DOINA BlCA, OANA BAL/~U, L. V~K~,S. Centre forFundamental and Advanced Technical Research of Romanian Academy,. Timisoara, Romania. P.C.FANNIN ...
The comparative study of particle size distribution in
magnetic fluids *) M. T1MKO, P. KOPCANSKY, M. KONERACKA hlstitute of Experimental Physics, Slovak Academy of Sciences, Ko~ice, Slovakia A. SKUM1EL, M. LABOWSKI, A. JOZEFCZAK
Institute of Acoustics Adam Mickiewicz University, Poznan, Poland DOINA BlCA, OANA BAL/~U, L. V~K~,S
Centre forFundamental and Advanced Technical Research of Romanian Academy, Timisoara, Romania P.C.FANNIN, A.T.GIANNITSIS
Department of Electronic and Electrical Engineering, Trinity College, Dublin2, Ireland Received 15 June 2001; final version 5 October 2001 Water- and physiology- solution- based biocompatible magnetic fluids have been studied in order to determine the size of magnetic particles and their colloidal stability. The results of magnetorheological measurements at room temperature and measurements of the frequency-dependent complex magnetic susceptibility indicate that the fluids have good stability and that the particles are finely dispersed without aggregation. The mean particle diameter for physiology- solution- based magnetic fluid, estimated from measurements of anisotropy of the magnetic susceptibility, was found to be 9.4rim. This value is in good agreement with an estimate of ll.6nm obtained from transmission electron microscopy (TEM) particularly when allowance is made for the thickness of surfactant layer (approx. 2nm).
PACS: 75.50.Mm, 75A0.Cx Key words: magnetic fluid, particle size, magnetic susceptibility 1
Introduction
The knowledge of polydispersity profile of tile nanoparticle size is very important since physical, chemical and physico-chemical properties are strongly dependent on nanoparticte diameter and its distribution. Measurements of magnetization and T E M have been traditionally used to obtain the particle size. As useful methods for estimation of particle diameter the measurements of the frequency- dependent complex magnetic susceptibility [1] and measurements of the anisotropy of tile magnetic susceptibility [2] were used. hi this paper, we present a method of biocompatible sample of physiology- solution- and water- based magnetic fluid preparation. Also, particle diameters obtained from magnetization , magnetic susceptibility and T E M *) Presented at ll-th Czech and Slovak Conference on Magnetism, Ko~ice, 20-23 August 2001 Czechoslovak Journal of Physics, Vol. 52 (2002), Suppl. A
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M. Timko et al. measurements are compared with one another and magnetorheological results axe discussed from the point of view aggregation of magnetic particles. 2
Sample preparation and experimental methods
Two types of samples were considered, (a) a water- b ~ e d and (b) a physiologysolution- based magnetic fluid. The samples were obtained by applying specific preparation procedures the main steps of which are given below. (a) Coprecipitation of Fe 2+, Fe 3+ ions (excess of NaOH;~ 80~ -~ subdomain Fe304 nanoparticles -~ repeated washing/purification --* chemisorbtion of the laurie acid anion, followed by the 1)hysical adsorbtion of a secondary layer of lauric acid -~ dispersion of Fe304 nanoparticles in water -~ magnetic sedimentation/filtration --~ water- based magnetic fluid. (b) Coprecipitation of Fe 2+, F e 3+ ions (excess of NH4OH; ~ room temperature)-~ subdomain FeaO4 nanoparticles -~ repeated washing/purification to obtain p H = 7 --* chemisorbtion of natriun oleate with detergent --~ dispersion of Fe304 nanoparticles in physiology solution (9% wt NaC1 aqueous solution) -~ centrifugation -~ physiology- solution- based magnetic fluid. Examination of the nanosized magnetic particlcs by TEM was done using a Tesla BS 500 microscope normally operated at 90 kV and 80000 X magnification by replication technique. From the TEM image population above 1000 particles was analysed. Magnetization measurements were carried out on a VSM magnetometer in external magnetic field up to 6T. Complex susceptibility was measured at room temperature by means of the toroidal technique using a HP 4192A LF hnpedance Analyser over the fi'equency range of 10 Hz to 1MHz [1]. Mea~surements of static magnetic susceptibility were carried out in a cylindrical solenoid, which was connected to the inductance meter and placed in the cell. Comparison of tile solenoid inductance for cell filled with the ferrofluid and empty cell, allowed to determine the real component of magnetic susceptibility [2]. Magnetorheological measurements were performed by nmans of the special cell adapted to a RHEOTEST-2 type rheometer described in [3]. 3
Results and discussion
TEM investigations on tile (a)and (b)type samples gave tile mean diameters Dv/TE M (a) = 11.2nm and Dv/TEM(b) ---- 11.6nm and the same standard deviation (~TEM(a) ---- S T E M ( b ) ---- 2.5nm. Tile values of saturation magnetization estimated from VSM measurements were 180 G and 171 G for the sample (a)and(b), respectively. Using tile method of Chantrell et al. [4], the lognormal parameters of the particle size distribution were found to be: mean particle diameters Dv/VSM ~ 9.1n~n and 9.3nm, and standard deviation 5VSM = 2.Snm and 2.4urn for sample (a) and (b), respectively. The relative increase of the effective viscosity due to the magnetic field for as prepared (nominal magnetization 180 G and 171 G for sample (a) and A282
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The c o m p a r a t i v e study of particle size d i s t r i b u t i o n in m a g n e t i c fluids . . . 2,4
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Fig. 1. The relative increase of the effective viscosity due to the magnetic field,
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(b), respectively) and diluted samples (with lower values of nominal magnetization), 7//r/0, is given in Fig.1. The results of Fig.1 reveal that the magnetorheological effect is more pronounced for more concentrate samples, due to field induced agglomerates formation. The relative increase of effective viscosity for the (a) and (b) type samples is practically of the same magnitude, which is in agreement with TEM data. Also, the magnitude of the effect, 7//7/0 ~, 1.65, is relatively small and therefore it may be concluded that the samples (a) and (b) are of relatively good colloidal stability. As both samples have very similar properties, we performed next experiments for sample (b) only. Tile normalized plots of susceptibility X' (w)/X(O) and X" (w)/X(O) against frequency for the sample (b) are shown in Fig 2. The existence of the loss-peak only in the MHz region showed that the dominant relaxation mechanism should be of the NGel type. Using fornmla TN = Toa (0" = K V / k T ) for the N~el relaxation [5] with +-N -- 3.10-Ss (calculated for fma• from Fig.2), r0 = 10-8s and K = 2.2 x lOaJ/m 3 [6], we obtained a mean particle diameter Dv = 10.5nm. From Fig. 2 it can be seen that the profiles of the susceptibility components are approximately constant up to 10 kHz, without any low frequeucy absorptiou peak in this frequency range. This is indicative of a finely dispersed magnetic particles without aggregation. This conclusion is supported by measurements of magnetorheological properties at room temperature. Fig.3 illustrates the anisotropy of the real part of the magnetic susceptibility of the sample (b). The coefficients XII and X• describe the magnetic susceptibility of the nmgnetic fluid in the directions parallel and 1)erpendicular to that of the external nmgnetic field and are mathematically defined in [7]. The maximum of the function (XJ_ - Xli) is located at Ht)c = 40.3 k A / m (Fig.3), what means that the magnetic moment of a magnetic particle is (2.97-4-0.15).10-19Am 2, and hence the mean particle diameter is Dv = 9.4nm. The obtained value is in good agreement with data from VSM D~/VSM = 9.3nm and complex susceptibility D~ = 10.5ran. The difference between particle diameter t
t
t
C z e c h 9 J. P h y s . 5 2 ( 2 0 0 2 )
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M. Timko et al.: The comparative s t u d y of particle size distribution ...
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estimated from magnetic measurements and T E M (Dv/TEIvI (b) = l l . 6 n m ) i s caused by surfactant layer, the thickness of which reaches up to 2 n m for natrium oleate. 4
Conclusion
The colloidal stable biocompatible magnetic fluids based on water and physiology solution were prepared. Their colloidal stability was confirmed by magnetorheological and magnetic susceptibility measurements. The mean particle diameters estimated from the magnetic nmasurements are in good agreement with T E M if allowance is made for the thickness of a surfactant layer. Funds for this research were provided by the Slovak Academy of Sciences Project No.7020, NATO project No.LST.CLG. 977500 and KBN Research Grant No.8T07B 02720. P.C.F. acknowledges the Irish ttigher Education Authority. References
[1] P.C.Fannin, B. K. P. Scaife, S. W. Charles: J. Phys. E Sci. Instrum. 19 (1986) 238. [2] A. Skumiel et al: Anisotropy of ultra.sound propagation and magnetic susceptibility in viscous ferrofluid, will be presented at Ultrasonic International - Delft (2001). [3] L.Vekas, D. Bica, 1. Potencz, D. Ghorghe, O. Balau, M. Rasa: Progr. Coll. Polym. Sci., (2001) - to appear. [4] R.W. Chantrell, J. Popplewell, S.W.Charles: IEEE Trans. Magn. 14 (1978) 975. [5] W. F. Brown: ehys; Rev. 130(1963) 1677. [6] J.-L. Dormann, D. Fiorani, E. Tronc: Adv. Cheni. Phys. 9 (1997) 283-494. [7] E. Blooms, A. Cerbers, M. M. Maiorov: M a g n e t i c Fluids, ~vValter de Gruyter, New York, (1997)
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