FIELD OF THE INVENTION This invention relates to a process for the production of thin superparamagnetic films and nanoparticles encapsulated in a polymer matrix, and more particularly this invention relates to the cathodic electrodeposition of composite materials, including inorganic materials and polymers, from solutions of metal salts containing dissolved polymers and processing additives.

BACKGROUND OF THE INVENTION The development of nanostructured organic-inorganic hybrid materials presents new challenges and opportunities for future technologies [1-6]. The nanocomposites combine the advantageous properties of organic and inorganic components. Nanostructured magnetic materials are now being extensively studied for high-capacity magnetic storage media, integrated circuits, color imaging, magnetic refrigerators and biomedical applications.

Below a critical size, nanocrystalline magnetic particles may be single-domain and show the unique phenomenon of superparamagnetism [7,8]. A critical obstacle in assembling and maintaining a nanoscale magnetic material is its tendency to aggregate. To overcome this, nanoparticles of magnetic materials have been isolated in a polymer matrix to form advanced hybrid materials [7- 14].

Formation of hybrid magnetic materials by other methods than those discussed hereinafter has been the subject of significant research activity during recent years. Current methods, such as self-assembly, sol-gel, blending and microemulsion are slow, expensive and often result in particle aggregation. Recently anodic electrodeposition was applied to prepare hybrid films. However, anodic electrodeposition is based on a different mechanism and has several disadvantages compared to the method disclosed herein.

Anodic deposition has limited use due to the fact that noble metal substrates are required for deposition. However, the major disadvantage of the anodic method is that magnetic particles are highly agglomerated during electrodeposition. With agglomerated particles, the superparamagnetic properties cannot be achieved in fabricated materials.

Novel applications of superparamagnetic materials are inevitably related to the development of advanced techniques for deposition of thin films.

Cathodic electrolytic deposition of thin films is a new technique in ceramic processing. The feasibility of electrodeposition of various thin film materials from aqueous solutions has recently been demonstrated. Review papers describing materials science aspects, mechanisms, kinetics of deposition and applications of electrolytic films are now available [15-17]. This method brings new opportunities in electrosynthesis of nanostructured thin films and powders from aqueous solutions of metal salts [18-21]. An important discovery was the feasibility of electrochemical intercalation of water-soluble polyelectrolytes into cathodic deposits prepared by electrolytic deposition [22].

We have begun to use charged polymers for preparation of organoceramic films [23-25]. More recent studies have illustrated the importance of this method for various applications [26,27]. Uniform and adherent films could be produced at current densities in the range 1-5 mA/cm2. Electrodeposition performed in presence of cationic surfactants at current densities in the range 10-50 mA/cm2 could result in formation of nanoparticles encapsulated in a polymer matrix.

Electrodeposition can also be used for deposition of neutral polymers and hybrid films based on neutral polymers [26]. For example, PVA is a neutral polymer. It is known that aqueous PVA solutions can be gelled by boric acid or borax. Gelling of PVA is a base catalyzed process. The gelling phenomena take place in basic medium and result from the didiol complex formation between borate ions B (OH) 4 and OH groups of PVA, interchain crosslinking and formation of three-dimentional networks. The method of PVA films formation described in [24] is based on a local pH increase and formation of borate ions B (OH) 4 near the cathode, followed by crosslinking of PVA molecules and gelling. Cathodic electrodeposition of PVA films was

performed from 5% aqueous PVA solutions containing small additives of boric acid or borax. Atomic concentration of boron in solutions was in the range 0.2- 20 g-at. Bol. In the basic medium at the cathode surface the concentration of borate ions increases, resulting in PVA crosslinking and formation of cathodic deposits. Uniform films can be prepared on various conductive substrates.

The method enables control of the deposit thickness by variation of deposition time and current density. The literature data presented above indicate that cationic polyelectrolytes or neutral polymers can be deposited from aqueous solutions on cathodic substrates. On the other hand, oxide materials can be deposited using cathodic electrolytic deposition [15-17]. Analysis of potential diagrams [28] indicate that individual oxides and complex oxides (Fe304, NiFe204, MnFe204) with important magnetic properties can be deposited using cathodic electrodeposition.

It would be very advantageous to provide a method for co-deposition of polymers and magnetic nanoparticles and formation of magnetic hybrid films and nanoparticles encapsulated in a polymer matrix using electrodeposition.

SUMMARY OF THE INVENTION The present invention provides a method which is suitable for industrial production of thin superparamagnetic films and nanoparticles encapsulated in a polymer matrix.

The method disclosed for the preparation of superparamagnetic hybrid films and nanoparticles encapsulated in a polymer matrix is based on in situ synthesis of inorganic nanoparticles in an organic matrix from solutions of metal salts containing processing additives and a dissolved polymer.

Formation of the hybrid films including the nanoparticles encapsulated in the polymer matrix is achieved by electrodeposition of inorganic nanoparticles formed from the metals and simultaneous deposition of a polymer matrix film with the nanoparticles dispersed throughout the polymer matrix film.

In this method, based on cathodic electrosynthesis, magnetic particles are produced in situ in the polymer matrix. The method allows control over particle interactions and preventing them from agglomeration. Particle size can be controlled on the nanometer scale.

The present invention enables: 1) formation of hybrid superparamagnetic films based on magnetic inorganic materials and cationic polyelectrolytes or neutral polymers, including optically transparent superparamagnetic films ; and 2) formation of colloidal superparamagnetic nanoparticles encapsulated in a polymer shell.

In one aspect of the invention there is provided a method of synthesizing a composite material comprised of a polymer and inorganic magnetic nanoparticles comprising the steps of: preparing a solution including a salt of a selected metal, a polymer dissolved therein, and selected additives; and depositing the polymer onto a substrate thereby producing a polymer matrix film and simultaneously electrodepositing inorganic magnetic nanoparticles formed from the selected metal with the inorganic nanoparticles being encapsulated in the polymer matrix film.

In another aspect of the invention there is provided a hybrid organic- inorganic composite material exhibiting superparamagnetic properties produced by a method comprising the steps of: preparing a solution including a salt of a selected metal, a polymer dissolved therein, and selected additives; and depositing the polymer onto a substrate thereby producing a polymer matrix film and simultaneously electrodepositing inorganic magnetic nanoparticles formed from the selected metal with the inorganic nanoparticles being encapsulated in the polymer matrix film.

BRIEF DESCRIPTION OF THE DRAWNGS The features of this invention will be better understood from the following detailed description taken in conjunction with the drawings wherein: Figure 1 shows magnetization versus applied magnetic field at 298 K for superparamagnetic films based on Fe304 and poly (diallyidimethylammonium chloride).

Figure 2 shows magnetization versus applied magnetic field at 20 K for superparamagnetic films based on Fe304 and poly (diallyidimethylammonium chloride).

Figure 3 shows magnetization versus H/T at different temperatures for superparamagnetic films based on Fe304 and poly (diallyidimethylammonium chloride).

Figure 4 shows temperature dependence of the dc magnetization for zero-field cooled (ZFC) and field cooled (FC) superparamagnetic films based on Fe304 and poly (diallyldimethylammonium chloride).

Figure 5 shows temperature dependence of the real part of complex magnetic susceptibility (%') at a frequency of 1 kHz for superparamagnetic films based on Fe304 and poly (diailyldimethylammonium chloride).

DETAILED DESCRIPTION OF THE INVENTION The method disclosed herein is based on cathodic electrodeposition of hybrid films from solutions of metal salts containing dissolved polymers. In this method, magnetic nanoparticles are produced in situ in a polymer matrix. By isolating the magnetic nanoparticles in a polymer matrix, the agglomeration of particles is avoided and as a result, it is possible to obtain a highly homogeneous composite material which exhibits superparamagnetic properties down to very low temperatures. Formation of hybrid films or encapsulated nanoparticles is achieved by electrodeposition.

Formation of hybrid materials can be achieved by different methods: (i) by heterocoagulation of cationic polyelectrolytes and inorganic nanoparticles formed by electrosynthesis at the electrode surface ; (ii) by electrochemical intercalation of the inorganic nanoparticles into a polymer matrix formed on the electrode surface.

Fabricated films exhibit superparamagnetism at room temperature, combined with optical transparency and other functional properties. This means that the materials exhibit a combination of relatively high magnetization at room temperature (-15 emu/g) and zero coercivity.

Properties, composition, nanostructure and morphology of the films can be tailored according to specific requirements for various applications. This can be achieved by variation of bath composition, deposition parameters and mass transport conditions for organic and inorganic components.

In this method a film is produced on a substrate with the film being a composite of a polymer matrix and superparamagnetic or magnetic nanoparticles of metal oxides or mixed (complex) metal oxides. The composite film is produced by electrodepositing from a solution containing metal salts, a dissolved polymer and various additives. The processes occur simultaneously, namely electrodeposition of the polymers and electrodeposition (electrosynthesis + deposition) of the metal oxide ceramic particles.

The metal salts may be chlorides, nitrates, sulphates or acetates of the metals Fe, Ni, Mn, Co and Cr to form simple oxides. Alternatively, magnetic nanoparticles comprised of mixed metal oxides or complex oxides may be electrodeposited from solutions containing mixed salts. In the case of complex oxides, the metal salts may be chlorides, nitrates, sulphates or acetates of the metals Fe, Ni, Mn, Co, Cr, Zn and Cu.

. The polymer dissolved in solution may be a water soluble charged cationic polyelectrolyte. For example, the cationic polyelectrolyte may be poly (diallyidimethylammonium chloride), polyethelenimine, poly (allylamine hydrochloride), poly (acrylamide-co-diallydimethylammonium chloride), poly (2- hydroxypropyl-N, N-dimethylammonium chloride).

Alternatively, the polymer dissolved in solution may be water soluble polyvinyl alcohol. The additives may include polyacrylic acid, boric acid, borax, hydrochloric acid, nitric acid, sulfuric acid, KCI, NaCI, KNO3, NaN03, and acetyltrimethylammonium bromide. In the case of polyvinyl alcohol, electrodeposition is based on electrochemical crosslinking of the polymer molecules at the cathode surface and the above-mentioned inorganic additives are used for the crosslinking. In other cases, polymers are deposited without changes in their chemistry. Electrodeposition of polymers and electrosynthesis + intercalation of oxide particles occur simultaneously.

Polymers and metal salts are both in starting solutions. The present invention is advantageous in that readily available industrial polymers may be used.

Thus, there are several possible mechanisms of electrodeposition of polymers, for example electrophoretic deposition in the case where the polymers are charged polymers (polyelectrolytes). Alternatively, the

mechanism may be cathodic electrochemical crosslinking in the case of the polymer being polyvinyl alcohol.

The polymer dissolved in solution may be present in a concentration range from about 0.2 g/l to about 5 g/l. The polymer may have a molecular weight of in a range from about 15,000 to about 500,000. The metal may be present in the solution in a concentration range of about 1 mM to about 100 mM.

The following non-limiting example is provided to exemplify the invention, and not to limit it in any way.

EXAMPLE In this example, by using cationic polyelectrolytes for electrodeposition, magnetic nanoparticles were created in situ in a polymer matrix at the electrode surface. More specifically, the process of electrodeposition and the properties of hybrid iron oxide-poly (diallyldimethylammonium chloride) films are presented.

Ferric chloride hexahydrate (FeCI3 6H20), ferrous chloride tetrahydrate (FeCI2 4H2O) and poly (diallyidimethylammonium chloride) (PDDA) from Aldrich were used to formulate two stock solutions for electrodeposition.

Solutions for deposition contained 3.3 mM Fecal3, 1.65 mM Fez) 2 and 0. 5-1 g/l PDDA. Deionized water was deaerated prior to solution preparation using 93% Ar-7% H2 gas. The gas flow was maintained through the solutions during deposition and through the chamber for film drying. The electrochemical cell for deposition included a cathodic substrate centered between two parallel platinum counterelectrodes. The films were deposited on Pt foil cathodes (50x50x0. 1 mm) at a current density of 10 mA/cm2.

The Pt substrates were weighed before and after deposition experiments followed by drying at room temperature for 48 h. After drying the electrolytic deposits were scraped from the Pt electrodes for thermogravimetric (TG) analysis and magnetic measurements. The thermoanalyzer (Netzsch STH-409) was operated in air between room temperature and 1200°C at a heating rate of 5°C/min.

Magnetic properties were studied using a Quantum Design PPMS-9 system. DC magnetization studies were performed using the extraction magnetometer option. Magnetization hysteresis loops were measured in the field range up to 10 kOe at temperatures ranging from 2 to 298 K. The external magnetic field was changed in the sweep mode at the sweep rate of 10 Oe/min. The temperature dependence of the magnetization was studied by both zero-field-cooled (ZFC) and field-cooled (FC) procedures. The sample was first cooled to 1.9 K in the ZFC mode and then magnetization was measured during heating to 298 K under the applied field of 400 Oe. The sample was subsequently cooled back to 1.9 K under an applied field of 400 Oe (FC) and the measurements of magnetization were carried out during heating to 298 K. Measurements of complex magnetic susceptibility (% =x'- in") were performed in the frequency range of 10-104 Hz and a temperature of 1.9-298 K using an ac magnetic field of 40e. The microstructure of the deposits were studied using a Philips 515 scanning electron microscope (SEM).

In the cathodic electrodeposition method, the high pH of the cathodic region brings about formation of colloidal particles, which precipitate on the electrode. Reduction of water is the reaction at the cathode that generates OH- : 2H20 +2e- H2 + 20H' (1) Intercalation of PDDA into electrolytic deposits is achieved via heterocoagulation of oppositely charged PDDA and colloidal particles of oxides or hydroxides formed near the cathode [22]. Electrosynthesis of iron oxide was performed in situ in the polymer matrix. The polymer matrix is necessary to prevent oxide particle agglomeration caused by van der Waals forces and magnetostatic inter-particle interactions.

Results of thermodynamic modeling [28-30] indicate that iron species precipitate as Fe304 under basic conditions at a molar ratio of Fe 2+/Fe 3+1 2 under a non-oxidizing environment: Fe + 2Fe + 80H-o Fe304 + 4H20 (2) Cathodic electrolytic deposition is similar to the wet chemical method of ceramic powder processing that utilizes an electrogenerated base instead of

alkali. Therefore, it could be. suggested that iron species in our experiments precipitate as Fe304.

Electrodeposition resulted in the formation of cathodic deposits.

Deposit weight increased with deposition time. SEM observations indicate that films of different thickness in the range up to 5 jim can be obtained.

We utilized TG analysis and magnetic measurements to study the composition and properties of the prepared films. TG data indicate that by variation of PDDA concentration in solutions in the range 0.5-1 g/l, the amount of Fe304 can be varied in the range 24.6-41. 9 wt%. Fe304 content in the hybrid films decreases with increasing PDDA content in solution. These results indicate a possibility of variation of composition and properties of the films to meet the needs of various applications.

Figures 1 to 5 show magnetic properties of hybrid films containing 41.9 wt% Fe304. Our results indicate that the magnetic properties of prepared films meet the experimental criteria for superparamagnetism [31,32]. Indeed, no hysteresis was observed at temperatures higher than ~20 K (Figs. 1 and 2). Magnetization curves recorded in the range 20-298 K showed zero remanence and zero coercivity. The magnetization curves at different temperatures are superimposed in a plot of M versus H/T. Small deviations between the curves in Fig. 3 could be attributed to particle size distribution, changes in spontaneous magnetization with temperature and anisotropy effects [31,32]. These data are consistent with the superparamagnetic behavior of nanoparticles.

As expected, the saturation magnetization of hybrid films was found to be lower than that of bulk Fe304. However, the magnetization of hybrid films was comparable to the magnetization of bulk composite materials prepared by other methods [7,9, 13]. Magnetic hysteresis loops were observed at 5 K in prepared deposits. Similar hysteresis loops were reported for other hybrid materials below the blocking temperature [7,9].

Zero remanence and zero coercivity are observed in the superparamagnetic state for very small particles because thermal fluctuations can prevent the existence of a stable magnetization. Below the blocking temperature, magnetic particles become magnetically frozen, and as a result,

remanence and coercivity appear on the plot of magnetization as a function of applied field.

Low field magnetization measurements in ZFC and FC modes are important for the characterization of superparamagnetic materials [9,29].

Results of the ZFC and FC magnetization measurements are shown in Fig. 4.

The ZFC magnetization measurements show a peak at Tmax = 25 K, indicative of a characteristic blocking temperature for superparamagnetic particles. It is important to note that TmaX for superparamagnetic material depends on the strength of the magnetic field and particle size distribution [9].

Above the blocking temperature, all the nanoparticles are in the superparamagnetic state. As a result, at temperatures higher than Tmax, the ZFC and FC curves are superimposed. Similar behavior was observed in other materials [29,33, 34]. A separation of the ZFC and FC curves was observed at lower temperatures. This observation is consistent with the behavior of ultrafine magnetic particles below the blocking temperature [9].

These observations were also supported by ac measurements. Temperature dependence of %'showed a maximum (Fig. 5) at a frequency dependent temperature (Tmax). Measurements of x' (T) at frequencies f = 10-104 Hz indicate that Tmax increases with increasing frequency. We attributed Tmax to the blocking temperature TB, defined as the temperature for which the relaxation time is equal to 1/f. Temperature dependence of relaxation time was found to obey the Arrhenius law [34] : X = 10exp (E/KT) (3) where AE is the energy barrier between two easy directions of magnetization, K is the Boltzmann constant, T is the temperature and 0 is a constant.

The experimental data obtained indicate that superparamagnetic films based on iron oxide and PDDA can be produced by electrodeposition.

An important advantage of electrodeposition is the ability of agglomerate-free processing of nanostructured materials. It enables synthesis of oxide particles in situ in a polymer matrix. Electrodeposition not only produces hybrid materials but also synthesizes the film. By this means, an electrogenerated base is used instead of alkali, thus reducing risk of film contamination. The composition, microstructure and morphology of these

films can be tailored by variation of bath composition and mass transport conditions for organic and inorganic components. There is no need to reiterate advantages of electrodeposition for formation of uniform films on substrates of complex shape and selected areas of the substrates [15, 17].

A method of synthesis of superparamagnetic films has been disclosed herein. This method has the advantage of permitting nanostructured iron oxides to be synthesized in situ in a polymer matrix on an electrode to form hybrid organic-inorganic films. The amount of the deposited material, film composition and properties can be varied with variation of deposition time and polymer concentration in solution. The method opens new opportunities in the development of hybrid nanostructured magnetic materials.

The process disclosed herein has the advantages of common, low cost materials and equipment, high purity of prepared hybrid nanocomposites, and rigid control of film thickness and deposition rate. Properties, composition, nanostructure and morphology of the films and colloidal particles can easily be tailored, thus allowing preparation of a wide variety of nanomaterials for different applications. The technology could easily be transferred from laboratory to the manufacturing scale.

The present invention enables development of novel materials (films or colloidal particles) with tailored combination of magnetic and optical properties. Such materials cannot be prepared by other methods. Due to the use of an electric field, the method allows formation of uniform and adherent films on substrates of complex shape or selected areas of electronic substrates (patterning).

The problem of agglomeration of magnetic nanoparticles is solved by carrying out the electrosynthesis of magnetic particles in situ in a polymer matrix. As a result the fabricated composite materials exhibit superparamagnetic properties. The method offers the opportunity to develop a wide range of other nanostructured materials with a tailored combination of magnetic, optical, ferroelectric, piezoelectric and other functional properties.

Electrochemical technology has been used in the electronic industry for manufacturing integrated circuits. Electrodeposition is an established industrial process for producing films of magnetically-soft metals and alloys for recording and data storage. Nanocomposites of hybrid materials are now

extensively studied as high-capacity magnetic storage media. This invention extends the electrodeposition technique to the production of magnetically soft hybrid materials, which can be used by the electronic industry.

Further, optically transparent hybrid magnetic materials are good candidates for replacement of garnets in opto-electronic devices. Transparent magnetic materials have many other applications including microwave magneto-optical modulation of visible lasers, optical deflection and isolation, magneto-optic displays, and holograms. Materials made by the disclosed method can also be utilized for applications in magnetic inks and magnetic fluids.

Hybrid materials can be utilized in biomedical applications, e. g. , for drug delivery or tumor detecting and treatment. In-vivo magnetic fields can guide encapsulated magnetic particles with attached anti-cancer drugs toward tumors. High frequency magnetic fields heat up magnetic particles attached to a tumor, destroying the tumor tissue. Medical applications require biocompatibility. The encapsulation of magnetic particles protects them from degradation and provides biocompatibility. All these applications require particles with magnetism that turns"on"in the magnetic field and turns"off' upon removal of the field. The hybrid superparamagnetic materials produced by the present method exhibit zero coercivity and meet these requirements.

Hybrid polymer-iron oxide materials are currently used for magnetic resonance imaging and for monitoring mental or neuro-degenerative diseases. The materials produced by the method disclosed herein may be used in these applications.

As used herein, the terms"comprises"and"comprising"are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in this specification including claims, the terms"comprises"and "comprising"and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components.

The foregoing description of the preferred embodiments of the invention has been presented to illustrate the principles of the invention and not to limit the invention to the particular embodiment illustrated. It is intended

that the scope of the invention be defined by all of the embodiments encompassed within the following claims and their equivalents.

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