Nanoparticles and formulations for printing

Abstract

A method for generating reactive species in a medium in which light irradiates the medium including a nanoparticle. A photoinitiator composed of semiconductor nanoparticles for photo-polymerization and 2D and 3D printing.

Claims

1. A method for photopolymerization, the method comprising light irradiating a photoinitiator in a form of at least one nanoparticle, in presence of at least one material susceptible to photopolymerization, wherein the nanoparticle is: a semiconductor heterostructure coated with a plurality of inorganic and/or organic ligands on its surface; or a Type-1 semiconductor heterostructure coated with inorganic and/or organic ligands on its surface.

2. The method according to claim 1, wherein the medium is an organic solvent-free solution.

3. The method according to claim 1, wherein the nanoparticle is a Type-1 nanoparticle surface-associated with inorganic ligands.

4. The method according to claim 1, wherein the nanoparticle is a Type-1 semiconductor heterostructure coated with inorganic ligands on its surface, and wherein the medium is solvent free.

5. A photoinitiator in the form of at least one nanoparticle surface-coated with inorganic ligands, the at least one nanoparticle being selected from semiconductor homostructures, heterostructures, doped nanoparticles, Type-1 nanoparticles, reversed Type-1 nanoparticles, Type-2 nanoparticles, quasi Type-2 nanoparticles and of semiconductor-metal hybrid nanoparticles.

6. The photoinitiator according to claim 5, wherein the nanoparticle is a semiconductor heterostructure or a Type-1 semiconductor heterostructure.

7. The method according to claim 1, wherein the nanoparticle is selected from spherical, dot-shaped, rod-shaped, wire, cubic, cylindrical, whisker-like, platelet, multipod, frame, doped nanoparticles, seeded nanoparticles, core/shell or multi-shell nanoparticle structures, single tip nanoparticle structures, dumbbells or body decorated nanoparticle structures.

8. The method according to claim 1, wherein the nanoparticle is formed of a material or combination of materials selected from Group II-VI semiconductors, Group III-V semiconductors, Group IV-VI semiconductors, Group IV elemental or compound semiconductors, Group III-VI semiconductors, Group I-VI semiconductors, ternary semiconductors, I-VII semiconductors, V-VI semiconductors, II-V semiconductors, I-III-VI.sub.2 semiconductors, oxides, quaternary semiconductors and alloys thereof.

9. The method according to claim 1, wherein the inorganic ligands are selected from one or more anions of P, S, As, TI, Se, Te, I, CI, Br, O, F and N.

10. The method according to claim 1, wherein the inorganic ligands are selected from As.sub.3.sup.3−, As.sub.4.sup.2−, As.sub.5.sup.3−, As.sub.7.sup.3−, As.sub.11.sup.3−, AsS.sub.3.sup.3−, As.sub.2.sup.−Se.sub.6.sup.3−, As.sub.2.sup.−Te.sub.6.sup.3−, As.sub.10Te.sub.3.sup.2−, Au.sub.2Te.sub.4.sup.2−, Au.sub.3Te.sub.4.sup.3−, Bi.sub.3.sup.3−, Bi.sub.4.sup.2−, Bi.sub.5.sup.3−, GaTe.sup.2−, Ge.sub.9.sup.2−, Ge.sub.9.sup.4−, Ge.sub.2S.sub.6.sup.4−, HgSe.sub.2.sup.2−, Hg.sub.3Se.sub.4.sup.2−, In.sub.2Se.sub.4.sup.2−, In.sub.2Te.sub.4.sup.2−, Ni.sub.5Sb.sub.17.sup.4−, PO.sub.3.sup.3−, PO.sub.4.sup.3−, POCl.sub.3, P.sub.2O.sub.7.sup.4−, P.sub.3O.sub.10.sup.5−, Pb.sub.5.sup.2−, Pb.sub.7.sup.4−, Pb.sub.9.sup.4−, Pb.sub.2Sb.sub.2.sup.2−, Sb.sub.3.sup.3−, Sb.sub.4.sup.2−, Sb.sub.7.sup.3−, SbSe.sub.4.sup.3−, SbSe.sub.4.sup.5−, SbTe.sub.4.sup.5−, Sb.sub.2Se.sub.3.sup.−, Sb.sub.2Te.sub.5.sup.4−, Sb.sub.2Te.sub.7.sup.4−, Sb.sub.4Te.sub.4.sup.4−, Sb.sub.9Te.sub.6.sup.3−, Se.sub.2.sup.2−, Se.sub.3.sup.2−, Se.sub.4.sup.2−, Se.sub.5,6.sup.2−, Se.sub.6.sup.2−, Sn.sub.5.sup.2−, Sn.sub.9.sup.3−, Sn.sub.9.sup.4−, SnS.sub.4.sup.4−, SnSe.sub.4.sup.4−, SnTe.sub.4.sup.4−, SnS.sub.4Mn.sub.2.sup.5−, SnS.sub.2S.sub.6.sup.4−, Sn.sub.2Se.sub.6.sup.4−, Sn.sub.2Te.sub.6.sup.4−, Sn.sub.2Bi.sub.2.sup.2−, Sn.sub.8Sb.sup.3−, SnO.sub.3.sup.−, SnO.sub.3.sup.2−, SnO.sub.4.sup.4−, Te.sub.2.sup.2−, Te.sub.3.sup.2−, Te.sub.4.sup.2−, Tl.sub.2Te.sub.2.sup.2−, TlSn.sub.8.sup.3−, TlSn.sub.8.sup.5−, TlSn.sub.9.sup.3−, TlTe.sub.2.sup.2−, SnS.sub.4Mn.sub.2.sup.5−, ZnCl.sub.4.sup.2−, Zn(NO.sub.3).sub.4.sup.2−, S.sup.2−, HS.sup.−, Se.sup.2−, HSe.sup.−, Te.sup.2−, HTe.sup.−, TeS.sub.3.sup.2−, NH.sub.2.sup.−, I.sup.−, Cl.sup.− and N.sub.3.sup.−, SnS.sub.4.sup.4−, Sn.sub.2S.sub.6.sup.4−, Sn.sub.2S.sub.7.sup.6−) and SbS.sub.4.sup.3−.

11. The method according to claim 1, being a method for single- and two-photon-polymerization.

12. The method according to claim 1, being a method for 2D or 3D printing comprising irradiating a solution comprising at least one said nanoparticle in combination with at least one material capable of undergoing polymerization.

13. The method according to claim 1, being a method for surface photocuring, the method comprising irradiating a medium comprising at least one said nanoparticle and at least one material prone to photocatalytic conversion upon light irradiation by visible and/or near IR range and/or UV range light.

14. A method for photopolymerization, the method comprising light irradiating a photoinitiator in a form of at least one nanoparticle in the presence of at least one material susceptible to photopolymerization, wherein the nanoparticle is: a semiconductor nanoparticle coated with a plurality of inorganic ligands on its surface; or a semiconductor heterostructure coated with a plurality of inorganic and/or organic ligands on its surface; or a Type-1 semiconductor heterostructure coated with inorganic and/or organic ligands on its surface; wherein the inorganic ligands are selected from As.sub.3.sup.3−, As.sub.4.sup.2−, As.sub.5.sup.3−, As.sub.7.sup.3−, As.sub.11.sup.3−, AsS.sub.3.sup.3−, As.sub.2.sup.−Se.sub.6.sup.3−, As.sub.2.sup.−Te.sub.6.sup.3−, As.sub.10Te.sub.3.sup.2−, Au.sub.2Te.sub.4.sup.2−, Au.sub.3Te.sub.4.sup.3−, Bi.sub.3.sup.3−, Bi.sub.4.sup.2−, Bi.sub.5.sup.3−, GaTe.sup.2−, Ge.sub.9.sup.2−, Ge.sub.9.sup.4−, Ge.sub.2S.sub.6.sup.4−, HgSe.sub.2.sup.2−, Hg.sub.3Se.sub.4.sup.2−, In.sub.2Se.sub.4.sup.2−, In.sub.2Te.sub.4.sup.2−, Ni.sub.5Sb.sub.17.sup.4−, PO.sub.3.sup.3−, PO.sub.4.sup.3−, POCl.sub.3, P.sub.2O.sub.7.sup.4−, P.sub.3O.sub.10.sup.5−, Pb.sub.5.sup.2−, Pb.sub.7.sup.4−, Pb.sub.9.sup.4−, Pb.sub.2Sb.sub.2.sup.2−, Sb.sub.3.sup.3−, Sb.sub.4.sup.2−, Sb.sub.7.sup.3−, SbSe.sub.4.sup.3−, SbSe.sub.4.sup.5−, SbTe.sub.4.sup.5−, Sb.sub.2Se.sub.3.sup.−, Sb.sub.2Te.sub.5.sup.4−, Sb.sub.2Te.sub.7.sup.4−, Sb.sub.4Te.sub.4.sup.4−, Sb.sub.9Te.sub.6.sup.3−, Se.sub.2.sup.2−, Se.sub.3.sup.2−, Se.sub.4.sup.2−, Se.sub.5,6.sup.2−, Se.sub.6.sup.2−, Sn.sub.5.sup.2−, Sn.sub.9.sup.3−, Sn.sub.9.sup.4−, SnS.sub.4.sup.4−, SnSe.sub.4.sup.4−, SnTe.sub.4.sup.4−, SnS.sub.4Mn.sub.2.sup.5−, SnS.sub.2S.sub.6.sup.4−, Sn.sub.2Se.sub.6.sup.4−, Sn.sub.2Te.sub.6.sup.4−, Sn.sub.2Bi.sub.2.sup.2−, Sn.sub.8Sb.sup.3−, SnO.sub.3.sup.−, SnO.sub.3.sup.2−, SnO.sub.4.sup.4−, Te.sub.2.sup.2−, Te.sub.3.sup.2−, Te.sub.4.sup.2−, Tl.sub.2Te.sub.2.sup.2−, TlSn.sub.8.sup.3−, TlSn.sub.8.sup.5−, TlSn.sub.9.sup.3−, TlTe.sub.2.sup.2−, SnS.sub.4Mn.sub.2.sup.5−, ZnCl.sub.4.sup.2−, Zn(NO.sub.3).sub.4.sup.2−, S.sup.2−, HS.sup.−, Se.sup.2−, HSe.sup.−, Te.sup.2−, HTe.sup.−, TeS.sub.3.sup.2−, NH.sub.2.sup.−, I.sup.−, Cl.sup.− and N.sub.3.sup.−, SnS.sub.4.sup.4−, Sn.sub.2S.sub.6.sup.4−, Sn.sub.2S.sub.7.sup.6−) and SbS.sub.4.sup.3−.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

(2) FIGS. 1A-B show optical (FIG. 1A) and structural characterization (FIG. 1B, TEM) of the CdSe/CdS seeded rod heterostructure used as model system in Example 1.

(3) FIGS. 2A-B present gelation of SR9035 (FIG. 2B) and acrylamide (FIG. 2A) achieved after illumination of only tens of seconds on solution containing monomers and CdSe/CdS nanorods with organic surface coating in water. The CdS shell was synthesized by hot injection method. The heterostructure SCNC multi-functionality can be seen from the fluorescence of the post-polymerized structure emanating from these particles.

(4) FIGS. 3A-C present an example of photopolymerization with heterostructures coated by organic ligands and “solvent free” formulations. FIG. 3A presents a polymerized object achieved by irradiation on formulation comprised of CdSe/CdS coated by organic ligands as photoinitiators, benzyl alcohol as the solvent and SR-9036A as the monomers. FIG. 3B demonstrates “solvent free” polymerization, showing FTIR measurement which follows the opening of the double bond of hydroxyethyl acrylate monomers during the excitation of CdSe/CdS seeded nanorods as the PINs.

(5) FIG. 3C shows a “solvent free” high resolution printing of fluorescent gear with the CdSe/CdS as photoinitiators in a 2 photon polymerization printer.

(6) FIGS. 4A-B show optical (FIG. 4A) and structural characterization (FIG. 4B, TEM) of the CdS/ZnS rod/shell nanorods heterostructure used as a model system in Example 2.

(7) FIG. 5 presents gelation of SR9035 achieved after only 30 sec of illumination on solution containing monomers and CdS/ZnS nanorods with organic coating in water. The ZnS shell was synthesized by colloidal ALD.

(8) FIGS. 6A-C shows enhanced production of hydroxyl radicals by CdS nanorods coated with S.sup.2− as inorganic surface ligand coating in comparison to organic coating, and a demonstration of the capacity to use them as photoinitiators for radical polymerization. FIG. 6A shows comparison of hydroxyl radical formation by TPA assay during the excitation of CdS nanorods with PEI as organic surface coating or S.sup.2− as inorganic surface ligand coating. The figure shows enhanced photocatalytic activity for the latter. FIG. 6B is an image showing a gel that was formed following one minute light excitation of water based dispersion comprising of SR-9035 as monomers and CdS nanorods with inorganic surface ligand coating (S.sup.2−) as photoinitiators. FIG. 6C provides an image showing a gel that was formed following one minute light excitation of “solvent free” formulation comprising hydroxyethyl acrylate and SR-9035 as monomers and cross linker, respectively and CdS nanorods with inorganic surface ligand coating (S.sup.2−) as photoinitiators.

(9) FIG. 7 demonstrates the capacity to use nanoparticles coated with Sb.sub.2S.sub.6 ligands as inorganic surface ligand coating as photoinitiators for radical polymerization. Kinetic FTIR measurements showed fast polymerization of “solvent free” formulation comprised of hydroxyethyl acrylate and two types of PINs: CdS nanorods or CdS—Au semiconductor-metal hybrid nanoparticles coated with Sn.sub.2S.sub.6.sup.−4 as inorganic ligands. Control experiment with Sn.sub.2S.sub.6.sup.−4 and hydroxyethyl acrylate didn't show photo-polymerization.

(10) FIGS. 8A-B provide a TEM image (FIG. 8A) of Type-1 semiconductor heterostructures of ZnSe/ZnS with organic coating and FTIR data, demonstrating the capacity to use them as photoinitiators for radical polymerization. FTIR measurements (FIG. 8B) show high conversion degree of acrylic monomers during light excitation of ZnSe/ZnS PINs before and after exposure to oxygen.

DETAILED DESCRIPTION OF EMBODIMENTS

(11) The invention discloses high-performance photoinitiators in the form of nanoparticles, PINs, e.g., heterostructure SCNC, which may be used in a variety of applications ranging from biological and chemical technologies to industrial and environmental technologies.

EXAMPLES

Example 1: CdSe/CdS Seeded Rods Heterostructures Photoinitiator Dispersion and Example of Photoinitiator Activity

(12) CdSe/CdS seeded nanorods were synthesized by seeded growth approach yielding rods (FIG. 1). TEM images showed the resulting nanorods exhibit good size distribution, with average dimensions of 41±4 nm in length and 4.5±0.5 nm in diameter. The NRs were found to have an emission peak at 610 nm and fluorescence quantum yield of 47%±3% upon excitation at 405 nm. A ligand exchange procedure was applied, through coating by PEI (polyethyleneimine), to render the nanoparticles dispersible in water.

(13) In FIG. 1A the absorption and emission spectra of CdSe/CdS seeded nanorods, respectively, are shown. The nanorods exhibit a sharp absorption rise at 480 nm, attributed to the CdS rod absorption onset, and an emission peak at 610 nm. The transmission electron micrograph (TEM) of CdSe/CdS nanorods with dimensions of 41±4 nm in length and 4.5±0.5 nm in diameter is shown in FIG. 1B.

(14) To determine the polymerization capacity of these nano-photoinitiator catalysts, two polymerization mediums comprising aqueous solutions of CdSe/CdS nanorods coated with PEI as photoinitiator were prepared. The first contained acrylamide monomers and 3% w/w SR-9035 as a cross-linker and the second contained only SR-9035 as the monomers. The solutions were irradiated with an LED at 405 nm. FIG. 2 shows the resulting two fluorescent discs under UV light. As shown in FIG. 2, light excitation of SCNC solution resulted in fast polymerization of the both SR9035 (FIG. 2B) and acrylamide monomers (FIG. 2A). This is a clear demonstration of efficient polymerization of monomer solution with heterostructure SCNCs as photoinitiators following tens of seconds of light excitation. The preservation of the SCNC fluorescence property also demonstrates the ability to use the heterostructure SCNC as multi-functional agents to both serve as photoinitiators in the polymerization stage, and then as emitting entities in the polymerized product.

(15) The capacity to use the nanocrystals as photoinitiators also in solutions free of water, was further demonstrated with the CdSe/CdS nanocrystals. FIG. 3A shows gelation in a vial after light induced polymerization with hydrophobic CdSe/CdS seeded nanorods coated with the original ligands from the synthesis as the PINs, organic-based formulation comprising benzyl alcohol as the solvent and SR-9036a as the monomers. FIG. 3B further shows by FTIR measurement “solvent free” polymerization with CdSe/CdS seeded nanorods as the PINs and hydroxyethyl acrylate as monomers and liquid media. The curve shows almost full conversion of the acrylic monomers' double bond to a single bond due to photoinitiation by the excited nanoparticles.

(16) FIG. 3C shows the capacity to use heterostructure nanocrystals for high resolution two photon printing. A fluorescent gear structure was printed in a Nanoscribe printer with 2-Hydroxyethyl acrylate as the monomers and liquid media and with CdSe/CdS nanorods as 2 photon photoinitiators and emitting particles.

Example 2: CdS/ZnS Rod/Shell Nanorods Photoinitiator Dispersion and Example of Photoinitiator Activity

(17) CdS nanorods were coated with ZnS shell for the synthesis of CdS/ZnS heterostructure by colloidal atomic layer deposition (C-ALD) synthesis. FIG. 4 presents the absorption spectrum of the nanorods and a TEM image of these nanoparticles.

(18) The polymerization capability of the CdS/ZnS heterostructure nanorods was examined by irradiating an aqueous dispersion of CdS/ZnS nanorods coated with PEI and SR-9035 as the monomers using a 405 nm LED (FIG. 5). Excitation of an ink solution containing SR-9035 and CdS/ZnS heterostructure nanorods as PI resulted in fast gelation of the solution (30 sec). The shell growth was achieved by colloidal ALD approach.

Example 3: Polymerization with CdS Nanorods with Inorganic Ligands as Ns

(19) CdS nanorods were transferred to aqueous solutions by phase transfer with PEI as organic surface coating or by colloidal ALD treatment to replace the organic ligands from the synthesis step with S.sup.2− as inorganic surface ligand coating. The light-induced hydroxyl radical production by the two systems was compared by terephthalic acid (TPA) assay. This experiment showed significantly enhanced production of hydroxyl radicals by CdS nanorods with the inorganic coating (FIG. 6A). Then, a polymerization medium containing the CdS nanorods coated by S.sup.2− as inorganic ligands was irradiated with UV LED at 405 nm, and showed fast polymerization of the acrylic monomers in water (FIG. 6B) and in “solvent free” formulation (FIG. 6C).

(20) An example for polymerization by photoinitiators with additional inorganic ligands, such as Sn.sub.2S.sub.6.sup.− is presented in FIG. 7. CdS nanorods and CdS—Au hybrid nanoparticles coated by Sn.sub.2S.sub.6.sup.−4 as inorganic ligands were used as PINS for the polymerization of “solvent free” formulation comprised of hydroxyethyl acrylate as the liquid medium and monomers. Rapid polymerization was observed by FTIR measurements during the irradiated of the sample with UV LED at 405 nm.

Example 4: ZnSe/ZnS Seeded Rods Heterostructures Photoinitiator Dispersion and Example of Photoinitiator Activity

(21) Type-1 semiconductor heterostructures of ZnSe/ZnS were transferred to water using PEI as surface coating. The photo-initiation capacity of these nanoparticles was examined by FTIR measurements and showed efficient polymerization water-based formulation comprising acrylamide as monomers and SR-9035 as a cross-linker.

EXPERIMENTAL DESCRIPTION

(22) Synthesis of Semiconductor Nanoparticles:

(23) Cadmium-chalcogenide based SCNC—as model systems—were synthesized by previously described protocols based on a seeded growth approach. Briefly, CdSe were synthesized by fast injection of selenium dissolved in trioctylphosphine (TOP) solution into a four necked flask containing cadmium oxide (CdO), trioctylphosphine oxide (TOPO) and n-octadecylphosphonic acid (ODPA) at 350° C. under argon atmosphere. CdS were synthesized by fast injection of sulfur dissolved in TOP solution into a four necked flask containing CdO, 1-octadecene (ODE) and oleic acid at 260° C. under argon atmosphere. Both reactions were quenched by removing the heating mantle and cooling with a fan. The crude reaction mixtures were precipitated with acetone followed by centrifugation. For further purification, the particles were dissolved in toluene and the precipitation procedure was repeated several times.

(24) Shell growth on the CdSe and CdS seeds was then achieved as follows: the seeds were mixed with elemental sulfur dissolved in TOP and rapidly injected at 360° C. into a four neck flask containing TOPO, ODPA, CdO, and hexylphosphonic acid (HPA) for the synthesis of the CdSe/CdS and CdS nanorods (NRs). After cooling, the crude solution was dissolved in toluene, and methanol was added in order to precipitate the SCNC and remove excess of precursors and ligands.

(25) Colloidal Atomic Layer Deposition (C-ALD):

(26) As-synthesized CdS NRs with oleylamine ligands are dispersed in toluene and with methanol by centrifugation. The supernatant is discarded and the NRs are redispersed in hexane. Following another centrifugation the supernatant is taken aside and 40% (NH.sub.4).sub.2S aqueous solution in methylformamide (MFA) is added to the nanoparticles in hexane. The mixture is vortexed and the MFA layer is taken. The NRs in MFA are washed with hexane and precipitated using 1:1:1 MFA:acetonitrile:toluene and centrifugation.

(27) Formation of a second half layer of cations (e.g. Zn), salt with a weak nucleophile anion (e.g. Nitrate) in MFA solution is added to the NR solution. The mixture is vortexed and oleylamine in hexane is added to the solution and vortexed vigorously, until the nanoparticles are transferred into the hexane phase.

(28) Nanoparticle Characterization:

(29) Transmission Electron Microscopy (TEM) characterization was performed using a Tecnai T12 G2 Spirit and Tecnai F20 G2 TEMs. All size statistics are done with “Scion image” program on 200 particles. Absorption was measured with a JASCO V-570 UV-vis-near IR spectrophotometer. Extinction coefficient values of the NRs were calculated using a previously reported method.

(30) Phase Transfer:

(31) NPs were transferred with polyethylenimine (PEI) as a polymer coating. NPs solution (1 mL) was mixed with PEI (0.15 g; MW 25,000) in chloroform (1 mL) for 1 hour. Then the particles are precipitated and washed with cyclohexane (1:1 chloroform/cyclohexane), followed by centrifugation. TDW is added to the precipitate and residues of PEI are removed by centrifugation.

(32) Ligand Exchange with Inorganic Ligands:

(33) Nanorods are dissolved in hexane and mixed with solution of Na.sub.4Sn.sub.2S.sub.6 in N-methylformamide (NMF). The biphasic solution is stirred for one hour. The upper layer is discarded, and the lower layer is washed with hexane. The nanorods in the NMF layer are precipitated with acetone and finally redispersed in the solvent of choice.

(34) Preparation of UV Curable Ink Formulation:

(35) UV curable inks were prepared by (1) mixing 5 gr of monomer solution 10 g of Acrylamide and 2.5 g PEGylated diacrylate 600 (SR610); (2) mixing 10 g of acrylamide monomers, 1 g ethoxylated trimethylolpropane triacrylate (SR9035) serving as cross-linker, and 5 g TDW; (3) dissolving SR9035 in TDW. The monomer solutions were then mixed with different SCNC concentrations, at a volume ratio of 1:1. (4) PINs were dispersed in benzyl alcohol and mixed with ethoxylated (30) bisphenol A dimethacrylate (SR9036A). Solvent free formulations were prepared by dispersing the PINs in (5) 2-hydroxyethyl acrylate and SR9035 or (6) 2-hydroxyethyl acrylate as is.