(482c) Effect of Polymer Grafting On the Bilayer Gel to Liquid Crystalline Transition

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.