Coarse-grained molecular models of the surface of hair

16 December 2021, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


We present a coarse-grained molecular model of the surface of human hair, which consists of a lipid monolayer, in the MARTINI framework. Using molecular dynamics simulations, we identify a lipid grafting distance that yields a monolayer thickness consistent with atomistic simulations and experimental measurements of hair surfaces. Coarse-grained models for fully-functionalised, partially damaged, and fully damaged hair surfaces are created by randomly replacing neutral thioesters with anionic sulfonate groups. This mimics the progressive removal of fatty acids from the hair surface by bleaching. We study the structure of the lipid monolayer at different degrees of damage using molecular dynamics simulations in vacuum as well as in polar (water) and non-polar (n-hexadecane) solvents. We also compare the wetting behaviour of water and n-hexadecane on the hair surfaces through contact angle measurements conducted using molecular dynamics simulations and experiments. Our model captures the experimentally-observed transition of the hair surface from hydrophobic (and oleophilic) to hydrophilic (and oleophobic) as the level of bleaching damage increases. By using surfaces with different damage ratios, we obtain contact angles from the simulations that are in good agreement with experiments for both solvents on virgin and bleached human hairs. In both the molecular dynamics simulations and further experiments using biomimetic surfaces, the cosine of the water contact angle increases linearly with the sulfonate group surface coverage. We expect that the proposed systems will be useful for future molecular dynamics simulations of the adsorption and tribological behaviour of hair surfaces.


Hair surface
Molecular models
Nanodroplet wetting
Lipid monolayer

Supplementary materials

Electronic Supplementary Information (ESI)
The supplementary material contains additional material, including the MARTINI force field parameters, a CG water model discussion, surface coverage maps, and further wetting data (droplet size effects, hexadecane contact angle fits, droplet density profiles, visual comparison to experiments). Also, AA-MD simulation data is given in more detail here.


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