Preparation method of independent gradient LB film

Abstract

The invention belongs to the field of self-assembly of nano materials, and provides a preparation method of an independent gradient Langmuir-Blodgett (LB) film. The preparation method comprises the following steps: spreading an organic solution of an amphiphilic block copolymer on the water surface to spontaneously form a stable Langmuir single layer, and then controllably transferring the regular single layer to a solid substrate under proper film forming pressure, film forming speed, film drawing speed and film drawing pressure by utilizing an LB film technology to obtain the independent gradient LB film. According to the method, the mutually independent LB films with discontinuous pressure gradients or molecular density gradients are obtained on the same solid substrate, the LB films have multiple mutually independent nano structures, possibility is provided for research on an aggregation mechanism of a Langmuir single layer, and the method is suitable for being used in the fields of anti-counterfeiting, coating and the like.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial self-assembly and provides a method for preparing an independent gradient LB film. Background Art

[0002] LB thin film technology is an advanced tool capable of fabricating highly ordered ultrathin films at the molecular and atomic levels. This technique involves transferring a Langmuir monolayer from an air / water interface onto a solid substrate under constant surface pressure. Advances in this technology over the past few decades have allowed for the fabrication of uniform LB films using a variety of molecular materials, such as lipids, polymers, and nanoparticles. These films have wide applications in sensors, electronic devices, and biomaterials. When a Langmuir monolayer is compressed, its structure continuously changes due to variations in molecular density. Traditional LB films are fabricated under constant surface pressure on the Langmuir monolayer, meaning that only a single structure can be obtained in deposition experiments. Therefore, it is difficult to observe structural changes in the monolayer during compression, and this technique cannot reveal the aggregation mechanism of Langmuir monolayer films.

[0003] As early as 2007, Wang et al. reported a continuous gradient LB film method in their article "Langmuir-Blodgett Films Formed by Continuously Varying Surface Pressure. Characterization by IR Spectroscopy and Epifluorescence Microscopy". This method prepared phospholipid LB films by transferring a phospholipid monolayer onto a solid substrate under continuously varying surface pressure (COVASP). This method allows for complete isothermal structural characterization in a single experiment. The transfer surface pressure of each COVASP-LB film segment is calibrated based on the substrate deposition location and instantaneous surface pressure. However, this method cannot obtain the initial LB film structure and cannot prepare uniform nanostructures under constant pressure. Summary of the Invention

[0004] To address the current technical challenges, we propose a method for preparing independently gradient Langmuir (LB) films. By transferring a monolayer onto a single solid substrate, an initial LB film and other films under several constant surface pressures are obtained in a single experiment. This method enables the fabrication of LB films with discontinuous pressure or molecular density gradients on the same solid substrate, each possessing multiple independent nanostructures. This facilitates the observation of structural changes that may occur during monolayer compression and the determination of the Langmuir monolayer aggregation mechanism, making it suitable for applications in anti-counterfeiting and coating fields. Technical solution

[0005] In this invention, we selected an asymmetric block copolymer polystyrene with a relatively long PS block. b - Polymethyl methacrylate (PS- b Using PMMA as the research system, its organic solution was spread on the deionized water surface of the LB membrane analyzer's tank. Under appropriate film-forming pressure, film-forming speed, film-pulling speed, and film-pulling pressure, the regular monolayer was controllably transferred to a solid substrate to obtain an independent gradient LB membrane. First, the LB membrane analyzer's tank was filled with deionized water as a subphase, and then the solid substrate was immersed in the water well in the center of the tank. A certain volume of sample solution was evenly spread on the water surface using a micro-injector. The film-forming speed, film-forming pressure, film-pulling speed, and film-pulling pressure of the LB membrane analyzer were set, and then the barriers at both ends of the tank were moved according to the film-forming speed to compress the Langmuir monolayer. Subsequently, the deposition unit was controlled to pull the solid substrate upward at a certain film-pulling speed, while the barriers moved slowly to maintain a constant film-pulling pressure, thereby slowly transferring the water surface monolayer onto the continuously rising substrate. After the deposition at a certain pressure was completed, the above steps were repeated to continue pulling the substrate to deposit the LB membrane at the next pressure, until the entire substrate was completely exposed above the water surface, thus obtaining an independent gradient LB membrane. Finally, the various structures of the independent gradient LB film were determined by AFM.

[0006] The organic solvents mentioned are chloroform or tetrahydrofuran.

[0007] The concentration of the solution is 0.5-2 mg / mL.

[0008] The parameters of the LB membrane analyzer are as follows: film forming pressure is 0.2-20 mN / m; film forming speed is 0.1-10 mm / min; film pulling speed is 1-5 mm / min; film pulling pressure is 0.2-20 mN / m.

[0009] The solid substrate is a silicon wafer, mica sheet, or glass sheet. Example 1

[0010] The specific steps of the preparation method are as follows: (1) PS- b -PMMA is dissolved in chloroform at a concentration of 0.5 mg / mL as a spreading solution; (2) Take 23 x 10 mm 2 The silicon wafer was immersed in the water well of the LB membrane analyzer to 18 mm below the water surface. 20 µL of sample solution was extracted using a micro syringe (50 µL) and evenly dripped onto the water surface in the LB membrane tank. After the solvent evaporated for 15 min, a uniform copolymer Langmuir monolayer was formed at the gas / liquid interface. (3) At a low obstacle moving speed, the substrate is lifted upward by 6 mm at a speed of 2 mm / min to obtain its initial LB film; (4) Control the LB membrane analyzer to compress the monolayer to a membrane pressure of 0.5 mN / m at a speed of 5 mm / min, and then lift the substrate by 6 mm to obtain the LB membrane under this pressure; (5) Repeat step (4) to further lift the substrate by 6 mm to obtain an LB film at 2 mN / m. This allows for the production of PS- at 0, 0.5, and 2.0 mN / m on the same substrate. b -Independent gradient LB film of PMMA. Example 2

[0011] Repeat the steps of Example 1 to obtain PS- at 0, 7, and 20 mN / m on the same substrate. b -Independent gradient LB film of PMMA. Compared with the prior art, the present invention has the following beneficial effects.

[0012] This method enables the formation of independent LB films with discontinuous pressure or molecular density gradients on the same solid substrate. These LB films possess multiple independent and uniform nanostructures, providing a basis for studying the aggregation mechanism of Langmuir monolayers and making them suitable for use in fields such as anti-counterfeiting and coatings. Attached Figure Description

[0013] Figure 1 The images show the AFM morphology of the independent gradient LB films prepared in Examples 1 (ac) and 2 (df) of this invention.

Claims

1. A method for preparing LB films with discontinuous pressure gradients or molecular density gradients that are independent of each other on the same solid substrate.

2. A method for preparing an independent gradient LB film, comprising the following steps: (1) Preparation of an organic solution of an amphiphilic block copolymer; (2) Fill the water tank of the LB membrane analyzer with deionized water as the subphase, and then immerse the solid substrate in the water well in the center of the water tank; A certain volume of sample solution is evenly spread on the water surface using a micro-syringe; The LB film analyzer was set with film formation rate, film formation pressure, film pulling speed, and film pulling pressure. Then, the barriers at both ends of the water tank were moved at the film formation rate to compress the Langmuir monolayer. The deposition unit was then controlled to pull the solid substrate upwards at a certain film pulling speed, while the barriers moved slowly to maintain a constant film pulling pressure, thus allowing the water surface monolayer to slowly transfer onto the continuously rising substrate. After deposition at a certain pressure was completed, the above steps were repeated to continue pulling the substrate to deposit the LB film at the next pressure, until the entire substrate was completely exposed above the water surface, thus obtaining an independent gradient LB film.

3. (3) Various nanostructures of independent gradient LB films were determined by atomic force microscopy (AFM).

4. The preparation method according to claim 2, characterized in that, The study system used amphiphilic block copolymers; organic solvents: chloroform or tetrahydrofuran; solution concentration: 0.5-2 mg / mL.

5. The preparation method according to claim 2, characterized in that, The parameters of the LB membrane analyzer are as follows: film forming pressure is 0.2-20 mN / m; film forming speed is 0.1-10 mm / min; film pulling speed is 1-5 mm / min; film pulling pressure is 0.2-20 mN / m.

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