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Authors
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Osaki, T. ; Werner, C.
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Title
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Ionization Characteristics and Structural Transitions of Alternating Maleic Acid Copolymer Films
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Date
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02.10.2003
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Number
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11383
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Abstract
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Alternating maleic acid copolymers dissolved in aqueous solutions exhibit characteristic two-stepdissociation profiles and pH-induced structural transitions in dependence on the comonomer unit. Inextension of these findings, we analyzed a set of thin films of maleic acid copolymers (poly(octadecene-<I>alt</I>-maleic acid), POMA; poly(propylene-<I>alt</I>-maleic acid), PPMA; poly(styrene-<I>alt</I>-maleic acid), PSMA)randomly attached to planar glass surfaces by covalent binding. Streaming potential/streaming currentmeasurements with a microslit electrokinetic setup (MES) were applied to determine zeta potential (<IMG SRC="/images/gifchars/zeta.gif" BORDER=0 >)and surface conductivity (<I>K</I><SUP><IMG SRC="/images/gifchars/sigma.gif" BORDER=0 ></SUP>) data of the polymer layers in aqueous solutions of varied pH. The resultsconfirmed the two-step dissociation behavior for all immobilized copolymers. A dramatic increase of <I>K</I><SUP><IMG SRC="/images/gifchars/sigma.gif" BORDER=0 ></SUP>was observed for PPMA and PSMA-but not for POMA-layers at alkaline pH values, indicating thatelectrostatic repulsion of ionized groups controls the extension of the confined layers as long as hydrophobicinteractions between the comonomers do not inhibit this effect. The isoelectric points (IEPs) show that forPPMA and PSMA layers the acidic functions dominate the interfacial charging and exhibit an enhancedacidity which can be explained by hydrogen bonds between the anion formed in the first dissociation andthe proton of the adjacent undissociated group. In contrast, the layered POMA exhibits significantly lessacidic IEP values due to the large comonomer. Hysteresis effects of the <IMG SRC="/images/gifchars/zeta.gif" BORDER=0 > versus pH profiles were observedfor dissociation and <br />association of the copolymers. This was explained by the reduced dynamics of structuraltransitions in the immobilized layers as compared to the dissolved molecules.
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Publisher
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Langmuir
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Wikidata
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Citation
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Langmuir 19 (2003) 5787-5793
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DOI
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https://doi.org/10.1021/la034439r
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Tags
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