Micrometer-Scaled Gradient Surfaces Generated Using Contact Printing of Octadecyltrichlorosilane

Abstract

Gradient surfaces are widely employed in biological studies for protein adsorption and cell attachment and growth. They also offer great potential in the areas of fluid flow and combinatorial experimental design for obtaining material properties and behaviors. Gradient surfaces are created with organosilanes by using the diffusion techniques proposed by Ewling and modified by Chaudhury. However, these techniques have limitations. They either generate a significant amount of organic waste or require well-controlled deposition conditions. In this paper, we propose a fast, convenient, reproducible, and inexpensive method that generates gradient surfaces with minimum waste generation. Particularly, we have adopted Whitesides's contact-printing technique to achieve a gradient by gradually varying the contact time over the contacted area using octadecyltrichlorosilane. Elastomeric stamps with different geometries and various radii of curvature are used to generate gradient surfaces at both millimeter and micrometer scales. With this approach, we are able to generate micrometer-scaled gradient surfaces with a gradient steepness 1−3 orders of magnitude higher than those generated using diffusion-based techniques. The energy gradient on these surfaces is verified by the dewetting of polymer (e.g., polystyrene) thin films and by the movement of picoliter and nanoliter water droplets on the surface devoid of other driving forces such as gravity, temperature gradients, or a pressure drop.

Local Heating of Discrete Droplets Using Magnetic Porous Silicon-Based Photonic Crystals

“…Because each droplet can be independently controlled, highly integrated, scalable and flexible architectures can be implemented. 10 A number of techniques have been described for the actuation of droplets on solid surfaces including the use of thermocapillary effects, 14 photochemical effects, 15 electrochemical gradients, 16 surface tension gradients, 17 temperature gradients, 18 air pressure, 19 structured surfaces, 20 dielectrophoresis, 21 and electrostatic methods. 8 An extension of this approach is a liquid-liquid microfluidic system for manipulating freely suspended microliter or nanoliter droplets.…”

Rapid Movement of Water Droplets on the Hydrophobic Surface of ZnO Nanorod Array Impregnated by Lubricant

“…Therefore, researchers have developed various methods to generate wettability gradient surfaces, such as vapor-phase di®usion, [20][21][22][23] photodegradation, 13 gradual immersion 24,25 and microcontact printing. 26,27 On these wettability gradient surfaces, the surface tension of the droplet can overcome the larger hysteresis e®ects that make the movement of micrometer-sized drops more di±cult, and the droplets are expected to move on the surfaces. Nevertheless, the experimental results reveal that the motion distance of droplets is short, and the movement speed is slow, because the motion of the droplet is hindered by viscous drag on the wettability gradient surfaces.…”

Droplet on a regularly patterned solid. Wenzel’s regime and meso-scale roughness

“…Pinning effect may cause a strong wetting hysteresis [44] and wetting anisotropy [45]. The droplet on anisotropic structured surfaces exhibits different CAs along the directions parallel and perpendicular to the surface features [46]; a difference of up to 25% in CA measured for the same droplet was observed [47]. The significance of the triple-line influence on the apparent CA depends on the degree of non-uniformity of the surface roughness; the effect matters much for strongly non-uniform roughness [48].…”