Hello Marshall and folks, Hach Water Analysis Handbook, 3rd edition, 1997, P 1277, ¶ 4:
"A minute particle interacts with incident light by absorbing the light energy and then, as if a point light source itself, reradiating the light energy in all directions. This omni directional reradiation constitutes the "scattering" of the incident light. The special distribution of scattered light depends on the ratio of particle size to wavelength of incident light. Particles much smaller than the wavelength of incident light exhibit a fairly symmetrical scattering distribution with approximately equal amounts of light scattered both forward and backward. Next ¶ As particle sizes increase in relation to wavelength, light scattered from different points of the sample particle create interference patterns that are additive in the forward direction. This constructive interference results in forward-scattered light of a higher intensity than light scattered in other directions [P. 1278] In additions smaller particles scatter shorter (blue) wavelengths more intensely while having little effect on longer (red) wavelengths. Conversely, larger particles scatter long wavelengths more readily than they scatter short wavelengths of light." End excerpt. The text goes on about particle shape, particle color, and lots of other variables, leading one towards boggle.... If you don't have a copy of the book I will---when the new scanner is operational---send you a copy of the 6 pages from the book if you like. No math is included in the text. Hach will send you the entire book if you ask. James Osbourne Holmes FTNWO -----Original Message----- From: Marshall Dudley [mailto:[email protected]] Sent: Wednesday, November 22, 2000 2:06 PM To: [email protected] Subject: Re: CS>development work "James Osbourne, Holmes" wrote: > I think it is a bit more complex: some are absorbed; Right. > some are reflected; Right. > > some are refracted and the angles of reflection vary with wavelength; True, this is lumped together with reflected as scattering, and is ultimately what is termed Tyndall effect. > some > are absorbed and re-emitted at a different wavelength. I am not aware of any being absorbed and re-emitted, except for the energy from the light creates heat and the silver will have the black body radiation associated with the temperature. Normally absorbed and re-emitted is considered fluorescence, and I don't think silver behaves this way. Do you have any cites or references on this? > All of this changes > with particle size and concentration of particles. It changes with particle size, as I have quoted previously, the Tyndall increases to the third power with the size. The increase in Tyndall and absorption are both linear with concentration (provided the concentration does not reach a point where aggregation occurs).. > Some devices take > advantage of this behavior to determine particle size based on the changes > between the light in and light out. Yes, I have used this myself. Using the Hack scanning spectrophotometer, I scan a specimen and can get a crude idea of the particle size distribution from the absorption spectrum from infrared to uv. If I could obtain some samples with defined and narrow particle size ranges to calibrate from, I think I could do a very good job of using this technique to profile particle size of CS samples, but have not been able to source any such standards. Marshall -- The silver-list is a moderated forum for discussion of colloidal silver. To join or quit silver-list or silver-digest send an e-mail message to: [email protected] -or- [email protected] with the word subscribe or unsubscribe in the SUBJECT line. To post, address your message to: [email protected] Silver-list archive: http://escribe.com/health/thesilverlist/index.html List maintainer: Mike Devour <[email protected]>
