(19)
(11)EP 3 092 283 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
22.07.2020 Bulletin 2020/30

(21)Application number: 14824071.6

(22)Date of filing:  19.12.2014
(51)International Patent Classification (IPC): 
C09K 11/02(2006.01)
C09K 11/56(2006.01)
C09K 11/70(2006.01)
C09K 11/54(2006.01)
(86)International application number:
PCT/GB2014/053775
(87)International publication number:
WO 2015/101777 (09.07.2015 Gazette  2015/27)

(54)

SURFACE-MODIFIED NANOPARTICLES

OBERFLÄCHENMODIFIZIERTE NANOPARTIKEL

NANOPARTICULES À SURFACES MODIFIÉES


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 06.01.2014 US 201461924060 P

(43)Date of publication of application:
16.11.2016 Bulletin 2016/46

(73)Proprietor: Nanoco Technologies Ltd
Manchester M13 9NT (GB)

(72)Inventors:
  • VO, Cong-Duan
    Manchester M15 5JP (GB)
  • PANG, Hao
    Manchester M33 6NF (GB)
  • NAASANI, Imad
    Manchester M20 2UL (GB)

(74)Representative: Dauncey, Mark Peter 
Marks & Clerk LLP 1 New York Street
Manchester M1 4HD
Manchester M1 4HD (GB)


(56)References cited: : 
US-A1- 2010 123 155
US-A1- 2011 306 079
US-B2- 7 588 828
US-A1- 2010 193 767
US-A1- 2013 190 493
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    CROSS-REFERENCE TO RELATED APPLICATIONS:



    [0001] This application claims the benefit of U.S. Provisional Application No. 61/924,060 filed on January 6, 2014.

    STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT: Not Applicable


    BACKGROUND OF THE INVENTION


    1. Field of the Invention.



    [0002] The present invention generally relates to nanoparticles. More particularly, it relates to methods for modifying the external surface of semiconductor nanoparticles.

    2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98.


    Nanoparticles



    [0003] There has been substantial interest in the preparation and characterization of compound semiconductors consisting of particles with dimensions in the order of 2-100 nm, often referred to as quantum dots (QDs) and/or nanoparticles. Studies in this field have focused mainly on the size-tunable electronic, optical and chemical properties of nanoparticles. Semiconductor nanoparticles are gaining interest due to their potential in commercial applications as diverse as biological labeling, solar cells, catalysis, biological imaging, and light-emitting diodes.

    [0004] Two fundamental factors (both related to the size of the individual semiconductor nanoparticles) are primarily responsible for their unique properties. The first is the large surface-to-volume ratio: as a particle becomes smaller, the ratio of the number of surface atoms to those in the interior increases. This leads to the surface properties playing an important role in the overall properties of the material. The second factor is that, for many materials (including semiconductor nanoparticles), the electronic properties of the material change with particle size. Moreover, because of quantum confinement effects, the band gap typically becomes gradually larger as the size of the nanoparticle decreases. This effect is a consequence of the confinement of an "electron in a box," giving rise to discrete energy levels similar to those observed in atoms and molecules, rather than a continuous band as observed in the corresponding bulk semiconductor material. Semiconductor nanoparticles tend to exhibit a narrow bandwidth emission that is dependent upon the particle size and composition of the nanoparticle material. The first excitonic transition (band gap) increases in energy with decreasing particle diameter.

    [0005] Semiconductor nanoparticles of a single semiconductor material, referred to herein as "core nanoparticles," along with an outer organic passivating layer, tend to have relatively low quantum efficiencies due to electron-hole recombination occurring at defects and dangling bonds situated on the nanoparticle surface that can lead to non-radiative electron-hole recombinations.

    [0006] One method to eliminate defects and dangling bonds on the inorganic surface of the nanoparticle is to grow a second inorganic material (typically having a wider band-gap and small lattice mismatch to that of the core material) on the surface of the core particle to produce a "core-shell" particle. Core-shell particles separate carriers confined in the core from surface states that would otherwise act as non-radiative, recombination centers. One example is ZnS grown on the surface of CdSe cores. Another approach is to prepare a core-multi shell structure where the "electron-hole" pair is completely confined to a single shell layer consisting of a few monolayers of a specific material such as a quantum dot-quantum well structure. Here, the core is typically a wide bandgap material, followed by a thin shell of narrower bandgap material, and capped with a further wide-bandgap layer. An example is CdS/HgS/CdS grown using substitution of Hg for Cd on the surface of the core nanocrystal to deposit just a few monolayers of HgS that is then overgrown by monolayers of CdS. The resulting structures exhibit clear confinement of photo-excited carriers in the HgS layer.

    [0007] The most-studied and prepared semiconductor nanoparticles to date have been so-called "II-VI materials," for example, ZnS, ZnSe, CdS, CdSe, and CdTe, as well as core-shell and core-multi shell structures incorporating these materials. However, cadmium and other restricted heavy metals used in conventional QDs are highly toxic elements and are of major concern in commercial applications. The inherent toxicity of cadmium-containing QDs prevents their use in applications involving animals or humans. For example, recent studies suggest that QDs made of a cadmium chalcogenide semiconductor material can be cytotoxic in a biological environment unless protected. Specifically, oxidation or chemical attack through a variety of pathways can lead to the formation of cadmium ions on the QD surface that can be released into the surrounding environment. Although surface coatings such as ZnS can significantly reduce the toxicity, it may not completely eliminate it because QDs can be retained in cells or accumulated in the body for a long period of time, during which their coatings may undergo some form of degradation that exposes the cadmium-rich core.

    [0008] The toxicity affects not only the progress of biological applications but also other applications including optoelectronic and communication because heavy metal-based materials are widespread in many commercial products including household appliances such as IT and telecommunication equipment, lighting equipment, electrical and electronic tools, toys, leisure and sports equipment. Legislation to restrict or ban certain heavy metals in commercial products has been already passed in many jurisdictions throughout the world. For example, European Union Directive 2002/95/EC, known as the "Restrictions on the use of Hazardous Substances in electronic equipment" (or RoHS), bans the sale of new electrical and electronic equipment containing more than certain levels of lead, cadmium, mercury, hexavalent chromium along with polybrominated biphenyl (PBB) and polybrominated diphenyl ether (PBDE) flame retardants. This law requires manufacturers to find alternative materials and develop new engineering processes for the creation of common electronic equipment. In addition, on 1 June 2007, a European Community Regulation came into force concerning chemicals and their safe use (EC 1907/2006). This Regulation deals with the Registration, Evaluation, Authorization and Restriction of Chemical substances and is known as "REACH". The REACH Regulation imposes greater responsibility on industry to manage the risks from chemicals and to provide safety information on the substances. It is anticipated that similar laws and regulations will be extended worldwide including China, Korea, Japan and the U.S. Thus, there is significant economic incentive to develop alternatives to Group II-VI QD materials.

    [0009] Other semiconductor nanoparticles that have generated considerable interest include nanoparticles incorporating Group III-V and Group IV-VI materials, such as GaN, GaP, GaAs, InP, and InAs. Due to their increased covalent nature, III-V and IV-VI highly crystalline semiconductor nanoparticles are more difficult to prepare and much longer annealing times are usually required. However, there are now reports of III-VI and IV-VI materials being prepared in a similar manner to that used for the II-VI materials. Methods for synthesizing core and core-shell nanoparticles are disclosed, for example, in United States Patent Nos. 6,379,635, 7,803,423, 7,588,828, 7,867,556, and 7,867,557.

    Surface Modification



    [0010] Many applications of nanoparticles require that the semiconductor nanoparticle be compatible with a particular medium. For example, some biological applications such as fluorescence labeling, in vivo imaging and therapeutics require that the nanoparticles be compatible with an aqueous environment. For other applications, it is desirable that the nanoparticles be dispersible in an organic medium such as aromatic compounds, alcohols, esters, or ketones. For example, ink formulations containing semiconductor nanoparticles dispersed in an organic dispersant have been proposed for use in fabricating thin films of semiconductor materials for photovoltaic (PV) devices.

    [0011] A particularly attractive potential field of application for semiconductor nanoparticles is in the development of next generation light-emitting diodes (LEDs). LEDs are becoming increasingly important in, for example, automobile lighting, traffic signals, general area lighting, and liquid crystal display (LCD) backlighting and display screens. Nanoparticle-based light-emitting devices have been made by embedding semiconductor nanoparticles in an optically clear (or sufficiently transparent) LED encapsulation medium, typically a silicone or an acrylate, which is then placed on top of a solid-state LED. The use of semiconductor nanoparticles potentially has significant advantages over the use of more conventional phosphors. For example, semiconductor nanoparticles provide the ability to alter the emission spectrum of an LED-based illumination device. Semiconductor nanoparticles also have strong absorption properties and low scattering when the nanoparticles are well dispersed in a medium. The nanoparticles may be incorporated into an LED encapsulating material. It is important that the nanoparticles be well dispersed in the encapsulating material to prevent loss of quantum efficiency. Methods developed to date are problematic because the nanoparticles tend to agglomerate when formulated into conventional LED encapsulant materials, thereby reducing the optical performance of the nanoparticles. Moreover, even after the nanoparticles have been incorporated into the LED encapsulant, oxygen can still migrate through the encapsulant to the surfaces of the nanoparticles, which can lead to photo-oxidation and, as a result, a drop in quantum yield (QY).

    [0012] The compatibility of a nanoparticle with a medium as well as the nanoparticle's susceptibility to agglomeration, photo-oxidation and/or quenching, is mediated largely by the surface composition of the nanoparticle. The coordination about the final inorganic surface atoms in any core, core-shell or core-multi shell nanoparticle is incomplete, with highly reactive "dangling bonds" on the surface, which can lead to particle agglomeration. This problem may be overcome by passivating (capping) the "bare" surface atoms with protective organic groups, referred to herein as capping ligands or a capping agent. The capping or passivating of particles not only prevents particle agglomeration from occurring, the capping ligand also protects the particle from its surrounding chemical environment and provides electronic stabilization (passivation) to the particles, in the case of core material. The capping ligand is usually a Lewis base bound to surface metal atoms of the outermost inorganic layer of the particle. The nature of the capping ligand largely determines the compatibility of the nanoparticle with a particular medium. These capping ligand are usually hydrophobic (for example, alkyl thiols, fatty acids, alkyl phosphines, alkyl phosphine oxides, and the like). Thus, the nanoparticles are typically dispersed in hydrophobic solvents, such as toluene, following synthesis and isolation of the nanoparticles. Such capped nanoparticles are typically not dispersible in more polar media.

    [0013] For many commercial applications of QDs it is desirable to incorporate the QDs in an encapsulating material, such as an LED encapsulant or a polymer. In such situations it is important that the QDs remain as fully mono-dispersed as possible and without significant loss of quantum efficiency. However, QDs can agglomerate when formulated into encapsulant matrices, reducing the optical performance of the quantum dots. Moreover, once the quantum dots are incorporated into the encapsulant, oxygen can migrate through the encapsulant to the surfaces of the quantum dots, which can lead to photo-oxidation and, as a result, a drop in quantum yield (QY).

    [0014] One way of addressing the problem of oxygen migration to the QDs has been to incorporate the QDs into a medium having low oxygen permeability to form "beads" of such a material containing QDs dispersed within the bead. The QD-containing beads can then be dispersed within an LED encapsulant. Examples of such bead materials include polymers having low oxygen permeability. Such beads are described in U.S. Pub. No. 2011/0068322 and U.S. Pub. No. 2010/0123155. However, polymers that are highly impermeable to oxygen often are not the most compatible with the QDs. It has been found that QDs are generally more compatible with hydrophobic resins, such as acrylates, compared to more hydrophilic resins, such as epoxies. Thus, polymer films made of QDs dispersed in acrylates tend to have higher initial quantum yields (QYs) than QD films using hydrophilic resins such as epoxy resins. The higher initial QY may be due to the compatibility of the QD with the hydrophobic polymer. However, films of hydrophobic resins, such as acrylates, tend to be permeable to oxygen, while epoxy resin polymers and similar hydrophilic polymers tend to be better at excluding oxygen. Thus, the QY of QDs in hydrophobic polymers can decrease precipitously over time due to oxidation.

    [0015] Attempts have been made to surface modify nanoparticles. For example, US 2013/190493 A1 describes associating ligand interactive agents with the surface of a nanoparticle, cross-linking to produce a sheath and then associating surface modifying ligands with the ligand interactive agents to impart particular solubility and/or compatibility properties. US 2010/193767 A1 describes encapsulating nanoparticles in a self-assembled layer of amphiphilic, cross-linkable, multi-unsaturated fatty acids and their derivatives. US 2011/306079 A1 describes a number of methods for making watersoluble nanoparticles comprising core/shell nanoparticle coated with a surface layer comprising hydrophilic ligands.

    [0016] Thus, there is a need in the art for nanoparticles that are compatible with polymers that are effective at excluding oxygen, such as epoxides while maintaining the integrity and photo-physical properties of the nanoparticle. The present invention is directed to overcoming, or at least reducing, the effects of one or more of the problems discussed above.

    BRIEF SUMMARY OF THE INVENTION



    [0017] Disclosed herein are surface-modified nanoparticles. The surfaces of the nanoparticles are modified with amphiphilic block copolymers, the block copolymer comprising a polyalkylene glycol-poly(alkylene sulfide) block copolymer or a first block that is a reversible addition fragmentation chain transfer agent (RAFT-CTA) and a second block that is a polyalkylene glycol. The surface modification renders the QDs more compatible with oxygen-excluding matrices, such as epoxy resins, polyurethane resins, polyester resins or any hydrophilic inorganic/organic hybrid resins such as (meth)acrylate-functionalized, polyhedral, oligomeric, silsesquioxane (POSS).

    [0018] An aspect of the present invention provides a surface-modified nanoparticle comprising: a nanoparticle having a core and an external surface; a plurality of amphiphilic block copolymers on the external surface, wherein the block copolymer comprises a polyalkylene glycol-poly(alkylene sulfide) block copolymer or a first block that is a reversible addition fragmentation chain transfer agent (RAFT-CTA) and a second block that is a polyalkylene glycol. The amphiphilic block copolymer may be adsorbed on the external surface of the nanoparticle. The nanoparticle may be a metal oxide. The nanoparticle may be selected from the group consisting of: iron oxides, titanium oxides, zinc oxide, zirconium oxide, and aluminum oxide. The nanoparticle may be a magnetic nanoparticle. The nanoparticle may be a gold nanoparticle. The nanoparticle may be a silver nanoparticle. The nanoparticle may comprise a luminescent semiconductor material. The nanoparticle may be selected from the group consisting of: CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, InP, InAs, InSb, AIP, AIS, AlAs, AlSb, GaN, GaP, GaAs, GaSb, PbS, PbSe, Si, Ge and combinations thereof. The nanoparticle may be a cadmium-free nanoparticle. The nanoparticle may be a core-shell nanoparticle wherein the core is substantially comprised of a first material and the shell is substantially comprised of a second material different from the first material. The core-shell nanoparticle may comprise a plurality of shells with adjacent shells substantially comprised of different materials. The core-shell nanoparticle may comprise a shell material selected from the group consisting of ZnS, ZnO, MgS, MgSe, MgTe and GaN. The core-shell nanoparticle may comprise a core comprised substantially of InP, first shell comprised substantially of ZnS, and a second shell comprised substantially of ZnO. The block copolymer may comprise a block that has affinity for an epoxide resin. The block copolymer may have the general formula

    where m and n are integers. The block copolymer may have the general formula

    where n is a positive integer.

    [0019] A further aspect of the present invention provides a method for modifying the surface of nanoparticles comprising: preparing a solution of nanoparticles in a solvent; exposing the nanoparticle solution to a solution of an amphiphilic block copolymer in a solvent, wherein the block copolymer comprises a polyalkylene glycol-poly(alkylene sulfide) block copolymer or a first block that is a reversible addition fragmentation chain transfer agent (RAFT-CTA) and a second block that is a polyalkylene glycol. The solvent may be toluene. Exposing the nanoparticle solution to a solution of an amphiphilic block copolymer may be performed under an inert atmosphere. Exposing the nanoparticle solution to a solution of an amphiphilic block copolymer may be accomplished with an excess of amphiphilic block copolymer. The method may further comprise: adding epoxy resin components to the mixture of nanoparticles and amphiphilic block copolymer. The method may further comprise: depositing a film of the nanoparticle-containing resin on a substrate.

    [0020] The foregoing summary is not intended to summarize each potential embodiment or every aspect of the present disclosure.

    BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)



    [0021] Figure 1 shows emission spectra of unmodified QDs (A) and PEG2000-PPS10-treated QDs (B).

    DETAILED DESCRIPTION OF THE INVENTION



    [0022] One aspect of the present invention is a nanoparticle that is rendered compatible with oxygen-excluding matrices, such as epoxy resins. It should be noted that the terms quantum dot, QD, nanoparticle, and nanocrystal are used interchangeably herein to mean nanoparticles such as those described in the Background section, above. The instant disclosure is not limited to any particular type of nanoparticle. Nanoparticles of metal oxides (for example, iron oxides, magnetic nanoparticles, titanium oxides, zinc oxide, zirconium oxide, aluminum oxide), gold nanoparticles and silver nanoparticles can be all treated and surface-modified using the methods described herein. In preferred embodiments, the nanoparticle may include a semiconductor material, preferably a luminescent semiconductor material. The semiconductor material may incorporate ions from any one or more of Groups 2 to 16 of the periodic table, and may include binary, ternary and quaternary materials, that is, materials incorporating two, three or four different ions respectively. By way of example, the nanoparticle may incorporate a semiconductor material, such as, but not limited to, CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, InP, InAs, InSb, AIP, AIS, AlAs, AlSb, GaN, GaP, GaAs, GaSb, PbS, PbSe, Si, Ge and combinations thereof. According to various embodiments, nanoparticles may have diameters of less than around 100 nm, less than around 50 nm, less than around 20 nm, less than around 15 nm and/or may be in the range of around 2 to 10 nm in diameter.

    [0023] Nanoparticles that include a single semiconductor material, e.g., CdS, CdSe, ZnS, ZnSe, InP, GaN, etc. may have relatively low quantum efficiencies because of non-radiative electron-hole recombination that occurs at defects and dangling bonds at the surface of the nanoparticles. In order to address these issues in some measure, the nanoparticle cores may be at least partially coated with one or more layers (also referred to herein as "shells") of a material different than that of the core, for example a different semiconductor material than that of the "core." The material included in the (or each) shell may incorporate ions from any one or more of Groups 2 to 16 of the periodic table. When a nanoparticle has two or more shells, each shell may be formed of a different material. In an exemplary core/shell material, the core is formed from one of the materials specified above and the shell includes a semiconductor material of larger band-gap energy and similar lattice dimensions as the core material. Exemplary shell materials include, but are not limited to, ZnS, ZnO, MgS, MgSe, MgTe and GaN. An exemplary multi-shell nanoparticle is InP/ZnS/ZnO. The confinement of charge carriers within the core and away from surface states provides nanoparticles of greater stability and higher quantum yield.

    [0024] While the disclosed methods are not limited to any particular nanoparticle material, an advantage of the disclosed methods is that these methods can be used to modify the surface of cadmium-free nanoparticles, that is, nanoparticles comprising materials that do not contain cadmium. It has been found that it is particularly difficult to modify the surface of cadmium-free nanoparticles. Cadmium-free nanoparticles readily degrade when prior art methods, such as prior art ligand exchange methods, are used to modify the surface of such cadmium-free nanoparticles. For example, attempts to modify the surface of cadmium-free nanoparticles have been observed to cause a significant decrease in the luminescence quantum yield (QY) of such nanoparticles. Examples of cadmium free nanoparticles include nanoparticles comprising semiconductor materials, e.g., ZnS, ZnSe, ZnTe, InP, InAs, InSb, AIP, AIS, AlAs, AlSb, GaN, GaP, GaAs, GaSb, PbS, PbSe, Si, Ge, and particularly, nanoparticles comprising cores of one of these materials and one or more shells of another of these materials.

    [0025] Typically, as a result of the core and/or shelling procedures employed to produce the core, core/shell or core/multishell nanoparticles, the nanoparticles are at least partially coated with a surface binding ligand such as myristic acid, hexadecylamine and/or trioctylphosphineoxide. Such ligands are typically derived from the solvent in which the core and/or shelling procedures were carried out. While ligands of this type can increase the stability of the nanoparticles in non-polar media, provide electronic stabilization, and/or negate undesirable nanoparticle agglomeration, as mentioned previously, such ligands typically prevent the nanoparticles from stably dispersing or dissolving in more polar media, such as epoxy resins.

    [0026] The instant disclosure describes methods for rendering QDs more compatible with epoxy resins by modifying the surface of a QD by adsorbing amphiphilic block co-polymerson the surface. The block copolymer comprises a polyalkylene glycolpoly(alkylene sulfide) block copolymer or a first block that is a reversible addition fragmentation chain transfer agent (RAFT-CTA) and a second block that is a polyalkylene glycol .

    [0027] According to one embodiment, the second block comprises a polyalkylene oxide. According to one embodiment, the second block includes polyethylene oxide (PEG).

    [0028] One example of a suitable block copolymer is a polyalkylene glycolpoly(alkylene sulfide) block copolymer such as polyethylene glycol-b-poly(propylene sulfide) (PEG-PPS):

    where n and m are integers. The values of n and m may be selected to optimize the interaction of the copolymer with the QD surface and with the matrix. According to certain embodiments, n and m are independently from about 5 to about 500, about 5 to 100, or about 5 to about 50. According to one specific example, n is 45 and m is 10. According to one embodiment, PEG-PPS copolymers with a short PPS block (m=10) provide an optimum balance between compatibility with an epoxy matrix and steric hindrance with molecules on the QD surface. PEG-PPS block copolymers can be synthesized using a procedure described in Wang et al., Polymer, 2009, 50, 2863. Briefly, thiolate-terminated propylene sulfide oligomer is reacted with PEG chain bearing a thiol reactive 2-bromoacetate terminal group.

    [0029] Another example of a macromolecule suitable for modifying the surface of a QD, as described herein, is a macromolecule having a first block that is a reversible addition fragmentation chain transfer agent (RAFT-CTA) and a second block that is a polyalkylene glycol. A specific example of such a macromolecule is polyethylene glycol macro RAFT CTA (PEG-CTA):



    [0030] As with the PEG-PPS copolymer described above, the value of n for the PEG-CTA macromolecule can be selected to provide an optimum balance between compatibility with an epoxy matrix and steric hindrance with molecules on the QD surface. Particular examples include n=10, 45, and 113.

    [0031] PEG-CTA macromolecule, as illustrated above, can be synthesized as described in C.D. Vo et al., J. Polym. Sci. Part A Polym. Chem., 2010, 48, 2032. Briefly, oligo- ethylene glycol methyl ether is reacted with the RAFT CTA in the presence of a coupling agent such as N, N'-dicyclohexyl carbodiimide (DCCI), as shown here:



    [0032] The synthesis of the RAFT-CTA is described in Lai, J. T. et al., Macromolecules, 2002, 35, 6754.

    [0033] The QD surface can be modified with the amphiphilic macromolecules by exposing the QD to a solution of the macromolecule. For example, a toluene solution of QD can be added to a toluene solution of the copolymer and the combined solution can be stirred for a time sufficient to allow surface modification to occur. According to some embodiments, the surface modification is performed in an inert atmosphere, such as under nitrogen. For example, a mixture of QDs and an excess of amphiphilic macromolecules can be stirred at about 20°C for several hours under nitrogen allowing surface modification to occur.

    [0034] Once the QD surface has been modified with the amphiphilic copolymer, matrix components, such as epoxy resin components, can be added to the mixture of QD and copolymer. Films of the QD-containing resins can then be prepared on substrates. Any method of film preparation can be used. Exemplary methods of preparing films include drop coating, spin coating, and doctor blading. The films can be cured by conventional methods known in the art.

    [0035] The embodiments disclosed herein can be further understood with reference to the following representative examples. The examples illustrate that amphiphilic macromolecules as surface modifiers for QDs improve the dispersion and quantum yield of the QDs in epoxy resin. The strategy can be extended to other macromolecules and block copolymers, for example, poly(ethylene glycol)-b-poly(glycidyl acrylate)- CTA (PEG-PGA-CTA) whose PEG and PGA are highly compatible with epoxy. The synthesis of PEG-CTA and PEG-PPS is simple under mild conditions. It is possible to synthesize these polymers in large scale from commercially available chemicals (see CDVo et al. J. Polym. Sci. Part A Polym. Chem., 2010, 48, 2032 and Wang et al., Polymer, 2009, 50, 2863). The surface of QDs can be modified using PEG-CTA via simple mixing of the two components without the need to use multi-step reactions under hash reaction conditions, which can lead to lower quantum yield. The method is therefore easy to scale up. The PEG-CTA contains RAFT chain transfer agent (see CDVo et al. Macromolecules 2007, 40, 7119 and CDVo et al. J. Polym. Sci. Part A Polym. Chem. 2010, 48, 2032), which can protect the QDs from free radicals while PEG-PPS containing polypropylene sulfide can protect QD from oxidation thanks to its oxidative responsiveness.

    EXAMPLES


    EXAMPLE 1: SYNTHESIS OF PEG-CTA



    [0036] PEG-CTA (n = 10) was synthesized as follows. Oligomer ethylene glycol methyl ether (Mn = 550 g/mol or n = 10; 2 gram, 3.63 mmol) was first dissolved in 10 mL toluene and then the toluene was evaporated under reduced pressure. THF (5 mL) was added to dissolve the oligomer under nitrogen before a solution of RAFT CTA (1.32g, 3.63 mmol) in 5mL THF and then a mixture of DCCI (0.75 g, 3.63 mmol) and 4-pyrrilido pyridine (53.8 mg, 0.363 mmol) in 5 mL THF were added. The mixture was stirred under nitrogen at 20°C for 6 days and then refluxed for 4 hours prior to further purification using a silica column.

    EXAMPLE 2: SYNTHESIS OF PEG-PPS



    [0037] PEG-PPS was synthesized as described in Wang et al., Polymer, 2009, 50, 2863, referenced above.

    EXAMPLE 3: MODIFICATION OF QD SURFACES WITH PEG-CTA AND PEG-PPS



    [0038] Red QDs (Red CFQD® heavy metal-free quantum dots available from Nanoco Technologies, Ltd. Manchester, U.K.) were modified with PEG2000-CTA and with PEG2000-PPS10. Mixtures of the above amphiphilic macromolecules and quantum dots with a weight ratio of about 1.25/1 in toluene were stirred at 20°C overnight under nitrogen allowing surface modification to occur.

    [0039] Epoxy films were prepared incorporating samples of each of the modified QDs and unmodified QDs. Typically, films were prepared by first mixing the toluene-removed modified QDs or unmodified QDs with a mixture of epoxy 135A and epoxy 135B (1:1, w/w), then depositing 80 microliters of the resultant resin into a small glass plate (19mm x 14mm x 0.5mm) and finally curing on an 80°C heating plate under N2 overnight. Films incorporating unmodified QDs display macroscopic aggregation of the QDs, while films of the PEG2000-CTA - modified and the PEG2000-PPS10 - modified show that the QDs remain well dispersed within the epoxy film.

    [0040] Optical microscopy images of the red QDs in epoxy films at 50X and 200X magnification using pristine QDs, PEG550-CTA-treated QD, PEG2000-CTA- treated QD, and PEG2000-PPS10-treated QD show, in higher magnification, that QDs modified with amphiphilic macromolecules aggregate less in epoxy resin, compared to unmodified QDs.

    [0041] Figure 1 shows the emission spectra of A) unmodified, and B) PEG2000-PPS10-modified QDs in epoxy films recorded using a Labsphere™ integrating sphere. The ratio of the emission /excitation peak area of the PEG-PPS treated film is higher than that of the unmodified film. EQEs/LED absorbance of 25%/29% and 24/71% were determined for the unmodified and PEG-PPS-modified QD epoxy films respectively. It is clear that LED absorbance of the modified films is higher than that of the unmodified film, indicating better dispersion of the QDs in the modified film as shown in optical microscope images.

    [0042] Table 1 shows the quantum yield of the unmodified and modified QDs (in epoxy), as measured using a Hamamatsu device.
    TABLE 1
    QDQY Uncured FilmQY Cured FilmAppearance
    Unmodified. (InP/ZnS/ZnO; PLtoluene = 608 nm, FWHM = 61nm; QY = 74%) 35 25 QD aggregation.
    PEG2000-modified using cymel treatment, prepared as described in U.S. Pub. No. 2013/0190493, - 20 Transparent.
    PEG2000-modified. - 29 Opaque/homogeneous distribution.
    Unmodified. (InP/ZnS/ZnO: PLtoluene = 611nm, FWHM = 57 nm; QY = 78%) 41 23 QD aggregation.
    PEG550-CTA -modified. 41 26 Opaque/homogeneous distribution.
    PEG2000-CTA -modified. 42 27 Opaque/homogeneous distribution.
    PEG2000-PPS10 -modified. 44 29 Opaque/homogeneous distribution.


    [0043] The data summarized in Table 1 demonstrates the improvement in optical properties of QDs upon modification of the QD surface, as described herein.


    Claims

    1. A surface-modified nanoparticle comprising:

    a nanoparticle having a core and an external surface;

    a plurality of amphiphilic block copolymers on the external surface,

    wherein the block copolymer comprises a polyalkylene glycol-poly(alkylene sulfide) block copolymer or a first block that is a reversible addition fragmentation chain transfer agent (RAFT-CTA) and a second block that is a polyalkylene glycol.


     
    2. The surface-modified nanoparticle recited in claim 1 wherein the amphiphilic block copolymers are adsorbed on the external surface of the nanoparticle.
     
    3. The surface-modified nanoparticle recited in claim 1 wherein the nanoparticle is a metal oxide.
     
    4. The surface-modified nanoparticle recited in claim 3 wherein the nanoparticle is selected from the group consisting of: iron oxides, titanium oxides, zinc oxide, zirconium oxide, and aluminum oxide.
     
    5. The surface-modified nanoparticle recited in claim 1 wherein the nanoparticle:

    (i) is a magnetic nanoparticle; or

    (ii) is a gold nanoparticle; or

    (iii) is a silver nanoparticle; or

    (iv) is a cadmium-free nanoparticle.


     
    6. The surface-modified nanoparticle recited in claim 1 wherein the nanoparticle comprises a luminescent semiconductor material.
     
    7. The surface-modified nanoparticle recited in claim 1 wherein the nanoparticle is selected from the group consisting of: CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, InP, InAs, InSb, AIP, AIS, AlAs, AlSb, GaN, GaP, GaAs, GaSb, PbS, PbSe, Si, Ge and combinations thereof
     
    8. The surface-modified nanoparticle recited in claim 1 wherein the nanoparticle is a core-shell nanoparticle wherein the core is substantially comprised of a first material and the shell is substantially comprised of a second material different from the first material.
     
    9. The surface-modified nanoparticle recited in claim 8 wherein the core-shell nanoparticle comprises:

    (i) a plurality of shells with adjacent shells substantially comprised of different materials; or

    (ii) a shell material selected from the group consisting of ZnS, ZnO, MgS, MgSe, MgTe and GaN.


     
    10. The surface-modified nanoparticle recited in claim 8 wherein the core-shell nanoparticle comprises a core comprised substantially of InP, first shell comprised substantially of ZnS, and a second shell comprised substantially of ZnO.
     
    11. The surface-modified nanoparticle recited in claim 1 wherein the block copolymer comprises a block that has affinity for an epoxide resin.
     
    12. The surface-modified nanoparticle recited in claim 1 wherein the polyalkylene glycol-poly(alkylene sulfide) block copolymer has the general formula

    where m and n are integers.
     
    13. The surface-modified nanoparticle recited in claim 1 wherein the block copolymer comprising the first block that is a reversible addition fragmentation chain transfer agent (RAFT-CTA) and the second block that is a polyalkylene glycol has the general formula

    where n is a positive integer.
     
    14. A method for modifying the surface of nanoparticles comprising:

    preparing a solution of nanoparticles in a solvent;

    exposing the nanoparticle solution to a solution of an amphiphilic block copolymer in a solvent,

    wherein the block copolymer comprises a polyalkylene glycol-poly(alkylene sulfide) block copolymer or a first block that is a reversible addition fragmentation chain transfer agent (RAFT-CTA) and a second block that is a polyalkylene glycol.


     
    15. The method for modifying the surface of nanoparticles recited in claim 14 wherein:

    (i) the solvent is toluene; or

    (ii) exposing the nanoparticle solution to the solution of the amphiphilic block copolymer is performed under an inert atmosphere; or

    (iii) exposing the nanoparticle solution to the solution of the amphiphilic block copolymer is accomplished with an excess of the amphiphilic block copolymer; or

    (iv) the method further comprises adding epoxy resin components to the mixture of nanoparticles and the amphiphilic block copolymer;
    optionally the method further comprising depositing a film of the nanoparticle-containing resin on a substrate.


     


    Ansprüche

    1. Oberflächenmodifiziertes Nanopartikel umfassend:

    ein Nanopartikel, das einen Kern und eine externe Oberfläche aufweist;

    eine Mehrzahl amphiphiler Blockcopolymere auf der externen Oberfläche,

    wobei das Blockcopolymer ein Polyalkylenglycol-Poly(alkylensulfid)-Blockcopolymer oder einen ersten Block, der ein reversibles Additionsfragmentations-Kettenübertragungsmittel -(RAFT-CTA) ist, und einen zweiten Block, der ein Polyalkylenglycol ist, umfasst


     
    2. Oberflächenmodifiziertes Nanopartikel, das in Anspruch 1 aufgeführt ist, wobei die amphiphilen Blockcopolymere an der externen Oberfläche des Nanopartikels adsorbiert sind.
     
    3. Oberflächenmodifiziertes Nanopartikel, das in Anspruch 1 aufgeführt ist, wobei das Nanopartikel ein Metalloxid ist.
     
    4. Oberflächenmodifiziertes Nanopartikel, das in Anspruch 3 aufgeführt ist, wobei das Nanopartikel aus der Gruppe ausgewählt ist bestehend aus: Eisenoxiden, Titanoxiden, Zinkoxid, Zirkoniumoxid und Aluminiumoxid.
     
    5. Oberflächenmodifiziertes Nanopartikel, das in Anspruch 1 aufgeführt ist, wobei das Nanopartikel:

    (i) ein magnetisches Nanopartikel ist; oder

    (ii) ein Goldnanopartikel ist; oder

    (iii) ein Silbernanopartikel ist; oder

    (iv) ein cadmiumfreies Nanopartikel ist.


     
    6. Oberflächenmodifiziertes Nanopartikel, das in Anspruch 1 aufgeführt ist, wobei das Nanopartikel ein lumineszierendes Halbleitermaterial umfasst.
     
    7. Oberflächenmodifiziertes Nanopartikel, das in Anspruch 1 aufgeführt ist, wobei das Nanopartikel aus der Gruppe ausgewählt ist bestehend aus: CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, InP, InAs, InSb, AlP, AlS, AlAs, AlSb, GaN, GaP, GaAs, GaSb, PbS, PbSe, Si, Ge und Kombinationen davon.
     
    8. Oberflächenmodifiziertes Nanopartikel, das in Anspruch 1 aufgeführt ist, wobei das Nanopartikel einen Kern-Schale-Nanopartikel ist, wobei der Kern im Wesentlichen aus einem ersten Material besteht und die Schale im Wesentlichen aus einem zweiten Material besteht, das von dem ersten Material verschieden ist.
     
    9. Oberflächenmodifiziertes Nanopartikel, das in Anspruch 8 aufgeführt ist, wobei das Kern-Schale-Nanopartikel Folgendes umfasst:

    (i) eine Mehrzahl von Schalen mit anliegenden Schalen, die im Wesentlichen aus verschiedenen Materialien bestehen; oder

    (ii) ein Schalenmaterial ausgewählt aus der Gruppe bestehend aus ZnS, ZnO, MgS, MgSe, MgTe und GaN.


     
    10. Oberflächenmodifiziertes Nanopartikel, das in Anspruch 8 aufgeführt ist, wobei das Kern-Schale-Nanopartikel einen Kern, der im Wesentlichen aus InP besteht, eine erste Schale, die im Wesentlichen aus ZnS besteht, und eine zweite Schale, die im Wesentlichen aus ZnO besteht, umfasst.
     
    11. Oberflächenmodifiziertes Nanopartikel, das in Anspruch 1 aufgeführt ist, wobei das Blockcopolymer einen Block umfasst, der Affinität für ein Epoxidharz aufweist.
     
    12. Oberflächenmodifiziertes Nanopartikel, das in Anspruch 1 aufgeführt ist, wobei das Polyalkylenglycol-Poly(alkylensulfid)-Blockcopolymer die allgemeine Formel

    aufweist, wobei m und n ganze Zahlen sind.
     
    13. Oberflächenmodifiziertes Nanopartikel, das in Anspruch 1 aufgeführt ist, wobei das Blockcopolymer, das den ersten Block, der ein reversibles Additionsfragmentations-Kettenübertragungsmittel (RAFT-CTA) ist, und den zweiten Block, der ein Polyalkylenglycol ist, umfasst, die allgemeine Formel

    aufweist, wobei n eine positive ganze Zahl ist.
     
    14. Verfahren zum Modifizieren der Oberfläche von Nanopartikeln, umfassend:

    Herstellen einer Lösung von Nanopartikeln in einem Lösungsmittel;

    Aussetzen der Nanopartikellösung einer Lösung eines amphiphilen Blockcopolymers in einem Lösungsmittel gegenüber,

    wobei das Blockcopolymer ein Polyalkylenglycol-Poly(alkylensulfid)-Blockcopolymer oder einen ersten Block, der ein reversibles Additionsfragmentations-Kettenübertragungsmittel -(RAFT-CTA) ist, und einen zweiten Block, der ein Polyalkylenglycol ist, umfasst.


     
    15. Verfahren zum Modifizieren der Oberfläche von Nanopartikeln, die in Anspruch 14 aufgeführt sind, wobei

    (i) das Lösungsmittel Toluol ist; oder

    (ii) das Aussetzen der Nanopartikellösung der Lösung des amphiphilen Blockcopolymers gegenüber unter einer inerten Atmosphäre ausgeführt wird; oder

    (iii) das Aussetzen der Nanopartikellösung der Lösung des amphiphilen Blockcopolymers gegenüber mit einem Überschuss des amphiphilen Blockcopolymers erreicht wird; oder

    (iv) das Verfahren ferner das Zusetzen von Epoxidharzkomponenten zu der Mischung von Nanopartikeln und des amphiphilen Blockcopolymers umfasst;
    wobei das Verfahren wahlweise ferner das Absetzen eines Films des Nanopartikel enthaltenden Harzes auf einem Substrat umfasst.


     


    Revendications

    1. Nanoparticule à surface modifiée comprenant:

    une nanoparticule ayant un cœur et une surface externe;

    une pluralité de copolymères séquencés amphiphiles sur la surface externe,

    le copolymère séquencé comprenant un copolymère séquencé de poly(alkylène glycol)-poly(sulfure d'alkylène) ou une première séquence qui est un agent de transfert de chaîne réversible par addition-fragmentation (RAFT-CTA) et une seconde séquence qui est un poly(alkylène glycol).


     
    2. Nanoparticule à surface modifiée énoncée dans la revendication 1, les copolymères séquencés amphiphiles étant adsorbés sur la surface externe de la nanoparticule.
     
    3. Nanoparticule à surface modifiée énoncée dans la revendication 1, la nanoparticule étant un oxyde métallique.
     
    4. Nanoparticule à surface modifiée énoncée dans la revendication 3, la nanoparticule étant sélectionnée dans le groupe constitué: des oxydes de fer, des oxydes de titane, de l'oxyde de zinc, de l'oxyde de zirconium, et de l'oxyde d'aluminium.
     
    5. Nanoparticule à surface modifiée énoncée dans la revendication 1, la nanoparticule:

    (i) étant une nanoparticule magnétique; ou

    (ii) étant une nanoparticule d'or; ou

    (iii) étant une nanoparticule d'argent; ou

    (iv) étant une nanoparticule sans cadmium.


     
    6. Nanoparticule à surface modifiée énoncée dans la revendication 1, la nanoparticule comprenant un matériau semi-conducteur luminescent.
     
    7. Nanoparticule à surface modifiée énoncée dans la revendication 1, la nanoparticule étant sélectionnée dans le groupe constitué de: CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, InP, InAs, InSb, AlP, AlS, AlAs, AlSb, GaN, GaP, GaAs, GaSb, PbS, PbSe, Si, Ge et de leurs combinaisons.
     
    8. Nanoparticule à surface modifiée énoncée dans la revendication 1, la nanoparticule étant une nanoparticule à cœur-écorce dans laquelle le cœur est sensiblement composé d'un premier matériau et l'écorce est sensiblement composée d'un second matériau différent du premier matériau.
     
    9. Nanoparticule à surface modifiée énoncée dans la revendication 8, la nanoparticule à cœur-écorce comprenant:

    (i) une pluralité d'écorces avec des écorces adjacentes composées sensiblement de différents matériaux; ou

    (ii) un matériau d'écorce sélectionné dans le groupe constitué de ZnS, ZnO, MgS, MgSe, MgTe et GaN.


     
    10. Nanoparticule à surface modifiée énoncée dans la revendication 8, la nanoparticule à cœur-écorce comprenant un cœur composé sensiblement de InP, une première écorce composée sensiblement de ZnS, et une seconde écorce composée sensiblement de ZnO.
     
    11. Nanoparticule à surface modifiée énoncée dans la revendication 1, le copolymère séquencé comprenant une séquence qui présente une affinité pour une résine époxyde.
     
    12. Nanoparticule à surface modifiée énoncée dans la revendication 1, le copolymère séquencé de poly(alkylène glycol)-poly(sulfure d'alkylène) ayant la formule générale

    dans laquelle m et n sont des nombres entiers.
     
    13. Nanoparticule à surface modifiée énoncée dans la revendication 1, dans laquelle le copolymère séquencé comprenant la première séquence, qui est un agent de transfert de chaîne réversible par addition-fragmentation (RAFT-CTA), et la seconde séquence, qui est un poly(alkylène glycol), a la formule générale

    dans laquelle n est un nombre entier positif.
     
    14. Procédé de modification de la surface de nanoparticules comprenant:

    la préparation d'une solution des nanoparticules dans un solvant;

    l'exposition de la solution de nanoparticule à une solution d'un copolymère séquencé amphiphile dans un solvant,

    le copolymère séquencé comprenant un copolymère séquencé de poly(alkylène glycol)-poly(sulfure d'alkylène) ou une première séquence qui est un agent de transfert de chaîne réversible par addition-fragmentation (RAFT-CTA) et une seconde séquence qui est un poly(alkylène glycol).


     
    15. Procédé de modification de la surface de nanoparticules énoncé dans la revendication 14 dans lequel:

    (i) le solvant est le toluène; ou

    (ii) l'exposition de la solution de nanoparticule à la solution du copolymère séquencé amphiphile étant effectuée sous une atmosphère inerte; ou

    (iii) l'exposition de la solution de nanoparticule à la solution du copolymère séquencé amphiphile étant accomplie avec un excès du copolymère séquencé amphiphile; ou

    (iv) le procédé comprenant en outre l'addition de composants de résine époxy au mélange de nanoparticules et de copolymère séquencé amphiphile;
    le procédé comprenant optionnellement en outre le dépôt d'un film de la résine contenant la nanoparticule sur un substrat.


     




    Drawing








    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description




    Non-patent literature cited in the description