title: Adsorption of branched-linear polyethyleneimine-ethylene oxide conjugate on hydrophilic silica investigated by ellipsometry and Monte Carlo simulations.
abstract: The adsorption of and conformation adopted by a branched-linear polymer conjugate to the hydrophilic silica-aqueous solution interface have been studied by in situ null ellipsometry and Monte Carlo simulations. The conjugate is a highly branched polyethyleneimine structure with ethyleneoxide chains grafted to its primary and secondary amino groups. In situ null ellipsometry demonstrated that the polymer conjugate adsorbs to the silica surface from water and aqueous solution of 1 mM asymmetric divalent salt (calcium and magnesium chloride to emulate hard water) over a large pH range. The adsorbed amount is hardly affected by pH and large charge reversal on the negatively charged silica surface occurred at pH = 4.0, due to the adsorption of the cationic polyelectrolyte. The Monte Carlo simulations using an appropriate coarse-grained model of the polymer in solution predicted a core-shell structure with no sharp boundary between the ethyleneimine and ethyleneoxide moieties. The structure at the interface is similar to that in solution when the polymer degree of protonation is low or moderate while at high degree of protonation the strong electrostatic attraction between the ethyleneimine core and oppositely charged silica surface distorts the ethyleneoxide shell so that an "anemone"-like configuration is adopted. The adsorption of alkyl benzene sulfonic acid (LAS) to a preadsorbed polymer layer was also investigated by null ellipsometry. The adsorption data brought additional support for the existence of a strong polymer adsorption and showed the presence of a binding which was further enhanced by the decreased solvency of the surfactant in the salt solution and confirmed the surface charge reversal by the polymer adsorption at pH = 4.0.
authors.affiliation: Physical Chemistry 1, Lund University, Box 124, SE-221 00 Lund, Sweden.
authors.forename: Daniel George
authors.initials: DG
authors.lastname: Angelescu
authors.forename: Tommy
authors.initials: T
authors.lastname: Nylander
authors.forename: Lennart
authors.initials: L
authors.lastname: Piculell
authors.forename: Per
authors.initials: P
authors.lastname: Linse
authors.forename: Björn
authors.initials: B
authors.lastname: Lindman
authors.forename: Jürgen
authors.initials: J
authors.lastname: Tropsch
authors.forename: Jürgen
authors.initials: J
authors.lastname: Detering
mesh_terms: D000327:Adsorption; D005027:Ethylene Oxide / Q000737:chemistry*; D057927:Hydrophobic and Hydrophilic Interactions; D015394:Molecular Structure; D009010:Monte Carlo Method; D011094:Polyethyleneimine / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*
chemical_list: D011108:Polymers; D012822:Silicon Dioxide; D011094:Polyethyleneimine; D005027:Ethylene Oxide