I have developed Silver NPs with PEG-PVP combinations but sometimes I get various coloration changes, I do not understand which colour is the endpoint of my reaction between precursor and reducing agents e.g. I get the following colours
Yellow bright, Yellowish Orange, Greenish yellow and grey color.
Pleae help.....
Ya, different particle sizes and shapes will result in different colors. The optical properties (absorption and scattering of light) are very sensitive to size, shape and composition in nanamaterials.
The principle behind is Surface Plasmon resonance. You can search in Google and study elaborately if you, eager. Noble metals like Ag, Au and Pt have these properties. The geometrical shape of nanparticle plays a major role in determining the plasmon resonance, while the spectrum have hypsochromic shift (red shift) with increasing particle size. In addition, simple heat treatment can modify a particle shape resulting in change in optical plasmon resonant properties. Such classification and tunning of the shape and optical properties of individual AgNPs makes them excellent candidate for optical microscopy and biological assays. Pls find an attachment for your refernce part.
In your part you have mentioned PEG and PVP they also act as capping agent stabilising structure directing agent with their capping ligands............
further any doubt pls reply back with out any hesitation, Najmul
Pls check this link too...............
http://www.ingentaconnect.com/content/asp/jnn/2013/00000013/00000008/art00099
Please refer the "Results and Discussion" in the paper attached. Paragraph two describes the color of the silver nanoparticles colloid. As mentioned by Zhenyu Bo and Adam, the color of your colloidal solution can give your an idea of the size of silver cluster.
Yes, the colour of the colloid depends upon the size of the NPs so according your requirement you can stop your reaction.
You may try to increase the concentration of the surfactants or reduce the concentration of silver ions to improve the dispersion and reduce particle size variation or possible aggregations.
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