KR102438575B1 - Multi-functional bioinspired paper for thermal management and Electro Magnetic Interference Shielding, Method of fabrication for the same - Google Patents

Abstract

The functional film of the present invention is a nacre-bioinspired paper, and includes graphene nanoplatelet (GnP) and aramid nanofiber (ANF). The functional film of the present invention may be used in a film having heat dissipation and/or electromagnetic wave shielding performance applicable to electronic devices, particularly wearable electronic devices.

Description

Multi-functional bioinspired paper for thermal management and Electro Magnetic Interference Shielding, Method of fabrication for the same

The present invention relates to a multifunctional natural mimic film having heat dissipation and EMI shielding performance at the same time, and more particularly, to a high heat dissipation EMI shielding film having a structure similar to the nano-interlayer structure present in a pearl oyster shell, and a method for manufacturing the same.

As electronic products increase in performance and become miniaturized and, in particular, become thinner and thinner, the capacity and high integration of electronic devices in various electronic products are made together. have.

For example, small electronic devices such as LEDs, smart phones, and tablet PCs emit more heat, so it is important to effectively dissipate heat from these devices. It is important to dissipate the heat generated because the use of

If the heat generated during the operation of these electronic devices continues to be locally accumulated, the internal temperature of the device continues to rise, causing malfunction of the device or shortening the lifespan. It is reported that when the temperature rises to about 10°C, the lifespan of the device is reduced by about half.

Accordingly, there is a growing demand for a film having excellent heat dissipation performance having high thermal conductivity and insulating properties. In particular, as the development of wearable electronic devices is accelerated in recent years, the demand for the development of a flexible and excellent heat dissipation film that can be applied to the wearable device is also increasing.

An object of the present invention is to provide a functional film having excellent thermal conductivity, electromagnetic wave shielding performance and incombustibility, and excellent mechanical flexibility as a multifunctional film applicable to electronic devices, particularly wearable electronic devices.

The functional film according to an embodiment of the present invention includes graphene nanoplatelet (GnP) and aramid nanofiber (ANF).

In the functional film according to an embodiment of the present invention, the GnP is characterized in that polydopamine is coated.

In the functional film according to an embodiment of the present invention, the aramid nanofibers are acid-treated.

In the functional film according to an embodiment of the present invention, the GnP and the aramid nanofibers are cross-linked.

In the functional film according to an embodiment of the present invention, the GnP and the aramid nanofiber are halogen, an amine group (-NH ₂ ) and a crosslinking agent having at least one functional group selected from the group consisting of a hydroxyl group (-OH) It is characterized in that it is cross-linked.

In the functional film according to an embodiment of the present invention, the GnP and the aramid nanofibers are made of hexachlorophosphazene (phosphonitrilic chloride trimer, PNCT), borate, polyethyleneimine and phenyldiamine. It is characterized in that it is cross-linked by at least one selected from the group.

In the functional film according to an embodiment of the present invention, the GnP is characterized in that it is aligned parallel to the surface of the aramid nanofiber.

A method of manufacturing a functional film according to an embodiment of the present invention comprises: coating a graphene nanoplatelet (GnP) with polydopamine; Acid treatment (acid treatment) of the aramid nanofibers; mixing the polydopamine-coated GnP, acid-treated aramid nanofibers, and a crosslinking agent; casting and drying the mixture into a release film; and peeling the dried film.

The crosslinking agent is characterized in that it has at least one functional group selected from the group consisting of halogen, an amine group (-NH ₂ ), and a hydroxyl group (-OH).

The crosslinking agent is characterized in that it comprises at least one selected from the group consisting of hexachlorophosphazene (phosphonitrilic chloride trimer, PNCT), borate, polyethyleneimine, and phenyldiamine.

The film having both heat dissipation and EMI shielding properties according to an embodiment of the present invention includes the above-described functional film.

The functional film of the present invention has a dense structure in which polydopamine-coated GnP and oxidized aramid nanofibers are highly aligned, so that it has very good thermal conductivity in the plane direction and has excellent mechanical properties such as tensile strength and elongation at break.

In addition, GnP has high electrical conductivity capable of absorbing electromagnetic radiation, and GnP is well aligned to cause multiple reflections, thereby securing excellent electromagnetic wave shielding performance.

As it was confirmed that the functional film of the present invention is light and ultra-thin, and exhibits high resistance to bending cycles, it has excellent flexibility and thus can be applied to flexible electronic devices. In addition, it has been proven to be effective in preventing the spread of fire and maintaining thermal stability due to its excellent flame retardancy.

Through the functional film according to the present invention, heat dissipation performance can be effectively improved, and usability as an electronic product can be improved. That is, when the high-functional film according to the present invention is used in an electronic circuit, it is possible to prevent malfunction and shorten the lifespan.

1 (a) is a schematic schematic diagram of a method for manufacturing a functional film of the present invention, (b) and (c) are SEM images of a film according to an embodiment of the present invention, (d) is XPS spectra data, (e) is XPS spectra deconvolution of the p 2p peak, (f) is a schematic diagram of the functional film of the present invention
Figure 2 (a) is a stress-strain curve of the fGnP@PANF film according to the weight ratio of fGnP, (b) is the result of measuring Young's modulus (E) and toughness (U), ( C) is the stress-strain curve of the fGnP@PANF film according to the PNCT content, (d) is the result of measuring Young's modulus (E) and toughness (U), (e) and (f) ) are side-view SEM images of fGnP@PANF films bent after tensile testing, and (g) and (h) are top-view SEM images.
3 (a) is the stress-strain behavior of the fGnP50@PANF film according to the folding cycle, (b) is the stress-strain behavior according to the thickness of the fGnP50@PANF film, and (C) is After different folding cycles of the fGnP50@PANF film, the relative tensile stress (σ/σ ₀ ), (d) is the relative toughness (U/U ₀ ) after different folding cycles of the fGnP50@PANF film, (e) is a photograph of the folded fGnP50@PANF film and the fGnP50@PANF film after tensile testing.
4 (a) is the in-plane (plane direction) and through-plane (thickness direction) thermal conductivity of the fGnP@PANF film according to the fGnP content, (b) is a comparison of the thermal conductivity in the plane direction, (C) is a comparison of the thermal conductivity and tensile strength between the fGnP@PANF film of the present invention and the conventional boron nitride (BN) and graphene sheet (GS)-based films, (d) is the thermal conductivity in the plane direction according to the filler content will be measured
5 (a) is the electrical conductivity according to the content of fGnP, (b) is the total EMI shielding effect (SE _T ) according to the content of fGnP is the result of investigation in the frequency range of 2-18 GHz, (C) is the fGnP @PANF The total EMI shielding effectiveness (SE _T ) according to the thickness of the film is the result of investigation in the frequency range of 2-18 GHz, and (d) is the measurement result of ASSE _T is the result
6 is a photograph of the film of the present invention exposed to a flame.
7 is (a) is a heat release rate (HRR) curve of the fGnP@PANF film and its precursor, (b) is a TGA (thermogravimetric analysis) curve of the fGnP@PANF film and its components.
8 is a result of comparing the heat dissipation properties of the fGnP@PANF film, the polyimide film (PI film), and the Al alloy 7075.

Hereinafter, various embodiments of the present document will be described with reference to the accompanying drawings. The examples and terms used therein are not intended to limit the technology described in this document to specific embodiments, and should be understood to cover various modifications, equivalents, and/or substitutions of the embodiments.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The functional film having both heat dissipation and EMI shielding properties of the present invention is a multifunctional natural mimic film having a nano-layered structure like a pearl shell, and can be used as a heat dissipation film and/or EMI shielding film applicable to electronic devices, particularly wearable electronic devices. can The functional film of the present invention has excellent thermal conductivity, EMI shielding effect and nonflammability, and excellent mechanical flexibility.

The functional film of the present invention includes graphene nanoplatelet (GnP) and aramid nanofiber (ANF). Specifically, GnP may be coated with polydopamine (PDA). In addition, the aramid nanofibers may be acid-treated and oxidized aramid nanofibers.

These polydopamine-coated GnP and oxidized aramid nanofibers can be cross-linked. Specifically, polydopamine-coated GnP and oxidized aramid nanofibers can be crosslinked through various crosslinking agents having reactive PDA chains and functional groups that can be chemically crosslinked with functional groups on the surface of oxidized aramid nanofibers. Specifically, polydopamine-coated GnP and oxidized aramid nanofibers may be cross-linked through a cross-linking agent having at least one functional group selected from the group consisting of halogen, amine group (-NH ₂ ) and hydroxyl group (-OH). . For example, it may be cross-linked by at least one selected from the group consisting of hexachlorophosphazene (phosphonitrilic chloride trimer, PNCT), borate, polyethyleneimine, and phenyldiamine. Preferably it can be crosslinked by PNCT. Here, the polydopamine-coated GnP may be aligned parallel to the surface of the aramid nanofiber.

In the functional film of the present invention, for example, polydopamine-coated GnP may serve as a “brick”, and aramid nanofibers may serve as a “mortar” connecting bricks. In polydopamine-coated GnP, reactive PDA chains and functional groups on the surface of oxidized aramid nanofibers react with PNCT, so that they can be densely linked by PNCT. Specifically, the -OH functional group of polydopamine-coated GnP (fGnP) and -Cl, which is the halogen functional group of PNCT, may be cross-linked. In addition, -OH and/or -COOH of oxidized aramid nanofibers (oANF) may cross-link with -Cl, which is a halogen functional group of PNCT.

That is, as the polydopamine-coated GnP and oxidized aramid nanofibers have a highly aligned dense structure, the surface thermal conductivity can be significantly improved. In addition, very good mechanical strength can be secured by promoting stress transmission. In addition, GnP has high electrical conductivity capable of absorbing electromagnetic radiation, and GnP is well aligned to cause multiple reflections, thereby securing excellent electromagnetic wave shielding performance.

Accordingly, the functional film of the present invention can be applied to a heat dissipation film and/or an EMI shielding film. In addition, the functional film of the present invention may be applied as a functional film having both a heat dissipation function and an EMI shielding function.

A method of manufacturing a functional film according to an embodiment of the present invention comprises: coating a graphene nanoplatelet (GnP) with polydopamine; Acid treatment (acid treatment) of the aramid nanofibers; mixing the polydopamine-coated GnP, acid-treated aramid nanofibers, and a crosslinking agent; casting and drying the mixture into a release film; and peeling the dried film.

In this case, the crosslinking agent may include various crosslinking agents having a reactive PDA chain and a functional group that can be chemically crosslinked with a functional group on the surface of the oxidized aramid nanofiber. Specifically, the crosslinking agent may have at least one functional group selected from the group consisting of halogen, an amine group (-NH ₂ ), and a hydroxyl group (-OH). For example, the crosslinking agent may be at least one selected from the group consisting of hexachlorophosphazene (phosphonitrilic chloride trimer, PNCT), borate, polyethyleneimine, and phenyldiamine. Preferably, the crosslinking agent may be PNCT.

Hereinafter, it will be described in detail through specific embodiments of the present invention.

However, the following examples are only for illustrating the present invention, and the present invention is not limited by the following examples.

Example 1 Preparation of polydopamine-coated GnP (polydopamine-coated GnP) Preparation

GnP (graphene nanoplatelet) powder was first dispersed in N-methyl-2-pyrrolidone (NMP) at a concentration of 5 mg·mL ^-1 . The mixture was then tip sonicated for 3 hours and left for 2 days to settle the aggregated graphene sheets. The supernatant GnP suspension was filtered (Nylon membrane, pore size 0.2 μm) and washed several times with DI water. The obtained GnP slurry was freeze-dried to obtain a fine GnP powder without coarse particles. The purified GnP powder was redispersed in a mixture of ethanol and deionized water (DI wter) (80/20, v/v) at a concentration of 1 mg·mL ⁻¹ by mild sonication for 30 minutes. A dopamine precursor was then added to the dispersion to make the dopamine to GnP ratio 1:10. The mixture was then stirred at room temperature for 1 day to polymerize the dopamine precursor to form a polydopamine layer on the GnP surface. Polydopamine-coated GnP (hereinafter referred to as “fGnP”) powder was obtained after filtration and freeze-drying.

Example 2 Preparation of Oxidized Aramid Nanofibers

Aramid fibers were first cut into pieces of 1 cm in length, and then washed successively with acetone and ethanol to remove dust and impurities on the fiber surface, and finally dried in an oven at 60 °C. Then dry aramid fibers (1.2 g) and KOH (1.8 g) were added to DMSO (600 ml). 24 ml deionized water (deionized water to DMSO volume ratio 1:25) was added to the mixture. Then, the mixture was stirred with a magnetic stirrer at room temperature for 4 hours to obtain aramid nanofiber (ANF) in DMSO solution by a proton donor-assisted deprotonation approach. Acid treatment of ANF was performed as follows. ANF powder was dispersed in a mixture of HNO ₃ (8.75 wt %) and H ₂ SO ₄ (37.5 wt %) (1 : 3, v/v) acids. The solution was then heated in an autoclave at 120 °C for 4 h. Oxidized ANF (oANF) was obtained after thorough washing with deionized water and lyophilization. oANF was redispersed in deionized water at a concentration of 10 mg·mL ⁻¹ through mild sonication for 30 min.

Example Preparation of 3-fGnP@PANF

The calculated amount of fGnP obtained in Example 1 was redispersed in deionized water of different weight content, and then added to the oANF suspension obtained in Example 2 with continuous stirring by a magnetic bar. The total mass concentration of fGnP and nanofibers in deionized water was maintained at 5 wt %. The weight ratio of fGnP to oANF in the mixture ranged from 0 to 90 wt % with 10 wt % intervals. Then, in order to obtain a composition in the form of a slurry, a weight ratio of hexachlorophosphazene (phosphonitrilic chloride trimer, PNCT) and fGnP, which is a crosslinking agent, was added to each mixture in a weight ratio of 1:5 and 1:10, and then added to each mixture at 8000 rpm for 1 hour. Homogenize with a mechanical stirrer. The slurry was stirred for 24 hours to allow the PNCT to adsorb to the surface of fGnP and oANF, and then placed in a desiccator under vacuum to remove air bubbles.

The bubble-free slurry was cast on a PET release sheet (20 x 20 cm), dried slowly at 40 °C for 48 hours and at 80 °C for 24 hours, to a thickness of about 20 to 60 μm by evaporation-induced self-assembly. A thin film similar to a phosphor film was obtained. This thin film is a nacre-like bioinspired film composed of fGnP and ANF crosslinked by PNCT. Hereinafter referred to as “fGnP@PANF”. The thickness of the film was controlled by changing the mass of the slurry cast on the PET release film.

For comparison, fGnP-based cellulose nanofiber (CNF) (fGnP@PCNF) and fGnP-based polyimide (fGnP@PI) films were also prepared. The calculated amounts of fGnP and PNCT were mixed with the CNF dispersion (5 mg·mL ^{- 1} ) using a homogenizer at 8000 rpm for 1 h. The suspension was then cast and dried to obtain a fGnP@PCNF film.

Similarly, a calculated amount of fGnP was mixed with poly(amic acid) in a dimethylacetamide (DMAc) solution (5 mg·mL ^{- 1} ) using a homogenizer at 8000 rpm for 1 h. The solution was cast into a release film and heated at 100 °C for 2 hours, 200 °C for 1 hour and 300 °C for 1 hour to obtain an fGnP@PI film.

On the other hand, if the fGnP and oANF suspensions mixed with PNCT as a crosslinking agent are used, large-area fabrication of fGnP@PANF films is possible by evaporation-induced self-assembly. Referring to Figure 1 (a), the suspension was poured into a release film with an area of 200 x 50 cm ² and dried slowly to induce the formation of an ordered structure of fGnP in the ANF matrix. After that, the dried film can be peeled off and heat-treated for cross-linking to obtain an fGnP@PANF film as a final product.

Figure 1 (b) is a SEM image of the fGnP@PANF film prepared with 50 wt% of fGnP, (C) is a SEM image of the fGnP@PANF film prepared with 90 wt% of fGnP. Referring to Figure 1 (b) and (C), it can be seen that the fGnP@PANF film has a highly ordered dense structure similar to the hierarchical brick and mortar structure of nacre. The ANF fibers acted as a mortar to tightly bind the fGnP, and the fGnP fillers were aligned parallel to the ANF surface. Since fGnP has high strength, fGnP@PANF films are expected to have excellent mechanical properties. In addition, the highly ordered orientation of fGnP fillers with high thermal conductivity is likely to play an important role in improving the in-plane thermal conductivity.

Figure 1 (d) is the XPS spectra observation result of the fGnP@PANF film. (e) shows the XPS spectra deconvolution of the p 2p peak. Referring to Figure 1 (d), it can be seen that the fGnP@PANF film is composed of C, O, N and P elements. Referring to (e) of FIG. 1 , P-O (132.8 eV) and P-C (133.8 eV) peaks formed in the crosslinking reaction between oANF and PNCT and fGnP and PNCT can be confirmed, respectively.

Referring to Figure 1 (f), it shows the cross-linking between the fGnP layer and oANF through PNCT.

2A is a stress-strain curve of the fGnP@PANF film according to the weight ratio of fGnP. The number 'x' in fGnPx@PANF represents the weight percentage of fGnP in fGnP-ANF. (b) is the result of measuring the Young's modulus (E) and toughness (U) of the fGnP@PANF film. At this time, the amount of the crosslinking agent PNCT was fixed at 5 wt%.

As the fGnP content increased from 20 wt % to 90 wt %, the mechanical properties of the fGnP@PANF film improved and reached a maximum value, especially at a fGnP content of 50 wt %. Specifically, referring to (a) of FIG. 2 , σ of the fGnP@PANF film increased from 252 to 437 MPa and then decreased to 94 MPa. ε increased from 5.4% to 8.4% and then decreased to 1.5%. Referring to (b) of FIG. 2 , E increased from 10.3 to 19.7 GPa and then decreased to 8.4 GPa, and U increased from 8.6 to 23.9 MJ·m ⁻³ and then decreased to 0.9 MJ·m ⁻³ .

Meanwhile, to investigate the effect of PNCT content on the mechanical properties of fGnP@PANF films, the mechanical properties of other fGnP50@PANF films were compared with different PNCT content. Referring to (C) and (d) of Figure 2, the optimal mechanical properties of the fGnP50@PANF film were achieved when the PNCT content was 5 wt%, and when the PNCT content was further increased to 10 wt%, the fGnP50@PANF film was The strength decreased slightly.

The folding durability of the fGnP@PANF film was investigated considering its excellent toughness and ductility. First, the effect of repeated folding cycles on the mechanical properties of fGnP50@PANF films was investigated. Referring to (a) of Figure 3, the tensile stress of the fGnP50@PANF film is well preserved even after 10000 folding cycles, suggesting excellent sustainability and lifespan of the mechanical properties of the film. In addition, referring to FIG. 3 (b), there was no difference in the mechanical properties of the fGnP50@PANF films having different thicknesses. 3 (c) and (d) show the relative tensile stress (σ/σ ₀ ) and relative toughness (U/U ₀ ) (tensile strength of the film after some folding cycles) of the fGnP50@PANF film after different folding cycles. or, defined as the ratio between toughness and the tensile strength or toughness of the original film). Referring to (c) and (d) of Figure 3, it can be seen that the relative tensile stress and the relative toughness fluctuated around 1. In addition, referring to FIG. 3(e), the fracture location of the film in the tensile test was different from the folded location, which shows excellent folding durability and flexibility. In addition, no breakage was observed even after the fGnP@PANF film was crumpled and unfolded with bare hands, and the crumpled fGnP@PANF film could withstand a weight of 500 g without breakage. The fGnP@PANF film can also be folded into complex shapes such as bats through film folding. These results show that the fGnP@PANF film has excellent mechanical flexibility and excellent folding durability.

2 (e) to (h) are SEM images showing the fracture surface of the fGnP50@PANF film after the tensile test. Referring to (e) to (h) of Figure 2, it can be seen that the fracture surface well preserves a highly ordered structure.

The thermal conductivity of the fGnP@PANF film was evaluated under various conditions. Referring to (a) of FIG. 4 , it shows that the thermal conductivity of the fGnP@PANF film in the in-plane (plane direction) and through-plane (thickness direction) increases as the fGnP content increases. The thermal conductivity in the plane direction increases at a very high rate of increase, while the thermal conductivity in the thickness direction shows a much lower rate of increase. The in-plane thermal conductivity of the fGnP50@PANF film reached 68.2 W·m ^-1 ·K ^-1 , which is about 195 higher than that of the PNCT cross-linked ANF (PANF) without fGnP (0.35 W·m ^{-1 ·} K ^-1 ). times higher. In addition, the thermal conductivity in the plane direction of fGnP90@PANF was about 142 W·m ^-1 ·K ^-1 , which was almost 70 times higher than the thermal conductivity in the thickness direction (2.2 W·m ^{-1 ·} K ^-1 ). The high in-plane thermal conductivity of the fGnP@PANF film may be due to the high intrinsic thermal conductivity in the basic direction of graphene. In addition, the highly stacked layer structure of graphene can create a large contact area and effectively form a thermally conductive path in the plane direction. High thermal conductivity in the plane direction is essential for heat dissipation of flexible electronic devices.

Meanwhile, in order to confirm the effect of PANF on the thermal conductivity in the plane direction of the fGnP@PANF film, the thermal conductivity of fGnP@PI and fGnP@PCNF, which are comparative examples, was measured. As a result, the thermal conductivity of fGnP@PI was 52.3 W·m ^-1 ·K ^-1 , and the thermal conductivity of fGnP@PCNF was measured as 58.4 W·m ^{-1 ·} K ^-1 , the fGnP50@PANF thermal conductivity of the present invention ( 68.2 W·m ^-1 ·K ^-1 ) was 17% and 30% higher, respectively.

The synergistic effect of fGnP and ANF by covalent bonding of the present invention is higher than most graphene sheets (GS) or BN-based 1D nanofiber films with different interfacial interactions, including hydrogen bonding and π-π. It has the advantage of high thermal conductivity. This suggests that it can be effectively applied to a flexible electronic device.

Figure 4 (C) is a comparison of the thermal conductivity and tensile strength between the fGnP@PANF film of the present invention and the conventional BN and GS-based films. Referring to FIG. 4(c), it can be seen that the fGnP@PANF film of the present invention has very good in-plane thermal conductivity and excellent tensile strength compared to the BN-based and GS-based 1D nanofiber nanocomposite films. Also, referring to FIG. 4(d), the fGnP@PANF film exhibits higher in-plane thermal conductivity than several BN- and GS-based nanocomposite films at all filler content levels.

On the other hand, the thermal conductivity per unit density of the fGnP@PANF film is much higher than that of stainless steel, iron and copper alloys. These results show that the fGnP@PANF film of the present invention can replace metal/alloy in thermal management of flexible electronic devices.

On the other hand, GnP is a filler with excellent electrical conductivity with an intrinsic electrical conductivity of 10 ⁷ S·m ^-1 . GnP plays an important role in increasing the electrical conductivity of the film by efficiently creating an electrically conductive network along a highly aligned planar structure. do Therefore, the electrical conductivity of the film greatly increases with increasing fGnP content in the fGnP@PANF film. While the electrical conductivity required for the actual application of the EMI (Electro Magnetic Interference Shielding) shielding material is 1 S·m ^-1 , referring to FIG. The conductivity is 32 S m ^{- 1} , It shows that it can be compared with other GS-based composites. Meanwhile, the electrical conductivity of the fGnP90@PANF film with a fGnP content of 90 wt % reached 5521 S·m ⁻¹ . The high electrical conductivity of the fGnP@PANF film could be attributed to the high intrinsic electrical conductivity of GnP with a very large aspect ratio of 2500 to 3000 and the formation of a continuous electrically conductive path due to the well-ordered layer structure of the GnP sheet in fGnP@PANF. Therefore, the fGnP@PANF film is expected to exhibit excellent EMI shielding performance due to its high electrical conductivity and aligned layer structure.

EMI SE refers to the ability of a material to block electromagnetic waves (EMW). It is expressed in decibels (dB) and is defined as:

EMI SE= 10 log(P _in /P _out )

Here, P _in is the input power and P _out is the output transmit power.

The higher the EMI SE value, the better the EMW can be blocked.

Figure 5 (b) is the total EMI shielding effect (SE _T ) according to the content of fGnP is the result of investigation in the frequency range of 2-18 GHz, Figure 5 (c) is the total EMI according to the thickness of the fGnP@PANF film The shielding effectiveness (SE _T ) is the result of investigation in the frequency range of 2-18 GHz.

Referring to (b) of FIG. 5 , the fGnP content of the fGnP@PANF film showed a gradual increase in EMI SE _T as the fGnP content increased by 10 to 30 wt % at a thickness of 21 μm. The fGnP30@PANF film with an fGnP of 30 wt % has an average EMI SE _T of 26 dB, which clearly meets the EMI SE requirements for commercial products (20 dB) in practical applications. When the fGnP content was 90 wt %, a maximum value of 47 dB was reached.

In general, the thickness has a great effect on the EMW shielding, and the EMI SE _T of the fGnP50@PANF film increased as the thickness increased, like other shielding materials. The average EMI SE _T of the fGnP50@PANF film increased from 26 dB to 58 dB as the thickness increased from 11 μm to 63 μm. The good shielding performance of the fGnP@PANF film can be attributed to i) the high electrical conductivity of the GnP capable of absorbing electromagnetic radiation, and ii) the alignment of the GnP with a sufficient amount of reflective surface within the GnP to cause multiple reflections of the EMW.

Due to the trend toward miniaturization of flexible electronic devices, a film having a light weight and a thin thickness while having a higher shielding performance is required. To evaluate the shielding performance of EMI materials of different densities, SE _T was Specific EMI SE _T (SSE _T ) divided by density was proposed. The absolute effect (ASSE _T ), defined as the SSE _T divided by the thickness ( l ), was measured to compare the shielding performance of the fGnP@PANF film and other materials.

Referring to (d) of Figure 5, it shows that increasing the content of fGnP can effectively improve the ASSE _T of the fGnP@PANF film. For example, when the fGnP component increases to 90wt %, the ASSE _T of the fGnP90@PANF film obtains a high value of 12611 dB·cm ² ·g ^-1 at 10 GHz. The ASSE _T of the fGnP90@PANF film showed the highest value among various shielding materials including graphene, CNT and metal-based composites.

Meanwhile, referring to FIG. 6 , the fGnP@PANF film of the present invention shows excellent flame retardancy and heat resistance. The fGnP@PANF film maintained its initial shape after exposure to flame for 5 h.

7 (a) shows the heat release rate (HRR) of the fGnP@PANF film and its precursor. ANF showed a broad HRR curve at a temperature ranging from 470 °C to 600 °C, and showed a peak of HRR of 116 W g ^-1 at 543 ° C, and the total heat release (THR) was 5.1 kJ g ^-1 . On the other hand, acid-treated ANF showed a broad HRR curve at a temperature in the range of 420 ° C to 600 ° C, and showed a peak of HRR of 219.8 W g ^-1 at 532 ° C, and the total heat release (THR) was 11.3 kJ . g ^-1 . The high THR of acid-treated ANF compared to native ANF is due to the introduction of oxygen functional groups by acid treatment. On the other hand, the fGnP@PANF film containing the phosphorus crosslinker has a much lower THR than the film without the phosphorus crosslinker. The fGnP50@PANF film showed an HRR peak of 3.6 W g ^-1 at 556 °C and a THR of 0.1 kJ g ^-1 , whereas the fGnP50@ANF film showed an HRR peak of 2.5 W g ^-1 at 549 ° C. and the total heat release (THR) was 0.9 kJ·g ^-1 .

Figure 7 (b) shows the thermal stability of the fGnP@PANF film and its components. oANF has poor thermal stability, is thermally unstable, and begins to decompose at about 100 °C. The main mass loss of oANF occurred in the temperature range of 500–600 °C and showed a residual mass of 35 wt% at 900 °C. GnP and fGnP show good thermal stability, GnP decomposes slowly, leaving a char yield of 78% at 900 °C, whereas fGnP was about 73 wt%. This indicates that the PDA coating of GnP is about 6.4 wt%. It can be seen that the fGnP@PANF film containing the phosphorus crosslinking agent exhibits higher thermal stability and carbonization layer formation compared to the film without the phosphorus crosslinking agent. The fGnP50@PANF film exhibited a high residual mass of 69 wt% at 900 °C, whereas the residual mass of fGnP50@ANF was about 61 wt% at 900 °C. The excellent flame retardancy and thermal stability of the fGnP@PANF film is due in part to the intrinsic advantageous parameters of the components and the presence of phosphorus-crosslinking agents.

8 is a result of comparing the heat dissipation properties of the fGnP@PANF film, the polyimide film (PI film), and the Al alloy 7075. The fGnP50@PANF film was mounted on a cylinder holder and a NIR lamp (2W) was irradiated to the center of the film at a distance of about 10 cm, and the temperature distribution of the film surface was recorded through an infrared camera. For comparison, polyimide film (PI film) (0.3 W·m ^-1 ·K ^- ) and Al alloy 7075 (120 W·m ^-1 ·K ^- ) were also tested with the same settings. Referring to FIG. 8 , the highest temperature of the PI film was confined to the center at 197 °C, whereas the fGnP50@PANF film and the Al alloy rapidly released heat and showed a uniform temperature distribution. The highest temperatures observed at the center of the fGnP50@PANF film and the Al alloy are about 95.1 °C and 76.5 °C, respectively. Due to the low thermal conductivity (58 W·m ^{−1 ·} K ⁻¹ ) of the fGnP50@PANF film, the temperature was higher than that of the Al alloy.

Through these results, it was confirmed that the fGnP@PANF film of the present invention can be used as a heat dissipation film in a flexible electronic device.

Features, structures, effects, etc. described in the above embodiments are included in at least one embodiment of the present invention, and are not necessarily limited to one embodiment. Furthermore, features, structures, effects, etc. illustrated in each embodiment can be combined or modified for other embodiments by those of ordinary skill in the art to which the embodiments belong. Accordingly, the contents related to such combinations and modifications should be interpreted as being included in the scope of the present invention.

In addition, although the embodiments have been described above, these are merely examples and do not limit the present invention, and those of ordinary skill in the art to which the present invention pertains are exemplified above in a range that does not depart from the essential characteristics of the present embodiment. It can be seen that various modifications and applications that have not been made are possible. For example, each component specifically shown in the embodiments may be implemented by modification. And differences related to such modifications and applications should be construed as being included in the scope of the present invention defined in the appended claims.

Claims (11)

A functional film comprising graphene nanoplatelet (GnP) and aramid nanofiber (ANF), wherein the GnP and the aramid nanofiber are cross-linked. According to claim 1,
The GnP is a functional film, characterized in that polydopamine (polydopamine) is coated. According to claim 1,
The functional film, characterized in that the aramid nanofiber is acid-treated. delete According to claim 1,
The GnP and the aramid nanofibers are crosslinked by a crosslinking agent having at least one functional group selected from the group consisting of halogen, amine group (-NH ₂ ) and hydroxyl group (-OH). According to claim 1,
The GnP and the aramid nanofibers are crosslinked by at least one selected from the group consisting of hexachlorophosphazene (phosphonitrilic chloride trimer, PNCT), borate, polyethyleneimine and phenyldiamine. Functional film characterized. According to claim 1,
The GnP is a functional film, characterized in that aligned parallel to the surface of the aramid nanofibers. coating GnP (graphene nanoplatelet) with polydopamine;
Acid treatment (acid treatment) of the aramid nanofibers;
mixing the polydopamine-coated GnP, acid-treated aramid nanofibers, and a crosslinking agent;
casting and drying the mixture into a release film; and
Method for producing a functional film comprising the step of peeling the dried film. 9. The method of claim 8,
The crosslinking agent is a method for producing a functional film, characterized in that it has at least one functional group selected from the group consisting of halogen, amine group (-NH ₂ ) and hydroxyl group (-OH). 9. The method of claim 8,
The crosslinking agent, hexachlorophosphazene (phosphonitrilic chloride trimer, PNCT), borate (Borate), polyethyleneimine (Polyethyleneimine) and phenyldiamine (Phenylenediamine) method of manufacturing a functional film, characterized in that at least one selected from the group consisting of . A film having heat dissipation and EMI shielding properties at the same time comprising the functional film according to any one of claims 1 to 3, and any one of claims 5 to 7.

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