CN109592689B - Silica aerogel based on linear organic silicon oligomer, preparation method and application - Google Patents
Silica aerogel based on linear organic silicon oligomer, preparation method and application Download PDFInfo
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Abstract
The invention discloses a silica aerogel based on linear organic silicon oligomer, a preparation method and application. The silica aerogel is mainly formed by performing polycondensation, gelation and normal pressure drying on linear organic silicon oligomer, the contact angles of the silica aerogel with water and oil are both 0 degree, and the oil absorption and the water absorption are both more than 100 wt%. The preparation method comprises the following steps: uniformly mixing organic siloxane, an acidic aqueous solution and alcohol, and heating to prepare a sol precursor containing linear organic silicon oligomer; mixing the sol precursor with a diluent, adding a catalyst, standing to form gel, and then standing and aging; and mechanically crushing and drying the aged gel to obtain the silica aerogel. The invention does not need any solvent replacement, any modification process or freeze drying or supercritical drying, and the aerogel is directly dried under normal pressure, and compared with all other aerogels prepared by normal pressure drying, the aerogel can absorb oil and a large amount of water.
Description
Technical Field
The invention relates to a silica aerogel, in particular to a silica aerogel which is prepared by utilizing a normal pressure drying technology and has a nano porous structure and is based on linear organic silicon oligomer, a preparation method and application thereof, belonging to the technical field of nano porous materials.
Background
Aerogel is a porous nano material, and is the lightest solid material with the best heat insulation performance in the world at present. The silica aerogel has a high specific surface area (400-1500 m)2A/g), a high porosity (80-99.8%), a low density (0.003-0.6 g/cm)3) And low thermal conductivity (0.013-0.038W/mk), and the like, so that the material has very important application in the fields of high-temperature resistance, heat insulation, ultralow density, acoustic impedance coupling, gas adsorption and filtration, catalyst carriers, drug carriers and the like.
A common method for preparing silica aerogels is supercritical drying, for example, published patents CN102583407A and CN102642842B both disclose methods for preparing aerogels using supercritical drying, in which the solvent in the wet gel is displaced by a supercritical fluid, and the original structure of the gel is well maintained after final drying. However, the supercritical drying usually requires special equipment and operation at high pressure and high temperature, and on one hand, the equipment used is expensive, difficult to operate and high in cost; on the other hand, a great potential safety hazard exists. Therefore, although aerogels have the above-mentioned excellent properties, their wide use in daily life is limited due to too high preparation costs.
For this reason, great research efforts are focused on reducing the production cost of silica aerogel, and for example, published patents CN101503195, CN102020285A and CN103043673A disclose methods for preparing aerogel by using atmospheric drying: the liquid in the gel pore channel is exchanged into a solvent with low surface tension through multiple times of solvent exchange, such as n-hexane and the like, and the surface of the pore channel is modified into hydrophobicity, so that the capillary force in the gel pore channel is greatly reduced, the gel is very small in shrinkage in the drying process, and the original form can be basically maintained. However, since the drying under normal pressure requires many times of solvent exchange of gel pore channels and surface hydrophobization, the preparation period is very long, and the operation is cumbersome, so that it is difficult to realize industrial production.
On the other hand, silica aerogels prepared by the atmospheric pressure drying method are inevitably subjected to hydrophobic modification, which increases the preparation process and the cost, and causes pollution and byproducts by a hydrophobic reagent. Furthermore, due to the hydrophobic modification, all silica aerogels prepared by the atmospheric drying method have hitherto been shown to be superhydrophobic, and although capable of absorbing large amounts of oil, are not capable of absorbing water.
Disclosure of Invention
Aiming at the defects and material limitations of the prior art, the invention mainly aims to provide a super-hydrophilic silica aerogel based on linear organosilicon oligomer and a normal-pressure drying preparation method thereof.
Still another object of the present invention is to provide the use of the aforementioned superhydrophilic linear silicone oligomer-based silica aerogel.
In order to achieve the purpose, the technical scheme adopted by the invention comprises the following steps:
the embodiment of the invention provides a preparation method of silica aerogel based on linear organic silicon oligomer, which comprises the following steps:
(1) uniformly mixing organic siloxane, an acidic aqueous solution and alcohol, and heating to prepare a sol precursor containing linear organic silicon oligomer;
(2) mixing the sol precursor with a diluent, adding a catalyst, standing to form gel, and then standing and aging;
(3) and (3) mechanically crushing and drying the aged gel obtained in the step (2) to obtain the silica aerogel.
The embodiment of the invention also provides a silica aerogel based on the linear organic silicon oligomer, and the silica aerogel is mainly formed by performing polycondensation, gelation and normal-pressure drying on the linear organic silicon oligomer.
In some preferred embodiments, the silica aerogel is a powder having an average particle size of 50nm to 1000 μm.
Further, the silica aerogel contains pores with the aperture of 1-500 nm and the specific surface area of 150-2200 m2The pore volume is 0.5-6 cm3And the contact angles of the particles and water and oil are both 0 degrees.
The embodiment of the invention also provides a method for carrying out super-hydrophilic modification on the surface of an object, which comprises the following steps: and uniformly coating the silica aerogel based on the linear organic silicon oligomer on the surface of an object, and applying pressure of 0.5-10 MPa after coating to form the super-hydrophilic coating.
Compared with the prior art, the invention has the advantages that:
(1) the super-hydrophilic silica aerogel micro powder has oleophylic property and hydrophilic property, and is prepared by normal pressure drying, and the synthesis method has the characteristics of simple process, extremely short production period, low cost and the like, and can be used for avoiding all solvent replacement processes in the conventional normal pressure drying method, avoiding any modification process, freeze drying or supercritical drying, directly drying under normal pressure, greatly shortening the preparation period and saving resources;
(2) compared with all other aerogels prepared by normal pressure drying, the silica aerogel micro powder obtained by the method has excellent performances of amphipathy, high oil absorption and water absorption, narrow particle size distribution, high specific surface area and the like;
(3) the invention develops a modification application method of the aerogel as the super-hydrophilic coating for the first time, and has the advantages of simple operation, suitability for various interfaces and even biological interfaces, mechanical friction resistance, strong stability, easy removal and the like; the super-hydrophilic coating can be used for a traditional inorganic interface and a life interface and has excellent friction resistance.
Drawings
FIG. 1 is a mass spectrum of a sol precursor obtained in example 1 of the present invention.
FIG. 2 is a schematic view showing the molecular structures of sol precursors obtained in examples 1 to 6 of the present invention.
FIG. 3 is a graph showing the adsorption and desorption of silica aerogel fine powder obtained in example 1 of the present invention under the isothermal condition of nitrogen.
FIG. 4 is a graph showing the pore size distribution of the silica aerogel fine powder obtained in example 1 of the present invention.
FIG. 5a is a scanning electron microscope photograph of the silica aerogel fine powder obtained in example 1 of the present invention.
FIG. 5b is a photograph showing the contact angle of the silica aerogel fine powder obtained in example 1 of the present invention.
FIG. 6 is a graph showing the adsorption and desorption of silica aerogel fine powder obtained in example 2 of the present invention under the isothermal condition of nitrogen.
FIG. 7 is a graph showing the pore size distribution of the silica aerogel fine powder obtained in example 2 of the present invention.
FIG. 8 is a scanning electron microscope photograph of the silica aerogel fine powder obtained in example 2 of the present invention.
FIG. 9 is a graph showing the adsorption and desorption of silica aerogel fine powder obtained in example 3 of the present invention under the isothermal condition of nitrogen.
FIG. 10 is a graph showing the pore size distribution of the silica aerogel fine powder obtained in example 3 of the present invention.
FIG. 11 is a scanning electron microscope photograph of the silica aerogel fine powder obtained in example 3 of the present invention.
FIG. 12 is a graph showing the adsorption and desorption of silica aerogel fine powder obtained in example 4 of the present invention under the isothermal condition of nitrogen.
FIG. 13 is a graph showing the pore size distribution of the silica aerogel fine powder obtained in example 4 of the present invention.
FIG. 14 is a scanning electron microscope photograph of the silica aerogel fine powder obtained in example 4 of the present invention.
FIG. 15 is a graph showing the adsorption and desorption of silica aerogel fine powder obtained in example 5 of the present invention under nitrogen isothermal conditions.
FIG. 16 is a graph showing the pore size distribution of the silica aerogel fine powder obtained in example 5 of the present invention.
FIG. 17 is a scanning electron microscope photograph of the silica aerogel fine powder obtained in example 5 of the present invention.
FIG. 18 is a graph showing the adsorption and desorption of silica aerogel fine powder obtained in example 6 of the present invention under nitrogen isothermal conditions.
FIG. 19 is a graph showing the pore size distribution of the silica aerogel fine powder obtained in example 6 of the present invention.
FIG. 20 is a scanning electron microscope photograph of the silica aerogel fine powder obtained in example 6 of the present invention.
FIG. 21 is a photograph of the modified leaf of comparative example 1 taken with the experimental apparatus.
FIG. 22 is a photograph taken from the modified laboratory apparatus of comparative example 1.
Detailed Description
In view of the deficiencies in the prior art, the inventors of the present invention have made extensive studies and extensive practices to provide technical solutions of the present invention. The invention firstly provides amphiphilic silica aerogel micro powder and a preparation method and application thereof.
The preparation of hydrophilic silica aerogels still relies on supercritical drying, i.e., non-hydrophobized wet silica gels are subjected to supercritical drying to produce hydrophilic silica aerogels. The silica aerogel (namely the amphiphilic silica aerogel) which is hydrophilic and oleophilic is prepared by a normal pressure drying method, the preparation cost is reduced, the application range can be expanded from heat insulation to the fields of biological medicines, cosmetics and the like, and the silica aerogel has important scientific and practical application values.
One aspect of the embodiments of the present invention provides a method for preparing a silica aerogel based on linear organosilicon oligomers, comprising three key steps:
(1) synthesizing a sol precursor; (2) synthesizing and aging gel; (3) and (4) drying the gel.
Specifically, the preparation method of the silica aerogel based on the linear organosilicon oligomer comprises the following steps:
(1) uniformly mixing organic siloxane, an acidic aqueous solution and alcohol, and heating to prepare a sol precursor containing linear organic silicon oligomer;
(2) mixing the sol precursor with a diluent, adding a catalyst, standing to form gel, and then standing and aging;
(3) and (3) mechanically crushing and drying the aged gel obtained in the step (2) to obtain the silica aerogel.
In some embodiments, the organosiloxane comprises any one or a combination of two or more of ethyl orthosilicate, methyl orthosilicate, methyltrimethoxysilane, methyltriethoxysilane, dimethylmethoxysilane, dimethylethoxysilane, and the like, without limitation thereto.
Further, the acidic aqueous solution includes a dilute solution of hydrochloric acid, sulfuric acid, oxalic acid, acetic acid, or nitric acid, and is not limited thereto.
Further, H in the acidic aqueous solution+The content is 10-6～10-1mol/L。
Further, the alcohol includes any one or a combination of two or more of methanol, ethanol, isopropanol, propanol, butanol, tert-butanol, and the like, and is not limited thereto.
Furthermore, the silicon atom number of the organic silicon oligomer is 5-10, and Si in the framework is connected through Si-O-Si bonds to form linear molecules.
Further, the molar ratio of the organic siloxane, the acidic aqueous solution and the alcohol in the step (1) is 1: 1.8-2.2: 1 to 10.
Further, the heating temperature is 80-150 ℃, and the time is 5-12 hours.
In some more preferred embodiments, the synthesis of the sol precursor comprises: uniformly mixing 1mol of organic siloxane, 1.8-2.2 mol of acidic aqueous solution and 1-10 mol of alcohol, heating and stirring to prepare the sol precursor containing the linear organic silicon oligomer.
In some embodiments, the volume ratio of the sol precursor, diluent, and catalyst in step (2) is 1: 0.1-3: 0.01 to 0.5.
Further, the standing and aging time is more than 5 h.
Further, the temperature of the standing aging is from room temperature to the boiling temperature of the catalyst.
In some more preferred embodiments, the synthesis and aging of the gel comprises mixing the sol precursor with a diluent, adding the catalyst after sufficient stirring, forming the gel after standing, and standing and aging after the gel is formed.
Further, the diluent includes any one or a combination of two or more of methanol, ethanol, isopropanol, propanol, butanol, t-butanol, n-hexane, cyclohexane, n-heptane, acetonitrile, toluene, tetrahydrofuran, benzyl alcohol, perfluoroalkane, and the like, or a composite solution of the above solutions, and is not limited thereto.
Further, the catalyst includes any one or a combination of two or more of sodium hydroxide, potassium hydroxide, urea, ammonia water, pyridine, trimethylammonium chloride, triethylamine, and the like, and is not limited thereto.
Further, the dosage of the catalyst is 1-50% of the volume fraction of the sol precursor.
In some embodiments, step (3) specifically comprises: and (3) mechanically crushing the aged gel obtained in the step (2), naturally airing for 5-10 h, and finally drying in a blast drying device for 5-10 h to completely dry the aerogel to obtain the silica aerogel.
Further, the mechanical pulverization includes roller mill pulverization, mechanical blender pulverization, colloid mill pulverization, cutting oscillation pulverization, juicer pulverization, and the like, without being limited thereto.
Further, the drying environment is one atmosphere at room temperature and is placed in a dry and ventilated place.
Further, the temperature of the air-blast drying equipment is 80-250 ℃.
Further, the time of the forced air drying is 5-10 h.
In conclusion, the invention synthesizes a linear organic silicon polymer short chain (oligomer) through structural design, and the gel synthesized by using the polymer as a precursor can be directly dried (namely dried under normal pressure) under the condition of one atmospheric pressure to obtain the super-hydrophilic silica aerogel. The method breaks through the performance limitation of preparing the aerogel by the traditional normal pressure drying method, for example, the aerogel prepared by the traditional normal pressure drying method is hydrophobic, and the aerogel prepared by the invention is super-hydrophilic, so that the application range of the aerogel is greatly expanded.
The other aspect of the embodiment of the invention also provides a silica aerogel based on linear organosilicon oligomers, the silica aerogel is mainly formed by polycondensation, gelation and normal pressure drying of the linear organosilicon oligomers, and the main chemical component is SiO2。
Furthermore, the silica aerogel is powder, and the average grain diameter is 50 nm-1000 μm.
Further, the silica aerogel has a porous structure, the pore diameter of pores contained in the porous structure is 1-500 nm, and the specific surface area is 150-2200 m2The pore volume is 0.5-6 cm3And the contact angles of the particles and water and oil are both 0 degrees.
Furthermore, the aerogel has amphipathy, and also has oil absorption (such as gasoline, kerosene, benzene and derivatives thereof, various alkanes, alkenes and the like) and water absorption performance, and after the aerogel absorbs liquid to saturation, the oil absorption and the water absorption of the aerogel are calculated by adopting a precision balance to obtain the oil absorption and the water absorption of the aerogel which reach over 100 wt%.
Further, the oil includes gasoline, kerosene, benzene and/or benzene derivatives, alkane or alkene, etc., and is not limited thereto.
In conclusion, the silica aerogel micro powder disclosed by the invention has excellent performances of amphiphilicity, high oil absorption and water absorption, narrow particle size distribution, high specific surface area and the like.
In another aspect of the embodiments of the present invention, there is also provided a use of the aforementioned silica aerogel based on linear silicone oligomers.
Another aspect of an embodiment of the present invention also provides a method for performing superhydrophilic modification on a surface of an object, including: and uniformly coating the silica aerogel based on the linear organic silicon oligomer on the surface of an object, and applying pressure of 0.5-10 MPa after coating to form the super-hydrophilic coating.
As one preferable scheme, the amphiphilic silica aerogel micro powder is placed on the surface of an object to be modified, and a set pressure is applied to the amphiphilic silica aerogel micro powder, so that the amphiphilic silica aerogel micro powder is uniformly coated on the surface of the object to form a super-hydrophilic coating.
Further, the dosage of the silica aerogel micro powder is 0.1-20 g/m2。
Further, the surface of the object is a dry, anhydrous smooth or rough surface.
Further, the object includes any one of glass, metal, polymer fiber, plastic film, rubber, wood, leaves, insect body surface, feathers, and the like, without being limited thereto.
Furthermore, the modified surfaces are all super-hydrophilic, have strong moisture absorption and have certain antifogging function.
In conclusion, the silica aerogel based on the linear organic silicon oligomer is used as the super-hydrophilic coating for modification, and has the advantages of simple operation, suitability for various interfaces and even biological interfaces, mechanical friction resistance, strong stability, easy removal and the like; the super-hydrophilic coating can be used for a traditional inorganic interface and a life interface and has excellent friction resistance.
The technical scheme of the invention is further explained in detail by a plurality of embodiments and the accompanying drawings. However, the examples are chosen only for the purpose of illustrating the invention and are not to be construed as limiting the scope of the invention.
Example 1
(1) Synthesis of a sol precursor: taking 1mol of methyl orthosilicate and 1.8mol of hydrochloric acid aqueous solution (the content of hydrochloric acid is 10)-4And 1 mol) of ethanol, and stirring the mixture at 80 ℃ for 12 hours to obtain the linear organic silicon polymer precursor with 5-10 silicon atoms. The mass spectrum of the precursor is shown in figure 1, and the molecular structure is shown in figure 2. It is to be noted here why the molar ratio of methyl orthosilicate to water is 1: 1.8, if the molar ratio of the two is 1: (<1.8), only cyclic silanes are formed after hydrolysis, and the molar ratio is 1: (>2.2), the hydrolysate has too many functional groups to be easily crosslinked, and cannot form linear silicon polymerization short chains.
(2) Synthesis and aging of gel: and taking 10 parts of the obtained sol precursor and 30 parts of ethanol, fully mixing the sol precursor and the ethanol, adding 5 parts of sodium hydroxide, stirring for 20 minutes at room temperature, and standing for 5 hours to form gel. The gel was then placed in an oven at 50 ℃ and aged for 6 hours.
(3) Preparation of silica aerogel-drying at atmospheric pressure: and crushing the aged gel by using a colloid mill, airing at room temperature for 8 hours, naturally cleaning most of the solvent, transferring the gel into a blast drying oven at 250 ℃, drying for 5 hours without any pressurizing or depressurizing device, and taking out to obtain the super-hydrophilic silica aerogel micro powder. According to BET isothermal adsorption characterization, it can be found that the silica aerogel fine powder has a nano porous structure, the isothermal adsorption and desorption curves of the silica aerogel fine powder refer to fig. 3, the pore size distribution refer to fig. 4, the scanning electron microscope image refers to fig. 5a, the contact angle photograph refers to fig. 5b, and other physical parameters such as specific surface area, pore size, pore volume, density, contact angle and the like are shown in table 1. After the aerogel absorbs liquid to saturation, weighing and calculating by using a precision balance to obtain that the oil absorption and the water absorption of the aerogel are both more than 100 wt%.
(4) 100mg of the obtained aerogel micro powder is taken and placed on the surface of a lotus leaf with the square meter of 0.5, the aerogel micro powder is uniformly coated on the leaf surface by using a smooth plastic plate to obtain the super-hydrophilic lotus leaf, modified insecticides and the like can be spread on the leaf surface to kill germs, and unmodified super-hydrophobic leaf surfaces cannot be spread by aqueous pesticides.
Example 2
(1) Synthesis of a sol precursor: taking 1mol of ethyl orthosilicate and 2.2mol of hydrochloric acid aqueous solution (the hydrochloric acid content is 10)-6And (3) uniformly mixing the three components by mol) and 10mol of methanol, and stirring at 150 ℃ for 5 hours to obtain the linear organic silicon polymer precursor with 5-10 silicon atoms. The molecular structure of the precursor is schematically shown in FIG. 2. It is to be noted here why the molar ratio of ethyl orthosilicate to water is 1: 2.2, if the molar ratio of the two is 1: (<1.8), only cyclic silanes are formed after hydrolysis, and the molar ratio is 1: (>2.2), the hydrolysate has too many functional groups to be easily crosslinked, and cannot form linear silicon polymerization short chains.
(2) Synthesis and aging of gel: and taking 10 parts of the obtained sol precursor and 1 part of methanol, fully mixing the sol precursor and the methanol, adding 0.1 part of urea, stirring for 30 minutes at room temperature, and standing for 5 hours to form gel. The gel was then placed in an oven at 80 ℃ and aged for 9 hours.
(3) Preparation of silica aerogel-drying at atmospheric pressure: and crushing the aged gel by using a colloid mill, airing at room temperature for 5 hours, naturally cleaning most of the solvent, transferring the gel into a blast drying oven at 150 ℃, drying for 10 hours without any pressurizing or depressurizing device, and taking out to obtain the super-hydrophilic silica aerogel micro powder. According to the BET isothermal adsorption characterization, it can be found that the silica aerogel fine powder has a nano porous structure, the isothermal adsorption and desorption curves of the silica aerogel fine powder refer to fig. 6, the pore size distribution refers to fig. 7, the scanning electron microscope image refers to fig. 8, and other physical parameters such as specific surface area, pore size, pore volume, density, contact angle and the like are shown in table 1.
(4) And (3) placing 50mg of the obtained aerogel micro powder on a plastic film (PET), and uniformly coating the aerogel on the surface of the plastic film by using a smooth metal plate to obtain an amphiphilic plastic film which becomes the super-hydrophilic oil film.
Example 3
(1) Synthesis of a sol precursor: taking 1mol of methyl orthosilicate and 2.0mol of sulfuric acid aqueous solution (the sulfuric acid content is 10)-3And 2mol of ethanol, and stirring the mixture at 100 ℃ for 12 hours to obtain the linear organic silicon polymer precursor with 5-10 silicon atoms. The molecular structure of the precursor is schematically shown in FIG. 2. It is to be noted here why the molar ratio of methyl orthosilicate to water is 1: 2, if the molar ratio of the two is 1: (<1.8), only cyclic silanes are formed after hydrolysis, and the molar ratio is 1: (>2.2), the hydrolysate has too many functional groups to be easily crosslinked, and cannot form linear silicon polymerization short chains.
(2) Synthesis and aging of gel: and taking 10 parts of the obtained sol precursor, taking 30 parts of tetrahydrofuran, fully mixing the sol precursor and the tetrahydrofuran, adding 5 trimethyl ammonium chloride, stirring for 30 minutes at room temperature, and standing for 5 hours to form gel. The gel was then placed in an oven at 50 ℃ and aged for 8 hours.
(3) Preparation of silica aerogel-drying at atmospheric pressure: and crushing the aged gel by using a colloid mill, airing at room temperature for 6 hours, naturally cleaning most of the solvent, transferring the gel into an air drying oven at 80 ℃, drying for 10 hours without any pressurizing or depressurizing device, and taking out to obtain the super-hydrophilic silica aerogel micro powder. According to the BET isothermal adsorption characterization, it can be found that the silica aerogel fine powder has a nano porous structure, the isothermal adsorption and desorption curve of the silica aerogel fine powder is shown in fig. 9, the pore size distribution is shown in fig. 10, the scanning electron microscope is shown in fig. 11, and other physical parameters such as specific surface area, pore size, pore volume, density, contact angle and the like are shown in table 1.
(4) And (3) placing 500mg of the obtained aerogel micro powder on a rubber glove, and coating the aerogel on the surface of the rubber glove by using a glass plate to obtain the super-hydrophilic glove, wherein the contact angle is 0 degree.
Example 4
(1) Synthesis of a sol precursor: taking 1mol of methyltriethoxysilane and 2.1mol of acetic acid aqueous solution (the acetic acid solubility is 10)-5And 2 mol) of propanol, and stirring the three solutions at 80 ℃ for 12 hours to obtain the linear organic silicon polymer precursor with 5-10 silicon atoms. The molecular structure of the precursor is schematically shown in FIG. 2. It is to be noted here why the molar ratio of methyltriethoxysilane to water is 1: 2.1, if the molar ratio of the two is 1: (<1.8), only cyclic silanes are formed after hydrolysis, and the molar ratio is 1: (>2.2), the hydrolysate has too many functional groups to be easily crosslinked, and cannot form linear silicon polymerization short chains.
(2) Synthesis and aging of gel: and taking 10 parts of the obtained sol precursor, taking 5 parts of n-hexane, fully mixing the sol precursor and the n-hexane, adding 1 part of ammonia water, stirring at room temperature for 20 minutes, and standing for 5 hours to form gel. The gel was then placed in an oven at 30 ℃ and aged for 6 hours.
(3) Preparation of silica aerogel-drying at atmospheric pressure: and crushing the aged gel by using a colloid mill, airing at room temperature for 8 hours, naturally cleaning most of the solvent, transferring the gel into a blast drying oven at 120 ℃, drying for 8 hours without any pressurizing or depressurizing device, and taking out to obtain the super-hydrophilic silica aerogel micro powder. According to the BET isothermal adsorption characterization, it can be found that the silica aerogel fine powder has a nano porous structure, the isothermal adsorption and desorption curve of the silica aerogel fine powder is shown in fig. 12, the pore size distribution is shown in fig. 13, the scanning electron microscope is shown in fig. 14, and other physical parameters such as specific surface area, pore size, pore volume, density, contact angle and the like are shown in table 1.
(4) Placing 5mg of the obtained aerogel micro powder on the surface of ginkgo leaf, wearing a plastic glove, and lightly coating the aerogel on the surface of the ginkgo leaf to obtain the amphiphilic ginkgo leaf with a contact angle of 0 degree.
Example 5
(1) Synthesis of a sol precursor: taking 1mol of methyltrimethoxysilane and 1.9mol of formic acid solution (the content of formic acid is 10)-1And 8 mol) of butanol, and uniformly mixing the three, stirring at 100 ℃ for 12 hours to obtain the linear organic silicon polymer precursor with 5-10 silicon atoms. The molecular structure of the precursor is schematically shown in FIG. 2. Here, theIt is to be noted why the molar ratio of methyltrimethoxysilane to water is 1: 1.9, if the molar ratio of the two is 1: (<1.8), only cyclic silanes are formed after hydrolysis, and the molar ratio is 1: (>2.2), the hydrolysate has too many functional groups to be easily crosslinked, and cannot form linear silicon polymerization short chains.
(2) Synthesis and aging of gel: and taking 10 parts of the obtained sol precursor and 30 parts of isopropanol, fully mixing the sol precursor and the isopropanol, adding 9 parts of ammonia water, stirring at room temperature for 20 minutes, and standing for 5 hours to form gel. The gel was then placed in an oven at 90 ℃ and aged for 6 hours.
(3) Preparation of silica aerogel-drying at atmospheric pressure: and crushing the aged gel by using a colloid mill, airing at room temperature for 8 hours, naturally cleaning most of the solvent, transferring the gel into a 180-DEG C blast drying oven, drying for 7 hours without any pressurizing or depressurizing device, and taking out to obtain the super-hydrophilic silica aerogel micro powder. According to the BET isothermal adsorption characterization, it can be found that the silica aerogel micro powder has a nano porous structure, the isothermal adsorption and desorption curve of the silica aerogel micro powder is shown in fig. 15, the pore size distribution is shown in fig. 16, the scanning electron microscope is shown in fig. 17, and other physical parameters such as specific surface area, pore size, pore volume, density, contact angle and the like are shown in table 1.
Example 6
(1) Synthesis of a sol precursor: taking 1mol of methyl orthosilicate and 2.0mol of nitric acid aqueous solution (the content of nitric acid is 10)-3And 2mol of methanol, and stirring the three components at 110 ℃ for 10 hours to obtain the linear organic silicon polymer precursor with 5-10 silicon atoms. The molecular structure of the precursor is schematically shown in FIG. 2. It is to be noted here why the molar ratio of methyl orthosilicate to water is 1: 2, if the molar ratio of the two is 1: (<1.8), only cyclic silanes are formed after hydrolysis, and the molar ratio is 1: (>2.2), the hydrolysate has too many functional groups to be easily crosslinked, and cannot form linear silicon polymerization short chains.
(2) Synthesis and aging of gel: and taking 10 parts of the obtained sol precursor, taking 10 parts of methanol, fully mixing the sol precursor and the methanol, adding 9 parts of triethylamine, stirring for 30 minutes at room temperature, and standing for 5 hours to form gel. The gel was then placed in an oven at 40 ℃ and aged for 6 hours.
(3) Preparation of silica aerogel-drying at atmospheric pressure: and crushing the aged gel by using a colloid mill, airing at room temperature for 10 hours, naturally cleaning most of the solvent, transferring the gel into a blast drying oven at 150 ℃, drying for 10 hours without any pressurizing or depressurizing device, and taking out to obtain the super-hydrophilic silica aerogel micro powder. According to the BET isothermal adsorption characterization, it can be found that the silica aerogel fine powder has a nano porous structure, the isothermal adsorption and desorption curve of the silica aerogel fine powder is shown in fig. 18, the pore size distribution is shown in fig. 19, the scanning electron microscope is shown in fig. 20, and other physical parameters such as specific surface area, pore size, pore volume, density, contact angle and the like are shown in table 1.
Comparative example 1
The silicon oxide aerogel prepared by adopting the nonlinear organic silicon oligomer is a common silicon oxide aerogel prepared by drying under normal pressure, the blade and the hand are respectively modified by adopting the same method, the result shows that the contact angle with water after modification is 1500, and the super-hydrophilicity can not be realized, the image collected by experimental equipment after the blade is modified is shown in figure 21 (non-picture), and the image collected by experimental equipment after the hand is modified is shown in figure 22 (non-picture).
TABLE 1 Structure and Performance parameters of silica aerogel micropowder obtained in examples 1-6
In conclusion, the super-hydrophilic silica aerogel micro powder obtained by the technical scheme of the invention has the properties of high specific surface area, super-hydrophilicity and the like; the invention develops a modification application method of the aerogel as the amphiphilic coating for the first time, and has the advantages of simple operation, suitability for various interfaces and even biological interfaces, mechanical friction resistance, strong stability, easy removal and the like; the super-amphiphilic coating can be used for a traditional inorganic interface and a life interface and has excellent friction resistance.
In addition, the present inventors have also conducted experiments with other raw materials and conditions listed in the present specification by referring to the manner of examples 1 to 6, and have also obtained silica aerogels based on linear silicone oligomers having excellent properties of amphiphilicity, high oil and water absorption, narrow particle size distribution, high specific surface area, and the like.
It should be understood that the above describes only some embodiments of the present invention and that various other changes and modifications may be affected therein by one of ordinary skill in the related art without departing from the scope or spirit of the invention.
Claims (13)
1. A preparation method of silica aerogel based on linear organosilicon oligomer is characterized by comprising the following steps:
(1) uniformly mixing organic siloxane, acidic aqueous solution and alcohol, and heating at 80-150 ℃ for 5-12H to prepare a sol precursor containing linear organic silicon oligomer, wherein the organic siloxane is selected from any one or a combination of more than two of ethyl orthosilicate, methyl orthosilicate, methyltrimethoxysilane, methyltriethoxysilane, dimethylmethoxysilane and dimethylethoxysilane, the number of silicon atoms of the organic silicon oligomer is 5-10, Si in a framework is connected through Si-O-Si bonds to form linear molecules, and H in the acidic aqueous solution is connected through Si-O-Si bonds to form linear molecules+The content is 10-6~10-1mol/L, the mol ratio of the organic siloxane to the acidic aqueous solution to the alcohol is 1: 1.8-2.2: 1-10;
(2) mixing the sol precursor with a diluent, adding a catalyst, standing to form gel, and standing for aging, wherein the volume ratio of the sol precursor to the diluent to the catalyst is 1: 0.1-3: 0.01 to 0.5;
(3) mechanically crushing the aged gel obtained in the step (2), naturally drying for 5-10 h, and finally performing forced air drying at 80-250 ℃ for 5-10 h to obtain silicon oxide aerogel;
said baseThe silica aerogel of the linear organic silicon oligomer is powder, the average particle size is 50 nm-1000 mu m, the aperture of holes contained in the silica aerogel is 1-500 nm, and the specific surface area is 150-2200 m2The pore volume is 0.5-6 cm3The contact angles of the aerogel with water and oil are both 0 degrees, and the oil absorption and water absorption of the silica aerogel are both more than 100 wt%.
2. The method of claim 1, wherein: the acidic aqueous solution is selected from dilute solutions of hydrochloric acid, sulfuric acid, oxalic acid, acetic acid or nitric acid.
3. The method of claim 1, wherein: the alcohol is selected from any one or combination of more than two of methanol, ethanol, isopropanol, propanol, butanol and tert-butanol.
4. The method of claim 1, wherein: the standing and aging time is more than 5 h.
5. The method of claim 1, wherein: the temperature of the standing aging is from room temperature to the boiling point temperature of the catalyst.
6. The method of claim 1, wherein: the diluent is selected from any one or the combination of more than two of methanol, ethanol, isopropanol, propanol, butanol, tert-butanol, n-hexane, cyclohexane, n-heptane, acetonitrile, toluene, tetrahydrofuran, benzyl alcohol and perfluoro-alkane.
7. The method of claim 1, wherein: the catalyst is selected from any one or the combination of more than two of sodium hydroxide, potassium hydroxide, urea, ammonia water, pyridine, trimethyl ammonium chloride and triethylamine.
8. The method of claim 1, wherein: the mechanical pulverization is selected from roller mill pulverization, mechanical stirring mill pulverization, colloid mill pulverization, cutting oscillation pulverization or fruit juice mill pulverization.
9. The method of claim 1, wherein: the oil is selected from gasoline, kerosene, benzene and/or benzene derivatives, alkanes or alkenes.
10. A method for modifying the surface of an object with super-hydrophilicity, which is characterized by comprising the following steps: uniformly coating the silica aerogel based on linear organosilicon oligomers prepared by the method of any one of claims 1-9 on the surface of an object, and applying a pressure of 0.5-10 MPa after coating to form a super-hydrophilic coating.
11. The method of claim 10, wherein the method further comprises: the dosage of the silica aerogel micro powder is 0.1-20 g/m2。
12. The method of claim 10, wherein the method further comprises: the surface of the object is a dry, anhydrous, smooth or rough surface.
13. The method of claim 10, wherein the method further comprises: the object is selected from glass, metal, polymer fiber, plastic film, rubber, wood, tree leaves, insect body surface or feathers.
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