The pore size of membrane filters is crucial for their effectiveness in various applications, including dissolution sample filtration, sterilization, water purification, and air filtration. Measuring the pore size accurately ensures the membrane performs as expected. Here's an in-depth look at the method used to determine membrane pore size:
Bubble Point Method
The bubble point method is a common and practical technique for determining the pore size of microporous membranes. Here's how it works:
Wetting the Membrane: The membrane is first wetted with a suitable liquid, which can be water or an organic solvent, ensuring that the liquid fills the pores completely.
Mounting the Membrane: The wetted membrane is placed in a holder where one side of the membrane is exposed to the liquid, and the other side is exposed to air.
Applying Pressure: Air pressure is gradually increased on the air side of the membrane.
Observing Bubble Formation: At a specific pressure, the air will force the liquid out of the largest pores, creating a steady stream of bubbles on the liquid side. This pressure is noted as the bubble point pressure.
Calculating Pore Size: The bubble point pressure is inversely proportional to the pore size. Using the Young-Laplace equation, the pore size can be calculated:
𝑑=4𝛾cos𝜃/𝑃
d is the pore diameter.
γ is the surface tension of the liquid.
θ is the contact angle between the liquid and the membrane.
P is the bubble point pressure.
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