Yep. Pore size is critical.
Why would folks post on the container they are filtering into?!? It is an essentially irrelevant detail.
If you’re doing small volumes, Eg:
Then a “syringe filter” at 0.2um will suffice, and the container your filtering INTO could be your coffee cup.
Making more? Get a buchner and a flask.
Scaled again? Use your buddies CLS or a modified beer keg as a receiver…
Hydrophillic 0.22 um filters seem to work better than hydrophobic ones like PTFE, PPE etc. in this case. I have noticed slow to no filtration from PTFE filters before
I can only speak from my own personal experience here, and I’ve always used Nylon and PES to great success. I can’t really comment on PTFE or other similar materials but it would make sense that hydrophilic membranes would perform better considering the foundation of a nanoemulsion is often water based.
Thanks a million for the response . I really do appreciate all you on here. Getting me more knowledgeable day by day ! This forum is a huge blessing to me . Y’all the real MVP’s!!
Another question I have is as far as smaller volumns with using the syringe filter( because I’ll only be doing about 50ml batches at a time) how long does it take for sample to pass through the filter. Obviously I’m hoping to not have to wait around for hours lol…being such small micron sizes we are talking worries me it’s going to be a super long drawn out process making it not worth the time potentially. I know someone mentioned a vacuum pump but I’m guessing that’s for larger volumns that need to be filtered through Buchner and flask?
Thank you man I more than appreciate the in depth responses you guys give me on here. Really deepens my overall knowledge and for that I’m forever thankful!
If you have a proper nanoemulsion, the average particle size should be below 0.2u anyway, so we’re filtering the solution through a filter that has a larger pore size than the bulk of your material.
The reason we use 0.22 micron is two fold, first is that filtering through this pore size is generally considered sterile filtration. We can certainly debate this topic, but the generally accepted consensus is that anything filtered through a 0.22 micron is “sterile”. Assuming you are using sonication as the mode of emulsion, the sonication horn is going to flake off small pieces of the horn into the solution. Filtering will capture all of these.
If you are only filtering 50mL batches at a time, it shouldn’t take more than a couple minutes. Surface area available to filter through will impact your speed of filtration. So if you filter your 50mL solution through a 1 inch diameter vs a 2 inch diameter filter paper, the larger surface area should provide a greater filtration speed, at least to start with as the filter paper starts to catch anything above the 0.22 micron size and that’s when filtration will start to slow.
You will most likely not be able to gravity filter this, so you have three options:
Vacuum assisted filtration. This is self explanatory but can create some foaming if you use surfactants in your nanoemulsion. Not a huge deal, but can become annoying to deal with.
Positive Pressure Displacement. This can be broken down into the other two options. First would be using air pressure to push your material through the filter (this could be similar to using a syringe filter as well). You can use a peristaltic pump to push the material through the filter as well.
Each method will be better suited for certain filtering techniques. Vacuum assisted is ideal for buchner funnel filtration. If you are using a capsule filter or some kind of enclosed vessel with a filter at the base, the other two methods can be employed.
Please keep in mind that if you do encounter resistance in the filter due to large particle sizes slowing down the rate of filtration, using a positive pressure technique can cause the filter to blow out, or may cause other issues related to pressure build up. Vacuum assisted filtration may not have the same maximum speed of filtration, but you also don’t risk blowing out a filter or back pressure building up.
There are a lot of nuances here, but at the end of the day this is just a simple filtration process. Set up a vacuum flask, connect the hose barb to a vacuum, attach a filtration apparatus on top that contains the filter membrane, pour in your 50mL solution, turn the vacuum on. That’s the gist of it. Or pour your 50mL solution into a 100mL syringe and put a syringe filter on the tip. If you encounter excess resistance, turn the syringe upside down, draw the solution back slightly, replace the filter tip with a new filter, then resume filtration.
You rock man seriously !! Usually I almost always need to ask a couple more questions after my initial to get more clarity but you really broke things down in a very comprehensive way for me. Better response than I could of possibly asked for. Thanks for the help this will make the whole process much easier for me now 
