KR20250120800A - METHOD FOR MANUFACTURING CONDUCTIVE polymer FILM WITH NANO-NETWORK STRUCTURE, CONDUCTIVE polymer FILM MANUFACTURED THEREBY, AND BENDING SENSOR COMPRISING THE SAME - Google Patents

Abstract

The present invention relates to a method for producing a conductive polymer film having a nano-network structure, comprising the steps of (a) forming an oxidizing layer having a nano-network structure patterned with a plurality of circular pores on a substrate, (b) forming a conductive polymer layer between the oxidizing layer having the nano-network structure and the substrate, and (c) removing the oxidizing layer having the nano-network structure, a conductive polymer film produced thereby, and a bending sensor including the same.

Description

Method for manufacturing conductive polymer film with nano-network structure, conductive polymer film manufactured thereby, and bending sensor comprising the same

The present invention relates to a method for manufacturing a conductive polymer film that can be applied as a sensing part material of a bending sensor, a conductive polymer film manufactured thereby, and a bending sensor including the same.

Since their first synthesis in the 1970s, conjugated conductive polymers have attracted considerable attention due to their excellent optical, mechanical, and electronic properties, and have been applied in various fields such as photocatalysis, bioelectronics, strain sensors, bending sensors, and photovoltaics.

Among the various synthetic methods for conductive polymers, vapor phase polymerization (VPP) has the advantage of being able to produce conductive polymer films on substrates or templates of various shapes when it is difficult to apply the polymer in a liquid or solution form. However, as the demand for increasingly complex device structures increases, there is an urgent need to develop a technology that can pattern conductive polymers at a high resolution on the submicrometer level.

In particular, existing bending sensors that use a conductive polymer film without a pattern in the sensing section for detecting deformation detect the degree of deformation based on the principle that when deformation is applied, micro-sized cracks occur in the conductive polymer film, causing the electrical resistance of the film to increase. However, the sensitivity of the sensor is not up to expectations, and therefore, development of a conductive polymer film with a new structure is necessary to implement a sensor with improved sensitivity.

International Patent Publication No. WO 2016/166148 (Registration Date: October 20, 2016)

The technical problem to be solved by the present invention is to provide a method for manufacturing a conductive polymer film having a nano-scale pattern that can contribute to improving the performance of various devices, such as improving the sensitivity of a bending sensor, a conductive polymer film manufactured thereby, and a bending sensor including the same.

In order to achieve the above technical task, the present invention proposes a method for producing a conductive polymer film having a nano-network structure, comprising the steps of (a) forming an oxidizing layer having a nano-network structure patterned with a plurality of circular pores on a substrate, (b) forming a conductive polymer layer between the oxidizing layer having the nano-network structure and the substrate, and (c) removing the oxidizing layer having the nano-network structure.

At this time, the method for forming the nano-network structured oxidizing layer in the above step (a) is not particularly limited, but it is preferable to form a patterned oxidizing layer through a colloidal lithography process.

In the case where the nano-network structured oxidizing layer is formed through a colloidal lithography process in the above step (a), the step (a) may include: (a-1) preparing a template for colloidal lithography including a substrate and a non-close-packed hemispherical colloidal crystal monolayer formed on the substrate, (a-2) depositing an oxidizing agent on the non-close-packed hemispherical colloidal crystal monolayer, and (a-3) removing the colloidal crystal to form an oxidizing layer having a pattern composed of a plurality of circular pores.

At this time, the step of manufacturing a template for the colloidal lithography process in the step (a-1) may be performed by manufacturing a colloidal multilayer crystal made of polystyrene (PS) or the like, etching a surface layer of the colloidal multilayer crystal, separating the surface layer from the colloidal multilayer crystal using a stamp made of an elastic polymer such as polydimethylsiloxane (PDMS), transferring the surface layer onto a substrate, and then applying pressure to form a non-close-packed hemispherical colloidal crystal monolayer on the substrate.

In addition, the method for forming a nano-network structure conductive polymer layer between the nano-network structure oxidizer layer and the substrate in the above step (b) is not particularly limited, but it is preferable to form a nano-network structure conductive polymer layer through vapor phase polymerization (VPP) in which an oxidizer forming the oxidizer layer and a vapor phase conductive polymer monomer are reacted.

At this time, the type of conductive polymer monomer provided for vapor phase polymerization (VPP) in the step (b) is not particularly limited, and may be, for example, 3,4-ethylenedioxythiophene (EDOT), pyrrole, 3-hexylthiophene (3HT), 3-heptylpyrrole (3HP), thiophene, or furan, and the conductive polymer obtained by polymerizing each of the monomers may be poly(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPy), poly(3-hexylthiophene) (P3HT), poly(3-heptylpyrrole) (P3HP), polythiophene, or polyfuran.

In addition, the oxidizing agent constituting the oxidizing agent layer of the nano-network structure is iron(III) p -toluenesulfonate (FTS), iron (III) trifluoromethanesulfonate, iron(III) chloride, p - toluenesulphonic acid, iodine, bromine, molybdophosphoric acid, ammonium persulfate, DL-tartaric acid (), polyacrylic acid, copper chloride, copper bromide, ferric chloride, naphthalenesulfonic acid, iron(III)-perchlorate, Cu(ClO ₄ ) ₂ 6H ₂ O, It may be one or a mixture of two or more selected from the group consisting of cerium(IV) ammonium nitrate and cerium(IV) sulfate, but is not necessarily limited thereto.

And, in another aspect of the present invention, the present invention proposes a conductive polymer film having a nano-network structure manufactured by the above manufacturing method.

Furthermore, in another aspect of the present invention, a bending sensor is proposed that includes a conductive polymer film of the nano-network structure in a sensing unit that detects bending stress.

A bending sensor including a conductive polymer film having a nano-network structure manufactured according to the present invention as a sensing unit exhibits significantly improved sensitivity to bending compared to a sensor using a conventional patternless conductive polymer film, since bending stress is concentrated at the connection portion of the circular pore pattern of the conductive polymer film, causing cracks to occur even with small bending.

Figure 1 is a schematic diagram sequentially showing the process for manufacturing a patterned PEDOT film through colloidal lithography and vapor phase polymerization (VPP) in the present invention.
Figure 2 is a scanning electron microscope (SEM) image of colloidal crystals manufactured at each step in the manufacture of a colloidal crystal template in the present invention (a: multilayer polystyrene (PS) colloidal crystal, b: surface-etched crystal, c and d: transferred non-coated hemispherical colloidal crystal monolayers).
Fig. 3(a) is a SEM image of an FTS oxidizer layer coated on a colloidal crystal template, Fig. 3(b) is a SEM image of a patterned FTS oxidizer layer after colloid removal, Figs. 3(c) and 3(d) are SEM images of a PEDOT film taken at different magnifications, Figs. 3(e) and 3(f) are elemental analysis results of the patterned FTS oxidizer layer, and Figs. 3(g) and 3(h) are SEM images of an FTS pattern layer and a PEDOT pattern layer, respectively, obtained using a colloidal crystal mask manufactured using PS particles having a diameter of 1 μm.
FIG. 4(a) and FIG. 4(b) are SEM images of a close-packed colloidal crystal monolayer template and a patterned PEDOT film manufactured using the same, respectively; FIG. 4(c) and FIG. 4(d) are SEM images of a non-close-packed spherical colloidal crystal monolayer and a patterned PEDOT film manufactured using the same; FIG. 4(e) and FIG. 4(f) are SEM images of a PEDOT film formed on a colloidal hemisphere array and a collapsed PEDOT film after dissolving colloidal particles, respectively; and FIG. 4(g) is a schematic diagram showing the colloidal particle removal process after FTS coating (top) and after PEDOT film formation (bottom).
FIGS. 5(a) to 5(f) are SEM images (a to c) and AFM images (d to f) of patterned PEDOT films prepared according to different vapor phase polymerization (VPP) process times (30 min (a and d), 60 min (b and e), and 90 min (c and f)), FIG. 5(g) shows the results of measuring optical transmittance at 550 nm for patterned and unpatterned PEDOT films prepared according to different VPP process times, and FIG. 5(h) shows the results of measuring IV and conductivity (inset) of patterned PEDOT films prepared according to different VPP process times.
Figures 6(a) and 6(b) show the results of bending cycle tests performed at various bending radii for an unpatterned PEDOT film and a patterned PEDOT film, respectively, Figure 6(c) shows the results of measuring the relative resistance change ( ΔR/R ₀ ) according to the bending radius for a patterned PEDOT film and an unpatterned PEDOT film, and Figure 6(d) shows the simplified simulation results showing the stress distribution of the porous structure (left) and the planar structure (right) corresponding to the patterned PEDOT film and the unpatterned PEDOT film, respectively.

In describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description will be omitted.

Embodiments according to the concept of the present invention may be subject to various modifications and take various forms. Therefore, specific embodiments are illustrated in the drawings and described in detail in this specification or application. However, this is not intended to limit embodiments according to the concept of the present invention to specific disclosed forms, and it should be understood that all modifications, equivalents, and alternatives included within the spirit and technical scope of the present invention are included.

The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly indicates otherwise. In this specification, it should be understood that the terms "comprises" or "has" indicate the presence of a described feature, number, step, operation, component, part, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

Hereinafter, the present invention will be described in more detail by way of examples.

The embodiments described herein may be modified in various ways, and the scope of this specification is not to be construed as limited to the embodiments described below. The embodiments described herein are provided to more fully explain this specification to those of ordinary skill in the art.

<Example>

FIG. 1 schematically illustrates the fabrication process of a patterned PEDOT film as a conductive polymer film with a nano-network structure according to the present invention. First, a non-packed hemispherical colloidal crystal monolayer was fabricated from a multilayer colloidal crystal through thermal transfer (FIGS. 1(i)-(v)). Then, iron(III) p - toluenesulfonate (FTS) oxidizer was deposited through the prepared colloidal crystal template (FIGS. 1(vi) and (vii)). Finally, a porous PEDOT pattern with a honeycomb structure was fabricated through vapor phase polymerization (VPP) using the pre-patterned FTS oxidizer layer (FIGS. 1(viii)-(x)).

A more detailed manufacturing process of the PEDOT film through a combination of colloidal lithography and vapor phase polymerization (VPP) as illustrated in Fig. 1 is as follows.

First, polystyrene (PS) particles with diameters of 460 nm and 1 μm were synthesized using emulsifier-free emulsion polymerization and dispersion polymerization, respectively. Multilayer colloidal crystals were prepared using a vertical deposition method. First, the prepared PS colloidal particles were dispersed in deionized water (0.1 wt%, 40 mL) with 0.001 wt% poly(vinylpyrrolidone) (Mw = 55000, Sigma Aldrich). Then, slide glasses were coated by immersing them in the PS colloidal suspension and stored overnight at 70°C.

To transfer the surface layer of the colloidal crystal, the crystal sample was exposed to O ₂ plasma (90 W, 2 min) in a Tergeo plasma cleaner (PIE Scientific). Then, a flat polydimethylsiloxane (PDMS) stamp was brought into contact with the surface-etched multilayer colloidal crystal and a pressure of approximately 100 kPa was applied. The PDMS stamp was removed from the sample, removing the surface layer from the multilayer colloidal crystal. The colloidal particles embedded in the stamp were then placed on a target substrate heated to approximately 115°C, and the PDMS stamp was removed from the substrate to form a non-close-packed hemispherical colloidal crystal monolayer.

Next, 5 wt% iron(III) p -toluenesulfonate (FTS, Sigma Aldrich) dissolved in 1-butanol was spin-coated at 2000 rpm for 30 s on the substrate coated with a hemispherical colloidal crystal monolayer. The PS colloidal template was dissolved by sonication in toluene for 10 min to remove the FTS layer covering the colloidal particles, thereby obtaining a prepatterned FTS substrate. The prepatterned FTS substrate was then transferred to a vapor-phase polymerization reactor (150 mL) equipped with a petri dish containing 3,4-ethylenedioxythiophene (EDOT, 99%, Acros Organic) at the bottom. After vapor-phase polymerization at 60°C for 30–90 min, the substrate was removed from the reactor and immersed in distilled water to remove the remaining FTS oxidizer, thereby obtaining a PEDOT film with a nano-network structure patterned with numerous circular pores.

Figure 2 shows SEM images of colloidal crystal templates at each step of the manufacturing process. First, multilayer colloidal crystals composed of polystyrene (PS) particles with a diameter of 460 nm are manufactured using a vertical deposition method (Figure 2(a)). Then, the surface is etched with _O2 plasma for 2 minutes until the particle diameter is reduced to approximately 350 nm (Figure 2(b)). Then, the surface-etched colloidal crystals are pressed and detached with a PDMS stamp at a pressure of 100 kPa to remove a single layer of close-packed colloidal crystals, which are then transferred to a target substrate. When the substrate surface is heated to 115°C (the glass transition temperature (Tg) of PS), the PS particles partially melt and adhere to the substrate, allowing the PDMS stamp to be removed. This forms a single layer of PS hemispheres with periodic and uniform arrangements (Figures 2(c) and (d)).

The oxidizer patterning process was performed using a closed-packed hemispherical colloidal crystal monolayer as a template. Figure 3(a) shows the surface coated with FTS oxidizer formed on a colloidal hemispherical array. The colloidal particle array visible through the FTS layer demonstrates that the shape and arrangement of the colloids are maintained throughout the coating process. When the FTS-coated colloidal array is immersed in toluene, the PS particles dissolve, leaving a regular honeycomb-structured FTS pattern, as shown in Figure 3(b). Using this prepatterned FTS layer as a template, PEDOT can be selectively synthesized on the FTS-covered surface via vapor phase polymerization (VPP). The PEDOT film is expected to grow beneath the FTS oxidizer layer via a bottom-up mechanism. After the VPP process, the remaining FTS oxidizer and unreacted monomers are removed by washing with distilled water. Figure 3(c) shows the porous honeycomb structure of the fabricated PEDOT film, which is similar to the morphology and periodicity of the previous FTS layer. The width of the patterned features was approximately 60-100 nm (Figure 3(d)), while the average pore size was approximately 350 nm. Energy-dispersive X-ray spectroscopy (EDS) was performed on the pre-patterned FTS sample (Figure 3(e)) and the PEDOT patterned sample (Figure 3(f)). Peaks corresponding to carbon (0.277 keV), oxygen (0.525 keV), and sulfur (2.307 keV) were clearly observed in both samples, whereas no peaks corresponding to iron (0.776 keV (Lα), 6.398 keV (Kα)) were observed in Figure 3(f), indicating that the PEDOT film was formed without FTS residue.

The pore size in the patterned polymer structure can be controlled by varying the size of the colloidal particles used to fabricate the initial template. Figures 3(g) and 3(h) show FTS and PEDOT patterns obtained using a colloidal crystal mask fabricated using PS particles with a diameter of 1 μm. The corresponding PEDOT honeycomb structure has pores of 790 nm, indicating the potential for flexible application of lithographic methods to fabricate tailored PEDOT films.

The structural characteristics of the colloidal crystal template are important in the subsequent patterning process for fabricating porous PEDOT films. The packing density determines the substrate area for the oxidizing agent coating, upon which the PEDOT film is synthesized. In the case of close-packed colloidal crystals, most of the FTS layer is coated with colloidal particles rather than the substrate, so this portion is expected to be removed during particle removal.

Figures 4(a) and 4(b) show a densely packed colloidal crystal monolayer and a patterned PEDOT structure formed using it as a template, respectively. Due to the lack of FTS oxidizing agent coating on the substrate, a thin, hollow shell structure is formed rather than a porous honeycomb-structured film. This structure reduces the mechanical stability and electrical conductivity of the PEDOT film.

Another possible template alternative is a non-close-packed spherical colloidal crystal, as illustrated in Figure 4(c). Here, the close-packed array defines the substrate region to be coated with the oxidizing agent. However, the small contact area between the substrate and the spherical particles does not provide sufficient coverage to form proper pores (see the inset of Figure 4(d)). The structure of the PEDOT film depicted in Figure 4(d) exhibits a nanobowl array instead of regular hexagonal pores.

The order of the particle removal steps is crucial for obtaining a porous film with a desirable honeycomb structure. Figure 4(e) shows a PEDOT film synthesized on a FTS-coated colloidal hemispherical array before the particle removal step. The film exhibits a rough surface morphology due to the presence of colloidal particles beneath the film. After the colloidal particles are removed, the textured surface collapses, forming a nano-donut shape, as shown in Figure 4(f). Figure 4(g) shows that the surface structure is formed differently depending on whether particle removal is performed before or after the PEDOT film formation. FTS, a brittle inorganic material, can be easily removed during the dissolution process of the colloidal particles, providing a well-defined, pre-patterned oxidizer. On the other hand, the PEDOT film is a soft, flexible polymer layer. Therefore, the portion of the film covering the particles is not removed during the dissolution process but rather collapses, forming a donut-shaped, void-free morphology.

Although the pre-patterned FTS oxidizer layer is a key factor in determining the structure of the PEDOT film, the film morphology also varies depending on the VPP process time. Figures 5(a) to 5(f) show the changes in film morphology as the VPP time varies from 30 to 90 minutes. While the film thickness (700-820 nm) is largely independent of the process time, the formation of pores is strongly dependent on the VPP process time. With a VPP process time of 30 minutes, most pores are formed where the colloidal particles are located (Figures 5(a) and (d)). As the VPP process time increases, the pores are gradually filled (Figures 5(b) and (e)). After 90 minutes of VPP, approximately half of the pores remain (Figures 5(c) and (f)). This can be interpreted as a result of the film thickness reaching a saturation point during the VPP process. As the polymer thickness increases, diffusion becomes limited, hindering the synthesis of polymer films that depend on the diffusion of the oxidizer into the growing polymer layer. While vertical diffusion of the oxidizer is restricted, horizontal diffusion can still occur. Therefore, as the oxidizer layer leaches into the pores, polymerization occurs on the exposed substrate, filling the pores.

Figure 5(g) shows the optical transmittance of patterned and unpatterned PEDOT films grown on glass slides with varying VPP process times. The transmittance of both films decreases with increasing VPP process time. However, the patterned PEDOT film exhibits superior transparency compared to the unpatterned film, which is due to the presence of pores, which provide more light transmission paths. Figure 5(h), which shows the measurement results of the electrical properties of the porous PEDOT film, shows that the patterned PEDOT film exhibited overall ohmic behavior. As the VPP process time increases, the film contains fewer pores, which expands the number of electrical paths and leads to higher electrical conductivity (inset of Figure 5(h)).

The porous PEDOT film manufactured in the above examples has excellent transparency and high electrical conductivity, so it can be synthesized on a flexible plastic substrate and applied as a sensing part of a strain/bending sensor. Figures 6(a) and 6(b) show the patterned PEDOT films at different bending radii (outer bending, bending radius ( R ) = 5.3, 6.6, and 9.5 mm). Compared with the unpatterned film, the patterned PEDOT film exhibits a larger relative resistance change ( ΔR/R ₀ ) with respect to bending stress. At R = 5.3 mm, ΔR/R ₀ increased by 424% from 0.42 (unpatterned film) to 1.78 (patterned film). The increases in ΔR/R ₀ due to the patterning effect were 275% and 525% at R = 6.6 mm and 9.5 mm, respectively. Figure 6(c) is a graph showing the change in relative resistance change ( ΔR/R ₀ ) of a patterned sample and an unpatterned sample as a function of bending radius, where the graph of the patterned sample has a steeper slope, indicating that it has higher sensitivity to bending than the unpatterned sample.

Resistance changes in flexible strain/bending sensors are typically caused by cracking that occurs when stress is applied to the conductive material. For unpatterned sensors, stress is assumed to be evenly distributed across the entire surface, leading to uniform cracking. However, patterned structures with pores are expected to concentrate stress at the narrow junctions between the pores, which would facilitate cracking in these areas, resulting in superior sensing performance. To elucidate the variation in stress distribution depending on the film geometry, a simulation was performed to investigate the stress distribution under bending deformation, as shown in Figure 6(d). The simulations were performed using simplified geometries of perforated and flat films to represent patterned and unpatterned PEDOT films, respectively. As expected, stress is concentrated at the narrow junctions between the pores in the patterned structure, whereas it is evenly distributed in the unpatterned flat structure.

The present approach of improving the sensitivity and transparency of the sensor by modifying the geometric structure of the PEDOT film is distinct from other recent studies on PEDOT-based sensors that rely on forming composites with other materials such as CNTs, nanowires, fabrics, and elastomers to enhance flexibility or sensitivity.

The present invention is not limited to the above embodiments, but can be manufactured in various different forms, and a person having ordinary skill in the art to which the present invention pertains will understand that the present invention can be implemented in other specific forms without changing the technical idea or essential characteristics of the present invention. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

Claims (7)

(a) a step of forming an oxidizing layer having a nano-network structure patterned with a plurality of circular pores on a substrate;
(b) forming a conductive polymer layer between the oxidizing layer of the nano-network structure and the substrate; and
(c) a step of removing the oxidizing layer of the nano-network structure;
Method for producing a conductive polymer film with a nano-network structure.
In the first paragraph,
In the above step (a)
A method characterized in that an oxidizing layer having a nano-network structure is formed through a colloidal lithography process including steps (a-1) to (a-3).
Method for manufacturing a conductive polymer film with a nano-network structure:
(a-1) A step of manufacturing a template including a substrate and a non-close-packed hemispherical colloidal crystal monolayer formed on the substrate;
(a-2) a step of depositing an oxidizer on the above-mentioned secret hemispherical colloidal crystal monolayer; and
(a-3) A step of removing colloidal crystals to form an oxidizing layer having a pattern consisting of a large number of circular pores.
In the first paragraph,
In the above step (b)
A conductive layer having a nano-network structure is formed between a substrate and an oxidizer layer by reacting a conductive polymer monomer and an oxidizer contained in the oxidizer layer through vapor phase polymerization (VPP).
Method for producing a conductive polymer film with a nano-network structure.
In the third paragraph,
The above conductive polymer monomer is
3,4-Ethylenedioxythiophene (EDOT), pyrrole, 3-hexylthiophene (3HT), 3-heptylpyrrole (3HP), thiophene or furan,
The above conductive polymer is,
characterized by being poly(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPy), poly(3-hexylthiophene) (P3HT), poly(3-heptylpyrrole) (P3HP), polythiophene or polyfuran.
Method for producing a conductive polymer film with a nano-network structure.
In the first paragraph,
The above oxidizing agent is
Iron(III) p -toluenesulfonate (FTS), iron(III) trifluoromethanesulfonate , iron(III) chloride, p- toluenesulphonic acid, iodine, bromine, molybdophosphoric acid, ammonium persulfate, DL -tartrate, polyacrylic acid, copper chloride, copper bromide, ferric chloride, naphthalenesulfonic acid, iron(III)-perchlorate, Cu( _ClO4 ) ₂ · _6H2O , cerium(IV) ammonium nitrate characterized in that it is a mixture of one or more selected from the group consisting of ammonium nitrate and cerium(IV) sulfate.
Method for producing a conductive polymer film with a nano-network structure.
A conductive polymer film having a nano-network structure manufactured by the manufacturing method described in any one of claims 1 to 5.
A bending sensor having a sensing unit including a conductive polymer film having a nano-network structure as described in claim 6.