Salt-Induced, Continuous Deposition of Supramolecular Iron(III)-Tannic Acid Complex

다국어 초록 (Multilingual Abstract)

<P>One-step assembly of iron(III)-tannic acid (Fe<SUP>3+</SUP>-TA) complex forms nanothin (∼10 nm) films on various substrates within minutes. In this deposition scheme, however, the film does not grow continuously over time even though Fe<SUP>3+</SUP>-TA complex is still abundant in the coating solution. In this paper, we report that the salt addition dramatically changes the one-off coating characteristic to continuous one, and each salt has its optimum concentration (<I>C</I><SUB>MFT</SUB>) that produces maximum film thickness. For detailed investigation of the salt effects, we employed various salts, including LiCl, NaCl, KCl, CaCl<SUB>2</SUB>, SrCl<SUB>2</SUB>, BaCl<SUB>2</SUB>, NaBr, and NaNO<SUB>3</SUB>, and found that only cations played an important role in the continuous deposition of the Fe<SUP>3+</SUP>-TA complex, with smaller <I>C</I><SUB>MFT</SUB> values for the cations of higher valency and larger size. On the basis of the results, we suggested that the positively charged cations screened the negative surface charges of Fe<SUP>3+</SUP>-TA complex particles, leading to coagulation and continuous deposition, further supported by the ζ-potential measurement and time-resolved dynamic light-scattering analysis.</P>
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