Description
Oleophilic polymer brushes serve as liquid-infused slippery surfaces that facilitate e.g. the motion of water drops. Similarly, they can act as flexible surface-grafted transport layers for oil in advanced lubrication techniques. Here, we demonstrate that swelling and wetting properties of model oils on poly n-alkyl methacrylate bottle brushes can be tuned by varying the length of n-alkyl side chains of the brush. While brushes with short lauryl side chains swell easily and display complete wetting for pure alkanes [1], brushes with longer octadecyl side chains remain collapsed and display partial wetting at room temperature along with weak adhesion in AFM force curves. Non-linear optical sum frequency generation suggests that this is caused by CH3-terminated ordering of the side chains. Upon increasing temperature, such brushes undergo a two-stage transition, where first the bulk of the polymer melts, accompanied by partial swelling but still finite contact angles. Only when the surface ordering disappears a few degrees higher, brushes fully swell and become completely wetted. At the same time, AFM force curves display long pull-off distances of several hundred nanometers suggesting pulling of bunches of polymer molecules (and occasionally also individual one). We rationalize the surface-ordering of the of the alkyl chains in terms of the well-known surface freezing of pure alkanes, which – remarkably – has also been reported for bulk poly n-alkyl methacrylates. We discuss possibilities of thermo-responsive lubricant transport based on these phase transition.[1] Ö. Kap, S. Hartmann, H. Hoek, S. de Beer, I. Siretanu, U. Thiele, F. Mugele, Nonequilibrium configurations of swelling polymer brush layers induced by spreading drops of weakly volatile oil, J. Chem. Phys. 158, 174903 (2023).
| Period | 1 Sept 2024 |
|---|---|
| Event title | 38th ECIS conference, 2024 |
| Event type | Conference |
| Conference number | 18 |
| Location | Kopenhagen , DenmarkShow on map |
Documents & Links
- abstract_Mugele_Surface freezing_template
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