Where can I find a picture of a typical silica particle used for LC packing? Literature reference or internet (probably will not be able to locate a book reference)

Are pores essentially all dead ended..ie no flow through?

What is typical width to depth ratio, ie are they not very deep.

Bill,
Not to sound silly but grab a catalog from some of the column manufacturers, they usually have a photomicrograph or EM photo of the packings. I get bombarded periodically by mail which has these photos in them.

Regards,
Mark

The LC particles are fully porous throughout the structure. You can view them as balls of wet sand. This means that none of the pores are dead ended.

I made pictures of 3.5, 5 um, 10 um spherical silica gels and 50 um irregular silica gel (Kromasil, Daiso and Davisil). I can send this to you via email. Let me know if you need them.

Yes, silicas are fully porous materials. I got some pictures in my article on "Silica and its Derivatization" in Wiley's Encyclopedia of Analytical Chemistry (2000), 11450-11472. I'll check tomorrow, if I still have some reprints.

You got two different types of structures. One looks like little beads glued together, and the other looks like a coral. This depends on the preparation technique. Without question, both are fully porous throughout the structure, as the previous message said.

Bill,

Just to augment the comment by A.Mouse above, one can think of silica particles as an agglomerate colloidal silica particles, fused together into a spherical aggregate. The primary colloidal particles are fused together in such a way as to produce primary porosity in the size range comparable to the size of the primary particles. Depending upon the synthesis details, there can also be significantly larger pores interconnecting the primary pores. Also, depending upon the way the colloidal particles are fused together, there may or may not be some closed end pores at some of the fusion points although for the most part as mentioned above the pore structure is open. Of course, a wide variety of other pore structures are also possible but this description fits most of the commercial HPLC materials.

If all the pores are open ended, then how does stagnant mobile phase and the problems it causes with mass transfer arise?

Because liquid as a bulk is moved by pressure gradient in LC. Pressure difference between two axial points of a particle is not high enough to cause any substantial flow through the pores (id 100-300A) while you have a passage around particle with id about 1-3 mcm. Id ratio is 1:100 and the cross section ratio is 1:10,000. The cross section is reversely proportional to the flow resistance in the narrow passages.

thanks to all for taking the time to respond in detail. The information needed was provided.