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

The effect of concentration of particles on the permeation of water can be gauged from a simpleexperiment where the concentration of nanoparticles was increased over the course of filtrationexperiment. At a low pressure value of 0.2 bar, a maximum concentration of (1.43 X 10 -7 g.ml -1 ) wasachieved beyond which the membrane was completely clogged (Figure – 3.7).The final class of the nano-objects is represented by Silica nanoparticles which are the stiffest andbiggest amongst the nano-objects studied in this work. Two series of silica NPs (SP1 & SP2) wereprepared by a modified Stober process 28 . The synthesis was carried out in isopropanol at 20 o C with theconcentrations of various reactants governed by the following relation:[NH 3 ] = 0.81[TEOS]), [H 2 O] = 6.25[TEOS]where, [TEOS] was taken to be 0.22 MAn excess of water in the system facilitates thorough hydrolysis of Triethylorthosilicate (TEOS)which gives high mass fraction. Ammonia (NH 3 ) accelerates the hydrolysis and condensation of TEOSwhile supplying –OH ions adhering on the particles, thus stabilizing the suspension via repulsion againstVan der Waals attractive force 28 . The reported optimum concentration of NH 3 with respect to TEOS wasused as it was observed that a high concentration leads to coagulation while too low concentrations ledto longer reaction time or even no silica particles formation.1210Number of Particles864SP1 - iSP1 - ii2057698395107119131143155167179191203215227239251263275287299311323335347359371383395407Particle Size (nm)Figure – 3.8: Bimodal size distribution obtained for silica nanoparticles ( SP1) showing two population of NPs81