Morphology of Star Triptych Copolymer by Dissipative Particle Dynamics
Date Issued
2006
Date
2006
Author(s)
Chou, Shih-Hao
DOI
zh-TW
Abstract
Mutually immiscible triblock copolymers are able to form various multicompartment micelles. Exploring their morphologies involves a large parameter space, including chain architecture, block length, and concentration. However, DPD simulation provides a relatively cheap and fast approach to predict possible morphologies. The complex structure within the multidomain micelle can be easily examined.
In this work, we observe discrete micelles and "segmented worm"micelles formed by miktoarm star OEF, which are consistent with the experimental results. The former consists of a F core, surrounded by a few E nanodomains. In general, two E nanodomain are found on the top and bottom of the F core to form "sandwich" micelles. The O blocks emanate from the E-F interface and curl around to protect the hydrophobic core. The latter displays an elongated, wormlike structures.The worms are layered with alternating section of F and E blocks along
the long axis. The O coronas are shared by E and F layers to shield them from the highly unfavorable exposure to water. The segmented worm micelle is always formed for star (x-6-7) as long as the polymer concentration is high enough. The onset concentration for the formation of segmented worm micelles is increased with the hydrophilic O block length. When the hydrophilic O block is large (x=20), the O block screen
the hydrophobic core effectively and the sandwich micelles can survive at higher concentration. On the other hand, for stars with shorter O blocks (x=10), the fluctuation of O concentration in the corona may expose the hydrophobic core from time to time. As a consequence, in forming a segmented worm, the different sandwich micelles are able to share their
O coronas. When the concentration is even higher, the segmented micelles may join together to form segmented network.
In addition to miktoarm star, various morphologies of
multicompartment micelles can be disclosed by linear triblock
copolymers OEF, OFE, and EOF. For linear OEF (x-6-7) triblocks, the CSC structure can be evidently identified with the F core, E shell, and O corona. Nonetheless, the spread of the E blocks on the surface of the F core is not uniform due to E-F incompatibility. As the O block (x) is increased, the aggregation number of the micelle declines. For linear OFE
(x-7-6) with shorter O blocks, the E blocks form a core that is surrounded by an incomplete skin layer of the F block. Since the O blocks protect mainly the F skin, part of the E core is exposed to water. However, when the O block is long enough to curl around to shield the E domain, the core
consists of two separate but adjacent domains (E and F). When the concentration is high enough, the sandwich micelle (F-E-F) is formed by merging two F skin layer micelles. Its formation can remove the exposure of the E core of the skin layer micelle to water. For linear EOF (6-x-7) with longer O blocks, a micelle with two neighboring E and F layers is shielded by the O loops. However, as the O block is too short, only the
combination of several two-layer micelles can provide enough protection by the O blocks. Consequently, segmented worm micelles are formed.
Subjects
耗散粒子動力學
分子模擬
dissipative particle dynamics
molecule simulation
triblock copolymer
Type
thesis
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