EP3005547A1 - Device for converting heat energy into electrical energy with heat-sensitive molecules - Google Patents

Abstract

The invention relates to a system for recovering heat energy and converting said heat energy into electrical energy by means of heat-sensitive molecules (141, 142) to which magnetic particles (150) are connected, the heat-sensitive molecules being able to move said magnetic particles in relation to a conductive circuit in order to generate an induced current in said circuit.

Description

 DEVICE FOR CONVERTING THERMAL ENERGY IN ELECTRICAL ENERGY

 A THERMO-SENSITIVE MOLECULES

DESCRIPTION TECHNICAL FIELD

The present invention relates to the field of devices for converting thermal energy into electrical energy, and provides for the realization of a device for converting thermal energy into electrical energy by means of a magnetic particle movement generated consecutively to a temperature variation.

 It applies in particular to the realization of an energy recovery system provided with such a device for converting thermal energy into electrical energy.

PRIOR ART In order to power electronic devices or microsystems while limiting the use of batteries, many types of energy recovery systems have appeared.

 The document "WO2011 / 144525 A2" has for example a device for converting a mechanical energy into electrical energy, using a movable magnet mechanically actuated and which is disposed in the center of a coil. When the magnet is moved, its movement generates a current in the coil.

Electronic circuits, when operating, produce heat. This heat is generally not used and must be removed in order not to damage the circuits. Other sources of heat whose unused heat is unused are also present in our environment. There is the problem of finding a new thermal energy recovery system in which a conversion of thermal energy into electrical energy would be implemented.

DISCLOSURE OF THE INVENTION The present invention relates first of all to a device for converting thermal energy into electrical energy comprising: a support, a conductive circuit in which an induced current is intended to circulate, a set of magnetic particles attached to the support via fastening means adapted to hold the magnetic particles in at least a first position with respect to said conductive circuit when the device is subjected to a first temperature, the fastening means being formed of attachment molecules of less a first type, sensitive to temperature, so that when the attachment molecules of the first type are subjected to a given temperature variation of the first temperature to the second temperature, the attachment means move the magnetic particles of the first position to a second position with respect to said driver circuit, the displacement of the particles from the first position to the second position inducing a current in said conductive circuit.

 Thus the movement of the particles makes it possible to vary the magnetic field as seen by the conducting circuit and to generate an electric current induced in this conductive circuit.

 By magnetic particles is meant magnetic particles. These particles may be based on a ferromagnetic material. The magnetization of the ferromagnetic material may be natural or may have been imparted for example by an electromagnet.

 In particular, the attachment molecules may be polymer molecules that are sensitive to temperature, also known as heat-sensitive polymers.

The attachment molecules of the first type may be molecules having a LCST1 transition characteristic temperature located between said first temperature and said second temperature and be adapted for, when they are subjected to said given temperature variation, to go from a first configuration to a second configuration.

 This configuration change is preferably reversible so that the heat-sensitive fastening molecules are further configured so that when subjected to an inverse temperature variation ie, between the second temperature and the first temperature, they pass from said second temperature. configuration to said first configuration.

 The heat-sensitive fastening molecules can thus be provided so that, when subjected to a temperature variation from the second temperature to the first temperature, the fastening means move the magnetic particles from the second position to the first position with respect to said driver circuit.

 The attachment molecules of the first type may be such that in the first configuration they have an affinity for the given water, whereas in the second configuration, the attachment molecules have an affinity for water that is the inverse of said given affinity. .

 Thus, when, for example, in the first configuration the attachment molecules are hydrophilic, in the second configuration the attachment molecules are hydrophobic.

 Advantageously, the attachment means further comprise attachment molecules of at least a second type.

 The attachment molecules of the second type may also be temperature sensitive. The attachment molecules of the second type may also be polymer molecules.

 The magnetic particles can thus be attached to a first zone of the support by means of the attachment molecules of the first type and to a second zone of the support by means of attachment molecules of the second type.

According to a first implementation possibility, the attachment molecules of the second type may be molecules having a characteristic transition temperature between a third temperature and a fourth temperature, the attachment molecules of the second type being further configured so that when subjected to a temperature change from the third temperature to the fourth temperature the attachment molecules of the second type change affinity for the water.

 According to this first possibility, it is possible to convert heat energy into electrical energy over several temperature ranges.

 According to a second possibility of implementation, the attachment molecules of the first type may have an affinity for the water given at the first temperature, while the attachment molecules of the second type have another affinity for water, inverse of said affinity given at the first temperature, the attachment molecules of the second type having an affinity for the water given at a second temperature, the attachment molecules of the first type having an affinity for water inverse to said affinity given at said second temperature.

 According to this second possibility, it is possible to convert heat energy into electrical energy over several temperature ranges.

 In this case, if for example at the first temperature the attachment molecules of the first type are hydrophilic, while the attachment molecules of the second type are hydrophobic, the second temperature the attachment molecules of the first type are hydrophobic, the attachment molecules of the second type are at the same time hydrophilic.

 More generally, the attachment molecules may be such that they are capable of passing from a solvophilic character to a solvophobic character as a result of a temperature variation.

 Advantageously, the attachment molecules may be temperature-sensitive polymer molecules chosen from one or more of the following polymers: PolyNipam, Polyvinylcaprolactam, Hydroxypropylcellulose, Polyoxazoline, Polyvinylmethylether, Polyethyleneglycol.

The magnetic particles may be attached to a first region of the support by means of attachment molecules and to a second region of the support by means of other attachment molecules, the conductive circuit being disposed on the support so as to form a conductive winding around an axis passing through said first zone and said second zone of the support, and producing a non-zero angle, in particular orthogonal, with respect to a main plane of the support.

 Advantageously, the magnetic particles are formed of a body based on a magnetic material coated with a hook layer bonded to said attachment molecules.

 According to one possible implementation, the support may be a substrate based on polymeric material. The support can also be provided based on a material and a thickness making it flexible.

 The present invention also provides an energy recovery system comprising a device for converting thermal energy into electrical energy as defined above, as well as means for applying a variable thermal flux to said device for converting thermal energy into electrical energy. .

 The present invention also provides a method for producing a device for converting thermal energy into electrical energy as defined above, in which the attachment molecules are based on a temperature-sensitive polymer, the process comprising at least a step of grafting the magnetic particles to said polymer molecules.

 According to one possible implementation, the method may further comprise forming in the first substrate at least a first cavity and at least a second cavity around the first cavity, said attachment molecules being fixed in the first cavity. second cavity, the conductive circuit being formed in the second cavity.

 The method may include steps of:

 attaching a first set of polymer attachment molecules to the first substrate,

fixing a second set of polymer attachment molecules on a second substrate, and then assembling the first substrate and the second substrate. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood on reading the description of exemplary embodiments given, purely by way of indication and in no way limiting, with reference to the appended drawings in which:

 FIGS. 1A, 1B, 1C, 1D illustrate an example of a device for converting thermal energy into electrical energy as implemented according to the invention;

 FIGS. 2A-2F, 3A-3C and 4A-4B illustrate an exemplary method of producing a device for converting thermal energy into electrical energy according to the invention;

 FIGS. 5A-5B illustrate grafting reactions of polymer particles on a substrate that can be implemented during the manufacture of a device according to the invention.

 Identical, similar or equivalent parts of the different figures bear the same numerical references so as to facilitate the passage from one figure to another.

 The different parts shown in the figures are not necessarily in a uniform scale, to make the figures more readable.

DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS An example of a device for converting thermal energy into electrical energy, as implemented according to the invention, will now be described with reference to FIGS. 1A-1D.

 FIG. 1A illustrates a general principle of operation of such a device provided with a support 100, intended to be subjected to a thermal flux φ, and on which magnetic particles 150 are arranged.

The device also comprises a conductive circuit 120, which may be in the form of a winding, for example a spiral, disposed around the magnetic particles 150. The magnetic particles 150 are magnetized and can be based on of a material, in particular ferromagnetic, having a natural magnetization or having a magnetization generated by means of an electromagnet.

 The magnetic particles 150 are bonded or attached to the support 100 by means of attachment means 140 sensitive to temperature, themselves linked or attached to the support 100 and intended to move the particles 150 relative to the conductive circuit 120, depending a variation of the temperature at which these attachment means 140 are subjected.

 The operating principle of the conversion is based notably on the Faraday / Lenz law: rot E = -dB / dt with E: the electric field, B: the magnetic field and t: the time.

 A temperature variation acting on the attachment means 140 is capable of triggering a movement of the magnetic particles (magnet) relative to the support 100 and to the conducting circuit 120, this movement making it possible to vary the magnetic field as seen by the conducting circuit 120 and generating an induced electric current in this conductive circuit 120. The origin of this electric current is an electric field which is orthogonal to said magnetic field.

 Thus, the device makes it possible to produce an induced current by means of the movement of the magnetic particles 150 magnetized with respect to the conductive winding 120, this movement being itself triggered by the fastening means 140 reacting to a temperature variation. a heat flux φ that has been recovered.

 The heat flux φ that can be recovered can come from a source of light radiation, for example a laser source.

In the device according to the invention, the attachment means 140 of the magnetic particles 150 are molecules, called thermosensitive molecules or thermostimulables, that is to say molecules sensitive to temperature, the configuration of which is susceptible to to be modified, by a variation of temperature beyond and / or below a characteristic temperature of these molecules, and without change of state of the molecules, and while preserving the constituent chemical elements of the molecules. The configuration change of the molecules following a temperature variation is such that their volume as well as some of their properties are modified.

 The configuration change of the attachment molecules of the device is preferably reversible when they undergo an inverse temperature variation.

 The molecules may, for example, have a variable solvophile / solvophobic character as a function of temperature.

 The attachment molecules 140 may be molecules having an affinity to the variable water molecules as a function of temperature, and which are configured to be able to pass for example from a hydrophilic state to a hydrophobic state when they undergo a given variation temperature. The molecules 140 are preferably chosen so that this change in affinity to water is reversible, the molecules 140 then being capable of passing from a hydrophobic state to a hydrophilic state when they are subjected to an inverse temperature variation. . In particular, the attachment molecules 140 may be molecules with a molecular weight greater than 200 so that the change in affinity allows a change of arrangement, for example a significant wetting angle variation.

 The attachment molecules 140 may in particular be molecules of actionable polymers liable to undergo a modification of their physical properties under the action of a temperature variation exceeding or passing below a threshold temperature, characteristic of these molecules, called LCST (LCST for "lower critical solution temperature" or lower critical solubility).

The attachment molecules 140 of the magnetic particles 150 may be, for example, thermosensitive or thermo-activatable polymer molecules of the poly (N-isopropylacrylamide) or PNIPAM type. Such a polymer undergoes a reversible macromolecular transition from a hydrophilic state to a hydrophobic state around its lower critical temperature of solubility LCST. This transition is rapid and is between 30 ° C and 37 ° C. Thus, when the attachment molecules 140 are for example based on PNIPAM and subjected to a first temperature Ti, located below the LCST transition temperature, they have a hydrophilic character and are soluble in water.

When the attachment molecules 140 based on PNIPAM are subjected to a second temperature T ₂ > Ti and located above their transition temperature, they have a hydrophobic nature and insoluble in water.

 Other types of activatable polymers can be used depending on the targeted temperature range, for example polyvinylcaprolactam (having an LCST = 37 ° C.), hydroxypropylcellulose (having an LCST between 40 ° C. and 56 ° C.), polyoxazoline (having an LCST of the order of 70 ° C), polyvinyl methyl ether (having an LCST of the order of 45 ° C), polyethylene glycol (having an LCST between 100 ° C and 130 ° C).

 According to one possible embodiment, the attachment means 140 of the magnetic particles 150 may be formed of several types of thermo-sensitive or thermo-activatable polymers, with different respective LCST transition temperatures, so as to be able to cover different ranges of temperature, that is to say to be able to set in motion the magnetic particles 150 for temperature variations in different temperature ranges and possibly distinct.

 FIG. 1B illustrates a particular detailed embodiment in which the support 100 of the particles 150 is in the form of a flexible substrate 101 and based on a polymer material, for example PEN (polyethylene naphthalate) or PET (polyethylene terephthalate) , or PI (Polyimide), on which the conductive circuit 120 is also arranged.

The substrate 101 comprises a central cavity 102 in which the magnetic particles 150 and the attachment molecules 140 are disposed, as well as a peripheral cavity 104, arranged around the central cavity 102, and in which the conductive circuit 120 is housed. In this example, the conducting circuit 120 is formed of a set of conductive tracks 121 wound around the central cavity 102 in which the magnetic particles 150 are located. These magnetic particles 150 may be formed of a body 151 based on magnetic material, in particular ferromagnetic such as for example nickel, neodymium iron boron (Nd ₂ Fei ₄ B), Samarium cobalt (SmCos), an alloy of Nickel and Cobalt (NiCo), a material based on Strontium and ferrite such as SrFei ₂ 0i9, or based on Barium and ferrite such as BaFei ₂ Oig. The body 151 is coated with a layer 152 for attaching the particles with the attachment molecules. The layer 152 may also have a role of protection against oxidation. This attachment layer 152 may for example be based on SiO ₂ so as to facilitate adhesion with heat-sensitive polymer molecules such as PNIPAM, they themselves fixed or attached to the substrate 101.

 The particles 150 may have a diameter or a critical dimension, for example of the order of 50 nm.

 The body 151 may have a diameter or critical dimension, for example between 10 nm and 40 nm, while the layer 152 may have a thickness of between 40 nm and 10 nm.

 In this example, the magnetic particles 150 are intended to be displaced in one direction, producing a non-zero angle with respect to the main plane of the substrate 101, in particular orthogonal or substantially orthogonal to the main plane of the substrate 101 (the principal plane of the substrate being defined as a plane passing through it and parallel to the plane [O; x; y] in Figure 1B). The advantage of having a movement of the particles along the z axis in this example makes it possible to maximize the electric field E and thus the current generated in the conducting circuit 120.

 The magnetic particles 150 are attached, for example by grafting, to different types of temperature-sensitive polymer attachment molecules 141, 142, these attachment molecules 141, 142 being themselves fixed or attached to the substrate 101, for example by grafting.

The magnetic particles 150 are, in this example, attached to a first region 131 of the support by means of thermosensitive polymer molecules 141 of a first type, having a characteristic transition temperature LCST1 which can be situated for example between 20 ° C. and 50 ° C. So when the temperature goes up and exceeds the LCST1 transition characteristic temperature, the thermostimulatory molecules 141 of the first type may for example become hydrophobic and undergo a change in volume.

 It is possible to modify the LCST transition temperature of the heat-sensitive polymers by adding a salt (to decrease their LCST transition temperature) or by adding a suitable surfactant or polymer solvent (to increase their transition temperature LCST).

 Similarly, a modification of the LCST temperature for a thermostimulable polymer family can be achieved by forming a copolymer, the copolymer optionally having a charge or an amphiphilic moiety.

 In this embodiment, the magnetic particles 150 are also attached to a second zone 132 of the support via thermosensitive polymer molecules 142 of a second type.

 According to one possibility of implementation, the attachment molecules 142 of the second type may have a characteristic LCST2 transition temperature different from that LCST1 of the attachment molecules of the first type, and such that LCST2 is located between a third temperature T3 ( different from T1 and T2) and a fourth temperature T4.

 The attachment molecules 142 of the second type can then be configured so that when they are subjected to a temperature change from the third temperature to the fourth temperature, their affinity for water is changed by passing for example a hydrophilic character with a hydrophobic character or vice versa.

 Alternatively, the heat-sensitive attachment molecules 142 of the second type have a temperature-dependent affinity for water in a manner opposite to that of the heat-sensitive attachment molecules of the first type.

In this particular embodiment, at a given temperature, when molecules 142 of the second type are hydrophobic, the molecules 141 of the first type are at the same time hydrophilic, while at another temperature, when molecules of the second type 142 are hydrophilic, the molecules of the first type 141 are hydrophobic.

 Such an embodiment can be obtained for example when the heat-sensitive attachment molecules 141 of the first type are PNIPAM molecules having a characteristic transition temperature LCST1 located for example in a temperature range between 20 ° C and 50 ° C.

 The thermosensitive attachment molecules 142 of the second type may be, for their part, molecules having a characteristic temperature UCST2 (UCST for "upper critical solution temperature") in a temperature range between 20 ° C and 50 ° C. The attachment molecules 142 may for example be of hydrogel type and pass from a hydrophobic character to a hydrophilic character above a temperature greater than UCST2. The attachment molecules 142 may for example be based on PDMAPS (poly-3-dimethyl (methacryloyloxyethyl) ammonium propane sulphonate) having, for example, a UCST of between 32 ° C. and 35 ° C. or based on poly (propylsulfonatedimethylammoniumethylmethacrylate) of which the UCST is of the order of 30 ° C.

 More generally, the attachment molecules 141, 142 may have a variable solvophile / solvophobic character as a function of temperature.

 A variation of the temperature on the device induces a mechanical movement of the thermo-stimulable polymer molecules 141 and / or 142 causing the movement of the magnetic particles 150 which are grafted onto the thermostimulable molecules 141, 142. The current density flowing in the circuit is proportional to the movement of the magnetic particles 150.

In this embodiment, the first zone 131 on which the heat-sensitive polymer molecules 141 are grafted is located at the bottom of the central cavity 102, while the second zone 132 on which the heat-sensitive polymer molecules 142 are grafted, is itself arranged. in front of the first zone 131, on a portion of the support forming a cover 160 for the central cavity 102. A vertical oscillatory movement can thus be implemented. The cover 160 covering the central cavity 102 may include openings 163 to allow a fluid to enter and exit the central cavity 102. The openings 163 may in particular allow moisture to enter the cavity 102.

 When the temperature-sensitive molecules 141, 142 exhibit a variation in affinity to the water molecule as a function of temperature, it may be important to allow a good moisture input into the central cavity 102. In moisture supply, the water or moisture can be confined in the cavity 102 by providing on the inner walls of this cavity one or more zones having a good affinity with water such as polyimide (PI), polydimethylsiloxane (PDMS), or even depositing a layer SAM (self-assembled monolayer) polar such as a layer of 2,2- (ethylenedioxy) diethanethiol, Hexa (ethylene glycol) dithiol, Tetra (ethylene glycol) dithiol, (11- Mercaptoundecyl tetra (ethylene glycol), (11-Mercaptoundecyl) hexa (ethylene glycol), triethylene glycol mono-11-mercaptoundecyl ether.

 This SAM layer or layers can be formed on a metal zone for example such as gold (Au), and / or silver (Ag), and / or copper (Cu).

 In FIGS. 1C-1D, a movement of the particles 150 within a conversion device of the type of that described above is illustrated.

 The magnetic particles 150 are firstly held by the molecules 141, 142 in a first position with respect to said conductive circuit 120 when the device is subjected to a first temperature Tl <LCST1 (with LCST1 the transition temperature of the molecules of the first type ). In this first position the particles 150 are situated at a height h 1 (measured in the z direction in FIG. 1C), for example of the order of 500 nm, with respect to the substrate 101.

A change in temperature from the first temperature to a second temperature above the temperature results in a displacement of the attachment molecules that move the magnetic particles 150 from the first position to a second position with respect to said conductive circuit 120. This displacement of the magnetic particles from the first position to the second position induces a current in said conductive circuit 120. In this second position, the particles 150 are located at a height h ₂ for example of the order of 1 μιη, compared to substrate 101.

 According to another exemplary embodiment, it is possible to arrange the temperature sensitive fastening molecules 140 and the magnetic particles 150 which are grafted onto them directly on conductive tracks of a conductive circuit, the conducting circuit playing in this case the role of support.

 An example of a method for producing a device for converting thermal energy into electrical energy, according to the invention, will now be described in connection with FIGS. 2A-2F, 3A-3C and 4A-4B.

 The starting material is a substrate 101, which can be flexible and based on a polymeric material such as, for example, PEN (polyethylene naphthalate), or PET (polyethylene terephthalate), or PI (polyimide). The substrate 101 may have a thickness (measured in a direction orthogonal to the [0, x, y] plane of the orthogonal coordinate system [0, x, y, z] in FIG. 2A) for example between 25 μιη and 125 μιη.

 In the substrate 101, first cavities 102, 104 are produced, including a central cavity 102 and a peripheral cavity 104 arranged around the central cavity 102.

The cavities 102, 104 may be formed for example by an etching, which may be carried out by means of a laser or with the aid of a plasma for example based on (0 ₂ + SF 6) or wet type with for example, a solution of the methylbenzoate type.

 The central cavity 102 and the peripheral cavity 104 may be separated by walls 103 formed by etching of the substrate 101.

 The height H of the cavities 102, 104 (measured in a direction orthogonal to the plane [0, x, y] of the orthogonal coordinate system [0, x, y, z] in FIG. 2A) may be for example between 1 μιη and 5 μιη.

Then (FIG. 2B) contacting conductive zones 105a, 105b are formed on certain localized regions of the substrate 101, in particular located in the peripheral cavity 104. For this purpose, it is possible to carry out, through a mask M, a deposit of conductive material, for example by sputtering. The deposited material may be a metal, for example stainless such as gold and have a thickness for example between 30 nm and 300 nm.

 Then (FIG. 2C), on a given conductive zone 105b among the zones

105a, 105b contact recovery conductors, at least one insulating zone 107 is formed by depositing a dielectric material, for example by screen printing or by ink jet.

 The dielectric material may be chosen so as to have a low dielectric constant and may for example be polyimide or a fluorinated polymer with a thickness of, for example, between 100 nm and 1 μιη. This deposit may be followed by annealing of a duration for example between 10 minutes and 20 minutes at a temperature for example of the order of 100 ° C.

 A conductive circuit 120 is then formed in the peripheral cavity 104 (FIG. 2D). This circuit 120 may be in the form of a conductive winding produced by deposition of a metal layer, for example based on Ag, or Au, or Cu, according to a technique which may be for example PVD (deposit physical vapor phase) through a mask or screen printing, or by an inkjet technique.

 The thickness of the deposited metal layer may be for example between 100 nm and 5 μιη.

 An etching can then be performed to define conductive tracks 121 for the conductive circuit 120. This conductive circuit 120 has one end disposed on the conductive zone 105a while another end is in contact with another conductive zone 105b, the the remainder of the winding being disposed either on the substrate 100 or on the insulating zone 107.

Then (FIG. 2E), in the central cavity 102, a first attachment zone 131 is formed on the substrate 100 on which magnetic particle attachment means are intended to be arranged later. This zone 131 may for example be based on copper oxide formed by screen printing, or by ink jet. The deposition is carried out in a thickness of, for example, between 100 nm and 1 μιη at the bottom of the central cavity 104. As a variant, it is possible to provide a fixing zone based on copper formed by deposition of copper oxide followed by a deoxidation annealing carried out for example using pulses of UV radiation.

 Next (FIG. 2F), a first set of thermostimulable or thermosensitive molecules 141 of a first type, for example thermosensitive polymers, is grafted onto the attachment zone 131.

The grafted molecules 141 may already be provided at one of their ends with magnetic particles 150, formed of a body 151 based on a magnetic ferromagnetic material such as, for example, Ni or Nd ₂ Fei ₄ B, or SmCos, or NiCo, or SrFei ₂ 0i9, or BaFei Oig ₂ and coated with a primer 152 which can also play the role of protective layer and for example be based on Si0 _2. The temperature at which the fixing or grafting step of the molecules 141 is carried out may depend on their LCST1 transition temperature. The magnetic particles 150 may have been previously grafted onto the molecules 141, using a graft promoting solvent, for example dichloromethane. The magnetic particles may have natural magnetization or have been magnetized by means of an electromagnet.

 The thermosensitive or thermostimulable molecules 141 of the first type may be, for example, PNIPAM molecules having a water affinity variable in a temperature range, for example between 20 ° C. to 50 ° C., and passing from a hydrophilic character. to a hydrophobic character when subjected to a temperature beyond their LCST1 transition temperature.

 The method also comprises, previously, or simultaneously, or after carrying out the steps which have just been described in connection with FIGS. 2A-2F, the production on another substrate 201, for example a PEN-based polymer substrate, or PET base, or based on PI, thickness for example between 25 μιη and 50 μιη, a second zone 232 attachment on which magnetic particle attachment molecules are intended to be arranged later (Figure 3A ).

The fixing zone 232 may for example be based on copper oxide CuO and have a thickness for example between 100 nm and 1 μιη. According to another for example, the attachment zone 232 may be a copper zone obtained by reducing a layer of copper oxide (FIG. 3A).

 On the second substrate 201, a graft is made on the second attachment zone 232 of a set of thermosensitive or thermostimulable molecules 142 (FIG. 3B). The thermosensitive or thermostimulable molecules grafted onto the second substrate 201 are of a second type, different from that of the grafted molecules on the first substrate 101.

 The thermosensitive or thermostimulable molecules 142 of the second type may be temperature-sensitive polymers having an LCST2 transition temperature.

 The thermosensitive or thermostimulable molecules 142 of the second type may have an affinity for variable water in a temperature range, for example between 20 ° C. and 50 ° C., and which in this range varies inversely with that or opposite to that of thermosensitive or thermo-stimulable molecules 141 of the first type. For example, PDMAPS (poly-3-dimethyl (methacryloyloxyethyl) ammonium propane sulfonate has a typical transition temperature UCST = 32 ° C.

 According to another implementation possibility, the thermosensitive or thermo-stimulable molecules 142 of the second type may have an affinity for the variable water molecules in a temperature range that is different from that in which the affinity for the molecules of water water of thermosensitive or thermo-stimulable molecules 141 of the first type varies.

 Next, one or more adhesive zones 260 are formed to allow assembly with the first substrate 101 and the second substrate 201.

 Adhesive zones 260 may in particular be made on the second substrate 201, for example in a peripheral region of the latter (FIG. 3C).

The adhesive zones 260 may for example be formed by screen printing or by manual dispensing of a layer, for example epoxy, which is not conductive or NCP (NCP for "Non Conductive Paste"). Alternatively, the adhesive zones 260 can be made using a SAM layer (SAM for "Self-Assembled Monolayer" or mono-layer auto assembly) of isocyanate type and comprising ethyl, amine or benzyl groups.

 Such a SAM layer can make it possible to ensure a bonding between the two substrates 101 and 201, in particular when these substrates 101, 201 are based on PEN or PET. This SAM layer may be deposited on the PEN or PET material of the second substrate 201 after having carried out a preliminary treatment with a UV / O3 (ultraviolet / ozone) plasma of several minutes on a peripheral region of the substrate 201. this treatment, the areas on which thermostimulable molecules have been placed, and in particular the attachment zone 231, can be masked in order to avoid being damaged.

 The second substrate 200 is then transferred to the first substrate 100 (FIG. 4A). This transfer can be achieved by bonding using alignment marks provided on the substrates 101, 201.

 The two substrates 101, 201 can be bonded by applying the adhesion zones 260, formed, for example, of epoxy glue (NCP) or of the SAM layer (self-assembled monolayer) on top of the walls 103 separating the cavities 102. , 104.

 This bonding step may be followed by annealing at 100 ° C. for about ten minutes in order to solidify the adhesive layer or create bonds between the two substrates 101, 201.

 The second substrate 201 may make it possible to form a closure cap for the central cavity 102.

 Openings 163 (FIG. 4B) can then be made in the second substrate 201 forming a cover, for example using a laser.

 These openings 163 allow a fluid exchange between the outside of the device and the inside of the central cavity 102, and in particular to allow moisture to enter the central cavity 102.

In the method which has just been described, the grafting steps of the attachment molecules on the support illustrated respectively in FIG. 2F and in FIG. 3B can be carried out by means of a silane coupling agent carrying an isocyanate group. . An example of a reaction is given here with a polyethylene glycol (PEG) isocyanate. Such a reaction can take place in anhydrous dichloromethane:

H (OCH ₂ CH ₂ ) nO H + OCN (CH 2) ₃ Si (OEt) 3

 A covalent urethane bond is thus formed.

For grafting, other silane coupling agents carrying an isocyanate function may be employed:

The substrate 101 or 201 on which the graft is made can be dipped in an anhydrous solution of H (OCH ₂ CH ₂ ) nOCO NH (CH ₂ ) ₃ Si (OEt) ₃ and CH ₂ Cl ₂ .

 Figure 5A illustrates two types of reactions leading to the formation of grafted molecules on a substrate 101.

 Hydrolysis first takes place with atmospheric water first at room temperature. Then a heat treatment can be performed.

 This type of grafting is not necessarily limited to a polymer substrate but can be implemented on other types of substrates, for example based on metal and oxide.

 To enable grafting, the interest functions present on the thermosensitive polymer may be:

 an alcohol to form a urethane (PEG, polyvinylmethylether, hydroxypropylcellulose);

 a carboxylic acid to form an amide (PolyNipam, hydroxypropylcellulose);

 an amine to form a urea (polyvinyl methyl ether, PEG).

 Other methods of grafting are possible:

The surface of the substrate 101 may be modified and the thermostimulable polymer bearing a reactive function on the surface (which may be the surface of a nanoparticle) may be reacted. FIG. 5B illustrates another example of grafting in which the reaction of an alanine bis-catechol on a substrate 101 leads to the formation of a catecholate, the NH 2 of the amino acid function of alanine remaining free to react. with a thermosensitive polymer chain bearing a reactive group. Preferably, this reactive group is a succinimidyl ester group.

 Such a type of grafting is described for example in the document "Anchor Biometry for Surface-lnitiated Polymerization from Metal Substrates", Messersmith et al., J. AM. CHEM. SOC. 2005.

 The table below illustrates a reactivity of esters bearing a PEG group.

The following table illustrates the reactivity of one type of a particular succinimidyl ester by altering the hydrolysis conditions.

This table illustrates the reactivity of different PEG agents measured by hydrolysis at pH 8, 25 ° C, and measured by the UV absorbance of the hydrolyzed succinimidyl (NHS) group.

If the surface of the substrate on which the graft is carried carries NH ₂ pendant amino groups, preferably primary, PEG succinimidyl esters could also react. These primary amino groups can be obtained by hydrolysis of silane coupling agents such as:

NH ₂ (CH ₂ ) _n If Rlx (Y) ₃ -x

With n = 3 to 6, R1 = Me, and, x = 0 to 2, Y = Cl or OR where R = Me or Et.

 Another grafting mode uses the method called "diazonium-induced anchoring process" (DIAP). This type of grafting is described for example in the document by Mevellec et al. "Grafting Polymers on Surfaces: A New Powerful and Versatile Diazonium-Based One-Step Process in Aqueous Media," Chem. Mater. 2007, 19, 6323-6330.

 An aryl diazonium salt is grafted onto the surface of the substrate leaving an aniline group neutralized with HCl, which can be reactivated to primary amine by adding a base. We then return to the previously described grafting cases where the surface is covered with amino-primary groups.

 An example of a particular application of a device according to the invention may be that of a tactile device, for example a keyboard, provided with keys operated by means of a detection of a temperature variation due to the presence of 'a finger.

 The finger thus plays, in this example, the role of thermal energy source for activating thermosensitive molecules which, when they change their configuration, make it possible to move magnetic particles, this displacement inducing a current in a conductive circuit. This generated current can be translated by a dedicated electronic reading circuit of the touch device which then makes it possible to address the activated key. In this example, a power supply of the touch keyboard is not essential.

Claims

A device for converting thermal energy into electrical energy comprising:  a support (100),  a conductive circuit (120) in which an induced current is intended to flow,  a set of magnetic particles (150) attached to the support by means of attachment means (140) able to hold the magnetic particles in at least a first position relative to said conducting circuit (120) when the device is subjected to a first temperature, the attachment means comprising thermosensitive polymer attachment molecules (141) of at least a first type, the polymer attachment molecules (141) being temperature-sensitive, so that, when the of the first type are subjected to a given temperature variation from the first temperature to a second temperature, the attachment means moves the magnetic particles from the first position to a second position with respect to said conductive circuit (120), the displacement magnetic particles from the first position to the second position inducing a current in said conductive circuit (120). 2. Device according to claim 1, wherein the attachment molecules 141 of the first type are molecules having a characteristic transition temperature (LCST1) located between the first temperature and the second temperature and are adapted for when subjected to said given temperature variation of a first configuration to a second configuration, the attachment molecules of the first type being further adapted for when subjected to an inverse temperature variation between the second temperature and the first temperature, passing from said second configuration to said first configuration. 3. Device according to claim 2, wherein in the first configuration the attachment molecules (141) have a hydrophilic or hydrophobic affinity for water, given, in the second configuration, the attachment molecules (141) having an affinity for the inverse water of said given affinity. 4. Device according to one of claims 1 to 3, characterized in that the attachment means further comprise attachment molecules (142) of at least a second type, sensitive to temperature. 5. Device according to claim 4, wherein the magnetic particles (150) are attached to a first region (131) of the support by means of the attachment molecules 141 of the first type and to a second zone (132) of the support by by means of attachment molecules 142 of the second type. 6. Device according to claim 4 or 5, wherein the attachment molecules (142) of the second type are molecules having a characteristic transition temperature (LCST2) located between a third temperature and a fourth temperature, the attachment molecules of the second type being further configured such that when subjected to a temperature change from the third temperature to the fourth temperature to change affinity for water. 7. Device according to one of claims 4 or 5, wherein the attachment molecules (141) of the first type have an affinity for the water given at the first temperature, the attachment molecules of the second type having another affinity for water, the inverse of said affinity given at the first temperature, the attachment molecules (142) of the second type having a given affinity for water at a second temperature, the attachment molecules (141) of the first a type having an affinity for water inverse to said affinity given at said second temperature. 8. Device according to one of claims 1 to 7, wherein the magnetic particles are attached to a first area 131 of the support by means of attachment molecules and a second area 132 of the support through molecules of wherein the conductive circuit 120 is disposed on the support so as to form a conductive winding about an axis passing through said first zone and said second zone of the support, and producing a non-zero angle, in particular orthogonal, with respect to to a main plane of the support. 9. Device according to one of claims 1 to 8, wherein the particles (150) are formed of a body (151) based on a magnetic material coated with a hook layer (152) bonded to said molecules attachment. 10. Device according to one of claims 1 to 9, wherein the carrier (100) is a substrate based on polymeric material. 11. The device according to one of claims 1 to 10, wherein said temperature-sensitive attachment molecules comprise one or more of the following polymers: PolyNipam, Polyvinylcaprolactam, Hydroxypropylcellulose, Polyoxazoline, Polyvinylmethylether, Polyethyleneglycol. 12. System for recovering and converting thermal energy into electrical energy comprising:  - a device for converting thermal energy into electrical energy according to one of claims 1 to 11,  means for applying a variable thermal flux to said device for converting thermal energy into electrical energy. 13. A method of producing a device according to one of claims 1 to 12, in which the attachment molecules are based on polymer temperature sensitive, the method comprising at least one step of grafting the magnetic particles to said polymer molecules. The method according to claim 13, wherein the support is formed of a first substrate, comprising producing in the first substrate (101) at least a first cavity (102) and at least a second cavity (104). ) around the first cavity, said attachment molecules being fixed in the second cavity, the conductive circuit (120) being formed in the second cavity (102). The method of claim 13 or 14, comprising steps of:  - attaching a first set of temperature sensitive polymer attachment molecules (141) to the first substrate (101),  - attaching a second set of temperature sensitive polymer attachment molecules (142) to a second substrate (201), and assembling the first substrate (101) and the second substrate (201) to form said support (100) .