TY - JOUR
T1 - Direct impact of nonequilibrium aggregates on the structure and morphology of pdadmac/SDS layers at the air/water interface
AU - Campbell, Richard A.
AU - Yanez Arteta, Marianna
AU - Angus-Smyth, Anna
AU - Nylander, Tommy
AU - Noskov, Boris A.
AU - Varga, Imre
PY - 2014/7/29
Y1 - 2014/7/29
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=84905011302&partnerID=8YFLogxK
U2 - 10.1021/la500621t
DO - 10.1021/la500621t
M3 - Article
C2 - 24988363
AN - SCOPUS:84905011302
SN - 0743-7463
VL - 30
SP - 8664
EP - 8674
JO - Langmuir
JF - Langmuir
IS - 29
ER -