A Neutron Reflectivity Study of Surfactant Self-Assembly in Weak Polyelectrolyte Brushes at the Sapphire鈭扺ater Interface
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- 作者：Mauro Moglianetti ; John R. P. Webster ; Steve Edmondson ; Steven P. Armes ; Simon Titmuss
- 刊名：Langmuir
- 出版年：2011
- 出版时间：April 19, 2011
- 年：2011
- 卷：27
- 期：8
- 页码：4489-4496
- 全文大小：951K
- 年卷期：v.27,no.8(April 19, 2011)
- ISSN：1520-5827
文摘
Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes grown by surface-initiated polymerization from a polyanionic macroinitiator adsorbed at the sapphire鈭抴ater interface have been used as a substrate to study the interaction between the weak polyelectrolyte PDMAEMA and the oppositely charged surfactant sodium dodecyl sulfate (SDS) with neutron reflectivity. At pH 3, multilayered structures are formed in which the interlayer separation (40 脜) is comparable to the dimensions of a SDS bilayer or micelle. The number of repeating layers that form depends on brush thickness, ranging from three layers in a relatively thin brush (5 nm dry thickness) to 15 layers in a relatively thick brush (17 nm dry thickness). In the 5 nm brush, addition of 0.01 mM SDS leads to brush deswelling, and the distinct layered structure only forms when the SDS concentration reaches 1 mM, with the brush reswelling slightly at 5 mM SDS. In the thicker (11 and 17 nm) brushes, distinct layered structures form at 0.1 mM SDS, in which the molar SDS/DMAEMA ratio is greater than unity. Exposing the 17 nm brush/SDS complex to 1 M NaNO3 results in the complete removal of the surfactant and recovery of the bare brush structure. At pH 9, there is significant surfactant uptake by the brush, but no multilayer structures are formed. The brush presents a high concentration of DMAEMA segments that are localized to within 500鈭?000 脜 of the sapphire interface. At pH 9 the high local concentration of hydrocarbon segments in the brush screens the hydrophobic tails of the surfactants from the unfavorable interaction with water, leading to significant surfactant uptake by the brush. At pH 3 the high local concentration of charges inside the brush additionally screens the repulsive interactions between the surfactant headgroups, making surfactant uptake even more favorable, leading to the formation of multilayered surfactant aggregates confined within the brush.