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Abstract
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Dissipative particle dynamics simulations were performed to investigate the self-assembly
of dipalmitoylphosphatidylcholine (DPPC) as a model lipid membrane on the surface of carbon
nanotubes (CNTs). The influence of surface curvature of CNTs on self-assembly was investigated by
performing simulations on solutions of DPPC in water in contact with CNTs of different diameters:
CNT (10, 10), CNT (14, 14), CNT (20, 20), and CNT (34, 34). DPPC solutions with a wide range of
concentrations were chosen to allow for formation of lipid structures of various surface densities,
ranging from a submonolayer to a well-organized monolayer and a CNT covered with a lipid
monolayer immersed in a planar lipid bilayer. Our results are indicative of a sequence of phase-
ordering processes for DPPC on the surface of CNTs. At low surface coverages, the majority of
hydrocarbon tail groups of DPPC are in contact with the CNT surface. Increasing the surface
coverage leads to the formation of hemimicellar aggregates, and at high surface coverages close to
the saturation limit, an organized lipid monolayer self-assembles. An examination of the mechanism
of self-assembly reveals a two-step mechanism. The first step involves densification of DPPC on the
CNT surface. Here, the lipid molecules do not adopt the order of the target phase (lipid monolayer on
the CNT surface). In the second step, when the lipid density on the CNT surface is above a threshold
value (close to saturation), the lipid molecules reorient themselves to form an organized monolayer
around the tube. Here, the DPPC molecules adopt stretched conformations normal to the surface, the
end hydrocarbon groups adsorb on the surface, and the head groups occupy the outermost part of
the monolayer. The saturation density and the degree of lipid ordering on the CNT surface depend
on the surface curvature. The saturation density increases with increased surface curvature, and
better-ordered structures are formed on less curved surfaces
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