- Email: [email protected]
Preparation and characterization of magnetic PVC nanocomposites
Journal of Non-Crystalline Solids 353 (2007) 799–801 www.elsevier.com/locate/jnoncrysol
Preparation and characterization of magnetic PVC nanocomposites I.G. Ya´n˜ez-Flores
b
a,*
, R. Betancourt-Galindo a, J.A. Matutes Aquino b, O. Rodrı´guez-Ferna´ndez a
a Centro de Investigacio´n en Quı´mica Aplicada, Blvd. Enrique Reyna Hermosillo, No. 140 CP 25000 Saltillo, Coahuila, Mexico Centro de Investigacio´n en Materiales Avanzados, Miguel de Cervantes, No. 120, Complejo Industrial Chihuahua, Chihuahua, Mexico
Available online 23 February 2007
Abstract A new method was developed in order to achieve an excellent dispersion of magnetite onto a polymer matrix. For that a ferrofluid was prepared containing nanometric size (15 nm) magnetite and di-octyl phthalate (PVC plasticizer), this ferrofluid was dispersed in a polyvinyl chloride (PVC) plastisol and magnetic PVC films were made by static casting from plastisols and ferrofluids based on magnetite. Flexible films were characterized by vibration sample magnetometry, and stress-strain testing; rheometry was used to characterize the ferrofluid and the (PVC) plastisols containing ferrofluid (inverse ferrofluid). The effect of magnetite content on the magnetic and mechanical properties of the films was studied and showed an increase on magnetization values with magnetic loading and a variation in the stress-strain with magnetic loading as function of magnetic load content. It was found that the inverse ferrofluid showed a Bingham fluid behavior. Ó 2007 Elsevier B.V. All rights reserved. PACS: 47.65.cb; 62.20. X; 51.60.+a Keywords: Magnetic properties; Nanocomposites; Nanoparticles; Polymers and organics; Rheology
1. Introduction Ferrofluids (FF) consist of colloidal ferro or ferrimagnetic, single-domain nanoparticles dispersed in either polar or non-polar liquid carriers. Although they can respond to the action of external magnetic fields, stable FF manifests only a relatively modest magnetorheological effect [1–4], mainly when compared to magnetorheological fluids (MRF), containing micrometer-sized particles [5–7]. When the FF are prepared in non-polar carriers, particle aggregation due to van der Waals attraction leads to low colloidal stability and a large rate of sedimentation of the aggregates formed in the suspensions. One procedure that has been envisaged to reduce this unwanted behavior is to coat the particles with certain long-chain molecules, particularly
*
Corresponding author. Tel.: +52 844 4389462; fax: +52 844 4389463. E-mail address: [email protected] (I.G. Ya´n˜ez-Flores).
0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.12.109
those containing a polar group and a tail with dielectric properties matching those of the carrier liquid [4]. In this work, we report on the synthesis of oleate-coated magnetite nanoparticles and its use to prepare ferrofluid based on plasticizer as carrier liquid and also the use of this ferrofluid to prepare polyvinyl chloride (PVC) plastisols. Finally, the magnetic properties of ferrofluid and ferrofluids containing PVC were determined. The PVC plastisols were cured in order to obtain the films. It is known that plain ferrofluids can also be transformed in MRF’s by the suspension of non-magnetic particles, like micron-size polystyrene or silica spheres. These non-magnetic particles create a hole which appears to possess a magnetic moment, corresponding to the displaced fluid [8]. A collection of identical holes will thus behave as a many-body system with dipolar interactions which may be controlled by an external field. However, in the absence of the field there are no apparent magnetic interactions between the particles due to the ideal paramagnetic behavior of the ferrofluid.
800
I.G. Ya´n˜ez-Flores et al. / Journal of Non-Crystalline Solids 353 (2007) 799–801
This kind of fluids is known in the literature as inverse ferrofluids [9,10].
3.0 2.5 2.0
2. Experimental 2.1. Materials The chemicals used in the synthesis of magnetite particles, the carrier liquids and the oleic acid employed to prepare the ferrofluids were purchased from Aldrich with analytical quality, and used as received.
Magnetization (emu/g)
1.5 1.0 0.5 0.0 -0.5
5 phr FF DOP 25 phr FF DOP 35 phr FF DOP 50 phr FF DOP
-1.0 -1.5
2.2. Ferrofluid preparation In a recent paper [11], we described the basic scheme for preparing magnetite particles and surfactant-stabilized ferrofluids. The ferrofluid used was prepared with di-octyl phthalate, DOP, as carrier liquid. 2.3. Plastisol preparation Plastisols were prepared using an emulsion PVC (K = 69), 100 phr, parts per hundred of resin, Ba/Cd thermal stabilizer (2 phr) and di-octyl phtlalate, DOP (140 phr) as plasticizer. 2.4. Films preparation The films were prepared using the plastisol and the ferrofluid based on plasticizer. In the case of films containing magnetite the plasticizer was substituted with the ferrofluid containing magnetite, always keeping the same plasticizer concentration. 2.5. Magnetic properties of the films The magnetization curves of the films were obtained in a Lakeshore 7300 magnetometer at room temperature.
-2.0 -2.5 -15000
-10000
-5000
0
5000
10000
15000
Magnetic field (Oe)
Fig. 1. Magnetization curves of films containing different concentrations of ferrofluid.
ferrofluid. The magnetization curves suggest superparamagnetic behavior for the films with no observed hysteresis. Flow curves were obtained for ferrofluid and PVC plastisols containing ferrofluid (inverse fluids) at different values of an applied magnetic field. Fig. 2 shows a comparison of the shear rate for a conventional ferrofluid versus of an inverse ferrofluid with PVC. The ferrofluid without PVC shows a Newtonian behavior in the full range of the studied shear rates. The PVC plastisol, however, shows a remarkable change in viscosity at low shear rates. The possible explanation of this behavior is that the big magnetic particles, in the ferrofluid, form chains that contribute to an increase in the viscosity. This magnetoviscous effect has already been studied by Odenbach in different ferrofluids, [4]. On the other hand, in Fig. 3 the inverse ferrofluids containing PVC particles show a non-linear flow behavior. First, the inverse ferrofluids behave like a solid
2.6. Rheological measurements 40
A Physica MCR300 rheometer was used to measure the magnetorheological properties of the inverse fluids at different values of the applied magnetic field.
Tensile properties Dumbbell shaped film specimens were measured at room temperature using an Instron tensometer, with a crosshead speed of 50 mm/min. Ultimate Tensile strength and elongation were determined. 3. Results and discussion
Shear stress, Pa
2.7. Mechanical measurements
Ferrofluid PVC Plastisol
30
20
10
0 0
Fig. 1 shows the magnetization results for four films containing different concentration of ferrofluid. As expected, the magnetization increase with the loading of
50
100
150
200
250
Shear rate, 1/s
Fig. 2. Comparison of shear stress versus shear rate of a ferrofluid and PVC plastisol containing ferrofluid.
I.G. Ya´n˜ez-Flores et al. / Journal of Non-Crystalline Solids 353 (2007) 799–801
Table 1 shows the results of the mechanical measurements on the films. As the ferrofluid concentration increased, and consequently the magnetite content, the tensile strength reaches a maximum at 25 phr suggesting an optimal loading of magnetite in maximizing the tensile strength of the PVC film, the polymer matrix is not able to accept more magnetite without loosing tensile strength; on the other hand, elongation at break decreased as the magnetite loading increased as expected.
50
Shear stress, Pa
40
30
H 282.10 kA/m H 229.10 kA/m H 155.97 kA/m H 73.45 kA/m H 0.159 kA/m
20
801
10
4. Conclusions 0
0
50
100
150
200
250
300
Shear rate, 1/s
Fig. 3. Shear stress versus shear rate as a function of the magnetic field.
Table 1 Mechanical properties concentrations
of
films
containing
different
ferrofluid
Ferrofluid concentration (phr)
Tensile strength (MPa)
Elongation at break (%)
0 5 15 25 35 50
2.74 2.75 2.88 2.96 2.74 0.62
370 290 220 210 190 110
We have developed a new method to prepare magnetic nanocomposites based on PVC plastisols containing ferrofluid. The PVC plastisol behaves like an inverse ferrofluid. PVC films obtained by static casting showed an increase in magnetization with increased loading of magnetite. Tensile strength showed a maximum when 25 phr of ferrofluid were used. It is important to mention that it was possible to increase the magnetic properties but tensile strength was negatively affected when more than 25 phr of ferrofluid was used. Acknowledgement The authors acknowledge CONACyT for the economical support throughout the project SEP 2004-C01-46044. References
material, increasing the shear stress while the shear rate is not changing. This behavior is typical for a Bingham fluid. Also it can be noticed that as the magnetic field is increased, a higher stress is needed to induce flow. This effect is understandable since the chains of non-magnetic particles (PVC) formed in the fluids have the ability to sustain a stress with no continuous deformation due to the induced magnetic moment of the PVC particles. Second, when the chains are broken, the inverse ferrofluid flows and shows a liquid behavior with a shear thinning, presumably due to the breaking of agglomerates formed from the broken chains. The transition from the solid to liquid behavior is characterized by the apparent yield stress, which can be obtained by the extrapolation of the flow curve to zero shear rate.
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
R.E. Rosensweig, Sci. Am. 247 (1982) 136. R.E. Rosensweig, Ann. Rev. Fluid Mech. 19 (1987) 437. R.E. Rosensweig, Chem. Eng. Commun. 67 (1988) 1. S. Odenbach, Colloids Surface A – Physicochem. Eng. Aspects 217 (2003) 171. P.P. Phule´, J.M. Ginder, MRS Bull. 23 (1998) 19. J.M. Ginder, MRS Bull. 23 (1998) 26. G. Bossis, O. Volkova, S. Lacis, A. Meunier, in: S. Odenbach (Ed.), Ferrofluids, Springer-Verlag, Berlin, 2002, p. 202. A.T. Skjeltorp, Phys. Rev. Lett. 51 (1983) 2306. B.J. de Gans, N.J. Duin, D. van den Ende, J. Mellema, J. Chem. Phys. 113 (2000) 2032. B.J. de Gans, C. Blom, A.P. Philipse, J. Mellena, Phys. Rev. E 60 (1999) 4518. O. Ayala-Valenzuela, J. Matutes-Aquino, R. Betancourt-Galindo, L.A. Garcı´a-Cerda, O. Rodrı´guez Ferna´ndez, A.T. Giannitsis, P.C. Fannin, J. Magn. Magn. Mater. 294 (2005) 37.
Preparation and characterization of magnetic PVC nanocomposites I.G. Ya´n˜ez-Flores
b
a,*
, R. Betancourt-Galindo a, J.A. Matutes Aquino b, O. Rodrı´guez-Ferna´ndez a
a Centro de Investigacio´n en Quı´mica Aplicada, Blvd. Enrique Reyna Hermosillo, No. 140 CP 25000 Saltillo, Coahuila, Mexico Centro de Investigacio´n en Materiales Avanzados, Miguel de Cervantes, No. 120, Complejo Industrial Chihuahua, Chihuahua, Mexico
Available online 23 February 2007
Abstract A new method was developed in order to achieve an excellent dispersion of magnetite onto a polymer matrix. For that a ferrofluid was prepared containing nanometric size (15 nm) magnetite and di-octyl phthalate (PVC plasticizer), this ferrofluid was dispersed in a polyvinyl chloride (PVC) plastisol and magnetic PVC films were made by static casting from plastisols and ferrofluids based on magnetite. Flexible films were characterized by vibration sample magnetometry, and stress-strain testing; rheometry was used to characterize the ferrofluid and the (PVC) plastisols containing ferrofluid (inverse ferrofluid). The effect of magnetite content on the magnetic and mechanical properties of the films was studied and showed an increase on magnetization values with magnetic loading and a variation in the stress-strain with magnetic loading as function of magnetic load content. It was found that the inverse ferrofluid showed a Bingham fluid behavior. Ó 2007 Elsevier B.V. All rights reserved. PACS: 47.65.cb; 62.20. X; 51.60.+a Keywords: Magnetic properties; Nanocomposites; Nanoparticles; Polymers and organics; Rheology
1. Introduction Ferrofluids (FF) consist of colloidal ferro or ferrimagnetic, single-domain nanoparticles dispersed in either polar or non-polar liquid carriers. Although they can respond to the action of external magnetic fields, stable FF manifests only a relatively modest magnetorheological effect [1–4], mainly when compared to magnetorheological fluids (MRF), containing micrometer-sized particles [5–7]. When the FF are prepared in non-polar carriers, particle aggregation due to van der Waals attraction leads to low colloidal stability and a large rate of sedimentation of the aggregates formed in the suspensions. One procedure that has been envisaged to reduce this unwanted behavior is to coat the particles with certain long-chain molecules, particularly
*
Corresponding author. Tel.: +52 844 4389462; fax: +52 844 4389463. E-mail address: [email protected] (I.G. Ya´n˜ez-Flores).
0022-3093/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2006.12.109
those containing a polar group and a tail with dielectric properties matching those of the carrier liquid [4]. In this work, we report on the synthesis of oleate-coated magnetite nanoparticles and its use to prepare ferrofluid based on plasticizer as carrier liquid and also the use of this ferrofluid to prepare polyvinyl chloride (PVC) plastisols. Finally, the magnetic properties of ferrofluid and ferrofluids containing PVC were determined. The PVC plastisols were cured in order to obtain the films. It is known that plain ferrofluids can also be transformed in MRF’s by the suspension of non-magnetic particles, like micron-size polystyrene or silica spheres. These non-magnetic particles create a hole which appears to possess a magnetic moment, corresponding to the displaced fluid [8]. A collection of identical holes will thus behave as a many-body system with dipolar interactions which may be controlled by an external field. However, in the absence of the field there are no apparent magnetic interactions between the particles due to the ideal paramagnetic behavior of the ferrofluid.
800
I.G. Ya´n˜ez-Flores et al. / Journal of Non-Crystalline Solids 353 (2007) 799–801
This kind of fluids is known in the literature as inverse ferrofluids [9,10].
3.0 2.5 2.0
2. Experimental 2.1. Materials The chemicals used in the synthesis of magnetite particles, the carrier liquids and the oleic acid employed to prepare the ferrofluids were purchased from Aldrich with analytical quality, and used as received.
Magnetization (emu/g)
1.5 1.0 0.5 0.0 -0.5
5 phr FF DOP 25 phr FF DOP 35 phr FF DOP 50 phr FF DOP
-1.0 -1.5
2.2. Ferrofluid preparation In a recent paper [11], we described the basic scheme for preparing magnetite particles and surfactant-stabilized ferrofluids. The ferrofluid used was prepared with di-octyl phthalate, DOP, as carrier liquid. 2.3. Plastisol preparation Plastisols were prepared using an emulsion PVC (K = 69), 100 phr, parts per hundred of resin, Ba/Cd thermal stabilizer (2 phr) and di-octyl phtlalate, DOP (140 phr) as plasticizer. 2.4. Films preparation The films were prepared using the plastisol and the ferrofluid based on plasticizer. In the case of films containing magnetite the plasticizer was substituted with the ferrofluid containing magnetite, always keeping the same plasticizer concentration. 2.5. Magnetic properties of the films The magnetization curves of the films were obtained in a Lakeshore 7300 magnetometer at room temperature.
-2.0 -2.5 -15000
-10000
-5000
0
5000
10000
15000
Magnetic field (Oe)
Fig. 1. Magnetization curves of films containing different concentrations of ferrofluid.
ferrofluid. The magnetization curves suggest superparamagnetic behavior for the films with no observed hysteresis. Flow curves were obtained for ferrofluid and PVC plastisols containing ferrofluid (inverse fluids) at different values of an applied magnetic field. Fig. 2 shows a comparison of the shear rate for a conventional ferrofluid versus of an inverse ferrofluid with PVC. The ferrofluid without PVC shows a Newtonian behavior in the full range of the studied shear rates. The PVC plastisol, however, shows a remarkable change in viscosity at low shear rates. The possible explanation of this behavior is that the big magnetic particles, in the ferrofluid, form chains that contribute to an increase in the viscosity. This magnetoviscous effect has already been studied by Odenbach in different ferrofluids, [4]. On the other hand, in Fig. 3 the inverse ferrofluids containing PVC particles show a non-linear flow behavior. First, the inverse ferrofluids behave like a solid
2.6. Rheological measurements 40
A Physica MCR300 rheometer was used to measure the magnetorheological properties of the inverse fluids at different values of the applied magnetic field.
Tensile properties Dumbbell shaped film specimens were measured at room temperature using an Instron tensometer, with a crosshead speed of 50 mm/min. Ultimate Tensile strength and elongation were determined. 3. Results and discussion
Shear stress, Pa
2.7. Mechanical measurements
Ferrofluid PVC Plastisol
30
20
10
0 0
Fig. 1 shows the magnetization results for four films containing different concentration of ferrofluid. As expected, the magnetization increase with the loading of
50
100
150
200
250
Shear rate, 1/s
Fig. 2. Comparison of shear stress versus shear rate of a ferrofluid and PVC plastisol containing ferrofluid.
I.G. Ya´n˜ez-Flores et al. / Journal of Non-Crystalline Solids 353 (2007) 799–801
Table 1 shows the results of the mechanical measurements on the films. As the ferrofluid concentration increased, and consequently the magnetite content, the tensile strength reaches a maximum at 25 phr suggesting an optimal loading of magnetite in maximizing the tensile strength of the PVC film, the polymer matrix is not able to accept more magnetite without loosing tensile strength; on the other hand, elongation at break decreased as the magnetite loading increased as expected.
50
Shear stress, Pa
40
30
H 282.10 kA/m H 229.10 kA/m H 155.97 kA/m H 73.45 kA/m H 0.159 kA/m
20
801
10
4. Conclusions 0
0
50
100
150
200
250
300
Shear rate, 1/s
Fig. 3. Shear stress versus shear rate as a function of the magnetic field.
Table 1 Mechanical properties concentrations
of
films
containing
different
ferrofluid
Ferrofluid concentration (phr)
Tensile strength (MPa)
Elongation at break (%)
0 5 15 25 35 50
2.74 2.75 2.88 2.96 2.74 0.62
370 290 220 210 190 110
We have developed a new method to prepare magnetic nanocomposites based on PVC plastisols containing ferrofluid. The PVC plastisol behaves like an inverse ferrofluid. PVC films obtained by static casting showed an increase in magnetization with increased loading of magnetite. Tensile strength showed a maximum when 25 phr of ferrofluid were used. It is important to mention that it was possible to increase the magnetic properties but tensile strength was negatively affected when more than 25 phr of ferrofluid was used. Acknowledgement The authors acknowledge CONACyT for the economical support throughout the project SEP 2004-C01-46044. References
material, increasing the shear stress while the shear rate is not changing. This behavior is typical for a Bingham fluid. Also it can be noticed that as the magnetic field is increased, a higher stress is needed to induce flow. This effect is understandable since the chains of non-magnetic particles (PVC) formed in the fluids have the ability to sustain a stress with no continuous deformation due to the induced magnetic moment of the PVC particles. Second, when the chains are broken, the inverse ferrofluid flows and shows a liquid behavior with a shear thinning, presumably due to the breaking of agglomerates formed from the broken chains. The transition from the solid to liquid behavior is characterized by the apparent yield stress, which can be obtained by the extrapolation of the flow curve to zero shear rate.
[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
R.E. Rosensweig, Sci. Am. 247 (1982) 136. R.E. Rosensweig, Ann. Rev. Fluid Mech. 19 (1987) 437. R.E. Rosensweig, Chem. Eng. Commun. 67 (1988) 1. S. Odenbach, Colloids Surface A – Physicochem. Eng. Aspects 217 (2003) 171. P.P. Phule´, J.M. Ginder, MRS Bull. 23 (1998) 19. J.M. Ginder, MRS Bull. 23 (1998) 26. G. Bossis, O. Volkova, S. Lacis, A. Meunier, in: S. Odenbach (Ed.), Ferrofluids, Springer-Verlag, Berlin, 2002, p. 202. A.T. Skjeltorp, Phys. Rev. Lett. 51 (1983) 2306. B.J. de Gans, N.J. Duin, D. van den Ende, J. Mellema, J. Chem. Phys. 113 (2000) 2032. B.J. de Gans, C. Blom, A.P. Philipse, J. Mellena, Phys. Rev. E 60 (1999) 4518. O. Ayala-Valenzuela, J. Matutes-Aquino, R. Betancourt-Galindo, L.A. Garcı´a-Cerda, O. Rodrı´guez Ferna´ndez, A.T. Giannitsis, P.C. Fannin, J. Magn. Magn. Mater. 294 (2005) 37.