> You need the submicron particle to travel on a larger liquid particule for it to adhere to the filter lattice
That's what intuition would suggest, but intuition turns out to be wrong when dealing with filters for microscopic things. There are at least four mechanisms by which a filter can trap particles, three of which work on particles smaller than the pores [1].
Briefly:
1. Big particles don't fit between the fibers of the filter. Think fish in a fish net. This is called sieving.
2. Particles too small for sieving but heavier than the surrounding flow don't make the turns as well as the surrounding flow when the flow goes around the fibers. The particles can get embedded in the fibers. This mechanism is called inertial impaction.
3. The smallest might be too small to actually be affected much by the flow of the surrounding fluid through the filter. The move by diffusion, and many will randomly hit the fibers and get stuck.
4. Particles too big for diffusion but too light for inertial impaction still can run into fibers and get stuck. This is called interception.
The effectiveness of sieving, inertial impaction, and interception all follow S shaped curves that start out low for small particles, then at some point start rising, and then level out. The sieving curve's rise is almost vertical. The rise for inertial impaction is steep but not nearly as steep as it is for sieving. The curve for interception's rise is much more relaxed.
The effectiveness for diffusion goes the other way. Much more effective for very small particles, then above some size drops down and is low from then on.
When you put all these together, you get a curve that is effective at the small end, and at some point as size goes up effectiveness drops, reaching a minimum, and then rises again to reach high effectiveness for particles above some certain size.
There is also a fifth mechanism in some filters where electrostatic attraction between the fibers and the particles catches some particles.
That's what intuition would suggest, but intuition turns out to be wrong when dealing with filters for microscopic things. There are at least four mechanisms by which a filter can trap particles, three of which work on particles smaller than the pores [1].
Briefly:
1. Big particles don't fit between the fibers of the filter. Think fish in a fish net. This is called sieving.
2. Particles too small for sieving but heavier than the surrounding flow don't make the turns as well as the surrounding flow when the flow goes around the fibers. The particles can get embedded in the fibers. This mechanism is called inertial impaction.
3. The smallest might be too small to actually be affected much by the flow of the surrounding fluid through the filter. The move by diffusion, and many will randomly hit the fibers and get stuck.
4. Particles too big for diffusion but too light for inertial impaction still can run into fibers and get stuck. This is called interception.
The effectiveness of sieving, inertial impaction, and interception all follow S shaped curves that start out low for small particles, then at some point start rising, and then level out. The sieving curve's rise is almost vertical. The rise for inertial impaction is steep but not nearly as steep as it is for sieving. The curve for interception's rise is much more relaxed.
The effectiveness for diffusion goes the other way. Much more effective for very small particles, then above some size drops down and is low from then on.
When you put all these together, you get a curve that is effective at the small end, and at some point as size goes up effectiveness drops, reaching a minimum, and then rises again to reach high effectiveness for particles above some certain size.
There is also a fifth mechanism in some filters where electrostatic attraction between the fibers and the particles catches some particles.
[1] https://donaldsonaerospace-defense.com/library/files/documen...