(482c) Effect of Polymer Grafting On the Bilayer Gel to Liquid Crystalline Transition
AIChE Annual Meeting
Wednesday, November 11, 2009 - 3:49pm to 4:06pm
Grafted polymers on the surface of lipid membranes have potential applications in liposome based
drug delivery and supported membrane systems.
The effect of polymer grafting on the phase behaviour of bilayers
made up of single tail lipids is investigated using
dissipative particle dynamics.
The bilayer is maintained in a tensionless state using a barostat. Simulations are carried out
by varying the grafting fraction, defined as the ratio of the number of polymer molecules to
the number of lipid molecules, and the length of the lipid tails.
At low grafting fractions the bilayer shows a sharp transition from the
gel (L β) to the liquid crystalline (L α) phase
This main melting transition temperature is lowered
as the grafting fraction is increased and above a critical value of the grafting fraction additional low temperature phases are
observed in the main transition.
At low temperatures the L β phase is transformed
to the tilted, L β' phase and upon further increase in temperature the interdigitated
L βI phase is observed. The temperature range over which the intermediate L β' and L βI phases are observed
is a function of the lipid tail length and the grafting fraction.
The presence of the intermediate phases is attributed to the increase in area per head group
due to the lateral pressure exerted by the polymer brush. The polymer brush height, area expansion
and decrease in the melting temperatures as a function of the grafting fraction
were found to follow the scalings predicted by the self consistent mean field theories for grafted
polymer membranes. Our study shows that
the grafted polymer density can be used to effectively control the temperature range and occurrence
of a given bilayer phase.