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Related Concept Videos

Surface Tension, Capillary Action, and Viscosity02:57

Surface Tension, Capillary Action, and Viscosity

Surface Tension
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded by other molecules and are attracted equally in all directions by the cohesive forces within the liquid. However, the molecules on the surface of a liquid are attracted only by about one-half as many molecules. Because of the unbalanced molecular attractions on the surface molecules, liquids contract to form a shape that minimizes the number...
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To be visualized by an electron microscope, either transmission or scanning, biological samples need to be fixed (stabilized) so the electron beam does not destroy them and dried thoroughly (desiccated/dehydrated) so the vacuum does not affect them. Fixation needs to be done as quickly as possible because the sample properties will start changing as soon as it is removed from its natural environment. For example, in a tissue sample, the oxygen levels begin decreasing, causing an altered...
Surface Tension and Surface Energy01:16

Surface Tension and Surface Energy

When a paint brush is immersed in water, the bristles wave freely inside the water. When it is taken out, the bristles stick together. The reason behind this effect is surface tension.
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Surface Tension01:24

Surface Tension

Surface tension is defined as the force per unit length (γ) acting along the surface of a liquid. It arises due to strong intermolecular forces of attraction. A molecule located inside the bulk of the liquid is surrounded by other molecules and experiences equal forces in all directions. However, a molecule at the surface experiences unbalanced forces because there are more neighboring molecules below than above. This creates a net inward force that pulls surface molecules toward the interior,...
The Electrical Double Layer01:30

The Electrical Double Layer

In the region where two bulk phases meet, an intricate electric charge distribution arises due to charge transfer, ion adsorption, molecular orientation, and charge distortion. This complex distribution is commonly referred to as the electrical double layer.When a solid electrode interfaces with ions in an electrolyte solution, the speed of electron transfer dictates the rates of oxidation and reduction. The electrode acquires a charge through the escape of atoms into the solution as cations or...
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Surface tension is a fundamental property of fluids, occurring at the boundary between a liquid and a gas or between two immiscible liquids. This phenomenon arises from the cohesive forces between molecules at the fluid's surface, creating an effect similar to a stretched elastic membrane. Inside each fluid, molecules are equally attracted in all directions by neighboring molecules, but surface molecules experience a net inward force, resulting in surface tension.
Surface tension varies with...

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Taking Advantage of Reduced Droplet-surface Interaction to Optimize Transport of Bioanalytes in Digital Microfluidics
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Droplet Actuation on Gradient Electrowetting Surface.

Enqing Liu1,2, Gaifang Chen1, Junyan Tian1

  • 1State Key Laboratory of Integrated Chips and Systems, College of Integrated Circuits and Micro-Nano Electronics, Fudan University, Shanghai, China.

Small (Weinheim an Der Bergstrasse, Germany)
|March 16, 2026
PubMed
Summary
This summary is machine-generated.

Gradient electrowetting (GEW) offers programmable droplet manipulation without fixed electrodes. This new method uses light patterns on a semiconductor surface to control droplet movement, simplifying microfluidic systems.

Keywords:
droplet actuationgradient electrowettingphotoconductive materialphoto‐programmable droplet driving

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Area of Science:

  • Microfluidics and Lab-on-a-Chip Technologies
  • Surface Science and Engineering
  • Optoelectronics and Photonics

Background:

  • Droplet manipulation is vital for microfluidics and water harvesting.
  • Electrowetting-on-dielectrics (EWOD) provides flexibility but is limited by fixed electrode patterns.
  • Existing EWOD methods restrict droplet path reconfigurability.

Purpose of the Study:

  • To introduce a continuous droplet-driving method using gradient electrowetting (GEW).
  • To enable programmable droplet actuation without pre-defined electrode patterns.
  • To simplify microfluidic system architecture and control.

Main Methods:

  • Utilized a photoactive semiconductor surface (amorphous silicon, α-Si).
  • Established a continuous electric potential gradient by imposing current.
  • Manipulated potential distribution using optical patterns projected onto the α-Si layer.
  • Achieved droplet driving and merging via light-induced electrowetting force.

Main Results:

  • Demonstrated continuous droplet driving and merging capabilities.
  • Showcased freely programmable droplet movement without discrete electrodes.
  • Successfully simplified the droplet manipulation system architecture.
  • Validated GEW as a viable alternative to traditional EWOD.

Conclusions:

  • GEW on photoactive surfaces provides a simplified and programmable approach to droplet manipulation.
  • This method overcomes the reconfigurability limitations of conventional EWOD.
  • GEW offers a complementary technology for advanced microfluidic applications.