Author Topic: Calculating number of atoms inside of a nanoparticle and on the surface  (Read 6483 times)

Offline RickinWI

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I seem to  recall that there are about 100 -- 150 silver atoms in one of our silver particles but I have no clue how to calculate that.
So many VARIABLES & so little TIME.

Offline kephra

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There are a lot more than that. 
Colloidal Silver is only a bargain if you make it yourself.

Offline kephra

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@PeterXXL:  Although you got the wrong answer so far, I want to tell you that I like your idea of calculating the surface atoms by subtracting the inside volume from the outside.  When I first did these calcs, I did it based on the surface area, but the packing ratio may be different for the surface atoms. 

Also, since we are comparing volumes, its unnecessary to bother with the 4/3 pi in the calcs.
So we can just cube the ratios of radii, and apply the packing ratio.
For example: A 12 nm particle has a radius of 6 nm, so the amount of atoms which will fit inside is (6/.155)3*.74 which comes out to 42923

Using your method to find the number of surface atoms, we have 42923 - ((6-.155)/.155)3* .74 = 3241
This gives a value of 7.55% for the percentage of surface atoms for a 12nm particle.
Colloidal Silver is only a bargain if you make it yourself.

Offline RickinWI

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43,000 atoms!  WoW,  I guess I was off by a few  ;)
So many VARIABLES & so little TIME.

SanchoPanza

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You might know you're a redneck if....
You have a feeling they just "make some of this stuff up" on the Forum...

Wooosh.....

But I applaud the brilliance here!

-Sancho

Offline kephra

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Well I am a redneck at heart :)  Git 'R Done!
Colloidal Silver is only a bargain if you make it yourself.

Offline PeterXXL

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@PeterXXL:  Although you got the wrong answer so far, I want to tell you that I like your idea of calculating the surface atoms by subtracting the inside volume from the outside.  When I first did these calcs, I did it based on the surface area, but the packing ratio may be different for the surface atoms. 

Also, since we are comparing volumes, its unnecessary to bother with the 4/3 pi in the calcs.
So we can just cube the ratios of radii, and apply the packing ratio.
For example: A 12 nm particle has a radius of 6 nm, so the amount of atoms which will fit inside is (6/.155)3*.74 which comes out to 42923

Using your method to find the number of surface atoms, we have 42923 - ((6-.155)/.155)3* .74 = 3241
This gives a value of 7.55% for the percentage of surface atoms for a 12nm particle.


Based on that, I made an Excel table as follows (Silver):

Particle diameter size in nm
5
10
12
15
20
25
30
35
40
45
50
Radius
2.5
5
6
7.5
10
12.5
15
17.5
20
22.5
25
Atoms in particle
3105
24840
42923
83834
198718
388121
670672
1065003
1589742
2263519
3104965
Atoms on the surface
542
2239
3241
5091
9098
14260
20577
28049
36676
46458
57395
Percentage of atoms on the surface
17.5%
9.0%
7.6%
6.1%
4.6%
3.7%
3.1%
2.6%
2.3%
2.1%
1.8%

So we can conclude that it should be more than enough to use 17.5% of the molar weight of the silver when calculating amount of stabilizing and capping agents to use for reduced colloidal silver, as we can be sure that the particles are tat least 5 nm large (most are probably around 10 nm).
« Last Edit: July 22, 2015, 12:44:41 PM by PeterXXL »

Offline kephra

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Thats a nice table.  Thanks for doing the work.

Considering that a 50nm particle has 1000 times as many silver atoms as a 5nm particle, that means for a given ppm of silver, the 50nm size has only .1% of the number of particles.  Is it any wonder that smaller particle size is way more effective just due to the greater number of nanoparticles?

Concerning the amount of stabilizer:  I think your assumption is true provided that the rate of stabilization is faster than the rate of production.  Just like the rate of anode scavenging is important, so is this, but I think it is a safe assumption to make at the low currents we home users make our colloidal silver with.  Otherwise, the particles may grow past the safe area faster than they are capped.  If that happens, the particles can continue to grow out of control.

Of course, this also assumes the presence of a separate reducing agent, since the lower amount would preclude using the stabilizer as the primary reducing agent.

I know that with some agents, the amount limits the particle size to a maximum, and increasing the amount of stabilizer results in smaller particles.  Infinite stabilizer does not result in infinitely small particles though :)

Another problem is knowing the molecular weight of the stabilizer.  Some are not defined.  Lecithin for example exists in many variations depending on the source.  Maltodextrin exists in various forms with different molecular weights.  Gelatin is another. 

Lecithin has published MWs varying from 600 to 800 daltons for example.
Colloidal Silver is only a bargain if you make it yourself.

SanchoPanza

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That's a really nice table Peter, thanks for the efforts!

Sorry to interrupt here, but I have a redneck question.
If we could make 5nm particles, what color would the colloidal silver be?

Thank you,
-Sancho

Offline kephra

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Light green.
This picture shows high ppm samples. (100+ ppm)
Colloidal Silver is only a bargain if you make it yourself.

SanchoPanza

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Thank you Sir. Excellent reference!
Looking at those samples, It appears our "yellow" results are in the 5-7nm range?
The 10nm sample looks like it would dilute down to more of a pinkish color.
The others are not even close.

Is green to small of a particle for us to consume?
Can that size still be capped effectively with Gelatin?

-Sancho

Offline kephra

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Quote
Is green to small of a particle for us to consume?
Can that size still be capped effectively with Gelatin?
Unknown.

But being light green does not guarantee that particle is spherical and 5 nm as other shapes exhibit different colors.  You see green because the particles filter out both red and blue.  A rod shaped particle does this by having a long axis (red absorber) and a short axis (blue absorber).  There have been reports with gold nanorods being toxic.  I don't know if this is the case with silver nanorods, but I am not going to risk it. 
Colloidal Silver is only a bargain if you make it yourself.

Offline PeterXXL

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Thank you Sir. Excellent reference!
Looking at those samples, It appears our "yellow" results are in the 5-7nm range?
The 10nm sample looks like it would dilute down to more of a pinkish color.
The others are not even close.

Is green to small of a particle for us to consume?
Can that size still be capped effectively with Gelatin?

-Sancho


The 100 ppm batches (and higher concentration diluted to 100 ppm) that I've made look most similar to the picture of the 10 nm sizes to me.


Also, if there's particles in different sizes then my conclusion is that it look somewhat turbid. I've noticed that for batches of above 20 ppm when there has been too little of the stabilizing agent.
« Last Edit: July 25, 2015, 12:46:37 PM by PeterXXL »

SanchoPanza

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Aahh, Thank you both.
My experience is limited to 20ppm colors.
I will consider green to be not as good then.

-Sancho

fishing4fun

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Light green.
This picture shows high ppm samples. (100+ ppm)
Do these colors indicate particle size no matter what process was made to achieve those colors?
There using sodium borohydride and trisodium citrate as reducing agents, Silver nitrate, sodium hydroxide, Ethyl alcohol and acetone & double deionized (DI) water.
And the process were mostly here doing is totally different so is the color the same for every process or can it be different?
« Last Edit: July 25, 2015, 05:11:50 PM by fishing4fun »