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Magnetic Effects on Electrolyte Solutions in Pulse and Alternating Fields
Journal of Colloid and Interface Science 209, 374 –379 (1999) Article ID jcis.1998.5898, available online at http://www.idealibrary.com on
Magnetic Effects on Electrolyte Solutions in Pulse and Alternating Fields Jun Oshitani, Ryosuke Uehara, and Ko Higashitani1 Department of Chemical Engineering, Kyoto University, Yoshida, Sakyo, Kyoto 606-8501, Japan E-mail: [email protected] Received June 19, 1998; accepted September 30, 1998
loop with a section of alternating magnetic exposure where several pairs of permanent magnets with north and south poles facing each other are placed alternately along the tube and found that there is a velocity at which the magnetic effect is maximized (27). Similar investigations have been conducted using the flow loop with a magnetic section composed of a pair of permanent magnets. In these loops, the fluid flows through the section instantaneously so that a pulse-like magnetic field is applied to the flowing fluid. Nevertheless the magnetic effects have been claimed to exist (28 –31). If the data are reliable, the pulse and alternating fields or the gradient magnetic field must be much more effective for magnetic effects than the static field. It is also known that the many magnetic effects on living organisms (32–38) have been examined using the alternating field of wide range of frequency. In the present study, it is examined how the pulse and alternating magnetic fields contribute to the magnetic effects compared to that seen with the static field. The flow loops are not employed here to avoid contamination of the test solution during the experiment, but a rotational device with permanent magnets is constructed such that the pulse and alternating fields are able to be applied to the sample in a stationary cell.
The contribution of the pulse and alternating magnetic fields on the magnetic effects is examined and compared with that of the static field, using a rotational device by which the pulse and alternating fields are able to be applied to the stationary sample. The followings are found: (i) the substantial time required to reach the maximum magnetic effect in the pulse and alternating fields is much smaller than the time in the static field, (ii) the magnetic effect does depend on the frequency of magnetic field, and (iii) the pulse and alternating magnetic fields make the quasi-stable structure more stable than the static field. The results are discussed and compared with the magnetic effects in flow loops reported elsewhere. © 1999 Academic Press Key Words: magnetic effect; atomic force microscope; adsorbed layer; alternating magnetic field; pulse magnetic field; memory effect.
INTRODUCTION
A large number of investigations have been carried out on the magnetic effects on aqueous systems and the existence has been confirmed by various experimental evidences (1–21). The mechanism, however, is not clarified yet, because the magnetic effects observed cannot be explained by the simple electromagnetic theory as follows: (i) the effects appear for nonmagnetic materials in the magnetic field of low flux density; (ii) the effects remain for a sufficiently long period after the magnetic exposure, which is called “memory effect” (2, 4, 8, 14 –21), and (iii) there are some conflicting data (22–26). Higashitani et al. have conducted a series of well-controlled experiments of magnetic effects on electrolyte solutions and clarified the conditions under which the effects appear (15–21). Recently these conditions were confirmed on the molecular level using an atomic force microscope (AFM) (19, 20). In these experiments, uniform static magnetic fields were applied to the samples and the following common feature was found: the effect reveals itself gradually with the magnetic exposure time, t e, and reaches to a plateau value at t e . 10 –30 min. Kronenberg investigated the magnetic effect using a flow 1
To whom correspondence should be addressed.
0021-9797/99 $30.00 Copyright © 1999 by Academic Press All rights of reproduction in any form reserved.
EXPERIMENTS
In this study, the thickness of the layer of water molecules and ions adsorbed on the surface and the surface potential in an electrolyte solution are measured using an AFM, and the magnetic effects are evaluated by their change before and after the magnetic exposure to the solution. The experimental conditions used here are exactly the same as those used in the previous experiment (19, 20), except for the type of magnetic field applied. Hence the details are given elsewhere (19, 20), but the outline is described below. Solution Pure water with a relative resistance of 17.3 MV-cm that is purified by both distillation and reverse osmosis is used. The aqueous solution of 1 3 1024 kmol/m3 KCl of reagent grade is employed because the magnetic effects have been constantly
374
MAGNETIC EFFECTS IN PULSE AND ALTERNATING FIELDS
375
observed in this solution (17, 19, 20). The solution is kept in a temperature-controlled bath of 25 6 0.5°C. The AFM probe coated with SiO2 is used when the magnetic effect on the thickness of the adsorbed layer is examined, while a colloidal probe with a 4.0-mm silica particle is employed when the effect on the surface potential is evaluated. The mica, which is cleaved just before the experiment to be free from contamination, is used as the plate smooth on the molecular level. Magnetic Field Three different magnetic fields are employed: the pulse, alternating and static fields. The apparatus is shown schematically in Fig. 1. The iron yoke is composed of two disks of 15 cm in diameter and 1.5 cm in thickness which are placed parallel and connected by a cylindrical shaft 2 cm in diameter. The shaft is able to be rotated at up to 5400 rpm by a DC motor. For the pulse field, two permanent magnets (2 3 3 3 6 cm3) is mounted firmly on the each disk such that north and south poles are facing each other with a 2.5 cm gap. The sample in the cell of 10 cm3 in volume is placed between the
FIG. 2. The apparent magnetic exposure time t app and the substantial magnetic exposure time t e. (a) The pulse field, (b) the alternating field.
magnets, fixing the cell firmly on the lower stationary stage. Because each magnet covers about 61 of the area of the disk surface, the pulse field given by this apparatus is expressed approximately as shown in Fig. 2a. Here the apparent exposure time t app is defined as the period during which the sample is placed between the rotating magnets, and the substantial exposure time t e is the period during which the sample is actually exposed to the magnetic field. Hence t e ' t app/6 in this case. In the case of alternating field, two pairs of magnets are mounted such that the magnetic fields are directed alternately. This alternating field is illustrated schematically as shown in Fig. 2b and t e ' t app/3. When the effect in the static field is examined, the sample is placed between the stationary magnets. The magnetic flux density between the magnets is 0.4 T, which is known to be strong enough to have the maximum magnetic effect (15–21). Measurement of Magnetic Effect The AFM used is a Nanoscope-III D (Digital Instruments). The colloidal probe is used in determining the surface potential, because the large surface amplifies the contribution to the long-range interaction between the surfaces. The force curve, the relation of the interaction force F vs the separation distance between surfaces h, is able to be drawn by measuring the long-range interaction between surfaces in a solution. The corresponding theoretical force curve between a plate and a sphere of radius R in a 1:1 electrolyte solution is given by the DLVO theory (39) as F 5 C k exp~2k h!,
[1]
where C and k are given by
FIG. 1. Schematic drawing of the apparatus to generate the pulse, alternating and static magnetic fields.
C 5 4 pe 0e R c 1c 2,
[2]
k 5 ~2n 0Z 2e 2/ e 0e kT! 1/ 2.
[3]
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Here e0 and e are the permitivity of free space and the relative permitivity of the solution respectively, c1c2 are the product of the surface potentials of the silica particle and mica plate, n 0 is the number concentration of ions, Z is the valency of ions, e is the elementary charge of electron, k is the Boltzmann constant, and T is the temperature. C and k are the parameters of the potential of the solid surfaces and the ionic concentration of the bulk, respectively, whose magnitudes are able to be determined by fitting the data with Eq. [1]. It is known that Eq. [1] is appropriate only for low surface potential. Nevertheless, Eq. [1] is employed here because of the following reasons: (i) the equation is of simple form to handle and can be fitted well with the present data and (ii) the magnetic effects are evaluated by the ratios of C and k for solutions with the magnetic exposure to those for solutions without the exposure, but not by the absolute values of C and k. When the magnetic effect on the apparent thickness of the adsorbed layer is examined, the AFM probe without the particle is used. The strong van der Waals attractive force makes the probe jump on the mica surface when the probe approaches closely to the mica. After this contact, the probe will penetrate into the adsorbed layer until the final contact with the mica surface. The distance that the probe can penetrate, d, is regarded as a measure of the total thickness of the adsorbed layers on both surfaces. Experimental Procedure The AFM liquid cell is filled with a solution immediately after the solution is exposed to the magnetic field. After the movement of the solution is settled completely, force measurements are carried out about 50 times for one experimental condition, and the values of k, C, and d are determined by averaging the measured values. The same procedure but without the magnetic exposure is repeated, and the magnetic effect is evaluated using the ratios km/k0, Cm/C0, and d m/d 0 where the subscripts m and 0 denote “with the magnetic exposure” and “without the magnetic exposure,” respectively. The deviation of these ratios from unity indicates the degree of magnetic effect. RESULTS
Effects on Bulk Solution, Surface Potential, and Thickness of Adsorbed Layer Figure 3 shows the values of km/k0, Cm/C0, and d m/d 0 , when the solutions are exposed separately to the three types of magnetic fields for t app 5 30 min. It is clear that the values of km/k0 are not affected by the magnetic exposure, independently of the type of magnetic field applied. This implies that the bulk properties are not influenced at least explicitly by the magnetic exposure. The values of Cm/C0 are smaller than unity, that is, the apparent surface potential is reduced by the magnetic exposure.
FIG. 3. Values of km/k0, Cm/C0, and d m/d 0 for the pulse, alternating, and static fields, respectively. (KCl concentration 5 1 3 1024 kmol/m3, magnetic flux density 5 0.4 T, t app 5 30 min, frequency of pulse and alternating fields 5 30 Hz.)
On the other hand, the values of d m/d 0 increase, that is, the adsorbed layer is thickened by the magnetic exposure. We consider that these data are consistent each other, because thickening the adsorbed layer will increase the potential drop within the adsorbed layer, which results in the reduction of the apparent surface potential. All these data are consistent also with the previous results in static magnetic fields (15–21). Hereafter, we evaluate the magnetic effects using only the data of d m/d 0 , because the data of Cm/C0 and d m/d 0 give us essentially the same information but d m/d 0 is a more direct measure for magnetic effects. Reliability of Data We have been accumulating a large number of experimental data on the magnetic effects in the various systems (15–21), and we found that the main features of the magnetic effects which are evaluated using the average values of measured data are consistent each other, independent of the difference in the measuring methods, time, and investigators. Hence we consider that the comparison between the averaged data with and without the magnetic exposure is satisfactory. Nevertheless, it is important to know whether the comparison using the averaged data are statistically meaningful or not. According to the Welch test (40), the difference of the average values of X, uX# m 2 X# 0 u, is significant if the following relation with the level of significance a 5 0.01 is satisfied: uX# m 2 X# 0u
YÎ
SD
s 2m s 20 a 1 .t . Nm N0 2
[4]
Here X# m and X# 0 are the average values of X, s m and s 0 are the standard deviations, N m and N 0 are the number of measurements, and t is the t-distribution. The data for the pulse field given in Fig. 3 are substituted into Eq. [4] as an example. It is clear that the data satisfy the Welch test as shown in Table 1.
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MAGNETIC EFFECTS IN PULSE AND ALTERNATING FIELDS
TABLE 1 Statistical Evaluation
X
X# m
X# 0
sm
s0
Nm
N0
C d
9.881 0.648
10.331 0.603
0.780 0.068
0.650 0.072
50 50
50 50
YÎ
uX# m 2 X# 0 u
2.906 3.214
s20 s2m 1 Nm N0
SD
t
a 2
2.687 2.687
Note. The data are for the pulse and alternating fields. Subscripts m and 0 denote with magnetic exposure and without magnetic exposure, respectively. a 5 0.01.
This result confirms that the comparison between the averaged data with and without the magnetic exposure is statistically significant and satisfactory. Effect of Type and Frequency of Magnetic Fields Figure 4a shows the dependence of the value of d m/d 0 on the apparent exposure time t app for the pulse and alternating fields of 30 Hz and for the static field. The values of d m/d 0 gradually increase with t app and become the same plateau value independently of the type of magnetic fields. However, the time re-
quired to reach the maximum effect is about 6 min in the pulse field, about 10 min in the alternating field, and about 20 min in the static field, and the time at which the magnetic effect reveals itself also follows this order. The same data are replotted against the substantial exposure time t e in Fig. 4b. It is important to note that the substantial time required to reach the maximum magnetic effect is only about 1 min in the pulse field and about 3 min in the alternating field, which are much smaller than the time in the static field, 20 min. Figure 5 shows the dependence of the relation of d m/d 0 vs t e on the frequency of the pulse field. The time at which the magnetic effect appears decreases with increasing frequency up to 90 Hz. Since the maximum frequency achieved by the present apparatus is 90 Hz, we are unable to know whether this is the maximum value or the plateau value. Nevertheless, we can say that the magnetic effect does depend on the frequency of magnetic field. Memory Effect The existence of “memory effect” has been confirmed in the series of our experiments. Here it is examined how the type of magnetic field influences the memory effect. The value of d m/d 0 is evaluated after the sample is exposed to the magnetic field for t app 5 30 min and left standing for a given period t s. Figure 6 shows the dependence of d m/d 0 on t s. It is clear that
FIG. 4. Dependence of d m/d 0 in the pulse, alternating and static fields on (a) the apparent magnetic exposure time t app and (b) the substantial magnetic exposure time t e. (KCl concentration 5 1 3 1024 kmol/m3, magnetic flux density 5 0.4 T, frequency of pulse and alternating fields 5 30 Hz.)
FIG. 5. Dependence of d m/d 0 on t e for various frequencies of pulse field. (KCl concentration 5 1 3 1024 kmol/m3, magnetic flux density 5 0.4 T.)
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OSHITANI, UEHARA, AND HIGASHITANI
FIG. 6. Dependence of d m/d 0 on the standing period t s for the pulse, alternating and static fields. (KCl concentration 5 1 3 1024 kmol/m3, magnetic flux density 5 0.4 T, t app 5 30 min, frequency of pulse and alternating fields 5 30 Hz.)
the magnetic effect remains for at least 5 days in the case of the pulse and alternating fields, while it starts to decay at t s 5 3 days and disappears at t s ' 5 days in the static field. In the preceding reports (15–21) we proposed the mechanism that some quasi-stable structure of water molecules, ions, and hydrated ions is formed on the surface and the structure remains until a strong external disturbance is given to the solution. If this is the case, the pulse and alternating magnetic fields make the quasi-stable structure more stable than the static field.
Now we consider whether there is any possible mechanism to explain why the magnetic effect depends on the gradient of magnetic flux density. In the investigations of the magnetic effects on living organisms, the eddy current induced by the change of magnetic field has been considered to play an important role (32). When the magnetic field passes by the sample cell, the sample will experience the high gradient magnetic field. Then the eddy current, that is, the ionic eddy motion, will be generated within the solution, such that the additional magnetic field will be generated within the eddy and so the high gradient magnetic field will be formed near the ionic current. It is known that an extremely strong force will act even on a paramagnetic substance in a high gradient magnetic field (32, 43). Since water molecules are diamagnetic, a strong attractive force will act between ions and water molecules. This hypothesis is not proven experimentally by any means, but this is the only mechanism we can think of at present. It has been claimed that the magnetic effect appears in the fluid flowing through the flow loop with a pair of small magnets, without explaining why such a short exposure time is effective. The present results that (i) high gradient magnetic
DISCUSSION
As shown in Fig. 4b, the substantial exposure time to have the maximum magnetic effect in the pulse and alternating fields is much shorter than in the static field. This implies that the rate of change of magnetic flux density is very important to generate the magnetic effect. Then the alternating field is expected to be more effective than the pulse field. However, the order is reversed as shown in Fig. 4b. We do not have any clear explanation for this, but we consider the data obtained to be reliable, because they are reproducible and the very similar dependence of the magnetic effect on the type of magnetic fields was observed in the formation of CaCO3 crystals (41) and in the measurement of the zeta potential of colloidal particles (42), as shown in Figs. 7a and 7b respectively, where the experiments were conducted using the same apparatus shown in Fig. 1. We emphasize that the feature is very similar among the data in Fig. 4b and Figs. 7a and 7b, although the sample solutions, the properties measured, the date of measurements, and the investigators are completely different from each other. Hence we can say at least that the rapid change of the magnetic flux density does reduce significantly the exposure time for the maximum magnetic effect, although the reason for the difference between the magnetic effects by the pulse and alternating fields remains to be unclarified.
FIG. 7. Dependence of magnetic effects on the substantial exposure time t e in the previous experiments. (a) The maximum values of the absorbance, A m, in the CaCO3 crystal formation are measured by a spectrophotometer and the ratio of A m-values in solutions with and without the magnetic exposure, m Am m/A 0 , is plotted against t e (41). (b) The zeta potentials of polystyrene latex particles, z, are measured by a microelectrophoresis and the ratio of z-values in solutions with and without the magnetic exposure, zm/z0, is plotted against t e (42). (Magnetic flux density 5 0.4 T for pulse and alternating fields and 0.45 T for static field, frequency of pulse and alternating fields 5 30 Hz.)
MAGNETIC EFFECTS IN PULSE AND ALTERNATING FIELDS
field shortens the exposure time to obtain the maximum magnetic effect considerably and (ii) the magnetic effect remains as a memory seem to support the magnetic effects observed in the flow loop. CONCLUSIONS
The contribution of the pulse and alternating magnetic fields on the magnetic effects is examined and compared with that of the static field, using a rotational device by which the pulse and alternating fields are able to be applied to the stationary sample. The following conclusions are drawn. (i) The substantial time required to reach the maximum magnetic effect in the pulse and alternating fields is much smaller than the time in the static field. This is consistent with the data of magnetic effects in the formation of CaCO3 crystals and the zeta potential of colloidal particles. (ii) The magnetic effect does depend on the frequency of magnetic field. (iii) The pulse and alternating magnetic fields make the quasi-stable structure more stable than the static field. (iv) The present results seem to support the magnetic effects observed in the flow loops, in which the fluids are exposed to the magnetic field for a short time. REFERENCES 1. Klassen, V. I., and Zinov’ev, Y. Z., Kolloidn. Zh. 29, 758 (1967). 2. Klassen, V. I., Zhilenko, G. V., Berger, G. S., Lapatukhin, I. V., Erygin, G. D., and Klyuchnikov, N. G., Dokl. Akad. Nauk. SSSR 183, 1123 (1968). 3. Viswat, E., Hermans, L .J. F., and Beenakker, J. J. M., Phys. Fluids 25, 1794 (1982). 4. Ayrapetyan, S. N., Grigorian, K. V., Avanesian, A. S., and Stamboltsian, K. V., Bioelectromagnetics 15, 133 (1994). 5. Rai, S., Singh, U. P., and Singh, A. K., Electro-Magnetobiol. 14, 23 (1995). 6. Dushkin, S. S., and Ievstratov, V. N., “Magnetic Water Treatment in Chemical Undertaking.” Khmiya, Moscow, 1986. 7. Yamaoka, K., Sugimoto, S., Kimura, T., Akiyama, R., and Kobayashi, R., J. Jpn. Goetherm. Energy Assoc. 25, 31 (1988). 8. Ellingsen, F. T., and Kristiansen, H., Vatten 35, 309 (1979). 9. Pandolof, L., Colale, R., and Paiaro, G., Chim. Ind. 69, 88 (1987). 10. Martynova, O. I., Tebenekhin, E. F., and Gusev, B. T., Kolloidn. Zh. 29, 692 (1967). 11. Chiba, A., Kawazu, K., Nakano, O., Tamura, T., Yoshihara, S., and Sato, E., Corros. Sci. 36, 539 (1994). 12. Ghabashy, M. E., Sedahmed, G. H., and Mansour, I. A. S., Br. Corros. J. 17, 36 (1982).
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13. Lin, I. J., and Yotvat, J., J. Magn. Magn. Mater. 83, 525 (1990). 14. Nakashima, K., and Yamamoto, H., J. Toyota Nat. Tech. Coll. 20, 67 (1987). 15. Higashitani, K., Okuhara, K., and Hatade, S., J. Colloid Interface Sci. 152, 125 (1992). 16. Higashitani, K., Kage, A., Katamura, S., Imai, K., and Hatade, S., J. Colloid Interface Sci. 156, 90 (1993). 17. Higashitani, K., Iseri, H., Okuhara, K., Kage, A., and Hatade, S., J. Colloid Interface Sci. 172, 383 (1995). 18. Higashitani, K., Oshitani, J., and Ohmura, N., Colloids Surf. A 109, 167 (1996). 19. Higashitani, K., and Oshitani, J., Trans. IChemE, 75-B, 115 (1997). 20. Higashitani, K., and Oshitani, J., J. Colloid Interface Sci. 204, 363 (1998). 21. Oshitani, J., Yamada, D., Miyahara, M., and Higashitani, K., J. Colloid Interface Sci., in press. 22. Kirgintsev, A. N., and Sokolov, V. M., Russ. J. Phys. Chem. 40, 1107 (1966). 23. Ushakov, O. I., and Sherbakov, L. M., Russ. J. Phys. Chem. 44, 729 (1970). 24. Mirumyants, S. O., Vandyukov, E. A., and Tukhvatullin, R. S., Russ. J. Phys. Chem. 46, 124 (1972). 25. Gonet, B., Bioelectromagnetics 6, 169 (1985). 26. Yoon, J., and Lund, D. B., J. Food Sci. 59, 964 (1994). 27. Kronenberg, K. J., IEEE Trans. Magn. 21, 2059 (1985). 28. Busch, K. W., Busch, M. A., Parker, D. H., Darling, R. E., and McAtee, J. L., Corrosion 42, 211 (1986). 29. Sinezhuk, B. D., Fedoruk, T. Y., and Mal’ko, S. V., Sov. J. Wat. Chem. Tech. 9, 407 (1987). 30. Ishibashi, S., Sato, T., Haneda, K., and Kato, Y., Nippon Ohyoh Jikigaku Kaishi 20, 509 (1996). 31. Iwasaki, M., and Ueno, S., IEEE Trans. Magn. 33, 4254 (1997). 32. Shiga, T., Miyamoto, M., and Ueno, S., “Ziba no Seitai eno Eikyo.” Teraspaia, Tokyo, 1991. 33. Zimmerman, S., Zimmerman, A. M., Winters, W. D., and Cameron, I. L., Bioelectromagnetics 11, 37 (1990). 34. Falugi, C., Grattarola, M., and Prestipino, G., Biophys. J. 51, 999 (1987). 35. Yamada, S., Kawasaki, M., Gunji, Y., Roman, P., Harada, S., and Yamamoto, H., IEEE Trans. Magn. 32, 5115 (1996). 36. Walleczek, J., and Budinger, T. F., FEBS Lett. 314, 351 (1992). 37. Goodman, R., Blank, M., Lin, H., Dai, R., Khorkova, O., Soo, L., Weisbrot, D., and Henderson, A., Bioelectrochem. Bioenerg. 33, 115 (1994). 38. Roy, S., Noda, Y., Eckert, V., Traber, M. G., Mori, A., Liburdy, R., and Packer, L., FEBS Lett. 376, 164 (1995). 39. Israelachvili, J. N., “Intermolecular and Surface Forces.” Academic Press, London, 1985. 40. Ishimura, S., “Bunsan Bunnseki no Hanashi.” Tokyo Tosho, Tokyo, 1998. 41. Katamura, S., M.S. Thesis, Kyushu Institute of Technology, Kitakyushu, 1993. 42. Iseri, H., M.S. Thesis, Kyushu Institute of Technology, Kitakyushu, 1994. 43. Ueno, S., and Iwasaki, M., IEEE Trans. Magn. 30, 4698 (1994).
Magnetic Effects on Electrolyte Solutions in Pulse and Alternating Fields Jun Oshitani, Ryosuke Uehara, and Ko Higashitani1 Department of Chemical Engineering, Kyoto University, Yoshida, Sakyo, Kyoto 606-8501, Japan E-mail: [email protected] Received June 19, 1998; accepted September 30, 1998
loop with a section of alternating magnetic exposure where several pairs of permanent magnets with north and south poles facing each other are placed alternately along the tube and found that there is a velocity at which the magnetic effect is maximized (27). Similar investigations have been conducted using the flow loop with a magnetic section composed of a pair of permanent magnets. In these loops, the fluid flows through the section instantaneously so that a pulse-like magnetic field is applied to the flowing fluid. Nevertheless the magnetic effects have been claimed to exist (28 –31). If the data are reliable, the pulse and alternating fields or the gradient magnetic field must be much more effective for magnetic effects than the static field. It is also known that the many magnetic effects on living organisms (32–38) have been examined using the alternating field of wide range of frequency. In the present study, it is examined how the pulse and alternating magnetic fields contribute to the magnetic effects compared to that seen with the static field. The flow loops are not employed here to avoid contamination of the test solution during the experiment, but a rotational device with permanent magnets is constructed such that the pulse and alternating fields are able to be applied to the sample in a stationary cell.
The contribution of the pulse and alternating magnetic fields on the magnetic effects is examined and compared with that of the static field, using a rotational device by which the pulse and alternating fields are able to be applied to the stationary sample. The followings are found: (i) the substantial time required to reach the maximum magnetic effect in the pulse and alternating fields is much smaller than the time in the static field, (ii) the magnetic effect does depend on the frequency of magnetic field, and (iii) the pulse and alternating magnetic fields make the quasi-stable structure more stable than the static field. The results are discussed and compared with the magnetic effects in flow loops reported elsewhere. © 1999 Academic Press Key Words: magnetic effect; atomic force microscope; adsorbed layer; alternating magnetic field; pulse magnetic field; memory effect.
INTRODUCTION
A large number of investigations have been carried out on the magnetic effects on aqueous systems and the existence has been confirmed by various experimental evidences (1–21). The mechanism, however, is not clarified yet, because the magnetic effects observed cannot be explained by the simple electromagnetic theory as follows: (i) the effects appear for nonmagnetic materials in the magnetic field of low flux density; (ii) the effects remain for a sufficiently long period after the magnetic exposure, which is called “memory effect” (2, 4, 8, 14 –21), and (iii) there are some conflicting data (22–26). Higashitani et al. have conducted a series of well-controlled experiments of magnetic effects on electrolyte solutions and clarified the conditions under which the effects appear (15–21). Recently these conditions were confirmed on the molecular level using an atomic force microscope (AFM) (19, 20). In these experiments, uniform static magnetic fields were applied to the samples and the following common feature was found: the effect reveals itself gradually with the magnetic exposure time, t e, and reaches to a plateau value at t e . 10 –30 min. Kronenberg investigated the magnetic effect using a flow 1
To whom correspondence should be addressed.
0021-9797/99 $30.00 Copyright © 1999 by Academic Press All rights of reproduction in any form reserved.
EXPERIMENTS
In this study, the thickness of the layer of water molecules and ions adsorbed on the surface and the surface potential in an electrolyte solution are measured using an AFM, and the magnetic effects are evaluated by their change before and after the magnetic exposure to the solution. The experimental conditions used here are exactly the same as those used in the previous experiment (19, 20), except for the type of magnetic field applied. Hence the details are given elsewhere (19, 20), but the outline is described below. Solution Pure water with a relative resistance of 17.3 MV-cm that is purified by both distillation and reverse osmosis is used. The aqueous solution of 1 3 1024 kmol/m3 KCl of reagent grade is employed because the magnetic effects have been constantly
374
MAGNETIC EFFECTS IN PULSE AND ALTERNATING FIELDS
375
observed in this solution (17, 19, 20). The solution is kept in a temperature-controlled bath of 25 6 0.5°C. The AFM probe coated with SiO2 is used when the magnetic effect on the thickness of the adsorbed layer is examined, while a colloidal probe with a 4.0-mm silica particle is employed when the effect on the surface potential is evaluated. The mica, which is cleaved just before the experiment to be free from contamination, is used as the plate smooth on the molecular level. Magnetic Field Three different magnetic fields are employed: the pulse, alternating and static fields. The apparatus is shown schematically in Fig. 1. The iron yoke is composed of two disks of 15 cm in diameter and 1.5 cm in thickness which are placed parallel and connected by a cylindrical shaft 2 cm in diameter. The shaft is able to be rotated at up to 5400 rpm by a DC motor. For the pulse field, two permanent magnets (2 3 3 3 6 cm3) is mounted firmly on the each disk such that north and south poles are facing each other with a 2.5 cm gap. The sample in the cell of 10 cm3 in volume is placed between the
FIG. 2. The apparent magnetic exposure time t app and the substantial magnetic exposure time t e. (a) The pulse field, (b) the alternating field.
magnets, fixing the cell firmly on the lower stationary stage. Because each magnet covers about 61 of the area of the disk surface, the pulse field given by this apparatus is expressed approximately as shown in Fig. 2a. Here the apparent exposure time t app is defined as the period during which the sample is placed between the rotating magnets, and the substantial exposure time t e is the period during which the sample is actually exposed to the magnetic field. Hence t e ' t app/6 in this case. In the case of alternating field, two pairs of magnets are mounted such that the magnetic fields are directed alternately. This alternating field is illustrated schematically as shown in Fig. 2b and t e ' t app/3. When the effect in the static field is examined, the sample is placed between the stationary magnets. The magnetic flux density between the magnets is 0.4 T, which is known to be strong enough to have the maximum magnetic effect (15–21). Measurement of Magnetic Effect The AFM used is a Nanoscope-III D (Digital Instruments). The colloidal probe is used in determining the surface potential, because the large surface amplifies the contribution to the long-range interaction between the surfaces. The force curve, the relation of the interaction force F vs the separation distance between surfaces h, is able to be drawn by measuring the long-range interaction between surfaces in a solution. The corresponding theoretical force curve between a plate and a sphere of radius R in a 1:1 electrolyte solution is given by the DLVO theory (39) as F 5 C k exp~2k h!,
[1]
where C and k are given by
FIG. 1. Schematic drawing of the apparatus to generate the pulse, alternating and static magnetic fields.
C 5 4 pe 0e R c 1c 2,
[2]
k 5 ~2n 0Z 2e 2/ e 0e kT! 1/ 2.
[3]
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OSHITANI, UEHARA, AND HIGASHITANI
Here e0 and e are the permitivity of free space and the relative permitivity of the solution respectively, c1c2 are the product of the surface potentials of the silica particle and mica plate, n 0 is the number concentration of ions, Z is the valency of ions, e is the elementary charge of electron, k is the Boltzmann constant, and T is the temperature. C and k are the parameters of the potential of the solid surfaces and the ionic concentration of the bulk, respectively, whose magnitudes are able to be determined by fitting the data with Eq. [1]. It is known that Eq. [1] is appropriate only for low surface potential. Nevertheless, Eq. [1] is employed here because of the following reasons: (i) the equation is of simple form to handle and can be fitted well with the present data and (ii) the magnetic effects are evaluated by the ratios of C and k for solutions with the magnetic exposure to those for solutions without the exposure, but not by the absolute values of C and k. When the magnetic effect on the apparent thickness of the adsorbed layer is examined, the AFM probe without the particle is used. The strong van der Waals attractive force makes the probe jump on the mica surface when the probe approaches closely to the mica. After this contact, the probe will penetrate into the adsorbed layer until the final contact with the mica surface. The distance that the probe can penetrate, d, is regarded as a measure of the total thickness of the adsorbed layers on both surfaces. Experimental Procedure The AFM liquid cell is filled with a solution immediately after the solution is exposed to the magnetic field. After the movement of the solution is settled completely, force measurements are carried out about 50 times for one experimental condition, and the values of k, C, and d are determined by averaging the measured values. The same procedure but without the magnetic exposure is repeated, and the magnetic effect is evaluated using the ratios km/k0, Cm/C0, and d m/d 0 where the subscripts m and 0 denote “with the magnetic exposure” and “without the magnetic exposure,” respectively. The deviation of these ratios from unity indicates the degree of magnetic effect. RESULTS
Effects on Bulk Solution, Surface Potential, and Thickness of Adsorbed Layer Figure 3 shows the values of km/k0, Cm/C0, and d m/d 0 , when the solutions are exposed separately to the three types of magnetic fields for t app 5 30 min. It is clear that the values of km/k0 are not affected by the magnetic exposure, independently of the type of magnetic field applied. This implies that the bulk properties are not influenced at least explicitly by the magnetic exposure. The values of Cm/C0 are smaller than unity, that is, the apparent surface potential is reduced by the magnetic exposure.
FIG. 3. Values of km/k0, Cm/C0, and d m/d 0 for the pulse, alternating, and static fields, respectively. (KCl concentration 5 1 3 1024 kmol/m3, magnetic flux density 5 0.4 T, t app 5 30 min, frequency of pulse and alternating fields 5 30 Hz.)
On the other hand, the values of d m/d 0 increase, that is, the adsorbed layer is thickened by the magnetic exposure. We consider that these data are consistent each other, because thickening the adsorbed layer will increase the potential drop within the adsorbed layer, which results in the reduction of the apparent surface potential. All these data are consistent also with the previous results in static magnetic fields (15–21). Hereafter, we evaluate the magnetic effects using only the data of d m/d 0 , because the data of Cm/C0 and d m/d 0 give us essentially the same information but d m/d 0 is a more direct measure for magnetic effects. Reliability of Data We have been accumulating a large number of experimental data on the magnetic effects in the various systems (15–21), and we found that the main features of the magnetic effects which are evaluated using the average values of measured data are consistent each other, independent of the difference in the measuring methods, time, and investigators. Hence we consider that the comparison between the averaged data with and without the magnetic exposure is satisfactory. Nevertheless, it is important to know whether the comparison using the averaged data are statistically meaningful or not. According to the Welch test (40), the difference of the average values of X, uX# m 2 X# 0 u, is significant if the following relation with the level of significance a 5 0.01 is satisfied: uX# m 2 X# 0u
YÎ
SD
s 2m s 20 a 1 .t . Nm N0 2
[4]
Here X# m and X# 0 are the average values of X, s m and s 0 are the standard deviations, N m and N 0 are the number of measurements, and t is the t-distribution. The data for the pulse field given in Fig. 3 are substituted into Eq. [4] as an example. It is clear that the data satisfy the Welch test as shown in Table 1.
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MAGNETIC EFFECTS IN PULSE AND ALTERNATING FIELDS
TABLE 1 Statistical Evaluation
X
X# m
X# 0
sm
s0
Nm
N0
C d
9.881 0.648
10.331 0.603
0.780 0.068
0.650 0.072
50 50
50 50
YÎ
uX# m 2 X# 0 u
2.906 3.214
s20 s2m 1 Nm N0
SD
t
a 2
2.687 2.687
Note. The data are for the pulse and alternating fields. Subscripts m and 0 denote with magnetic exposure and without magnetic exposure, respectively. a 5 0.01.
This result confirms that the comparison between the averaged data with and without the magnetic exposure is statistically significant and satisfactory. Effect of Type and Frequency of Magnetic Fields Figure 4a shows the dependence of the value of d m/d 0 on the apparent exposure time t app for the pulse and alternating fields of 30 Hz and for the static field. The values of d m/d 0 gradually increase with t app and become the same plateau value independently of the type of magnetic fields. However, the time re-
quired to reach the maximum effect is about 6 min in the pulse field, about 10 min in the alternating field, and about 20 min in the static field, and the time at which the magnetic effect reveals itself also follows this order. The same data are replotted against the substantial exposure time t e in Fig. 4b. It is important to note that the substantial time required to reach the maximum magnetic effect is only about 1 min in the pulse field and about 3 min in the alternating field, which are much smaller than the time in the static field, 20 min. Figure 5 shows the dependence of the relation of d m/d 0 vs t e on the frequency of the pulse field. The time at which the magnetic effect appears decreases with increasing frequency up to 90 Hz. Since the maximum frequency achieved by the present apparatus is 90 Hz, we are unable to know whether this is the maximum value or the plateau value. Nevertheless, we can say that the magnetic effect does depend on the frequency of magnetic field. Memory Effect The existence of “memory effect” has been confirmed in the series of our experiments. Here it is examined how the type of magnetic field influences the memory effect. The value of d m/d 0 is evaluated after the sample is exposed to the magnetic field for t app 5 30 min and left standing for a given period t s. Figure 6 shows the dependence of d m/d 0 on t s. It is clear that
FIG. 4. Dependence of d m/d 0 in the pulse, alternating and static fields on (a) the apparent magnetic exposure time t app and (b) the substantial magnetic exposure time t e. (KCl concentration 5 1 3 1024 kmol/m3, magnetic flux density 5 0.4 T, frequency of pulse and alternating fields 5 30 Hz.)
FIG. 5. Dependence of d m/d 0 on t e for various frequencies of pulse field. (KCl concentration 5 1 3 1024 kmol/m3, magnetic flux density 5 0.4 T.)
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OSHITANI, UEHARA, AND HIGASHITANI
FIG. 6. Dependence of d m/d 0 on the standing period t s for the pulse, alternating and static fields. (KCl concentration 5 1 3 1024 kmol/m3, magnetic flux density 5 0.4 T, t app 5 30 min, frequency of pulse and alternating fields 5 30 Hz.)
the magnetic effect remains for at least 5 days in the case of the pulse and alternating fields, while it starts to decay at t s 5 3 days and disappears at t s ' 5 days in the static field. In the preceding reports (15–21) we proposed the mechanism that some quasi-stable structure of water molecules, ions, and hydrated ions is formed on the surface and the structure remains until a strong external disturbance is given to the solution. If this is the case, the pulse and alternating magnetic fields make the quasi-stable structure more stable than the static field.
Now we consider whether there is any possible mechanism to explain why the magnetic effect depends on the gradient of magnetic flux density. In the investigations of the magnetic effects on living organisms, the eddy current induced by the change of magnetic field has been considered to play an important role (32). When the magnetic field passes by the sample cell, the sample will experience the high gradient magnetic field. Then the eddy current, that is, the ionic eddy motion, will be generated within the solution, such that the additional magnetic field will be generated within the eddy and so the high gradient magnetic field will be formed near the ionic current. It is known that an extremely strong force will act even on a paramagnetic substance in a high gradient magnetic field (32, 43). Since water molecules are diamagnetic, a strong attractive force will act between ions and water molecules. This hypothesis is not proven experimentally by any means, but this is the only mechanism we can think of at present. It has been claimed that the magnetic effect appears in the fluid flowing through the flow loop with a pair of small magnets, without explaining why such a short exposure time is effective. The present results that (i) high gradient magnetic
DISCUSSION
As shown in Fig. 4b, the substantial exposure time to have the maximum magnetic effect in the pulse and alternating fields is much shorter than in the static field. This implies that the rate of change of magnetic flux density is very important to generate the magnetic effect. Then the alternating field is expected to be more effective than the pulse field. However, the order is reversed as shown in Fig. 4b. We do not have any clear explanation for this, but we consider the data obtained to be reliable, because they are reproducible and the very similar dependence of the magnetic effect on the type of magnetic fields was observed in the formation of CaCO3 crystals (41) and in the measurement of the zeta potential of colloidal particles (42), as shown in Figs. 7a and 7b respectively, where the experiments were conducted using the same apparatus shown in Fig. 1. We emphasize that the feature is very similar among the data in Fig. 4b and Figs. 7a and 7b, although the sample solutions, the properties measured, the date of measurements, and the investigators are completely different from each other. Hence we can say at least that the rapid change of the magnetic flux density does reduce significantly the exposure time for the maximum magnetic effect, although the reason for the difference between the magnetic effects by the pulse and alternating fields remains to be unclarified.
FIG. 7. Dependence of magnetic effects on the substantial exposure time t e in the previous experiments. (a) The maximum values of the absorbance, A m, in the CaCO3 crystal formation are measured by a spectrophotometer and the ratio of A m-values in solutions with and without the magnetic exposure, m Am m/A 0 , is plotted against t e (41). (b) The zeta potentials of polystyrene latex particles, z, are measured by a microelectrophoresis and the ratio of z-values in solutions with and without the magnetic exposure, zm/z0, is plotted against t e (42). (Magnetic flux density 5 0.4 T for pulse and alternating fields and 0.45 T for static field, frequency of pulse and alternating fields 5 30 Hz.)
MAGNETIC EFFECTS IN PULSE AND ALTERNATING FIELDS
field shortens the exposure time to obtain the maximum magnetic effect considerably and (ii) the magnetic effect remains as a memory seem to support the magnetic effects observed in the flow loop. CONCLUSIONS
The contribution of the pulse and alternating magnetic fields on the magnetic effects is examined and compared with that of the static field, using a rotational device by which the pulse and alternating fields are able to be applied to the stationary sample. The following conclusions are drawn. (i) The substantial time required to reach the maximum magnetic effect in the pulse and alternating fields is much smaller than the time in the static field. This is consistent with the data of magnetic effects in the formation of CaCO3 crystals and the zeta potential of colloidal particles. (ii) The magnetic effect does depend on the frequency of magnetic field. (iii) The pulse and alternating magnetic fields make the quasi-stable structure more stable than the static field. (iv) The present results seem to support the magnetic effects observed in the flow loops, in which the fluids are exposed to the magnetic field for a short time. REFERENCES 1. Klassen, V. I., and Zinov’ev, Y. Z., Kolloidn. Zh. 29, 758 (1967). 2. Klassen, V. I., Zhilenko, G. V., Berger, G. S., Lapatukhin, I. V., Erygin, G. D., and Klyuchnikov, N. G., Dokl. Akad. Nauk. SSSR 183, 1123 (1968). 3. Viswat, E., Hermans, L .J. F., and Beenakker, J. J. M., Phys. Fluids 25, 1794 (1982). 4. Ayrapetyan, S. N., Grigorian, K. V., Avanesian, A. S., and Stamboltsian, K. V., Bioelectromagnetics 15, 133 (1994). 5. Rai, S., Singh, U. P., and Singh, A. K., Electro-Magnetobiol. 14, 23 (1995). 6. Dushkin, S. S., and Ievstratov, V. N., “Magnetic Water Treatment in Chemical Undertaking.” Khmiya, Moscow, 1986. 7. Yamaoka, K., Sugimoto, S., Kimura, T., Akiyama, R., and Kobayashi, R., J. Jpn. Goetherm. Energy Assoc. 25, 31 (1988). 8. Ellingsen, F. T., and Kristiansen, H., Vatten 35, 309 (1979). 9. Pandolof, L., Colale, R., and Paiaro, G., Chim. Ind. 69, 88 (1987). 10. Martynova, O. I., Tebenekhin, E. F., and Gusev, B. T., Kolloidn. Zh. 29, 692 (1967). 11. Chiba, A., Kawazu, K., Nakano, O., Tamura, T., Yoshihara, S., and Sato, E., Corros. Sci. 36, 539 (1994). 12. Ghabashy, M. E., Sedahmed, G. H., and Mansour, I. A. S., Br. Corros. J. 17, 36 (1982).
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