The Monolayer Structure of the Branched Nonyl Phenol Oxyethylene Glycols at the Air−Water Interface

Abstract

The structure of the monolayers formed by a group of monodisperse nonyl phenol ethoxylates with parasubstituted 1-butylpentyl chains (para-(C 4 H 9 ) 2 CHC 6 H 4 (OC 2 H 4 ) n OH, abbreviated to BNPE n , n ) 4, 8, and 12) at the air-water interface has been determined by surface tension measurements and neutron reflection. The critical micellar concentration (cmc) was found to be 1.1 ( 0.3 × 10 -5 M for BNPE 4 , 4.0 ( 0.3 × 10 -5 M for BNPE 8 and 8.0 ( 0.3 × 10 -5 M for BNPE 12 and the limiting area per molecule (A cmc ) at the cmc to be 46 ( 3, 61 ( 4, and 75 ( 5 Å 2 , respectively. The values of A cmc are almost identical to those obtained from dodecyl ethoxylates (C 12 E n ) for the same size of the headgroups, suggesting that A cmc for these nonionic surfactants is determined by the size of the headgroups and is not affected by the chemical structure of the hydrophobic chains. The thicknesses of the nonyl phenol layers projected onto the surface normal direction were found to be 18 ( 3 Å for BNPE 4 , 19 ( 3 Å for BNPE 8 , and 22 ( 3 Å for BNPE 12 . In all cases they were about twice as thick as the fully extended chain, suggesting a broad distribution of the hydrophobic chain across the layer and hence a strong mixing of the chain with the ethoxylate groups.

Synthesis, Surface Properties, and Self‐Aggregation Behavior of a Branched N,N‐Dimethylalkylamine Oxide Surfactant

“…It clearly emerges that the branched surfactant occupies a larger area per molecule compared to the linear analog, because of the steric hindrance between the bulkier hydrophobic moieties and their lower tendency to cooperatively align perpendicular to the air/water interface. As reported for other branched surfactants, this results in a more disordered monolayer (Green et al, ). C 10 DAO‐branched also presents a lower γ mic , as the higher CMC increases adsorption at the air/water interface.…”

Synthesis of trimellitic anhydride microcapsule toner by liquid‐phase separation

“…This feature is similar to the behavior of alkyl chain surfactants. It should, however, be pointed out that straight and branched alkyl chain surfactants usually follow the reduction of logarithmic CMC with increasing carbon numbers in the alkyl chain 32. For nonionic surfactants, such as differently branched alkyl phenol ethoxylates and alkyl ethoxylates (C m E n ), increase in each carbon number in the hydrophobic chain leads to a factor of 10 in their CMC reduction.…”

Synthesis, aggregation behavior and interfacial activity of branched alkylbenzenesulfonate gemini surfactants

“…Obviously, alkyl side branches generate much more significant increase in CAC and A min for the gemini surfactants than the corresponding single-chain surfactants [19,21]. Normally, the branching of alkyl chains brings about two main effects on the aggregation of surfactants, i.e., steric hindrance and enhanced hydrophobic interaction in the hydrophobic microdomain of aggregates.…”

“…Conventional surfactants with branched hydrophobic chains have been reported, and the effects of branched structure on surfactant micellization and interfacial properties have also been described [16][17][18][19][20][21][22]. For example, Varadaraj et al [16] found that the branching of the hydrophobic chains of ethoxy sulfate and sulfate surfactants resulted in a more porous micelle structure where more water penetrates into the hydrophobic regions of the micelles than in the micelles of the corresponding linear surfactants.…”

“…The activity differences between the branched and linear surfactants at decane/water interface were not as pronounced as at air/water interface. Lu et al [19] studied the monolayer structure of branched nonionic surfactants nonyl phenol oxyethylene glycols at air/water interface by surface tension measurements and neutron reflection, and found much thicker hydrophobic layer relative to the surfactant with fully extended chain. Moreover, morphologies of surfactant aggregates are dependent on the extents and positions of branches relative to headgroups.…”