Programmable Droplet Transport Using Mechanically Adaptive Chemical Gradients with Anisotropic Microtopography

Abstract

The effect of anisotropic surface roughness on the spontaneous transport of droplets on chemical wettability gradients has not been investigated. Understanding the details of this process has the potential to unlock new fluid handling functionality critical to the development of next‐generation surfaces with intelligent control capabilities. Herein, the fabrication of chemical gradients with mechanically tunable anisotropic microtopography (microwrinkles with directional roughness) is described and the use of these surfaces in programable microdroplet transport is reported. In particular, the interplay between chemical gradient intensity, microwrinkle orientation, and droplet velocity/trajectory was investigated, enabling the rational synthesis of surface fluidic systems capable of mechanically programmable 2D droplet manipulations, vertical droplet transport, and droplet combination. These findings highlight the sophisticated capabilities of mechanically switchable droplet handling systems and demonstrate new avenues for designing intelligent materials with programable transport properties for potential use in surface/microfluidics, water harvesting, energy generation, bioanalysis, and microreactor design.

Functional PDMS Elastomers: Bulk Composites, Surface Engineering, and Precision Fabrication

“…[ 205 ] In addition, their team has investigated the effect of anisotropic PDMS surface roughness on droplet spontaneous transport. [ 206 ] In particular, the correlation between chemical gradient strength, micro‐wrinkle orientation, and droplet velocity/trajectory was investigated. Knowing the details of this process shows the potential to unlock new fluid handling capabilities, which are essential for the development of next‐generation intelligent surfaces.…”

Robotic digital microfluidics: a droplet-based total analysis system

“…33 Consequently, enhanced efficiency of some operations, e.g., mixing, leads to shortening the duration of the assays (see ESI † Video S2). Besides, the droplet route can be flexibly designed considering the assay, while in some DMF platforms, droplets are transported in particular directions that cannot be changed after fabrication (such as EWOD and surface gradient 22,34 ). In contrast, RDMF cannot transport multiple droplets at the same time, which EWOD offers.…”

“…In contrast, mechanical approaches offer more straightforward manipulation techniques for a wide range of droplet sizes. 27 Implementing vibrating surfaces, 21 rotating surfaces, 20 and wetting gradients on the surface 22,28 are some of the reported mechanical techniques. Wire-guided droplet manipulation is a mechanical approach in which a robotic arm moves a metal wire above a superhydrophobic surface.…”

Designing of anisotropic gradient surfaces for directional liquid transport: Fundamentals, construction, and applications

“…Chemical gradient surface has been applied to control droplet transport with a direction toward the more lyophilic (LI) side. 66 , 67 , 68 , 69 , 70 In 1992, Chaudhury and Whitesides first proposed a type of drop directional transport pathway caused entirely by surface chemical gradient. 54 By exposing a silicon wafer to heterogeneous decyltrichlorosilane vapor to construct a surface free-energy gradient, the water was induced to move directionally from the hydrophobic (larger contact angle) to the hydrophilic side (smaller contact angle), guided by the asymmetry forces of surface tension acting on the liquid/solid contact line.…”