Effect of hydrophilic- and hydrophobic-chain lengths on the phase behaviorof A-B-type silicone surfactants in water

Citation
H. Kunieda et al., Effect of hydrophilic- and hydrophobic-chain lengths on the phase behaviorof A-B-type silicone surfactants in water, J PHYS CH B, 105(23), 2001, pp. 5419-5426
Citations number
36
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
23
Year of publication
2001
Pages
5419 - 5426
Database
ISI
SICI code
1520-6106(20010614)105:23<5419:EOHAHL>2.0.ZU;2-X
Abstract
The phase behavior of a long hydrophobic chain A-B-type silicone surfactant , Me3SiO-(Me2SiO)(m-2)-Me2SiCH2CH2CH2-O-(CH2CH2O)(n)H (Si-m C3EOn), in wate r was investigated by phase study and small-angle X-ray scattering (SAXS). The types of liquid crystals or self-organized structures are highly depend ent on both EO-chain (n) and poly(dimethylsiloxane)-chain (m) lengths or th e volume ratio of the EO chain to the total surfactant, nV(EO)/V-S, which i s related to the classical Griffin's HLB value. Reverse discontinuous cubic phase (I-2) for Si14C3EO7.8 and Si25C3EO7.8,12.2,15.8, reverse hexagonal p hase (H-2) for Si14C3EO12, lamelar (L-alpha) phase for Si14C3EO15.8 and Si2 5C3EO51.6, and hexagonal (H-1) and discontinuous cubic (I-1) phases for Si5 .8C3EO36.6,(51.6) are formed. Hence, both hydrophobic and hydrophilic chain s affect the surfactant layer curvature, but in an opposite way. On the oth er hand, the effective cross sectional area per surfactant at the hydrophob ic surface of self-organized structures, as, increases with increasing m (o r n) at constant n (or m). as is related to the amphiphilicity of surfactan t (surfactant size). Since the surfactant layer curvature changes from posi tive to negative with increasing m at constant n, the l(eff)/l(max) decreas es with m, where l(eff) is the effective hydrophobic-chain length and l(max ) is the length of the chain in its fully extended form. Namely, the entrop y loss of a long hydrophobic chain would be largely increased when it is st retched, and thus, long hydrophobic chain tends to be in a shrunk-bulky sta te. This causes the expansion of ns and the change in the surfactant layer curvature from positive to negative. In a similar mechanism, as increases w ith increasing the EO-chain length, n, but the surfactant layer curvature c hanges from negative to positive.