A preparation method of a phase inversion window controlled methylimidazole ionic liquid oil-in-water nanoemulsion

Abstract

The application relates to a preparation method of a phase inversion window controlled methyl imidazole type ionic liquid oil-in-water nanoemulsion, and belongs to the technical field of emulsification and dispersion. The application realizes efficient crushing and stable dispersion of an oil phase in a water phase by constructing a transition emulsification system in a phase inversion critical interval and combining intermittent ultrasonic intensification; meanwhile, the adsorption and regulation of the methyl imidazole type ionic liquid at the oil / water interface promote the rapid rearrangement and densification of an interface layer, so that the oil-in-water nanoemulsion with a nanometer scale particle size, a narrow particle size distribution and good storage stability is obtained. The preparation method process is short, the process condition is mild, and the requirement for equipment is relatively low; stable emulsification can be realized through controllable intermittent ultrasonic and temperature control measures, key process parameters are easy to adjust, good repeatability and amplification feasibility are achieved, the method is suitable for large-scale preparation and engineering application, and has excellent industrial popularization prospect.

Description

Technical Field

[0001] This invention belongs to the field of emulsification and dispersion technology, and relates to a method for preparing a water-in-oil nanoemulsion of methylimidazolium ionic liquid with phase inversion window control. Background Technology

[0002] Oil-in-water emulsions are a typical colloidal dispersion system with significant application value in mineral flotation reagent dispersion, functional material precursor preparation, interfacial assembly, and multiphase mass transfer. Existing oil-in-water emulsions typically rely on mechanical stirring, high-shear homogenization, or the addition of conventional surfactants to disperse the oil phase in the aqueous phase. However, in practical applications, the following problems are still prevalent: First, it is difficult to further reduce the oil droplet size, resulting in emulsions that are mostly at the micrometer scale with a wide particle size distribution; second, the system is sensitive to temperature fluctuations, shear disturbances, and changes in water quality conditions, easily leading to droplet coalescence, stratification, or stability degradation; third, maintaining stability often requires high amounts of surfactant, which may lead to poor compatibility with subsequent processes or increased environmental burden, making it difficult to meet the requirements for "nanoscale, homogenization, and controllable stability" of emulsions.

[0003] Phase inversion is a commonly used technique for preparing nanoemulsions. It involves continuously adding an aqueous phase (or vice versa) to an oil phase, causing a continuous phase inversion at a specific critical point to obtain the target emulsion. Compared to traditional high-shear emulsification methods, phase inversion typically achieves lower interfacial tension and more complete interfacial rearrangement in the phase inversion critical region. The droplets tend to spontaneously refine during phase inversion, resulting in emulsion systems with smaller particle sizes and better dispersibility. Furthermore, the phase inversion process can be controlled by multiple factors such as the water-to-oil ratio, emulsifier system, and ionic strength, offering greater flexibility in formulation design and improving the storage stability and anti-agglomeration ability of the emulsion. However, existing phase inversion emulsification methods generally suffer from the following problems: Firstly, the system often crosses the phase inversion critical point all at once during the addition of water or oil, causing abrupt changes in the emulsion structure, making it difficult to finely control the phase inversion process and easily leading to a wider particle size distribution or even local instability. Secondly, traditional phase inversion methods often rely on adjusting a single parameter, such as the water-to-oil ratio or the amount of emulsifier, lacking effective control over the interfacial rearrangement behavior within the phase inversion critical region.

[0004] Ultrasonic technology, due to its cavitation effect, microjets, and localized instantaneous high energy density, can significantly enhance oil-water interface renewal and droplet breakage during emulsification, thereby reducing the dispersed phase particle size and improving dispersion uniformity. However, relying solely on ultrasound, the interfacial layer often struggles to achieve continuous and stable reconstruction, easily leading to droplet re-agglomeration after ultrasound shutdown or structural coarsening over time, resulting in insufficient emulsion stability.

[0005] Methylimidazole ionic liquids possess characteristics such as designable structure, tunable polarity, and strong interfacial adsorption capacity. Their molecular structure can simultaneously contain hydrophilic groups and hydrophobic alkyl chains, theoretically enabling them to form an adsorption layer at the oil / water interface and participate in interfacial stabilization. However, current technologies still lack a process route that can precisely control the phase inversion critical window during preparation and match the ionic liquid interface modulation with the ultrasonic disruption process, in order to stably obtain oil-in-water emulsions with nanoscale particle sizes suitable for practical applications.

[0006] Therefore, there is an urgent need to provide a method for preparing oil-in-water nanoemulsions by synergistically reconstructing the interface structure through phase inversion window control and ultrasonic enhancement, in order to solve the problems of difficult particle size reduction and insufficient stability in existing emulsification processes. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing a water-in-oil nanoemulsion of methylimidazolium ionic liquid with phase inversion window control. By constructing a transitional emulsification system in the phase inversion critical range and combining it with intermittent ultrasonic enhancement, the oil phase is efficiently broken down and stably dispersed in the aqueous phase. At the same time, the adsorption and regulation effect of methylimidazolium ionic liquid at the oil / water interface is utilized to promote the rapid rearrangement and densification of the interface layer, thereby obtaining a water-in-oil nanoemulsion with nanoscale particle size, narrow particle size distribution and good storage stability.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A method for preparing a water-in-oil nanoemulsion of a methylimidazolium ionic liquid with inversion window control includes the following steps:

[0010] Step 1. Preparation of the aqueous phase:

[0011] The aqueous phase includes an initiating phase aqueous solution A1 and a triggering phase aqueous solution A2, wherein, by mass fraction, the aqueous phase contains 5%~10% A1 and 90%~95% A2;

[0012] The preparation method of the initiator aqueous solution A1 is as follows: add methylimidazolium ionic liquid to deionized water at room temperature and stir until a homogeneous solution is obtained.

[0013] The trigger phase aqueous solution A2 is prepared by uniformly dissolving the electrolyte in neutral deionized water.

[0014] Step 2. First stage: Intermittent pulsed ultrasound treatment:

[0015] Initiator solution A1 was added to the oil phase at a set rate, and then the first stage of intermittent pulsed ultrasound was performed to obtain a water-in-oil overemulsion system.

[0016] Step 3. Second stage: intermittent pulsed ultrasound treatment:

[0017] The oil-in-water overemulsion system was subjected to a second stage of intermittent pulsed ultrasonic treatment, and the trigger phase solution A2 was added in a programmed manner to obtain a water-in-water nanoemulsion of methylimidazolium ionic liquid controlled by the phase inversion window.

[0018] The methylimidazolium-based ionic liquid oil-in-water nanoemulsion comprises, by mass fraction, 60%–90% aqueous phase and 10%–40% oil phase.

[0019] In step 2, during the first stage of intermittent pulsed ultrasound, the system temperature is 40℃~45℃, the ultrasound power is 10W-40W, the ultrasound working time is 6s~15s, and the interval time is 4s~12s; the total time from the start of the first stage to the end of the entire stage is taken as the total time of the first stage of intermittent pulsed ultrasound, which is 5min~10min.

[0020] In step 3, during the second stage of intermittent pulsed ultrasound, the system temperature is 40℃~45℃, the ultrasound power is 10W~50W, the ultrasound working time is 6s~12s, and the interval time is 4s~10s; the total time from the start of the second stage to the end of the entire stage is taken as the total time of the second stage of intermittent pulsed ultrasound, which is 2min~8min.

[0021] In step 1, the methylimidazolium ionic liquid is one of 1-octyl-3-methylimidazolium bromide, 1-dodecyl-3-methylimidazolium bromide, and 1-hexadecyl-3-methylimidazolium bromide; the methylimidazolium ionic liquid accounts for 0.05%~0.2% of the mass of the aqueous phase;

[0022] The electrolyte is KCl or NaCl; the electrolyte accounts for 0.06% to 0.3% of the mass of the aqueous phase.

[0023] In step 2, the oil phase is a nonpolar alkane, selected from one or a mixture of several of kerosene, diesel oil, and paraffin oil;

[0024] The set speed is 5 mL / min - 20 mL / min;

[0025] In step 3, the programmed addition method is to divide A2 into 10 equal parts and add them with an interval of 10-20 seconds between adjacent parts;

[0026] In step 3, ultrasonication is maintained during the addition of the trigger phase aqueous solution A2 to complete the interface rearrangement; then, the aqueous phase is added to allow the system to cross the window and complete the phase transition.

[0027] This invention utilizes a programmed feeding method to create a phase inversion critical window in the initial emulsion system, followed by controlled intermittent ultrasonic treatment of the transition system. This allows the oil phase to form fine, narrowly distributed droplets in the aqueous phase. The resulting dispersion structure is less prone to significant droplet formation and coarsening during subsequent settling, thus maintaining a relatively stable colloidal dispersion. By synergistically limiting the concentration of the methylimidazolium ionic liquid, the premixing conditions of the aqueous and oil phases, the staged feeding strategy, and the ultrasonic treatment mode and temperature control conditions, stable construction of an oil-in-water nanoemulsion dispersion structure can be achieved, improving the consistency and controllability of the system.

[0028] The method for preparing a phase-inverted window controlled methylimidazolium ionic liquid oil-in-water nanoemulsion disclosed in this invention has the following beneficial effects:

[0029] (1) This invention introduces intermittent ultrasonic enhancement of the emulsification process and combines the adsorption and structural regulation of methylimidazolium ionic liquids at the oil / water interface. Under the action of ultrasonic cavitation and microjets, the oil phase is broken, refined and redispersed, and nonpolar alkanes are uniformly dispersed in the aqueous phase. This results in a water-in-oil nanoemulsion system with smaller particle size and more uniform distribution, thereby improving the dispersibility and structural stability of the emulsion.

[0030] (2) This invention utilizes the synergistic effect of process control and ultrasonic treatment at the phase inversion critical window to form a stable oil-in-water emulsion without relying on a complex multi-component system; the preparation process parameters are controllable, the process route is clear, and the repeatability is good, which helps to reduce the process complexity and overall cost in the emulsion preparation process;

[0031] (3) The emulsified hydrocarbon dispersion system obtained by the present invention has good water phase compatibility and dispersion uniformity. Under static conditions, it is not easy to exhibit obvious stratification, aggregation or local enrichment of oil phase, which is conducive to obtaining an emulsion system with stable structure and consistent performance.

[0032] (4) The preparation method of the present invention has a relatively short process flow, mild process conditions, and relatively low equipment requirements; stable emulsification can be achieved through controllable intermittent ultrasound and temperature control measures, key process parameters are easy to adjust, and it has good repeatability and scale-up feasibility. It is suitable for large-scale preparation and engineering application and has good prospects for industrial promotion. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the preparation process of an ultrasound-based methylimidazolium ionic liquid oil-in-water emulsion according to the present invention. Detailed Implementation

[0034] This invention provides a method for preparing a water-in-oil nanoemulsion of a methylimidazolium ionic liquid controlled by a phase inversion window, the process flow of which is as follows: Figure 1 As shown, it includes the following steps:

[0035] Step 1. Preparation of the aqueous phase:

[0036] The aqueous phase includes an initiating phase aqueous solution A1 and a triggering phase aqueous solution A2, wherein, by mass fraction, the aqueous phase contains 5%~10% A1 and 90%~95% A2;

[0037] A methylimidazolium ionic liquid (one of 1-octyl-3-methylimidazolium bromide, 1-dodecyl-3-methylimidazolium bromide, or 1-hexadecyl-3-methylimidazolium bromide) was added to deionized water at room temperature (20℃-25℃) and stirred until a homogeneous solution was obtained, which was used as the initiating phase aqueous solution A1.

[0038] Dissolve the electrolyte KCl or NaCl uniformly in neutral deionized water to obtain the trigger phase aqueous solution A2.

[0039] By mass fraction, the aqueous phase contains 5%~10% A1, 90%~95% A2, 0.05%~0.2% methylimidazolium ionic liquid, and 0.06%~0.3% electrolyte.

[0040] Step 2. First stage: Intermittent pulsed ultrasound treatment:

[0041] Using one or a mixture of non-polar alkane kerosene, diesel oil, and paraffin oil as the oil phase, an initiator solution A1 is added to the oil phase at a rate of 5 mL / min-20 mL / min using a peristaltic pump. The first stage of intermittent pulsed ultrasound is performed at a system temperature of 40℃-45℃: the ultrasonic power is 10W-40W, the duration of each ultrasound session is 6s-15s, the interval is 4s-12s, and the total duration of the first stage of intermittent pulsed ultrasound is 5min-10min, resulting in a water-in-oil overemulsion system.

[0042] Step 3. Second stage: intermittent pulsed ultrasound treatment:

[0043] The second stage of intermittent pulsed ultrasonic treatment was performed on the water-in-oil overemulsion system at a temperature of 40℃~45℃. The ultrasonic power was set to 10W-50W, the duration of each ultrasonic session was 6s~12s, and the interval was 4s~10s, for a total duration of 2min~8min. After the start of the second stage of intermittent ultrasonic treatment, the trigger phase aqueous solution A2 was divided into 10 equal portions and added in stages, with an interval of 10s-20s between adjacent portions. This resulted in a water-in-oil nanoemulsion of methylimidazolium ionic liquid with a phase inversion window controlled by a mass fraction of 60%~90% aqueous phase and 10%~40% oil phase.

[0044] In the method provided by the present invention, a second stage of intermittent pulsed ultrasonic treatment is applied to the water-in-oil transition emulsion, and the trigger phase A2 is added to the system obtained in step 3 in a programmed manner to induce emulsion phase transition.

[0045] In the method provided by this invention, during the programmed addition of the trigger phase aqueous solution A2, the apparent viscosity of the system is recorded as a function of water addition. During the programmed addition of the trigger phase aqueous solution A2, a "first decrease, then increase, then decrease" pattern appears, and the viscosity decreases sharply. After all of the trigger phase aqueous solution A2 has been added, the system enters the phase inversion window and maintains ultrasonic action within this window to complete the interface rearrangement. Subsequently, the aqueous phase is added to allow the system to cross the window and complete the phase transformation, resulting in a methylimidazolium-based ionic liquid oil-in-water nanoemulsion.

[0046] The embodiments of the present invention will now be described in further detail with reference to the accompanying drawings.

[0047] The following embodiments are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0048] In the following examples, unless otherwise specified, "solution" refers to its aqueous solution, and the reagents and materials are commercially available.

[0049] Example 1:

[0050] This embodiment provides a method for preparing a water-in-oil nanoemulsion of a methylimidazolium ionic liquid with phase inversion window control, comprising the following steps:

[0051] Step 1: Preparation of aqueous phase A:

[0052] Aqueous phase A comprises A1 and A2. 1-Dodecyl-3-methylimidazole bromide is added to neutral deionized water at 23°C and stirred until fully dissolved to obtain a homogeneous and stable aqueous phase A1. A1 accounts for 5% of the total mass of aqueous phase A, and the 1-dodecyl-3-methylimidazole bromide ionic liquid accounts for 0.05% of the mass of aqueous phase A. KCl is added to neutral deionized water and stirred until completely dissolved to obtain A2; A2 accounts for 95% of the total mass of aqueous phase A, and the KCl accounts for 0.06% of the mass of aqueous phase A.

[0053] Step 2: Preparation of water-in-oil emulsion using intermittent pulsed ultrasound in the first stage:

[0054] Using kerosene as the oil phase, the oil phase was placed in a beaker, and Al was uniformly added to the oil phase at a rate of 10 mL / min using a peristaltic pump. An ultrasonic probe was inserted, and the first segment of intermittent pulsed ultrasound was applied without mechanical stirring. The ultrasonic power was 10 W; the pulse mode was: ultrasonic working time of 10 s and interval of 5 s. The total duration of the first segment of ultrasound was 10 min. During the ultrasound process, the system temperature was controlled at 40℃ through intermittent operation and external cooling, resulting in a water-in-oil transition emulsion system.

[0055] Step 3: Second stage intermittent pulse ultrasound:

[0056] A second stage of intermittent pulsed ultrasound treatment was applied to the water-in-oil transition emulsion. The trigger phase aqueous solution A2 was divided into 10 equal portions and added, with an interval of 10 seconds between adjacent portions. The power of the second stage of intermittent pulsed ultrasound was 20W; the pulse working mode was: ultrasound working time of 10 seconds and interval of 5 seconds. The total treatment time of the second stage of pulsed ultrasound was 5 minutes. During the ultrasound process, the system temperature was controlled at 40℃ through intermittent operation and external cooling.

[0057] During the addition of the trigger phase aqueous solution A2, the apparent viscosity of the system was recorded as a function of water addition. The system exhibited a pattern of "first decreasing, then increasing, and then decreasing" with a sharp decrease in viscosity. After all the trigger phase aqueous solution A2 was added, the system entered the phase inversion window and maintained ultrasonic treatment within this window to complete the interface rearrangement. Subsequently, the aqueous phase was added to allow the system to cross the window and complete the phase transition, resulting in a methylimidazolium-based ionic liquid oil-in-water nanoemulsion with a phase inversion window controlled by a mass fraction of 90% aqueous phase and 10% oil phase.

[0058] As shown in Table 1, the PDI of the emulsion obtained in this embodiment is 0.32, the D50 is 308 nm, and the surface tension is 25.5 mN / m. After centrifugation at 4000 rpm for 15 min, the centrifugal separation height of the emulsion is 0 cm. This indicates that under the process flow of this embodiment, the interfacial tension is effectively reduced, and the emulsion droplets can fully complete the interfacial rearrangement within the phase inversion window to form a relatively dense interfacial film. This results in smaller droplet size and more concentrated distribution, and the emulsion can still maintain phase stability and not separate under the action of centrifugal force. The mechanism can be attributed to the following: under the synergistic effect of programmed water addition and two-stage intermittent pulsed ultrasound, the system gradually crosses the phase inversion critical region, and the interfacial components have sufficient time for adsorption-rearrangement-densification. At the same time, the intermittent stage is conducive to heat release and cavitation intensity reduction, avoiding local overemulsification and re-agglomeration caused by continuous high energy input.

[0059] Example 2:

[0060] This embodiment provides a method for preparing a water-in-oil nanoemulsion of a methylimidazolium ionic liquid with phase inversion window control, comprising the following steps:

[0061] Step 1: Preparation of aqueous phase A:

[0062] Aqueous phase A comprises A1 and A2. 1-Octyl-3-methylimidazolium bromide is added to neutral deionized water at 24°C and stirred until fully dissolved to obtain a homogeneous and stable aqueous phase A1, which comprises 10% of the total volume of aqueous phase A. The 1-octyl-3-methylimidazolium bromide ionic liquid comprises 0.07% of the mass of aqueous phase A. NaCl is added to neutral deionized water and stirred until completely dissolved to obtain A2; A2 comprises 90% of the total volume of aqueous phase A, and the mass of NaCl comprises 0.1% of the mass of aqueous phase A.

[0063] Step 2: Preparation of water-in-oil emulsion using intermittent pulsed ultrasound in the first stage:

[0064] Using diesel fuel as the oil phase, the oil phase was placed in a beaker, and Al was uniformly added to the oil phase at a rate of 5 mL / min using a peristaltic pump. An ultrasonic probe was inserted, and the first segment of intermittent pulsed ultrasound was applied without mechanical stirring. The ultrasonic power was 20 W; the pulse working mode was: ultrasonic working time of 6 s and interval of 4 s. The total action time of the first segment of ultrasound was 8 min. During the ultrasound process, the system temperature was controlled at 42℃ through intermittent operation and external cooling, resulting in a water-in-oil transition emulsion system.

[0065] Step 3: Second stage intermittent pulse ultrasound:

[0066] A second stage of intermittent pulsed ultrasound treatment was applied to the water-in-oil transition emulsion. The trigger phase aqueous solution A2 was divided into 10 equal portions and added, with an interval of 15 seconds between adjacent portions. The power of the second stage of intermittent pulsed ultrasound was 10W; the pulse working mode was: ultrasound working time of 12 seconds and interval of 10 seconds. The total treatment time of the second stage of pulsed ultrasound was 8 minutes. During the ultrasound process, the system temperature was controlled at 42℃ through intermittent operation and external cooling.

[0067] During the addition of the trigger phase aqueous solution A2, the apparent viscosity of the system was recorded as a result of the addition of water. The system exhibited a pattern of "first decreasing, then increasing, and then decreasing" with a sharp decrease in viscosity. After all the trigger phase aqueous solution A2 was added, the system entered the phase inversion window and maintained ultrasonic treatment within this window to complete the interface rearrangement. Subsequently, the aqueous phase was added to allow the system to cross the window and complete the phase transformation, resulting in a methylimidazolium-based ionic liquid oil-in-water nanoemulsion with a phase inversion window controlled by a mass fraction of 75% aqueous phase and 25% oil phase.

[0068] Example 3:

[0069] This embodiment provides a method for preparing a water-in-oil nanoemulsion of a methylimidazolium ionic liquid with phase inversion window control, comprising the following steps:

[0070] Step 1: Preparation of aqueous phase A:

[0071] Aqueous phase A comprises A1 and A2. 1-Hexadecyl-3-methylimidazole bromide is added to neutral deionized water at 25°C and stirred until fully dissolved to obtain a homogeneous and stable aqueous phase A1, which comprises 7% of the total volume of aqueous phase A. The 1-hexadecyl-3-methylimidazole bromide ionic liquid comprises 0.2% of the mass of aqueous phase A. KCl is added to neutral deionized water and stirred until completely dissolved to obtain A2; A2 comprises 93% of the total volume of aqueous phase A, and the mass of KCl comprises 0.1% of the mass of aqueous phase A.

[0072] Step 2: Preparation of water-in-oil emulsion using intermittent pulsed ultrasound in the first stage:

[0073] Using paraffin oil as the oil phase, the oil phase was placed in a beaker, and Al was uniformly added to the oil phase at a rate of 20 mL / min using a peristaltic pump. An ultrasonic probe was inserted, and the first segment of intermittent pulsed ultrasound was applied without mechanical stirring. The ultrasonic power was 40 W; the pulse mode was: ultrasonic working time of 15 s and interval of 12 s. The total duration of the first segment of ultrasound was 5 min. During the ultrasound process, the system temperature was controlled at 45℃ through intermittent operation and external cooling, resulting in a water-in-oil transition emulsion system.

[0074] Step 3: Second stage intermittent pulse ultrasound:

[0075] A second stage of intermittent pulsed ultrasound treatment was applied to the water-in-oil transition emulsion. The trigger phase aqueous solution A2 was divided into 10 equal portions and added, with an interval of 15 seconds between adjacent portions. The power of the second stage of intermittent pulsed ultrasound was 50W; the pulse working mode was: ultrasound working time of 6 seconds and interval of 4 seconds. The total treatment time of the second stage of pulsed ultrasound was 2 minutes. During the ultrasound process, the system temperature was controlled at 45℃ through intermittent operation and external cooling.

[0076] During the addition of the trigger phase aqueous solution A2, the apparent viscosity of the system was recorded as a function of water addition. The system exhibited a pattern of "first decreasing, then increasing, and then decreasing" with a sharp decrease in viscosity. After all the trigger phase aqueous solution A2 was added, the system entered the phase inversion window and maintained ultrasonic treatment within this window to complete the interface rearrangement. Subsequently, the aqueous phase was added to allow the system to cross the window and complete the phase transition, resulting in a methylimidazolium-based ionic liquid oil-in-water nanoemulsion with a phase inversion window controlled by a mass fraction of 60% aqueous phase and 40% oil phase.

[0077] Example 4:

[0078] This embodiment provides a method for preparing a water-in-oil nanoemulsion of a methylimidazolium ionic liquid with phase inversion window control, comprising the following steps:

[0079] Step 1: Preparation of aqueous phase A:

[0080] Aqueous phase A comprises A1 and A2. 1-Dodecyl-3-methylimidazole bromide is added to neutral deionized water at 20°C and stirred until fully dissolved to obtain a homogeneous and stable aqueous phase A1, which comprises 5% of the total volume of aqueous phase A. The 1-dodecyl-3-methylimidazole bromide ionic liquid comprises 0.1% of the mass of aqueous phase A. KCl is added to neutral deionized water and stirred until completely dissolved to obtain A2; A2 comprises 95% of the total volume of aqueous phase A, and the mass of KCl comprises 0.3% of the mass of aqueous phase A.

[0081] Step 2: Preparation of water-in-oil emulsion using intermittent pulsed ultrasound in the first stage:

[0082] A mixture of kerosene and diesel oil (mass ratio 1:1) was used as the oil phase. The oil phase was placed in a beaker, and Al was uniformly added to the oil phase at a rate of 15 mL / min using a peristaltic pump. An ultrasonic probe was inserted, and the first segment of intermittent pulsed ultrasound was applied without mechanical stirring. The ultrasonic power was 15 W; the pulse mode was: ultrasonic working time of 10 s and interval of 10 s. The total duration of the first segment of ultrasound was 9 min. During the ultrasound process, the system temperature was controlled at 41℃ through intermittent operation and external cooling, resulting in a water-in-oil transition emulsion system.

[0083] Step 3: Second stage intermittent pulse ultrasound:

[0084] A second stage of intermittent pulsed ultrasound treatment was applied to the water-in-oil transition emulsion. The trigger phase aqueous solution A2 was divided into 10 equal portions and added, with an interval of 18 seconds between adjacent portions. The power of the second stage of intermittent pulsed ultrasound was 40W; the pulse working mode was: ultrasound working time of 8 seconds and interval of 6 seconds. The total treatment time of the second stage of pulsed ultrasound was 6 minutes. During the ultrasound process, the system temperature was controlled at 41℃ through intermittent operation and external cooling.

[0085] During the addition of the trigger phase aqueous solution A2, the apparent viscosity of the system was recorded as a result of the addition of water. The system exhibited a pattern of "first decreasing, then increasing, and then decreasing" with a sharp decrease in viscosity. After all the trigger phase aqueous solution A2 was added, the system entered the phase inversion window and maintained ultrasonic treatment within this window to complete the interface rearrangement. Subsequently, the aqueous phase was added to allow the system to cross the window and complete the phase transition, resulting in a methylimidazolium-based ionic liquid oil-in-water nanoemulsion with a phase inversion window controlled by a mass fraction of 65% aqueous phase and 35% oil phase.

[0086] Example 5:

[0087] This embodiment provides a method for preparing a water-in-oil nanoemulsion of a methylimidazolium ionic liquid with phase inversion window control, comprising the following steps:

[0088] Step 1: Preparation of aqueous phase A:

[0089] Aqueous phase A comprises A1 and A2. 1-Hexadecyl-3-methylimidazole bromide is added to neutral deionized water at 25°C and stirred until fully dissolved to obtain a homogeneous and stable aqueous phase A1, which comprises 7% of the total volume of aqueous phase A. The 1-hexadecyl-3-methylimidazole bromide ionic liquid comprises 0.15% of the mass of aqueous phase A. NaCl is added to neutral deionized water and stirred until completely dissolved to obtain A2; A2 comprises 93% of the total volume of aqueous phase A, and the mass of NaCl comprises 0.3% of the mass of aqueous phase A.

[0090] Step 2: Preparation of water-in-oil emulsion using intermittent pulsed ultrasound in the first stage:

[0091] A mixture of kerosene and paraffin oil (mass ratio 1:1) was used as the oil phase. The oil phase was placed in a beaker, and Al was uniformly added to the oil phase at a rate of 10 mL / min using a peristaltic pump. An ultrasonic probe was inserted, and the first segment of intermittent pulsed ultrasound was applied without mechanical stirring. The ultrasonic power was 20 W; the pulse mode was: ultrasonic working time of 12 s and interval of 12 s. The total duration of the first segment of ultrasound was 8 min. During the ultrasound process, the system temperature was controlled at 43℃ through intermittent operation and external cooling, resulting in a water-in-oil transition emulsion system.

[0092] Step 3: Second stage intermittent pulse ultrasound:

[0093] A second stage of intermittent pulsed ultrasound treatment was applied to the water-in-oil transition emulsion. The trigger phase aqueous solution A2 was divided into 10 equal portions and added, with an interval of 15 seconds between adjacent portions. The power of the second stage of intermittent pulsed ultrasound was 30W; the pulse working mode was: ultrasound working time of 7 seconds and interval of 8 seconds. The total treatment time of the second stage of pulsed ultrasound was 7 minutes. During the ultrasound process, the system temperature was controlled at 43℃ through intermittent operation and external cooling.

[0094] During the addition of the trigger phase aqueous solution A2, the apparent viscosity of the system was recorded as a function of water addition. The system exhibited a pattern of "first decreasing, then increasing, and then decreasing" with a sharp decrease in viscosity. After all the trigger phase aqueous solution A2 was added, the system entered the phase inversion window and maintained ultrasonic treatment within this window to complete the interface rearrangement. Subsequently, the aqueous phase was added to allow the system to cross the window and complete the phase transition, resulting in a methylimidazolium-based ionic liquid oil-in-water nanoemulsion with a phase inversion window controlled by a mass fraction of 70% aqueous phase and 30% oil phase.

[0095] Example 6:

[0096] This embodiment provides a method for preparing a water-in-oil nanoemulsion of a methylimidazolium ionic liquid with phase inversion window control, comprising the following steps:

[0097] Step 1: Preparation of aqueous phase A:

[0098] Aqueous phase A comprises A1 and A2. 1-Octyl-3-methylimidazolium bromide is added to neutral deionized water at 21°C and stirred until fully dissolved to obtain a homogeneous and stable aqueous phase A1. A1 accounts for 5% of the total mass of aqueous phase A, and the 1-octyl-3-methylimidazolium bromide ionic liquid accounts for 0.18% of the mass of aqueous phase A. NaCl is added to neutral deionized water and stirred until completely dissolved to obtain A2; A2 accounts for 95% of the total mass of aqueous phase A, and the mass of NaCl accounts for 0.06% of the mass of aqueous phase A.

[0099] Step 2: Preparation of water-in-oil emulsion using intermittent pulsed ultrasound in the first stage:

[0100] A mixture of diesel and paraffin oil (mass ratio 1:1) was used as the oil phase. The oil phase was placed in a beaker, and Al was uniformly added to the oil phase at a rate of 8 mL / min using a peristaltic pump. An ultrasonic probe was inserted, and the first segment of intermittent pulsed ultrasound was applied without mechanical stirring. The ultrasonic power was 30 W; the pulse mode was: ultrasonic working time of 8 s and interval of 6 s. The total duration of the first segment of ultrasound was 6 min. During the ultrasound process, the system temperature was controlled at 42℃ through intermittent operation and external cooling, resulting in a water-in-oil transition emulsion system.

[0101] Step 3: Second stage intermittent pulse ultrasound:

[0102] A second stage of intermittent pulsed ultrasound treatment was applied to the water-in-oil transition emulsion. The trigger phase aqueous solution A2 was divided into 10 equal portions and added, with an interval of 12 seconds between adjacent portions. The power of the second stage of intermittent pulsed ultrasound was 10W; the pulse working mode was: ultrasound working time of 6 seconds and interval of 10 seconds. The total treatment time of the second stage of pulsed ultrasound was 8 minutes. During the ultrasound process, the system temperature was controlled at 42℃ through intermittent operation and external cooling.

[0103] During the addition of the trigger phase aqueous solution A2, the apparent viscosity of the system was recorded as a function of water addition. The system exhibited a pattern of "first decreasing, then increasing, and then decreasing" with a sharp decrease in viscosity. After all the trigger phase aqueous solution A2 was added, the system entered the phase inversion window and maintained ultrasonic treatment within this window to complete the interface rearrangement. Subsequently, the aqueous phase was added to allow the system to cross the window and complete the phase transition, resulting in a methylimidazolium-based ionic liquid oil-in-water nanoemulsion with a phase inversion window controlled by a mass fraction of 80% aqueous phase and 20% oil phase.

[0104] Example 7:

[0105] This embodiment provides a method for preparing a water-in-oil nanoemulsion of a methylimidazolium ionic liquid with phase inversion window control, including the following steps: Step 1: Preparation of aqueous phase A:

[0106] Aqueous phase A comprises A1 and A2. 1-Dodecyl-3-methylimidazolium bromide is added to neutral deionized water at 24°C and stirred until fully dissolved to obtain a homogeneous and stable aqueous phase A1, which comprises 10% of the total volume of aqueous phase A. The 1-octyl-3-methylimidazolium bromide ionic liquid comprises 0.2% of the mass of aqueous phase A. KCl is added to neutral deionized water and stirred until completely dissolved to obtain A2; A2 comprises 90% of the total volume of aqueous phase A; the KCl mass comprises 0.2% of the mass of aqueous phase A.

[0107] Step 2: Preparation of water-in-oil emulsion using intermittent pulsed ultrasound in the first stage:

[0108] A mixture of kerosene, diesel oil, and paraffin oil (mass ratio 1:1:1) was used as the oil phase. The oil phase was placed in a beaker, and Al was uniformly added to the oil phase at a rate of 6 mL / min using a peristaltic pump. An ultrasonic probe was inserted, and the first segment of intermittent pulsed ultrasound was applied without mechanical stirring. The ultrasonic power was 20 W; the pulse mode was: ultrasonic working time of 10 s and interval of 8 s. The total duration of the first segment of ultrasound was 8 min. During the ultrasound process, the system temperature was controlled at 40℃ through intermittent operation and external cooling, resulting in a water-in-oil transition emulsion system.

[0109] Step 3: Second stage intermittent pulse ultrasound:

[0110] A second stage of intermittent pulsed ultrasonic treatment was applied to the water-in-oil transition emulsion. The trigger phase aqueous solution A2 was divided into 10 equal portions and added, with an interval of 20 seconds between adjacent portions. The power of the second stage of intermittent pulsed ultrasonic treatment was 20W; the pulse working mode was: ultrasonic working time of 10 seconds and interval of 5 seconds. The total treatment time of the second stage of pulsed ultrasonic treatment was 7 minutes. During the ultrasonic treatment, the system temperature was controlled at 40℃ through intermittent operation and external cooling.

[0111] During the addition of the trigger phase aqueous solution A2, the apparent viscosity of the system was recorded as a result of the addition of water. The system exhibited a pattern of "first decreasing, then increasing, and then decreasing" with a sharp decrease in viscosity. After all the trigger phase aqueous solution A2 was added, the system entered the phase inversion window and maintained ultrasonic treatment within this window to complete the interface rearrangement. Subsequently, the aqueous phase was added to allow the system to cross the window and complete the phase transition, resulting in a methylimidazolium-based ionic liquid oil-in-water nanoemulsion with a phase inversion window controlled by a mass fraction of 85% aqueous phase and 15% oil phase.

[0112] Comparative Example 1:

[0113] Step 1: Preparation of aqueous phase A:

[0114] At 23°C, 1-dodecyl-3-methylimidazole bromide and KCl were added to deionized water with a neutral pH and stirred until fully dissolved to obtain a homogeneous and stable aqueous phase A. The 1-dodecyl-3-methylimidazole bromide ionic liquid accounted for 0.05% of the mass of aqueous phase A, and the KCl accounted for 0.06% of the mass of aqueous phase A.

[0115] Step 2: Preparation of water-in-oil emulsion using intermittent pulsed ultrasound:

[0116] Using kerosene as the oil phase, the oil phase was placed in a beaker, and component A was uniformly added to the oil phase at a rate of 10 mL / min using a peristaltic pump. An ultrasonic probe was inserted, and intermittent pulsed ultrasound was applied without mechanical stirring. The ultrasonic power was 10 W; the pulse working mode was: ultrasonic working time of 10 s and interval of 5 s. The total ultrasonic treatment time was 10 min. During the ultrasonic process, the system temperature was controlled at 40 °C through intermittent operation and external cooling, resulting in an oil-in-water emulsion with a mass fraction of 85% aqueous phase and 15% oil phase.

[0117] Table 1 shows that the surface tension of the emulsion obtained in Comparative Example 1 increased to 33.8 mN / m, while the droplet size increased (D50 = 670 nm) and the distribution became wider (PDI = 0.74). Under the action of centrifugation, the weaker interfacial film was more easily damaged, inducing droplet aggregation and phase separation, thus resulting in a clear 1 cm stratification after centrifugation. The above results indicate that without phase inversion control, the system may cross the phase inversion critical point in one go during water addition, leading to abrupt changes in the interfacial structure and local phase heterogeneity, resulting in insufficient interfacial rearrangement and an insufficiently dense and stable interfacial film formed on the droplet surface.

[0118] Comparative Example 2:

[0119] Step 1: Preparation of aqueous phase A:

[0120] Aqueous phase A comprises A1 and A2. A suitable amount of neutral deionized water is taken at 23℃ to obtain a homogeneous and stable aqueous phase A1, which accounts for 5% of the total mass of aqueous phase A. 1-Dodecyl-3-methylimidazolium bromide ionic liquid accounts for 0% of the mass of aqueous phase A. KCl is added to neutral deionized water and stirred until completely dissolved to obtain A2; A2 accounts for 95% of the total mass of aqueous phase A; and the mass of KCl accounts for 0.06% of the mass of aqueous phase A.

[0121] Step 2: Preparation of water-in-oil emulsion using intermittent pulsed ultrasound in the first stage:

[0122] Using kerosene as the oil phase, the oil phase was placed in a beaker, and Al was uniformly added to the oil phase at a rate of 10 mL / min using a peristaltic pump. An ultrasonic probe was inserted, and the first segment of intermittent pulsed ultrasound was applied without mechanical stirring. The ultrasonic power was 10 W; the pulse mode was: ultrasonic working time of 10 s and interval of 5 s. The total duration of the first segment of ultrasound was 10 min. During the ultrasound process, the system temperature was controlled at 40℃ through intermittent operation and external cooling, resulting in a water-in-oil transition emulsion system.

[0123] Step 3: Second stage intermittent pulse ultrasound:

[0124] A second stage of intermittent pulsed ultrasound treatment was applied to the water-in-oil transition emulsion. The trigger phase aqueous solution A2 was divided into 10 equal portions and added, with an interval of 10 seconds between adjacent portions. The power of the second stage of intermittent pulsed ultrasound was 20W; the pulse working mode was: ultrasound working time of 10 seconds and interval of 5 seconds. The total treatment time of the second stage of pulsed ultrasound was 5 minutes. During the ultrasound process, the system temperature was controlled at 40℃ through intermittent operation and external cooling.

[0125] During the addition of the trigger phase aqueous solution A2, the apparent viscosity of the system was recorded as the water was added. When the viscosity decreased first, then increased and then decreased again and a sharp decrease occurred, the system was determined to have entered the phase inversion window. The ultrasonic action was maintained within this window to complete the interface rearrangement. Subsequently, the aqueous phase was added to allow the system to cross the window and complete the phase transformation, resulting in an oil-in-water emulsion with 90% aqueous phase and 10% oil phase by mass fraction.

[0126] As shown in Table 1, the emulsion obtained in Comparative Example 2 lacks key interfacial stabilizing components, making it difficult to effectively reduce interfacial tension and build an interfacial film in the phase inversion critical region. This deficiency is directly reflected in a significantly high surface tension (52.0 mN / m), insufficient emulsification leading to the formation of large droplets (D50 = 10 μm) and oil-water separation, with a centrifugal separation height reaching 2 cm. The mechanism is that the lack of interfacial adsorption and electrostatic stabilization by ionic liquids makes it difficult for the interfacial film to form quickly and its strength is insufficient. The droplets easily aggregate and rapidly destabilize, resulting in the worst overall stability.

[0127] Comparative Example 3:

[0128] Step 1: Preparation of aqueous phase A:

[0129] Aqueous phase A comprises A1 and A2. 1-Dodecyl-3-methylimidazole bromide is added to neutral deionized water at 23°C and stirred until fully dissolved to obtain a homogeneous and stable aqueous phase A1. A1 accounts for 5% of the total mass of aqueous phase A, and the 1-dodecyl-3-methylimidazole bromide ionic liquid accounts for 0.05% of the mass of aqueous phase A. KCl is added to neutral deionized water and stirred until completely dissolved to obtain A2; A2 accounts for 95% of the total mass of aqueous phase A, and the KCl accounts for 0.06% of the mass of aqueous phase A.

[0130] Step 2: Preparation of water-in-oil emulsion using intermittent pulsed ultrasound in the first stage:

[0131] Using kerosene as the oil phase, the oil phase was placed in a beaker, and Al was uniformly added to the oil phase at a rate of 10 mL / min using a peristaltic pump. An ultrasonic probe was inserted, and the first segment of intermittent pulsed ultrasound was applied without mechanical stirring. The ultrasonic power was 10 W; the pulse mode was: ultrasonic working time of 10 s and interval of 3 s. The total duration of the first segment of ultrasound was 10 min. During the ultrasound process, the system temperature was controlled at 40℃ through intermittent operation and external cooling, resulting in a water-in-oil transition emulsion system.

[0132] Step 3: Second stage intermittent pulse ultrasound:

[0133] A second stage of intermittent pulsed ultrasound treatment was applied to the water-in-oil transition emulsion. The trigger phase aqueous solution A2 was divided into 10 equal portions and added, with an interval of 10 seconds between adjacent portions. The power of the second stage of intermittent pulsed ultrasound was 20W; the pulse working mode was: ultrasound working time of 10 seconds and interval of 3 seconds. The total treatment time of the second stage of pulsed ultrasound was 5 minutes. During the ultrasound process, the system temperature was controlled at 40℃ through intermittent operation and external cooling.

[0134] During the addition of the trigger phase aqueous solution A2, the apparent viscosity of the system was recorded as a function of water addition. When the viscosity decreased first, then increased, and then decreased again, and a sharp decrease occurred, the system was determined to have entered the phase inversion window. Within this window, ultrasonic treatment was maintained to complete the interface rearrangement. Subsequently, the aqueous phase was added to allow the system to cross the window and complete the phase transition, resulting in a methylimidazolium-based ionic liquid oil-in-water nanoemulsion with a phase inversion window controlled by a mass fraction of 90% aqueous phase and 10% oil phase.

[0135] Particle size and surface tension were tested on the emulsions obtained in Example 1 and different comparative examples. Then, the different emulsions were centrifuged at 4000 rpm for 15 min, and the centrifugation separation height was measured. The results are shown in Table 1.

[0136] Table 1. Comparison of particle size distribution parameters, centrifugal stability and surface tension of emulsions from different samples;

[0137] ;

[0138] Among them, PDI is the polydispersity index, and the smaller the value, the narrower the particle size distribution and the more uniform the system; D50 is the median droplet size; centrifugal stratification height is the stratification height that appears after the sample is centrifuged, which is used to characterize the centrifugal stability of the emulsion. The smaller the stratification height, the better the stability; the surface tension is measured in mN / m, and the lower the value, the more sufficient the interfacial tension reduction and the stronger the interfacial adsorption / stabilization effect.

[0139] As shown in Table 1, although the emulsion obtained in Comparative Example 3 could still form an emulsion, the results showed that the PDI further increased to 0.92, the D50 increased to 842 nm, and slight stratification of 0.3 cm appeared after centrifugation, with the surface tension increasing to 38.6 mN / m. The mechanism is that too short an interval time will cause the energy input to exhibit an "over-dense pulse" rhythm, and the interfacial adsorption and rearrangement process is not completed before being subjected to cavitation disturbance again. At the same time, the temperature rise and local shear accumulation of the system are more obvious, which easily causes the emulsion droplets to re-aggregate during the formation process, resulting in a wider particle size distribution and a reduced degree of densification of the interfacial film. Therefore, the slight stratification under the action of centrifugal force indicates that its centrifugal stability is inferior to that of Example 1. It can be seen that appropriately extending the interval stage (such as 5 s in Example 1) can provide the necessary time for interfacial rearrangement and heat release, which is beneficial to obtaining an emulsion system with smaller particle size, narrower distribution and higher stability.

[0140] In summary, the data in Table 1 show that the process of the present invention can achieve more complete interfacial rearrangement and interfacial film densification in the phase inversion critical region, significantly reduce surface tension and inhibit droplet aggregation, thereby obtaining emulsions with smaller particle size, narrower distribution and higher centrifugal stability. However, the absence of phase inversion window control, lack of ionic liquid interfacial stabilization, or mismatch of intermittent rhythms will all lead to insufficient interfacial film construction, widened particle size distribution and varying degrees of centrifugal stratification, resulting in decreased system stability.

Claims

1. A method for preparing a water-in-oil nanoemulsion of a methylimidazolium ionic liquid controlled by a phase inversion window, characterized in that, Includes the following steps: Step 1. Preparation of the aqueous phase: The aqueous phase includes an initiating phase aqueous solution A1 and a triggering phase aqueous solution A2, wherein, by mass fraction, the aqueous phase contains 5%~10% A1 and 90%~95% A2; The preparation method of the initiator aqueous solution A1 is as follows: add methylimidazolium ionic liquid to deionized water at room temperature and stir until a homogeneous solution is obtained. The trigger phase aqueous solution A2 is prepared by uniformly dissolving the electrolyte in neutral deionized water. Step 2. First stage: Intermittent pulsed ultrasound treatment: Initiator solution A1 was added to the oil phase at a set rate, and then the first stage of intermittent pulsed ultrasound was performed to obtain a water-in-oil overemulsion system. Step 3. Second stage: intermittent pulsed ultrasound treatment: The oil-in-water overemulsion system was subjected to a second stage of intermittent pulsed ultrasonic treatment, and the trigger phase solution A2 was added in a programmed manner to obtain a water-in-water nanoemulsion of methylimidazolium ionic liquid controlled by the phase inversion window. The methylimidazolium-based ionic liquid oil-in-water nanoemulsion comprises, by mass fraction, 60%–90% aqueous phase and 10%–40% oil phase; In step 3, the programmed addition of the trigger phase solution A2 involves dividing A2 into 10 equal portions and adding them with an interval of 10-20 seconds between adjacent portions.

2. The method for preparing a phase-inverted window controlled methylimidazolium ionic liquid oil-in-water nanoemulsion according to claim 1, characterized in that, In step 2, during the first stage of intermittent pulsed ultrasound, the system temperature is 40℃~45℃, the ultrasound power is 10W-40W, the ultrasound working time is 6s~15s, and the interval time is 4s~12s. The total time from the start of the first stage to the end of the entire stage is the total time of the first stage of intermittent pulsed ultrasound, which is 5min~10min.

3. The method for preparing a phase-inverted window controlled methylimidazolium ionic liquid oil-in-water nanoemulsion according to claim 1, characterized in that, In step 3, during the second stage of intermittent pulsed ultrasound, the system temperature is 40℃~45℃, the ultrasound power is 10W~50W, the ultrasound working time is 6s~12s, and the interval time is 4s~10s. The total time taken from the start of the second stage to the end of the entire stage is the total time of the second stage of intermittent pulsed ultrasound, which is 2min~8min.

4. A method for preparing a phase-inverted window controlled methylimidazolium ionic liquid oil-in-water nanoemulsion according to claim 2 or 3, characterized in that, In step 1, the methylimidazolium ionic liquid is one of 1-octyl-3-methylimidazolium bromide, 1-dodecyl-3-methylimidazolium bromide, and 1-hexadecyl-3-methylimidazolium bromide; the methylimidazolium ionic liquid accounts for 0.05% to 0.2% of the mass of the aqueous phase.

5. A method for preparing a phase-inverted window controlled methylimidazolium ionic liquid oil-in-water nanoemulsion according to claim 2 or 3, characterized in that, The electrolyte is KCl or NaCl; the electrolyte accounts for 0.06% to 0.3% of the mass of the aqueous phase.

6. A method for preparing a phase-inverted window controlled methylimidazolium ionic liquid oil-in-water nanoemulsion according to claim 2 or 3, characterized in that, In step 2, the oil phase is a nonpolar alkane, selected from one or a mixture of kerosene, diesel oil, and paraffin oil.

7. A method for preparing a phase-inverted window controlled methylimidazolium ionic liquid oil-in-water nanoemulsion according to claim 2 or 3, characterized in that, In step 2, the set speed is 5 mL / min-20 mL / min.

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