INVESTIGADORES
WILKE Natalia
congresos y reuniones científicas
Título:
Compressibility of a two phase monolayer system at the air/water interface. Effect of the phase area percent
Autor/es:
F. VEGA MERCADO, B. MAGGIO Y N. WILKE
Reunión:
Congreso; XXXVIII Reunión anual de la Sociedad Argentina de Biofísica; 2009
Resumen:
Many
biologically important monolayers show coexistence of discrete domains of
long-range ordered condensed phase dispersed in a continuous, disordered,
liquid-expanded phase. In this work, we studied the viscous and elastic
compressibility modulus and the shear viscosity of monolayers exhibiting phase
coexistence with the aim of elucidating the contribution of each phase
properties on the observed monolayer properties. With this purpose, mixed
monolayers of different proportions of distearoilphosphatidylcholine (dspc) and
dimiristoilphosphatidylcholine (dmpc) were prepared and their rheological
properties were analyzed.
We find that the isothermal compressibility modulus shows
a non-ideal behavior with the mole fraction. At 10 mN m-1, the compressibility
of the mixed monolayer is independent of the dspc amount up to about 60% of
dspc (40% of the monolayer area occupied by the condensed phase). For higher
dspc content, the modulus increases linearly.
The diffusion coefficient of the domains inserted in
the monolayer, which depends on the shear viscosity, decreases to zero as the
content of dspc is increased in the mixture. Both independent measurements are
consistent because when the domain crowding is high, domains are unable to exchange
nearest neighbors, becoming trapped within a cage formed by the neighbors. In
these conditions, domain-domain repulsion prevails over the thermal entropy and
the monolayer becomes less compressible.
On the other hand, we found that the increase in the
compressibility modulus at high dspc content is related to an increase in the
loss component, which is also in agreement with the decrease in the domain
Brownian movement and the increase in domain-domain interaction.