Hi. First of all you should determine which type of droplets you want to generate. oil in water or water in oil. depending on that, you should make the main channel hydrophilic or hydrophobic, respectively. there are some parameters which can contribute to the droplet size such as flow rate ratio, wettability, viscosity and channels geometry. 

Droplet generation. Available from: https://www.researchgate.net/post/Droplet_generation [accessed Jul 10, 2017].

Dear Binbin Cui,

At first  i would like to know that, which geometry configuration you are using? Is it T-junction, flow-focusing or Co-flow?

For any geometry droplet size is function of  ( Flow rate of continuous phase, dispersed phase, both fluids viscosity, interfacial tension and  wall adhesion property)

I. At fixed dispersed  phase flow rate and constant fluid properties( viscosity  of both fluids and interfacial tension ) droplet size can be controlled  by changing the continuous  phase flow rate

similarly, at fixed continuous  phase flow and constant fluid properties by altering the dispersed phase  droplet size can be controlled.

Hope this will useful for you

Best of luck

@sekhar

Dear Somasekhara Goud and Ali Kalantarifard,

I am using flow-focusing configuration and making water-in-oil droplet. The pinching point of droplets (or the narrows gap) is 30um. If I don't treat the channel, the droplet size is around 40um. I tried to tune the droplet size by increasing the aqueous flow rate, but the dynamic range is limited to ~39-48um (before I treat the channel with the aquapel). After I treat the channel with aquapel, the diameter should increase a lot theoretically but I didn't see much difference( the dynamic range is still ~38-50um). I suspect the aquapel is in bad quality first, but the contact angle experiment shows the aquapel is still potent. Then I remember that I didn't flush the channel well after I treat the channel with aquapel (I should flush it with HFE 7500 oil). So is it possible that the overlong treatment of aquaple or drying of aquapel inside the channel will somehow change the geometry of the channel ? (I check the adhesive layer thickness from the aquapel, which is around 5-10nm)

Thank you guys very much!

Dear Binbin,

I would like to know about your theoretical  equation or model. Can share that information, i want to refer  it once.  Typically, the device is treated to make it hydro-

phobic by flushing Aquapel through the channels, and then baking them in an oven set approximately  20 min.

Source: Flow regime mapping of high inertial gas – liquid droplet microflows in flow ‑ focusing geometries.

To the best of my knowledge, most of the people are using Aquapel. However,  currently i am focusing on numerical work, we are about to start experimental work. 

I hope you will get solution form experimental experts.

Wish you all the best .

@sekhar

Dear Sekhar,

I have no equation or model for it. I download the mask design from the following paper:

https://www.nature.com/nprot/journal/v12/n1/extref/nprot.2016.154-S5.zip

Best regards

Bin

Hi Binbin

Some references on attachment 1

https://pubs.acs.org/doi/full/10.1021/nn500810n

2

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0ahUKEwjCuJatzNfWAhXpA5oKHVXaAscQFgg3MAM&url=http%3A%2F%2Fpubs.acs.org%2Fdoi%2Fpdf%2F10.1021%2Fnn500810n&usg=AOvVaw1Kjx92tyXYuUSxEji1EFZy

3

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0ahUKEwjCuJatzNfWAhXpA5oKHVXaAscQFghAMAQ&url=http%3A%2F%2Fwww.nature.com%2Fnprot%2Fjournal%2Fv12%2Fn1%2Ffull%2Fnprot.2016.154.html%3FWT.feed_name%3Dsubjects_physical-sciences&usg=AOvVaw1DKF7UeA6k4J-4Qzm44txz

4

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0ahUKEwjCuJatzNfWAhXpA5oKHVXaAscQFghEMAU&url=https%3A%2F%2Fwww.nature.com%2Farticles%2Fncomms10392&usg=AOvVaw0ooAdjID8-KX0AMaz406ED

5

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=7&cad=rja&uact=8&ved=0ahUKEwjCuJatzNfWAhXpA5oKHVXaAscQFghLMAY&url=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC3885349%2F&usg=AOvVaw1zq4H52FS4qshLZlOuBEiz

6

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&cad=rja&uact=8&ved=0ahUKEwjCuJatzNfWAhXpA5oKHVXaAscQFghRMAc&url=https%3A%2F%2Fwww.ncbi.nlm.nih.gov%2Fpmc%2Farticles%2FPMC4838355%2F&usg=AOvVaw1RWA_z1k95mTiDfRFbP9RG

7

https://sms.crpp-bordeaux.cnrs.fr/Download/PBCS_Gruner_Philipp_klein.pdf

8

https://file.scirp.org/pdf/Soft_2012123110014772.pdf

9

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4128248/

10

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0ahUKEwi4p73lzdfWAhXFYpoKHSVDAdIQFgg0MAM&url=https%3A%2F%2Fwww.nature.com%2Farticles%2Fncomms10392&usg=AOvVaw0ooAdjID8-KX0AMaz406ED

11

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0ahUKEwi4p73lzdfWAhXFYpoKHSVDAdIQFgg7MAQ&url=http%3A%2F%2Fwww.nature.com%2Fnprot%2Fjournal%2Fv12%2Fn1%2Ffull%2Fnprot.2016.154.html&usg=AOvVaw3JqRjihyi3T-HPu8GttrQY

12

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0ahUKEwi4p73lzdfWAhXFYpoKHSVDAdIQFgg_MAU&url=http%3A%2F%2Fpubs.rsc.org%2Fen%2Fcontent%2Farticlepdf%2F2016%2FLC%2FC5LC00823A&usg=AOvVaw0W9ACKrbsvnUUcV5tsOb_x

13

https://sms.crpp-bordeaux.cnrs.fr/Download/PBCS_Gruner_Philipp_klein.pdf

14

https://file.scirp.org/pdf/Soft_2012123110014772.pdf

15

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=13&cad=rja&uact=8&ved=0ahUKEwj4obqcztfWAhWyZpoKHV_QAgw4ChAWCEEwAg&url=http%3A%2F%2Fpubs.acs.org%2Fdoi%2Ffull%2F10.1021%2Fac4026048%3Fsrc%3Drecsys&usg=AOvVaw1dmNlqM8bH3uJ2P61o6aQs

16

https://tel.archives-ouvertes.fr/tel-01273988/document

17

https://freidok.uni-freiburg.de/dnb/download/10783

18

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=17&cad=rja&uact=8&ved=0ahUKEwj4obqcztfWAhWyZpoKHV_QAgw4ChAWCFQwBg&url=http%3A%2F%2Fpeds.oxfordjournals.org%2Fcontent%2F29%2F9%2F355.full&usg=AOvVaw2DwgMT-8uXYFHieLfKWXSB

19

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=18&cad=rja&uact=8&ved=0ahUKEwj4obqcztfWAhWyZpoKHV_QAgw4ChAWCFcwBw&url=https%3A%2F%2Fntnlab.com%2Fwp-content%2Fuploads%2F2016%2F11%2FJ249ActiveDropletFormationReview.pdf&usg=AOvVaw1fJHMpE09FnlSeQfcQe6yv

20

https://daim.idi.ntnu.no/masteroppgaver/015/15742/masteroppgave.pdf

Hi there. The droplet size depends on flow rate ratio or capillary number which is in terms of velocity, kinematic viscosity of the carrier fluid and interfacial tension between two fluids you are using. Therefore, the wettabality (hydrophobicity), flow rate ratio (or velocity ratio) of the fluids and viscosity are important. Btw, it is important which geometry you are using for droplet generation. T junction or flow focusing or other geometries. I am talking about T junction. 

Dear Binbin,

Precise and effective control of droplet generation is critical for applications of droplet microfluidics ranging from materials synthesis to lab-on-a-chip systems. Methods for droplet generation can be either passive or active, where the former generates droplets without external actuation, and the latter makes use of additional energy input in promoting interfacial instabilities for droplet generation. Droplet generation originates from fluid instabilities. In passive microfluidic devices, introduction of one immiscible fluid (dispersed fluid) into another (continuous fluid) typically leads to the formation of droplets in one of the five modes: squeezing,dripping,jetting,tip-streaming and tip-multi-breaking.

Active droplet generation is achieved by incorporating additional components into microfluidic systems. The state-of-the-art techniques mainly apply electrical, magnetic, centrifugal, optical, thermal and mechanical methods, by which electrical, magnetic and centrifugal forces are introduced, and the flow, viscosity, interfacial tension, channel wettability and fluid density are varied.

The microfluidic channel provides the boundary of microflow and thus its geometry would impact the droplet generation as well. Typical microfluidic geometries used in generating droplets, among them, some use viscous shear forces to break off droplets with three types of most frequently used structures being cross-flow, co-flow and flow-focusing geometries.

The delivery of the promising potential of droplet microfluidics relies on our fundamental understanding of the mechanisms responsible for and the development of effective techniques for droplet generation.

Hope it is helpful to you.

Ashish