Grafting of Functional Monomers on Biomaterials - Biointerfaces: Where Material Meets Biology - page 335

d n 3 r 4 n g | 2

Figure 11.2 Positive ion ToF-SIMS images. Bright red areas show the presence of the
CF 1 ion on the surface on (A) unmodified ePTFE, and (B) MOEP grafted
ePTFE.

substrate as detailed in Section 11.3.1 and this must be kept in mind when
analysing the lateral distribution of a graft co-polymer.

11.3.5 Penetration Depth of Grafted Chains
Considering the two scenarios in Figure 11.3, both polymer substrates (A and
B) have the same degree of grafting. In one grafted sample (A) the depth of
the graft co-polymer is shallow, while in the other grafted sample (B) the graft
co-polymer has penetrated deep into the substrate; however, it is presented at
the surface in a patchy manner. Depending on the penetration depth of the
technique used to analyse the surface different information will be obtained.
If, on the one hand, a technique that evaluates the entire depth of the grafted
region is used (e.g., ATR-FTIR) then the outcome of the analysis would be that
both substrates were similar. If, on the other hand, a technique that exam-
ines only the outmost surface is used (e.g., ToF-SIMS or contact angle) then
the outcome would be that the substrates are very different. In essence, none

.

Figure 11.3 Schematic illustration of two polymer substrates (A and B) with the

same degree of grafting. (A) The depth of the graft co-polymer is
shallow; (B) the graft co-polymer has penetrated deep into the sub-
strate, but at the surface it is presented in a patchy manner.