4(%3)3 - Ecole nationale supérieure de chimie de Montpellier

When compared to poly(styrene) NPs, the silica NPs are more stiffer and rigid in nature. Hence,when comparing the nanoparticles having same size of above two species, the poly(styrene) ones willpass through the membrane easily by easily undergoing deformation and thus lower retention. On theother hand, the silica ones can only form aggregates having much more irregular shapes thus furthercomplicating their translocation and consequently giving a higher retention.The perforations observed on the top surface of the membrane (Figure – 3.21a), does not meanthat healing process has been hindered in case of a stiffer nano-object. When the size distribution ofthese perforations is compared with the size distribution of silica SP1 NPs, a significant difference can beseen (Figure – 3.22). The explanation of still opened pore can either be due to entrapment of silica NPsinside the membranes thus destabilizing the natural equilibrium of the micelles which would otherwisein usual case, force them to come back to their original position to heal the space created.76Number of Perforations54321017 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 85 89 93 97 101Diameter (nm)Figure – 3.22: Size distribution of perforations observed in the Scanning Electron Microscopy image of top surface ofa membrane fed with silica SP1 NPs.The transverse section SEM image of one such membrane fed with SP1 series NPs reveals a layerof agglomerated NPs within the membrane before they reached the end of the membrane (Figure –3.23). Above this layer, other NPs can also be seen. The thickness of the membrane was found to be well96