Synthesis method and application of 4-trimethoxysilyl styrene

Abstract

The invention provides a synthetic method and application of 4-trimethoxysilyl styrene, and the synthetic method comprises the following steps: (1) taking trimethoxysilyl benzene as a raw material, and carrying out Friedel-Crafts acylation reaction on trimethoxysilyl benzene and acetic anhydride to synthesize 4-trimethoxysilyl acetophenone; (2) reducing the 4-trimethoxysilyl acetophenone through sodium borohydride to synthesize 4-trimethoxysilyl phenyl ethanol; and (3) dehydrating the 4-trimethoxysilyl phenyl ethanol under the condition of Lewis acid to synthesize the 4-trimethoxysilyl styrene. The invention develops a novel synthetic method of 4-trimethoxysilyl styrene, the Grignard reaction is avoided, a dangerous Grignard reagent does not need to be used, the condition is mild and controllable, the safety is greatly improved, and the synthetic method is suitable for industrial production; meanwhile, reactions in all steps are common reactions, the reaction operation is simple and convenient, the yield is remarkably improved, raw materials are cheap and easy to obtain, and the production cost is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the field of organosilicon chemistry, and in particular to a synthesis method of 4-trimethoxysilylstyrene and application thereof. Background Art

[0002] Heat-resistant resins such as polyimide and polybenzoxazole can be widely used in the semiconductor field due to their excellent electrical insulation, high temperature resistance, chemical resistance and mechanical properties. For example, they can be used as interlayer insulation of microelectronic chips, surface passivation, and packaging materials for electronic and electrical components. As the scale of semiconductor integration becomes larger and larger, microcircuit processes tend to be three-dimensional multilayer structures, and equipment manufacturing develops towards miniaturization and multifunctionality, new challenges are posed to the physical and chemical properties of heat-resistant resins. Among these new challenges, the adhesion of heat-resistant resins to various substrates in various complex environments is particularly important. In order to improve the adhesion of polyimide, polybenzoxazole, etc. to the substrate, the substrate can be pretreated with a silane coupling agent or the like, or a silane coupling agent can be added to the resin precursor compound, and a polymerizable silicon-containing monomer can also be added during the synthesis of the resin precursor. Among them, the method of adding a silane coupling agent to the resin compound is the simplest and most direct.

[0003] At present, there are many types of silane coupling agents used in conjunction with heat-resistant resins. They can increase the adhesion between the precursor of polyimide and other resins and the substrate after film formation, but for the cured resin coating, the adhesion is significantly reduced due to the high temperature process. Because most of these silane coupling agents have poor high temperature resistance, some or most of them are decomposed during the thermal curing process.

[0004] Patent document US8883391B2 discloses a silane coupling agent, 4-trimethoxysilylstyrene. After the resin coating is added with the silane coupling agent, the adhesion to the substrate is still excellent even after high-temperature heat treatment above 350°C. This is because in the structure of the silane coupling agent, the alkoxysilane is directly bonded to the aromatic ring, has a strong bonding energy, and has excellent heat resistance. Therefore, it is difficult to decompose even after high-temperature heating treatment above 350°C or heat treatment in air.

[0005] However, the previous preparation methods of 4-trimethoxysilylstyrene all adopted the Grignard reaction, and its synthesis methods mainly include: 1) 4-Chlorostyrene is used as the raw material to form a Grignard reagent with Mg, and then reacts with trimethylsilyl chloride to obtain the product with a yield of 46%. The specific reaction is as follows:

[0006] 2) 4-bromostyrene is used as the raw material to form a Grignard reagent with Mg, and then reacts with tetramethoxysilane to obtain the product with a yield of 35%. The specific reaction is as follows: .

[0007] In the Grignard reaction process, magnesium metal is required to form a Grignard reagent to promote the reaction. This reagent is quite unstable and dangerous, and the final yield of this reaction is low, which makes 4-trimethoxysilylstyrene expensive. Summary of the invention

[0008] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide a method for synthesizing 4-trimethoxysilylstyrene and its application, so as to solve the problems in the prior art that 4-trimethoxysilylstyrene is synthesized by Grignard reaction, the reaction is dangerous, the stability is poor, and the yield is low.

[0009] In order to achieve the above-mentioned object and other related objects, the present invention provides the following technical solutions: The first aspect of the present invention provides a method for synthesizing 4-trimethoxysilylstyrene, comprising the following steps: (1) Using trimethoxysilylbenzene as raw material, 4-trimethoxysilylacetophenone was synthesized by Friedel-Crafts acylation reaction with acetic anhydride; (2) 4-Trimethoxysilyl acetophenone was reduced with sodium borohydride to synthesize 4-trimethoxysilylphenyl ethanol; (3) 4-Trimethoxysilylphenylethanol was dehydrated under Lewis acid conditions to synthesize 4-trimethoxysilylstyrene.

[0010] The specific synthetic route is as follows: .

[0011] In step (1), trimethoxysilylbenzene and acetic anhydride are reacted with a catalyst to synthesize 4-trimethoxysilylacetophenone through a Friedel-Crafts acylation reaction.

[0012] Preferably, the catalyst is selected from anhydrous aluminum chloride.

[0013] More preferably, the amount of the catalyst is 5-10%.

[0014] Preferably, the Friedel-Crafts acylation reaction in step (1) is carried out in a solvent 1, wherein the solvent 1 is selected from at least one of dichloromethane, chloroform, petroleum ether and carbon disulfide.

[0015] Preferably, the mass ratio of trimethoxysilylbenzene to acetic anhydride is 2:(0.8~2).

[0016] The specific reactions are as follows: .

[0017] Step (1) specifically comprises the following steps: dissolving trimethoxysilylbenzene in solvent 1, adding acetic anhydride with stirring, cooling the system to below 5°C in an ice bath, adding a catalyst and continuing to stir, then slowly heating the reaction system to reflux for a period of time, and after the reaction is completed, cooling the system to room temperature, and obtaining 4-trimethoxysilylacetophenone through post-treatment.

[0018] The post-treatment includes: slowly pouring the reaction solution into 50% sodium bicarbonate ice water, maintaining the system pH at 8-10, separating the liquids, extracting the aqueous layer once with 200 ml of dichloromethane, combining the organic layers, washing the organic layers with water until neutral, drying over anhydrous sodium sulfate, filtering, recovering the solvent from the filtrate, and distilling the residue under reduced pressure to obtain 4-trimethoxysilylacetophenone.

[0019] In step (2), 4-trimethoxysilylacetophenone is reduced in alcohol by sodium borohydride to synthesize 4-trimethoxysilylphenylethanol.

[0020] Preferably, the alcohol is selected from methanol or ethanol.

[0021] The specific reactions are as follows: .

[0022] Step (2) specifically comprises the following steps: dissolving 4-trimethoxysilyl acetophenone in alcohol, cooling in an ice bath to below 10° C., adding sodium borohydride and reacting in an ice bath, heating the system to 50° C. and continuing the reaction for a period of time, and after the reaction is completed, cooling the system to room temperature, and performing post-treatment to obtain 4-trimethoxysilyl phenyl ethanol.

[0023] The post-treatment includes: adding acetone to the reaction solution cooled to room temperature, continuing the reaction for a period of time, pouring the reaction solution into ice water after the reaction is completed, extracting twice with ethyl acetate, washing the organic layer with water until neutral, drying with anhydrous sodium sulfate, filtering, recovering the solvent from the filtrate under reduced pressure, and distilling the residue under reduced pressure to obtain 4-trimethoxysilylphenylethanol. In step (3), since silane is easily hydrolyzed under acidic conditions, the present invention uses Lewis acid instead of acid to dehydrate 4-trimethoxysilylphenylethanol under Lewis acid conditions to synthesize 4-trimethoxysilylstyrene.

[0024] Preferably, the Lewis acid is selected from boron trifluoride ethyl etherate, silicon dioxide or zirconium oxide.

[0025] Preferably, the dehydration reaction in step (3) is carried out in solvent 2, and the solvent 2 is selected from at least one of dichloromethane, chloroform, petroleum ether and tetrahydrofuran.

[0026] The specific reactions are as follows: .

[0027] Step (3) specifically comprises the following steps: adding 4-trimethoxysilylphenylethanol to solvent 2, cooling to below 10° C. in an ice bath, adding boron trifluoride etherate and stirring evenly, heating the system to reflux for a period of time, and after the reaction is completed, slowly cooling the system to room temperature, and obtaining the product 4-trimethoxysilylphenylstyrene through post-treatment.

[0028] The post-treatment includes: slowly pouring the reaction solution into ice water, separating the liquids, washing the organic layer with water, drying it over anhydrous sodium sulfate, filtering it, recovering the solvent from the filtrate, and distilling the residue under reduced pressure to obtain the product 4-trimethoxysilylstyrene.

[0029] The second aspect of the present invention provides the use of 4-trimethoxysilylstyrene synthesized by the method of the first aspect as a silane coupling agent to improve the adhesion between heat-resistant resin and different substrates (silicon, ceramics, metals, etc.).

[0030] Furthermore, the heat-resistant resin includes at least one of polyimide, polybenzoxazole and precursors thereof.

[0031] Furthermore, the substrate includes at least one of silicon, silicon dioxide, ceramics, and metal.

[0032] According to a third aspect of the present invention, a resin composition is provided, comprising a heat-resistant resin and 4-trimethoxysilylstyrene synthesized by the method of the first aspect.

[0033] Wherein, the heat-resistant resin includes at least one of polyimide, polybenzoxazole and their precursors.

[0034] Preferably, the mass of 4-trimethoxysilylstyrene in the resin composition is 0.1-20% of the mass of the heat-resistant resin; more preferably, 1-10%. When the mass of 4-trimethoxysilylstyrene is less than 0.1%, it cannot exert a satisfactory adhesion promotion effect; and when it is more than 20%, the stability of the resin composition may be damaged. At this time, when the resin composition is applied to the surface of the substrate, the mechanical properties and heat resistance of the heat-resistant resin film formed are seriously reduced.

[0035] The fourth aspect of the present invention provides a method for improving the adhesion between a heat-resistant resin and a substrate, the method comprising the following steps: first adding 4-trimethoxysilylstyrene synthesized by the above method to the heat-resistant resin, stirring evenly, and then coating the resulting mixture onto the surface of the substrate.

[0036] Furthermore, the substrate includes at least one of silicon, silicon dioxide, ceramics, and metal.

[0037] Furthermore, the ceramic includes SiN ceramic, and the metal includes aluminum, alumina, TiNiAg, etc.

[0038] The addition of 4-trimethoxysilylstyrene can improve the adhesion of the heat-resistant resin on the surface of the substrate.

[0039] The amount of 4-trimethoxysilylstyrene used is 0.1 to 20% by mass of the heat-resistant resin, and more preferably 1 to 10%.

[0040] As described above, the synthesis method of 4-trimethoxysilylstyrene and its application of the present invention have the following beneficial effects: 1. The present invention develops a new method for synthesizing 4-trimethoxysilylstyrene, which avoids the Grignard reaction and does not require the use of dangerous Grignard reagents. The synthesis process is mild and controllable, the safety is greatly improved, and it is suitable for industrial production. At the same time, each step of the reaction of the present invention is a common reaction, the reaction operation is simple, the yield is significantly improved, and the raw materials are cheap and easy to obtain, which effectively reduces the production cost.

[0041] 2. The silane coupling agent 4-trimethoxysilylstyrene prepared by the present invention has a styrene structure directly connected to alkoxysilane, which has excellent heat resistance and also has an active group double bond, which has a significant promoting effect on the adhesion of heat-resistant resins to various substrates, and can improve the adhesion of heat-resistant resin films to different substrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is the NMR spectrum of 4-trimethoxysilylstyrene prepared in Example 3 of the present invention.

[0043] Figure 2 This is a liquid chromatogram of 4-trimethoxysilylstyrene prepared in Example 3 of the present invention. DETAILED DESCRIPTION

[0044] The following is a description of the implementation of the present invention by means of specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0045] Example 1 (1) Synthesis of 4-trimethoxysilylacetophenone: Take 198 grams of trimethoxysilylbenzene, dissolve it in 500 milliliters of dichloromethane, add 112 grams of acetic anhydride, stir, cool the system to below 5°C in an ice bath, add 6.65 grams of anhydrous aluminum chloride, continue stirring for 30 minutes, then slowly heat the reaction system to reflux reaction for 5 hours, after the reaction is completed, cool the system to room temperature, then slowly pour the reaction solution into 50% sodium bicarbonate ice water, keep the system pH at 8-10, separate the liquids, extract the water layer once with 200 milliliters of dichloromethane, combine the organic layers, wash the organic layers with water until neutral, dry them with anhydrous sodium sulfate, filter, recover the solvent from the filtrate, and distill the residue under reduced pressure to obtain 225 grams of colorless liquid, i.e. 4-trimethoxysilylacetophenone, with a yield of 94%.

[0046] Example 2 (2) Synthesis of 4-trimethoxysilylphenylethanol: Take 120 g of 4-trimethoxysilylacetophenone, dissolve it in 400 ml of methanol, cool it to below 10°C in an ice bath, add 11.4 g of sodium borohydride, continue the reaction in an ice bath for 1 h, heat the system to 50°C and continue the reaction for 4 h. After the reaction, cool the system to room temperature, add 50 ml of acetone to the reaction solution, and continue the reaction for 2 h. After the reaction, pour the reaction solution into ice water, extract it twice with 200 ml of ethyl acetate, wash the organic layer with water until neutral, dry it over anhydrous sodium sulfate, filter it, and recover the solvent from the filtrate under reduced pressure. The residue is distilled under reduced pressure to obtain 113 g of colorless liquid, i.e. 4-trimethoxysilylphenylethanol, with a yield of 94%.

[0047] Example 3 (3) Preparation of 4-trimethoxysilylstyrene: Take 121 grams of 4-trimethoxysilylphenylethanol, add 300 milliliters of dichloromethane, cool to below 10°C in an ice bath, add 120 milliliters of boron trifluoride etherate, continue stirring for 30 minutes, heat the system to reflux reaction for 8 hours, after the reaction is completed, slowly cool the system to room temperature, slowly pour the reaction solution into 200 milliliters of ice water, separate the liquids, wash the organic layer with water, dry it with anhydrous sodium sulfate, filter, recover the solvent from the filtrate, and distill the residue under reduced pressure to obtain 101 grams of light yellow liquid, i.e., the product 4-trimethoxysilylphenylstyrene, with a yield of 91%. The NMR spectrum and liquid chromatogram of the product are shown in the attached figure. Figure 1 and 2 shown.

[0048] Example 4 (3) Preparation of 4-trimethoxysilylstyrene: Take 121 g of 4-trimethoxysilylphenylethanol, add 300 ml of chloroform, add 60 g of silica, heat the system to reflux reaction for 24 hours, after the reaction is completed, slowly cool the system to room temperature, filter to remove silica, pour the filtrate into ice water, separate the liquids, wash the organic layer with water, then dry the organic layer over anhydrous sodium sulfate, filter, reduce the pressure of the filtrate to recover the solvent, and distill the residue under reduced pressure to obtain 94 g of light yellow liquid, i.e., the product 4-trimethoxysilylstyrene, with a yield of 84%.

[0049] Example 5 A resin composition comprises a polybenzoxazole precursor resin and 10 wt% of 4-trimethoxysilylstyrene, and a preparation method thereof comprises the following steps: In a 500 ml flask equipped with a stirrer and a thermometer, 120 g of N-methylpyrrolidone was placed, and then 20.14 g (55 mmol) of bis(3-amino-4-hydroxyphenyl)hexafluoropropane was added and stirred to dissolve. Subsequently, 9.48 g (120 mmol) of pyridine was added, and the flask was cooled to 5°C. Then, 10.15 g (50 mmol) of isophthaloyl chloride was slowly added in batches, and the temperature was maintained at 0-5°C. Then, stirring was continued at room temperature for 16 hours. The reaction solution was poured into 3 L of 10 wt% methanol aqueous solution, and a polymer was precipitated to obtain a white precipitate. After filtering, it was washed three times with deionized water, placed in a vacuum oven, and dried under reduced pressure at 60°C for 72 h to obtain a polybenzoxazole precursor resin A1.

[0050] 10.00 g of the polybenzoxazole precursor resin A1 and 30.00 g of γ-butyrolactone (GBL) solvent were added to a 100 ml three-necked flask and stirred. After the resin was completely dissolved, 1.00 g of the silane coupling agent 4-trimethoxysilylstyrene obtained in Example 3 was added. After fully dissolved, the mixture was filtered using a 1 μm filter membrane to obtain the resin composition.

[0051] Example 6 A resin composition comprises a polyimide resin and 10 wt% of 4-trimethoxysilylstyrene, and a preparation method thereof comprises the following steps: Under nitrogen protection, in a 500 ml flask equipped with a stirrer, a thermometer, a condenser and a water separator, 150 g of N-methylpyrrolidone and 20.14 g (55 mmol) of bis(3-amino-4-hydroxyphenyl)hexafluoropropane were added and stirred to dissolve; the flask was then cooled to 5°C, and 15.51 g (50 mmol) of 4,4'-oxydiphthalic anhydride was slowly added in batches, the temperature was kept at 0-5°C, and then stirring was continued at room temperature for 16 hours; then 0.5 g of isoquinoline and 20 ml of toluene were added, the temperature was raised to 160°C, refluxed and azeotropically dehydrated for 5 hours, toluene was evaporated, and the mixture was kept warm for another 2 hours and then cooled to room temperature; the reaction solution was poured into 3 L of 10 wt% methanol aqueous solution, and the polymer was precipitated to obtain a light yellow precipitate, which was filtered and washed three times with deionized water, placed in a vacuum oven, and dried under reduced pressure at 60°C for 72 hours to obtain a polyimide resin B1.

[0052] 10.00 g of the polyimide resin B1 and 30.00 g of γ-butyrolactone (GBL) solvent were added to a 100 ml three-necked flask and stirred. After the resin was completely dissolved, 1.00 g of the silane coupling agent 4-trimethoxysilylstyrene obtained in Example 3 was added. After fully dissolved, the mixture was filtered using a 1 μm filter membrane to obtain the resin composition.

[0053] Example 7 A resin composition, compared with Example 5, the only difference is that the amount of 1.00g of silane coupling agent 4-trimethoxysilylstyrene is changed to 2g.

[0054] Example 8 A resin composition, compared with Example 6, the only difference is that the amount of 1.00g of silane coupling agent 4-trimethoxysilylstyrene is changed to 0.1g.

[0055] Comparative Example 1 A resin composition is obtained, which is different from Example 5 only in that the silane coupling agent 4-trimethoxysilylstyrene is replaced by KBM-403 (Shin-Etsu Chemical), and the rest is the same as Example 5, to obtain a resin composition.

[0056] Comparative Example 2 A resin composition is obtained, compared with Example 6, the only difference being that the silane coupling agent 4-trimethoxysilylstyrene is replaced with KBM-573 (Shin-Etsu Chemical), and the rest is the same as Example 6, to obtain a resin composition.

[0057] Comparative Example 3 A resin composition is obtained, which is different from Example 5 only in that the silane coupling agent 4-trimethoxysilylstyrene is replaced with KBM-503 (Shin-Etsu Chemical) and the rest is the same as Example 5, to obtain a resin composition.

[0058] Comparative Example 4 A resin composition is obtained, which is different from Example 6 only in that the silane coupling agent 4-trimethoxysilylstyrene is replaced by KBM-903 (Shin-Etsu Chemical), and the rest is the same as Example 6, to obtain a resin composition.

[0059] Comparative Example 5 A resin composition is obtained, which is different from Example 5 in that the silane coupling agent 4-trimethoxysilylstyrene is not added, and the rest is the same as Example 5, to obtain a resin composition.

[0060] Adhesion peel test between resin composition and substrate The resin composition was coated on the substrates Si, SiO2, SiN, Al2O3, and TiNiAg, respectively, and then baked at 120°C for 3 minutes using a hot plate to obtain a resin film. Then, the prepared resin film was placed on a hot plate for staged temperature rise heat treatment: first at 90°C for 60 minutes, then at 150°C for 60 minutes, at 240°C for 60 minutes, and then at 320°C for 60 minutes to obtain a cured film.

[0061] The cured film was cut into a checkerboard shape with 10 rows and 10 columns at intervals of 2 mm. A peeling test was performed using a special transparent 3M tape in accordance with the national standard GB / T 9286-1998 (scratch test of paint and varnish films), and the number of peeled grids was recorded.

[0062] The cured film with squares was placed in a high pressure accelerated aging test chamber (Xiamen Easy Instrument Technology ST-PCT40) for 100 hours of PCT test (conditions: 121°C, 2 atmospheres of saturated steam). After the PCT test, the stripping test was performed using the tape in the same way and the results were recorded. If the number of strips removed in the stripping test was less than 10, it was considered good, and if it was 10 or more, it was considered bad.

[0063] The adhesion between the cured film samples prepared above and the substrate was tested, and the results are shown in Table 1 below.

[0064] Table 1. Peel test results of the resin compositions of Examples 5 to 8 and Comparative Examples 1 to 5

[0065] According to the test results, the silane coupling agent 4-trimethoxysilylstyrene prepared by the present invention can improve the adhesion of the resin to various substrates when added to polyimide resins and polybenzoxazole resins, and still shows high adhesion to different substrates even after PCT treatment. In Comparative Examples 1-4, silane coupling agents with different structures on the market all have different degrees of improving the adhesion of the resin to the substrate, but are significantly lower than the silane coupling agent 4-trimethoxysilylstyrene of the present invention.

[0066] In summary, the present invention has developed a new method for synthesizing 4-trimethoxysilylstyrene, which avoids the Grignard reaction, does not require the use of dangerous Grignard reagents, has mild and controllable conditions, greatly improves safety, and is suitable for industrial production; at the same time, each step of the reaction of the present invention is a common reaction, the reaction operation is simple, the yield is significantly improved, and the raw materials are cheap and easy to obtain, which effectively reduces the production cost. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0067] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for synthesizing 4-trimethoxysilylstyrene, characterized in that: The following steps are involved: (1) Using trimethoxysilylbenzene as raw material, 4-trimethoxysilylacetophenone was synthesized by Friedel-Crafts acylation reaction with acetic anhydride; (2) 4-Trimethoxysilyl acetophenone was reduced with sodium borohydride to synthesize 4-trimethoxysilylphenyl ethanol; (3) 4-Trimethoxysilylphenylethanol was dehydrated under Lewis acid conditions to synthesize 4-trimethoxysilylstyrene.

2. The method according to claim 1, characterized in that: In step (1), trimethoxysilylbenzene and acetic anhydride are reacted in the presence of a catalyst to synthesize 4-trimethoxysilylacetophenone through a Friedel-Crafts acylation reaction. The catalyst is selected from anhydrous aluminum chloride.

3. The method according to claim 1, characterized in that In step (2), 4-trimethoxysilylacetophenone is reduced in alcohol by sodium borohydride to synthesize 4-trimethoxysilylphenylethanol.

4. The method according to claim 1, characterized in that: In step (3), the Lewis acid is selected from boron trifluoride etherate, silicon dioxide or zirconium oxide.

5. The method according to claim 4, characterized in that The dehydration reaction in step (3) is carried out in solvent 2, wherein the solvent 2 is selected from at least one of dichloromethane, chloroform, petroleum ether and tetrahydrofuran.

6. The method according to claim 1, characterized in that The specific synthetic route is as follows: 。 7. Use of 4-trimethoxysilylstyrene synthesized by the method according to any one of claims 1 to 6 as a silane coupling agent.

8. A resin composition, characterized in that The resin composition comprises a heat-resistant resin and 4-trimethoxysilylstyrene synthesized by the method according to any one of claims 1 to 6.

9. The resin composition according to claim 8, characterized in that The mass of 4-trimethoxysilylstyrene in the resin composition is 0.1-20% of the mass of the heat-resistant resin.

10. A method for improving the adhesion between a heat-resistant resin and a substrate, characterized in that: The following steps are involved: First, add 4-trimethoxysilylstyrene synthesized by the method described in any one of claims 1 to 6 into the heat-resistant resin, stir evenly, and then apply the obtained mixture to the surface of the substrate.

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