Hello dear, you can make a dispersion with only the amount of your organic compounds that it will be employed in the dispersion, then make DLS analysis. Then, you can make the same with amount of nanoparticles that you will employ in the dispersion, then to make DLS analysis. Finally, you prepare the dispersion of your nanoparticles and organic compounds by using the same proportions of the dispersións mentioned above and made DLS analysis. You can observe the distributions of the component alone and compare it with the dispersion prepared from nanoparticles and organic compound. If your process is good. The distribution of the individual components has to disappear in the dispersion prepared employing both components. Furthermore the particle size has to be higher than that of the individual components. Additionally, from the distributions on intensity, volume and number you can infer about the effectiveness of your process.

If you can centrifuge the iron oxide particle in the dispersion solvent you should be able to quantitatively measure how much organic adsorbs to your particles by using quantitative phase separation approach methods.: 1. Prepare dilute dispersions of your iron oxide dispersion in a series of, for example, 100 mL volumetric flasks.Presumably you have already measured the weight concentration of iorn oxide in your dispersion and know precisely how much is in each volumetric flask. 2. Add varying amounts of your organic adsorbent, ranging from subsaturation to above saturation levels, based on your estimates of specific surface area (surface area per gram of iron oxide obtained from size distribution data or from TEM analyses. 3. Equilibrate with stirring overnight. 4. After vigorous stirring, fill centrifuge tubes with your test dispersions, and spin down the iron oixide, and decant the clear supernatant. If the supernatant is not clear, centrifuge it again. 5. Measure the amount of organic adsorbent in the supernatant and determine its concentration. 6. From the total solvent in your test dispersion (in the volumetric flask), you can then determine how much organic DID NOT adsorb to your iron oxide. 7. SInce you know how much organic material you added to each flask, subtrat the amount that was not adsorbed, and you are left with the amount adsorbed. 8. Divide this adsorbed amount by the grams of iron oxide in the flask, 9. Divide this amount by the concentration of organic in the continuous solvent phase determined above in step #5, and plot this quantity vs the concentration from step#5. This gives a straight line form of the Langmuir adsorption isotherm and from the slope and intercept you get the saturation amount of organic (eg, moles per gram of iron oxide) and a constant related to an adsorption equilibrium constant. 10. Try plotting your specific adsorption amounts as a function of st#5 concentration and see if the data rise to a flat monomlayer saturation level or not. You may need to alter the amounts of organic added, if you did not estimate well the range of the adsorption isotherm covered in our volumetric flask equilibration experiments. These experiments will provide quantitative insight into how much is adsorbed; it relies on being able to separate your nanoparticles from the dispersion by centrifugation.

If your organic adsorbs irreversibly, determine how mildly you can dry your iron oxide dispersion in a drying oven, perhaps a vacuum oven, so that you get rid of most of your solvent. Verify by doing a thermogravimetric analysis (TGA) ramp analysis to 600C to check for loss of solvent. Then dialyze your dispersion to get rid of organic in the solvent phase, dry your dispersion, and do a TGA analysis of your solid phase. You can analyze the TGA decomposition of your organic separately, and thereby know in what temperature range you should be able to observe its decomposition. If your organic adsorbs reversibly, centrifuge your organic coated dispersion and a control dispersion, recover the centrifuged pellets, dry, and run both by TGA.

If your nanoparticles do not centrifuge well in your bench top centrifuge, see if you can find access to a more powerful centrifuge.

FTIR, TGA, Zeta potential, 

 Thanks for all the answers. I have made these particles hydrophilic. As they are hydrophilic I have used Milli Q water as medium for dispersion. They have not settled down so coating must be there. But what should be the basic criterion of coating FT-IR or TGA? If peaks are not clear in FT-IR, are TGA results still sufficient to prove coating?

If the amount of organic added is not completely adsorbed, you will not learn much productive by doing TGA, unless you do the dialysis I described above. If you know the organic solubility in water, and you added considerably more to you dispersion than that quantity, you can assume that at least the difference is adsorbed. Centrifugation obviates the need for dialysis, and will give you material to study where the adsorption equilibrium of the organic will not matter much.

Do TGA on the coating organic material so you know where they decompose and if they are volatile or not. Then dry a quantity of your centrifuged pellet or of your dispersion (if you know that the organic added greatly exceeds the organic solubility in water) overnight in a weighing pan, and then heat it in vacuo for a couple of hours at a temperature above 100C (if possible) and considerably below the organic decomposition temperature. When you run the TGA if you do not see water coming off below 110C you will know your sample is dehydrated. Then see what weight loss you get at temperatures up to 600C. If the weight loss is reproducible, you can rely on the TGA estimate.