Question

3. Let’s compare the ‘bulk chemistry’ versus surface chemistry.
(a) A glass coverslip (1cm in diameter, 2mm in thickness) was treated by oxygen plasma and immersed in a solution of (3-aminopropyl)triethoxy silane (APTES). Through this process, the glass surface is modified with APTES which provides the primary amine functional groups on the surface. According to some characterization, it is estimated that the surface density of amine groups is 1 x 1013/cm2. What is the total number of amine groups on the surface per gram of a glass coverslip?
(b) In the second example, we are dissolving alginate in an aqueous buffer and converting its carboxyl groups into the amine groups. Assuming 10% conversion of its carboxyl groups at the end of the chemistry, calculate the total number of amine groups per gram of alginate.
(c) Explain why contamination during the surface chemistry can be a much bigger problem than the contamination during the bulk chemistry.
(d) In (a), how can one estimate the surface density of amine groups on the glass coverslip?

Answer 1

ans c) The surface chemistry of material has more contamination than does the bulk of material. The surface material undergone corrosion or other material degradation.The chemistry of surface may change rapidly with depth.

A stainless steel will commonly have enhanced chromium in the oxide layer and a depletion zone beneath the oxide in which there is less chromium than is found in bulk alloy. In a ceramic the sintered particle will have a different surface chemistry than that in bulk of particles.