A differentiated flexible light heater and method of making the same

Abstract

This invention discloses a differentiated flexible photoheater and its fabrication method, belonging to the technical field of flexible photothermal devices and functional composite materials. The differentiated flexible photoheater includes a flexible polymer substrate, a heat-absorbing layer, and an encapsulation layer. This invention achieves high adhesion between carbon nanotube films and the flexible polymer substrate through a laser-assisted composite process, enabling complex patterning and regionally differentiated thermal control. This structure combines flexibility, lightweight design, and high-efficiency photothermal conversion capabilities, and can be widely applied in flexible thermal management, smart wearables, biomedicine, and localized thermal stimulation systems.

Description

Technical Field

[0001] This invention relates to the field of flexible photothermal devices and functional composite materials, and in particular to a differentiated flexible photothermal heater and its preparation method. Background Technology

[0002] In recent years, with the rapid development of flexible electronics, smart wearable devices, electronic skin, flexible displays, intelligent thermal management systems, and biomedicine, flexible heaters capable of adapting to complex deformation environments have gradually become a research hotspot. Flexible heaters not only need to possess excellent thermal response performance but also need to maintain stable operation under complex mechanical deformation conditions such as bending, curling, stretching, and even torsion. Therefore, developing novel flexible heaters that combine flexibility, stability, and controllable heat distribution capabilities is of great significance for the development of next-generation smart electronic devices.

[0003] Carbon nanotube (CNT) films exhibit significant application potential in flexible photothermal devices due to their excellent electrical conductivity, broad-spectrum photothermal conversion capability, flexibility, thermal stability, and chemical stability. In particular, the carbon nanotube network structure maintains stable conductive pathways under large deformation conditions, while possessing a high specific surface area and excellent light absorption, thus enabling rapid and efficient thermal response. Furthermore, carbon nanotube films offer advantages such as light weight, thinness, and ease of integration with flexible substrates, making them promising for applications in flexible heaters, transparent heaters, and wearable thermal management systems.

[0004] However, existing flexible carbon nanotube heaters still have several key problems. First, most existing CNT heaters adopt a uniform structure, resulting in a relatively uniform overall temperature distribution. This makes it difficult to achieve differentiated thermal control within a spatial region, failing to meet application requirements such as localized heating, independent heating of multiple regions, or temperature gradient control. Second, traditional CNT films are typically attached to polymer substrates through simple transfer, coating, or lamination methods. Their interfacial bonding mainly relies on physical adsorption, which can easily lead to localized delamination, structural fracture, and performance degradation under repeated bending, stretching, or long-term use, thus affecting device stability and lifespan.

[0005] Furthermore, existing CNT patterning processes mostly rely on photolithography, mask printing, inkjet printing, or complex micro / nano fabrication processes, which are not only cumbersome and costly, but also difficult to achieve large-area rapid fabrication of complex patterned structures. In addition, multi-step wet processing can easily introduce impurities or damage the carbon nanotube conductive network, which is detrimental to improving device performance stability.

[0006] Therefore, there is an urgent need for a novel flexible photothermal heater structure and its fabrication method that can achieve high adhesion composite of carbon nanotube films and flexible substrates, complex patterned processing, and regionally differentiated heating, in order to meet the application needs of high-performance flexible heaters in fields such as smart wearables, flexible thermal management, biomedicine, and local thermal stimulation systems. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a differentiated flexible photoheater and its preparation method. Through a laser-assisted composite process, it achieves high bonding strength integration between carbon nanotube films and flexible polymer substrates such as PET, and constructs regional heating structures with different carbon nanotube content distributions.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: In a first aspect, the present invention provides a differentiated flexible photoheater, comprising a flexible polymer substrate and a heat-absorbing layer; The heat-absorbing layer is made of a pre-fabricated carbon nanotube film, which is then composited with the surface of the flexible polymer substrate after being irradiated by a laser. The laser irradiation softens or melts the surface of the flexible polymer substrate locally, causing the carbon nanotubes in the carbon nanotube film to embed into the surface of the flexible polymer substrate and form a mechanically interlocked structure. Furthermore, the heat-absorbing layer has regions with different carbon nanotube surface density distributions. Different regions have different resistance values ​​and photothermal response characteristics due to the different carbon nanotube surface densities, thereby achieving regional differentiated heating.

[0009] Furthermore, the flexible polymer substrate is selected from one or more of PET, PI, PDMS, and TPU.

[0010] Furthermore, the carbon nanotube film is an ordered carbon nanotube film, a random network carbon nanotube film, or a multilayer stacked carbon nanotube film.

[0011] Furthermore, regions with different carbon nanotube surface density distributions are formed by adjusting at least one of the following methods: carbon nanotube coverage density, number of carbon nanotube layers, and laser scanning parameters in different regions.

[0012] Furthermore, regions with different carbon nanotube surface density distributions can spatially form mesh-like structures, serpentine structures, gradient structures, or array structures.

[0013] Furthermore, it also includes an encapsulation layer that covers the heat-absorbing layer.

[0014] Secondly, the present invention also provides a method for preparing a differentiated flexible photoheater, applied to the aforementioned differentiated flexible photoheater, comprising the following steps: Step 1: Transfer the heat-absorbing layer made of a pre-fabricated carbon nanotube film to the surface of a flexible polymer substrate; Step 2: The carbon nanotube film is scanned and irradiated with a laser beam. The laser irradiation softens or melts the surface of the flexible polymer substrate locally, so that the carbon nanotubes in the carbon nanotube film are embedded in the surface layer of the flexible polymer substrate and form a mechanical interlocking structure. At the same time, by adjusting the laser scanning parameters or the initial distribution of carbon nanotubes in different regions, the carbon nanotube film forms a regionalized structure with different carbon nanotube surface densities. Step 3: Encapsulate the heat-absorbing layer after laser recombination with an encapsulation layer to obtain the differentiated flexible photoheater.

[0015] Furthermore, in step 2, the wavelength of the laser beam is 1064 nm.

[0016] Furthermore, in step 2, by adjusting the laser power, scanning speed, or number of scans in different regions, the surface density of carbon nanotubes in the corresponding regions is made to differ, thereby forming regional heating structures with different resistance values ​​and photothermal response characteristics.

[0017] Furthermore, the carbon nanotube film is a continuously covered carbon nanotube film before laser irradiation, and regions with different carbon nanotube surface densities are formed during laser irradiation through selective ablation or selective embedding-retention.

[0018] In summary, compared with the prior art, the beneficial effects of the above technical solution are: (1) The differentiated flexible photoheater provided by the present invention can efficiently absorb incident light energy in its heat-absorbing layer under light irradiation conditions and quickly convert it into heat energy through photothermal conversion mechanism to achieve precise heating of local areas; the heat-absorbing layer adopts a pre-made carbon nanotube film, which has excellent light absorption capacity and extremely low specific heat capacity, and can achieve rapid heating under low power light irradiation conditions. The photothermal conversion efficiency is significantly higher than that of traditional metal or carbon black materials. (2) Different carbon nanotube surface density regions constructed by laser-assisted composite process can produce different temperature rise responses under the same illumination conditions. The high-density region has higher photothermal conversion efficiency, faster heating and greater temperature rise amplitude; the low-density region is relatively mild, thereby realizing the temperature gradient regulation of the heating region and meeting the complex thermal management requirements; that is, by regionally regulating the carbon nanotube content, the differentiated heating and temperature distribution control of different regions can be achieved. (3) Laser-assisted composite process is used to achieve high adhesion between carbon nanotubes and polymer substrates, which improves the stability of the device under bending and stretching conditions; high-resolution patterning can be achieved without complex photolithography masks, and the process is simple and low-cost. (4) By adjusting the laser parameters (power, speed, number of scans, etc.), the surface density of carbon nanotubes in different regions can be precisely controlled to form structures such as grids, snakes, gradients or arrays, thereby realizing the customized design of complex temperature fields under illumination. It is suitable for scenarios with fine requirements for heat distribution, such as smart wearables and local thermal stimulation systems. Moreover, this differentiated flexible photoheater has the advantages of flexibility, lightweight and high-efficiency photothermal conversion capabilities, and can be applied to fields such as smart thermal management, flexible wearables, biomedicine and local thermal stimulation systems. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the flexible photothermal heater according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the laser-patterned carbon nanotube heat-absorbing layer in an embodiment of the present invention; Figure 3 This is a schematic diagram showing the distribution of different carbon nanotube density regions in an embodiment of the present invention; Figure 4 Infrared thermal imaging images showing the temperature distribution in different regions according to an embodiment of the present invention.

[0020] Explanation of reference numerals in the attached figures: 1. Flexible polymer substrate; 2. Heat-absorbing layer; 3. Encapsulation layer. Detailed Implementation

[0021] The principles and features of the present invention are described below with reference to all the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0022] This invention discloses a differentiated flexible photoheater and its preparation method.

[0023] In a first aspect, embodiments of the present invention provide a differentiated flexible photoheater.

[0024] Reference Figures 1-4 A differentiated flexible photoheater includes a flexible polymer substrate 1, a heat-absorbing layer 2, and an encapsulation layer 3. The heat-absorbing layer 2 can also be referred to as a carbon nanotube heat-absorbing layer. The encapsulation layer 3 covers the heat-absorbing layer 2.

[0025] The heat-absorbing layer 2 forms a stable composite structure with the flexible polymer substrate 1 through laser irradiation, and forms a regional heating structure with different carbon nanotube content distributions.

[0026] Specifically, the heat-absorbing layer 2 is made of a pre-fabricated carbon nanotube film, which is then composited with the surface of the flexible polymer substrate 1 after laser irradiation. The laser irradiation softens or melts the surface of the flexible polymer substrate 1 locally, causing the carbon nanotubes in the carbon nanotube film to embed into the surface layer of the flexible polymer substrate 1 and form a mechanically interlocked structure. Furthermore, the heat-absorbing layer 2 has regions with different carbon nanotube surface density distributions. Different regions have different resistance values ​​and photothermal response characteristics due to the different carbon nanotube surface densities, thereby achieving regional differentiated heating.

[0027] The flexible polymer substrate 1 and the heat-absorbing layer 2 are tightly bonded by laser-assisted composite method, which can be local melting composite, interfacial thermal adhesion, and microstructure interlocking.

[0028] It is particularly important to emphasize that: In this embodiment, forming a mechanically interlocking structure means that under laser irradiation, the surface of the flexible polymer substrate softens or melts locally, and the carbon nanotube (CNT) film originally located on the substrate surface is partially embedded into the softened polymer surface. Subsequently, the polymer cools and solidifies, shrinking in volume and firmly encapsulating and anchoring the carbon nanotubes inside the matrix. This bonding does not rely on chemical bonds or adhesives, but rather utilizes the physical morphological match between the carbon nanotubes and the polymer—the irregular, uneven surface of the carbon nanotube network forms an interlocking and connecting relationship with the solidified polymer, similar to "tree roots and soil" or "anchor and concrete."

[0029] In this embodiment, the flexible polymer substrate 1 adopts a PET (polyethylene terephthalate) film structure, which has good flexibility, transparency, and mechanical stability. In other embodiments, the flexible polymer substrate 1 can also be made of PI (polyimide), PDMS (polydimethylsiloxane), TPU (thermoplastic polyurethane), or other flexible polymer materials.

[0030] The heat-absorbing layer 2 adopts a carbon nanotube thin film structure, which can be an ordered carbon nanotube thin film, a random network carbon nanotube thin film, or a multilayer stacked carbon nanotube thin film. The carbon nanotube conductive network has excellent conductivity, flexibility, and photothermal conversion capability, enabling rapid thermal response.

[0031] By adjusting the carbon nanotube coverage density, number of carbon nanotube layers, or laser scanning parameters in different regions, different resistivity values ​​and photothermal response characteristics can be achieved in different regions. In this embodiment, the flexible photothermal heater includes high carbon nanotube density regions, medium carbon nanotube density regions, and low carbon nanotube density regions, such as... Figure 3 As shown.

[0032] The high-carbon nanotube density region exhibits lower electrical resistance and higher photothermal conversion efficiency; the medium-carbon nanotube density region exhibits moderate thermal response; and the low-carbon nanotube density region exhibits higher electrical resistance and lower thermal response. Through this regionalized structural design, differentiated heating and temperature distribution control can be achieved in different regions.

[0033] like Figure 4 As shown, infrared thermal imaging tests were performed on the flexible photothermal heater prepared in this embodiment. Under the same illumination conditions, different regions exhibited significantly different temperature rise characteristics. Among them, the high carbon nanotube density region ( Figure 4 The highest temperature is in Area 1 region, and the medium carbon nanotube density region is... Figure 4 The Area 2 region (within the middle) has the second highest temperature, followed by the low carbon nanotube density region ( Figure 4 The Area 3 region has the lowest temperature, thus forming a distinct regional temperature distribution and exhibiting significant differentiated heating capabilities.

[0034] This invention achieves high adhesion between carbon nanotube films and flexible polymer substrates through a laser-assisted composite process, enabling complex patterning and regionally differentiated thermal control. This structure combines flexibility, lightweight design, and efficient photothermal conversion capabilities, making it widely applicable in flexible thermal management, smart wearables, biomedicine, and localized thermal stimulation systems.

[0035] Secondly, embodiments of the present invention also disclose a method for preparing a differentiated flexible photoheater, used to prepare the differentiated flexible photoheater described in the first aspect, comprising the following steps: Step 1: Transfer the heat-absorbing layer 2, made of a pre-fabricated carbon nanotube film, to the surface of the flexible polymer substrate 1; Step 2: The carbon nanotube film is scanned and irradiated with a laser beam. The laser irradiation softens or melts the surface of the flexible polymer substrate locally, so that the carbon nanotubes in the carbon nanotube film are partially embedded in the surface layer of the flexible polymer substrate 1 and form a mechanical interlocking structure. At the same time, by adjusting the laser scanning parameters or the initial distribution of carbon nanotubes in different regions, the carbon nanotube film forms a regionalized structure with different carbon nanotube surface densities. Step 3: Encapsulate the heat-absorbing layer 2 after laser composite, i.e., encapsulation layer 3, to obtain the differentiated flexible photoheater.

[0036] Before laser irradiation, the carbon nanotube film is a continuous carbon nanotube film. During laser irradiation, regions with different carbon nanotube surface densities are formed through selective ablation or selective embedding-retention.

[0037] In step 2, the wavelength of the laser beam is 1064 nm, and the scanning speed is 50–2000 mm / s.

[0038] In step 2, by adjusting the laser power, scanning speed or number of scans in different regions, the surface density of carbon nanotubes in the corresponding regions is made to differ, thereby forming regional heating structures with different photothermal response characteristics.

[0039] In this embodiment of the invention, a high-quality carbon nanotube film is prefabricated, transferred to the surface of a flexible substrate, and then embedded into the substrate by laser irradiation to form a mechanical interlock.

[0040] It needs to be further emphasized that: The traditional method of laser-induced graphene, also known as "laser in-situ conversion," involves directly irradiating the surface of a flexible polymer substrate (usually polyimide, PI) with a laser beam. The high energy of the laser causes the polymer material in the irradiated area to undergo in-situ carbonization and graphitization, forming a porous graphene structure. This material is called laser-induced graphene. In this method, the conductive layer is "grown" from the polymer substrate itself, without the need for any external conductive materials. The laser simultaneously performs both material conversion and patterning.

[0041] In this invention, a pre-fabricated carbon nanotube film and laser-assisted composite technology are employed. First, a high-quality carbon nanotube film is independently prepared in advance. This film can be oriented, randomly networked, or multilayered, exhibiting excellent photothermal conversion capabilities. Then, the carbon nanotube film is completely transferred to the surface of a flexible polymer substrate. Next, a laser beam is used to scan and irradiate the carbon nanotube film according to a pre-defined pattern. The localized thermal effect of the laser causes the surface of the flexible polymer substrate to soften or even melt instantaneously. The molten polymer flows and fills the pores and gaps of the carbon nanotube network; simultaneously, the carbon nanotube film is locally pressed into the softened polymer surface. When the laser is removed, the polymer rapidly cools and solidifies, shrinking in volume and firmly anchoring the carbon nanotubes within the substrate, forming a mechanically interlocked structure.

[0042] In areas not irradiated by the laser, the carbon nanotube film maintains only simple physical contact with the substrate. By adjusting the laser parameters (power, speed, number of laser strikes) or the initial distribution of carbon nanotubes, such as coverage density and number of layers, regions with different carbon nanotube areal densities can be formed on the same device. Regions with high areal density have low electrical resistance and high photothermal conversion efficiency, while regions with low areal density have high electrical resistance and low photothermal conversion efficiency. When electricity or light is applied, these regions will produce differentiated thermal responses, thereby achieving precise control of the spatial temperature distribution. The core of this solution lies in firmly combining "high-quality conductive materials" and "flexible substrates" through laser melting embedding, which not only ensures that the performance of the heat-absorbing layer can be pre-optimized, but also significantly improves the bending stability of the flexible device through mechanical interlocking.

[0043] Compared to the traditional "laser in-situ conversion" method, this method has the following significant advantages: 1. Controllability of Material Source and Absorber Layer Quality. Traditional absorber layers are derived from the laser carbonization of the polymer substrate itself. The quality, porosity, and conductivity of the graphene in these layers are highly dependent on the laser parameters and the carbonization characteristics of the substrate material, resulting in a limited control window. Furthermore, the absorber layer typically exhibits a porous and disordered structure. In contrast, the embodiments of this invention utilize pre-prepared carbon nanotube films, allowing for precise design and optimization of their orientation, thickness, and network density before transfer. For example, highly oriented CNT films can be used to achieve anisotropic conductivity and light absorption properties, or multiple layers can be stacked to achieve performance gradients. This means that the absorber layer in this solution can achieve higher conductivity and more stable photothermal conversion performance, without being inherently limited by the substrate material and laser parameters.

[0044] 2. Interface Bonding Strength and Flexibility Stability. While the heat-absorbing layer and polymer substrate are an integrated structure without independent interface issues, this also means the heat-absorbing layer is essentially a brittle, porous carbon material after carbonization. Under repeated bending or large deformation conditions, microcracks or even fractures may occur within the heat-absorbing layer, affecting device performance. In this embodiment of the invention, a pre-fabricated carbon nanotube film is embedded into the substrate surface using laser to partially melt the polymer substrate, forming a mechanically interlocked structure. Carbon nanotubes themselves possess extremely high flexibility and tensile strength, and the embedded structure requires overcoming significant mechanical resistance to interface delamination. Therefore, under repeated bending, rolling, and even twisting conditions, the heat-absorbing layer and substrate will not delaminate, and the carbon nanotube network is not easily broken, resulting in significantly improved device lifespan and reliability.

[0045] 3. Universality of Substrate Materials. Traditional methods impose strict requirements on substrate materials, typically limiting selection to polymers rich in aromatic rings and easily laser-graphitized, most notably polyimide (PI). Other common flexible materials such as PET, PDMS, and TPU often fail to form high-quality graphene under laser irradiation, or may not undergo carbonization at all. Therefore, complex processes such as premixing carbon sources in the substrate, adding light-absorbing fillers, or employing multi-step transfer are usually required, increasing process complexity and material limitations. This method uses a pre-fabricated CNT film transfer followed by laser embedding. The laser only needs to soften or melt the substrate surface, without requiring carbonization or graphitization. Therefore, this method is applicable to almost any thermoplastic or softenable flexible polymer substrate, including low-cost PET, high-transparency PDMS, and high-flexibility TPU. This provides significant freedom in material selection for different applications, such as low-cost disposable devices, biocompatible devices, and high-strength devices.

[0046] 4. In this embodiment of the invention, the complete CNT film is first transferred, and then selectively irradiated with a laser. The CNTs in the laser-affected area are embedded in the substrate to form a heat-absorbing layer, while the CNT film in the non-irradiated area can be selectively removed (e.g., through simple cleaning or peeling) or retained as an auxiliary layer. This "complete coverage first, then selective fixation" mode makes the edges of the heated pattern clearer, and a finer pattern resolution can be achieved by controlling the laser parameters.

[0047] 5. In this embodiment of the invention, the quality of the pre-fabricated CNT film can be strictly controlled in advance through a mature film preparation process. The laser step only needs to achieve the relatively simple thermal effect of "molten embedding," and has a higher tolerance for minor fluctuations in laser parameters. Therefore, this solution is more suitable for mass production and industrialization.

[0048] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A differentiated flexible photoheater, characterized in that, It includes a flexible polymer substrate (1) and a heat-absorbing layer (2); The heat-absorbing layer (2) is made of a pre-fabricated carbon nanotube film, which is then combined with the surface of the flexible polymer substrate (1) after being irradiated by a laser. The laser irradiation softens or melts the surface of the flexible polymer substrate (1) locally, causing the carbon nanotubes in the carbon nanotube film to embed into the surface of the flexible polymer substrate (1) and form a mechanically interlocked structure. Furthermore, the heat-absorbing layer (2) has regions with different carbon nanotube surface density distributions. Different regions have different resistance values ​​and photothermal response characteristics due to the different carbon nanotube surface densities, thereby achieving regional differentiated heating.

2. The differentiated flexible photoheater according to claim 1, characterized in that: The flexible polymer substrate (1) is selected from one or more of PET, PI, PDMS, and TPU.

3. The differentiated flexible photoheater according to claim 1, characterized in that: The carbon nanotube film is an ordered carbon nanotube film, a random network carbon nanotube film, or a multilayer stacked carbon nanotube film.

4. A differentiated flexible photoheater according to claim 1, characterized in that: Regions with different carbon nanotube surface density distributions are formed by adjusting at least one of the following methods: carbon nanotube coverage density, number of carbon nanotube layers, and laser scanning parameters in different regions.

5. A differentiated flexible photoheater according to claim 4, characterized in that: Regions with different carbon nanotube surface density distributions can form spatial grid-like structures, serpentine structures, gradient structures, or array structures.

6. A differentiated flexible photoheater according to claim 1, characterized in that: It also includes an encapsulation layer (3) that covers the heat-absorbing layer (2).

7. A method for preparing a differentiated flexible photoheater, characterized in that, An application to a differentiated flexible photoheater as described in any one of claims 1-6, comprising the following steps: Step 1: Transfer the heat-absorbing layer (2) made of pre-fabricated carbon nanotube film to the surface of the flexible polymer substrate (1); Step 2: The carbon nanotube film is scanned and irradiated with a laser beam. The laser irradiation softens or melts the surface of the flexible polymer substrate (1) locally, so that the carbon nanotubes in the carbon nanotube film are embedded in the surface of the flexible polymer substrate (1) and form a mechanical interlocking structure. At the same time, by adjusting the laser scanning parameters or the initial distribution of carbon nanotubes in different regions, the carbon nanotube film forms a regionalized structure with different carbon nanotube surface densities. Step 3: The heat-absorbing layer (2) after laser composite is encapsulated with an encapsulation layer (3) to obtain the differentiated flexible photoheater.

8. The method for preparing a differentiated flexible photoheater according to claim 7, characterized in that: In step 2, the wavelength of the laser beam is 1064 nm.

9. The method for preparing a differentiated flexible photoheater according to claim 7, characterized in that: In step 2, by adjusting the laser power, scanning speed or number of scans in different regions, the surface density of carbon nanotubes in the corresponding regions is made to differ, thereby forming regional heating structures with different resistance values ​​and photothermal response characteristics.

10. The method for preparing a differentiated flexible photoheater according to claim 7, characterized in that: The carbon nanotube film is a continuous carbon nanotube film before laser irradiation. During laser irradiation, regions with different carbon nanotube surface densities are formed through selective ablation or selective embedding-retention.

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