Ming-Chang Yang (楊明長), Wei-Chih Wang (王威智)
Fe 3 O 4 @PMMA nanoparticles synthesis
Mixing the 25ml Fe3O4@bilayer lauric acid with 5g MMA and 0.01g initiator with 250ml pure water, the solution was reacted for 1 hr under 80℃, N2 gas, and 300rpm. The sample was analyzed by TEM, HR-SEM and HRAEM.
Coating lipid layer onto the Fe3O4@PMMA nanoparticles
Taking 40% or 0% cholesterol with PLG-90 (60%, 100%), the lipid mixture would be formed the lipid cake with the conventional thin film method. Then, 20ml of the solution of the
Fe3O4@PMMA nanoparticles and 80ml pure water were mixed together. Take 20ml of this solution for vertexing with the lipid cake, and then sonicate the solution with a sonicator. The sample was analyzed by TEM and HRAEM.
Results and Discussion
The wet chemical deposition method was used to prepare magnetic fluid. With the TEM
on the surface of magnetite. However, if the lauric acid was used as the dispersing agent, the magnetic nanoparticles would be dispersed much better (Fig. 2). Moreover, Fe3O4nanoparticles without lauric acid coated show much bigger in size distribution of zetasizer analysis than that of Fe3O4@bilayer lauric acid nanoparticles.
The morphology of the Fe3O4@bilayer lauric acid nanoparticles in SEM analysis shows that there are some materials coating onto the surface of the particles, so the size of the Fe3O4@bilayer lauric acid nanoparticles is much bigger than Fe3O4nanoparticles (Fig. 3 and Fig. 4).
However, with the TEM analysis, only the particles could be seen, so the size of
Fe3O4@bilayer lauric acid nanoparticles is no big difference with the size of the Fe3O4nanoparticles.
The slight difference in size analysis would be due the slight difference in the method to synthesize the Fe3O4nanoparticles and the method to synthesis Fe3O4@bilayer lauric acid nanoparticles. The average size of these magnetic nanoparticles, with the TEM analysis, the average size of Fe3O4
nanoparticles is about 8.4 nm, and the Fe3O4@bilayer lauric acid nanoparticles is about 7.2nm.
With the SEM analysis, the average size of Fe3O4nanoparticles is about 10.5 nm, the
Fe3O4@bilayer lauric acid nanoparticle is about 16.3 nm. With the TEM analysis, there is no big difference between the average size of Fe3O4and Fe3O4@bilayer lauric acid nanoparticles.
However, with the SEM analysis, the average size of the Fe3O4@bilayer lauric is much bigger than the average size of Fe3O4. And the average size of Fe3O4@monolayer lauric acid is slight bigger than the average size of Fe3O4nanoparticles.
The quality of the magnetic fluid is a very important experimental factor to synthesize magnetic complex materials in this study. Here, the dispersing agent –lauric acid was used to synthesize the magnetic fluid due to the reason that this kind of magnetic fluid is widely used and studied for a long time in magnetic fluid synthesis and magnetic liposome synthesis with dialysis method.
Due to the strong surface energy of Fe3O4nanoparticles and high density, 5.18 g/cm3, the Fe3O4nanoparticles would aggregate and deposit quickly after synthesizing. The size distribution of Fe3O4nanoparticles with zetasizer analysis, without coating the lauric acid, shows that the particles were seriously aggregated together and the peak of the Fe3O4nanoparticles in zetasizer analysis is 1255 nm.
After coating the bilayer lauric acid, the peak of the size distribution of the Fe3O4@bilayer lauric acid shows much smaller than without coating lauric acid in zetasizer analysis. The peak of Fe3O4@bilayer lauric acid nanoparticles is 43.4 nm in zetasizer analysis.
The typical TGA heating curves of Fe3O4, Fe3O4@bilayer lauric acid and lauric acid.is shown in Figure 5. The weight loss was in the temperature range of 170℃ –370℃. Moreover, the weight loss of the Fe3O4@bilayer lauric acid nanoparticles was characterized with two distinct steps.
However, the TGA result of the Fe3O4nanoparticles shows no much loss, due to there is no lauric acid used for coating onto the surface of the Fe3O4nanoparticles. And the pure lauric acid shows the complete weight loss, the cracking temperature of lauric acid is about 170℃.
The heating temperature of the fastest rate to burn out the lauric acid is about 228℃, which is much the same with the heating temperature of the fastest rate to burn out the primary lauric acid layer of the Fe3O4@bilayer lauric acid (237℃).
The TGA results were used to evaluate the surfactant packing density. Table 1 shows the percentage of the primary and secondary lauric acid on the surface of Fe3O4@bilayer lauric acid nanoparticles. Due to no ultracentrifugation process, the excess of the free lauric acid could not be removed without the ultracentrifugation, so the TGA result of the Fe3O4@bilayer lauric acid nanoparticles shows that there were slight amount of free lauric acid remained outside the
Fe3O4@bilayer lauric acid nanoparticles. Take the result of paper as a reference, the excess amount of the free lauric acid was about 5.37 %. However, the primary lauric acid layer of magnetic fluid is the same percentage with the magnetic fluid synthesized by ultracentrifugation process
With the seed polymerization method, the PMMA was coated onto the magnetic fluid
-(Fig. 6). The average size of Fe3O4@PMMA nanoparticles is about 41.6 nm and of Fe3O4is about 8.9 nm. From the morphology of the Fe3O4@PMMA nanoparticles (Fig. 7), it is obvious that there is no Fe3O4nanoparticle outside the Fe3O4@PMMA nanoparticles. It means that all the magnetite was wrapped by PMMA. Moreover, with the EDS analysis, it could be proved that there was really the Fe element exist in the Fe3O4@PMMA nanoparticles.
After synthesizing the Fe3O4@PMMA nanoparticles as the magnetic carriers, the lipid material - PLG90 was coated onto Fe3O4@PMMA nanoparticles. From Fig. 9 and Fig. 10, lipid layers were coated onto Fe3O4@PMMA nanoparticles. And the X-ray pattern, Fig. 11 shows that these peaks are peaks of Fe3O4nanoparticles.
Discuss the effect of sonication. Without the sonication, from Fig. 10, the serious aggregation would happen with the Fe3O4@PMMA nanoparticles and the lipid materials. However, after sonication, Fig. 11, the particles would be dispersed much well. And it is obvious that lipid layers were coated onto the surface of Fe3O4@PMMA nanoparticles.
Due to the flexibility of the lipid layer, the dispersing could also be controlled by the amount of the cholesterol. Here, different amount of cholesterol were used to improve the dispersing behavior of the Fe3O4@PMMA@lipid nanoparticles.
From Figs. 12 and 13, in the same amount of cholesterol, the Fe3O4@PMMA@lipid nanoparticles were much better dispersed at high power sonication. However, the
Fe3O4@PMMA@lipid nanoparticle with 0% cholesterol would be dispersed best than others (Fig.
14).
Conclusions
In this study, the lipid was coating onto the surface of magnetic Fe3O4@PMMA nanoparticles.
From the TEM analysis, it could be obviously to seen that the lipid could spontaneously coated onto the surface of the Fe3O4@PMMA nanoparticles. The different amount of the cholesterol could affect the dispersing behavior of the Fe3O4@PMMA@lipid nanoparticles. In the future, different kind of lipid should be also chose to form the thin film onto the surface of the Fe3O4@PMMA nanoparticles.
Coating the lipid layers onto the surface of the particles would have great applications in the future. Combination with the magnetic materials also could be a potential application, too. Here, reporting the conventional thin film with lipid to coat onto the surface of the Fe3O4@PMMA nanoparticles.
Acknowledgements
The lipid –Phospholipon 90 G supported from PHOSPHOLIPID GmbH Company in German is also acknowledged. Thanks for the helps in TEM and HRAEM from Miss Jaw in the
Instrument Center of NCHU, Miss Sheu and Mr. Yao in the Instrument Center of NCKU.
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Fig. 1 TEM photograph of Fe3O4nanoparticles.
The bar is 10 nm.
Fig. 2 TEM photograph of Fe3O4@biyer lauric acid nanoparticles The bar is 10 nm.
Fig. 3 SEM of Fe3O4nanoparticles Fig. 4 SEM of Fe3O4@bilayer lauric acid nanoparticles
Fig. 5 TGA of Fe3O4nanoparticles, Fe3O4@bilayer lauric acid nanoparticles and pure lauric acid Table 1 The percentage of the primary and secondary lauric acid of Fe3O4@bilayer lauric acid
nanoparticles
Primary layer Secondary layer Total amount Fe3O4
Fe3O4@bilayer lauric acid 8.8 % 22.46 % 31.26 % 68.74 % Ratio to Fe3O4remain 12.8 % 32.67 % 45.47 % 100 % Reference from paper base
on Fe3O4remain 12.5 % 27.2 % 39.7 % 100 % Excess of lauric acid 0.3% 5.37 %
Fig. 6 TEM photograph of Fe3O4@PMMA nanoparticles.
Fig. 7 (a) HR-SEM photograph
Nanoparticles
Fig. 8 The serious aggregation of the Fe3O4@PMMA@lipid nanoparticles without the sonication.
Fig. 9 The nanoparticles after sonication
Fig. 10 The HR-AEM picture of the
Fe3O4@PMMA@lipid nanoparticles
Fig. 11 X-ray pattern of Fe3O4@PMMA@lipid in (a) Fig. 9 and (b) Fig. 10
Fig. 12 The Fe3O4@PMMA@lipid nanoparticles with 40% cholesterol and low power sonication
Fig. 13 The Fe3O4@PMMA@lipid nanoparticles with 40% cholesterol and high power sonication
Fig. 14 The Fe3O4@PMMA@lipid nanoparticles with 0% cholesterol and high po