[bunsenburning]

Hello,

I recently synthesized silver nanoparticles from the reduction of Silver Nitrate by ethylene glycol, using polyvinylpyrrolindone (PVP) as a capping agent. The mixture turned a yellow color. I confirmed the existance of silver nanoparticles by UV/Vis, getting a surface plasmon resonance peak at ~430nm.

I sprayed the colloidial silver onto a glass slide, then vacuum annealed the slide for an hour. Then I tried to measure conductivity, and got no signal. I sprayed the slide twice more, and then annealed after each spray, and still no conductivity. The glass slide is an orange-yellow color. Why aren't the silver nanoparticles conducting electricity?

Thanks So Much!

[billnotgatez]

I am curious -
Are the nano particles so far apart and the stuff between the particles is so insulator that electricity will not flow?

[bunsenburning]

I am curious -
Are the nano particles so far apart and the stuff between the particles is so insulator that electricity will not flow?

That's what I was thinking, that the particles followed some sort of percolation model. That's why I did 3 coats, but still no results. I will probably due a couple more, but the slide keeps getting darker, and we are trying to keep transparency high.

[Arkcon]

This reference here: http://fnml.korea.ac.kr/publication/p130.pdf seems to do something similar, they use screen printing of their silver nanoparticles, instead of spraying.  Maybe that will help you gain some insight for your app -- even though they make the nanoparticles very differently.

[Enthalpy]

May I ask how you measure the conductivity of the film?

When I tried to measure the aluminium film on a space blanket (a bit under 100nm, nearly opaque), making the contacts was very difficult. Pressing two wires against the film is definitely insufficient. Dipping the ends in electrolytes makes less bad contacts. Any real measurement would demand at least a four-point method.

In case your aim is to make a conducting transparent coating, and IF the object's shape allows it, standard methods are evaporation/sputtering/etc. They avoid the percolation difficulty.

You might also consider a fine grid of evaporated (or printed) metal, then of usual thickness like 1µm. You might evaporate it through a stencil. Fingers narrow enough can't be seen and conduct electricity better than a film. Surface conductivity will bridge the gaps between the fingers.

[bunsenburning]

May I ask how you measure the conductivity of the film?

We measure the resistance using a four point method, but still no avail. It seems that I guess we should try something else.

[Enthalpy]

You might try with an AC magnetic field. Achieved percolation between the nanoparticles would allow eddy currents to flow. Then:
- a flat coil pressed against the film would reduce its inductance;
- the coupling between two flat coils would diminish if you insert the film between them.

The second method is more sensitive and is less difficult to link numerically with a resistivity. You could try with an RLC meter, especially if it can decouple a current source from a voltage measurement, and especially if it can vary its frequency a lot.

-----

One other possibility, because I still suspect the contacts are very difficult to make, would be an AC four-points measurement where you make capacitive "contacts" with the film, say with unsupported adhesive film to hold electrodes of aluminium film. You need a frequency where the capacitance gives a reactance smaller than the film's resistance, BUT where stray capacitance between the electrodes isn't the main contributor...

- Observe the effect without the metal film, to check what you measure...

- Add grounded metal screens to reduce the stray capacitance

-----

My gut feeling (and I have experience for that): I prefer the mutual inductance method.

[bunsenburning]

After much more work, I think it's actually an issue with PVP. PVP prevents the particles from aggregating, but puts an insulating layer around the particles. I've tried to vacuum anneal them off for about an hour, but I still read no conductivity. Any other methods for PVP removal?

[egmonterrubio]

After much more work, I think it's actually an issue with PVP. PVP prevents the particles from aggregating, but puts an insulating layer around the particles. I've tried to vacuum anneal them off for about an hour, but I still read no conductivity. Any other methods for PVP removal?

As he said, the problem is the PVP, you can either try to vaporize it or synthesize the nanoparticles without the PVP, it's better in a water based solution, using NaBH4, I've done it and the only problem is that you have to wait untill you evaporate the water for each layer you put.

[sissy25]

PVP has a decomposition temperature of 130 degrees but an autoignition temperature of 420 degrees. It will be very hard to remove without degrading your films. I suggest you to try an aqueous process, or maybe find another polymer with a lower temperature of autoignition. Because it will be very hard avoiding the aggregation of your particles without a surfactant.

[/quote]
As he said, the problem is the PVP, you can either try to vaporize it or synthesize the nanoparticles without the PVP, it's better in a water based solution, using NaBH4, I've done it and the only problem is that you have to wait untill you evaporate the water for each layer you put.
[/quote]

 Egmonterrubio, how do you do to avoid the aggregation?

[opsomath]

I actually came here to suggest that the problem is PVP. Can you stabilize your nanoparticles with citrate or another capping agent instead?

Alternatively, you may simply not have enough material on there. You should be able to get a rough estimate of the coverage by placing the slide in a UV spectrometer and comparing to some standard nanoparticle solutions which you would make up.

[almfranc]

There are some interesting thoughts on native ligand stripping

http://onlinelibrary.wiley.com/doi/10.1002/anie.201105996/abstract

not sure how well it works on polymers though!

[billnotgatez]

@almfranc
From your link I got

Many online resources available through the UCSC Library Web site are licensed by the university for off-campus use only by UC faculty, staff, and students. Use your library card number below to access licensed resources.

As a side note
This is a good time to mention that we do not support copyright infringement here
See forum rules

[almfranc]

@billnotgatez

Thanks for pointing that out, I spaced out and didn't remember I was logged into my University database when I sent that link! Try http://onlinelibrary.wiley.com/doi/10.1002/anie.201105996/abstract and if you have credentials/access you can read the whole article. I actually tried this method myself and it seems to work well for amines, at least.