Hi, people should normally mention intensity average size particle. The intensity size average particle is the quantity measured by DLS. The volume and number average size particle are calculated from the intensity average size particle. Therefore, the volume and number average size particle will depend on the material properties of iron oxide (in your case) that you introduce in the DLS software.

Hi, I agree with Gregory and Maarrten. The DLS data measureed by intensity, and based on this they calculat and Transfer to volume and number average size. And the big particlls have much more influence in the intensity than in volume and number. If you Change to volume and number size , you can easily observe that the peak of siye curve shift to small. However, the Dh in the Report will not Change.

In publications, intensity size is usually used, and there are some use volume size, number size of DLS is th last. For the number size, you can easily get the Information from TEM Images.

Another Problem is iron oxide particles intend to Aggregate or agglomerated together, maybe the size you get from DLS is not the first size of your particles. So that TEM is better.

Hi,

It is agreed that the DLS data is measured by intensity but main draw back for the nano-particles is there tendency to get agglomerated (Not all but most of them). To get a better idea of the size, it is intended to go for ultransonication or stir media mill to break the agglomerates prior to DLS.

If we go for TEM or SEM then we focus a particular area of the whole mass and to predict the size on the basis of TEM or SEM images is not wise-able (As per my opinion). Nano-particles are always exist in a range of different sizes so DLS is so far the best method to have an overall image of particle size distribution but the agglomeration of the particles may hamper the results. To over come this problem, refer to above suggested solutions to have a better results.

Please refer to the following paper to understand the procedure of stir media mill and precautions thereof.

http://www.sciencedirect.com/science/article/pii/S092777570700009X

Actually the average value determined by batch (unfractionated) DLS is not the intensity-weighted average size, but the intensity-weighted average diffusion coefficient. So the correct answer is that the average inverse size is intensity weighted, and the size itself is some complicated average which cannot simply be called number-, mass-, Z- or intensity- weighted. If you need an accurate size distribution and/or want to come up with a true X-averaged size, you need to precede DLS measurements by a separation technique such as field-flow fractionation - see www.wyatt.com/FFF-MALS and www.wyatt.com/Size.

www.wyatt.com/Size