INTEMA   05428
INSTITUTO DE INVESTIGACIONES EN CIENCIA Y TECNOLOGIA DE MATERIALES
Unidad Ejecutora - UE
artículos
Título:
Thermodynamic Model of Liquid-Liquid Phase Equilibrium in Solutions of Alkanethiol-Coated Nanoparticles
Autor/es:
EZEQUIEL R. SOULÉ; CRISTINA E. HOPPE; JULIO BORRAJO; ROBERTO J. J. WILLIAMS
Revista:
INDUSTRIAL & ENGINEERING CHEMICAL RESEARCH
Editorial:
AMER CHEMICAL SOC
Referencias:
Año: 2009
ISSN:
0888-5885
Resumen:
A thermodynamic model for a
mixture of alkanethiol-coated nanoparticles (NPs) and low molecular
weight (non-polymeric) solvent is developed, and calculations of
liquid-liquid phase equilibrium for different values of NP core radius,
alkanethiol chain length, solvent molar volume and alkanethiol-solvent
interaction parameter, are presented. The model takes into account the
swelling of the organic coronas and the dispersion of particles with
swollen coronas in the solvent. The energetic interaction between alkyl
chains and solvent is considered, both within the corona and between
the outer alkyl segments and free solvent. Swelling involves mixing of
alkanethiol chains and solvent in the corona and stretching of the
organic chains. Dispersion considers an entropic contribution based on
Carnahan Starling equation of state and an enthalpic term calculated
considering the surface contacts between alkyl segments placed in the
external boundary of the corona and the molecules of free solvent. Two
different kinds of phase equilibrium are found. One of them, observed
at high values of the interaction parameter, is the typical
liquid-liquid equilibrium for compact NPs in a poor solvent where a
complete phase separation is observed when cooling (increasing the
interaction parameter). The second liquid-liquid equilibrium is
observed at low values of the interaction parameter, where swelling of
coronas is favored. In this region two different phases co-exist, one
more concentrated in NPs that exhibit relatively compact coronas and
the other one more diluted in NPs with extended coronas. In diluted
solutions of NPs the deswelling of the fully extended coronas takes
place abruptly in a very small temperature range, leading to a solution
of compact NPs. This critical transition might find practical
applications similar to those found for the abrupt shrinkage of
hydrogels at a critical temperature.