Thermally Tailored Gradient Topography Surface on Elastomeric Thin Films

Abstract

We report a simple method for creating a nanopatterned surface with continuous variation in feature height on an elastomeric thin film. The technique is based on imprinting the surface of a film of thermo-curable elastomer (Sylgard 184), which has continuous variation in cross-linking density introduced by means of differential heating. This results in variation of viscoelasticity across the length of the surface and the film exhibits differential partial relaxation after imprinting with a flexible stamp and subjecting it to an externally applied stress for a transient duration. An intrinsic perfect negative replica of the stamp pattern is initially created over the entire film surface as long as the external force remains active. After the external force is withdrawn, there is partial relaxation of the applied stresses, which is manifested as reduction in amplitude of the imprinted features. Due to the spatial viscoelasticity gradient, the extent of stress relaxation induced feature height reduction varies across the length of the film (L), resulting in a surface with a gradient topography with progressively varying feature heights (hF). The steepness of the gradient can be controlled by varying the temperature gradient as well as the duration of precuring of the film prior to imprinting. The method has also been utilized for fabricating wettability gradient surfaces using a high aspect ratio biomimetic stamp. The use of a flexible stamp allows the technique to be extended for creating a gradient topography on nonplanar surfaces as well. We also show that the gradient surfaces with regular structures can be used in combinatorial studies related to pattern directed dewetting.

Dynamics of droplet impingement on bioinspired surface: insights into spreading, anomalous stickiness and break-up

“…Positive replica of naturally occurring rose petal and lotus leaves (electronic supplementary material, figure S1) are used as patterned surfaces, which are fabricated by sequential double replication of fresh lotus leaf and rose petals, respectively. First, a perfect negative replica of the leaf/petal, is obtained by pouring Sylgard 184 solution on them and subsequently cross-linking the PDMS at room temperature over a period of 3 days [32]. High-temperature cross-linking is deliberately avoided to ensure that there was no thermal damage to the leaf or the petal.…”

“…UV irradiation at 184.9 nm wavelength dissociates molecular oxygen to atomic oxygen, which recombines again with molecular oxygen to form ozone. The ozone subsequently dissociates to atomic oxygen by the action of UV-C irradiation at wavelength = 253.7 nm [32]. The atomic oxygen reacts with the siloxane group of cross-linked PDMS forming a stiff oxide layer on its surface.…”

Superhydrophobic and low-hysteresis coating based on rubber-modified TiO2/SiO2 nanoparticles

“…The surface energy of a hydrophilic coating is higher than the hydrophobic surfaces, and a water droplet can move on it due to solid-liquid interactions [6,7], arising from the gradient in surface energy. A gradient surface is a coating, in which its wettability varies from superhydrophobic to superhydrophilic [8]. These surfaces can be achieved by controlling the wettability of the coatings layer on a substrate [6,7].…”

Gradient wettability induced by deterministically patterned nanostructures

“…In addition, electrochemistry has also been applied to fabricate morphology gradients, where in-plane potential gradients are utilized to generate progressively varied nanopores 26 . Many other approaches based on magnetic 27 , thermal [28][29][30] , and humidity 31 gradients have also been used to fabricate gradient topography surfaces.…”