Apply surface wettability gradient to non-wetting capillary: A simulation study on spontaneous droplet flow

Dingni Zhang,Yuxiang Wang,Qianqian Shangguan

doi:10.1063/1.5047450

Dingni Zhang, Yuxiang Wang + Show 1 more

Open Access

https://doi.org/10.1063/1.5047450

Copy DOI

Journal: AIP Advances	Publication Date: Sep 1, 2018
Citations: 8	License type: cc-by

Affiliation: Shanghai Normal University, Monash University

Abstract

The present work simulates a concept about how to drive droplet flowing through non-wetting (hydrophobic) capillaries without any external force by using many-body dissipative particle dynamics. By decorating the capillary segments with wettability gradients, a droplet with proper radius can be absorbed by the non-wetting capillaries and then constantly flow through the capillary. The simulation results show the droplet can keep flowing through the whole capillaries under certain wettability gradients and the flow velocity also depends on the degree of the wettability gradients. The average wettability of the whole capillary is also essential for the continuous flowing, higher non-wetting capillaries can still keep the flowing with low wettability gradients due to less surface adhesion. A strategy on how to achieve longer flow pathway is also presented. It is also find that unbalanced uptake of droplet via lateral heterogeneous surfaces cannot stir the inside flow of the droplet. The simulation results could inspire the new design of microfluidics in which the transportation of droplet is an important aspect.

Highlights

Microfluidic systems have been proven to be useful platforms for many applications in physics, chemistry, biotechnology or even logical devices.[1]
After the creation of this original Dissipative particle dynamics (DPD), many new features have been developed and new variants have been added into DPD family, such as energy-conserving DPD,[15] smoothed DPD,[16] transport DPD,[17] charged DPD18 and DPD with short-range repulsive and long-range attractive forces.[19]
As common physical phenomena widely happening in nature, a hydrophilic capillary can absorb liquid from a reservoir and on the other hand, a hydrophobic capillary will drain the liquid out of itself, the relation between the wettability of the capillaries and the flow direction of liquid can be described by Eq (6): h

Summary

Introduction

Microfluidic systems have been proven to be useful platforms for many applications in physics, chemistry, biotechnology or even logical devices.[1]. Microfluidic systems have gained increasing popularity for its usefulness and economy. Some ways are employed to produce driving forces, such as electrostatic, thermal or optical sources. To use these sources of power, supporting devices like pumps, valves and connectors must be included. These supporting devices will add extra difficulties to the design of systems, or even introduce cross-contamination. To develop microfluidics without pumps and related supporting devices has become essential for the design of new types of microfluidics

Methods

Results

Conclusion