Surface micelles of CF3(CF2)(7)(CH2)(10)COOH on aqueous La3+ subphase investigated by atomic force microscopy and infrared spectroscopy

Citation
Yz. Ren et al., Surface micelles of CF3(CF2)(7)(CH2)(10)COOH on aqueous La3+ subphase investigated by atomic force microscopy and infrared spectroscopy, J PHYS CH B, 105(19), 2001, pp. 4305-4312
Citations number
20
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHYSICAL CHEMISTRY B
ISSN journal
1520-6106 → ACNP
Volume
105
Issue
19
Year of publication
2001
Pages
4305 - 4312
Database
ISI
SICI code
1520-6106(20010517)105:19<4305:SMOCOA>2.0.ZU;2-U
Abstract
CF3(CF2)(7)(CH2)(10)COOH spontaneously assembles into monodispersed nanomet er-sized micelles after spreading onto the aqueous lanthanum acetate subpha se in a Langmuir trough at 283 K, according to the atomic force microscope (AFM) images. Polarization modulation infrared reflection absorption spectr oscopy (PM-IRRAS) and ordinary polarized infrared spectroscopy are applied to study the surface micelles in situ on the aqueous subphase and ex situ o n the solid substrate, respectively. The long axes of the -(CH2)(7)- helix and -(CH2)(10)- chain are slightly inclined, with tilt angles of 25 +/- 3 d egrees, on the solid substrate and basically so inclined on the aqueous sub phase. The micelle formation comes from a subtle interplay of the steric hi ndrance imposed by the bulky -(CH2)7- helix and the van der Waals interacti on between the underlying -(CH2)10- chains. The micelle has a CH2 antisymme tric stretching [nu (as)(CH2)] frequency of 2918.0 +/- 0.1 cm(-1) on the so lid substrate and 2916.4 +/- 0.2 cm(-1) on the aqueous subphase, correspond ing to a predominantly trans zigzag planar chain conformation. This trans z igzag chain has a hexagonal packing in the micelle. Elevating the subphase temperature from 283 to 303 K and keeping the temperature at 303 K for some time (30-120 min) causes the micelles to fuse into each other, according t o the AFM images. In the fused monolayer, the hydrocarbon segment has a hig her nu (as)(CH2) frequency of similar to 2920 cm(-1), implying that some ga uche kinks appear during the thermal treatment. It is found that micelle fu sion occurs preferentially at zero surface pressure in loosely packed monol ayers rather than at 20 mN/m in tightly packed monolayers. Finally, the com bined in situ and ex situ infrared characterization of the surface micelles eliminates transfer artifacts concerning the headgroup orientation.