Researches at Cai Group 

Nanoscale Spreading, Wetting and Adsorption of Hydrocarbons on the Chemically & Topographically Patterned Surface

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A New View on Spreading

 

Intuitively, spreading just involves the liquid and the solid surface. Actually, in the spreading of liquid alkane, it is not the case. Molecules in vapor adsorb on the surface even before the liquid-solid contact line arrives.   

 

The actual spreading scenario is: Liquid spreads on an adsorbate layer (from vapor).

 

The theme of our research is to investigate the effects of the adsorbate layer on the spreading, wetting, capillary flow and tribological properties.

 

The Main method of our research is surface patterning, which can control and manipulate the size, geometry and positions of liquids on surface at nanoscale. 

 

Our experimental approach to tackle the spreading over the nanometer scale is to use the step patterning:

 

· a) n the first, we will fabricate a high-surface energy lyophilic (liquid attractive) pattern –OTSpd (the blue disk) on the low-surface energy, lyophobic  (liquid repelling) OTS film surface.

· b) Then the alkane will be dip-coated onto this pattern. 

· c) In the next step, we will use scanning probe lithography to engineer different patterns on OTS surface.

· d) we will use scanning probe lithographyt o modify the regions surrounding the alkane drop to different chemistries and topographies.   

· e) Finally, we will raise temperature to melt the alkane to liquid, and trigger  the spreading  of alkane over the engineered surfaces. Then cool the sample down, the alkane will freeze.  We can infer the spreading process from the solidified alkane pattern.

The two-step patterning. (a) alkane (red dot) assembled on the OTSpd pattern. (b) Fabrication of a new OTSpd region surrounding the alkane drop. (c) The surface after the removal of the alkane drop. a1, b1 and c1 are the schematic views. a2, b2, and c2 are the actual AFM scans over the same region corresponding to the schematic views.

Fascinating  Alkane Spreading Patterns

Alkane preferentially spreads along the border of the surface pattern. (Topography)

Alkane preferentially spreads along the border of the surface pattern. However, the alkane pattern does not really touch the border of the surface pattern. (Phase image)

Alkane spreads over the textured surface.  (Topography)

The Two-Step Patterning Method to control Liquid and Study Spreading

The OTSpd patterns created in two steps are homogenous and continuous