Apart from providing textures or roughening the PDMS for increasing the contact angle, is there any coating (silane based or whatsoever) which can be applied on textured PDMS to increase the contact ange further?
For being specific, by texturing the PDMS I am getting CA around 130 degrees but drop is sticking to the surface. My main goal is to move the droplet on textured PDMS surface with ease. In this regard, does coating affect the movement of droplet?
At the equilibrium one has the following connection between the wetting parameter Lambda and contact (dihedral) angle Theta:
Lambda = Cos Theta, where one has following relationship in terms of surface Helmholtz free energies: FSub substrate, FInt interface, and FFilm film:
Lambda= (FSub - Fİnt / FFilm. This connection shows that Lamdha =1 corresponds to perfect wetting with Theta= 0 ; Lambda=-1 shows dewetting having Theta=180o (point contact) ; Lambda=0 gives Theta =90o having semi-spherical appearance. For coherent interface without mismatch one expect to have FInt =0. This case corresponds to the maximum contact angle for given substrate material.
In order to get large contact angle (i.e.; small contact area) one should have an interface which has much higher surface free energy than the energy of substrate itself. I think if you can apply a very thin layer of TeflonTM fabric protector which repels any foreign objects and rolling would be also very easy because of very low friction coefficient.
CA about 130°C is possible to obtain with pillars and mushroom shaped texturation for a wide range of liquid surface tension. PFTS is well adapted to increase CA.
In order to describe droplet stickiness behavior you can measure CA hysteresys.
have a look on these papers, I think you can find more informations:
From micro to nano reentrant structures: hysteresis on superomniphobic surfaces
R Dufour, G Perry, M Harnois, Y Coffinier, V Thomy, V Senez
Colloid and Polymer Science 291 (2), 409-415
Engineering sticky superomniphobic surfaces on transparent and flexible PDMS substrate
R Dufour, M Harnois, Y Coffinier, V Thomy, R Boukherroub, V Senez
Langmuir 26 (22), 17242-17247
Contact angle hysteresis origins: Investigation on super-omniphobic surfaces
R Dufour, M Harnois, V Thomy, R Boukherroub, V Senez
Soft Matter 7 (19), 9380-9387
this paper might be helpful to you
http://www.ncbi.nlm.nih.gov/pubmed/22590992
Refer this linK:https://www.google.co.in/?gfe_rd=cr&ei=iwT4Vd7EBfDH8genyISwCw&gws_rd=ssl#q=increase+contact+angle
The below all the factors are important:SURFACE TENSION
SURFACE ENERGY OF SOLID SURFACES
INTERACTION FORCES BETWEEN LIQUID MOLECULES
SURFACE ROUGHNESS
TEMPERATURE OF LIQUID
It turns out that the surface roughness of the substrate in nano-scale dimensions becomes very important for the enhancement of the apparent sticking power of the droplets where the contact angle and contact surface don't have any meanings what soever because of the fractal nature of the underlying surface. Then the surface should be finished by ultrasonic grinding or painting with some polymerization technique as mentioned by some colleagues here.
Silane modification enhances the adhesion. For more details go through below link.
http://www.sciencedirect.com/science/article/pii/S0032386116301227
HMDS can be used. For more details go through below link.
https://www.mdpi.com/2079-6412/9/1/36/pdf
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