TY - JOUR
T1 - Structural Characterization of Frozen n-Heptane Solutions of
Metal-Containing Reverse Micelles
AU - A Longo; G Portale; W Bras; F Giannici; A Ruggirello; Turco Liveri V
AU - Turco Liveri, Vincenzo
AU - Ruggirello, Angela Monia
PY - 2007
Y1 - 2007
N2 - The microstructure of temperature-quenched solutions of reverse micelles formed by sodium, cobalt, ytterbium,
and cobalt/ytterbium bis(2-ethylhexyl)sulfosuccinate in n-heptane has been investigated by SAXS and EXAFS. Some
changes in the X-ray absorption spectra with respect to the same systems at room temperature have been observed.
The analysis of the SAXS spectra leads to the hypothesis that at 77 K the closed spherical structure of reverse micelles
is retained and that during the temperature quench they undergo a clustering process involving the transition from
a quite random dispersion to the formation of more or less large clusters of strongly packed reverse micelles. This
behavior is attributed to competitive effects caused by the temperature decrease. The prevalence of intermicellar
attractive interactions with respect to Brownian motions leading to a collapse to more compact structure is in competition
with the rapid decrease of reverse micelle diffusion rate involving a freezing of the local structures. In the case of
cobalt, ytterbium, and cobalt/ytterbium bis(2-ethylhexyl)sulfosuccinate reverse micelles, further information from
EXAFS measurements indicates that within the reverse micelle core exists a quite ordered nanosized domain composed
of water, surfactant counterions, and oxygen atoms of the SO3
- head groups. The conservation of local order and
inverse structure during the clustering phenomenon that results from the fast freezing with liquid nitrogen of solutions
of reverse micelles could have biological implications, i.e., the preservation of tissue samples at cryogenic temperatures.
AB - The microstructure of temperature-quenched solutions of reverse micelles formed by sodium, cobalt, ytterbium,
and cobalt/ytterbium bis(2-ethylhexyl)sulfosuccinate in n-heptane has been investigated by SAXS and EXAFS. Some
changes in the X-ray absorption spectra with respect to the same systems at room temperature have been observed.
The analysis of the SAXS spectra leads to the hypothesis that at 77 K the closed spherical structure of reverse micelles
is retained and that during the temperature quench they undergo a clustering process involving the transition from
a quite random dispersion to the formation of more or less large clusters of strongly packed reverse micelles. This
behavior is attributed to competitive effects caused by the temperature decrease. The prevalence of intermicellar
attractive interactions with respect to Brownian motions leading to a collapse to more compact structure is in competition
with the rapid decrease of reverse micelle diffusion rate involving a freezing of the local structures. In the case of
cobalt, ytterbium, and cobalt/ytterbium bis(2-ethylhexyl)sulfosuccinate reverse micelles, further information from
EXAFS measurements indicates that within the reverse micelle core exists a quite ordered nanosized domain composed
of water, surfactant counterions, and oxygen atoms of the SO3
- head groups. The conservation of local order and
inverse structure during the clustering phenomenon that results from the fast freezing with liquid nitrogen of solutions
of reverse micelles could have biological implications, i.e., the preservation of tissue samples at cryogenic temperatures.
UR - http://hdl.handle.net/10447/13525
M3 - Article
VL - 23
SP - 11482
EP - 11487
JO - Langmuir
JF - Langmuir
SN - 0743-7463
ER -