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The investigation of frequency response for the magnetic nanoparticulate assembly induced by time-varied magnetic field.

Sun J, Su Y, Wang C, Gu N - Nanoscale Res Lett (2011)

Bottom Line: It was found that the assembly was dependent upon the difference between colloidal relaxation time and field period.The same experiments on DMSA-coated γ-Fe2O3 nanoparticles exhibited that the relaxation time may be mainly determined by the magnetic size rather than the physical size.Our results may be valuable for the knowledge of dynamic assembly of colloidal particles.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory of Bioelectronics, Southeast University, Nanjing 210096, PR China. guning@seu.edu.cn.

ABSTRACT
The field-induced assembly of γ-Fe2O3 nanoparticles under alternating magnetic field of different frequency was investigated. It was found that the assembly was dependent upon the difference between colloidal relaxation time and field period. The same experiments on DMSA-coated γ-Fe2O3 nanoparticles exhibited that the relaxation time may be mainly determined by the magnetic size rather than the physical size. Our results may be valuable for the knowledge of dynamic assembly of colloidal particles.

No MeSH data available.


Schematic illustration of assembly mechanism based on the field periods and the colloidal relaxation time. If the relaxation time is above the period of field, the assembly can occur. If the relaxation time is below the period of field, there is no attractive force to drive the assembly.
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Figure 4: Schematic illustration of assembly mechanism based on the field periods and the colloidal relaxation time. If the relaxation time is above the period of field, the assembly can occur. If the relaxation time is below the period of field, there is no attractive force to drive the assembly.

Mentions: Based on the hydrodynamic size of DMSA-coated γ-Fe2O3 nanoparticles (Figure 1d), the DMSA-coated nanoparticles should also form the one-dimensional assemblies under the treatment of alternating magnetic field. However, the DMSA-coated nanoparticles actually formed the very small aggregates discretely dispersed on the Si wafer rather than the fibrous assemblies (Figure 3). The magnetic coupling between nanoparticles may account for the phenomenon. Here, the magnetic moments of nanoparticle inside one cluster is unable to merge into a large moment for the DMSA-coated nanoparticles. In the previous work of our group, we found the thickness of DMSA coating layer can be four molecules due to the crosslink of -SH groups [6]. The thick coating layer can hinder the composition of nanoparticulate moments because the dipolar interaction is sharply decreased with the distance between two moments increasing [8]. This hypothesis can be confirmed by comparing the ferromagnetic resonance (FMR) measurement of field-treated sample with that of naturally dried sample (Figure S3 in Additional file 1). For the bare γ-Fe2O3 nanoparticles, the resonance line width of field-treated sample narrowed evidently with respect to that of naturally dried sample, exhibiting that there exists the magnetic dipolar interaction among the nanoparticles [9]. However, for the DMSA-coated γ-Fe2O3 nanoparticles, the resonance line width of field-treated sample kept identical, exhibiting that there was no magnetic coupling among the nanoparticles. In this case, the relaxation time should be calculated based on the size of isolated nanoparticle rather than that of nanoparticulate cluster. The relaxation time of 11-nm particle was calculated to be 0.004 ms, far below the periods of external field of any frequency. It means that the variety of magnetic moments of nanoparticle can always keep up with the variety of external field so that the magnetic moments get parallel or approximatively parallel all the while. Since the parallel moments generate repulsive interaction, the final assemblies should be the discrete clusters. Moreover, due to the magnetic repulsive interaction, the size of clusters should be smaller than the original size of aggregates in the suspension. This inference is in accordance with the experimental results. The schematic illustration of assembly mechanism based on the relaxation time with respect to the field period was shown in Figure 4.


The investigation of frequency response for the magnetic nanoparticulate assembly induced by time-varied magnetic field.

Sun J, Su Y, Wang C, Gu N - Nanoscale Res Lett (2011)

Schematic illustration of assembly mechanism based on the field periods and the colloidal relaxation time. If the relaxation time is above the period of field, the assembly can occur. If the relaxation time is below the period of field, there is no attractive force to drive the assembly.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211873&req=5

Figure 4: Schematic illustration of assembly mechanism based on the field periods and the colloidal relaxation time. If the relaxation time is above the period of field, the assembly can occur. If the relaxation time is below the period of field, there is no attractive force to drive the assembly.
Mentions: Based on the hydrodynamic size of DMSA-coated γ-Fe2O3 nanoparticles (Figure 1d), the DMSA-coated nanoparticles should also form the one-dimensional assemblies under the treatment of alternating magnetic field. However, the DMSA-coated nanoparticles actually formed the very small aggregates discretely dispersed on the Si wafer rather than the fibrous assemblies (Figure 3). The magnetic coupling between nanoparticles may account for the phenomenon. Here, the magnetic moments of nanoparticle inside one cluster is unable to merge into a large moment for the DMSA-coated nanoparticles. In the previous work of our group, we found the thickness of DMSA coating layer can be four molecules due to the crosslink of -SH groups [6]. The thick coating layer can hinder the composition of nanoparticulate moments because the dipolar interaction is sharply decreased with the distance between two moments increasing [8]. This hypothesis can be confirmed by comparing the ferromagnetic resonance (FMR) measurement of field-treated sample with that of naturally dried sample (Figure S3 in Additional file 1). For the bare γ-Fe2O3 nanoparticles, the resonance line width of field-treated sample narrowed evidently with respect to that of naturally dried sample, exhibiting that there exists the magnetic dipolar interaction among the nanoparticles [9]. However, for the DMSA-coated γ-Fe2O3 nanoparticles, the resonance line width of field-treated sample kept identical, exhibiting that there was no magnetic coupling among the nanoparticles. In this case, the relaxation time should be calculated based on the size of isolated nanoparticle rather than that of nanoparticulate cluster. The relaxation time of 11-nm particle was calculated to be 0.004 ms, far below the periods of external field of any frequency. It means that the variety of magnetic moments of nanoparticle can always keep up with the variety of external field so that the magnetic moments get parallel or approximatively parallel all the while. Since the parallel moments generate repulsive interaction, the final assemblies should be the discrete clusters. Moreover, due to the magnetic repulsive interaction, the size of clusters should be smaller than the original size of aggregates in the suspension. This inference is in accordance with the experimental results. The schematic illustration of assembly mechanism based on the relaxation time with respect to the field period was shown in Figure 4.

Bottom Line: It was found that the assembly was dependent upon the difference between colloidal relaxation time and field period.The same experiments on DMSA-coated γ-Fe2O3 nanoparticles exhibited that the relaxation time may be mainly determined by the magnetic size rather than the physical size.Our results may be valuable for the knowledge of dynamic assembly of colloidal particles.

View Article: PubMed Central - HTML - PubMed

Affiliation: State Key Laboratory of Bioelectronics, Southeast University, Nanjing 210096, PR China. guning@seu.edu.cn.

ABSTRACT
The field-induced assembly of γ-Fe2O3 nanoparticles under alternating magnetic field of different frequency was investigated. It was found that the assembly was dependent upon the difference between colloidal relaxation time and field period. The same experiments on DMSA-coated γ-Fe2O3 nanoparticles exhibited that the relaxation time may be mainly determined by the magnetic size rather than the physical size. Our results may be valuable for the knowledge of dynamic assembly of colloidal particles.

No MeSH data available.