以耗散粒子動力學法研究嵌段高分子刷於選擇性溶劑中之表面結構

Surface Structures of Block Copolymer Brushes in Selective Solvent via Dissipative Particle Dynamics

李俊賢(Chun-Shian Li)

指導教授 ： 陳文章

共同指導教授 ： 諶玉真(Yu-Jane Sheng)

國立臺灣大學/工學院/高分子科學與工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.01849

摘要

本論文以耗散粒子動力學法研究疏溶劑鏈段於親溶劑主鏈末端的線性雙嵌段高分子刷(Linear diblock copolymer brush)、Y形嵌段高分子刷(Y-shaped block copolymer brush)系統以及親溶劑主鏈/疏溶劑側鏈段的梳狀嵌段高分子刷(Comb-like block copolymer)系統於選擇性溶劑中的形態演變與成因。
由理論結果顯示嵌段高分子刷於選擇性溶劑中疏溶劑鏈段會產生聚集。疏溶劑鏈段為剛硬rod的系統聚集形態尺寸比疏溶劑鏈段為柔軟coil的系統大，且系統表面粗糙度亦較高。當表面密度增高時，疏溶劑鏈段在主鏈尾端的Linear與Y-shaped系統其聚集顆粒會跟著變大，水平方向的成長尤其顯著。聚集形態隨著表面密度增高可由圓島狀、橢圓島狀、worm-like狀逐漸變化，甚至會變為network structure。Y-shaped系統的形態變化大致相同，但變化的過程較linear系統快。表面粗糙度在兩個系統中都是隨著表面密度先升後降。當親溶劑主鏈段長度較長時，疏溶劑鏈段聚集較小而分散，並沉入親溶劑鏈段中被包圍住，表面粗糙度也會較低。
Linear與Y-shaped系統中，親溶劑主鏈的RgZ與主鏈長度成線性關係，與homopolymer brush相同；疏溶劑鏈段的RgZ則與自由高分子相同，與主鏈長度成次方關係。表面密度愈大，疏溶劑鏈段的長度與形狀愈不會對親溶劑主鏈的Rg造成影響。
疏溶劑鏈段在側鏈的系統因為親溶劑主鏈段的立體效應，表面密度增加時聚集團塊在水平方向的形態變化較不明顯，且聚集團塊會往垂直方向發展。梳狀高分子最上方自由鏈段長度夠長時，能在表面發揮排擠效應，使表面不會形成大型水平方向的聚集團塊。梳狀高分子疏溶劑鏈段間的間隔夠大且表面密度夠高時，疏溶劑鏈段聚集團塊可以被垂直撐開而分層。由本研究可知高分子之構形、親疏溶劑鏈段比、及表面密度皆可對嵌段高分子刷表面結構有顯著影響。

關鍵字

嵌段高分子刷 ； 表面結構 ； 耗散粒子動力學法 ； 分子模擬

並列摘要

The surface structures of diblock copolymer brushes with various architectures of linear, Y-shaped and comb-like block copolymer brush were investigated by dissipative particle dynamics (DPD). The solvophilic polymer segment is anchored on the surface while that of solvophobic is either at top or side blocks.
In selective solvents, solvophobic blocks tend to form aggregates. The theoretical results suggest that copolymer brush with a rigid rod-like solvophobic block form larger aggregates and surface roughness than those of a soft coil-like solvophobic block. The aggregated size also grows with increasing surface density, especially in horizontal direction. The shapes of the surface aggregates are varied from small isolated islands, large islands, worm-like conformation, even network structures as the surface density increases. The Y-shaped brushes have a similar transformation process as that of the linear brushes but the surface density for the above transition is lower. The surface roughness increases first and then decreases as surface density increase. The copolymer brushes with a longer solvophilic segment possess less surface roughness since the aggregates tend to submerge under the solvophilic polymer domain.
For both linear and Y-shaped block copolymer brushes, the radius of gyration in the direction perpendicular to the surface (RgZ) has a linear relation with the solvophilic chain length, which is the same as that of the homopolymer brush system. However, the RgZ of the solvophobic block exhibits a power exponent of 0.6 to its length, same as free polymer chain in solution. In the case of a high surface density, the shape and length of solvophobic chains have an insignificant effect on the surface structures.
For the comb-like polymer brush systems, aggregates are inclined to the vertical direction rather than the horizontal direction, owing to the size exclusion effect of the main chains. If the free sections on top of the main chains are long enough, only small aggregates would be appeared on the surface. For systems with a high surface density, different layers of aggregates are found in the vertical direction if the gaps between the side chains are large enough. The present study suggests that the polymer architecture, copolymer segment ratio, and surface density play an important role of surface structures of copolymer brushes.

並列關鍵字

block copolymer brush ； surface structure ； dissipative particle dynamics (DPD)

參考文獻

[1] Zhao, B.; Brittain, W. J. Prog. Polym. Sci. 2000, 25, 67.

[5] Liu, Y.; Mu, L.; Liu, B.-H.; Kong, J.-L. Chem. Eur. J. 2005, 11, 2622.

[6] Alexander, S. J. J Phys (Paris) 1977, 38, 977.

[7] P. G. de Gennes Macromolecules 1980, 13, 1069.

[9] Chakrabarti A.; Toral, R. Macromolecules 1990, 23, 2016.