Cellulose Cholesteric Liquid Crystal Microbubbles Based on Solvent Extraction Technology and Their Preparation Method

Abstract

This invention relates to cellulose cholesteric liquid crystal microbubbles based on solvent extraction technology and their preparation method. The method includes: constructing microcapsules using microfluidic technology, with a core of cellulose aqueous solution, a water-insoluble, photocurable, and selectively permeable rigid polymer material as the shell. By combining confined space effects and solvent extraction, dehydration is induced within the capsules to generate microbubbles, while simultaneously causing cellulose molecules to self-assemble into cholesteric liquid crystals with a periodic structure. This ultimately yields cholesteric liquid crystal microbubbles with a transparent shell, a periodic structure intermediate layer, and a bubble core. Under white light irradiation, the microbubbles exhibit bright structural colors and can suspend in water, maintaining stable structural colors. Compared to existing technologies, this invention combines microfluidic technology, spatial confinement effects, and solvent extraction technology to prepare novel cholesteric liquid crystal materials, which have advantages such as stable color, suspension capability, and simple preparation operation.

Description

Technical Field

[0001] This invention relates to the field of advanced materials technology, and in particular to a cellulose cholesteric phase liquid crystal microbubble based on solvent extraction technology and its preparation method. Background Technology

[0002] Cholesteric liquid crystals are one-dimensional photonic crystals with a periodic helical structure. Due to their unique helical structure, they possess distinctive optical properties, exhibiting different structural colors to the naked eye and capable of color-changing under stimuli such as light, heat, and electricity. They have a wide range of applications in both military and civilian fields. Cellulose is a widely distributed polysaccharide in nature, constituting various structural colors in the plant kingdom. Some cellulose derivatives have attracted considerable attention due to their ability to self-assemble into cholesteric liquid crystals with a certain periodic structure at certain concentrations, and their excellent biocompatibility, biodegradability, optical stability, and renewability. Therefore, research on cellulose-based cholesteric liquid crystals has aroused widespread interest among scholars. However, due to the good water solubility of cellulose and its derivatives, the resulting cholesteric liquid crystal materials generally cannot be stored independently in aqueous solutions, often requiring oily solvents or cumbersome post-processing. Furthermore, cellulose and its derivatives only self-assemble into cholesteric liquid crystals at high concentrations, but these high concentrations result in highly viscous dispersions, making them difficult to process and mold. These factors limit the application of cellulose liquid crystals. Therefore, a novel method for preparing cellulose cholesteric liquid crystals still needs to be developed.

[0003] Microfluidics is a technology that precisely controls fluid flow and reactions within a micrometer-scale space, and it is a highly interdisciplinary field. Droplet microfluidics is an important branch of this technology, typically utilizing the shear force and surface tension of fluids to generate monodisperse micro- and nano-sized droplets. Each tiny droplet can serve as a spatially confined reaction chamber, avoiding cross-contamination during the reaction process and offering easy control. Furthermore, by adjusting the flow rate or other parameters of the microfluidic fluid, the size and combination of droplets can be precisely controlled. This is a simple and easily controlled technique that plays a crucial role in biomedical applications. More importantly, droplets and the microspheres or microcapsules they produce can act as confined spaces, promoting complete molecular reactions and the self-assembly of colloidal particles by limiting molecules and colloidal particles to a localized space. Because this process is highly independent and unaffected by external environmental interference, it has attracted widespread attention and has broad applications in various fields.

[0004] Solvent extraction is a common method for separating or purifying compounds. It can extract the desired substance from a solid or liquid. The equipment required for this method is simple and easy to operate. It is often used for the extraction and separation of trace substances and is widely applicable in environmental, biochemical and pharmaceutical fields.

[0005] However, there is currently no technology that combines microfluidics, confined space, and solvent extraction to prepare cellulose cholesteric liquid crystal microbubbles. Summary of the Invention

[0006] The purpose of this invention is to overcome the defects of the prior art by providing a cellulose cholesteric phase liquid crystal microbubble and its preparation method based on solvent extraction technology. Specifically, it utilizes a combination of microfluidics, confined space, and solvent extraction to prepare cellulose cholesteric phase liquid crystal microbubbles. This technology combines the advantages of microfluidics, confined space, and solvent extraction, and has the advantages of simple preparation process, strong independence, low interference, no need for complex equipment, low cost, and controllable product properties.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] The first objective of this invention is to provide a method for preparing cellulose cholesteric phase liquid crystal microbubbles based on solvent extraction technology. This method utilizes a combination of microfluidics, confined space, and solvent extraction to prepare cellulose cholesteric phase liquid crystal microbubbles, and includes the following steps:

[0009] S1. Prepare a cellulose aqueous solution of a certain concentration (initial low concentration) as the internal phase;

[0010] S2. Prepare a rigid polymer monomer solution containing a photoinitiator as an intermediate phase;

[0011] S3. Select an aqueous surfactant solution as the external phase;

[0012] S4. The inner phase obtained in step S1, the intermediate phase obtained in step S2, and the outer phase fluid obtained in step S3 are injected into a dual emulsion microfluidic chip with a coaxial channel structure. Under the combined action of shear force and surface tension between the incompatible fluids, the inner phase and intermediate phase fluids are broken into droplets, and the inner phase forms smaller droplets that are wrapped in larger droplets formed by the intermediate phase, thereby obtaining dual emulsion droplets.

[0013] S5. Under ultraviolet light irradiation, the outer layer of the double emulsion droplets polymerizes into a solid, thereby obtaining microcapsules of cellulose dispersion with a stable core-shell structure. The microcapsules are then subjected to ultraviolet light curing again in a collection bottle containing the outer phase to form microcapsules with a hard shell, thus obtaining the microcapsules in the collection bottle.

[0014] S6. After washing the microcapsules in the collection bottle obtained in step S5 with pure water, place them in the extractant for solvent extraction. Under the action of the extractant, the microcapsules continuously lose water and generate bubbles inside. As the bubble volume increases, the concentration of cellulose in the core increases continuously, and finally self-assembles into a cholesteric liquid crystal with structural color to obtain cellulose cholesteric liquid crystal microbubbles.

[0015] Furthermore, the internal phase solution described in S1 is a dispersion of cellulose or cellulose derivatives at an initial concentration (low concentration) that can self-assemble into cholesteric liquid crystals with bright structural colors at a relatively high concentration range. The cellulose or cellulose derivatives can be one of cellulose nanocrystals, hydroxypropyl cellulose molecules, etc.; to enhance the self-assembly of the above molecules at higher concentrations, functional material molecules such as acrylamide, photoinitiators, and crosslinking agents can also be added to the dispersion.

[0016] Furthermore, the higher concentration is a concentration that is higher than the initial concentration (low concentration) of the dispersion.

[0017] Furthermore, the concentrations at which cellulose derivatives, such as cellulose nanocrystals and hydroxypropyl cellulose molecules, self-assemble into cholesteric liquid crystals vary. For example, hydroxypropyl cellulose molecules can self-assemble into cholesteric liquid crystals with bright structural colors in a concentration range of 50%-70%. Therefore, the initial concentration ranges for cellulose and cellulose derivative dispersions in the internal phase solution will differ.

[0018] Furthermore, the intermediate phase solution described in S2 is a rigid polymer monomer solution containing a photoinitiator that is insoluble in water, photocurable, and exhibits selective permeability after curing. The shell formed after photocuring possesses a certain degree of rigidity and selective permeability; it can permeate through water molecules under the action of an extractant, but will not permeate through ions such as chloride or sodium ions, and external extractants will not backflow into the shell. The rigid polymer monomer is one such as ethoxylated trimethylolpropane triacrylate or trimethylolpropane triacrylate; the concentration of the photoinitiator is generally 1%.

[0019] Furthermore, the external phase solution mentioned in S3 is an aqueous solution of a surfactant, such as polyvinyl alcohol (PVA), F108, or a PVA-F108 combination solution.

[0020] Furthermore, dual emulsion droplets are prepared using coaxial microfluidic devices or capillary array microfluidic devices, thereby preparing microcapsules of cellulose dispersions with stable core-shell structures.

[0021] Furthermore, the extractant mentioned in S6 is one of the following solutions: ethanol, saturated sodium chloride, saturated potassium chloride, etc.

[0022] Furthermore, in the solvent extraction process described in S6, microcapsules with different shell thicknesses exhibit different reaction states under the action of the extractant.

[0023] Furthermore, when the r / R range of the initial microcapsules described in S6 is less than a certain low threshold (e.g., 0.8), the shell of the microcapsules does not change significantly before bubbles are generated under the action of the extractant.

[0024] Furthermore, when the r / R range of the initial microcapsules described in S6 is greater than a certain higher threshold (such as 0.9), the low-concentration cellulose dispersion microcapsules will not generate bubbles, and the shell of the microcapsules will always be in a collapsed state, eventually forming a bowl-shaped or similar shape.

[0025] Furthermore, when the r / R range of the initial microcapsules in S6 is between the aforementioned lower and higher thresholds, the shell of the low-concentration cellulose dispersion microcapsules will wrinkle and collapse before bubbles are generated, and the shell can recover its original shape when the core bubbles are generated.

[0026] Furthermore, the cholesteric liquid crystal microbubbles prepared in S6 have stable structural color, suspendability, and thermosensitive properties. When heated in a water bath, a red shift in the structural color of the cholesteric liquid crystal can be clearly observed. In addition, mixing some other functional material molecules, such as propylene glycol, acrylamide, ethylene glycol, etc., into the inner phase cellulose dispersion can expand the thermosensitive range of the prepared cholesteric liquid crystal.

[0027] Furthermore, the preparation method of cellulose cholesteric phase liquid crystal microbubbles requires the combination of microfluidics, confined space, and solvent extraction, all of which are indispensable.

[0028] Furthermore, the number of cores and color combinations of the cholesteric liquid crystal microbubbles (cellulose cholesteric phase liquid crystal microbubbles) prepared by the above method are controllable. By adjusting the initial concentration of different core compartments (the core of the microcapsule), different color combinations can be obtained.

[0029] The second objective of this invention is to provide a cellulose cholesteric liquid crystal microbubble based on solvent extraction technology. Unlike traditional microcapsules, this microbubble, in addition to encapsulating cholesteric liquid crystal, also possesses a bubble structure, allowing it to suspend freely in a liquid environment. Furthermore, this microbubble exhibits a bright structural color under white light irradiation and is stable in nature. It also possesses thermosensitive properties; when heated in a water bath, a noticeable red shift in the structural color of the cholesteric liquid crystal is observed.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1) The method for preparing cellulose cholesteric liquid crystal microbubbles based on solvent extraction technology of the present invention is a method for preparing a new cellulose cholesteric liquid crystal material that is convenient to operate, easy to control, does not require complex equipment, and is low cost. Its main principle is to construct a confined space based on microfluidic technology and induce cellulose self-assembly by solvent extraction, thereby obtaining cellulose cholesteric liquid crystal microbubbles with a core-shell structure.

[0032] 2) The cellulose cholesteric phase liquid crystal microbubbles prepared by the present invention based on solvent extraction technology have structural colors and can maintain the stability of their structural colors in aqueous solutions. They also have bubble structures, can be suspended in solutions, and can change color in response to temperature changes in the surrounding environment. Therefore, they have potential application value in underwater sensing, biomolecular detection and other fields. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the experiment of preparing mononuclear encapsulated low-concentration cellulose dispersion microcapsules using a coaxial microfluidic device according to the present invention.

[0034] Figure 2 This is a schematic diagram illustrating the experiment of preparing dual-core encapsulated cellulose microcapsules with different concentrations using a capillary array microfluidic device according to the present invention.

[0035] Figure 3 This is a schematic diagram showing the self-assembly of low-concentration cellulose microcapsules (microcapsules with a core-shell structure after photocuring of double emulsion droplets, i.e., microcapsules with a hard shell prepared in S5) into cholesteric liquid crystal microbubbles under the action of an extractant.

[0036] In the diagram: 1. Inner phase pipe; 2. Intermediate phase pipe; 3. Square pipe; 4. Outer phase pipe; 5. Inner seven-hole pipe. Detailed Implementation

[0037] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0038] Any preparation methods, materials, structures, or composition ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0039] From an inventive concept perspective, the microfluidic technology employed in this technical solution is a traditional dual-emulsion microfluidic system. A dual-emulsion is a nested emulsion system that can encapsulate and protect the excellent properties of some active materials, and has wide applications in drug delivery, chemical reactions, and separation. Dual-emulsion microfluidics can generate microemulsion droplets by altering the orbital morphology of the microchannels in the microfluidic chip and the flow characteristics of the emulsion. It has the ability to precisely control the monodispersity of the emulsion droplets, as well as the size and number of internal droplets, thereby obtaining microcapsules with different morphologies and compositions. Furthermore, these microcapsules can form confined spaces, encapsulating molecules, colloidal particles, etc., within this local space, promoting complete molecular reactions and the self-assembly of colloidal particles. Due to the core-shell structure of the microcapsules, the confined space formed by the core is unaffected by the external environment and possesses strong independence, thus having wide applications in multiple fields. Solvent extraction is one of the commonly used methods for separating or purifying compounds. Because of its wide range of extraction solvents, high selectivity, and simple operation, it has wide applications in materials science, biochemistry, and medicine.

[0040] In summary, based on the above advantages, this invention discloses a method for preparing novel cellulose cholesteric liquid crystal microbubbles by combining microfluidics, confined space self-assembly, and solvent extraction technologies. The microbubbles prepared by this application using microfluidics, confined space, and solvent extraction possess bright structural colors. These microbubbles differ from solid materials prepared by traditional methods and also from traditional microcapsules; they have an internal bubble structure and can freely suspend in a liquid environment. The preparation method includes: constructing microcapsules using microfluidics technology with a cellulose aqueous solution as the core, a water-insoluble, photocurable, and selectively permeable rigid polymer material as the shell; combining confined space and solvent extraction to induce dehydration within the capsules to generate microbubbles, while simultaneously causing hydroxypropyl cellulose molecules to self-assemble into a cholesteric liquid crystal with a periodic structure, ultimately obtaining cholesteric liquid crystal microbubbles with a transparent shell, a periodic intermediate layer, and a bubble core structure. Under white light, microbubbles exhibit bright structural colors. Because the bubble structure can be suspended in water and is stable, the microbubbles also retain the material's thermosensitive properties based on the material characteristics of the core hydroxypropyl cellulose cholesteric liquid crystal.

[0041] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the reagents, methods and equipment used are conventional reagents, methods and equipment in this technical field.

[0042] (1) Constructing a microfluidic chip: A microfluidic chip is constructed using coaxial assembly of glass capillaries (e.g., ...). Figure 1 As shown, mononuclear encapsulated low-concentration cellulose dispersion microcapsules were prepared using a coaxial microfluidic device; as shown... Figure 2As shown, a capillary array microfluidic device was used to prepare dual-core encapsulated cellulose microcapsules with different concentrations. The three-phase channels (inner, middle, and outer) were arranged in an axisymmetric manner by microscopic manipulation. The microcapsules were then connected and fixedly assembled on a glass slide using a square tube 3.

[0043] (2) Preparation of sample solution: Select a low-concentration aqueous cellulose dispersion as the inner phase, a rigid polymer monomer solution containing a photoinitiator that is insoluble in water, photocurable, and semi-permeable after curing as the intermediate phase, and an aqueous surfactant solution as the outer phase.

[0044] (3) Connect the device, adjust the flow rate of each phase, and prepare droplets.

[0045] (4) Ultraviolet light irradiation, curing and cross-linking, to prepare microcapsules.

[0046] (5) After collecting and cleaning the microcapsules, they are placed in the extractant for solvent extraction to prepare cholesteric phase liquid crystal microbubbles.

[0047] In step (1), the coaxial microfluidic chip device includes a glass slide, capillaries, a spotting needle, and quick-drying adhesive. An inner phase channel with a diameter of 30–80 μm is coaxially nested into an intermediate phase channel 2 with a diameter of 120–180 μm and an inner pore size of 580 μm. Then, through a square tube 3, the inner phase channel 1 and the intermediate phase channel 2 are coaxially nested into an outer phase channel 4 with an inner pore size of 580 μm. The size of droplets and microcapsules can be adjusted by changing the diameter of the inner phase channel 1 and the intermediate phase channel 2. The capillary array microfluidic device includes a coaxial microfluidic device and a capillary array disposed within the inner phase channel, such as… Figure 2 As shown, the inner phase channel including the capillary array is an inner tube with seven holes 5.

[0048] In step (2), the inner phase solution is a low-concentration aqueous dispersion of cellulose. The intermediate phase solution is a rigid polymer monomer solution that is insoluble in water, photocurable, and has semi-permeable properties after curing. The outer phase solution is an aqueous solution of a surfactant. For example, the inner phase solution can be a dispersion of hydroxypropyl cellulose (HPC) with a concentration range of 10%-28%, the intermediate phase solution can be ethoxylated trimethylolpropane triacrylate (ETPTA) with 1% photoinitiator added, and the outer phase solution can be a 2% F108 solution.

[0049] In step (3), the three-phase solutions in the syringe are connected to the inner and outer phase injection ports of the device through polyethylene tubes, respectively. Under the external force of the mechanical pump, the flow of fluid in the device channel is controlled.

[0050] In step (3), the size of the microcapsules and the number of cores can be controlled by adjusting the appropriate liquid flow rate and the chip channel type. For example, the commonly used internal phase flow rate ranges from 10 μL / h to 50 μL / h; the intermediate phase flow rate ranges from 0.1 mL / h to 1 mL / h; and the external phase flow rate ranges from 1 mL / h to 5 mL / h. The commonly used internal phase channel is a single-pore capillary (such as...). Figure 1 (as shown) and seven-hole capillary array (such as) Figure 2 (As shown).

[0051] In step (4), the initially prepared dual emulsion droplets are initially photocured by ultraviolet light in the chip's collection tube (external phase channel 4) to stabilize the core-shell distribution morphology of the microcapsules. Subsequently, the microcapsules fall into a collection bottle containing the external phase solution as the collection liquid and are irradiated again by an ultraviolet lamp, thereby achieving complete cross-linking and curing to form microcapsules with a hard shell.

[0052] In step (5), water is used for cleaning.

[0053] In step (5), if anhydrous ethanol is used for solvent extraction, generally speaking, the microcapsules need to be soaked in anhydrous ethanol for more than 0.5 hours before bubbles appear.

[0054] In step (5), the microcapsules (microcapsules with a rigid shell) containing a low-concentration cellulose dispersion prepared above are placed in an extractant such as ethanol. Under the action of the extractant, the core of the microcapsule gradually loses water and generates bubbles. Due to the selective permeability of the shell (such as ETPTA), hydroxypropyl cellulose molecules are well retained in the microcapsule. As the volume of the bubbles in the core increases, the concentration of the dispersion (such as hydroxypropyl cellulose) in the core also increases, eventually gradually self-assembling into a cholesteric liquid crystal with structural color. As the bubble volume increases, the pitch between the cellulose rod-shaped molecules gradually decreases, thereby causing the structural color of the cholesteric liquid crystal microbubbles to gradually shift to blue (e.g., ethanol). Figure 3 The resulting microbubbles have a bright and controllable structural color, and because their cores contain bubble structures, they can be freely suspended in a liquid environment.

[0055] Example 1

[0056] Mononuclear pure hydroxypropyl cellulose cholesteric phase liquid crystal microbubbles were prepared by solvent extraction.

[0057] A pure hydroxypropyl cellulose cholesteric phase liquid crystal microbubble was prepared according to the following method:

[0058] (1) Prepare the three-phase solution:

[0059] 1.1) Internal phase solution: A certain amount of HPC was added to an appropriate amount of pure water to prepare an HPC dispersion with a concentration of 20wt%-28wt%. The dispersion was collected after stirring with a stirrer for 48 hours and stored at room temperature.

[0060] 1.2) Intermediate phase solution: ETPTA dispersion containing 1% photoinitiator by volume, stored at room temperature away from light.

[0061] 1.3) External phase solution: Prepare an aqueous solution of surfactant F108 with a concentration of 2%.

[0062] (2) Assemble the chip device and connect the device.

[0063] 2.1) Assemble the chip device: The inner phase capillary (inner phase channel 1) with a single-hole capillary with an inlet diameter of 30-80 μm is coaxially nested inside the intermediate phase capillary (intermediate phase channel 2) with an inlet diameter of approximately 120-180 μm. The inner and middle tubes are then coaxially nested inside the outer capillary (outer phase channel 4) with an inner tube pore diameter of 580 μm using a square tube 3. The device is then fixed to a glass slide with quick-drying adhesive and the spotting needle is secured.

[0064] 2.2) Connection device: Load the internal, middle and external three-phase solutions into the syringe respectively, place the syringe on the mechanical pump, and connect the syringe to the spotting needle of the chip through the polyethylene tube.

[0065] (3) Adjust the flow rate to form droplets and cure by ultraviolet cross-linking.

[0066] 3.1) Flow rate adjustment: Adjust the sample flow rate to obtain single-nuclear droplets of a specific size. The commonly used internal phase flow rate range in this invention is 10 μL / h to 50 μL / h; the intermediate phase flow rate ranges from 0.1 mL / h to 1 mL / h; and the external phase flow rate ranges from 1 mL / h to 5 mL / h.

[0067] 3.2) Droplet formation and UV crosslinking curing: The dual emulsion droplets are initially irradiated with UV light in the outer tube of the microfluidic chip to simply fix their morphology. Then, they are further irradiated with UV light in the collection bottle to completely cure them and obtain well-formed mononuclear microcapsules.

[0068] (4) Place it in the extractant and perform solvent extraction.

[0069] The microcapsules prepared above were placed in anhydrous ethanol and observed under a microscope. Under the influence of ethanol, the microcapsules continuously lost water. Microcapsules with thin shells developed depressions and wrinkles before bubble formation, until bubbles formed in the core, at which point the shell returned to its original shape. The continuous water loss of the microcapsules led to a continuous increase in the concentration of HPC in the core, resulting in self-assembly into a cholesteric liquid crystal with a bright structural color. As the volume of the core bubble increased, the structural color of the cholesteric liquid crystal continuously underwent a blue shift. The resulting structural color was observable with the naked eye under a microscope within the visible light range, yielding cellulose cholesteric liquid crystal microbubbles.

[0070] Example 2

[0071] Dinuclear pure hydroxypropyl cellulose cholesteric phase liquid crystal microbubbles with different combinations were prepared by solvent extraction.

[0072] (1) Prepare the three-phase solution (internal, middle, and external phases), extractant:

[0073] 1.1) Internal phase solution: Two different concentrations of HPC aqueous solution were prepared according to Example 1 (the concentrations were both in the range of 20wt%-28wt%).

[0074] 1.2) Intermediate phase solution: ETPTA dispersion containing 1% photoinitiator by volume, stored at room temperature away from light.

[0075] 1.3) External phase solution: Prepare an aqueous solution of surfactant F108 with a concentration of 2%.

[0076] 1.4) Extractant: Anhydrous ethanol was selected as the hypertonic solution.

[0077] (2) Assemble the chip device and connect the device.

[0078] 2.1) Assembling the chip device: A seven-well capillary array is drawn on a Bunsen lamp. The inner phase capillary has an orifice diameter of 10-30 μm and is coaxially nested inside a middle phase capillary with an orifice diameter of approximately 150-280 μm. The combination of the inner and middle phase capillary is coaxially nested in the outer phase capillary. The three are connected by a square tube 3 and fixed to a glass slide with quick-drying adhesive. The other end of the seven-well capillary (the seven-well inner tube 5) is connected to a specific drawn capillary and fixed to a glass slide with quick-drying adhesive. The spotting needle is also fixed in place.

[0079] 2.2) Connection device: Load the internal, middle and external three-phase solutions into the syringe respectively, place the syringe on the mechanical pump, and connect the syringe to the chip's spotting needle and injection capillary with a polyethylene tube.

[0080] (3) Adjust the flow rate of the three phases inside, middle and outside to form droplets, and then cross-link and solidify them with ultraviolet light.

[0081] 3.1) Flow rate adjustment: Adjust the three-phase flow rate to obtain binuclear droplets of specific size and type. The commonly used internal phase flow rate range in this invention is 5 μL / h to 30 μL / h, the intermediate phase flow rate range is 0.1 ml / h to 0.3 ml / h, and the external phase flow rate range is 3 ml / h to 8 ml / h. The chip sample outlet is generally inserted directly into the collection bottle.

[0082] 3.2) Droplet formation and UV cross-linking curing: The formed double emulsion droplets with two component cores are initially cured by UV irradiation around the periphery of the collecting tube, and then fall into the collecting bottle containing the collecting liquid for final UV irradiation.

[0083] (4) Add the extractant and perform solvent extraction.

[0084] The prepared binuclear cellulose dispersion microcapsules with different initial core concentrations were placed in anhydrous ethanol and observed under a microscope. The binuclear cellulose dispersions with two different initial concentrations simultaneously underwent continuous dehydration. This continuous dehydration of the microcapsules led to a continuous increase in the concentration of HPC in the core, eventually resulting in self-assembly into cholesteric liquid crystals with bright structural colors, yielding cellulose cholesteric liquid crystal microbubbles. Due to the different initial core concentrations, the final structural color combinations varied as the core bubble volume increased, commonly including red-red, red-blue, red-green, green-green, green-blue, and blue-blue, among others.

[0085] Example 3

[0086] Mononuclear hydroxypropyl cellulose cholesteric phase liquid crystal microbubbles with a wide temperature-sensitive range were prepared by solvent extraction.

[0087] (1) Prepare the three-phase solution:

[0088] 1.1) Internal phase solution: A certain amount of HPC was added to an appropriate amount of pure water, and then 10% acrylamide was added relative to the mass ratio of HPC, so that the final concentration of HPC was 20wt%-28wt%. The mixture was stirred for 48 hours and then collected and stored at room temperature.

[0089] 1.2) Intermediate phase solution: ETPTA dispersion containing 1% photoinitiator by volume, stored at room temperature away from light.

[0090] 1.3) External phase solution: Prepare an aqueous solution of surfactant PVA with a concentration of 10%.

[0091] (2) Build the chip device and connect the device.

[0092] 2.1) Constructing the chip device: A single-hole capillary with an inner phase capillary orifice diameter of 30-80 μm is coaxially nested inside a capillary with an intermediate phase inner tube orifice diameter of approximately 120-180 μm. Using a square tube 3, the inner and middle tubes are coaxially nested inside an outer capillary with an inner tube pore diameter of 580 μm. The device is then fixed to a glass slide with quick-drying adhesive, and the spotting needle is secured.

[0093] 2.2) Connection device: Load the internal, middle and external three-phase solutions into the syringe respectively, place the syringe on the mechanical pump, and connect the syringe to the spotting needle of the chip through the polyethylene tube.

[0094] (3) Adjust the flow rate to form droplets and cure by ultraviolet cross-linking.

[0095] 3.1) Adjusting the sample flow rate: Adjust the sample flow rate to obtain a single-nuclear droplet of a specific size. The commonly used range for the internal phase flow rate in this invention is 10 μL / h to 50 μL / h; the range for the intermediate phase flow rate is 0.1 mL / h to 1 mL / h; and the range for the external phase flow rate is 1 mL / h to 5 mL / h.

[0096] 3.2) Droplet formation and UV crosslinking curing: The dual emulsion droplets are initially irradiated with UV light in the outer tube of the microfluidic chip to simply fix their morphology. Then, they are further irradiated with UV light in the collection bottle to completely cure them and obtain well-formed mononuclear microcapsules.

[0097] (4) Place it in the extractant and perform solvent extraction.

[0098] The microcapsules prepared above were placed in anhydrous ethanol and observed under a microscope. Under the action of ethanol, the microcapsules continuously lost water and generated bubbles. The continuous water loss of the microcapsules caused the concentration of HPC in the core to continuously increase. Later, they self-assembled into cholesteric liquid crystals with bright structural colors. As the volume of the core bubbles continued to increase, the structural color of the cholesteric liquid crystals also continuously underwent a blue shift, eventually yielding cellulose cholesteric liquid crystal microbubbles with blue structural colors.

[0099] (5) Cellulose cholesteric phase liquid crystal water bath heating

[0100] Cellulose cholesteric liquid crystal microbubbles with a blue structural color were heated in a water bath. As the temperature increased, the structural color of the microbubbles gradually shifted to red until it became colorless. The range of water bath temperature changes that displayed the structural color was significantly greater than that of pure hydroxypropyl cellulose cholesteric liquid crystal microbubbles (Example 1).

[0101] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing cellulose cholesteric liquid crystal microbubbles based on solvent extraction technology, characterized in that, The preparation method comprises the following steps: S1, configuring an initial concentration of cellulose aqueous solution as an inner phase; S2, configuring a hard polymer monomer solution containing a photoinitiator as an intermediate phase; S3, selecting a surfactant aqueous solution as an outer phase; S4, fluid injection of the inner phase obtained in step S1, the intermediate phase obtained in step S2, and the outer phase obtained in step S3 into a double emulsion microfluidic chip with a coaxial channel structure to obtain a double emulsion droplet; S5, under the irradiation of ultraviolet light, the outer layer is polymerized into a solid, thereby obtaining a microcapsule of cellulose dispersion liquid with a stable core-shell structure, and the microcapsule is subjected to ultraviolet curing again in a collection bottle to form a microcapsule with a hard shell layer; S6, the microcapsule with a hard shell layer obtained in step S5 is washed with pure water and then placed in an extractant to perform solvent extraction, the microcapsule continuously loses water under the action of the extractant, bubbles are generated in the interior, the concentration of the inner core cellulose continuously increases with the increase of the volume of the bubbles, and finally self-assembly is formed into a cholesteric liquid crystal with a structural color, i.e., the cellulose cholesteric liquid crystal microbubble; The double emulsion droplet is prepared by using a coaxial microfluidic device or a capillary array microfluidic device, so as to prepare a microcapsule of cellulose dispersion liquid with a stable core-shell structure. In the coaxial microfluidic device, an inner phase pipeline with a pipe diameter of 30-80 μm is coaxially nested and inserted into an intermediate phase pipeline with a pipe diameter of 120-180 μm and an inner hole diameter of 580 um, and then the inner phase pipeline and the intermediate phase pipeline are coaxially nested and connected to an outer phase pipeline with an inner hole diameter of 580 um through a square tube. The capillary array microfluidic device comprises the coaxial microfluidic device and a capillary array arranged on the inner phase pipeline.

2. The method of claim 1, wherein the cellulose cholesteric liquid crystal microbubbles are prepared based on a solvent extraction technique. In step S1, the inner phase is an initial low-concentration dispersion liquid of cellulose or cellulose derivative which can self-assemble into a cholesteric liquid crystal with bright structural color in a high concentration range. The cellulose or cellulose derivative is one of cellulose nanocrystals and hydroxypropyl cellulose molecules.

3. The method of claim 1, wherein the cellulose cholesteric liquid crystal microbubbles are prepared by a solvent extraction technique. In step S2, the intermediate phase is a hard polymer monomer solution containing a photoinitiator, which is insoluble in water, photocurable, and has a selective permeability effect after curing. The hard polymer monomer is one of ethoxylated trimethylolpropane triacrylate and trimethylolpropane triacrylate.

4. The method of claim 1, wherein the cellulose cholesteric liquid crystal microbubbles are prepared based on a solvent extraction technique. In step S3, the outer phase is a surfactant aqueous solution. The outer phase is one of polyvinyl alcohol, F108, or a PVA-F108 combination solution.

5. The method of claim 1, wherein the cellulose cholesteric liquid crystal microbubbles are prepared by a solvent extraction technique. In step S6, the extractant is one of ethanol, saturated sodium chloride solution, and saturated potassium chloride solution.

6. The preparation method of the cellulose cholesteric liquid crystal microbubble based on the solvent extraction technology according to claim 1, wherein in step S6, the microcapsules with different shell thicknesses have different reaction states under the action of the extractant during the solvent extraction process.

7. The method of claim 1, wherein the prepared cellulose cholesteric liquid crystal microbubbles have stable structural color, suspensibility and temperature sensitivity, and when heated in a water bath, the structural color of the cellulose cholesteric liquid crystal microbubbles is red-shifted; functional material molecules, including one of propylene glycol, acrylamide and ethylene glycol, are mixed in the inner phase cellulose dispersion liquid to expand the temperature sensitivity range of the prepared cellulose cholesteric liquid crystal microbubbles.

8. The method of claim 1, wherein the method combines microfluidics, confined space and solvent extraction.

9. The method of claim 1, wherein the cellulose cholesteric liquid crystal microbubbles are prepared by a solvent extraction technique. The number of inner cores and color combinations of the cellulose cholesteric liquid crystal microbubbles prepared by the method are controllable; by adjusting the initial concentration of different inner core compartments, different color combinations are obtained.

10. The cellulose cholesteric liquid crystal microbubbles prepared by the method of any one of claims 1-9.

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