Nanoparticles polystyrene beads

[vaasuh]

I'm doing a project with polystyrene nanobeads as standard size measurement on a device. We ordered some nanobeads from a company, 100nm, 1µm and 5µm. They are all 100mg/ml and solved in water with sds in it. When i dilute them to 1 mg/ml it seems the 1µm is a lot more dense then the 100 nm and 5µm, we contacted the company and they said everything was ok.

 

does anyone have experience with these nanobeads and is it normal or explainable that the 1µm look a lot more "milky" then the 100nm and 5µm when they are the same concentration?

[mississippichem]

Yes, that is normal. The larger particle size should make the solution more opaque. Remember that these beads are not soluble in the water. If not for the SDS surfractant, you would have just a bunch of particles at the bottom of your beaker.

 

As far as the appearance goes, think about scatteting and its relation to particle size.

[vaasuh]

They won´t sediment that fast they have almost the same density as the water(1,06 if I remember correct). It's possible to "clean" them and then dissolve them in normal water, the SDS solution is just to prevent clustering.

 

But when I understand correct what your saying the 100 nm should be the most milky one? I see the 100 nm and 5µm look the same and 1µm looks a lot less opaque.

 

I can post a picture to show it?

[mississippichem]

Yes please post pictures. I would have expected the larger particle size colloid to be more opaque from experience and theory.

 

Can you tell the details on how the density was measured?

 

Do you have a access to a dynamic light scattering machine to accurately measure particle size?

[vaasuh]

I didnt measure the density,the particles were ordered 100 mg/ml. We measured the size with PCS/DLS and these were correct 100 nm, 1µm and 5µm, we are not able to measure the density of the particles.

 

I hope the picutre works I never did this, from left to right it's 100nm, 1µm and 5µm:

 

http://postimage.org/image/79sbt2c1h/

http://s18.postimage.org/nksfpdojd/IMG_1207.jpg

 

picture doesn´t work maybe to big

 

It seems to me there is something wrong with the concentrations, because the 1µm seems a lot more dense I just wonder if its suppose to be like this.

Edited December 12, 2012 by vaasuh

[vaasuh]

I centrifuged 1 ml of each solution and the 1µm conaints a lot more pellet then the 5µm particles, but its the same concentration, is this correct?

 

the 100 nm particles i coulndt centrifuge the same way because I centrifuged it with a size exclusion membrane and lost a lot of particles.

 

Did you get to take a look at the pictures?