Chemistry at Air/Water Interface versus Reaction in a Flask: Tuning Molecular Conformation in Thin Films

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• 作者：Smita Mukherjee^† ; ; Alokmay Datta*^† ; ; Angelo Giglia^&#8225 ; ; Nicola Mahne^&#8225 ; ; Stefano Nannarone^&#8225 ; ^§ ;
• 刊名：Langmuir
• 出版年：2009
• 出版时间：March 17, 2009
• 年：2009
• 卷：25
• 期：6
• 页码：3519-3528
• 全文大小：438K
• 年卷期：v.25,no.6(March 17, 2009)
• ISSN：1520-5827

文摘

Atomic force microscopy and X-ray reflectivity studies of cobalt stearate Langmuir−Blodgett (LB) films (CoStp) deposited from a preformed bulk sample on quartz substrates showed formation of a Volmer−Weber type monolayer but no multilayers as compared to the excellent multilayers of cobalt stearate films (CoStn) deposited at the air/water interface by the usual LB technique, in spite of both showing bidentate bridging type coordination of cobalt ions with the carboxylate group. The difference is attributed to existence of different headgroup conformers, observed from Fourier transform infrared (FTIR) studies. The CoStp films had a higher energy ‘boat’ conformation with linear O−Co−O linkage, whereas CoStn formed a low energy conformer with a bent O−Co−O configuration (bond angle of 105°). Present results support the necessity of bidentate bridging coordination in multilayer deposition, but rejects its sufficiency by bringing out the crucial role played by air/water interface. Differences in surface pressure−molecular area isotherms and hydrocarbon tail−tail interactions (evident from FTIR spectra) of the films support the above statement. Methyl−methyl interactions observed in CoStn samples suggest hierarchy of supramolecular chemistry at the air/water interface in tuning the C−O−Co bond angle essential to satisfy the wetting condition with the substrate and subsequently form LB multilayers.