To answer properly we need more precision, what type of particle are you trying to synthesize? On a general basis, yes there is a significant effect of stirring in particles synthesis, the faster the stirring the smaller the particles (to a certain extend off course), and if you are looking for rode shape particles then the stirring should be as minimum as possible and sometimes no stirring is better (gold nanorods).

To answer properly we need more precision, what type of particle are you trying to synthesize? On a general basis, yes there is a significant effect of stirring in particles synthesis, the faster the stirring the smaller the particles (to a certain extend off course), and if you are looking for rode shape particles then the stirring should be as minimum as possible and sometimes no stirring is better (gold nanorods).

Thank You Philippe.

I am trying to synthesize two types of nanoparticles. one is lipid based nanoparticles and another is inorganic hydroxyapetite nanoparticles. I am looking for irregular shape or other than spherical shape nanoparticles. 

Static process in some cases could lead to local gradient of concentration resulted in increased polydispersity

Dear Darsheen,

As Philippe and Alexander said, the stirring conditions can be crucial to determine what kind of particle shape and size dispersity is obtained due to different growth rates (kinetic control) and mass transport gradient conditions after nuclei are already formed. Additionally, lipids might act as particle stabilizers (capping agents) which could also make the particles grow in preferential orientations (in the case of crystalline materials) as similar to some kind of surfactants (CTAB, etc.). It won´t be surprising if you obtain different sizes and shapes of your particles with this kind of molecules and different stirring rates. Please, also check if you are using strong reducer agents (NaBH4, etc.) or milder ones (citrate, CTAB, ascorbic acid, etc.) in order to control the seeding (nuclei size and shape) process and subsequently their controlled growth. 

Best luck

Kind regards,

 Thank You so much Rafael, Philippe and Alexander...

Effect of stirring rate will be more pronounced for lipid nanoparticles because stirring is responsible for size reduction in this case (upside-down or top-to-bottom process). Nanoparticles are formed liquid which may acquire slightly oblong shape at very high stirring rate especially when they are large. Particles may be allowed to solidify afterwards.

However, inorganic hydroxyapetite nanoparticles may form from bottom-to-top process where small molecules combine to form nano-scale particles. Thus effect of stirring may be less pronounced.   

Thank you Mubashar Rehman and R. Jagathesh Chandra Bose