Droplet directed transport material and method of making and use thereof

Abstract

The application provides a droplet directional transport material and a preparation method and application thereof, and relates to the technical field of microfluidics.The droplet directional transport material provided by the application comprises an elastic substrate and a rigid film with a wrinkle structure covering the surface of the elastic substrate;the preparation raw material of the elastic substrate comprises a base material, a photo-thermal nano material and an organic solvent;and the preparation raw material of the rigid film comprises one of gold, silver, platinum and lead.By covering the rigid film with the wrinkle structure on the surface of the elastic substrate, the photo-thermal effect can be used to achieve the erasing and regeneration of the wrinkle structure, and the droplet directional transport material provided by the application has the wrinkle structure with a wettability gradient, so that the reversible and repeatable droplet directional transport can be realized.

Description

Technical Field

[0001] This invention belongs to the field of microfluidics technology, specifically relating to a droplet-directed transport material, its preparation method, and its application. Background Technology

[0002] Directed transport of liquids or droplets on solid surfaces is a key technology in many engineering applications, commonly used in microfluidics, molecular detection, water mist collection, wastewater purification, and oil-water separation. For example, in molecular detection, directed droplet transport integrates sampling, sample addition, reaction, and analysis processes onto a microfluidic chip, significantly improving analytical efficiency; however, this method is cumbersome and inefficient. Water mist collection is an important means of addressing water shortages in arid regions; utilizing surfaces with directed droplet transport to collect airborne water mist can significantly improve collection efficiency. Oil-water separation, a key technology in chemical engineering, environmental protection, and energy, often requires substantial energy and time. Therefore, developing separation membrane materials with directed transport capabilities for droplet-directed transport technology can effectively improve transport performance and efficiency.

[0003] To improve the efficiency of directional droplet transport, researchers have attempted to utilize external field energy to overcome the pinning effect of solid surfaces, breaking the symmetry of liquid flow, thereby increasing directional transport efficiency and extending transport distance, and achieving precise control over transport direction and rate. In recent years, liquid directional transport materials and surfaces capable of rapidly responding to external stimuli such as mechanical force, light, electricity, heat, and magnetism have become a research hotspot, yielding significant progress. Among these, photoresponsive droplet directional transport methods offer advantages such as strong spatial and temporal controllability, non-contact operation, remote manipulation, and independence from complex electric or magnetic field devices. Therefore, developing novel photoresponsive droplet directional transport technologies has significant engineering application value in fields such as microfluidic chips, fluid optics, liquid logic circuit development, and bioanalysis and detection.

[0004] Currently, photoresponsive droplet directional transport methods mainly fall into two strategies. One involves inducing chemical changes on the surface of the transport material through light illumination to create a local wettability gradient, thereby triggering directional droplet transport. The other involves photo-induced changes in the microstructure of shape memory materials, altering the roughness of local areas and similarly generating a wettability gradient to induce directional droplet movement. The former relies on specific photosensitive materials (such as carbon black), limiting the types of solid / liquid materials it can utilize; while the latter typically lacks spontaneous reversibility and repeatability, restricting its application prospects. Summary of the Invention

[0005] The purpose of this invention is to provide a droplet-directed transport material, its preparation method, and its application. The droplet-directed transport material provided by this invention can achieve reversible and repeatable droplet-directed transport and is applicable to various solid / liquid material systems.

[0006] To achieve the objectives of this invention, the following technical solutions are provided:

[0007] A droplet-directed transport material includes an elastic substrate and a rigid film with a wrinkled structure covering the surface of the elastic substrate; the raw materials for preparing the elastic substrate include a substrate material, photothermal nanomaterials and an organic solvent; the raw materials for preparing the rigid film include one of gold, silver, platinum and lead.

[0008] Preferably, the period of the fold structure in the rigid film is 1 to 10 μm, and the amplitude is 0.1 to 1 μm.

[0009] Preferably, the thickness of the elastic substrate is 0.8–2 mm; and the thickness of the rigid film is 10–50 nm.

[0010] Preferably, the substrate is polydimethylsiloxane; the photothermal nanomaterial is Fe3O4 or Ti2O3.

[0011] Preferably, the organic solvent is n-hexane or toluene.

[0012] Preferably, the mass ratio of the substrate, photothermal nanomaterial, and organic solvent is 5–20:0.06–0.21:5–20.

[0013] The present invention also provides a method for preparing the droplet-oriented transport material described in the above technical solution, comprising the following steps:

[0014] An elastic substrate is obtained by mixing and curing a substrate, photothermal nanomaterials, and an organic solvent.

[0015] A film is deposited on the surface of the elastic substrate to obtain an elastic substrate covered with a rigid film;

[0016] The elastic substrate covered with a rigid film is heated and cooled to form a rigid film with a wrinkled structure on the surface of the elastic substrate, thus obtaining the droplet directional transport material.

[0017] Preferably, the heating temperature is 100–140°C and the heating time is 20–40 min.

[0018] The present invention also provides the application of the droplet directional transport material described in the above technical solution or the droplet directional transport material prepared by the preparation method described in the above technical solution in droplet directional transport.

[0019] Preferably, the application includes: irradiating the droplet-directed transport material with a laser to eliminate the wrinkled structure in the laser-irradiated area to form a droplet-directed transport channel, thereby realizing the directional transport of droplets;

[0020] After the directional transport is completed, laser irradiation is stopped, and the area where the wrinkled structure disappeared is allowed to re-form a wrinkled structure after cooling, so that the next droplet directional transport can be carried out.

[0021] This invention provides a droplet-oriented transport material, comprising an elastic substrate and a rigid film with a wrinkled structure covering the surface of the elastic substrate. The elastic substrate is prepared from raw materials including a substrate material, photothermal nanomaterials, and an organic solvent. The rigid film is prepared from raw materials including one of gold, silver, platinum, and lead. This invention achieves the erasure and regeneration of the wrinkled structure by covering the surface of the elastic substrate with a rigid film with a wrinkled structure, utilizing the photothermal effect. Furthermore, the droplet-oriented transport material provided by this invention has a wrinkled structure with a wettability gradient, requiring no additional energy supply, thus reducing energy and equipment consumption when applied to droplet-oriented transport.

[0022] This invention also provides the application of droplet-directed transport materials in droplet-directed transport. This invention uses laser irradiation of the droplet-directed transport material, causing the elastic substrate to expand due to heat. This expansion generates tensile stress on a rigid film with a wrinkled surface. The height of the wrinkled structure in the laser-irradiated area decreases until the wrinkles disappear and the surface flattens. This simple physical change alone can induce droplet-directed transport, offering strong spatial and temporal controllability and allowing for remote manipulation without relying on complex electric or magnetic field equipment. Furthermore, after the droplet-directed transport ends, laser irradiation is stopped, and cooling allows the internal stress to recover, causing the wrinkled structure to regenerate, demonstrating reversibility. Once the wrinkled structure is regenerated, the next droplet-directed transport can be performed, achieving repeatable droplet-directed transport. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram illustrating the working principle of the droplet directional transport material described in this invention applied to droplet directional transport. Figure 1 1 is an elastic substrate; 2 is a moving droplet sphere; 3 is a near-infrared laser; 4 is a rigid Au film with a wrinkled structure.

[0025] Figure 2 This is a surface morphology diagram of the droplet-directed transport material described in this invention;

[0026] Figure 3 The surface contact angle of the wrinkle-free region on the surface of the droplet-directed transport material described in this invention;

[0027] Figure 4 The surface contact angle is the area with a wrinkled structure on the surface of the droplet directional transport material described in this invention. Detailed Implementation

[0028] This invention provides a droplet-oriented transport material, comprising an elastic substrate and a rigid film having a wrinkled structure covering the surface of the elastic substrate; the raw materials for preparing the elastic substrate include a substrate material, photothermal nanomaterials and an organic solvent; the raw materials for preparing the rigid film include one of gold, silver, platinum and lead.

[0029] In this invention, unless otherwise specified, all raw materials used in the preparation are preferably commercially available products.

[0030] In this invention, the raw material for preparing the rigid thin film includes one of gold, silver, platinum, and lead, preferably gold. In this invention, the period of the wrinkle structure in the rigid thin film is preferably 1–10 μm, more preferably 2 μm; the amplitude is preferably 0.1–1 μm, more preferably 0.2 μm. In this invention, the thickness of the rigid thin film is preferably 10–50 nm. In this invention, the rigid thin film provides a Young's modulus that differs significantly from that of the elastic substrate, thereby resulting in a wrinkle morphology.

[0031] In this invention, the raw materials for preparing the elastic substrate include a substrate, photothermal nanomaterials, and an organic solvent. In this invention, the substrate is preferably polydimethylsiloxane (PDMS). In this invention, the substrate is also equipped with a PDMS (SYLGARD 184) curing agent, and the mass ratio of the substrate to the curing agent is preferably 5–20:1, more preferably 10:1. In this invention, the photothermal nanomaterial is preferably Fe3O4 or Ti2O3, more preferably Ti2O3. In this specific embodiment, the particle size of the Ti2O3 is preferably 0.1–1 μm, more preferably 0.25 μm. In this invention, the organic solvent is preferably n-hexane or toluene, more preferably n-hexane. In this invention, the mass ratio of the substrate, photothermal nanomaterials, and organic solvent is preferably 5–20:0.06–0.21:1:5–20, more preferably 10:0.1:20. In this invention, the thickness of the elastic substrate is preferably 0.8–2 mm, more preferably 1 mm. In this invention, the elastic substrate provides a difference in Young's modulus compared to the rigid film, causing a wrinkled structure to form on the material surface, which has the function of reversibility and repeatability in causing the wrinkled morphology to appear / disappear.

[0032] The present invention also provides a method for preparing the droplet-oriented transport material described in the above technical solution, comprising the following steps:

[0033] An elastic substrate is obtained by mixing and curing a substrate, photothermal nanomaterials, and an organic solvent.

[0034] A film is deposited on the surface of the elastic substrate to obtain an elastic substrate covered with a rigid film;

[0035] The elastic substrate covered with a rigid film is heated and cooled to form a rigid film with a wrinkled structure on the surface of the elastic substrate, thus obtaining the droplet directional transport material.

[0036] This invention involves mixing a substrate, photothermal nanomaterials, and an organic solvent, followed by curing to obtain an elastic substrate. Preferably, the substrate, photothermal nanomaterials, and organic solvent are mixed, ultrasonically treated, and then allowed to stand and dry sequentially to remove the organic solvent, yielding an elastic substrate precursor. The elastic substrate precursor is then mixed with a curing agent, and subsequently degassed and cured to obtain the elastic substrate.

[0037] In this invention, the frequency of the ultrasonic treatment is preferably 30–80 kHz; the power is preferably 300 W; and the time is preferably 12 h. In this invention, the ultrasonic treatment serves to fully fuse and uniformly disperse the photothermal nanomaterials and the substrate in the organic solvent.

[0038] In this invention, the preferred settling temperature is 25–30°C, and the preferred settling time is 1 hour. During the settling process, any unevenly dispersed photothermal nanomaterials precipitate at the bottom. After settling, the system is preferably further separated to remove the unevenly dispersed photothermal nanomaterials that have precipitated at the bottom. This invention does not impose any particular limitation on the separation method; any method well-known to those skilled in the art can be used.

[0039] In this invention, the drying temperature is preferably 40–60°C, more preferably 50°C; the drying time is preferably 9–12 hours, more preferably 10 hours. In this invention, organic solvents are removed by drying.

[0040] In this invention, the degassing temperature is preferably room temperature, and the time is preferably 0.5–1.5 hours, more preferably 1 hour; the degassing is preferably carried out in a sealed oven under vacuum and allowed to stand for degassing. In this invention, degassing removes air bubbles mixed in during the mixing of the substrate and photothermal nanomaterials, ensuring a more uniform photothermal effect. In this invention, the curing temperature is preferably 50–80°C, more preferably 70°C; the curing time is preferably 3–5 hours, more preferably 4 hours.

[0041] After obtaining the elastic substrate, the present invention performs a coating on the surface of the elastic substrate to obtain an elastic substrate covered with a rigid thin film. In the present invention, the coating method is preferably ion sputtering. In the present invention, the ion sputtering current is preferably 10-30 mA, more preferably 20 mA; the coating time is preferably 60-120 s, more preferably 120 s.

[0042] After obtaining an elastic substrate covered with a rigid film, the present invention heats the elastic substrate covered with the rigid film, and after cooling, forms a rigid film with a wrinkled structure on the surface of the elastic substrate, thus obtaining the droplet-oriented transport material. In the present invention, the heating temperature is preferably 100-140°C, more preferably 100°C; the heating time is preferably 20-40 min, more preferably 30 min. The present invention does not have a particular limitation on the cooling method, and any cooling method well known to those skilled in the art can be used. Under the action of heating and cooling, the rigid film buckles, the surface of the elastic substrate flexibly deforms, and the whole is formed into a droplet-oriented transport material with a wrinkled structure.

[0043] The present invention also provides the application of the droplet directional transport material described in the above technical solution or the droplet directional transport material prepared by the preparation method described in the above technical solution in droplet directional transport.

[0044] In this invention, the preferred application includes: irradiating the droplet-directed transport material with a laser to eliminate the wrinkled structure in the laser-irradiated area to form a droplet-directed transport channel, thereby achieving the directional transport of droplets;

[0045] After the directional transport is completed, laser irradiation is stopped, and the area where the wrinkled structure disappeared is allowed to re-form a wrinkled structure after cooling, so that the next droplet directional transport can be carried out.

[0046] In this invention, the laser irradiation is preferably near-infrared laser; the power of the near-infrared laser is preferably 0.5–2W, more preferably 0.5W; and the wavelength is preferably 808nm. In this invention, the laser irradiation time is preferably 10–60s, more preferably 10–20s. This invention does not have a specific limitation on the cooling method; any cooling method well-known to those skilled in the art can be used. This invention uses laser irradiation, which offers strong controllability in space and time, is non-contact, and can be controlled remotely, while not relying on complex electric or magnetic field equipment.

[0047] To further illustrate the present invention, the droplet directional transport material provided by the present invention will be described in detail below with reference to the accompanying drawings and embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0048] Example 1

[0049] Weigh 0.1 g Ti2O3 (particle size 0.25 μm), 10 g polydimethylsiloxane, and 20 mL n-hexane into a flask and sonicate at 40 kHz and 300 W for 12 h. Let the resulting mixture stand at 25 °C for 1 h to separate and remove the unevenly dispersed Ti2O3 precipitated at the bottom, obtaining a uniformly distributed solution. Dry the solution in a vacuum oven at 50 °C for 10 h to completely remove residual n-hexane, obtaining an elastic substrate precursor. Mix the elastic substrate precursor with 1 g curing agent, place the resulting mixture in a petri dish, degas under vacuum for 1 h, and then cure at 70 °C for 4 h to obtain an elastic substrate with a thickness of 1 mm.

[0050] The above-mentioned elastic substrate was placed in an ion sputtering coating instrument and gold was deposited for 120 seconds under 20mA conditions to obtain an elastic substrate covered with a rigid thin film.

[0051] The elastic substrate covered with the rigid film was heated at 100°C for 30 minutes and then naturally cooled to form a rigid film with a wrinkled structure (period of 2 μm and amplitude of 0.2 μm) on the surface of the elastic substrate, thus obtaining a droplet directional transport material.

[0052] Test case

[0053] A near-infrared laser with a power of 0.5W and a wavelength of 808nm was used to irradiate the droplet-directed transport material described in Example 1. The working principle is illustrated in the schematic diagram below. Figure 1 As shown.

[0054] Figure 1 This is a schematic diagram illustrating the working principle of the droplet directional transport material described in this invention applied to droplet directional transport; wherein 1 is an elastic substrate; 2 is a moving droplet sphere; 3 is a near-infrared laser; and 4 is a rigid Au film with a wrinkled structure.

[0055] Figure 2 This is a surface morphology diagram of the droplet-directed transport material described in this invention, by... Figure 2 It can be seen that the present invention has successfully prepared a wrinkled morphology.

[0056] Figure 3 The surface contact angle of the wrinkle-free region on the surface of the droplet-directed transport material described in this invention. Figure 4 The surface contact angle of the wrinkled area on the surface of the droplet-directed transport material of the present invention is determined by... Figure 1 and Figures 3-4The results show that localized near-infrared laser irradiation for 15 seconds causes the elastic substrate to expand due to heat, generating tensile stress on the rigid film with a wrinkled structure on its surface. The height of the wrinkled structure in the laser-irradiated area decreases until the wrinkles disappear and flatten (a process similar to "laser wrinkle removal"), forming a wrinkle-free area. This change in the geometric parameters of the wrinkled structure leads to a change in the surface contact angle. When a droplet is on the surface of the droplet-directed transport material, the surface contact angle of the wrinkle-free area is 98.1°, while that of the wrinkled area is 122.6°, showing a significant difference. This change in wettability creates a local wettability gradient between the laser-irradiated and unirradiated areas, driving the surface droplet to move in a specific wettability direction. This method induces droplet-directed transport solely through the physical changes caused by localized laser irradiation, without requiring additional energy. Furthermore, after the droplet-directed transport ends, laser irradiation is stopped, and the area where the wrinkled structure disappeared reforms after natural cooling, allowing for the next droplet-directed transport cycle. This achieves reversible and repeatable droplet-directed transport.

[0057] Furthermore, the near-infrared laser irradiation method of the present invention is adopted because the transmittance of the PDMS substrate to the near-infrared laser is >93%, while the transmittance of PDMS containing Ti2O3 at a wavelength of 808nm is close to 0, proving that the PDMS substrate is almost transparent. PDMS containing Ti2O3 can completely absorb near-infrared light. When high-energy-density near-infrared laser passes through PDMS and enters Ti2O3, it can be completely absorbed by Ti2O3 nanoparticles, resulting in better light utilization. At the same time, Ti2O3 has good photothermal conversion efficiency, making it possible for the wrinkled structure of the rigid film to disappear due to the thermal expansion of the elastic substrate.

[0058] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A droplet-directed transport material, comprising an elastic substrate and a rigid film having a wrinkled structure covering the surface of the elastic substrate; the elastic substrate is prepared from raw materials including a substrate material, photothermal nanomaterials, and an organic solvent; the rigid film is prepared from raw materials including one of gold, silver, platinum, and lead; The droplet-directed transport material has a wrinkled structure with a wettability gradient; the erasure and regeneration of the wrinkled structure are achieved through a photothermal effect; the photothermal effect is excited by laser irradiation; The droplet-directed transport material is irradiated with a laser to eliminate the wrinkled structure in the laser-irradiated area, thereby forming a droplet-directed transport channel and realizing the directional transport of droplets. After the directional transport is completed, laser irradiation is stopped, and the area where the wrinkled structure disappeared is allowed to re-form a wrinkled structure after cooling, so that the next droplet directional transport can be carried out.

2. The droplet-directed transport material according to claim 1, characterized in that, The period of the fold structure in the rigid film is 1~10μm, and the amplitude is 0.1~1μm.

3. The droplet-directed transport material according to claim 1, characterized in that, The thickness of the elastic substrate is 0.8~2mm; the thickness of the rigid film is 10~50nm.

4. The droplet-directed transport material according to claim 1, characterized in that, The substrate is polydimethylsiloxane; the photothermal nanomaterial is Fe3O4 or Ti2O3.

5. The droplet-directed transport material according to claim 1, characterized in that, The organic solvent is n-hexane or toluene.

6. The droplet-directed transport material according to claim 4 or 5, characterized in that, The mass ratio of the substrate, photothermal nanomaterial, and organic solvent is 5~20:0.06~0.21:5~20.

7. A method for preparing the droplet-oriented transport material according to any one of claims 1 to 6, comprising the following steps: An elastic substrate is obtained by mixing and curing a substrate, photothermal nanomaterials, and an organic solvent. A film is deposited on the surface of the elastic substrate to obtain an elastic substrate covered with a rigid film; The elastic substrate covered with a rigid film is heated and cooled to form a rigid film with a wrinkled structure on the surface of the elastic substrate, thus obtaining the droplet directional transport material.

8. The preparation method according to claim 7, characterized in that, The heating temperature is 100~140℃, and the time is 20~40min.

9. The application of the droplet-directed transport material according to any one of claims 1 to 6 or the droplet-directed transport material prepared by the preparation method according to any one of claims 7 to 8 in droplet-directed transport.

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