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Authors
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Zimmermann, R. ; Norde, W. ; Cohen Stuart, M.A. ; Werner, C.
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Title
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Electrokinetic Characterization of Poly(Acrylic Acid) and Poly(Ethylene Oxide) Brushes in Aqueous Electrolyte Solutions
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Date
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01.06.2005
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Number
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12482
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Abstract
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Surfaces carrying hydrophilic polymer brushes were prepared from poly(styrene)-poly(acrylic acid) andpoly(styrene)-poly(ethylene oxide) diblock copolymers, respectively, using a Langmuir-Blodgett techniqueand employing poly(styrene)-coated planar glass as substrates. The electrical properties of these surfacesin aqueous electrolyte were analyzed as a function of pH and KCl concentration using streaming potential/streaming current measurements. From these data, both the zeta potential and the surface conductivitycould be obtained. The poly(acrylic acid) brushes are charged due to the dissociation of carboxylic acidgroups and give theoretical surface potentials of -160 mV at full dissociation in 10<SUP>-</SUP><SUP>3</SUP> M solutions. Thesurface conductivity of these brushes is enormous under these conditions, accounting for more than 93%of the total measured surface conductivity. However, the mobility of the ions within the brush was estimatedfrom the density of the carboxylic acid groups and the surface conductivity data to be only about 14% ofthat of free ions. The poly(ethylene oxide) (PEO) brushes effectively screen the charge of the underlyingsubstrate, giving a very low<br /> zeta potential except when the ionic strength is very low. From the data, ahydrodynamic layer thickness of the PEO brushes could be estimated which is in good agreement withindependent experiments (neutron reflectivity) and theoretical estimates. The surface conductivity in thissystem was slightly lower than that of the polystyren substrate. This also indicates that no significantamount of preferentially, i.e., nonelectrostatically attracted, ions taken up in the brush.
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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 21 (2005) 5108-5114
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DOI
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https://doi.org/10.1021/la050191p
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Tags
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