Patent Application
20060009536
The present invention relates to a sol-gel material, and more particularly, to a functionalized sol-gel material, a method of preparing the same, and a sol-gel film derived therefrom.
Organic-inorganic hybrid materials possess not only the advantages of organic materials, such as processibility and flexibility, but also the advantages of inorganic materials, like high mechanical strength and high thermal properties, and hence are studied internationally and are widely applied in various fields. In general, a hybrid material is prepared by mixing an organic material and an inorganic material, which are associated by molecular forces therebetween, such as, for example, London-van der Waals force or hydrogen bonding, on a nanometer scale. Therefore, the hybrid material is formed without phase separation in the macroscopic view, and further combines the properties of the organic material and the inorganic material.
Due to the poor thermal properties of organic materials, organic-inorganic hybrid materials cannot be prepared in a conventional ceramic-manufacturing process. Instead, a sol-gel process is usually adopted to fabricate organic-inorganic hybrid materials. Sol-gel process including a hydrolysis step and a condensation step performed at a low temperature. Consequently, organic materials can be introduced into inorganic materials without degradation.
The organic-inorganic hybrid materials prepared by the sol-gel process, however, are easily influenced by surrounding conditions, such as, for instance, temperature or humidity. As a result, the organic-inorganic sol-gel materials tend to age, which decreases the shelf life thereof. Additionally, the organic-inorganic sol-gel materials with a nanometer dimension incline to aggregate with one another. To stabilize the properties and the sizes of the organic-inorganic sol-gel materials, chelating agents are required in preparing the same. The chelating agents are, for example, methacrylic acid, acetic acid, and acetyl acetone.
On the other hand, the solid content of the organic-inorganic sol-gel materials prepared by the sol-gel process is usually around 20% to 30%, of which the viscosity is not high enough for preparing a thick sol-gel film. Unfortunately, raising the solid content by increasing reaction time and reactant concentrations directly results in gelation of the organic-inorganic sol-gel materials. Moreover, phase separation occurs if the viscosity of the organic-inorganic sol-gel materials is increased by adding another polymer solution with higher viscosity.
It is the objective of the present invention to provide a method of preparing a functionalized sol-gel material without using chelating agents. The functionalized sol-gel material is stable on a nanometer scale, through which a thick sol-gel film is further fabricated.
According to the aforementioned objective of the present invention, on the one hand, a functionalized organic-inorganic sol-gel material and a preparation method thereof are provided. An organic material and an inorganic material are separately mixed with corresponding solvents, followed by mixing the solvents and heating the same for a period of time to form a sol-gel material. The inorganic material is a metal alkoxide of which the un-saturation degree of the metal atom therein is greater than zero, while the organic material is an organically modified Si-alkoxide. The interaction between the sol-gel materials is effectively reduced, which prevents the sol-gel materials from aggregating with one another, by selecting proper solvents at the beginning of preparation. Therefore, the functionalized organic-inorganic sol-gel material with a stable nanometer dimension is formed by means of the selected solvents instead of any chelating agents.
According to the aforementioned objective of the present invention, on the other hand, a method for preparing a thick sol-gel film derived from a functionalized sol-gel material is provided. The solid content of a functionalized sol-gel material is dramatically raised by transferring the sol-gel material into a selected solvent. A thick and uniform film is then formed more easily, since the solid content of the sol-gel material has been increased. Hence, the sol-gel material after being transferred can be used to fabricate directly a thick film with no need of other adhesives, like polymer solution with higher viscosity.
The foregoing aspects, as well as many of the attendant advantages and features of this invention will become more apparent by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
It is found that an organic-inorganic sol-gel material with a stable dimension on a nanometer scale is prepared with no need of chelating agents, if the stability of a reactive solution is properly controlled according to the following equations at the beginning of preparation.
Equation (1) represents the attraction energy (Vatt) between two spherical particles (medium 1) dispersed in a medium 3, where A13 is the Hamaker constant and H(x, y) is the Hamaker function, which depends on the inter-particle distance and on the particle radius. An approximate expression for A13 is given by equation (2), where ε1 and ε3 are the dielectric constants of the media, n1 and n3 are their refractive indexes in the visible range, νe is the absorption frequency of the media assumed to be the same for both of them, k is the Boltzmann constant (1.38×10−23 J·K−1), T is the absolute temperature, and h is the Planck's constant (6.626×10−34 J·s).
According to these equations, the interaction between particles is dependent on the properties of a medium where the particles are dispersed. Consequently, the attraction energy between particles is reduced if an adequate medium is selected; the particles are thus less attracted to one another and aggregate less. Therefore, particles with stable dimensions are obtained without using any chelating agents. By this principle, a functionalized sol-gel material, a method for preparing the same, and a thick sol-gel film derived therefrom in accordance with the preferred embodiments of the present invention are disclosed in detail as follows, taken in conjunction with the accompanying drawings.
One aspect of the present invention is to provide a metal alkoxide and an organically modified Si-alkoxide having a predetermined functional group as precursors to form a functionalized sol-gel material. Additionally, solvents are selected according to the principle mentioned above before preparing the material. As a result, stable reactive surroundings for the material are provided at the beginning of preparation.
The metal alkoxide can be formulated as M(OR)x, where M is a metal atom, x is the valence of M, and R represents C1-C12 alkyl. Further, the un-saturation degree of the metal atom (i.e. the difference between the coordination number and the valence of M) is greater than zero. The metal atom is, for example, titanium (Ti), zirconium (Zr), germanium (Ge), tin (Sn), or cerium (Ce). The aforesaid metal alkoxide may be zirconium butoxide (Zr(OBu)4) or zirconium proxide (Zr(OPr)4), and is preferably zirconium butoxide in the embodiment. Furthermore, the organically modified Si-alkoxide can be expressed as R1Si(OR)3 or R1R2Si(OR)2, where R represents C1-C12 alkyl, and R1 and R2 are hydrocarbyl groups that may be different or the same. The predetermined functional group (R1 or R2) may be an epoxy group or an amine group (—NH), or an unsaturated functional group, such as a vinyl group, an acryl group, or a photosensitive derivative thereof. Moreover, methacryloxypropyl tri-methoxysilane (MPTMS) is preferably used in the embodiment.
Reference is made to
The resultant material is a transparent solution, which also implies that the resultant particles are on a nanometer (nm) scale and are well dispersed in the solvents. The Fourier Transformation infrared (FTIR) spectrum of the particles is shown in
Further, the attraction energy (A13) of THF as calculated by the aforementioned equation (2) is 11.1 or so. As a result, the interaction between the particles is decreased by THF, which prevents the particles from attracting one another and aggregating. Therefore, a sol-gel particle with stable dimensions is prepared through adequate solvents. Moreover, THF is only an exemplary solvent, and is not intended to limit the invention. Other solvents that provide stable reactive surroundings, for instance, toluene (A13 is about 12.1) or propylene glycol monoether acetate (PMAc) (A13 is about 9.6), are also used to prepare an organic-inorganic sol-gel material with stable dimensions.
On the other hand, the aforenamed precursors and the proportions thereof are merely in favor of illustrating the embodiment. It is appreciated that any substitutes, although not described or shown herein, which embody the principles of the invention, are included within the spirit and scope of the invention. For instance, a sol-gel material having an epoxy group on a nanometer scale is formed through 3-glycidoxypropyl trimethoxysilane (GLYMO), in the case where solvents are appropriately selected at the beginning of preparation.
In this embodiment, an organic-inorganic sol-gel material is formed in alcohol under the same preliminary conditions as those in embodiment 1. The material in alcohol is further compared with materials formed in different solvents, which results are listed in Table 1.
It is found from Table 1 that, a transparent solution and nano-particles are obtained if an adequate solvent is selected. Consequently, particles attract one another and aggregate less, and thus have stable sizes, because solvents decrease the interaction between particles. On the contrary, larger particles are given in alcohol, and the resultant solution is opaque. Furthermore, the dielectric constant of solvents is preferably smaller than 10.
For preparing a thick sol-gel film, the solid content of a sol-gel material is increased by transferring the same into another solvent in accordance with the present invention. The sol-gel material of Embodiment 1 herein is only an example to describe the process for convenience, which is not proposed to limit the invention.
Reference is made to
A thick and uniform sol-gel film is derived directly from a transferred sol-gel material in accordance with the embodiment. Consequently, no binder is required, and no phase separation occurs. Additionally, the thickness of a sol-gel film can be controlled by adjusting the solid content of a sol-gel material. Further, the transmission of the sol-gel film coated on a glass is above 90% in the visible range of 400 nm to 700 nm and at wavelengths of 1310 nm and 1550 nm. The baking temperature or species of the initiator and the third solvent are exemplary descriptions only, and are not proposed to limit the invention.
According to the aforementioned preferred embodiments of the present invention, a functionalized organic-inorganic sol-gel material is prepared without any chelating agents in selected solvents. The resultant sol-gel particles are on a nanometer scale, and are stably dispersed in the selected solvents. On the other hand, a thick sol-gel film is fabricated by means of the sol-gel material of which solid content is effectively increased by transferring the same into another solvent.
While the invention has been particularly shown and described with reference to the preferred embodiments thereof, these are, of course, merely examples to help clarify the invention and are not intended to limit the invention. It will be understood by those skilled in the art that various changes, modifications, and alterations in form and details may be made therein without departing from the spirit and scope of the invention, as set forth in the following claims.
