Preparation of Magnetic Iron-Oxide Nanoparticles Using Water-in-Oil Microemulsion - Lab Report Example

TS-05 РRЕРАRАTIОN ОF МАGNЕTIС NАNОРАRTIСLЕS OF IRON USING МIСRОЕMULSIОN Name: Institution: Date: Abstract Magnetic nanoparticles display remarkable phenomena and have wide applications. Microemulsion systems are important because they produce homogenous and monodispersed nanoscale particles at room temperature without the requirement for expensive instruments. Nanoparticles of iron oxide find applications as catalysts, material nanocompositesmagenetic resonance imaging (MRI), drug delivery, pigment in manufacture of paints and many more. This work presents preparation of magnetic iron oxide nanoparticles using an in-situ technique of microemulsion systems. Preparation of a microemulsion system involves dissolving AOT in iso-octane, then adding 1-butanol and FeCl-2 aqueous salt solution. The system of a microemulsion was stirred slowly to allow a transparent microemulsion suspension to be formed. Using the same procedure, a second microemulsion containing NaOH solution was also prepared. The two microemulsion systems were then mixed by a volumetric ratio of 1:1 to form a precipitation. Particles were recovered, then washed using deionized water and acetone and dried. Experimental: Materials: Sodium bis(2-ethylhexyl) sulfosuccinate (AOT) is used as the surfactant, oil such as iso-octane, heptane and hexane that are used as the continuous organic phase, sodium hydroxide (NaOH) is used as source for hydroxide ions, iron (II) chloride that is used as the source of iron and also deionised is used as the aqueous medium. Measurement and calculation of the amount of samples: There is a difference in the amount of samples based on changes in the calculations, the parts below will show new calculation for preparation of microemulsions and Iron-oxide nanoparticles. 1) Calculation for W/O microemulsion: The following calculations are for the preparation of water-in-oil (W/O) microemulsion with AOT and oil (iso-octane and heptane). The total volume of each microemulsion will be 25 ml. Molar ratio (W) will be assumed as 50 and 25. The surfactant (AOT) with molar will be assumed as 0.3, 0.2 and 0.1 mol/L The experiment is in ambient temperature, 25 °C. This calculation is applicable for different oils which are iso-octane and heptane. With W = 50 and AOT = 0.3 (as sample) H2O = 0.3 * 50 = 15 mol/L Molecular weight (MW) of H2O = 18.015 g/mol Weight of H2O = 50 * 0.3 * 18.015 * = = 6.756 g Density of H2O = 0.996 g/cm3 Volume of H2O = = 6.78 cm3 Since 1 cm3 = 1 ml so, Volume of H2O = 6.78 ml Volume of oil = total volume – volume of H2O = 25 – 6.78 = 18.22 ml The amount of AOT is calculated by following method: Molecular weight (MW) of AOT = 444.5 g/mol Weight of AOT = 0.3 * 444.5 * = 3.33 g This table below summarises the amount for samples with different values of AOT and at same molar ratio of 50. Table 1: Amount of samples with different values of AOT at molar ratio of 50 Molar ratio (W) (assume) Moles of AOT (assume) Moles of H2O (calculated) Volume of H2O (ml) (calculated) Volume of oil (ml) (calculated) Amount of AOT (g) (calculated) 50 0.3 15 6.78 18.22 3.33 0.2 10 4.52 20.48 2.22 0.1 5 2.26 22.74 1.11 The procedure of calculation for molar ratio of 25 will be same as above, and the result will be summarised in the table below for samples with different values of AOT and at same molar ratio of 25. Table 2: Amount of samples with different values of AOT at molar ratio of 25 Molar ratio (W) (assume) Moles of AOT (assume) Moles of H2O (calculated) Volume of H2O (ml) (calculated) Volume of oil (ml) (calculated) Amount of AOT (g) (calculated) 25 0.3 7.5 3.39 21.61 3.33 0.2 5 2.26 22.74 2.22 0.1 2.5 1.12 23.87 1.11 Procedures of preparation: 1) Label 3 volumetric flasks with different amounts of AOT. 2) Add measured volume of oil (iso-octane and heptane) to all volumetric flasks at room temperature. 3) Shake the volumetric flask until all of the AOT has been dissolved in oil. 4) Add measured amount of deionised water that should be drop by drop by using syringe to each volumetric flask. 5) Shake the volumetric flask slowly until the solution becomes transparent microemulsion. 6) Record the observation. General description of samples The pictures below show the microemulsion samples prepared with a molar ratio of 50 (fig.1a) and 25(fig.1b) respectively, using heptane as organic phase oil. The experiment is at room temperature, 25 °C. Fig. 1: a. microemulsion samples, W = 25, heptane Fig. 1b. W = 50, heptane The other two samples shown in the pictures below show the microemulsion samples prepared with a molar ratio of 50 (fig.2a) and 25(fig.2b) respectively, using iso-octane as organic phase oil. Fig. 1c. W = 25, iso-octane Fig. 1d. W = 50, iso, octane Generally, the samples in figure 1 (from 1a. through to 1d.) above show milky dispersions in the microemulsion sample solutions that vary from slightly cloudy and partly transparent to milky appearence. The samples shown in fig. 1c & 1d depict slightly cloudy microemulsion solutions when the amount of AOT added is low (AOT = 1.11 g). However, as the amount of AOT added increases up to 3.33 g, some particle suspensions begin to appear, and the solution begins to appear cloudier, with slight diminish of clarity and transparency. The AOT is dissolved in both heptane and iso-octane oils. Results and discussion: 1) Effect of AOT concentration In this section, the effect of changing the amount of AOT in the microemulsion was investigated for different oils and molar ratio. The UV results depicted in figure 2 below suggest that as the concentration of AOT affects the optical density of the microemulsion solution. Figure 2(a & b): Adsorption spectra obtained for nanoparticles of colloidal iron oxide at different concentrations of surfactant, and molar ratios of 50 and 25 respectively, using heptane oil. Figure 2(c & d): Adsorption spectra obtained for nanoparticles of colloidal iron oxide at different concentrations of surfactant, and molar ratios of 50 and 25 respectively, using iso-octane oil. The UV-Vis presented in Fig. 2 shows that the UV-absorbance of nanoparticles increases as the concentration of the surfctant increases. The UV-Vis peaks shifts (increase) as the amount of AOT in the microemulsion increases from 1.11 to 3.33g. This is observed for both molar ratios of 50 and 25. However, the peaks at a molar ratio of 25 are higher compared to the peaks at a molar ratio of 50. The nanoparticles are produced when the surfactant reacts with the macro-crystals. The head groups of the Surfctant stabilize the nanoparticles produced in the water pools. This results therefore, indicate that the uptake of nanopartcles can be increased by increasing the concentration of the surfactant at a given constant mole ratio of water to surfactant. A higher concentration of surfactant corresponds to a higher population of reverse micelles in the oil phase, and thus, the potentially higher uptake of nanoparticles. In addition, as the concentration of the surfactant increases, the collisions between nanoparticle-populated reverse micelles, which results in an increases in particle collision and aggregation (Husein, Rodil and JuanH.Vera 2005). A similar obsevation can be made when the iso-octane oil is used, as depicted in fig. 2(c & d). From fig. 2(c & d), the UV-Vis peak increases as the concentration of AOT increases for the two molar ratios when iso-octane oil is used as organic phase. The absorption peak of the nanoparticles is dependent on their concentration. An increase in absorbance is related to increase in concentration of the colloidal nanoparticles, increase in nanoparticle size and excess ions, and increase in surfactant concentration. This implies that, as the AOT concentration increases, the mean size of the nanoparticles aloso increases. These trends are in agreement with the findings by Nashaat Nassar & Maen Husein (2005). Increasing the concentration of the surfactant increases the nanoreactors, and the later increases the concentration of the nanoparticle colloids. 2) Effect of molar ratios In this section the effect of change of molar ratio was investigated using heptane as organic phase, and the same surfactant concentration, so that the only varying factor is the molar ratio. The figures below shows the UV-Vis spectra at a surfactant amount of 1.11g to 3.33g. Figure 3 (a, b & c): UV-Vis spectra showing the effect of increasing the molar ratio from 25 to 50 at a constant concentration of AOT, using heptane oil. Water is a very essential component of a microemulsion system. The mole ratio of water to surfactant is one of the most important parameters that reflect the rigidity of the surface layer of the surfactant, and the ability to lower liquid-liquid interfacial tensions. Increasing the water content reduces the rigidity of the surfacatant suraface layer and promotes aggregation of particles (Nassar and Husein 2007). The mole ratio also determines the size of water pools, which accommodate the nanoparticles. These are key properties that are useful in the preparation of water in oil (W/O) emulsions. The nature of the emulsions formed is dependent on the hydrophilic-hydrophobic surfactant molecules balance. The UV-Vis spectra in figure 3 (a, b & c) depict that increase in molar ratio results in shifting of the UV-Vis spectrum; the UV absorption increases with increase in molar ratio, if the AOT concentration is kept constant. This trend is attributed to the increase of nanoparticle size as well as particle concentration. A smaller values of molar ratio, a relatively higher proportion of water molecules is bound to the head groups of the surfactant abd this limits the amount of water required to solubilize the iron (III) chloride. As the mole ratio increases to a higher value, the UV absorbance increases. Increasing the water content decreases the rigidity of of the surfactant protective layer, which leads to particle aggregation (Wongwailikhit and Horwongsakul 2011). The stability of the microemulsion is dependent on the interfacial tension between the water-oil phases. The molar ratio contributes to the interficial tension; it reduces as the molar ratio increases. Viscosity on the other hand increases as the molar ratio increases (Malik, Wani and Hashim 2012). 3 Effect of change oil (between heptane and iso-octane) In this section, the effect of changing the oil used as organic phase was studied. The figures below show UV-Vis obtained for different oils, keeping the AOT concentration and mole ratio constant. Figure 4(a, b, c & d): UV-Vis spectra showing the effect of change of oil used as the continuous organic phase at constant AOT and molar ratio. The figures 4(a, b, c & d) show the effect of changing oil in the preparation of the microemulsion. The UV-Vis spectra of the molar ratio of 25 depict that there is increased absorbance when the heptane oil is used, compared to when iso-octane is used. However, this trend is not consistent at the molar ratio of 50 as observed in figure 4c. & d. Here, as the molar ratio increases from 25 to 50, the microemulsion solution prepared using iso-octane tends to have a relatively higher UV absorption compared to the solution with heptane oil. This can imply that the molar ratio affects the properties of the oil used. 2 Calculation for microemulsion: The following calculations are for the preparation of microemulsion with AOT, oil (iso-octane, heptane and hexane) and NaOH or FeCl2.4H2O There are two microemulsions, first one with NaOH solution and second one with FeCl2 solution. The total volume of each microemulsion will be 25 ml. Molar ratio (W) will be assumed as 25 and 15. Molar of the surfactant (AOT) will be assumed as 0.3, 0.2 and 0.1 mol/L The experiment is in ambient temperature, 25 °C. This calculation is applicable for different oils which are iso-octane, heptane and hexane. 2.1) Calculation for NaOH microemulsion: With W = 50 and AOT = 0.3 (as sample) H2O = 0.3 * 50 = 15 mol/L Assume the Molecular weight (MW) of solution as of H2O = 18.015 g/mol Weight of H2O = 25 * 0.3 * 18.015 * = 3.38 g Density of solution has change to = 1.4 g/cm3 Volume of H2O = = 2.41 cm3 Since 1 cm3 = 1 ml so, Volume of H2O = 2.41 ml Volume of oil = total volume – volume of H2O = 25 – 2.41 = 22.59 ml The amount of AOT is calculated by following method: Molecular weight (MW) of AOT = 444.5 g/mol Weight of AOT = 0.3 * 444.5 * = 3.33 g This table below summarises the amount for samples with different values of AOT and at same molar ratio of 25. Table 3: Amounts of samples with different values of AOT at molar ratio of 25 Molar ratio (W) (assume) Moles of AOT (assume) Moles of H2O (calculated) Volume of H2O (ml) (calculated) Volume of oil (ml) (calculated) Amount of AOT (g) (calculated) 25 0.3 7.5 2.41 22.59 3.33 0.2 5 1.61 23.39 2.22 0.1 2.5 0.8 24.2 1.11 The procedure of calculation for molar ratio of 25 will be same as above, and the result will be summarised in the table below for samples with different values of AOT and at same molar ratio of 15. Table 4: Amounts of samples with different values of AOT at molar ratio of 15 Molar ratio (W) (assume) Moles of AOT (assume) Moles of H2O (calculated) Volume of H2O (ml) (calculated) Volume of oil (ml) (calculated) Amount of AOT (g) (calculated) 15 0.3 4.5 1.45 23.55 3.33 0.2 3 0.97 24.03 2.22 0.1 1.5 0.48 24.52 1.11 General Description of the samples All the samples of microemulsions prepared using a solution of NaOH are shown in figure 5 shown below. Fig. 5a. Fig. 5b. Fig. 5c. Fig. 5d. Fig. 5e. Fig. 5f. Figure 5 (a, b, c & d): Samples of microemulsions with NaOH solutions, prepared using iso-octane, heptane and hexane oil, and different amounts of AOT as shown on the labels on each bottle containing the sample microemulsion. In fig. 5a, 5b & 5c, the samples appear slightly clear and transparent, with some suspensions. As the amount of AOT increases from 1.11 g to 3.33 g, the amount of suspensions formed increases and the solutions become slightly cloudy. These three solutions have a molar ratio of 15. The samples shown in figure 5d, 5e & 5f depict cloudy microemulsion solutions when the amount of AOT added is low (AOT = 1.11 g). However, as the amount of AOT added increases up to 3.33 g, some particle suspensions begin to appear and the solution begins to appear milky, becoming less transparent. These three solutions have a molar ratio of 25. The AOT is dissolved in all the oils. Results and discussion: 1) Effect of AOT concentration In this section, the effect of AOT concentration was studied for microemulsion with NaOH solution, using all the three oils (heptane, hexane and iso-octane). The molar ratio and the type of oil used is kept constant, so that the only varying factor is the amount of AOT added. The figures below (6a through to 6f) show the UV-Vis absorption spectra for the three oils at molar absorption of 25 and 15 with varying amounts of AOT. Fig. 6a (W=25, Hexane) Fig. 6b (W=15, Hexane) Fig. 6c (W=25, Heptane) Fig. 6d (W=15, Heptane) Fig. 6e (W=25, iso-octane) Fig. 6f (W=15, iso-octane) Figure 6 (a, b, c, d, e & f): The UV-Vis spectra for microemulsion with NaOH solution, using heptane, hexane and iso-octane oils with different AOT concentrations and molar ratios. The UV-Vis presented in Figures 6 (a & b), where hexane oil is used, shows that the UV-absorbance of nanoparticles increases as the concentration of the surfctant (AOT) increases. The UV-Vis peak shifts (increase) as the amount of AOT in the microemulsion increases from 1.11 to 3.33g. The threshold absorption is observed to shift from a wavelength of 390nm to around 420nm. This is observed for both molar ratios of 25 and 15. A similar obsevation can be made when the iso-octane oil is used, as depicted in fig. 6(c & d), where heptane is used, and also in fig. 6(e&f), where iso-octane is used . Here, the UV-Vis peak increases as the concentration of AOT increases for the molar ratio of 25 and 15. A higher concentration of surfactant is associated with a higher population of reverse micelles in the oil phase, and thus, the potentially higher uptake of the nanoparticles in the microemulsion solution. In addition, as the amount of AOT increases, the collisions between nanoparticle and populated reverse micelles increases. LI, et al. (2009) explains that the threshold absorption is dependent on the concentration of the nanoscale particles in the microemulsion. In addition to AOT concentration, an increase in absorbance is related to increase in concentration of the colloidal nanoparticles, as well as increase in their size and presence of excess ions (Nassar and Husein 2006). This implies that, as the AOT concentration increases, the mean size of the nanoparticles aloso increases. These trends are in agreement with the findings by Nashaat Nassar & Maen Husein. Increasing the concentration of the surfactant increases the nanoreactors, and the later increases the concentration of the nanoscale particle colloids. 2) Effect of molar ratios In this section, the effect of changing the molar ratio was investigated for microemulsion with a solution of NaOH. The amount of AOT was kept constant, so that the only varying factor was the molar ratio. The figures below show the UV-Vis spectra obtained for different molar ratios, at AOT amount of 2.22 g and 3.33 g. At a lower molar ratio of 15, the UV absorbance of the microemulsion is relatively higher compared to that with a molar ratio of 25. Fig. 7a. AOT = 1.11g Fig. 7b. AOT = 2.22g Fig. 7c. AOT = 3.33g Figure 7 (a, b & c): UV-Vis absorption spectra for the microemulsion with NaOH solution showing the effect of molar ratio for different AOT amounts. In figure 7 (a & c), it can be seen that UV absorption increases as the molar ratio increased from 15 to 25. The threshold absorption wavelength shifts from a wavelength of about 380nm to 400nm with AOT amount of 1.11g, while in figure 7c, where the amount of AOT added is 3.33g, the wavelength shifts from about 400nm to 420nm. This trend is not observed in figure 7b, where the microemulsion with a lower molar ratio of 15 shows a higher UV absorption. This can be attributed to particle aggregation due to higher water content. The molar ratio also has an effect on the interficial tension. Increasing the molar ratio decreases the interficial tension and increases the viscousity of the microemulsion. 3. Effect of using NaOH instead of water The amount of NaOH used affect the concentration of nanoparticles of iron oxide produced. According to Husein, Rodil and Vera (2003), using water dilutes the microemulsion solution, and therefore a less concentrated microemulsion solution of iron oxide nanoparticles is expected. The effect of water is often described by the water to surfactant molar ratio. By varying the molar ratio, the amount of water in a given microemulsion system can be varied. The water content has an effect on the size and rate of growth of the nanoparticles synthesized in a microemulsion system if the other factors are kept constant. The surfactants become hydrated at specific water content, and increasing the water content favours the formation of emulsions that are thermodynamically stable and have several phases. The micelle interface becomes rigid when it is water bound, which lowers the intermicellar exchange as well as nanoparticle growth rate. As the water content increases, the rate of particle growth increases, until a point when addition of more water just adds to the bulk water pool (Kanan, Yousef and Kayali 2012). As more water is used, the concentration of iron oxide nanoparticles is reduced. 2.2) Calculation for FeCl2.4H2O microemulsion: With W = 50 and AOT = 0.3 (as sample) H2O = 0.3 * 25 = 15 mol/L Assume the Molecular weight (MW) of solution as of H2O = 18.015 g/mol Weight of H2O = 25 * 0.3 * 18.015 * = 3.38 g Density of solution has change to = 1.3 g/cm3 Volume of H2O = = 2.59 cm3 Since 1 cm3 = 1 ml so, Volume of H2O = 2.6 ml Volume of oil = total volume – volume of H2O = 25 – 2.6 = 22.4 ml The amount of AOT is calculated by following method: Molecular weight (MW) of AOT = 444.5 g/mol Weight of AOT = 0.3 * 444.5 * = 3.33 g This table below summarises the amount for samples with different values of AOT and at same molar ratio of 25. Table 5: Amounts for samples used in the preparation of FeCl2.4H2O microemulsion with different values of AOT at molar ratio of 25. Molar ratio (W) (assume) Moles of AOT (assume) Moles of H2O (calculated) Volume of H2O (ml) (calculated) Volume of oil (ml) (calculated) Amount of AOT (g) (calculated) 25 0.3 7.5 2.6 22.4 3.33 0.2 5 1.73 23.27 2.22 0.1 2.5 0.87 24.13 1.11 The procedure of calculation for molar ratio of 25 will be same as above, and the result will be summarised in the table below for samples with different values of AOT and at same molar ratio of 15. Table 6: Amounts for samples used in the preparation of FeCl2.4H2O microemulsion with different values of AOT at molar ratio of 15. Molar ratio (W) (assume) Moles of AOT (assume) Moles of H2O (calculated) Volume of H2O (ml) (calculated) Volume of oil (ml) (calculated) Amount of AOT (g) (calculated) 15 0.3 4.5 1.56 23.44 3.33 0.2 3 1.04 23.96 2.22 0.1 1.5 0.52 24.48 1.11 General Description of the samples Fig. 8a Fig. 8b Fig. 8c Fig. 8d Fig. 8e Fig. 8f Figure 8(a, b, c, d &e): Samples of FeCl2.4H2O microemulsion for different AOT amounts and molar ratio, using different oils. Generally, all the solutions appear clear yellow due to yellow suspensions, but the intensity of the colour varies from sample to sample. In fig.8a, where heptane is used and the molar ratio = 15, the intensity of the clear yellow colour increases as the amount of AOT added increases from 1.11g to 3.33g. This trend is observed in all the samples, irrespective of the type of oil or the molar ratio. However, in fig.8b and 8f, where the oil used is hexane, at all the molar ratios, the colour transition is more intense, with the sample containing AOT amount of 3.33g becoming dark yellow, with increased number of suspensions. Results and discussion: The figures below show the absorption spectra of iron II chloride obtained for different molar ratios of 25 and 15, and also when the organic phase oil used was changed from hexane to heptane. Figure 9: Absorption spectra of Iron II chloride microemulsion showing the effect of different concentrations of AOT. In fig. 9a and 9b, the organic oil used was hexane, while in fig. 9c and 9d, the oil used was heptane. 1 Effect of AOT concentration In this section, the effect of AOT concentration was studied. The molar ratio and the type of oil used was not changed, so that the only varying parameter was the concentration of AOT in all the cases. The concentration of AOT has a significant effect on the absorption of the Iron II chloride microemulsion formed with Hexane as an organic phase oil, as depicted by clearly distinguished spectra in the figures 9a and 9b above. In the microemulsion solution with molar ratio of 25 and hexane oil used in the organic phase, it is observed that as the concentration of the AOT increases, the threshold absorption and wavelength at peak absorbance also increases. The same trend is also observed with microemulsion solution with a molar ratio of 15. The UV peaks lie in the wavelength range of between 390 and 420 nm. In figure 9c and 9d, the spectra of the Iron II chloride microemulsion is shown for molar ratios of 25 and 15 respectively, in which the organic phase oil used was heptane. It is observed that the highest AOT concentration (AOT = 3.33 g) depicts the highest absorbance, which decreases as the concentration of AOT reduces (down to AOT = 1.11 g). Increase in the AOT concentration is associated with increase in nanoreactors. This in turn increases the concentration of nanoparticles in the microemulsion and this affects the optical behaviour of the system. 2 Effect of molar ratios In this section, the effect of change of molar ratio was investigated. The amount of AOT in each case remained constant, and the oil used as an organic phase was iso-octane. This means that the only varying factor was the molar ratio. The figures below show the absorption spectra for different amounts of AOT. Figure 10: UV-Vis absorption spectra showing the effects of different molar ratios using iso-octane oil for various AOT amounts (9a. AOT = 1.11g, 9b. AOT = 2.22g and 9c. AOT = 3.33g) From the absorption spectra in figure 10, the absorption trends show that there is a relatively higher absorption at a molar ratio of 25 compared to when the molar ratio is reduced to 15. The threshold absorption wavelength also increases from around 400 to 420 nm as the amount of AOT increases from 1.11 g to 3.33 g. This observations show that the change in molar ratio has an effect on the optical properties of the resulting nanoparticle dispersion. As stated earlier, water plays an essential role in any microemulsion system, and so is the molar ratio of water to surfactant. The absorption threshold increases as the molar ratio increases, as shown by the red shift of the absorption trend line. This increase in absorbance can be explained by the increase in concentration of nanoparticles, as well as increase in their sizes. This trend is in agreement with the results reported by Nashaat Nassar & Maen Husein. Increasing the molar ratio decreases the interficial tension and increases the viscousity of the microemulsion. 3. Effect of using FeCl2 instead of water: Using FeCl2 instead of water results to formation of another layer in the microemulsion. This is usually caused by the increased ionic strength in the microemulsion, which causes it to collapse (Mann and Hannington 1988). References Read More

2) Effect of molar ratios In this section the effect of change of molar ratio was investigated using heptane as organic phase, and the same surfactant concentration, so that the only varying factor is the molar ratio. The figures below shows the UV-Vis spectra at a surfactant amount of 1.11g to 3.33g. Figure 3 (a, b & c): UV-Vis spectra showing the effect of increasing the molar ratio from 25 to 50 at a constant concentration of AOT, using heptane oil. Water is a very essential component of a microemulsion system.

The mole ratio of water to surfactant is one of the most important parameters that reflect the rigidity of the surface layer of the surfactant, and the ability to lower liquid-liquid interfacial tensions. Increasing the water content reduces the rigidity of the surfacatant suraface layer and promotes aggregation of particles (Nassar and Husein 2007). The mole ratio also determines the size of water pools, which accommodate the nanoparticles. These are key properties that are useful in the preparation of water in oil (W/O) emulsions.

The nature of the emulsions formed is dependent on the hydrophilic-hydrophobic surfactant molecules balance. The UV-Vis spectra in figure 3 (a, b & c) depict that increase in molar ratio results in shifting of the UV-Vis spectrum; the UV absorption increases with increase in molar ratio, if the AOT concentration is kept constant. This trend is attributed to the increase of nanoparticle size as well as particle concentration. A smaller values of molar ratio, a relatively higher proportion of water molecules is bound to the head groups of the surfactant abd this limits the amount of water required to solubilize the iron (III) chloride.

As the mole ratio increases to a higher value, the UV absorbance increases. Increasing the water content decreases the rigidity of of the surfactant protective layer, which leads to particle aggregation (Wongwailikhit and Horwongsakul 2011). The stability of the microemulsion is dependent on the interfacial tension between the water-oil phases. The molar ratio contributes to the interficial tension; it reduces as the molar ratio increases. Viscosity on the other hand increases as the molar ratio increases (Malik, Wani and Hashim 2012).

3 Effect of change oil (between heptane and iso-octane) In this section, the effect of changing the oil used as organic phase was studied. The figures below show UV-Vis obtained for different oils, keeping the AOT concentration and mole ratio constant. Figure 4(a, b, c & d): UV-Vis spectra showing the effect of change of oil used as the continuous organic phase at constant AOT and molar ratio. The figures 4(a, b, c & d) show the effect of changing oil in the preparation of the microemulsion.

The UV-Vis spectra of the molar ratio of 25 depict that there is increased absorbance when the heptane oil is used, compared to when iso-octane is used. However, this trend is not consistent at the molar ratio of 50 as observed in figure 4c. & d. Here, as the molar ratio increases from 25 to 50, the microemulsion solution prepared using iso-octane tends to have a relatively higher UV absorption compared to the solution with heptane oil. This can imply that the molar ratio affects the properties of the oil used.

2 Calculation for microemulsion: The following calculations are for the preparation of microemulsion with AOT, oil (iso-octane, heptane and hexane) and NaOH or FeCl2.4H2O There are two microemulsions, first one with NaOH solution and second one with FeCl2 solution. The total volume of each microemulsion will be 25 ml. Molar ratio (W) will be assumed as 25 and 15. Molar of the surfactant (AOT) will be assumed as 0.3, 0.2 and 0.1 mol/L The experiment is in ambient temperature, 25 °C. This calculation is applicable for different oils which are iso-octane, heptane and hexane. 2.1) Calculation for NaOH microemulsion: With W = 50 and AOT = 0.

3 (as sample) H2O = 0.3 * 50 = 15 mol/L Assume the Molecular weight (MW) of solution as of H2O = 18.

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