Interfacial Tension
Pressure difference across a curved interface between two static fluids is determined by the surface tension and the local curvature of the boundary. This physical phenomenon, known as laplace pressure, causes the internal pressure of a small droplet or bubble to exceed the pressure of the surrounding continuous phase. The relationship is governed by the Young-Laplace equation, which dictates that the pressure difference is inversely proportional to the radius of curvature.
Microfluidic Behavior
In microfluidic systems, this pressure difference drives the movement of liquid fronts through channels of varying cross-sections. When a liquid encounters a sudden constriction or expansion, the change in meniscus curvature generates a capillary pressure barrier that can be utilized to control flow without moving parts.
Scale Dependence
Because the effect scale is inversely proportional to the channel or droplet size, it becomes the dominant force at the sub-millimeter scale while remaining negligible in larger systems.
Sensing Influence
Precision pressure sensors used in micro-volume applications must be designed to avoid capillary condensation or droplet formation on the sensing diaphragm, as these liquid structures generate localized pressure offsets that distort the measurement. Calibration protocols often require dry gas conditions to eliminate the influence of these capillary forces during zero-point verification. If liquid contact is unavoidable, the sensor surface is treated with a hydrophobic coating to increase the contact angle, thereby minimizing the pressure generated by liquid menisci on the transducer.
