# Role of Functional Monomers upon the Properties of Bisphenol A Molecularly Imprinted Silica Films
## 3 Results and Discussion
### Morphology of BPA-MIP and NIP Films  
The surface morphology evaluation of prepared sol-gel films was firstly explored by scanning electron microscopy (SEM, Figure 3) and, afterwards, with atomic force microscopy (AFM, Figure 4). The SEM images of BPA-MIPMPTES and BPA-MIPQAMOT and their corresponding NIPMPTES and NIPQAMOT, respectively, are presented in Figure 3, where significant changes of surface morphology can be noticed. The micrographs of BPA-MIPs and NIPs films clearly indicated morphological differences even though the main network is chemically resemblant (Si-O-Si). Comparing the morphology of the NIPs with that of BPA-MIPs, the difference was striking. NIP films presented smoother surfaces with little visible asperities or pores, ascribed to the absence of imprinted sites. An overview at lower scales revealed an aggregated structure of the NIPMPTES film (Figure 3b) with rather large gaps instead of pores. Interestingly, BPA-MIPMPTES exhibited a dense structure of pores consisting of aggregated sols, in which case it can be due to the presence of monomer-template assemblies that clearly influenced the growth mode of the entire sol-gel network (Figure 3a). This porous structure of BPA-MIPMPTES films is very beneficial for the mass transfer, BPA rebinding, and may lead to shorter periods for equilibrium adsorption [39]. For BPA-MIPQAMOT films, an interesting, elongated structure (like pine branches) was observed in Figure 3c, unveiling again the result of a preferential arrangement and growth of the network in the presence of monomer-template assemblies. Unlike BPA-MIPMPTES, the surface of BPA-MIPQAMOT seemed to be more compact, which may be caused by the addition of TEOS that conferred rigidity to the whole structure. The topography and roughness of both BPA-MIP films and their corresponding NIPs were investigated by AFM (Figure 4), as well. The surface roughness of the sol-gel films was evaluated using the root-mean-square roughness (RMSR) function of XEI AFM software. Figure 4: 3D (**a**) and 2D (**b**) topography images by atomic force microscopy (AFM) of the surface of BPA-MIPMTTES/BPA-MIPQAMOT films, compared to control NIPs, scan area of 2 \(\times\) 2 \(\upmu\)m; RMSR values included on each AFM image (in red). Figure 3: Surface SEM micrographs of both sets of sol-gel films, at different magnitude levels: (**a**) BPA-MIPMTTES and (**b**) NIPMTTES at 1 mm/500 \(\upmu\)m scale with 20 \(\upmu\)m insets (**c**) BPA-MIPQAMOT and (**d**) NIPQAMOT at 50 \(\upmu\)m.  
As shown in Figure 4b, five different topographic images were chosen to calculate the arithmetic average leading to the RMSR results. The AFM images of NIPs and BPA-MIP films emphasized again the changes that occur in surface topography due to the presence of monomer-template assemblies. In agreement with the SEM analysis, the 3D images of the BPA-MIP\({}_{\text{MPTES}}\)/NIP\({}_{\text{MPTES}}\) films (Figure 4a) pair displayed a fully different porous architecture compared to the flatter and smoother surface of the other pair, BPA-MIP\({}_{\text{DAMOT}}\)/NIP\({}_{\text{DAMOT}}\) (Figure 4a). Compared to SEM, the AFM footage revealed a very dense porous structure for the BPA-MIP\({}_{\text{DAMOT}}\) film, as well. Yet, in this case the pore sizes are much smaller than the ones observed on the surface of BPA-MIP\({}_{\text{MPTES}}\), which may lead to a slow diffusion of BPA during rebinding trials and low binding efficiency [40]. The presence of BPA led to higher surface roughness values for BPA-MIP\({}_{\text{MPTES}}\) and BPA-MIP\({}_{\text{DAMOT}}\) (with a RMSR of 1.7 nm and 0.6 nm, respectively) compared to those of the corresponding NIPs (1.4 nm and 0.4 nm, respectively). The differences of RMSR values can be explained by the presence of template molecules that exert a steric effect during the growth of the sol-gel network. Meaning, the physical volume occupied by the template molecules, which translates later into imprinted cavities, is responsible for the formation of small gaps between the neighboring SiO\({}_{2}\) chains.