INVESTIGADORES
PALMA Santiago Daniel
artículos
Título:
Effect of Water Structure on the Formation of Coagels from Ascorbyl-Alkanoates
Autor/es:
LO NOSTRO, PIERANDREA; NINHAM, B.; LAURA FRATONI,; SANTIAGO DANIEL PALMA; HILARIO MANZO, RUBEN; ALBERTO ALLEMANDI, DANIEL; BAGLIONI, P.
Revista:
Langmuir
Referencias:
Año: 2003 vol. 19 p. 3222 - 3228
ISSN:
0743-7463
Resumen:
Ascorbyl-alkanoates (ascorbyl-O-CO-(CH2)n-2CH3, in briefASCn) behave as anionic surfactants. They
form coagels in aqueous dispersions at room temperature. On heating, these hydrated crystalline phases
transform into either micellar solutions or gel phases, depending on the hydrophobic chain length. The
different phase behavior reflects the interplay between interactions that involve the ionic headgroups and
water and those between the hydrophobic chains. Solute-induced modification of water structure might
then be expected to induce significant changes in the coagel-to-gel or coagel-to-micelle phase transitions.
Such effects, induced by sucrose and by urea, are here explored over a wide region of the ASCn/water phase
diagram (5% and 50% w/w). Differential scanning calorimetry and conductivity measurements are used
to probe structure in 1% ASC12/water samples at different temperatures. The coagel phase transition
temperature does not significantly increase with ASCn concentration, while the corresponding enthalpy
change increases linearly with surfactant concentration. The addition of sucrose or urea to the ASCn-O-CO-(CH2)n-2CH3, in briefASCn) behave as anionic surfactants. They
form coagels in aqueous dispersions at room temperature. On heating, these hydrated crystalline phases
transform into either micellar solutions or gel phases, depending on the hydrophobic chain length. The
different phase behavior reflects the interplay between interactions that involve the ionic headgroups and
water and those between the hydrophobic chains. Solute-induced modification of water structure might
then be expected to induce significant changes in the coagel-to-gel or coagel-to-micelle phase transitions.
Such effects, induced by sucrose and by urea, are here explored over a wide region of the ASCn/water phase
diagram (5% and 50% w/w). Differential scanning calorimetry and conductivity measurements are used
to probe structure in 1% ASC12/water samples at different temperatures. The coagel phase transition
temperature does not significantly increase with ASCn concentration, while the corresponding enthalpy
change increases linearly with surfactant concentration. The addition of sucrose or urea to the ASCnn/water phase
diagram (5% and 50% w/w). Differential scanning calorimetry and conductivity measurements are used
to probe structure in 1% ASC12/water samples at different temperatures. The coagel phase transition
temperature does not significantly increase with ASCn concentration, while the corresponding enthalpy
change increases linearly with surfactant concentration. The addition of sucrose or urea to the ASCnn concentration, while the corresponding enthalpy
change increases linearly with surfactant concentration. The addition of sucrose or urea to the ASCnn
aqueous dispersion induces changes in the phase transition temperatures. The phenomenon is related to
the water structure changes due to these cosolutes.