Difference between revisions of "Ferrofluids"

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__NOTOC__
 
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[[Image:Pferro1.gif|300px|right|thumb|Ferrofluid monolayer at low area fraction.]]
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[[Image:Pferro1.gif|300px|right|thumb|Fig1. Ferrofluid monolayer at low area fraction.]]
[[Image:Pferro2.gif|300px|right|thumb|Ferrofluid monolayer at high area fraction.]]
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[[Image:Pferro2.gif|300px|right|thumb|Fig2. Ferrofluid monolayer at high area fraction.]]
  
'''Ferrofluids'''  under construction
 
 
== What are Ferrofluids? ==
 
== What are Ferrofluids? ==
  
Dipolar magnetic fluids (also known as ferrofluids or ferrocolloids), are colloidal suspensions of ferromagnetic nanoparticles  (typical sizes 10-20nm),  usually stabilised by steric coatings (in non electrolyte carrier liquids) or by electrical double layers (in aqueous solutions). Sterical coatings are usualy made of a stabilizing dispersing agent (surfactant) which prevents particle agglomeration even when a strong magnetic field gradient is applied to the ferrofluid.  
+
<onlyinclude>Dipolar magnetic fluids (also known as ferrofluids or ferrocolloids), are colloidal suspensions of ferromagnetic nanoparticles  (typical sizes 10-20nm),  usually stabilised by steric coatings (in non electrolyte carrier liquids) or by electrical double layers (in aqueous solutions). Sterical coatings are usualy made of a stabilizing dispersing agent (surfactant) which prevents particle agglomeration even when a strong magnetic field gradient is applied to the ferrofluid. </onlyinclude>
 
The surfactant must be matched to the carrier type and must overcome the attractive van der Waals and magnetic forces between the particles.  A typical ferrofluid may contain by volume 5% magnetic solid, 10% surfactant and 85% carrier.
 
The surfactant must be matched to the carrier type and must overcome the attractive van der Waals and magnetic forces between the particles.  A typical ferrofluid may contain by volume 5% magnetic solid, 10% surfactant and 85% carrier.
  
Due to their size, ferrofluid particles can be considered as magnetic single-domains with a permanent magnetic moment $|\mathbf{m}|=m$ proportional to their volume  $\pi \sigma_m^3/6$, where $\sigma_m$ is the diameter of the magnetic core of the particle.  
+
Due to their size, ferrofluid particles can be considered as magnetic single-domains with a permanent magnetic moment <math>  |\mathbf{m}|=m </math> proportional to their volume  <math>\pi \sigma_m^3/6</math>, where <math> \sigma_m </math> is the diameter of the magnetic core of the particle.  
  
To know more about the basics of ferrofluids, see for instance[http://en.wikipedia.org/wiki/Ferrofluid link Ferrofluids in the Wikipedia.]
+
To know more about the basics of ferrofluids, see for instance [http://en.wikipedia.org/wiki/Ferrofluid the ferrofluids in the Wikipedia.]
  
 
== Synthesis of ferrofluids ==
 
== Synthesis of ferrofluids ==
  
The idea of making a liquid with magnetic properties seems to date back to the 40´s. Nonetheless, it seems that was
+
The idea of making a liquid with magnetic properties seems to date back to the 1779 when Gowan Knight tried to make a magnetic fluid by introducing iron filings into water. Unfortunately, the iron filings sedimented very quickly. In the XX century the issue was retaken by F. Bitter (1932), and W.C.Elmore (1938), but the particles they obtained were quite large and  not fully stable.  It seems that  
Stephen Papell Solomon ([http://www.freepatentsonline.com/3215572.html US Patent 3215572 ]) working for NASA in the 60´s the first to develop an easy and effective way of preparing such colloidal systems. You can also prepare your
+
Stephen Papell Solomon ([http://www.freepatentsonline.com/3215572.html US Patent 3215572 ]) working for NASA in the 60´s was the first to develop  
[http://chemistry.about.com/od/demonstrationsexperiments/ss/liquidmagnet.htm own ferrofluids at home]
+
an easy and effective way of preparing such colloidal systems. The idea was to be able to use these particles to control the flux of fuel in a zero gravity  environment. Since then, many synthesis have been developed to produce ferrofluid particles  in both non-polar and polar solvents, increase their stability, improve the control over their size and degree of polidispersity,  and produce particles with different materials and shapes.
 +
For recent reviews about the subject see (Lu2007) and (Tourinho1998).  
  
 
== Why are people Ferrofluids interesting? ==
 
  
Ferrofluids are interesting for two fold reason:
+
You can also prepare your own ferrofluids and have fun at home!  See for instance the educational article of Berger et al.  (Berger1999), as well as 
* Ferrofluids are systems exhibing anisotropic interactions leading to a very reach phase behaviour, rheological and magnetic properties. Thus ferrofluids are a paradigma of physical systems with anisotropic interactions.
+
[http://www.eng.yale.edu/koserlab/Synthesis.html (1)],
* The singular properties of ferrofluids in external magnetic fields  have found application in many areas, ranging from engineering,  to biomedical applications in cancer treatment (Rosensweig1985, Odenbach2002, Alexiou2003,Hilger2004, Scherer2005).
+
[http://mrsec.wisc.edu/Edetc/nanolab/ffexp/index.html (2)],
 +
[http://www.purposeproject.com/papers/Ferrofluids/Synthesis%20of%20Custom%20Ferrofluid_Compressed.pdf (3)],
 +
[http://www.sci-spot.com/Chemistry/liqimag.htm (4)],
 +
[http://chemistry.about.com/od/demonstrationsexperiments/ss/liquidmagnet.htm (5)],
 +
[http://chemeducator.org/sbibs/s0010003/spapers/1030204tm.htm (6)].
  
Applications of ferrofluids:
+
== Why are Ferrofluids interesting? ==
  
- Seals: vaccum pumps
+
Ferrofluids are interesting for a two fold reason:
- Enginering:  dampers, nanoactuators, mirrors
+
* Ferrofluids are systems exhibing anisotropic interactions leading to a very reach phase behaviour, as well as very interesting rheological and magnetic properties. Thus ferrofluids are a paradigma of physical systems with anisotropic interactions.
- Medicine:  cancer treatment, cell purification, …
 
-  Art
 
  
Put links to the best pages and best books or articles about the topic….
+
* The singular properties of ferrofluids in external magnetic fields  have found application in many areas, ranging from engineering,  to biomedical applications (Popplewell1984,Rosensweig1985, Odenbach2002, Alexiou2003,Hilger2004, Scherer2005). Just to mention a few examples:
 +
** [http://machinedesign.com/ContentItem/60952/Magneticfluidstackletoughsealingjobs.aspx Magnetic Seals] for instance in  [http://www.lesker.com/newweb/Sample_Manipulation/samplemanip_technicalnotes_1.cfm vaccum pumps] and [http://machinedesign.com/ContentItem/59476/TheattractionofFerrofluidBearings.aspx ferrofluid bearings].
 +
** [http://www.carbibles.com/images/magneride.jpg Car dampers], [http://www.iwf.tu-berlin.de/fachgebiete/wzm/forschung/forschung3/Magnetofluidisches%20Positioniersystem/view?searchterm=Hipper  nanoactuators], [http://www.ferrotec.com/products/ferrofluid/audio/audioBenefits.php loudspeakers], [http://wood.phy.ulaval.ca/ferrofluids/homemade.php adaptive optics (liquid mirrors)], [http://wcms1.rz.tu-ilmenau.de/fakmb/fileadmin/template/fgtm/video/lysenko_kurz.avi  biologically inspired robots].
 +
** [http://www.jaist.ac.jp/~shinya/english/image/theme2_fig.png Cancer treatment, cell separation, ultrasensitive analysis, MRI].
 +
** [http://www.kodama.hc.uec.ac.jp/protrudeflow/index.html Art].
  
Even in the absence of such external fields, ferrofluids have a
+
See also as an example the links
very complex microstructure, which is caused by the combination of
+
[http://www.ferrotec.com/company/about/history.php (1)], [http://www.magneticmicrosphere.com/resources/ferrofluid_app.php  (2)]  ...
interparticle interactions specific to magnetic fluids.  
 
  
 +
== Aggregating structures formed by Ferrofluids ==
  
=== Aggregating structures formed by Ferrofluids ===
+
Even in the absence of external fields, ferrofluids have a very complex microstructure, which is caused by the combination of
 +
interparticle interactions specific to magnetic fluids (see for instance figures 1 and 2).  Ferrofluid particles are known to self-assemble into a variety of magnetic equilibrium structures which depend on  several factors such as: system geometry, magnetic interactions, particle polydispersity, presence or absence of external fields, etc.
  
      Ferrofluid particles are known to self-assemble into a variety of magnetic equilibrium structures which depend on  
+
The number of probable cluster topologies in magnetic fluids is high: drops with high magnetic phase concentration (micron size), branched and fractal clusters (hundreds of nanometers in size), or chain- and ring-like structures (tens of nanometers).  Signs of clustering process in ferrofluids at zero field are known for more than 40 years (Hess1966). Nonetheless, despite the large amount of clues obtained in subsequent studies (Shen2001, Donselaar1999, Cebula1983, Gazeau2002), a direct experimental proof of the existence of clusters like chains, rings, etc.  has been elusive for many years, specially for those cases were dipole-dipole interactions were relatively week, like in magnetite nanoparticles (<math> Fe_3O_4 </math>). Thus, due to the lack of conclusive experiments, the understanding of how dipole-dipole interactions influence the clustering process and determine the subsequent microstructure and phase behaviour of ferrofluids has become a challenge. In bulk ferrofluids, those aspects have been studied in detail through theoretical (Gennes1970, Jordan1973, Osipov1996, Zubarev1995, Tavares1997, Tavares1999, Roij1996, Tlusty2000, Morozov2002, Mendelev2004, Ivanov2004) and simulation (Weis1993, Levesque1994, Jund1995, Camp2000, Pshenichnikov2000, Wang2002, Wang2003, Holm2006) works. Comprehensive reviews on these subject for bulk systems are also available, see (Teixeira2000, Cabuil2000, Huke2004, Holm2005).
several factors such as: system geometry, magnetic interactions, particle polydispersity, presence or absence of external
 
fields, etc.  
 
  
The number of probable cluster topologies in magnetic fluids
+
== Ferrofluid Monolayers ==
is high: drops with high magnetic phase concentration (micron size),
 
branched and fractal clusters (hundreds of nanometers in size), or
 
chain- and ring-like structures (tens of nanometers).  Signs of
 
clustering process in ferrofluids at zero field are known for more
 
than 40 years \cite{Hess1966}. Nonetheless, despite the large amount
 
of clues obtained in subsequent studies
 
\cite{Shen2001,Donselaar1999,Cebula1983,Gazeau2002}, a direct
 
experimental proof of the existence of clusters like chains, rings,
 
etc.  has been elusive for many years, specially for those cases were
 
dipole-dipole interactions were relatively week, like in magnetite
 
nanoparticles ($Fe_3O_4$). Thus, due to the lack of conclusive
 
experiments, the understanding of how dipole-dipole interactions
 
influence the clustering process and determine the subsequent
 
microstructure and phase behaviour of ferrofluids has become a
 
challenge. In bulk ferrofluids, those aspects have been studied in
 
detail through theoretical
 
\cite{Gennes1970,Jordan1973,Osipov1996,Zubarev1995,Tavares1997,Tavares1999,
 
  Roij1996,Tlusty2000,Morozov2002,Mendelev2004,Ivanov2004} and
 
simulation
 
\cite{Weis1993,Levesque1994,Jund1995,Camp2000,Pshenichnikov2000,Wang2002,Wang2003,Holm2006}
 
works. Comprehensive reviews on these subject for bulk systems are
 
also available, see
 
\cite{Teixeira2000,Cabuil2000,Huke2004,Holm2005}.
 
  
 +
The phase behaviour and microstructure of ferrofluid systems in reduced dimensions is not necessarily equivalent to that of 3D systems. In addition, thin-films and monolayers, have become recently a more successful experimental scenario to assert the existence of the clustering process (Klokkenburg2006, Butter2003, Puntes2001, Wen1999). In the experiments of Philipse and co-workers(Butter2003, Klokkenburg2006), images obtained by cryogenic transmission electron microscopy (cyro-TEM) give ample evidence of the existence of chain- and ring-like structures in ferrofluid monolayers, where all particles are trapped in one plane, but their magnetic moments are free to fluctuate in 3D (q2D monolayers).
  
=== Ferrofluid Monolayers ===
+
In recent years, several theoretical and computational works have been devoted to the study of ferrofluids in monolayers and
 +
thin-films. The thermodynamics, and magnetisation properties of quasi-two-dimensional (q2D) systems have been studied by Lomba et al. (Lomba2000), and Gao et al. (Gao1997).  Weis and co-workers (see (Weis2002b, Weis2003), and references therein), have performed Monte Carlo simulations of monolayers and systems of finite thickness involving dipolar interactions. They have shown that q2D dipolar systems, alone or in combination with other interactions, present a rich variety of structures, phases and phase transitions. In a recent q2D Monte Carlo study on dipolar hard spheres (DHS), Tavares et al. (Tavares2006) have reported  the structure of the fluid to be well described by an ideal mixture of self-assembling clusters at low and intermediate densities. Very recently,  Duncan-Camp (Duncan2006) have studied the kinetics of aggregation in monolayers using stochastic dynamics simulations. The results obtained in that work suggest that the conditions for defect-driven condensation (Tlusty2000) could be met by kinetic trapping, giving rise to a metastable phase transition between isotropic fluid phases. The structure formation and magnetic properties  of polydisperse ferrofluids in monolayers have been also recently addressed by theory and Monte Carlo simulations (Morimoto2003, Aoshima2004, Kristof2005).
  
The phase behaviour and microstructure of ferrofluid systems in reduced dimensions is not necessarily
+
== Current Research ==
equivalent to that of 3D systems.
 
  
Despite the progress obtained in previous studies
+
Despite the progress obtained in previous studies, the understanding of the phase behaviour and microstructure formation of ferrofluids in constrained geometries is only partial. The understanding of such features is of paramount importance in order to know better those systems and reduce the large amount of times devoted to trial-error in order to improve or design new applications based on ferrofluids.
\cite{Lomba2000,Weis2002b-2003,Duncan2004-2006,Tavares2006}, the understanding of the phase behaviour and microstructure
 
formation of ferrofluids in constrained geometries is only partial.
 
  
Thin-films and
+
Our current interest focuses on the peculiarities of the aggregation processes in both quasi-two dimensional  (monolayers) and bulk ferrofluid systems. We make use of  a combination of density functional theory, and molecular dynamics (MD) simulations. The microstructure formation and phase behaviour are studied thoroughly through a comparison of the theoretical, and computational results. The active areas of research about ferrofluids in our group at this moment are:
monolayers, have become recently a more successful experimental
 
scenario to assert the existence of the clustering process
 
\cite{Klokkenburg2006,Butter2003,Puntes2001,Wen1999}. In the
 
experiments of Philipse and co-workers
 
\cite{Butter2003,Klokkenburg2006}, images obtained by cryogenic
 
transmission electron microscopy (cyro-TEM) give ample evidence of
 
the existence of chain- and ring-like structures in ferrofluid
 
monolayers, where all particles are trapped in one plane, but
 
their magnetic moments are free to fluctuate in 3D (q2D
 
monolayers).
 
  
 +
* [[Ferrofluid monolayers: monodisperse particles]].
 +
* [[Ferrofluid monolayers: bidisperse particles]].
 +
* [[Structure factors of ferrofluids in the low-density low-aggregating limit]].
  
In recent years, several theoretical and computational works have
+
== Scientists ==
been devoted to the study of ferrofluids in monolayers and
+
* [[Joan Josep Cerdà]]
thin-films. The thermodynamics, and magnetisation properties of
+
* [[Christian Holm]]
quasi-two-dimensional (q2D) systems have been studied by Lomba et
+
* [[Sofia Kantorovich]]
al. \cite{Lomba2000}, and Gao et al. \cite{Gao1997}. Weis and
+
 
co-workers (see \cite{Weis2002b,Weis2003}, and references
+
== Collaborators ==
therein), have performed Monte Carlo simulations of monolayers and
+
* Group of Prof. Dr. [http://kmf.math.usu.ru/indexEng.html Alexey Ivanov]. Department of Mathematical Physics, The Urals State University, Ekaterinburg, Russia.
systems of finite thickness involving dipolar interactions. They
+
 
have shown that q2D dipolar systems, alone or in combination with
+
* [http://fcc.chem.uu.nl/peopleindex/ben/ben.htm Ben Erné ] from the group of Prof. [http://www.chem.uu.nl/fcc/www/peopleindex/albert/albert.htm  A. Philipse ] at [http://fcc.chem.uu.nl/fcc.html Van 't Hoff Laboratory for Physical and Colloid Chemistry].
other interactions, present a rich variety of structures, phases
+
 
and phase transitions. In a recent q2D Monte Carlo study on
+
== Publications ==
dipolar hard spheres (DHS), Tavares et al. \cite{Tavares2006} have
+
<bibentry> wang03a, wang03b, wang03c, huang05a, huang05b, holm05b, holm06a, holm06b, ivanov07a, cerda08a,  cerda08c, kantorovich08a,pyanzina09a</bibentry>
reported  the structure of the fluid to be well described by an
+
 
ideal mixture of self-assembling clusters at low and intermediate
+
== Links ==
densities. Very recently, Duncan-Camp \cite{Duncan2006} have
+
* {{Download|Jcerda_iciam07_v2.pdf| Talk in Zurich ICIAM07, about ferrofluid monolayers.}}
studied the kinetics of aggregation in monolayers using stochastic
+
* {{Download|poster_monolayers.pdf| Poster about ferrofluid monolayers.}}
dynamics simulations. The results obtained in that work suggest
+
 
that the conditions for defect-driven condensation
+
== References ==
\cite{Tlusty2000} could be met by kinetic trapping, giving rise to
+
 
a metastable phase transition between isotropic fluid phases. The
+
[Alexiou2003] Alexiou Ch, Jurgons R, Schmid R, Bergmann C, Henke J, Huenges E, and Parak F , J. Drug Target, (11), 139, (2003).
structure formation and magnetic properties  of polydisperse
+
 
ferrofluids in monolayers have been also recently addressed by
+
[Aoshima2004] Aoshima M, Satoh A, J. Coll. Int. Sci., (280), 83, (2004).
theory and Monte Carlo simulations
+
 
\cite{Morimoto2003,Aoshima2004,Kristof2005}.
+
[Berger1999]  Berger P, Adelman NB, Beckman KJ, Campbell J, Ellis AB, and Lisensky GC, J. Chem. Education, (76), 943, (1999).
 +
 
 +
[Butter2003] Butter K, Bomans PH, Frederik PM, Vroege GJ, Philipse AP, J. Phys.: Condens. Matter, (15), S1451, (2003).
 +
 
 +
[Cabuil2000] Cabuil V, Curr. Opin. Colloid Interface Sci., (5), 44, (2000).
 +
 
 +
[Camp2000] Camp PJ, Patey GN, Phys. Rev. E, (62), 5403, (2000).
 +
 
 +
[Cebula1983] Cebula DJ, Charles SW, and Popplewell J, J. Physique, (44), 207, (1983).
 +
 
 +
[Donselaar1999] Donselaar LN, Frederik PM, Bomans PH, Buining PA, Humbel BM, and Philipse AP, J. Magn. Magn. Matter, (201), 58, (1999).
 +
 
 +
[Duncan2006] Duncan PD, Camp PJ, Phys. Rev. Lett., (97), 107202, (2006).
 +
 
 +
[Gao1997] Gao GT, Zeng XC, and Wang W., J. Chem. Phys., (106), 3311, (1997).
 +
 
 +
[Gazeau2002] Gazeau F, Dubois E, Bacri JC, Boue F, Cebers A, and Perzynski R, Phys. Rev. E, (65), 031403, (2002).
 +
 
 +
[Gennes1970] de Gennes PG, and Pincus PA, Phys. Kondens. Matter.,(11), 189, (1970).
 +
 
 +
[Hess1966] Hess PH, and Parker PH, J. Appl. Polym. Sci. (10), 1915, (1966).
 +
 
 +
[Hilger2004] Hilger I, Andrä W, Hergt R, Hiergeist R, and Kaiser W A, Inorganic Materials, Recent Advances ed D Bahadur, S Vitta, and O. Prakash (2004, New Delhi: Narosa Publishing House).
 +
 
 +
[Holm2005] Holm C, Weis JJ, Curr. Op. Coll. Int. Sci., (10), 133, (2005).
 +
 
 +
[Holm2006] Holm C, Ivanov A, Kantorovich S, Pyanzina E, Reznikov E, J. Phys.: Condens. Matter, (18), S2737, (2006).
 +
 
 +
[Huke2004] Juke B, and Lücke M, Rep. Prog. Phys., (67), 1731, (2004).
 +
 
 +
[Ivanov2004] Ivanov AO, Wang Z., and C. Holm, Phys. Rev. E, (69), 031206, (2004).
 +
 
 +
[Jund1995] Jund P, Kim SG, Tománek, and Hetherington J, Phys. Rev. Lett., (74), 3049, (1995).
 +
 
 +
[Pshenichnikov2000] Pshenichnikov AF, and Mekhonoshin V, J. Magn. Magn. Mater, (213), 357, (2000).
 +
 
 +
[Jordan1973] Jordan PC, Mol. Phys., (25), 961, (1973).
 +
 
 +
[Klokkenburg2006] Klokkenburg M, Dullens RPA, Kegel WK, Erné) BH, Philipse AP, Phys. Rev. Lett., (96), 037203, (2006).
 +
 
 +
[Kristof2005] Kristóf T, Szalai I, Phys. Rev. E, (72), 041105, (2005).
 +
 
 +
[Levesque1994] Levesque D, Weis JJ, Phys. Rev. E, (49), 5131, (1994).
 +
 
 +
[Lomba2000] Lomba E, Lado F, Weis JJ, Phys. Rev. E, (61), 3838, (2000).
 +
 
 +
[Lu2007] An-Hui Lu, E. L. Sabas, and Ferdi Schüth, Angew. Chem. Int. Ed., (46), 1222, (2007).
 +
 
 +
[Mendelev2004] Mendelev VS, and Ivanov AO, Phys. Rev. E, (70), 051502, (2004).
 +
 
 +
[Morozov2002] Morozov KI, and Shliomis MI, 2002, Ferrofluids, Magnetically Controllable Fluids and Their Applications), Lect. Notes Phys., Springer, Berlin, 2002. Ed. Odenbach S.
 +
 
 +
[Morimoto2003] Morimoto H, Maekawa T, Matsumoto Y, Phys. Rev. E (68), 061505, (2003).
 +
 
 +
[Odenbach2002] Odenbach S (Ed.), Ferrofluids, Magnetically Controllable Fluids and Their Applications, Lect. Notes Phys., Springer, New York, 2002.
 +
 
 +
[Osipov1996] Osipov MA, Teixeira PIC, and Telo da Gama MM, Phys. Rev. E, (54), 2597, (1996).
 +
 
 +
[Popplewell1984] Popplewell J, Phys. Technol.,(15), 150, (1984).
 +
 
 +
[Puntes2001] Puntes VF, Krishnan KM, and Alivisatos AP, Science (291), 2115, (2001).
 +
 
 +
[Roij1996] van Roij R, Phys. Rev. Lett., (76), 3348, (1996).
  
 +
[Rosensweig1985] Rosensweig RE, Ferrohydrodynamics (Cambridge University Press, Cambridge, 1985).
  
=== Modelling Ferrofluids ===
+
[Scherer2005] Scherer C, Figueiredo AM, Brazilian J. of Phys., (35), 718, (2005).
  
 +
[Shen2001] Shen L, Stachowiak A, Fateen SK, Laibinis PE, and Hatton TA, Langmuir, (17), 288, 2001.
  
=== Our Current Research ===
+
[Tavares1997] Tavares JM, Telo da Gama MM, and Osipov MA, Phys. Rev. E, (56), R6252, (1997).
  
* Ferrofluid monolayers: monodisperse particles. [Link 1]  
+
[Tavares1999] Tavares JM, Weis JJ, and Telo da Gama MM, Phys. Rev. E, (59), 4388, (1999).
* Ferrofluid monolayers: bidisperse particles. [Link 2]
 
* Structure factors of ferrofluids in the low-density low-aggregating limit [Link 3]
 
  
 +
[Tavares2006] Tavares JM, Weis JJ, Telo da Gama MM, Phys. Rev. E, (73) 041507, (2006).
  
== Scientists ==
+
[Teixeira2000] Teixeira PIC, Tavares JM, and Telo da Gama MM, J. Phys.: Condens. Matter, (12), R411, (2000).
* [[Joan Josep Cerdà]]  
+
 
* [[Sofia Kantorovich]]
+
[Tlusty2000] Tlusty T, Safran SA, Science (290), 1328, (2000).
* [[Christian Holm]]
+
 
 +
[Tourinho1998] Tourinho FA, Braz. J. Phys. (28), doi:10.1590/S0103-97331998000400016, (1998).
 +
 
 +
[Wang2002] Wang Z, Holm C, and Müller HW,  Phys. Rev. E, (66), 021405, (2002).
 +
 
 +
[Wang2003] Wang Z, Holm C, Phys. Rev. E, (68), 041401, (2003).
 +
 
 +
[Weis1993] Weis JJ, Levesque D, Phys. Rev. Lett., (71), 2729, (1993).
 +
 
 +
[Weis2002b] Weis JJ, Tavares JM, and Telo da Gama MM, J. Phys.: Condens. Matter, (14), 9171, (2002).
 +
 
 +
[Weis2003] Weis JJ, J. Phys.: Condens. Matter, (15), S1471, (2003).
 +
 
 +
[Wen1999] Wen W, Pál KF, Zheng DW, and Tu KN, Phys. Rev. E, (59), R4758, (1999).
 +
 
 +
[Zubarev1995] Zubarev AY, and Iskakova LY, J. Exp. Theor. Phys., (80), 857, (1995).
  
== Collaborators ==
+
'''Ferrofluids page is still under construction ...'''
* Group of Prof. Alexey Ivanov, Ekaterimburg.
+
'''Help us to improve the page, send us your feedback.'''
== Publications ==
 
*
 
  
== Links ==
+
--[[User:Jcerda|Jcerda]] 15:11, 29 April 2008 (CEST)
* {{Download|xxxx| Posters, presentations & co }}
+
[[Category:Research]]

Latest revision as of 20:08, 5 September 2011

Fig1. Ferrofluid monolayer at low area fraction.
Fig2. Ferrofluid monolayer at high area fraction.

What are Ferrofluids?

Dipolar magnetic fluids (also known as ferrofluids or ferrocolloids), are colloidal suspensions of ferromagnetic nanoparticles (typical sizes 10-20nm), usually stabilised by steric coatings (in non electrolyte carrier liquids) or by electrical double layers (in aqueous solutions). Sterical coatings are usualy made of a stabilizing dispersing agent (surfactant) which prevents particle agglomeration even when a strong magnetic field gradient is applied to the ferrofluid. The surfactant must be matched to the carrier type and must overcome the attractive van der Waals and magnetic forces between the particles. A typical ferrofluid may contain by volume 5% magnetic solid, 10% surfactant and 85% carrier.

Due to their size, ferrofluid particles can be considered as magnetic single-domains with a permanent magnetic moment   |\mathbf{m}|=m proportional to their volume \pi \sigma_m^3/6, where  \sigma_m is the diameter of the magnetic core of the particle.

To know more about the basics of ferrofluids, see for instance the ferrofluids in the Wikipedia.

Synthesis of ferrofluids

The idea of making a liquid with magnetic properties seems to date back to the 1779 when Gowan Knight tried to make a magnetic fluid by introducing iron filings into water. Unfortunately, the iron filings sedimented very quickly. In the XX century the issue was retaken by F. Bitter (1932), and W.C.Elmore (1938), but the particles they obtained were quite large and not fully stable. It seems that Stephen Papell Solomon (US Patent 3215572 ) working for NASA in the 60´s was the first to develop an easy and effective way of preparing such colloidal systems. The idea was to be able to use these particles to control the flux of fuel in a zero gravity environment. Since then, many synthesis have been developed to produce ferrofluid particles in both non-polar and polar solvents, increase their stability, improve the control over their size and degree of polidispersity, and produce particles with different materials and shapes. For recent reviews about the subject see (Lu2007) and (Tourinho1998).


You can also prepare your own ferrofluids and have fun at home! See for instance the educational article of Berger et al. (Berger1999), as well as (1), (2), (3), (4), (5), (6).

Why are Ferrofluids interesting?

Ferrofluids are interesting for a two fold reason:

  • Ferrofluids are systems exhibing anisotropic interactions leading to a very reach phase behaviour, as well as very interesting rheological and magnetic properties. Thus ferrofluids are a paradigma of physical systems with anisotropic interactions.

See also as an example the links (1), (2) ...

Aggregating structures formed by Ferrofluids

Even in the absence of external fields, ferrofluids have a very complex microstructure, which is caused by the combination of interparticle interactions specific to magnetic fluids (see for instance figures 1 and 2). Ferrofluid particles are known to self-assemble into a variety of magnetic equilibrium structures which depend on several factors such as: system geometry, magnetic interactions, particle polydispersity, presence or absence of external fields, etc.

The number of probable cluster topologies in magnetic fluids is high: drops with high magnetic phase concentration (micron size), branched and fractal clusters (hundreds of nanometers in size), or chain- and ring-like structures (tens of nanometers). Signs of clustering process in ferrofluids at zero field are known for more than 40 years (Hess1966). Nonetheless, despite the large amount of clues obtained in subsequent studies (Shen2001, Donselaar1999, Cebula1983, Gazeau2002), a direct experimental proof of the existence of clusters like chains, rings, etc. has been elusive for many years, specially for those cases were dipole-dipole interactions were relatively week, like in magnetite nanoparticles ( Fe_3O_4 ). Thus, due to the lack of conclusive experiments, the understanding of how dipole-dipole interactions influence the clustering process and determine the subsequent microstructure and phase behaviour of ferrofluids has become a challenge. In bulk ferrofluids, those aspects have been studied in detail through theoretical (Gennes1970, Jordan1973, Osipov1996, Zubarev1995, Tavares1997, Tavares1999, Roij1996, Tlusty2000, Morozov2002, Mendelev2004, Ivanov2004) and simulation (Weis1993, Levesque1994, Jund1995, Camp2000, Pshenichnikov2000, Wang2002, Wang2003, Holm2006) works. Comprehensive reviews on these subject for bulk systems are also available, see (Teixeira2000, Cabuil2000, Huke2004, Holm2005).

Ferrofluid Monolayers

The phase behaviour and microstructure of ferrofluid systems in reduced dimensions is not necessarily equivalent to that of 3D systems. In addition, thin-films and monolayers, have become recently a more successful experimental scenario to assert the existence of the clustering process (Klokkenburg2006, Butter2003, Puntes2001, Wen1999). In the experiments of Philipse and co-workers(Butter2003, Klokkenburg2006), images obtained by cryogenic transmission electron microscopy (cyro-TEM) give ample evidence of the existence of chain- and ring-like structures in ferrofluid monolayers, where all particles are trapped in one plane, but their magnetic moments are free to fluctuate in 3D (q2D monolayers).

In recent years, several theoretical and computational works have been devoted to the study of ferrofluids in monolayers and thin-films. The thermodynamics, and magnetisation properties of quasi-two-dimensional (q2D) systems have been studied by Lomba et al. (Lomba2000), and Gao et al. (Gao1997). Weis and co-workers (see (Weis2002b, Weis2003), and references therein), have performed Monte Carlo simulations of monolayers and systems of finite thickness involving dipolar interactions. They have shown that q2D dipolar systems, alone or in combination with other interactions, present a rich variety of structures, phases and phase transitions. In a recent q2D Monte Carlo study on dipolar hard spheres (DHS), Tavares et al. (Tavares2006) have reported the structure of the fluid to be well described by an ideal mixture of self-assembling clusters at low and intermediate densities. Very recently, Duncan-Camp (Duncan2006) have studied the kinetics of aggregation in monolayers using stochastic dynamics simulations. The results obtained in that work suggest that the conditions for defect-driven condensation (Tlusty2000) could be met by kinetic trapping, giving rise to a metastable phase transition between isotropic fluid phases. The structure formation and magnetic properties of polydisperse ferrofluids in monolayers have been also recently addressed by theory and Monte Carlo simulations (Morimoto2003, Aoshima2004, Kristof2005).

Current Research

Despite the progress obtained in previous studies, the understanding of the phase behaviour and microstructure formation of ferrofluids in constrained geometries is only partial. The understanding of such features is of paramount importance in order to know better those systems and reduce the large amount of times devoted to trial-error in order to improve or design new applications based on ferrofluids.

Our current interest focuses on the peculiarities of the aggregation processes in both quasi-two dimensional (monolayers) and bulk ferrofluid systems. We make use of a combination of density functional theory, and molecular dynamics (MD) simulations. The microstructure formation and phase behaviour are studied thoroughly through a comparison of the theoretical, and computational results. The active areas of research about ferrofluids in our group at this moment are:

Scientists

Collaborators

  • Group of Prof. Dr. Alexey Ivanov. Department of Mathematical Physics, The Urals State University, Ekaterinburg, Russia.

Publications


Links

References

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--Jcerda 15:11, 29 April 2008 (CEST)