Patent Application
20180237927
The invention relates to methods for producing three-dimensional ordered porous microstructures. The methods disclosed herein have an advantage of reducing the processing time, while the three-dimensional ordered porous microstructures produced thereby exhibit excellent integrity and high reproducibility.
A highly ordered porous material having a pore size close to the wavelength of light may possess unique and useful optical properties, making it applicable in various technical fields, such as photocatalysis, biological carriers, adsorption, filtration, electrical insulation, semiconductors and micro-detection.
Taking advantage of their unique physical properties, the ordered porous microstructures may change the electromagnetic properties of light waves propagating therein. In such highly ordered porous material, electromagnetic waves will behave like electrons in a crystalline and can be controlled by, for example, changing the geometry, periodicity of pore regularity, structural pattern and dielectric constant of the porous material, without making any modification to the chemical structure of the porous material. As such, porous products with different optical properties may be created by adjusting photonic band-gap and the wavelength property of the porous material. New artificial crystalline material of this type has been called photonic crystal and considered as a class of new generation photoelectric material with high potential in various technical fields.
Ordered porous microstructures are basically made of medium material arranged periodically in one, two or three dimensions. One-dimensional ordered porous microstructures are generally referred to as optical multilayer films, which have commonly served as coatings on optical lenses. The periodic multilayer films exhibit one-dimensional photonic band-gaps in which photons are prohibited from propagating through the films and, as a result, certain wavelengths of light are reflected efficiently. Recently, periodic two- and three-dimensional microstructures have drawn considerable attention.
It is known in the art that a three-dimensional ordered porous microstructure having photonic crystal properties can be produced by self-assembling mono-sized polystyrene, poly(methyl methacrylate) or silicon dioxide nanospheres on a substrate by means of gravity sedimentation, centrifugation or vacuum filtration to create a three-dimensional ordered microstructure on the substrate, followed by using the three-dimensional ordered microstructure as a template in which inorganic siloxane monomers are then applied and subjected to a sol-gel reaction, and finally by removal of the substrate via calcination or extraction. However, the conventional process described above has to take several days to produce the three-dimensional ordered microstructure, making mass production unfavorable. Moreover, the microstructures thus fabricated often have a poor regularity, causing the three-dimensional ordered porous products produced thereby to suffer from the drawbacks of unsatisfied integrity and reproducibility and limited size.
R.O.C. Patent Publication No. 201544638 discloses a method for fabricating a three-dimensional ordered microstructure, which involves application of a shaping electric field to facilitate the self-assembling of particles, thereby forming a hexagonal closest packing of the particles. Compared with the conventional self-assembling processes, the electric field-driven self-assembling step of the method has advantages of time-saving and high productivity.
Nevertheless, there is still a need for technology that can produce three-dimensional ordered microstructures in a time-effective manner and produce large-area three-dimensional ordered porous microstructures with high integrity and reproducibility.
The methods for three-dimensional ordered porous microstructure disclosed herein can overcome the drawbacks described above.
In the first aspect provided herein is a method for producing a three-dimensional ordered porous microstructure, comprising the steps of:
In one preferred embodiment of the method disclosed above, the step of forming the three-dimensional ordered microstructure comprises placing the substrate into a suspension uniformly dispersed with the particles, applying a deposition electric field in a direction substantially perpendicular to the main surface, thereby depositing the particles onto the main surface, removing the substrate deposited with the particles from the suspension, and then applying a shaping electric field towards the substrate from periphery of the substrate, so that the particles deposited on the main surface are driven to self-assemble, thereby forming the three-dimensional ordered microstructure.
In the second aspect provided herein is a method for producing a three-dimensional ordered porous microstructure, comprising the steps of:
In one preferred embodiment of the method disclosed above, the step of forming the three-dimensional ordered microstructure comprises placing the substrate into a suspension uniformly dispersed with the particles, applying a deposition electric field in a direction substantially perpendicular to the main surface, thereby depositing the particles onto the sacrificial layer, removing the substrate deposited with the particles from the suspension, and then applying a shaping electric field towards the substrate from periphery of the substrate, so that the particles deposited on the main surface are driven to self-assemble, thereby forming the three-dimensional ordered microstructure.
In a preferred embodiment, the step of forming the three-dimensional ordered microstructure further comprises vertically orienting the substrate in the suspension before applying the deposition electric field.
In one preferred embodiment, the step of forming the three-dimensional ordered microstructure further comprises horizontally orienting the substrate before applying the shaping electric field.
In one preferred embodiment, the sacrificial material is selected from the group consisting of oxides, polymers and metals.
In one preferred embodiment, the inverse opal material is selected from the group consisting of metals, metal oxides and polymers.
In one preferred embodiment, the sacrificial material is sufficiently distinct from the inverse opal material in terms of a physical and chemical property.
Preferably, in the step of forming the three-dimensional ordered microstructure, at least some of the particles in the three-dimensional ordered microstructure achieve a close-packing arrangement.
In one preferred embodiment, the methods for producing a three-dimensional ordered porous microstructure further comprise a step of removing the sacrificial layer before or after the removal of the three-dimensional ordered microstructure.
In one preferred embodiment, the methods further comprise a step of patterning either the substrate or the sacrificial layer before the step of forming the three-dimensional ordered microstructure, such that the particles can only be deposited within confined regions on the substrate or the sacrificial layer.
According to a preferred aspect of the method disclosed herein, the three-dimensional ordered microstructure is formed by self-assembling the particles deposited on a substrate into a close-packing arrangement. The three-dimensional ordered microstructure is then used as a template, and a sacrificial layer is further used as a supportive structure, so as to produce a large-area three-dimensional ordered porous microstructure with high integrity and reproducibility.
The above and other objects, features and effects of the invention will become apparent with reference to the following description of the preferred embodiments taken in conjunction with the accompanying drawings, in which:
According to the invention, the term “three-dimensional ordered microstructure” may refer to any microstructure formed through a three-dimensional ordered arrangement of constituting particles. The term “ordered” as used herein may refer to the particles being arranged in a regular or periodic manner, preferably being spaced apart from one another in an equal distance. The particles which constitute the microstructure are normally made uniform in particle size, shape, chemical composition, inner texture and surface property, such that the non-covalent interactions among them are facilitated, whereby they spontaneously arrange themselves into a lattice-like regular structure. In a preferred embodiment, the particles are equal spheres having a uniform particle size, more preferably having a uniform particle size ranging from 1 nanometer to 1000 microns, such as from 10 nanometers to 100 microns. Non-limiting examples of the material that may be used to produce the particles include polymeric materials, inorganic materials and metallic materials. Examples of the polymeric materials include but are not limited to polystyrene (PS), poly(methyl methacrylate) (PMMA), polyacrylates, poly(benzyl methacrylate), poly(α-methyl styrene), poly(phenyl methacrylate), poly(biphenyl methacrylate), poly(cyclohexyl methacrylate), acrylonitrile-styrene copolymers and styrene-methyl methacrylate copolymers. Examples of the inorganic materials include but are not limited to titanium oxide, zinc oxide, cerium oxide, tin oxide, thallium oxide, barium oxide, aluminum oxide, yttrium oxide, zirconium oxide, copper oxide, nickel oxide and silicon oxide. Examples of the metallic materials include but are not limited to gold, silver, copper, platinum, aluminum, zinc, cerium, thallium, barium, yttrium, zirconium, tin, titanium, cadmium, iron and the alloys thereof. In a preferred embodiment, the particles used are polystyrene particles or silicon dioxide particles. Processes for manufacturing the micron- or nano-scale particles are known in the art. For instance, in the case where the particles used are made of polystyrene, an emulsifier-free emulsion polymerization process may be employed to synthesize polystyrene spheres having a particle size of hundred nanometers.
In a preferred embodiment, at least some of the particles in the three-dimensional ordered microstructure are in a close-packing arrangement, i.e., adjacent particles being tangent to one another and the centers of any three mutually tangent particles forming an equilateral triangle, while each particle has a coordination number of 12 and there leaves triangular voids among the particles. More preferably, at least some of the particles in the three-dimensional ordered microstructure are in a hexagonal closest packing (hcp) arrangement, a face centered cubic packing (fcc) arrangement, or a combined arrangement thereof. The inverse structure produced by using the three-dimensional ordered microstructure stated above as a template may be referred to herein as a three-dimensional ordered porous microstructure.
The three-dimensional ordered microstructure stated above can be formed by self-assembling of the particles. The term “self-assembling” or “self-assemble” as used herein may refer to a process of micron- or nano-scale particles aggregating into the three-dimensional ordered microstructure in response to the conditions present in the environment. In particular, self-assembling refers to a process in which the particles interact non-covalently with one another to spontaneously form three-dimensional ordered microstructure under near thermodynamic equilibrium conditions. The inventive methods may enhance the deposition of the particles by applying a deposition electric field and further facilitate the self-assembling of the particles by applying a shaping electric field.
According to the invention, the methods disclosed herein have an advantage of reducing the processing time, while the three-dimensional ordered porous microstructures produced thereby exhibit excellent integrity and high reproducibility.
The step of forming the three-dimensional ordered microstructure may be referred from the disclosure provided in R.O.C. Patent Publication No. 201544638, which is hereby incorporated by reference in its entirety. First, a suspension 20 is prepared, in which a plurality of colloid spherical particles 11 are uniformly dispersed. For example, in the case where the colloid spherical particles used are made of polystyrene or silicon dioxide, the suspension 20 may be prepared by uniformly dispersing the particles in a solvent. Suitable solvents include any known solvents which can achieve the purpose of uniformly dispersing the particles without chemically reacting with the particles and the other participants existing in the method. The solvent may be either an organic solvent or an aqueous solvent, including but not limited to water and C1-6 alkanols, preferably anhydrous ethanol. Since the colloid spherical particles 11 dispersed in the solvent are imparted with surface charges by applying an external electric field of appropriate strength, they are driven by the electric field to move towards the electrode of opposite charge. A substrate 30 is placed into the suspension 20, and a deposition electric field is applied in a direction substantially perpendicular to the substrate 30 (as shown in
In the step of forming a sacrificial layer 40, a sacrificial material 41 is filled into the interstitial voids 12 until it reaches a first predetermined thickness (as shown in
In the step of filling interstitial voids, an inverse opal material 51 is filled into the interstitial voids 12 of the three-dimensional ordered microstructure 10 until it reaches a second predetermined thickness on the sacrificial layer 40 (as shown in
In the step of removing the three-dimensional ordered microstructure, the particles 11 existing in the three-dimensional ordered microstructure 10 are removed after the inverse opal material 51 is cured (as shown in
As shown in
As shown in
As shown in
As shown in
Before utilizing the three-dimensional ordered porous microstructure 50 disclosed herein in a desired application, it can be easily separated from the substrate 30 by removing the sacrificial layer 40. In one preferred embodiment, the free-standing three-dimensional ordered porous microstructure 50 may serve as a three-dimensional porous scaffold. The step of removing the sacrificial layer 40 may be carried out either before or after the removal of the three-dimensional ordered microstructure 10. In other preferred embodiment, the free-standing three-dimensional ordered porous microstructure 50 may function as a porous template, into which other crystalline material may be filled. After the crystalline material is cured, the three-dimensional ordered porous microstructure 50 may be removed to obtain a three-dimensional ordered microstructure having a predetermined function.
According to one preferred embodiment of the invention, in the step of forming the three-dimensional ordered microstructure, the deposition electric field is applied to act on the particles such that the particles are deposited onto the substrate rapidly, and the shaping electric field is applied subsequently such that the particles deposited on the substrate surface are urged to jostle one another and self-assemble into a three-dimensional ordered microstructure composed of a close-packing of the particles. The methods disclosed herein have an advantage of reducing the processing time for producing three-dimensional ordered porous microstructures, while the three-dimensional ordered porous microstructures produced thereby exhibit excellent integrity and high reproducibility. As such, the inventive methods are beneficial for production of large-area three-dimensional ordered porous microstructures.
In addition, according to the methods for producing a three-dimensional ordered porous microstructure disclosed herein, either the main surface 31 of the substrate 30 or the sacrificial layer 40 may be patterned before the formation of the three-dimensional ordered microstructure thereon, such that the particles can only be deposited within confined regions on the substrate or the sacrificial layer. According to one preferred embodiment of the invention, the step of forming the three-dimensional ordered microstructure further comprises vertically orienting the substrate 30 in the suspension before applying the deposition electric field and/or horizontally orienting the substrate 30 before applying the shaping electric field.
Moreover, the step of forming the three-dimensional ordered microstructure may involve formation of the three-dimensional ordered microstructure composed of a close-packing of the particles on the main surface of the substrate by means of gravity sedimentation, centrifugation, vacuum filtration or electrophoresis.
The following examples are given for the purpose of illustration only and are not intended to limit the scope of the invention.
A 40 mL styrene monomer solution (99.6 wt %) was added into a 300 mL sodium bicarbonate (12 mM) and sodium styrene sulfonic acid solution. The mixture was stirred at 350 rpm for 1 hour, while its temperature was kept at 65° C. Then, potassium sulfate (0.25 g) was added into the mixture to initiate the polymerization reaction. After 16 hours, all the styrene monomers were completely consumed. In this example, polystyrene particles with diameters of 300, 405 and 600 nm were prepared by controlling the concentration of sodium styrene sulfonic acid solution at 0.8, 0.48, and 0.13 mM, respectively.
Suspensions of polystyrene particles at a concentration of 0.01 g/ml were prepared by dispersing the polystyrene particles of Example 1 in anhydrous ethanol, and the pH was adjusted to 9 using NH4OH. 2.5×2.5 cm2 indium tin oxide (ITO)-coated glass substrates were purchased from UNI-Ward Corporation, Taiwan (under a catalog No. UR-ITO007-0.7; each having a sheet resistance of 7Ω/□ and a thickness of 0.7 mm). A deposition electric field was applied at 10 Volts/cm in a direction generally perpendicular to an ITO-coated substrate described above for 10-15 minutes, thereby depositing the polystyrene particles on the ITO-coated substrate. Three-dimensionally ordered microstructures with a thickness of more than 12 μm were formed by using polystyrene particles having diameters of 300, 405 and 600 nm, respectively.
At the bottom side of each of the three-dimensionally ordered microstructures prepared in Example 2, a thin nickel layer was plated as a sacrificial layer. The Ni plating entailed a galvanostatic current of 2.5 mA/cm2 for 5-10 minutes, with the three-dimensionally ordered microstructures used as a working electrode and a 4×4 cm2 Ni foil employed as a counter electrode in a Watt's bath electrolyte. Next, a gold aqueous electroplating solution containing 0.05M HAuCl4, 0.42M Na2SO3, 0.42M Na2S2O3, and 0.3M Na2HPO4 was prepared. An Au layer was then deposited on top of the sacrificial Ni layer by applying a fixed voltage at 0.8V for 90 minutes, with a platinum foil (4×4 cm2) used as a counter electrode. Subsequently, the sample was immersed in ethyl acetate for 24 hours at 25° C. to dissolve away the polystyrene particles, so that a Ni—Au inverse opal film was formed. Finally, the Ni—Au inverse opal film was immersed in a 0.1M HNO3 solution at 25° C. to dissolve Ni, thereby forming a three-dimensional ordered porous microstructure made of gold. In this example, three-dimensional ordered porous microstructures were prepared using the three-dimensional ordered microstructures having particle diameters of 300, 405, and 600 nm as templates.
Compared with the conventional methods, the methods disclosed herein are characterized in that during the formation of the three-dimensional ordered microstructure, the deposition electric field is applied to act on the particles such that the particles are deposited onto the substrate rapidly, and the shaping electric field is applied subsequently such that the particles deposited on the substrate surface are urged to jostle one another and self-assemble into a three-dimensional ordered microstructure composed of a close-packing of the particles. As such, the methods disclosed herein have an advantage of reducing the processing time for producing three-dimensional ordered porous microstructures. The presence of the sacrificial layer in the invention may further help maintaining the structural integrity of the three-dimensional ordered porous microstructure when the microstructure is being separated from the substrate, thereby obtaining a large-area three-dimensional ordered porous microstructure with high integrity and reproducibility. Moreover, the three-dimensional ordered porous microstructure produced thereby may be employed as a template for fabrication of a highly ordered packed three-dimensional microstructure.
While the invention has been described with reference to the preferred embodiments above, it should be recognized that the preferred embodiments are given for the purpose of illustration only and are not intended to limit the scope of the present invention and that various modifications and changes, which will be apparent to those skilled in the relevant art, may be made without departing from the spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201510764258.3 | Nov 2015 | CN | national |
This application is a 371 of International Application No. PCT/CN2016/105422 filed Nov. 11, 2016, which claims priority to Chinese Patent Application No. 201510764258.3, filed Nov. 11, 2015, both of which are hereby incorporated by reference in their entirety. Part of the data disclosed in this application was published on Nov. 5, 2016 in Journal of Alloys and Compounds, entitled “Free-standing Au inverse opals for enhanced glucose sensing”.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2016/105422 | 11/11/2016 | WO | 00 |
