Spherulite Formation of Lipophilic Surfactant Induced by Noncrystalline Amphiphilic Diblock Copolymer
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- 作者：Shuizhu Wu ; Boling Ma ; Fang Zeng ; Jian Chen ; Jianqing Zhao ; Zhen Tong ; Yulan Luo
- 刊名：Crystal Growth & Design
- 出版年：2008
- 出版时间：December 3, 2008
- 年：2008
- 卷：8
- 期：12
- 页码：4589-4595
- 全文大小：461K
- 年卷期：v.8,no.12(December 3, 2008)
- ISSN：1528-7505
文摘
As the lipophilic surfactant tetraoctylammonium bromide (TOAB) was cast from its organic solutions, needle-shape crystals formed. However, with the addition of an amphiphilic noncrystalline diblock copolymer [(poly(acrylic acid-b-styrene)] into the TOAB solutions, spherulites formed in the solid films cast from the solutions. Under preferable conditions, millimeter-sized spherulites could be obtained. It has been found that some factors such as the type of solvent, the film-forming temperature, and the ratio of polymer to surfactant can affect the spherulite formation. Small angle X-ray scattering and wide-angle X-ray diffraction investigation suggests that the formation of the spherulites and the pure TOAB crystals are organized by closely packed lamellar structure, while the addition of diblock copolymer decreased the degree of order of TOAB crystals. Dynamic light scattering study reveals that, in organic solvents such as tetrahydrofuran, TOAB formed molecular-disperse solution, while the amphiphilic copolymer chains formed micelles with or without the presence of TOAB molecules in the solution. We suppose that the morphology change of TOAB crystal is induced by the diblock polymer chains: During the solvent-evaporating film formation, the hydrophobic PS blocks of the amphiphilic copolymer resided between some of the TOAB lamellar crystallites, which might cause the splaying and branching of the surfactant crystallites during the crystal growth and eventually lead to spherulite formation. This result could provide a useful way for spherulite formation, and open interesting opportunities for adjusting the crystal morphology and/or properties of lipophilic surfactant.