阅读说明：本技术 一种纤维素纳米晶/二氧化钛手性向列结构复合薄膜及其制备方法 (Cellulose nanocrystal/titanium dioxide chiral nematic structure composite film and preparation method thereof ) 是由 李晓锋 隋延秋 杨帆 常伟 李伟 于中振 于 2019-08-23 设计创作，主要内容包括：本发明涉及一种纤维素纳米晶/二氧化钛手性向列结构复合薄膜及其制备方法：将二氧化钛前驱体钛酸四丁酯溶于乙醇中,再缓慢滴入浓硫酸水解制备的纤维素纳米晶溶液中,通过室温环境下缓慢自然干燥来制备纤维素纳米晶/二氧化钛手性向列结构复合薄膜,纤维素纳米晶体在成膜过程中自组装成手性螺旋结构,钛酸四丁酯的水解产物在此过程中均匀的附着于纤维素纳米晶体周围,共同参与自组装过程。该方法通过一步法制备手性螺旋结构的复合薄膜,工艺简单,操作方便,不需要额外的设备,对环境的污染小,可实现宏量制备。制备的复合薄膜可用于光学器件,湿度传感器,防伪材料等。(The invention relates to a cellulose nanocrystal/titanium dioxide chiral nematic structure composite film and a preparation method thereof, wherein the preparation method comprises the following steps: dissolving titanium dioxide precursor tetrabutyl titanate in ethanol, slowly dropping concentrated sulfuric acid into a cellulose nanocrystalline solution prepared by hydrolysis, and slowly and naturally drying at room temperature to prepare the cellulose nanocrystalline/titanium dioxide chiral nematic structure composite film, wherein the cellulose nanocrystalline is self-assembled into a chiral spiral structure in the film forming process, and the hydrolysate of tetrabutyl titanate is uniformly attached to the periphery of the cellulose nanocrystalline and participates in the self-assembly process together. The method for preparing the composite film with the chiral helical structure by the one-step method has the advantages of simple process, convenient operation, no need of additional equipment, little pollution to the environment and realization of macro preparation. The prepared composite film can be used for optical devices, humidity sensors, anti-counterfeiting materials and the like.)

1. A composite film with a chiral nematic structure of cellulose nanocrystals/titanium dioxide and a preparation method thereof are characterized in that a titanium dioxide precursor is dissolved in a solvent, a stable solution is formed by stirring, concentrated sulfuric acid is slowly dripped into a cellulose nanocrystal suspension prepared by acidolysis, hydrolysis products of tetrabutyl titanate are uniformly attached to the periphery of the cellulose nanocrystals, participate in the self-assembly process together, and are slowly dried to form the composite film with the chiral nematic structure.

2. The method according to claim 1, characterized in that it comprises in particular the steps of:

Step 1: preparing cellulose nanocrystals, namely preparing a cellulose nanocrystal suspension by acidolysis with concentrated sulfuric acid;

Step 2: preparing a precursor stable solution, namely dissolving a titanium dioxide precursor in a solvent to obtain a precursor solution, and fully stirring to obtain a stable and uniform solution;

And step 3: preparation of mixed solution-slowly adding precursor solution into cellulose nanocrystal suspension;

And 4, step 4: film formation-evaporation drying to form a film.

3. The method according to claim 1 or 2, wherein the concentration of cellulose nanocrystals is 0.5-10 wt%, preferably 2.7-3.5 wt%.

4. The method according to claim 1 or 2, wherein the cellulose nanocrystals are used under acidic conditions and have a pH between 4 and 6.

5. The method according to claim 1 or 2, characterized in that the titanium dioxide precursor is selected from tetrabutyl titanate.

6. The method according to claim 1 or 2, wherein the solvent is selected from one or more of ethanol, methanol, tert-butanol and the like.

7. The cellulose nanocrystalline/titanium dioxide chiral nematic structure composite film prepared by the method of any one of claims 1-6.

Technical Field

The invention belongs to the technical field of material preparation, and relates to a method for preparing a cellulose nanocrystal/titanium dioxide chiral nematic structure composite film by self-assembly, in particular to a method for preparing the cellulose nanocrystal/titanium dioxide chiral nematic structure composite film by one step.

Background

Cellulose is a renewable resource abundant in nature, and in the fifties of the last century, R ä nby first reported the preparation of cellulose colloidal suspensions by controlled sulfuric acid catalyzed degradation of cellulose fibers, Battista obtained a batch preparation of microcrystalline cellulose from high quality wood pulp cellulose as a raw material, with hydrochloric acid assisted degradation and ultrasonic post-treatment, by sulfuric acid hydrolysis, it chemically reacted with hydroxyl groups on the cellulose surface, grafting negatively charged sulfonate groups on its surface, causing the whiskers to disperse completely and uniformly in water due to electrostatic repulsion.

In the prior art, the titanium dioxide material with the chiral structure can be prepared only by using the chiral template for multiple times and cannot be obtained in one step, and meanwhile, the titanium dioxide precursor is easy to hydrolyze, so that the preparation process is complex, and the cost in the synthesis process is greatly increased.

Disclosure of Invention

In order to solve the problems mentioned in the prior art, the invention provides a simple, easy, rapid and efficient method for preparing the cellulose nanocrystal/titanium dioxide chiral nematic structure composite film, and expands the way for preparing the nanocomposite.

The invention adopts the following technical scheme that a cellulose nanocrystalline/titanium dioxide chiral nematic structure composite film and a preparation method thereof, a titanium dioxide precursor is dissolved in solutions such as ethanol, the solutions are fully mixed and then slowly dropped into a cellulose nanocrystalline suspension, the mixture is uniformly stirred, injected into a polystyrene culture dish and dried, and the cellulose nanocrystalline/titanium dioxide chiral nematic structure composite film is obtained.

In a preferred embodiment of the present invention, the method specifically comprises the steps of:

Step 1: preparing cellulose nanocrystals, namely preparing a cellulose nanocrystal suspension by acidolysis with concentrated sulfuric acid;

Step 2: preparing a precursor stable solution, namely dissolving a titanium dioxide precursor in a solvent to obtain a precursor solution, and fully stirring to obtain a stable and uniform solution;

And step 3: preparation of mixed solution-slowly adding the precursor solution into the cellulose nanocrystal suspension by a metering pump;

And 4, step 4: film formation-slow evaporation drying to form a film.

In a preferred embodiment of the invention, the cellulose nanocrystals are obtained by acid hydrolysis with sulfuric acid, and the concentration is not too high or too low, preferably 2.7 to 3.5 wt%.

In a preferred embodiment of the invention, the cellulose nanocrystals should be used under acidic conditions, with a pH between 4 and 6.

in a preferred embodiment of the invention, the titanium dioxide precursor is selected from tetrabutyl titanate.

In a preferred embodiment of the present invention, the solvent is selected from one or more of ethanol, methanol, tert-butanol, and the like.

The invention also protects the cellulose nanocrystalline/titanium dioxide chiral nematic structure composite film prepared by the method.

Compared with the existing titanium dioxide material preparation technology, the self-assembly method for preparing the cellulose nanocrystal/titanium dioxide chiral nematic structure composite film has the following advantages:

(1) According to the invention, tetrabutyl titanate is used as a precursor, a cellulose nanocrystal solution prepared by mixing and acidolysis is prepared, and a hydrolysis product of tetrabutyl titanate enters a helical structure of the cellulose nanocrystal by utilizing the property that the cellulose nanocrystal can be self-assembled into the chiral helical structure, and finally the composite film with the chiral helical structure is prepared in one step by drying at room temperature.

(2) the invention has simple process, convenient operation, no need of additional equipment, small pollution to the environment and wide application prospect in the aspects of optical devices, humidity sensors, anti-counterfeiting materials and the like.

Drawings

The invention will be further described with reference to the accompanying drawings, which are only schematic illustrations and illustrations of the invention, and do not limit the scope of the invention.

Fig. 1 is a scanning electron microscope picture of a cellulose nanocrystal/titanium dioxide chiral nematic structure composite film prepared by self-assembly of a suspension containing 10wt% of tetrabutyl titanate and 90wt% of cellulose nanocrystals under the condition of pH =5 in example 1 of the present invention.

fig. 2 is a scanning electron microscope picture of a cellulose nanocrystal/titanium dioxide chiral nematic structure composite film prepared by self-assembly of a suspension containing 20wt% of tetrabutyl titanate and 80wt% of cellulose nanocrystals under the condition of pH =5 in example 2 of the present invention.

Fig. 3 is a scanning electron microscope picture of a cellulose nanocrystal/titanium dioxide chiral nematic structure composite film prepared by self-assembly of a suspension containing 30wt% of tetrabutyl titanate and 70wt% of cellulose nanocrystals under the condition of pH =5 in example 3 of the present invention.

Fig. 4 is a scanning electron microscope picture of a cellulose nanocrystal/titanium dioxide chiral nematic structure composite film prepared by self-assembly of a suspension containing 40wt% of tetrabutyl titanate and 60wt% of cellulose nanocrystals under the condition of pH =5 in example 4 of the present invention.

Fig. 5 is a scanning electron microscope picture of a cellulose nanocrystal/titanium dioxide chiral nematic structure composite film prepared by self-assembly of a suspension containing 50wt% of tetrabutyl titanate and 50wt% of cellulose nanocrystals under the condition of pH =5 in example 5 of the present invention.

fig. 6 is a scanning electron microscope picture of a cellulose nanocrystal/titanium dioxide chiral nematic structure composite film prepared by self-assembly of a suspension containing 10wt% of tetrabutyl titanate and 90wt% of cellulose nanocrystals under the condition of pH =4 in example 6 of the present invention.

Fig. 7 is a scanning electron microscope picture of a cellulose nanocrystal/titanium dioxide chiral nematic structure composite film prepared by self-assembly at pH =6 from an aqueous suspension containing 10wt% tetrabutyl titanate and 90wt% cellulose nanocrystals according to example 7 of the present invention.

FIG. 8 is a chart of the UV-Vis spectra of the samples of example 1 of the present invention with increased humidity.

Detailed Description

The following detailed description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings, will make the advantages and features of the invention easier to understand by those skilled in the art, and thus will clearly and clearly define the scope of the invention.