Magnetic fluid

Abstract

The present invention is in the field of fluids and the like comprising magnetic particles, such as ferromagnetic particles, anti-ferromagnetic particles, ferrimagnetic particles, synthetic magnetic particles, paramagnetic particles, superparamagnetic particles, such as magnetic fluids, a method of stabilizing magnetic particles, use of these fluids and functionalized particles. Such fluids have a large variety of applications, such as sealants, as a sensor, in biomedics, etc.

Claims

1. High density dispersion comprising magnetic particles, obtained by a method comprising the steps of providing a dispersion with magnetic particles in an amount of 10-30 wt. % relative to a total weight of the dispersion, directly thereafter providing a weak organic acid, or salt thereof, in an amount of 5*10.sup.6-0.1 Mole acid/gr magnetic particle, and interacting the weak organic acid and magnetic particles, and maintaining the pH at a basic value, wherein after providing the weak organic acid the dispersion is washed one to four times, and wherein a washed dispersion is re-dispersed in a solvent and wherein the dispersion is concentrated to more than 15% v/v, wherein the magnetic particles are present in an amount >15 vol. % relative to a total volume of the dispersion, and in an amount >45 wt. % relative to a total weight of the dispersion, and wherein a weak organic acid is present in an amount of 5*10.sup.6-0.1 Mole acid/gr magnetic particle on the magnetic particle.

2. High density dispersion according to claim 1, comprising a combination of magnetic particles.

3. High density dispersion according to claim 1, further comprising a thickener in a concentration of 20-80 wt. % relative to the total weight of the dispersion.

4. High density dispersion according to claim 1, further comprising a ionic liquid.

5. High density dispersion according to claim 1, wherein the magnetic particles have an average size of 2 nm-10 m, and wherein the magnetic particles comprise iron oxide.

6. High density dispersion according to claim 1, wherein the weak acid is a carboxylic acid comprising 4-20 carbon atoms.

7. Ionic liquid comprising a dispersion according to claim 1.

8. Method of forming a high density dispersion according to claim 1, comprising the steps of: providing a dispersion with magnetic particles in an amount of 10-30 wt. % relative to a total weight of the dispersion, directly thereafter providing a weak organic acid, or salt thereof, in an amount of 5*10.sup.6-0.1 Mole acid/gr magnetic particle, and interacting the weak organic acid and magnetic particles, and maintaining the pH at a basic value, wherein after providing the weak organic acid the dispersion is washed one to four times, and wherein a washed dispersion is re-dispersed in a solvent and wherein the dispersion is concentrated to at least 15% v/v relative to a total volume of the dispersion and to >45 wt. % relative to a total weight of the dispersion.

9. Method according to claim 8, wherein the magnetic particles.

10. Method according to claim 8, wherein the weak acid is a functionalized acid.

11. Method according to claim 8, wherein the dispersion with magnetic particles is provided at a temperature between 15 C.-95 C., wherein the weak organic acid is provided in an amount of 10.sup.4-0.01 Mole acid/gr magnetic particle, wherein the method is performed in air.

12. Method according to claim 8, wherein the solvent into which the dispersion is re-dispersed after washing, is water.

13. Method according to claim 8, wherein the weak organic acid is provided at a temperature between 15 C.-95 C.

Description

SUMMARY OF FIGURES

(1) FIG. 1A-1I show general chemical structures.

DETAILED DESCRIPTION OF FIGURES

(2) FIG. 1 shows general chemical structures of examples of compounds useful in the methods according to the invention. FIG. 1A shows an imidazolium based compound, FIG. 1B a piperidinium based compound, FIG. 1C a pyridinium based compound, FIG. 1D a pyrrolidinium based compound, FIG. 1E a sulfonium based compound, FIG. 1F an ammonium based compound, and FIG. 1G an phosphonium based compound. FIG. 1H shows functional group R.sub.1, whereas FIG. 1I shows functional group R.sub.2. Functional groups R.sub.3 and R.sub.4 may be selected from H, CH.sub.3 and R.sub.1 and R.sub.2. Functional groups R.sub.1-R.sub.4 are selected independently and may be (partly) the same, or not. The side group having m or o carbon atoms may be branched, whereas the side group having n carbon atoms is preferably straight.

Examples

(3) The invention although described in detailed explanatory context may be best understood in conjunction with the accompanying examples.

(4) Experimental Procedure to Obtain Water-Based Magnetic Fluid Stabilized with Citric Acid

(5) List of chemicals used:

(6) TABLE-US-00001 Iron(III)chloride hexahydrate FeCl.sub.36H.sub.2O Iron(II)chloride tetrahydrate FeCl.sub.24H.sub.2O Citric acid monohydrate C.sub.6H.sub.8O.sub.71H.sub.2O Ammonium hydroxide NH.sub.4OH Acetone (CH.sub.3).sub.2CO Demiwater H.sub.2O

(7) 1 Procedure

(8) a) Synthesis of Particles (Using a Coprecipitation Method at Room Temperature):

(9) 43.25 g of FeCl.sub.3.6H.sub.2O, 15.9 g of FeCl.sub.2.4H.sub.2O and surplus of demiwater were mixed. When after iron chlorides were dissolved, ammonium hydroxide was added over 15 seconds. The obtained dispersion was stirred for 5 minutes.

(10) b) Stabilization with Citric Acid (at Room Temperature) and Washing Steps with Water and Acetone:

(11) Thereafter, 50.43 g of citric acid were added. When the citric acid was added, the dispersion was stirred for 5 minutes, after which the beaker was placed on a Neodymium magnet for 5 minutes. The clear supernatant was decanted and separated from magnetic particles. Then, water was added to magnetic particles and stirred for 5 minutes until no more aggregates were remaining.

(12) When no more aggregates were visible, acetone was added and was placed on the magnet for 6 minutes. The dark yellow supernatant was removed and the particles were redispersed in sufficient water by stirring it until no more aggregates were visible. Then, acetone was added to the obtained dispersion and was placed on the magnet for 5 minutes. The clear yellow supernatant formed was decanted and only particles which remained on the magnet were redispersed in water and stirred until no more aggregates were visible. After, acetone was added to the dispersion and placed on the magnet for 2 minutes. The supernatant was decanted. Finally, a small volume of water was added until the particles were redispersed and a homogeneous magnetic fluid was obtained (Small volume does not mean the minimum volume of water to redisperse the particles as it is possible to increase the concentration of particles afterwards (see section c))).

(13) c) Increase of the Magnetic Fluid Concentration of Particles:

(14) After obtaining the magnetic fluid, the concentration of particles can be increased until the desired value by leaving magnetic fluid in an opened vessel at room temperature overnight or at a temperature between 40 and 60 C. for several hours.

(15) Oil-Based Magnetic Fluid Production Procedure

(16) List of chemicals used:

(17) TABLE-US-00002 Iron(III)chloride (40% v/v) FeCl.sub.3 Iron(II)sulphate heptahydrate FeSO.sub.47H.sub.2O Oleic Acid C.sub.18H.sub.34O.sub.2 Ammonium hydroxide NH.sub.4OH Acetone (CH.sub.3).sub.2CO Demiwater H.sub.2O

(18) 1 Procedure

(19) a) Synthesis of Particles (Using a Prior Art Coprecipitation Method at Room Temperature):

(20) 17 g FeSO.sub.4.7H.sub.2O, 36 g of FeCl.sub.3 and demiwater were mixed. When after iron chloride and iron sulphate were dissolved, ammonium hydroxide was added over 15 seconds. The obtained dispersion was stirred for 5 minutes.

(21) b) Stabilization with Oleic Acid and Washing Steps with Water and Acetone:

(22) Thereafter, 20 g of oleic acid was added. When the oleic acid was added, the dispersion was stirred for 15 minutes. After which the beaker was placed on a Neodymium magnet for 5 minutes. The clear supernatant was decanted and separated from magnetic particles. Then, water was added to magnetic particles and stirred for 5 minutes until no more aggregates were remaining.

(23) When no more aggregates were visible, acetone was added and was placed on the magnet for 6 minutes. The supernatant was removed and the particles were redispersed in sufficient water by stirring it until no more aggregates were visible. Then, acetone was added to the obtained dispersion and was placed on the magnet for 5 minutes. The supernatant formed was decanted and only particles which remained on the magnet were redispersed in water and stirred until no more aggregates were visible. After, acetone was added to the dispersion and placed on the magnet for 2 minutes. The supernatant was decanted. Finally, a small volume of oil-based carrier was added until the particles were redispersed and a homogeneous magnetic fluid was obtained.

(24) In the tables 1-2 below some further details of the present dispersions are given, specifically for water and oil based ferrofluids.

(25) TABLE-US-00003 TABLE 1 Volume and weight percentages of present water based ferrofluid dispersions. Water based Ferrofluid V/V % obtained wt. % obtained 15 48.3 20 57 25 63.4 30 69.1 40 77.6

(26) TABLE-US-00004 TABLE 2 Volume and weight percentages of present oil based ferrofluid dispersions. Oil based ferrofluids V/V % obtained wt. % obtained 15 50.2 20 58.9 25 65.6 30 71.3 40 79.3

(27) It should be appreciated that for commercial application it may be preferable to use one or more variations of the present system, which would similar be to the ones disclosed in the present application and are within the spirit of the invention.