Disclosure of Invention
The invention aims to provide a high-performance large-length-diameter-ratio nano silver wire and a preparation method thereof, which can achieve the effect of effectively preparing the nano silver wire by simultaneously adding a silver solution and a silver protective agent solution into a reductive mixed solution and finally performing centrifugal separation. The preparation method is reasonable and effective, and the prepared nano silver wire has the advantages of larger length-diameter ratio, smaller diameter and better performance compared with the prior product.
The technical scheme adopted by the invention for solving the problems is as follows: the high-performance silver nanowire with the large length-diameter ratio has the length-diameter ratio of 1200-1500 and the diameter of 20-25nm.
In the invention, the diameter of the existing nano silver wire on the market is 45-80nm mostly, and the length-diameter ratio is about 500, so the nano silver wire has the advantages of being thinner and longer, and has the advantages of better optical permeability and higher conductivity when a transparent conductive film is prepared at a later stage.
A preparation method of a high-performance silver nanowire with a large length-diameter ratio sequentially comprises the following steps:
s1, preparing a reducing mixed solution;
s2, preparing a silver solution;
s3, adding the silver solution and the silver protective agent solution into the reductive mixed solution to obtain a silver wire mixed solution;
s4, centrifuging the silver wire mixed solution to obtain a nano silver wire,
in the step S1, the solvent of the reducing mixed solution is a mixture of at least two polyols, in the step S3, the adding mode of the silver solution is injection and dropwise adding in sequence, and the adding amount of the silver solution in the injection mode accounts for 40-45% of the total weight.
In the invention, the reducing mixed solution and the silver protective agent solution both contain end-capping components for attaching on the side surfaces of the silver wires so as to enable the silver wires to grow along the long axis direction, and are different from the mode of only adding in the initial solution in the prior art, and the mode of adding in two times and adding with the silver solution for the second time further improves the end-capping effect, reduces the side growth of the silver wires and promotes the long axis direction growth, so that the performance advantages of being thinner and longer can be obtained.
In addition, the solvent of the reducing mixed solution in the prior art is a single polyol and is mostly glycerol, while the invention adopts a mode of mixing two diols, under the condition of a certain total number of hydroxyl groups, the dispersibility of the hydroxyl groups can be effectively increased, and the reduction effect is greatly improved, but the reason that the monohydric alcohol is not adopted is that the total number of the hydroxyl groups is the same, the total number of the monohydric alcohol is required to be too much, so that the concentration of silver ions is too low after the silver solution is added, and the silver wires grow too slowly.
The further preferred technical scheme is as follows: in the step S1, the reductive mixed solution is prepared by mixing a reductive solvent, a protective agent and a nucleating agent and then heating, wherein the heating temperature is 90-180 ℃, and the heating time is 0.5-2.5h.
The further preferred technical scheme is as follows: in the step S1, the reducing solvent is a mixture of ethylene glycol and propylene glycol, and the protective agent is any one of polyvinylpyrrolidone, polyvinyl alcohol, polyethylene oxide, and sodium dodecyl sulfate.
The further preferred technical scheme is as follows: in the step S1, the nucleating agent is any one of sodium chloride, sodium bromide, sodium iodide, sodium sulfate, sodium carbonate, sodium phosphate, and sodium sulfide.
The further preferred technical scheme is as follows: in the step S2, the silver solution includes a soluble silver salt and a silver salt solvent, the soluble silver salt is any one of silver nitrate, silver nitrite, and silver acetate, and the silver salt solvent is any one of ethylene glycol and propylene glycol.
The further preferred technical scheme is as follows: in the step S3, the silver protective agent solution is a polyvinylpyrrolidone solution or a bromine salt solution.
In the invention, the action principles of the polyvinylpyrrolidone component in the reducing mixed solution and the silver protective agent solution are the same, and the silver wire can be more protected by the side adhesion of the polyvinylpyrrolidone during the formation of the silver wire by the modes of adding the polyvinylpyrrolidone component in two times, adding the polyvinylpyrrolidone component in the second time, injecting the polyvinylpyrrolidone component together with the silver solution, and adding the polyvinylpyrrolidone component dropwise, so that the long-term stable growth of the long axial direction is ensured.
On the other hand, the bromine salt solution can also have the effect of increasing the length of the silver wire by supplementing a nucleating agent, and the two kinds of bromine salt solution have different action principles and the same effect as that of the polyvinyl pyrrolidone which can be used as a component of the silver protective agent solution.
The further preferred technical scheme is as follows: in the step S3, the injection time of the silver solution for injection accounting for 40 percent of the total weight of the added silver solution is 5-25 hours, the injection speed is 2.5-4.5ml/min, the dropwise addition time of the rest 60 percent of the silver solution for dropwise addition is 2-50 hours, the dropwise addition speed is 0.5-1.5ml/min, cooling and centrifuging are carried out after the dropwise addition is finished, and the nano silver wire is obtained through separation.
In the prior art, the silver wire formed by the single injection mode is often too thick, and the mode of injection and dropwise addition can not only ensure that the diameter of the silver wire is smaller, but also avoid the problem that the silver wire is easy to break and too short which can possibly occur by the single dropwise addition mode, so that the silver solution with the weight of 60 percent can ensure that the silver wire obtained by growth has both larger length-diameter ratio and diameter fineness due to dropwise addition.
The further preferred technical scheme is as follows: the polyvinylpyrrolidone solution used as the silver protectant solution comprises polyvinylpyrrolidone, a diethanolamine complexing agent, a dilute hydrochloric acid regulator and an ethylene glycol solvent.
The further preferable technical scheme is that the preparation method of the polyvinylpyrrolidone solution sequentially comprises the following steps:
s1, adding a dilute hydrochloric acid regulator into an ethylene glycol solvent until the pH value is 5.6-5.7 to obtain a silver protective agent solution base material;
s2, adding polyvinylpyrrolidone and a diethanolamine complexing agent into the silver protectant solution base stock to obtain a silver protectant solution intermediate stock with improved complexation degree;
and S3, adding the dilute hydrochloric acid regulator into the silver protective agent solution intermediate material again, and regulating the pH value to 4.5-4.9 to obtain the final silver protective agent solution.
In the invention, the larger the complexing degree of the polyvinylpyrrolidone is in a certain range, the larger the side attachment surface of the growing silver wire is, the more the silver wire can be driven to grow along the long axis direction, so the complexing agent diethanolamine and the dilute hydrochloric acid which is the acid environment regulator required for complexing can finally ensure that the formed silver wire is thinner and longer when the silver solution is injected and dripped, and the polyvinylpyrrolidone with relatively higher complexing degree is finally obtained by gradually acidifying the polyvinylpyrrolidone solution so as to be used as a protective agent when silver ions are added.
According to the invention, the silver solution and the silver protective agent solution are simultaneously added into the reductive mixed solution, and finally, the centrifugal separation is carried out, so that the effect of effectively preparing the nano silver wire is achieved. The preparation method is reasonable and effective, and the prepared nano silver wire has the advantages of larger length-diameter ratio, smaller diameter and better performance compared with the prior product.
Detailed Description
The following description is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention.
Example 1
As shown in figure 1, the high-performance large length-diameter ratio nano silver wire has the length-diameter ratio of 1250-1400 and the diameter of 20-25nm, and the preparation method comprises the following steps:
s1, firstly adding a mixture of ethylene glycol and propylene glycol into a reaction device, then adding polyvinylpyrrolidone, then adding sodium chloride, finally heating to 90 ℃, preserving heat for 0.5h, and then naturally cooling to obtain a reducing mixed solution.
And S2, another reaction device is started, ethylene glycol is added firstly, and then silver nitrate is added to obtain a silver solution.
And S3, starting a reaction device, adding an ethylene glycol solvent, adding diluted hydrochloric acid to adjust the pH value to 5.6, adding polyvinylpyrrolidone and a diethanol amine complexing agent, adding diluted hydrochloric acid for the second time, adjusting the pH value to 4.5 to obtain a silver protective agent solution, adding a silver solution accounting for 40% of the total weight into the reductive mixed solution in an injection mode in the continuous adding process of the silver protective agent solution, wherein the continuous injection adding time is 10 hours, the injection speed is 2.5ml/min, then performing slow dropwise adding operation, the dropwise adding speed is 0.5ml/min, the dropwise adding time is 25 hours, dropwise adding the rest 60% silver solution, and forming a nano silver wire.
And S4, cooling, centrifuging and separating the mixed solution mixed with the nano silver wires according to the existing mode to finally obtain the nano silver wire product with ultrahigh length-diameter ratio and smaller diameter size.
Example 2
As shown in the attached figure 2, the high-performance silver nanowire with large length-diameter ratio has the length-diameter ratio of 1350-1450 and the diameter of 20-25nm, and the preparation method comprises the following steps:
s1, adding a mixture of ethylene glycol and propylene glycol into a reaction device, adding polyvinyl alcohol, adding sodium phosphate, heating to 120 ℃, preserving heat for 1.5 hours, and naturally cooling to obtain a reducing mixed solution.
And S2, another reaction device is started, propylene glycol is added firstly, and then silver nitrite is added to obtain a silver solution.
And S3, continuously adding a bromine salt solution serving as a silver protective agent solution into the reducing mixed solution, adding a silver solution accounting for 40% of the total weight by an injection mode, wherein the continuous injection adding time is 10 hours, the injection speed is 4.0ml/min, then performing slower dropping operation, the dropping speed is 1.0ml/min, the dropping time is 25 hours, and dropping the rest 60% of silver solution, so that a nano silver wire is formed.
And S4, cooling, centrifuging and separating the mixed solution mixed with the nano silver wires according to the existing mode to finally obtain the nano silver wire product with ultrahigh length-diameter ratio and smaller diameter size.
The embodiments of the present invention have been described in detail, but the present invention is not limited to the above embodiments, and various modifications can be made within the knowledge of those skilled in the art without departing from the gist of the present invention. These are non-inventive modifications, which are intended to be protected by patent laws within the scope of the present invention.