Method For Preparing Raspberry Nanoparticles

Abstract

The present invention relates to a method for preparing a dispersed suspension of nanoparticles called “raspberry nanoparticles” having a diameter of less than or equal to 130 nm, the raspberry nanoparticles being optionally functionalised with a hydrophobic organic molecule. The present invention also relates to a suspension which comprises the raspberry nanoparticles and can be produced by the method and to the use thereof for making a surface superhydrophobic or superhydrophilic, depending on whether the nanoparticles are functionalised with a hydrophobic organic molecule. Finally, the present invention relates to a method for covering the surface using a suspension according to the invention in one single step.

Claims

1. A method for preparing a suspension comprising raspberry nanoparticles having a diameter of size X+2Y, each raspberry nanoparticle being composed of a nanoparticle having a diameter of size X on the surface of which nanoparticles having a diameter of size Y are covalently grafted, said method comprising at least the following successive steps: (a) Obtaining a suspension comprising nanoparticles having a diameter of size X in an aprotic solvent S1; (b) Adding an adhesion promoter to the suspension obtained after step (a) to obtain a first reaction medium; (c) Adding the reaction medium obtained after step (b) directly to a suspension comprising nanoparticles having a diameter of size Y dispersed in an aprotic solvent S1′, leading to the formation of raspberry nanoparticles having a diameter of size X+2Y to obtain a second reaction medium; (d) Optionally, adding a solvent S2 to the second reaction medium, then partially or fully removing aprotic solvent S1 and/or aprotic solvent S1′; (e) Recovering a suspension of raspberry nanoparticles having a diameter of size X+2Y dispersed in the aprotic solvent S1, the aprotic solvent S1′, the solvent S2 or mixtures thereof, wherein the nanoparticles having a diameter of size X or Y and the raspberry nanoparticles are kept in liquid medium throughout all the steps of the method, and the diameter of size X+2Y of the raspberry nanoparticles is less than or equal to 130 nm, and at least one of the diameters of size X or Y is of size less than 50 nm.

2. The method according to claim 1, wherein the ratio X/Y of the diameters is between 1 and 30.

3. The method according to claim 1, wherein the nanoparticles are composed of at least one inorganic material.

4. The method according to claim 1, wherein the adhesion promoter is an alkoxysilane or chlorosilane carrying a reactive function.

5. The method according to claim 1, wherein the nanoparticles having a diameter of size Y are added in excess at step (c) in relation to the nanoparticles having a diameter of size X.

6. A suspension obtainable by the method of claim 1, wherein the suspension contains raspberry nanoparticles having a diameter of size X+2Y less than or equal to 130 nm dispersed in the aprotic solvent S1, the aprotic solvent S1′, the solvent S2 or mixtures thereof.

7. The suspension according to claim 6, wherein the suspension also comprises nanoparticles having a diameter of size Y not grafted onto the nanoparticles of size X.

8. The method according to claim 1, further comprising after step (e) the successive steps: (f) Adding at least one hydrophobic organic molecule comprising a grafting function to the suspension recovered at step (e); (g) Recovering a suspension of raspberry nanoparticles having a diameter of size X+2Y less than or equal to 130 nm functionalised with the hydrophobic organic molecule in the aprotic solvent S1, the aprotic solvent S1′, the solvent S2 or mixtures thereof.

9. The method according to claim 8, wherein the hydrophobic organic molecule is a fluorinated molecule. ##STR00008##

10. A suspension obtainable by the method of claim 8, wherein the suspension contains raspberry nanoparticles having a diameter of size X+2Y less than or equal to 130 nm, functionalised with said hydrophobic organic molecule, dispersed in the aprotic solvent S1, the aprotic solvent S1′, the solvent S2 or mixtures thereof.

11. The suspension according to claim 10, wherein further comprising nanoparticles having a diameter of size Y functionalised with a layer of hydrophobic organic molecules and dispersed in the aprotic solvent S1, the aprotic solvent S1′, the solvent S2 or mixtures thereof.

12. A method for making a surface superhydrophilic comprising the steps of: (i) providing a surface, and (ii) applying the suspension of claim 6 to the surface provided in step (i).

13. A method for making a surface superhydrophobic comprising the steps of: (i) providing a surface (ii) applying the suspension of claim 10 to the surface provided in step (i).

14. A method for coating a surface comprising the steps of: (i) providing a surface (ii) depositing on the surface provided in step (i) the suspension of claim 6 by dip-coating, spin-coating, spray, flow-coating or wiping.

15. (canceled)

16. A method for coating a surface comprising the steps of: (i) providing a surface (ii) depositing on the surface provided in step (i) the suspension of claim 10 by dip-coating, spin-coating, spray, flow-coating or wiping.

17. The method according to claim 2, wherein the ratio X/Y of the diameters is between 3 and 10.

18. The method according to claim 3, wherein the at least one inorganic material is silicon, aluminium, titanium, zinc, germanium, and/or the oxides and/or the alloys thereof.

19. The method according to claim 4, wherein the reactive function is an isocyanate function.

20. The method according to claim 9, wherein the fluorinated molecule is of following formula: ##STR00009## where R is a (C.sub.1-C.sub.4) alkyl group.

Description

DESCRIPTION OF THE FIGURES

[0177] FIG. 1: NP15s in suspension in toluene, butyl acetate and MIBK according to Example 2.

[0178] FIG. 2: NP50s in suspension in toluene, butyl acetate and MIBK according to Example 2.

[0179] FIG. 3: NP100s in suspension in toluene, butyl acetate and MIBK according to Example 2.

[0180] FIG. 4: NP50s and NP15s in suspension in MIBK, without a drying step of the NPs according to Example 3.2.

[0181] FIG. 5: SEM images of the formulation of 130 nm RNPs in toluene according to Example 4.1.

[0182] FIG. 6: suspensions of RNP80s derived from different synthesis modes according to Example 6, in different solvents.

[0183] FIG. 7: SEM images of RNP80s synthesised in MIBK according to Example 13.

EXAMPLES

Example 1: Dispersion of Dry Silica Nanoparticles in a Protic Solvent

[0184] 1—Commercial silica particles (Nissan-Chem) of nominal diameter 15 nm, 50 nm and 100 nm (respectively NP15, NP50 and NP100) in suspension in IPA at 300 g/L were diluted in IPA to obtain a concentration of 1 g/L. These particles were therefore always kept in liquid medium. [0185] 2—In parallel, silica nanoparticles of nominal diameter 15 nm, 50 nm and 100 nm initially in suspension in isopropanol (IPA) were dried with a vane pump and resuspended in isopropanol (IPA) at a concentration of 1 g/L.

[0186] The solutions were agitated with a magnetic agitator, sonicated for 30 minutes, then agitated 30 minutes with the magnetic agitator to disperse the nanoparticles and prevent aggregates.

[0187] The mean hydrodynamic diameter of the particles obtained at 1) and 2) was measured by dynamic light scattering using Zetasizer Nano Series ZS apparatus by Malvern.

TABLE-US-00001 Mean hydrodynamic diameter 1- Particles before drying NP15 38 ± 24 nm NP50 74 ± 1 nm NP100 123 ± 1 nm 2- Dried, resuspended particles NP15 6082 ± 4900 nm NP50 83 ± 1 nm NP100 130 ± 1 nm

[0188] The mean diameter of the particles before drying is close to their nominal value (to within the hydrodynamic radius). DLS is therefore a suitable method for measuring the diameter of the nanoparticles and to estimate their dispersion.

[0189] After drying and resuspending in IPA, the mean diameter of NP50s and NP100s is close to their nominal value (to within the hydrodynamic radius) and is similar to the diameter obtained from particles which had remained in liquid medium.

[0190] In Case 2, resuspending in IPA of NP15s leads to very high measurements of mean hydrodynamic diameter (>6000 nm). Redispersion is poor on account of aggregates that have formed. It was not possible to remove these aggregates by agitation and sonication even when using a solvent promoting dispersion of silica nanoparticles (IPA).

[0191] This example shows that aggregation of particles increases with a decrease in their diameter and shows the difficulty and even impossibility of deagglomerating nanoparticles of small diameter. This justifies the maintaining in liquid medium to promote good dispersion of nanoparticles of diameter less than 50 nm.

Example 2: Dispersion of Dry Particles in Aprotic Solvents

[0192] Silica nanoparticles of nominal diameter 15 nm, 50 nm and 100 nm initially in suspension in isopropanol (IPA) were dried with a vane pump and redispersed in toluene, butyl acetate (BuAc) or methyl isobutyl ketone (MIBK) at a concentration of 20 g/L.

[0193] The suspensions were sonicated for 30 minutes, agitated 1 h and left to stand for 60 hours.

[0194] The stability of the suspensions was evaluated visually by observing settling of the particles and the presence or absence of a deposit at the bottom of the container (FIG. 1, FIG. 2 and FIG. 3). Irrespective of the solvent used, the NP15s settle to form a deposit at the bottom of the bottle (see FIG. 1).

[0195] NP50s fully settle in toluene. Settling is partial in butyl acetate and MIBK. Nevertheless, a deposit is seen at the bottom of the bottles (see FIG. 2).

[0196] NP100s settle in toluene and butyl acetate. The suspension of NP100s is stable in MIBK (see FIG. 3).

[0197] This example shows the difficulty of resuspending nanoparticles of diameter ≤50 nm in aprotic solvents. This justifies maintaining thereof in liquid medium to promote good dispersion of nanoparticles of diameter less than or equal to 50 nm.

Example 3: Substitution of a Polar Solvent by an Apolar Solvent Keeping the Silica Nanoparticles in Liquid Medium

Example 3.1: Nanoparticles (NPs) of Diameter 15 nm

[0198] A 500 mL three-necked flask was charged with: [0199] 10 mL of suspension of silica NP15s at 300 g/L in IPA [0200] 130 mL of solvent A

[0201] Solvent A was either toluene, or butyl acetate or methyl isobutyl ketone (MIBK). 90 mL of solvent were distilled to remove IPA and part of solvent A. In this manner the NP15s were moved from a suspension in a protic solvent to a suspension in an aprotic solvent without a desolvation step.

Example 3.2: Particles of Diameter 50 nm

[0202] A 500 mL three-necked flask was charged with: [0203] 10 mL of suspension of silica NP50s at 300 g/L in IPA [0204] 150 mL of solvent A

[0205] Solvent A was either toluene, or butyl acetate or methyl isobutyl ketone (MIBK).

[0206] 100 mL of solvent were distilled to remove IPA and part of solvent A. In this manner, the NP50s were moved from a suspension in a protic solvent to a suspension in an aprotic solvent without a desolvation step.

[0207] This example allows the initially protic solvent to be fully replaced by an aprotic solvent while remaining in liquid medium.

[0208] The colloidal suspension of NP15s and NP50s thus obtained were homogeneous and showed no sign of settling, an indication of good dispersion of the nanoparticles.

[0209] The suspensions derived from Examples 3.1. and 3.2. were diluted in MIBK at 20 g/L (see FIG. 4). After 60 hours, no settling was visible. The suspension is therefore stable.

[0210] Compared with Example 2, the suspensions of NP50s and NP15s in MIBK are less turbid and do not show any deposit at the bottom of the flask. The maintaining in liquid medium is therefore essential to maintain good dispersion of particles of diameter less than 50 nm.

Example 4: Synthesis of RNPs

Example 4.1: RNP130s Synthesised in Toluene

[0211] Silica NP100s in suspension IPA were suspended in toluene following the protocol described in Example 3 to obtain a stable dispersion of the nanoparticles.

[0212] The adhesion promoter used was an isocyanate silane (CAS 15396-00-6). It was added in excess to the reaction medium. The reaction was conducted for 15 h at ambient temperature to obtain grafting of the molecule onto the NP100s.

[0213] The excess isocyanate silane that had not reacted was removed by centrifugations, particle sedimentation and successive washings with toluene. The particles were resuspended in toluene. The NP100s functionalised by isocyanate silane were added to a suspension of silica NP15s in toluene obtained such as described in Example 3. The reaction medium was brought to 120° C. overnight to graft the silica NP15s onto the NP100s carrying reactive functions.

[0214] This protocol allows the obtaining of RNP130s in a mixture with non-grafted NP15s in suspension in toluene. At no time in this process are the NP15 particles desolvated.

[0215] SEM images of the formulations applied to the surfaces confirm the presence of dispersed raspberry nanoparticles (see FIG. 5).

Example 4.2: RNP80s Synthesised in MIBK

[0216] Silica NP50s in suspension in IPA were placed in suspension in MIBK following the protocol described in Example 3.2. to obtain a stable dispersion of the nanoparticles.

[0217] Isocyanate silane (CAS 15396-00-6) was added in stoichiometric amount to the suspension of silica NP50s in MIBK. The reaction was conducted for 15 h at ambient temperature to obtain grafting of the molecule onto the NP50s.

[0218] The NP50s functionalised by the isocyanate silane were then added to a suspension of silica NP15s in MIBK obtained such as described in Example 3.1. The reaction medium was brought to 110° C. overnight to graft the silica NP15s onto the NP50s carrying reactive functions.

[0219] This protocol allows the obtaining of RNP80s in a mixture with non-grafted NP15s in suspension in MIBK. At no time of this process are the NP15 particles desolvated.

Example 5: Syntheses of RNP80s. Comparison of the Method of the Invention with the Prior Art Method Described in Application WO2015177229

Example 5.1: RNP80s Synthesised with the Method of the Invention

[0220] Isocyanate silane (CAS 15396-00-6) was added in stoichiometric amount to a suspension of silica NP50s in PMA. The reaction was conducted for 15 h at 30° C. to obtain grafting of the molecule onto the NP50s.

[0221] The NP50s functionalised by isocyanate silane were then added to a suspension of silica NP15s in PMA. The reaction medium was brought to 80° C. for 24 h to graft the silica NP15s onto the previously functionalised NP50s.

[0222] This protocol allows the obtaining of RNP80s in a mixture with non-grafted NP15s in suspension in PMA according to the protocol of the invention.

[0223] At no time in this process were the NP15 particles desolvated.

Example 5.2: RNP80s Synthesised from Dry Particles

[0224] RNP80s were synthesised under the same conditions as described in Example 11.3. of application WO2015177229.

[0225] In a 100 mL anhydrous round-bottom flask equipped with a coolant under argon, 1 g of dry NP50s were placed in suspension in 30 mL of extra-dry toluene. The mixture was immersed in a sonication bath for 30 min then placed under magnetic agitation. 600 mg isocyanate silane (CAS 15396-00-6) were added using a syringe and the reaction medium was left under agitation overnight at ambient temperature. The mixture was centrifuged and the supernatant discarded. This step was carried out 3 times. The particles were then vacuum dried at 50° C. for several hours.

[0226] A 50 mL anhydrous round-bottom flask equipped with a coolant was charged under argon with 0.93 g of dry functionalised NP50s, 20 mL of extra-dry toluene and 0.67 g of dry NP15s. After sonication, the reaction medium was left under agitation and under reflux for 15 hours. This protocol allows the obtaining of RNP80s in a mixture with non-grafted NP15s in suspension in toluene, following the protocol described in WO2015177229.

[0227] This suspension was obtained from dry NP50s and NP15s.

Example 6: Stability of RNP80 Suspensions

[0228] Five suspensions were prepared from RNP80s derived from Examples 5.1 and 5.2: [0229] 1. Particles derived from 5.2 diluted at 20 g/L in 100% of toluene. [0230] 2. Particles derived from Example 5.2 vacuum dried and then dispersed at 20 g/L in 100% of toluene. [0231] 3. Particles derived from Example 5.2 diluted at 20 g/L in 20% of toluene (derived from synthesis) and 80% of PMA [0232] 4. Particles derived from Example 5.2 vacuum dried and then dispersed at 20 g/L in 100% of PMA [0233] 5. Particles derived from Example 5.1 diluted at 20 g/L in 100% of PMA

[0234] Suspensions 1 to 5 were sonicated and agitated then left to settle at ambient temperature for 15 days (see FIG. 6).

[0235] Suspensions 1 to 4, obtained with RNP80s synthetized from dry NP15s and dry NP50s are cloudy and a particle sedimentation layer can be seen as the bottom of the pill bottle. This indicates the presence of aggregates of large size which do not allow a colloidal suspension to be obtained. These suspensions are therefore not stable. As shown in Example 2, the aggregates are mostly derived from NP15s which were unable to be redispersed.

[0236] On the contrary, formulation 5 is limpid and no deposit can be seen at the bottom of the pill bottle, indicating that it does not settle. It is obtained with RNP80s synthesised with the method of the invention in which the NP15s are never desolvated. With this method, it is therefore possible to obtain a colloidal suspension not containing aggregates of large-size particles.

[0237] This experiment confirms that the suspensions obtained with RNP80s synthesised with the method of the invention, not requiring desolvation at any time of NP15s, are structurally different since much more stable than the suspensions obtained with the method described in WO2015177229.

Example 7: Syntheses of RNP130s. Comparison of the Method of the Invention with the Prior Art Method Described in Application WO2015177229

Example 7.1: RNP130s Synthesised with the Method of the Invention

[0238] Isocyanate silane (CAS 15396-00-6) was added in stoichiometric amount to a suspension of silica NP100s in PMA. The reaction was conducted for 15 h at 30° C. to obtain grafting of the molecule onto the NP100s.

[0239] The NP100s functionalised by isocyanate silane were added to a suspension of silica NP15s in PMA. The reaction medium was brought to 80° C. for 24 h to graft the silica NP15s onto the previously functionalised NP100s.

[0240] This protocol allows the obtaining of RNP130s in a mixture with non-grafted NP15s in suspension in PMA, following the protocol of the invention.

[0241] At no time of this process are the NP15 particles desolvated.

Example 7.2: RNP130s Synthesised from Dry Particles

[0242] RNP130s were synthesised by reproducing Example 11.3. of patent application WO2015177229. A 100 mL anhydrous round-bottom flask equipped with a coolant was charged under argon with dry NP100s in extra-dry toluene. The mixture was immersed in a sonication bath for 30 min then placed under magnetic agitation. Isocyanate silane (CAS 15396-00-6) was added in excess using a syringe and the reaction medium was left under agitation overnight at ambient temperature. The mixture was centrifuged and the supernatant discarded. This step was performed 3 times. The particles were then vacuum dried at 50° C. for several hours.

[0243] A 50 mL anhydrous round-bottom flask equipped with a coolant was charged under argon with the dry functionalised NP100s, extra-dry toluene and the dry NP15s. After sonication, the reaction medium was left under agitation 15 hours under reflux. This protocol allows the obtaining of RNP130s in a mixture with non-grafted NP15s in suspension in toluene, as described in WO2015177229.

[0244] This suspension was obtained from dry NP100s and NP15s.

Example 8: Stability of Suspensions of RNP130s

[0245] Five suspensions were prepared from the RNP130s obtained in Examples 7.1 and 7.2: [0246] 1. Particles derived from Example 7.2 diluted at 20 g/L in 100% of toluene. [0247] 2. Particles derived from Example 7.2 vacuum dried and dispersed at 20 g/L in 100% of toluene. [0248] 3. Particles derived from Example 7.2 diluted at 20 g/L in 20% of toluene (derived from synthesis) and 80% of PMA. [0249] 4. Particles derived from Example 7.2 vacuum dried then dispersed at 20 g/L in 100% of PMA. [0250] 5. Particles derived from Example 7.1 diluted at 20 g/L in 100% of PMA.

[0251] The suspensions were sonicated, agitated and left to stand for a few minutes.

[0252] Formulations 1 and 2 in toluene, obtained with RNP130s synthesised from dry NP15s and dry NP100s settle after a few minutes. The formulations are therefore not stable.

[0253] Formulations 3 and 4 in PMA, obtained with RNP130s synthesised from dry NP15s and dry NP100s are turbid. This is due to the presence of large-diameter aggregates in the formulation. As shown in Example 2, the aggregates are mostly derived from NP15s which were unable to be redispersed.

[0254] On the contrary, formulation 5 is limpid and not deposit can be seen at the bottom of the pill bottle. The particles in suspension are therefore of small diameter. There are no aggregates. This experiment confirms that the suspensions obtained with RNP130s synthesised with the method of the invention, at no time requiring desolvation of NP15s, are structurally different being more limpid than the suspensions obtained with the method described in WO2015177229.

Example 9: Measurements of the Mean Hydrodynamic Diameter of RNPs

[0255] RNP80s were synthesised as a variant to Example 5.1, whereby the mixture of particles was heated to 110° C. in the presence of DOTL.

[0256] RNP130s were synthesised in toluene according to Example 4.1.

[0257] The formulations were diluted in isopropanol so that the proportion of synthesis solvent (PMA or toluene) was less than 5% by volume.

[0258] The hydrodynamic radii of the particles were measured by dynamic light scattering using a Zetasizer (Malvern).

TABLE-US-00002 Theoretical Mean hydrodynamic Polydispersity diameter diameter index RNP80  80 nm 128 nm 0.071 RNP130 130 nm 185 nm 0.165

[0259] Distribution of the hydrodynamic diameters of the raspberry nanoparticles RNP80 and RNP130 is monodisperse, as shown by the low polydispersity indices. The hydrodynamic diameter values obtained, comprising the diameter of the particle and the solvation layer thereof, tally with expected values. These two results show that the diameter of the RNPs is twice smaller than the nominal diameter of the particles, which is characteristic of the absence of aggregates.

Example 10: Functionalisation of RPN130s by a Perfluoropolyether (PFPE) Silane

[0260] A PFPE trimethoxysilane of formula

##STR00006##

was dissolved in isopropanol containing raspberry nanoparticles 130 nm in diameter. The RNP130s were obtained by covalent grafting of NP15s onto NP100s following the protocol in Example 4.1. The mixture containing excess of the silane molecule was left under agitation overnight at ambient temperature.

[0261] The excess non-reacted silane was removed by centrifugations, particle sedimentation, and successive washings with Novec 7200 fluorinated solvent. The particles were resuspended in Novec 7200.

[0262] In this manner the particles are dispersed, are hydrophobic and always remain in liquid medium when removing the excess molecules and when changing the solvent.

Example 11: Functionalisation of RNP80s by a Perfluoropolyether (PFPE) Silane

[0263] A hydrofluorolefin, a mixture of the isomers of 1,2,3,3,4,4,5,5,6,6,7,7,7-tridecafluoro-1-methoxy-Hept-1-ene [69296-04-04] (HFO), was added to the suspension of RNP80s and NP15s obtained in Example 4.2, to replace MIBK. The MIBK was removed by centrifugation to cause sedimentation of the particles and resuspension thereof to obtain a suspension of RNP80s and NP15s in HFO

[0264] A PFPE trimethoxysilane of formula:

##STR00007##

was added in stoichiometric amount to the suspension of nanoparticles in HFO.

[0265] The mixture was left under agitation overnight at 110° C.

[0266] This example allows the obtaining of hydrophobic, dispersed particles which remain in liquid medium throughout their preparation time and storage thereof.

Example 12: Application of RNP80s to a Surface

[0267] RNP80s obtained in Example 4.2 were used to coat surfaces. The formulation was applied in 3 spray operations onto a glass surface and left to dry for one minute. The surfaces obtained were superhydrophilic.

[0268] After vapour phase hydrophobization by the molecule described in Example 5, the surfaces became superhydrophobic (AC.sub.H2O=152°, tilt=8°).

Example 13: Application of Hydrophobic RNP130s to a Surface

[0269] The hydrophobic RNP130s obtained in Example 10 were used to coat surfaces. The formulation was applied by dip-coating onto a glass surface and left to dry for one minute. The surfaces obtained are superhydrophobic (AC.sub.H2O=156′).

Example 14: Application of Hydrophobic RNP80s to a Surface

[0270] The hydrophobic RNP80s obtained in Example 11 were used to coat surfaces. The formulation was applied by spraying onto a glass surface and left to dry for one minute. The surfaces obtained are superhydrophobic (ACH2O=153°, tilt angle=1°). The RNP80s deposited on the surface can be seen in FIG. 7.