Carr Research Group

Education: B.S. from Peking University, Beijing, China6
M.S. from University of Calgary, Calgary, Alberta, Canada

Email: jyan@chem.umn.edu
Research Abstract:

Multilevel, Two-dimensional Polymerization:
a Novel Approach to Silica Surface Modification

In RPLC, incomplete coverage of silica substrate leaves unreacted silanol groups open for basic analytes to adsorb thus causing bad peak shapes, low column efficiencies and poor recoveries. It also allows the silica substrate to dissolves under attack by base . A dense, uniform, complete coverage of the surface should block surface silanol activity and protect the silica substrate from base attack, thus providing better separation for basic compounds and improved column stability.
We propose a novel multilevel, two-dimensional polymerization approach for silica surface modification and protection. This approach is based on the Self-Assembled Monolayer (SAM) method by Sagiv which was introduced into LC by M. Wirth. A trifunctional (trichloro) silane which also contains two carbon-carbon double bonds (e.g. divinylalkyltrichlorosilane as shown in Figure 1) is used as the monomer. First, the monomers will be self assembled onto silica particles coated with a monolayer of adsorbed water by reaction with surface silanol groups and by horizontal polymerization between adjacent chlorosilane groups. Secondly, a free radical initiator will be added to polymerize the double bonds. This step effectively forms a two-dimensional polymer network above the horizontal Si-O-Si bonds formed in the first step. In this polymerization step, a different secondary monomer (isoprene, divinyl benzene, myrcene) or small molecular weight polymer (PBD), can also be added to facilitate complete reaction of double bonds and to introduce new functional groups.
This modification approach provides three barriers between the silica surface and the mobile phase as shown in Figure 2. The chances that a molecule penetrate all barriers to react with surface silanol groups becomes diminishingly small. We believe that in this way we will achieve effectively complete coverage.

Figure 1 Structure of divinylalkyltrichlorosilane (R = H, CH3, CnH2n+1).

Figure 2 Three barriers on silica surface.