Technical Field

The present invention relates to a method for obtaining different self-assemblies of nanoparticles by using two solutions, each comprising at least one different nanoparticle.

Background of the Invention

Nanoparticles are materials with a size below 100 nm and they are used in many fields such as electronics, health, environment and energy. The said nanoparticles are economical, durable and lightweight due to their electrical, thermal and optical characteristics. However, there are no nanoparticle structures prepared by means of solutions so as to have a patterned self-assembly through the nanoparticles being in use today.

Therefore, there is a need for methods for obtaining different self-assemblies of nanoparticles by means of solutions.

The Japanese patent document no. JP2010080977A, an application included in the state of the art, discloses a method for patterning of a nanoscopic (nanoscale) deposit -which is a solid material- on a substrate. In the method, a sol-gel solution comprising the nanostructure is prepared to coat at least one nanostructure or nanoarray on a substrate. Then, the substrate is then submerged in the solution and it is ensured that the nanostructures are transferred to the substrate surface.

Summary of the Invention An objective of the present invention is to realize a method for obtaining different self-assemblies of nanoparticles by using two solutions, each comprising at least one different nanoparticle.

Detailed Description of the Invention

“Method of Obtaining a Nanoparticle Self-Assembly” realized to fulfil the objective of the present invention is shown in the figures attached, in which:

Figure l is a flow chart of the inventive method.

Figure 2 is a view of the self-assembly of the nested ring pattern obtained by the inventive method (r: radius of a circular colloidal quantum well (CQW) film, w: difference between the radii of two different superimposed circular CQW films).

Figure 3 is a view of the self-assembly of a linear binary pattern obtained by the inventive method.

The components illustrated in the figures are individually numbered, where the numbers refer to the following:

100. Method

The inventive method (100) for obtaining different self-assemblies of nanoparticles comprises the steps of putting a polar liquid into a container (101), immersing a substrate into polar liquid (102), preparing a solution A and B comprising nanoparticles (103), forming a nanoparticle array on the polar liquid surface by dripping solutions A and B into the polar liquid (104), and obtaining nanoparticles with different self-assemblies as a result of transferring the nanoparticle array formed on the polar liquid surface to the substrate surface by discharging the polar liquid included in the container from the container (105).

In the step of putting a polar liquid into a container (101) of the inventive method (100), diethylene glycol liquid is put into a container which is made of Teflon and has a circular shape.

In the step of immersing a substrate into polar liquid (102) of the inventive method (100), a substrate on which nanoparticle array is aimed to be formed is immersed into the bottom of the container comprising the polar liquid and it remains stable therein.

In the step of preparing a solution A and B comprising nanoparticles (103) of the inventive method (100), sodium myristate and cadmium nitrate tetrahydrate are dissolved in methanol at first and then mixed by means of vigorous agitation until the solution becomes voluminous. Thereafter, the solution is washed with methanol three times. Then, cadmium myristate precursor is prepared by drying the solution under vacuum for one day. Upon cadmium myristate precursor is prepared, 340 mg cadmium myristate, 20 mg Se and 30 ml octadecene are reacted in a 100 mL three-neck flask. The mixture combined in the flask is kept at 95°C under vacuum for 1 hour. Thereupon, the flask is heated to 240°C under argon gas flow and 100 mg cadmium acetate dihydrate is added into the flask rapidly at 195°C. Then, the mixture included in the flask is kept at 240°C for 10 minutes and 1 mL oleic acid is injected into the flask. Subsequently, the flask is put into a water bath and cooled to room temperature. Then, 6 ml of hexane is added into the mixture at room temperature and precipitation is carried out with ethanol by using centrifugation at 6000 rpm for 5 minutes. The precipitated core nanoparticles (colloidal quantum wells (CQW)) are dissolved in a non-polar solution. In one embodiment of the invention, the non-polar solution is hexane or octane. The precipitated colloidal quantum wells can be any of CdSe core, CdS core, CdS core, CdSe/CdS core/shell, CdSe/ZnS core/shell, CdSe/CdZnS core/shell, CdSe/CdTe core/crown and CdSe/CdSeTe core/crown. In another embodiment of the invention, the colloidal quantum wells may be CuInS, AglnS and CuAglnS. A solution A is prepared by combining one of the colloidal quantum wells and non-polar hexane or octane liquid obtained, in ratios selected in accordance with the parameters such as the diameter of the container used, the number of lines included in the self-assembly aimed to be obtained and the width of lines included in the self-assembly. Then, a solution B is prepared by combining another colloidal quantum well -that different from the colloidal quantum well used in the solution A- and non-polar hexane or octane liquid in ratios selected in accordance with the parameters such as the diameter of the container used, the number of lines included in the self-assembly and the width lines included in the self-assembly parameters.

In the step of forming a nanoparticle array on the polar liquid surface by dripping solutions A and B into the polar liquid (104) of the inventive method (100), the non-polar solution A prepared is taken into a syringe and the syringe is dripped in the middle of the polar liquid included in the container. The dripped solution A forms a circular shape on the polar liquid and since it has a less density than the density of the polar liquid, it can remain on the liquid surface without mixing with the polar liquid. Then, the solution B is dripped just in the middle of the same container. Since the colloidal quantum wells (nanoparticles) included in the solution B have the characteristic of applying repulsive force to the colloidal quantum wells on the surface of the polar liquid where the solution A is dripped, the colloidal quantum wells included in the solution A are pushed towards the edges of the container and then compressed in a ring form such that there is no space between them. Then, when solution B is dripped into the polar liquid, it does not diffuse among the colloidal quantum wells included in the solution A and forms a new ring-shaped pattern in the ring form formed by the solution A without getting mixed with the colloidal quantum wells included in the solution content. The process of dripping the solution A and solution B comprising the colloidal quantum wells is repeated respectively and the number of rings formed by means of the colloidal quantum wells on the polar liquid can be increased up to the desired number and a pattern with a nested ring appearance is obtained (Figure 2). In another embodiment of the invention, the solution A is taken into two separate syringes and the syringes are positioned reciprocatively so as to be close to the walls of the container. Then, the solution A is simultaneously dripped from the syringes onto the polar liquid. Thereafter, the B solutions are put into the syringes wherein the A solutions are included and the B solutions are simultaneously dripped onto the polar liquid. Upon the solution B is simultaneously dripped from two different syringes, the solution A located on the polar liquid surface is pushed from the container wall towards the centre of the container. Then, the solution A is added into the syringes again and dripped onto the polar liquid surface. A linear binary pattern is obtained by putting the solution A and the solution B into syringes respectively and dripping them into the polar liquid (Figure 3). By changing the orders and positions of dripping the colloidal quantum wells -which are included in the solution content- onto the polar liquid surface, it is possible to obtain different self-assemblies and the patterns specified in the description are not limiting.

In one embodiment of the invention, assuming that the syringe position and height on the container are stable and the container diameter d=58 mm, the widths of the self-assembly line can be calculated by using equation no. 1 :

> (1)

In the equation no. 1, is the concentration of the colloidal quantum well material. is the width of the line. is the coefficient. is the mg/mL of the unit. The unit In the step of obtaining nanoparticles with different self-assemblies as a result of transferring the nanoparticle array formed on the polar liquid surface to the substrate surface by discharging the polar liquid included in the container from the container (105) of the inventive method (100), the polar liquid included in the container is discharged from the container by using a liquid discharge outlet or a pump. The patterns with different patterns formed on the polar liquid surface inside the container by using the solution A and the solution B, are transferred to the substrate surface immersed in the bottom of the container as a result of the liquid discharge. Thus, the substrate with a desired colloidal quantum well assembly can be obtained.

There are some parameters that should be taken into account when forming a nested ring pattern. The first parameter is the dropping height or the distance between the syringe and the diethylene glycol surface. This height affects the speed at which the colloidal quantum wells hit the surface of the diethylene glycol liquid. The second parameter is the density of the colloidal quantum wells. This parameter affects the size of the circles formed on the liquid surface directly. Accordingly, the width of the n ^th circle depends on the density of the (n+ l ) ^th colloidal quantum well solution. In addition to this, the position of the n ^th circle depends on the density of the (n- 1 ) ^th colloidal quantum well solution. Many studies show that a linear relationship exists between the density of the colloidal quantum well solution and the widths of the formed circles. The third important parameter is the volume of the drop which is considered constant. Besides, the drop height is another parameter considered as a constant in this study. Widths of the circles formed can be in micrometre size. However, in order to form micrometre-sized circles, the process must be carried out very precisely. Nevertheless, it is quite easy to obtain circles in the order of millimetre.

When forming a binary pattern, there are some parameters to be considered. The first of the said parameters is the dropping height or the distance between the syringe needle and the diethylene glycol surface. This height must remain constant during the patterning process. Otherwise, unwanted differences may occur in the pattern dimensions. The second parameter is the volume of the drop. The volume of the drops of both materials dripped from the syringes, should be equal to each other. Also, in this type of patterning method, 3 conditions must be fulfilled in order to have a binary pattern with a linear interface. The first condition is to drip the droplets from two syringes at the same time. This makes the structure symmetrical and forms the line interface. The second condition is the requirement that the dripping projections of the syringes must always be in the same place. Any misplacement results in an asymmetric structure. The third condition is the requirement that the material density has to be optimized in order to realize the desired structure. For example, to form a linear interface, the material densities of the host nanoparticle solution and the second nanoparticle solution must be specific so as to form a narrow line.

Therefore, in an arrangement requiring such sensitivity, it is better to design a circuit for dropping of the drops simultaneously and not to perform the process manually.

With the inventive method (100), the patterns formed on a polar liquid surface by means of colloidal quantum well solutions are transferred to the substrate surface -that is included in the polar liquid- over the liquid-liquid interface. No reaction is carried out while forming a pattern on the polar liquid surface and no specific temperature is required for patterning. Surface tension phenomena of colloidal quantum wells and intermolecular forces are utilised in pattern formation.

Within these basic concepts; it is possible to develop various embodiments of the inventive “Method (100) of Obtaining a Nanoparticle Self-Assembly”; the invention cannot be limited to examples disclosed herein and it is essentially according to claims.