膜自組裝巨觀結構為PS形成的圓柱及P4VP-PDP所形成的間質，以溶解度參數較小的三種溶劑做溶劑退火時，薄膜巨觀結構為垂直於基板的圓柱；反之，以溶解度參數較大的三種溶劑做溶劑退火時，大尺度自組裝圓柱結構平行於基板。此差異是由於溶劑退火過程中4VP與PDP氫鍵的強弱不同所致。透過溶劑蒸氣調控薄膜微結構方向性的方法具有可逆性，可以透過不同溶解度參數的溶劑對同一片樣品反覆進行微結構方向調控。為了比較不同溶解度參數對於同一超分子薄膜的方向調控能力，本研究由六種溶劑當中挑選蒸氣壓相近的兩種組合：chloroform / THF 以及 toluene / p-dioxane，並以不同莫耳分率組成雙成分溶液，對超分子薄膜做溶劑退火，由AFM影像可以觀察薄膜微結構由平行於基板過渡到垂直於基板的變化。

Block copolymers (BCP) and supramolecules assembly (SMA) have drawn intense attention since they offer possibilities to produce nanoscale materials with controllable morphology. Several methods, such as electric field alignment, photo-responsive, thermal annealing and solvent annealing, have been used to align BCP nanostructures. In this study, a simple approach to control the microdomain orientation of BCP-based supramolecular thin films has been investigated. The approach involves the use of a variety of solvents with different solubility parameters to anneal thin films. In the study of the nanostructure of supramolecular thin films, amphiphilic block copolymer polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) with hydrogen-bonded 3-pentadecylphenol (PDP) were used. The AFM topography and phase images and cross-section TEM Image results suggested that annealing with lower solubility parameter solvents, such as toluene, led to the microdomains perpendicular to the surface while higher solubility parameter solvents, such as THF, cause the microdomains parallel to the surface. The orientation is reversible as these two types of solvents are used alternately. We attribute these dramatic results to the strength of hydrogen bonding between PDP and 4VP during solvent annealing. Under the vapors of low solubility parameter solvents, a strong hydrogen bonding is present during annealing, which in turn, forces the microdomains oriented perpendicular to the surface. The ability of solvents to orient microdomains of BCP-based supramolecular thin films was further examined by binary mixtures of solvents, chloroform/THF and toluene/p-dioxane. The transition between distinct orientations of perpendicular and parallel microdomains with a series of molar fraction of binary mixtures will be discussed in the thesis.