title: Direct impact of nonequilibrium aggregates on the structure and morphology of Pdadmac/SDS layers at the air/water interface.
abstract: We discuss different nonequilibrium mechanisms by which bulk aggregates directly modify, and can even control, the interfacial structure and morphology of an oppositely charged polyelectrolyte/surfactant (P/S) mixture. Samples are categorized at the air/water interface with respect to the dynamic changes in the bulk phase behavior, the bulk composition, and the sample history using complementary surface-sensitive techniques. First, we show that bulk aggregates can spontaneously interact with the adsorption layer and are retained in it and that this process occurs most readily for positively charged aggregates with an expanded structure. In this case, key nonequilibrium issues of aggregate dissociation and spreading of surface-active material at the interface have a marked influence on the macroscopic interfacial properties. In a second distinct mechanism, aggregates inherently become trapped at the interface during its creation and lateral flocculation occurs. This irreversible process is most pronounced for aggregates with the lowest charge. A third mechanism involves the deposition of aggregates at interfaces due to their transport under gravity. The specificity of this process at an interface depends on its location and is mediated by density effects in the bulk. The prevalence of each mechanism critically depends on a number of different factors, which are outlined systematically here for the first time. This study highlights the sheer complexity by which aggregates can directly impact the interfacial properties of a P/S mixture. Our findings offer scope for understanding seemingly mysterious irreproducible effects which can compromise the performance of formulations in wide-ranging applications from foams to emulsions and lubricants.
authors.affiliation: Institut Laue-Langevin, 6 rue Jules Horowitz, BP 156, 38042 Grenoble Cedex 9, France.
authors.forename: Richard A
authors.initials: RA
authors.lastname: Campbell
authors.forename: Marianna
authors.initials: M
authors.lastname: Yanez Arteta
authors.forename: Anna
authors.initials: A
authors.lastname: Angus-Smyth
authors.forename: Tommy
authors.initials: T
authors.lastname: Nylander
authors.forename: Boris A
authors.initials: BA
authors.lastname: Noskov
authors.forename: Imre
authors.initials: I
authors.lastname: Varga
mesh_terms: D000327:Adsorption; D000388:Air / Q000032:analysis; D005427:Flocculation; D007700:Kinetics; D011095:Polyethylenes / Q000737:chemistry*; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry*; D055672:Static Electricity; D013500:Surface Tension; D013501:Surface-Active Agents / Q000737:chemistry*; D013816:Thermodynamics; D014867:Water / Q000737:chemistry
chemical_list: D011095:Polyethylenes; D000644:Quaternary Ammonium Compounds; D013501:Surface-Active Agents; D014867:Water; C041004:poly-N,N-dimethyl-N,N-diallylammonium chloride; D012967:Sodium Dodecyl Sulfate