Hi Ali,,

That is an interesting idea and I am sure of some potential commercial interest? I guess it will depend on how fast the chemistry is in the droplets. Generally, ammonium hydroxide is used as the basic catalyst, so it may well diffuse out of the droplets as ammonia gas? It also may be detrimental to any surfactants that you are using if they are not stable to high pH? As long as the droplets are spaced then you can use either small amounts of a very poor surfactant (e.g. a wetting agent) or perhaps even no surfactant at all. Plastic or glass chips may also be a lot better than PDMS.

Sorry, that is what I would try, but I have no experience.

Best of luck, Clive

Hi Clive,

Thx for the comment. I have tried ammonia solution+CTAB+water+ethanol as a dispersed phase and TEOS and silicon oil as continuous phase (based on the Li 2010 paper: DOI: 10.1021/am100593b), but unlike their result I could make nano silica particle. However, they have made 130 um droplet and 137 um silica particle accordingly. As you said this synthesis method is based on the diffusion. So, I think it would lead to one particle per droplet but my results does not reflect that.

I wouldn't use silicon or mineral oil as the continuous phase, as the distribution coefficient of TEOS (log D 1.77, pH 7.4) will favour it diffusing into the oil phase, rather than remaining in the water (discrete phase). Try a fluorous oil and either little or no surfactant, you could use 1H,1H,2H,2H-perfluorooctan-1-ol (PFOH) as a wetting agent. However, adding a wetting agent will increase diffusion, so add the minimum possible. However, the droplets will not be stabilised and so will coalesce if they touch one another. A droplet generator chip with a long delay might work? You might need to add extra spacing oil to ensure their separation until the reaction is complete? I think as long as the walls of your device are fluorophilic, then you should be able to make droplets, but not sure how monodisperse they will be.

Cheers,

Clive

Thanks again Clive,

I read somewhere that the ethanol inside droplet enhances the reaction between water and TEOS. But lets say I will use fluorous oil, then my question is this: May I have one micro particle per droplet? Another problem is having stable droplets because I should take SEM image and show droplet monodispersity, due to that I have to collect all droplets (particles) inside a vial or eppendorf tube. However, as you said I can solve that problem by using droplet spacer (oil injection from a side channel).

Best,