Conductive film and method for making same

A method for making a conductive film includes: providing a carbon nanotube film defining a plurality of holes therein; attaching the carbon nanotube film on a substrate; adjusting a temperature of the carbon nanotube film in a range from about 7° C. to about 9° C.; dropping and rubbing a nanoparticle aqueous solution in the carbon nanotube film, the nanoparticles aqueous solution containing a plurality of nanoparticles; and adjusting the temperature of the carbon nanotube film in a range from about 24° C. to about 26° C. and drying the carbon nanotube film to obtain the conductive film on the substrate.

BACKGROUND

1. Technical Field

The present disclosure relates to conductive films and methods for making the same.

2. Description of Related Art

Conductivity of carbon nanotubes makes them possible to be used as conductive films. Generally, in such conductive film, the carbon nanotubes interconnect with each other to form an electrically conductive framework. However, holes exist in the conductive framework. This reduces a conductivity of the carbon-nanotube conductive film.

Therefore, what is needed is a conductive film and a method for making the same, which can overcome the limitations described.

DETAILED DESCRIPTION

Referring toFIG. 1, a conductive film100, according to a first embodiment, includes a carbon nanotube (CNT) film10and a plurality of conductive nanoparticles20.

The CNT film10defines a plurality of holes102therein. The conductive nanoparticles20are received in the holes102. It is to be understood that number of the nanoparticles20received in a hole102is determined by grain size of the nanoparticle20and dimensions of the corresponding hole102. The nanoparticle20is selected from a group consisting of gold, silver, copper, aluminum, and any combination thereof. Since the nanoparticles20are received in the holes102, conductivity of the conductive film100is enhanced.

Methods for making the CNT film10may include a direct growth method, a flocculating method, a pressing method or a pulling method.

The direct growth method is used to grow a CNT film directly on a substrate. The CNT film may be an aligned CNT film where CNTs are aligned in one or more directions, or a non-aligned CNT film where CNTs are twisted with each other and randomly distributed therein. The CNT film10may include two or more aligned CNT films stacked together. An angle α between the aligned directions of stacked CNTs in two adjacent CNT films is in a range of 0°≦α≦90°. The CNT films are held together by van der Waals attractive force.

The flocculating method for making a CNT film includes the following steps: adding a plurality of CNTs to a solvent to create a CNT floccule structure in the solvent; separating the CNT floccule structure from the solvent; and shaping the separated CNT floccule structure into the CNT film. The CNT film made by the flocculating method includes a plurality of isotropic CNTs twisted with each other and randomly distributed therein and can form the CNT film10directly.

The pressing method for making a CNT film includes the following steps: forming an array of CNTs on a substrate; and pressing the array of CNTs using a compressing apparatus, thereby forming a CNT film. The CNT film made by the pressing method includes a plurality of CNTs aligned in one or more direction. The CNT film10can be obtained by stacking at least two CNT films together.

The pulling method for making a CNT film includes the following steps: providing a CNT array, specifically, a super-aligned CNT array, on a substrate; and pulling out the CNT film from the CNT array with a pulling tool (e.g., adhesive tape, pliers, tweezers, or another tool allowing multiple CNTs to be gripped and pulled simultaneously). The CNT film is an aligned CNT film and includes a plurality of CNT parallel to each other. The CNT film10may include two or more aligned CNT films stacked together.

Referring toFIGS. 2A to 2B, a method for making the conductive film100, according to a second embodiment, is shown. The method includes the following steps of: providing a CNT film, the CNT film defining a plurality of holes therein; forming a curable adhesive layer300on a substrate200; attaching the CNT film on the curable adhesive layer300; curing the curable adhesive layer300to bond the CNT film; adjusting a temperature of the CNT film in a range from about 7° C. to about 9° C.; dropping and rubbing a nanoparticle aqueous solution500in the CNT film, the nanoparticles aqueous solution500containing a plurality of nanoparticles; adjusting the temperature of the CNT film in a range from about 24° C. to about 26° C. and drying the CNT film to obtain the conductive film100on the substrate200.

Material of the substrate200is a polyethylene terephthalate (PET). The substrate200may be curved inwards to form a container to allow aqueous solution therein to disperse uniformly in the CNT film. In this embodiment, a thickness of the substrate200is about 1 millimeter. The CNT film can be obtained by the above methods mentioned in the first embodiment.

A thickness of the curable adhesive layer300is about 3 to about 5 micrometers. The curable adhesive layer300is also curved inwards due to the curved substrate200.

A printing tool400in used in the step of attaching the CNT film on the curable adhesive layer300. The printing tool400includes a handle402, a connecting portion404, a rotating rod406, and a rolling ball408. The handle402is attached to the connecting portion404. The connecting portion404is substantially a hollow ball. The rotating rod406is rotatably connected to the connecting portion404. The handle402and the rotating rod406are connected to opposite sides of the connecting portion404. The rolling ball408is fixed to the rotating rod406and rotates with the rotation of the rotating rod406. The CNT film is attached to the outer circumference of the rolling ball408. Then the rolling ball408with the CNT film contacts the curable adhesive layer300and moves back and forth on the curable adhesive layer300. Therefore, the CNT film can be coated on the curable adhesive layer300uniformly.

In the step of curing the curable adhesive layer300, the curable adhesive layer300is a light-curable adhesive layer300and can be cured by an ultraviolet light for example. After the curing process, the CNT film can be bonded on the adhesive layer300.

In the step of adjusting the temperature of the CNT film in the range from about 7° C. to about 9° C., the substrate200with the CNT film can be placed in an atmosphere with the temperature of about 7° C. to about 9° C. Beneficially, the temperature of the CNT film is adjusted to about 8° C. The nanoparticle aqueous solution500is selected from a group consisting of a gold aqueous solution, a silver aqueous solution, a copper aqueous solution, an aluminum aqueous solution, any combination alloy of gold, silver and copper aqueous solution, and any combination aqueous solution thereof. In this embodiment, the nanoparticle aqueous solution500is a gold aqueous solution. When the temperature of the CNT film is about 8° C., the nanoparticle solution500is dropped in the substrate200and the rolling ball408moves back and forth to uniformly rub the nanoparticle aqueous solution500in the CNT film. Since the CNT is hydrophilic at the temperature in the range from about 7° C. to about 9° C., especially at the temperature of about 8° C., the nanoparticle aqueous solution500can fill the holes102of the CNT film10.

In the step of adjusting the temperature of the CNT film in the range from about 24° C. to about 26° C., the substrate200with the CNT film can be placed in an atmosphere with the temperature of about 24° C. to about 26° C. Beneficially, the temperature of the CNT film is adjusted to about 25° C. Since the CNT is hydrophobic at the temperature in the range from about 24° C. to about 26° C., especially at the temperature of about 25° C., the water in the nanoparticle aqueous solution500is repelled by the CNT film10and the nanoparticles in the nanoparticle aqueous solution500is left and received in the holes102.

Properties of hydrophilicity of the CNT at the temperature of about 7° C. to about 9° C. and hydrophobicity of the CNT at the temperature of about 24° C. to about 26° C. are utilized for making the conductive film100. Therefore, the nanoparticles20can be received in the holes102to enhance conductivity of the conductive film100.

A method for making a conductive film, according to a third embodiment, is also provided. The differences between the method of this embodiment and the method of the second embodiment are that steps of forming a CNT film on the curable adhesive layer and curing a curable adhesive layer are different from those in the second embodiment.

In this embodiment, after a step of forming a curable adhesive layer on a substrate, the method includes steps of: forming a first CNT sub-film on the curable adhesive layer300; curing the curable adhesive layer300to bond the first CNT sub-film; forming a second CNT sub-film on the first CNT sub-film to cooperatively obtain the CNT film on the curable adhesive layer300.

A thickness of the first CNT sub-film is about 50 to about 100 nanometers. An ultraviolet light is used for curing the curable adhesive layer300. A thickness of the second CNT sub-film is about 1 to about 2 micrometers. The first CNT sub-film and the second CNT sub-film are held together by van der Waals attractive force.

Since the second CNT sub-film is attached on the first CNT sub-film after the curable adhesive layer300is cured, more CNT frameworks in the obtained CNT film are exposed from the curable adhesive layer to be immersed in a nanoparticle aqueous solution in a subsequent step.

In alternative embodiments, the step of forming the curable adhesive layer300on the substrate200may be omitted. The CNT film is adhesive, because the CNTs have relatively large specific areas, so that the CNT film can be directly attached to the substrate200.