TY - JOUR
T1 - The Monolayer Structure of the Branched Nonyl Phenol Oxyethylene Glycols at the Air-Water Interface
AU - Green, S. R.
AU - Su, T. J.
AU - Lu, J. R.
AU - Penfold, J.
PY - 2000/2/24
Y1 - 2000/2/24
N2 - The structure of the monolayers formed by a group of monodisperse nonyl phenol ethoxylates with para-substituted 1-butylpentyl chains (para-(C4H9)2CHC6H 4(OC2H4)nOH, abbreviated to BNPEn, 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 BNPE4, 4.0 ± 0.3 × 10-5 M for BNPE8 and 8.0 ± 0.3 × 10-5 M for BNPE12 and the limiting area per molecule (Acmc) at the cmc to be 46 ± 3, 61 ± 4, and 75 ± 5 Å2, respectively. The values of Acmc are almost identical to those obtained from dodecyl ethoxylates (C12En) for the same size of the headgroups, suggesting that Acmc 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 BNPE4, 19 ± 3 Å for BNPE8, and 22 ± 3 Å for BNPE12. 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.
AB - The structure of the monolayers formed by a group of monodisperse nonyl phenol ethoxylates with para-substituted 1-butylpentyl chains (para-(C4H9)2CHC6H 4(OC2H4)nOH, abbreviated to BNPEn, 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 BNPE4, 4.0 ± 0.3 × 10-5 M for BNPE8 and 8.0 ± 0.3 × 10-5 M for BNPE12 and the limiting area per molecule (Acmc) at the cmc to be 46 ± 3, 61 ± 4, and 75 ± 5 Å2, respectively. The values of Acmc are almost identical to those obtained from dodecyl ethoxylates (C12En) for the same size of the headgroups, suggesting that Acmc 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 BNPE4, 19 ± 3 Å for BNPE8, and 22 ± 3 Å for BNPE12. 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.
UR - http://www.scopus.com/inward/record.url?scp=0034708185&partnerID=8YFLogxK
U2 - 10.1021/jp9919009
DO - 10.1021/jp9919009
M3 - Article
AN - SCOPUS:0034708185
SN - 1520-6106
VL - 104
SP - 1507
EP - 1515
JO - Journal of Physical Chemistry B
JF - Journal of Physical Chemistry B
IS - 7
ER -