TWI252213B - Preparation of silica aerogel crosslinked with organic molecule - Google Patents

Abstract

The present invention discloses a high-temperature stable, tough and hydrophobic organic-molecule-crosslinked silica aerogel prepared by carrying our a sol-gel process of inorganic siloxane to form a wet gel; adding an organic molecule having two terminal isocyanate groups to the wet gel, so that the isocyanate groups of the organic molecule reacts with hydroxyl groups contained in the wet gel; aging and supercritical drying the modified wet gel to form the organic-molecule-crosslinked silica aerogel. The hydrophobation of the aerogel of the present invention prevails after several times of high-temperature treatments, and the structure of the aerogel will not collapse caused by moisture.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preparing an organic molecularly crosslinked ceria aerogel, in particular to an organic molecule crosslinked oxidation with improved mechanical strength and hydrophobicity. A method for preparing a helium gel. This organic molecularly crosslinked ceria aerogel can be used as a thermal insulating material. In the prior art, when glass or ceramics are generally produced by a sol-gel method, siloxane is the most commonly used precursor, and the chemical formula of the decane oxide can be expressed as Si(OR)4. Wherein represents an alkyl group. The gel-melting process is mainly divided into two steps of hydrolysis and condensation: 1. Hydrolysis Reaction One of the OR-based oxides reacts with water, and most of these substances are easily hydrolyzed into murine oxides. One of the molecules, the 〇H group, is substituted for a 〇R group to form a decane oxide containing an OH group, and the alcohol is released, and the precursor Si(〇R)4 is scrambled with water to catalyze by acid or catalysis. The hydrolysis is carried out, and the chemical reaction mechanism is as follows:

(R〇)s SiOR + AH20 <^> HOSi(OR)3+ROH ^>Si{OH)A+AROH (1) Month ij drive with tetraethoxy Shi Xi Yuan $ / (Ο C2 open 5) 4 (tetraethylorthosilicate, or tetraethoxysilane, referred to as TEOS): (2)

Si(0C2H5)A^4H20^Si(OH)A+4C2H5OH 1252213 A oxane oxide containing a hydroxyl group, which readily reacts with an alkane or a hydroxyl group in other alkoxides to form a bridge. Bridging oxygen) releases alcohol or water', as shown by the following reaction formula, to form a wet gel of a silica dioxide network.

0H

0H

HO*—Si— q—Si—Off OH H2〇

OH 0H L HO—Si— ο-Ι Ο

OH l •Si— OHI 〇 OH

HO—Si—〇—Si—〇—Si— OH‘ A

〇 OH HO—Si— OH H〇一si OH

OB

OH then uses water to wash away the salt in the wet gel, and then exchanges the water with alcohol. Finally, the alcohol is removed by evaporation under high pressure; or the wet gel is dried directly by a supercritical fluid to produce an aerogel. To avoid the problem of collapse and cracking of the gel structure caused by strong surface tension from the liquid-gas interface when water or solvent evaporates. Cerium dioxide aerogels are lightweight, low-density, high-surface-memory materials (mes〇P〇rous materials) that are typically used in temperature-sensitive products to improve their energy efficiency. The aerogel will increase in ik time and deteriorate. This is because in a humid environment, 8 丨 atoms will be attacked by 0H nucleus phiiic aUack, causing 8丨-〇-Si bond rupture, resulting in The structure cracked. At the same time, in view of the long-term use of materials, aerogels need to provide water or hydrophobic properties to improve the moisture. On the other hand, since the chemical composition of the gas breaker is sulphur dioxide, it is as brittle as glass. 1252213 Aiming at improving the mechanical properties of sulphur dioxide and aerogels Sch· Schmidt and F. Schwertfeger (Journal of Non-Crystalline Solids 225 (1998) 364-368) first proposed the concept of gas/coil-bond molecular binder system, bonding The agent can be divided into a dry or wet system, and the dry system mainly comprises a thermoplastic polymer, which can be particles or fibers. Wet systems contain dispersants, suspending agents, foams or melted states. At present, GS KIM and SH HYUN (Journal of Materials Science 38 (2003) 1961_1966) propose to form a dry, wet and double-mixed composite of polyvinyl butyral (PVB) and aerogel, and find a dry mix. For composite materials, the aerogel addition ratio is only up to (~7〇 volume%), which is due to the difference in density between 卩¥6(0.23 5 £/〇1113) and aerogel (〇.128§/〇1113). Very large, resulting in poor mixing uniformity and the inability to apply a hot pressed layer to composite composites. On the other hand, for wet mix composites, the aerogel addition ratio is up to (~90% by volume), but the heat transfer coefficient is higher than that of the dry composite, because the heat transfer will take the continuous PVB phase. If the aerogel particles are coated with aerogel particles and the aerogel particles are not covered with P VB, the aerogel addition ratio can reach (~97·5 vol%), which can improve the first two modes. Disadvantages • Dry type cannot be evenly distributed and wet high heat transfer coefficient. Although the double-mixing method can obtain the heat transfer coefficient close to the original cerium oxide aerogel, the mouth has a small ρνΒ, and the rupture modulus is very low, so the mechanical brittleness is very poor. 0 SUMMARY OF THE INVENTION The present invention proposes an organic molecular crosslinking method. Improve the rupture modulus, different from the above-mentioned auscultation, do not need to add too much organic molecules, as long as each heat 1252213 plastic molecules cross-link between the backbones of the helium gel, does not need to form a continuous organic phase, so it will not The heat transfer coefficient is lowered too much; at the same time, the area of the joint region between the helium gel particles and the particles is increased, so that the fracture toughness is improved, and on the other hand, the hydrophobicity is also increased. In addition to the heat transfer and mechanical toughness, the organic molecularly crosslinked non-ferrous oxide aerogel of the present invention is also improved in hydrophobicity. The present invention uses tetramethoxysilane (TM 〇s) as a precursor to the oxidized stone. The sol-gel reaction of the present invention uses ethanol and ethyl acetoacetate (ETAC) as a co-solvent for the precursor and water, and ammonia (NH4〇H) as a catalyst. a wet gel obtained by further adding a solution of two isocyanate-terminated organic molecules to the sol-gel reaction, wherein the hydrogel contains a trans group which reacts with a terminal isocyanate group of the organic molecule, After the aging treatment and supercritical drying, the organic molecularly crosslinked ceria aerogel of the present invention can be synthesized. Suitable diisocyanate-terminated organic compounds suitable for use in the present invention include, but are not limited to, toluene diisocyanate, 'diphenylmethane diisocyanate', and diphenylmethane diisocyanate Hexarnethylene diisocyanate, Cycl〇hexane diisocyanate 'is〇ph〇rone diisocyanate' napht ialene diisocyanate ,

A phenylene diisocyanate, a diisocyanate S-blocked fluoropolymer, a diisocyanate-terminated prepolymer, or a mixture thereof. A suitable amount of the two isocyanate-terminated organic molecules is between (10) and TMOS 1252213. The right-handed, preferred embodiment of the present invention: a transparent, low-density organic molecularly crosslinked dioxane aerogel with improved stability, diligence, and hydrophobicity, using wow ethanol: H2Q: NH4〇H = 1: ΐΜ 2: 3: 4 χ. Embodiments The present invention provides a method for preparing organic molecules for crosslinking, comprising the steps of: cerium oxide aerogel

0 Preparation of wet gel ethyl acetate, ethanol, contained in a mixture containing tetramethoxy decane, ethyl hydrazine water and a base to carry out hydrolysis and condensation reaction of tetramethoxy decane to form a wet gel The molar ratio of Oxygen is 0H.2, wherein the molar ratio of ethyl acetoxyacetate to ethanol to tetradecyloxydecane is between 10-15 · 'water and tetradecyloxydecane. The molar ratio of the tetramethoxysilane in 2_4 is between 2χ1〇-3_6χ1〇_3; 11) contacting the wet gel with the two isocyanate-terminated organic molecules, the two isocyanate-terminated organic molecules are the TMOS The ear ratio is between 0·06 and 〇·〇8, wherein the hydroxyl group contained in the wet gel reacts with the terminal isocyanate group of the organic molecule; ill) the crosslinked wet gel obtained in the step ii) is contacted with a super A critical fluid to remove water, alcohol, alkali, and solvent trapped therein, thereby forming an organic molecule crosslinked ceria. Preferably, the two isocyanate-terminated organic molecules of step ii) are toluene diisocyanate, diphenylmethane diisocyanate, dihexyl diisocyanate, 1252213 (hexamethylene diisocyanate) ), cyclohexane diisocyanate, isophorone diiSocyanate, naphthalene diisocyanate, phenylene diisocyanate, diisocyanate, diisocyanate terminated A polymer, a diisocyanate-terminated prepolymer, or a mixture thereof. More preferably, the two isocyanate-terminated organic molecules are exohexyl diisocyanate. Preferably, the molar ratio of ethanol to tetramethoxynonane in step i) is 12; the molar ratio of water to tetramethoxynonane is 3; the molar ratio of base to tetramethoxynonane is 4xl 〇-3. Preferably, the base of step i) is aqueous ammonia. Preferably, the supercritical fluid is called the supercritical fluid of the carbon dioxide supercritical fluid, and the wet isolating solution prepared by the step i) of the invention is a mixture of the isocyanate solution and the propylene carbonate (pr〇pyi_“two'). The liquid is cleaned, and the ethanol in the wet gel is removed, and then the high thermal stability, the hydrophobicity-enhancing transparent and low-density organic differentiation of the aerogels are carried out in the preferred embodiment. The preparation method is as follows:

h Add tetramethoxy decane (TM 〇 S) to the ET (ammonia, catalyzed, hydrolyzed water, and tempered T r. The mouth condensation to form a wet gel. In order to serve low density and transparent dioxide The ratio needs to be maintained within a certain range 成份 ... Ingredients Mo AC • Ethanol: η2ο : 1252213 ΝΗ 4〇Η = 1:1: χ: γ: ζ, where χ is between ι〇~ΐ5; γ is between 2~ Ζ between 2χ1 〇-3~6xl (r 3. 2. Add an organic solution of a cross-isocyanate-terminated organic molecule such as diisonate, wherein the molar ratio of TM〇s to diisocyanate is 1:0 ·06 to 1:0.08. 3· Then at temperature 60, aging is about 2 to 5 days. 4. Finally, supercritical drying of carbon dioxide (temperature 8 (rc, pressure 15.7 MPa) 〇 Example (a 1 mole of tetradecyloxydecane and 1 molar ethyl acetate (ETAC) was dissolved in 12 moles of ethanol. 4χ10·3 moles of ammonium hydroxide was mixed with 3 moles of deionized water. The two solutions were slowly mixed in a reaction tank and uniformly stirred at 200 rpm for 30 minutes. (b) The reaction vessel was shielded from the outside air by a gas impermeable membrane and allowed to stand for 48 hours. Gelation. _ (c) Adding diisocyanate _ solution, pr〇pyiene carbonate, acetone (volume ratio = 1: 1 : 3) to clean the wet glue to remove the glue Ethanol solution · (d) After 12 hours, add hexamethylene diisocyanate (HMDI) solution (HMDI 0.078 mol dissolved in 500 ml of acetone solvent). (e) at a temperature of 1 ° ° Under C, aging treatment for 2 to 5 days to form a crosslinked wet gel. 11 1252213 (f), put the wet gel into a pressure cooker, and pass a carbon dioxide supercritical fluid for supercritical drying. The supercritical drying condition is (temperature 801, pressure 15·7 MPa) 〇

In the stomach, at 1 hour, the introduction of carbon dioxide supercritical fluid was stopped, and the pressure was gradually lowered ((MMPa/min) to normal pressure and then lowered to room temperature]. An organic: sub-crosslinked emulsified chopped gel was taken out.

The organic molecularly crosslinked cerium oxide aerogel prepared in this embodiment has a 0.005 kg/cm3, a BET specific surface area of 1 〇〇〇m2/g, a pore volume of 〇2 cm3/g, a pore size of about Inm, and a heat conduction system. The number is 5w/m_k. The water contact angle of the ceria aerogel after the second high temperature heat treatment (5 ° C, 0.5 hours). Further, the cross-linking of the organic molecules was measured as a water contact angle higher than 13 Å. .

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Claims (1)

1252213 X. Patent Application Range: 1 · Preparation method of a rare earth oxide aerogel of organic molecule parent, comprising the following steps: 1) preparing a wet gel, comprising a tetramethoxydecane, an ethylene group The mixture of ethyl acetate, ethanol, water and alkali is subjected to hydrolysis and condensation reaction of tetramethoxy decane to form a wet gel, wherein the molar ratio of ethyl acetoacetate to tetramethoxy decane is (1) 8_1· 2; the molar ratio of ethanol to tetramethoxy decane is between 10-15; the molar ratio of water to tetramethoxy decane is between 2 and 4; the molar ratio of tetramethoxy decane is between 2 and 1 〇 - 3_6χ1()_3 ; φ Π) contacting the wet gel with two isocyanate-terminated organic molecules, the two isocyanate-terminated organic molecules having a molar ratio to TMOS ranging from 〇·〇6 to 〇·〇8, Wherein the hydroxyl group contained in the wet gel reacts with the terminal isocyanide and acid ester groups of the organic molecule; 111) contacting the crosslinked wet gel obtained in the step U) with a supercritical fluid to remove the trapped in the supercritical fluid. Water, alcohol, and solvent, thus forming an organic molecule cross-linked dioxide. 2. The method of claim 1, wherein the two isocyanate of the step 丨丨) is a toluene diisocyanate, diphenylmethane diisocyanate, and diphenylmethane diisocyanate. , hexamethylene diisocyanate, cyclohexane diisocyanate, 'isophoric acid|isocyanus diisocyanate' nai _ isocyanate ί| Naphthalene diisocyanate), 13 1252213 phenyiene diis〇cyanate, a diisocyanate-terminated oligomer 'a diisocyanate-terminated prepolymer, or a mixture thereof, etc. 3. The method of claim 2 Wherein the two cyanate-terminated organic molecules of step ii) are exohexyl diisocyanate particles. , where step i) tetradecyloxydecane is 4x 1 (Γ3 〇 4. The molar ratio of ethanol to tetradecyloxydecane is 1 2 as in the method of claim 1, 2 or 3; the molar ratio of water to 3 is 3; Ear ratio 5. The method of claim </ RTI> </ RTI> wherein the test is ammonia. 6. The method of claim 3, wherein the stepped supercritical fluid is a carbon dioxide supercritical fluid. 7. The method of claim i, further comprising: washing the wet gel obtained in the step i) with a mixture containing a diisocyanate solution, a propylene earbonate and acetone, and removing the wet condensation The ethanol in the gel is then subjected to the step ϋ). 14