Method for producing a refractive index-adapted photocrosslinkable ceramic slurry and method for producing a refractive index-graded structure

Abstract

A method for producing a refractive index-adapted photocrosslinkable ceramic slurry is disclosed. The method comprises providing a photocrosslinkable organic matrix (110); and adding ceramic particles to the photocrosslinkable organic matrix (120); wherein the average diameter of the ceramic particles is ≤ 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slurry; wherein a filling level of ceramic particles is adjusted between 0 and 90 wt.% such that a desired refractive index is achieved; and wherein the diameter is measured by means of dynamic light scattering (DLS).The disclosure further provides a method for producing a refractive index-matched structure, a method for producing a refractive index-graded structure, the use of a photocrosslinkable ceramic slurry for producing a refractive index-matched structure and / or refractive index-graded structure, and a refractive index-matched photocrosslinkable ceramic slurry.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a method for producing a refractive index-matched photocrosslinkable ceramic slurry, a method for producing a refractive index-matched structure, a method for producing a refractive index-graded structure, the use of a photocrosslinkable ceramic slurry for producing a refractive index-matched structure and / or refractive index-graded structure, and a refractive index-matched photocrosslinkable ceramic slurry. TECHNICAL BACKGROUND

[0002] Refractive index-matched structures can be used for light manipulation, for example, in light transmission. Refractive index matching can enable the lossless transmission of light from a first medium, such as air, to a second medium, such as glass, with little to no reflection at the refractive index transitions.

[0003] For example, a refractive index-matched layer in the form of an anti-reflective coating can reduce reflections on a substrate surface coated with the anti-reflective coating.

[0004] Adjusting the refractive index of an optically transparent material is only possible within certain limits. For example, the refractive index of porous SiO2 can be varied within a range of approximately n=1.5 (e.g., dense quartz glass) and approximately n=1.2 for porous SiO2.

[0005] There are hardly any physical mechanisms and solutions in the state of the art to adjust and / or grade the refractive index of materials in their volume, e.g. locally.

[0006] Adjusting the refractive index in transparent materials is difficult, and porous systems, such as nanoporous SiO2, are typically used. These systems cannot usually be represented as three-dimensional structures, and in particular, grading of the structure is not possible. Porous SiO2 systems can be used as anti-reflective coatings, but due to their porosity, they are not particularly stable and / or sensitive to contamination.

[0007] It is an object of the present invention to provide refractive index-adapted structures as well as refractive index-graded structures. BRIEF DESCRIPTION OF THE INVENTION

[0008] This object is achieved by a method for producing a refractive index-adapted photocrosslinkable ceramic slip according to claim 1, by a method for producing a refractive index-adapted structure according to claim 2, by a method for producing a refractive index-graded structure according to claim 6, and by a refractive index-adapted photocrosslinkable ceramic slip according to claim 9. Further embodiments, configurations, and advantages emerge from the dependent claims and the following description.

[0009] According to one aspect of the present disclosure, a method for producing a refractive index-matched photocrosslinkable ceramic slurry is provided, comprising providing a photocrosslinkable organic matrix; and adding ceramic particles to the photocrosslinkable organic matrix. The average diameter of the ceramic particles is ≤ 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slurry, and a filling level of ceramic particles is adjusted between 0 and 90 wt.% to achieve a desired refractive index. The diameter is measured using dynamic light scattering (DLS).

[0010] The process enables the production of a refractive index-matched photocrosslinkable slurry, which can be crosslinked, for example, using light, to obtain a refractive index-matched structure. The amount of added ceramic particles determines the refractive index of the slurry.

[0011] According to another aspect of the present disclosure, a method for fabricating a refractive index-matched structure is provided, comprising providing a refractive index-matched photocrosslinkable ceramic slurry; and forming the refractive index-matched photocrosslinkable ceramic slurry into the refractive index-matched structure.

[0012] According to a further aspect of the present disclosure, a method for producing a refractive index-graded structure is provided, comprising providing a photocrosslinkable organic matrix; and adding ceramic particles to the photocrosslinkable organic matrix to form a photocrosslinkable ceramic slurry. The average diameter of the ceramic particles is ≤ 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slurry. The method further comprises locally exposing the photocrosslinkable ceramic slurry to light such that the photocrosslinkable ceramic slurry locally crosslinks; and exposing the photocrosslinkable ceramic slurry to light such that the structure is completely crosslinked. The diameter is measured using dynamic light scattering (DLS).

[0013] According to a further aspect of the present disclosure, a refractive index-adjusted photocrosslinkable ceramic slurry is provided. The slurry comprises a photocrosslinkable organic matrix and ceramic particles with an average diameter of the ceramic particles ≤ 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slurry. The filling level of ceramic particles in the photocrosslinkable organic matrix is ​​adjusted between 0 and 90 wt.% to achieve a desired refractive index. The diameter is measured using dynamic light scattering (DLS).

[0014] The details of one or more aspects of the disclosure are set forth in the accompanying figures and the following description. Other features, objects, and advantages of the principles described in this disclosure will be apparent from the description and drawings, as well as from the claims. BRIEF DESCRIPTION OF THE CHARACTERS

[0015] The invention is explained in more detail below using embodiments, without these being intended to limit the scope of protection defined by the claims.

[0016] The accompanying drawings illustrate embodiments and, together with the description, serve to explain the principles of the invention. The elements of the drawings are relative to one another and are not necessarily to scale. Like reference numerals designate similar parts. Fig. 1 schematically shows a method for fabricating a refractive index-matched structure according to embodiments of the present disclosure. Fig. 2 schematically shows a method for producing a refractive index graded structure according to embodiments of the present disclosure DETAILED DESCRIPTION

[0017] The principles described in this disclosure relate to refractive index-matched structures and refractive index-graded structures, as well as means and methods for their manufacture.

[0018] By mixing two non-light-absorbing materials with different refractive indices, all refractive indices can in principle be adjusted according to a mixture series. However, this is only possible if the materials are mixed in such a way that they appear homogeneous at the molecular or particulate level on an order of magnitude of approximately 1 / 10 of the relevant wavelength of light. For molecular mixtures, e.g., liquids, this condition is typically met. For particulate mixtures, e.g., particles mixed with a liquid, this is only met if the particles are smaller than 1 / 10 of the relevant transmitted wavelength. Furthermore, agglomeration and / or other forms of clustering of the particles in the liquid matrix must be prevented.

[0019] According to the invention, refractive index-graded structures can be adjusted by two-stage exposure. For example, two-dimensionally graded refractive indices can be introduced onto a ceramic slip applied as a thin layer by means of two-dimensional exposure. During the crosslinking process, the organic matrix in the slip typically shrinks and can thus increase the density of ceramic nanoparticles. This can lead to an increase in the refractive index. This may be due to the fact that an increased density of optically transparent particles with a higher refractive index than the organic matrix also leads to an increase in the refractive index of the composite material composed of ceramic nanoparticles and organic matrix. In a subsequent process step, the structure is essentially completely exposed to light, so that the organic matrix is ​​essentially completely crosslinked.The two-stage exposure therefore involves partial networking in a local area first, followed by global networking in the second subsequent step. Global networking can usually no longer achieve the same shrinkage as local networking, because the previously locally networked structure impedes the shrinkage during global networking, at least around the locally networked structure.

[0020] Three-dimensionally graded refractive indices can also be created using photopolymerization induced within the volume of the slurry. Volumetric polymerization can be achieved using, for example, xolography, two-photon polymerization, and / or holography, as well as other methods involving surface or point local exposure. Optical elements such as lenses and / or light guides can be inscribed into the volume of a component in this way.

[0021] Furthermore, the use of a photocrosslinkable ceramic slip makes shaping extremely simple and the composite material can, in addition to free-standing structures, also function as a filler in spaces between optical components as a refractive index-matched transition and / or as a refractive index-graded transition.

[0022] This disclosure describes a method for producing a refractive index-matched photocrosslinkable ceramic slip. The term "refractive index-matched" can refer, for example, to a targeted adjustment of the refractive index of a slip, for example, between n=1.1 and n=1.6. The refractive index is a wavelength-dependent variable; the information in this disclosure refers approximately to the visible range of light.

[0023] The method comprises providing a photocrosslinkable organic matrix. The matrix can preferably be a photocrosslinkable resin, which can comprise a crosslinkable monomer and / or a polymer crosslinkable therewith or with itself, a photoinitiator, and, if necessary, additives for controlling the rheological properties of the slurry and the reactivity of the monomer and polymer during their crosslinking triggered by the photoinitiator. The crosslinkable monomer and the crosslinkable polymer can each contain reactive groups. Crosslinking can involve a reaction of the reactive groups with each other. Thus, the photocrosslinkable resin can comprise photocrosslinkable mono- or polymers containing one or more terminal double bonds, such as acrylated polyethylene glycol (PEG-DA), 1,6-hexanediol diacrylate (HDDA), urethane dimethacrylate (UDMA), 2-hydroxyethyl methacrylate (HEMA), 4-acryloylmorpholine (ACMO), etc.Solvents, dispersants, plasticizers, inhibitors and / or sintering reagents may also be added.

[0024] The method further comprises adding ceramic particles to the photocrosslinkable organic matrix.

[0025] As a rule, the ceramic particles of the photocrosslinkable slip are spherical or nearly spherical and not fractured in nature, since such small particles are not produced by grinding, but by chemical reaction, e.g., in a hydrothermal synthesis. The particle size (also referred to as diameter) of suitable particles of a suitable slip is typically less than or equal to 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slip, e.g., the smallest. Furthermore, the particle size (also referred to as diameter) of suitable particles of a suitable slip can typically be less than or equal to 1 / 10 of a wavelength of the intended optical function of the slip and / or later of the structure formed from the slip.

[0026] In this description, the particle size is a value measured by dynamic light scattering (DLS). For example, Malvern Panalytical Ltd offers instruments for measurement via DLS (e.g., Zetasizer ® ).

[0027] The average diameter of the ceramic particles is ≤ 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slurry, in particular a smallest suitable wavelength, and / or preferably the wavelength of a planned optical function of the slurry and / or in particular later of the structure formed from it. The average diameter can refer to d50, in particular d90. In some embodiments, substantially all of the ceramic particles can have a diameter ≤ 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slurry, in particular a smallest suitable wavelength, and / or preferably the wavelength of a planned optical function of the slurry and / or in particular later of the structure formed from it.

[0028] According to one embodiment, a material of the ceramic particles is selected from materials for high-performance ceramics such as silicon nitride - Si3N4, zirconium oxide - ZrO2, aluminum oxide - Al2O3, spinels - MgAl2O4, silicon carbide - SiC, titanium oxide - TiO2, etc. The chemical formulas given correspond to an idealized chemical composition of the designated materials.

[0029] Typically, the ceramic slip does not contain any non-ceramic particles. If additional particles are added to the slip, the total particle diameter can be ≤ 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slip, in particular a smallest suitable wavelength, and / or the wavelength of a planned optical function of the slip and subsequently of the structure formed from it. A filling level of ceramic particles is set between 0 and 90 wt.%, preferably between 0 and 40 wt.%, so that a desired refractive index is achieved.

[0030] This disclosure further provides a method for fabricating a refractive index-matched structure. The method includes providing a refractive index-matched photocrosslinkable ceramic slurry according to the present disclosure and forming the refractive index-matched photocrosslinkable ceramic slurry into the refractive index-matched structure.

[0031] According to some embodiments, the method for producing a refractive index-matched structure may further comprise light-induced crosslinking of the organic matrix at the appropriate wavelength to form a ceramic green body.

[0032] According to some embodiments, the wavelength suitable for light-induced crosslinking of the ceramic slurry can be in a wavelength range from 100 nm to 850 nm, preferably in the range 350-550 nm, more preferably in the range 350-405 nm. When using a two-stage photocrosslinking, the wavelength suitable for light-induced crosslinking of the ceramic slurry can be in a combination of these wavelength ranges.

[0033] In embodiments, the light-induced crosslinking of the refractive index-matched structure may comprise a local exposure such that the photocrosslinkable ceramic slurry crosslinks locally.

[0034] Additionally, the light-induced crosslinking of the refractive index-matched structure may further comprise exposure to light such that the photocrosslinkable ceramic slurry is fully crosslinked. Such embodiments can produce a refractive index-matched and refractive index-graded structure.

[0035] According to a further aspect of this disclosure, a method for producing a refractive index-graded structure is provided. The term "refractive index-graded" can refer, for example, to at least two different refractive indices within a structure, in particular one manufactured integrally. For example, the structure comprises a first section with a first refractive index and a second section with a second refractive index, wherein the second refractive index differs from the first refractive index by at least 5%, in particular by at least 10%, preferably by at least 15%.

[0036] The method for producing a refractive index-graded structure comprises providing a photocrosslinkable organic matrix. Ceramic particles are added to the photocrosslinkable organic matrix to form a photocrosslinkable ceramic slurry.

[0037] The average diameter of the (ceramic) particles is ≤ 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slip, in particular the smallest suitable wavelength, and / or preferably the wavelength of a planned optical function of the slip and / or in particular later of the structure formed from it.

[0038] The method further comprises a first local exposure such that the photocrosslinkable ceramic slurry crosslinks locally in a first region. The method further comprises a second, subsequent exposure of the photocrosslinkable ceramic slurry such that the structure crosslinks in a second region encompassing the first region. The first exposure and the second exposure can be carried out at the same wavelength, duration, and / or intensity. The first region is typically smaller than the second region.

[0039] According to some embodiments, the local exposure can be performed two-dimensionally and / or three-dimensionally. The ceramic slurry can, for example, be spread into a film. In some embodiments, the slurry can be formed into a three-dimensional structure by injection molding or by filling a mold.

[0040] Local exposure can be achieved via x-ray spectroscopy, two-photon polymerization, and / or holography. Other methods for localized, area-wide or point-based exposure can also be used for local exposure. For example, 99.9% of the ceramic particles in the slurry can have a diameter ≤ 1 / 10 of the suitable wavelength, and 99.0% of the ceramic particles in the slurry can have a diameter ≤ 1 / 20 of the suitable wavelength. This enables longer optical path lengths for crosslinking.

[0041] In some embodiments, a filling level of ceramic particles in the photocrosslinkable organic matrix can be adjusted between 0 and 90 wt.%, in particular between 0 and 40 wt.%, such that a desired refractive index is achieved.

[0042] According to a further aspect, a refractive index-adapted photocrosslinkable ceramic slip is disclosed. The slip comprises a photocrosslinkable organic matrix and ceramic particles with an average diameter of the ceramic particles ≤ 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slip, in particular the smallest suitable wavelength, and / or in particular the wavelength of the intended optical function of the slip and / or in particular later of the structure formed from it.

[0043] A filling level of ceramic particles in the photocrosslinkable organic matrix is ​​adjusted between 0 and 90 wt.%, in particular between 0 and 40 wt.%, so that a desired refractive index is achieved.

[0044] In particular, reference is made below to embodiments of the disclosure, some examples of which are illustrated in the figures. Each example is intended to illustrate the disclosure, not to limit it. For example, features illustrated or described as part of embodiments may be used with other embodiments to yield further embodiments.

[0045] Fig. 1 schematically shows a method 100 for fabricating a refractive index-matched structure according to embodiments of the present disclosure.

[0046] The method 100 comprises providing a photocrosslinkable organic matrix 110. Ceramic particles are added 120 to the photocrosslinkable organic matrix. The average diameter of the ceramic particles is ≤ 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slurry. For example, the slurry can be configured to crosslink at a wavelength of approximately 400 nm. The average diameter d50, better d90, better of essentially all particles is then ≤ 40 nm.

[0047] The filling level of ceramic particles is adjusted between 0 and 90 wt.% so that a desired refractive index is achieved.

[0048] The method 100 further includes forming the refractive index-matched photocrosslinkable ceramic slurry into the refractive index-matched structure 130.

[0049] In embodiments, the method 100 may further comprise light-induced crosslinking of the organic matrix at the appropriate wavelength to form a ceramic green body 140.

[0050] The light-induced crosslinking can take place in such a way that the ceramic green body has a predetermined two-dimensional contour or a predetermined three-dimensional contour. For this purpose, for example, electromagnetic radiation, which brings about the photocrosslinking of the ceramic slurry, or at least the crosslinking of its organic matrix, can be directed onto a volume and / or a surface in such a way that the structure obtained by crosslinking has a desired two-dimensional geometry or three-dimensional geometry. The electromagnetic radiation can comprise two or more different wavelengths, such as approximately 400 nm and approximately 700 nm wavelength. The ceramic structure can thus be defined during crosslinking. This can take place, for example, by means of targeted beam guidance, for example with continuously or raster-guided laser light, or with the aid of photomasks and floodlight and / or laser light.For example, xolography can be used.

[0051] The resulting geometry of the ceramic structure can, for example, have a complex geometry. For example, the structure can have corners, straight, convex, and / or concave curved sections, such as edges (outer edges) and recesses, overhangs, and / or similar features. Likewise, it can have regularly or irregularly shaped openings, holes, and / or recesses distributed throughout its length.

[0052] The light-induced crosslinking of the refractive index-adapted structure may comprise a local exposure such that the photocrosslinkable ceramic slurry crosslinks locally in a first region.

[0053] Furthermore, the light-induced crosslinking of the refractive index-matched structure may comprise exposure such that the photocrosslinkable ceramic slurry crosslinks in a second region containing the first region.

[0054] Fig. 2 schematically shows a method 200 for manufacturing a refractive index graded structure according to embodiments of the present disclosure.

[0055] The method 200 comprises providing a photocrosslinkable organic matrix 110 and adding ceramic particles to the photocrosslinkable organic matrix so that a photocrosslinkable ceramic slurry is formed 120. The average diameter d50, better d90, better essentially all of the ceramic particles is ≤ 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slurry.

[0056] The filling level of ceramic particles can be adjusted so that a desired refractive index is achieved.

[0057] The method further comprises local exposure such that the photocrosslinkable ceramic slip is locally crosslinked 230. The local exposure 230 is carried out, for example, three-dimensionally via xolography.

[0058] The method further comprises exposing the photocrosslinkable ceramic slip such that the entire slip volume with embedded structure is completely crosslinked 240.

[0059] In the above description, a method for producing a refractive index-matched photocrosslinkable ceramic slurry, a method for producing a refractive index-matched structure, a method for producing a refractive index-graded structure, the use of a photocrosslinkable ceramic slurry for producing a refractive index-matched structure and / or a refractive index-graded structure, and a refractive index-matched photocrosslinkable ceramic slurry were presented with reference to specific examples. It should be noted that various aspects and embodiments disclosed herein may be combined in combinations other than the specific combinations illustrated in the figures.It is contemplated that various modifications may be made to the above embodiments without departing from the scope of the disclosure and the following claims.

Claims

[1] A method for producing a refractive index-adapted photocrosslinkable ceramic slip, comprising Providing a photocrosslinkable organic matrix (110); and Adding ceramic particles to the photocrosslinkable organic matrix (120); wherein the average diameter of the ceramic particles is ≤ 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slurry; wherein a filling level of ceramic particles is adjusted between 0 and 90 wt.% so that a desired refractive index is achieved; and where the diameter is measured using dynamic light scattering (DLS). [2] Method (100) for producing a refractive index-matched structure, comprising Providing a refractive index-matched photocrosslinkable ceramic slurry; and Shaping the refractive index-matched photocrosslinkable ceramic slurry into the refractive index-matched structure (130). [3] A method (100) for producing a refractive index-matched structure according to claim 2, further comprising light-induced crosslinking of the organic matrix at the appropriate wavelength to form a ceramic green body (140). [4] A method (100) for producing a refractive index-matched structure according to claim 3, wherein the light-induced crosslinking of the refractive index-matched structure comprises a local exposure such that the photocrosslinkable ceramic slurry crosslinks locally. [5] A method (100) for producing a refractive index-matched structure according to claim 4, wherein the light-induced crosslinking of the refractive index-matched structure further comprises exposure such that the photocrosslinkable ceramic slurry is fully crosslinked. [6] Method (200) for producing a refractive index graded structure, comprising Providing a photocrosslinkable organic matrix (110); and Adding ceramic particles to the photocrosslinkable organic matrix to form a photocrosslinkable ceramic slurry (120); wherein the average diameter of the ceramic particles is ≤ 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slurry; local exposure such that the photocrosslinkable ceramic slip locally crosslinks (230); and Exposing the photocrosslinkable ceramic slip to light such that the structure is completely crosslinked (240); where the diameter is measured using dynamic light scattering (DLS). [7] Method (200) for producing a refractive index graded structure according to claim 6, wherein the local exposure is carried out two-dimensionally and / or three-dimensionally, in particular wherein the local exposure is carried out via xolography, 2-photon polymerization and / or holography. [8] Use of a photocrosslinkable ceramic slurry to produce a refractive index-matched structure and / or refractive index-graded structure. [9] Refractive index-matched photocrosslinkable ceramic slurry, comprising a photocrosslinkable organic matrix; and ceramic particles with an average diameter of the ceramic particles ≤ 1 / 10 of a wavelength suitable for light-induced crosslinking of the ceramic slurry; wherein a filling level of ceramic particles in the photocrosslinkable organic matrix is ​​adjusted between 0 and 90 wt.% such that a desired refractive index is achieved; and where the diameter is measured using dynamic light scattering (DLS).

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