Surfactant-free oil-water two-phase emulsion and preparation method thereof

Abstract

The invention relates to the technical field of chemistry, in particular to a surfactant-free oil-water two-phase emulsion and a preparation method thereof, an abnormally stable emulsion can be prepared only by pure oil-water two-phase liquid without adding any third-party component due to the fact that a layer of film is generated at an oil-water interface. Ester groups of oil phase molecules on the membrane are anchored on an oil-water interface, droplet aggregation is effectively inhibited, the emulsion can still be used for preparing an oil-in-water emulsion, a water-in-oil emulsion and a double emulsion without adjustment of a surfactant, the emulsion shows excellent performance in the aspect of oil-water separation, the separation rate is up to 90% or above, and the oil-water separation effect is good. And a new thought and direction are provided for research and application of the pure two-phase emulsion.

Description

Technical Field

[0001] The present invention relates to the field of chemical technology, and specifically, to an oil-water two-phase emulsion without surfactant and a preparation method thereof. Background Art

[0002] An emulsion is a dispersion system composed of two immiscible liquid phases (usually an oil / water system), and its stability depends on the adsorption and self-assembly behavior of nanoparticles or colloidal particles at the liquid-liquid interface. Such systems have shown important technical value in fields such as the food industry, coating preparation, cosmetics development, and drug delivery due to their unique interfacial properties. It should be noted that traditional emulsion systems generally rely on the interfacial regulation of surfactants (such as sodium dodecyl sulfate and Tween series, etc.). Surfactants can induce repulsive interactions to prevent spontaneous coalescence. However, the inherent defects of such compounds in terms of biotoxicity, environmental accumulation, and sustainability have made it difficult to meet the innovation requirements of green chemistry and sustainable development concepts for chemical technology. Against this background, the development of two-phase emulsions without adding any surfactants or solvents has become an important research direction, and the emulsion can be prevented from coalescing within a few weeks through interfacial molecular interactions.

[0003] Currently, due to the wide use of surfactants, emulsified droplets are small in volume and difficult to settle, which has become a challenging problem in water-oil separation. Therefore, many stimulus-responsive small molecules or polymers are molecularly adsorbed or chemically grafted onto surfactant molecules to customize hydrophilic / hydrophobic properties, and these properties can achieve the effect of oil-water separation through external stimuli (such as temperature, pH, magnetic field, or light), but the effect is not very prominent. On this basis, researchers have developed superwetting membrane materials to achieve the separation of immiscible oil / water mixtures. Although the whole process is environmentally friendly and has no secondary pollution, and the purified oil or water can be directly recycled, the preparation process is very complex and some reagents are relatively expensive. Starting from the source, it is particularly important to develop an emulsion with simple operation and fast separation speed. Summary of the Invention

[0004] The content of the present invention is to provide an oil-water two-phase emulsion without surfactant and a preparation method thereof, in order to fill the technical gap in the existing technology that lacks oil-water two-phase emulsions without surfactant, and at the same time lay a foundation for the subsequent application of oil-water two-phase emulsions without surfactant in environmental protection and green chemical technology.

[0005] An oil-water two-phase emulsion without surfactant according to the present invention includes an oil phase and a water phase. The water phase is ultrapure water, and the oil phase is dioctyl phthalate, without adding any surfactant.

[0006] Preferably, by volume fraction, the emulsion comprises 1 / 3 aqueous phase and 2 / 3 oil phase.

[0007] Preferably, a thin film is formed on the oil-water interface of the emulsion, which can prevent the fusion of two oil droplets, and this thin film is spontaneously anchored at the oil-water interface by the ester group of dioctyl phthalate due to partial hydrophilicity.

[0008] Preferably, the emulsion can separately prepare water-in-oil two-phase emulsion and oil-in-water two-phase emulsion without surfactant.

[0009] The present invention provides a method for preparing a surfactant-free oil-water two-phase emulsion, which adopts one of the above two-phase emulsions and comprises the following steps:

[0010] Add 2 mL of dioctyl phthalate to 1 mL of ultrapure water, and then perform ultrasonic treatment at 100 W for 15 s to obtain a surfactant-free oil-water two-phase emulsion.

[0011] Preferably, the emulsion can prepare double emulsion. The specific steps are to first prepare an oil-in-water emulsion, and then add an equal volume of oil phase to the inside on this basis. After ultrasonic treatment, a double emulsion is successfully formed.

[0012] Preferably, the emulsion has high separation and recovery characteristics. The method of separation and recovery is to place the emulsion in an environment of -18 °C for 30 min. The aqueous phase will start to freeze, while the oil phase remains liquid. Then, centrifuge the emulsion at 10,000 rpm for 8 min to separate the frozen aqueous phase and the unfrozen oil phase.

[0013] The present invention provides a surfactant-free oil-water two-phase emulsion and a preparation method. A thin film is spontaneously formed on the interface of the oil phase and water. The ester groups of the oil phase molecules are anchored at the interface, effectively inhibiting the droplets from aggregating together, thus making this thin film extremely stable. Therefore, the emulsion can remain stable for a long time without surfactant or any other third-party components. The present invention comprehensively elaborates the new mechanism of the formation of water-in-oil emulsion, oil-in-water emulsion and double emulsion of the surfactant-free oil-water two-phase emulsion. The present invention explores the mechanism of its easy separation and high recovery, and finds that the separation and recovery rate of the emulsion is over 90%. This innovative research not only provides a new perspective for the formation mechanism of the surfactant-free oil-water two-phase emulsion, but also lays a foundation for its application in environmental protection and green chemical engineering technology. Description of the Drawings

[0014] Figure 1 Optical microscope images of surfactant-free oil-water two-phase emulsions with 3 different oil-water volume ratios;

[0015] Figure 2Rheology characteristic diagrams of surfactant-free oil-water two-phase emulsions with 3 different oil-water volume ratios;

[0016] Figure 3 Thermal stability data diagrams of surfactant-free oil-water two-phase emulsions with 3 different oil-water volume ratios;

[0017] Figure 4 Freeze-thaw stability data diagrams of surfactant-free oil-water two-phase emulsions with 3 different oil-water volume ratios;

[0018] Figure 5 Storage stability data diagrams of surfactant-free oil-water two-phase emulsions with 3 different oil-water volume ratios;

[0019] Figure 6 Molecular dynamics data diagrams of oil-in-water emulsions in surfactant-free oil-water two-phase emulsions with an oil-water volume ratio of 2:1;

[0020] Figure 7 Optical microscope diagrams of double emulsions prepared from oil-in-water emulsions in surfactant-free oil-water two-phase emulsions with an oil-water volume ratio of 2:1;

[0021] Figure 8 Separation and recovery data diagrams of surfactant-free oil-water two-phase emulsions with an oil-water volume ratio of 2:1;

[0022] Figure 9 Separation and recovery data diagrams during 10 cycles of surfactant-free oil-water two-phase emulsions with an oil-water volume ratio of 2:1. Detailed implementation manners

[0023] To further understand the content of the present invention, the present invention will be described in detail in combination with the accompanying drawings and embodiments. It should be understood that the embodiments are only for explaining the present invention rather than limiting it.

[0024] Embodiment 1

[0025] This embodiment provides a surfactant-free oil-water two-phase emulsion, including an oil phase and a water phase. More specifically, the emulsion has only one oil phase and one water phase and no third-party components are involved (no surfactants are added); the water phase is ultrapure water, and the oil phase is dioctyl phthalate.

[0026] By volume fraction, the emulsion includes 1 / 3 of the water phase and 2 / 3 of the oil phase.

[0027] The emulsion forms a thin film at the oil-water interface. This thin film can prevent the fusion of two oil droplets, and this film is spontaneously anchored at the oil-water interface by the ester groups of dioctyl phthalate due to partial hydrophilicity. This not only enables the emulsion to form quickly but also keeps it stable for several weeks. When the droplets of this emulsion approach each other, they exhibit unique interactions: they do not coalesce but bind together in an adhesive manner while maintaining their respective integrity.

[0028] The emulsion has good rheological properties and stability properties (including thermal stability, freeze-thaw stability, and storage stability).

[0029] The emulsion can respectively prepare water-in-oil surfactant-free oil-water two-phase emulsion and oil-in-water surfactant-free oil-water two-phase emulsion without surfactants, and the specific steps are as follows:

[0030] Adjust the oil-water volume ratio of the surfactant-free oil-water two-phase emulsion. When the volume of the oil phase exceeds the volume of the water phase by 1 time, the system will exhibit unique kinetic behavior. Under the action of external forces such as ultrasonic waves, positive waveform motion begins to occur at the oil-water interface. As the external force continues to act, the waveform gradually approaches a circle. In each half cycle of the fluctuation, the two ends of the waveform come into contact with each other, and finally a well-defined structure is formed: the upper layer is a water-in-oil emulsion, and the lower layer is an oil-in-water emulsion.

[0031] This embodiment provides a method for preparing a surfactant-free oil-water two-phase emulsion, which uses the above-mentioned surfactant-free oil-water two-phase emulsion and includes the following steps:

[0032] Add 2 mL of dioctyl phthalate to 1 mL of ultrapure water, and then perform ultrasonic treatment at 100 W for 15 s to obtain a surfactant-free oil-water two-phase emulsion.

[0033] The emulsion can prepare double emulsions. The specific steps are to first prepare an oil-in-water emulsion, and then add an equal volume of oil phase to its interior. After ultrasonic treatment at 100 W for 30 s, a double emulsion is successfully formed.

[0034] The emulsion has high separation and recovery characteristics. The method for separation and recovery is to place the emulsion in an environment at -18 °C for 30 min. The water phase will start to freeze, while the oil phase remains liquid. Then, centrifuge the emulsion at 10000 rpm for 8 min to separate the frozen water phase and the unfrozen oil phase.

[0035] This embodiment provides an oil-water two-phase emulsion without surfactant. A thin film is spontaneously formed on the interface of water by the oil phase. The ester groups of the oil-phase molecules are anchored to the interface, effectively inhibiting the droplets from aggregating together, thus making this thin film extremely stable. Therefore, the emulsion can remain stable for a long time without surfactant or any other third-party components. This embodiment comprehensively elaborates the new mechanism for the formation of oil-in-water emulsion, water-in-oil emulsion and double emulsion of the oil-water two-phase emulsion without surfactant. This embodiment explores the mechanism of its easy separation and high recovery, and finds that the separation recovery rate of this emulsion is as high as over 90%. This innovative research not only provides a new perspective for the formation mechanism of the emulsion, but also lays a foundation for its application in environmental protection and green chemical engineering technology.

[0036] Example 2

[0037] Performance tests were carried out in this embodiment as follows:

[0038] 1. The test method for the rheological properties of the oil-water two-phase emulsion without surfactant is as follows: The rheological behavior of the emulsion was analyzed using a stress-controlled rheometer. The sample was placed between two parallel plates (d = 49.978 mm), and the measurement position was 1 mm. The excess emulsion was removed, and a thin layer of paraffin oil was applied to the exposed edge of the emulsion gel to prevent water loss. The shear rate was increased from 1 s -1 to 100 s -1 , and the viscosity of the emulsion was recorded. At the same time, with the change of the angular frequency, the viscoelastic moduli, including the storage modulus (G') and the loss modulus (G''), were recorded. This test was repeated 3 times.

[0039] 2. The verification method for the thermal stability of the oil-water two-phase emulsion without surfactant is as follows: The freshly prepared emulsion was placed in a water bath and heated at a set temperature of 60 °C for 1 h. After heating, the emulsion was taken out and cooled naturally to room temperature, and its layering situation and physical property changes were observed. The states of the emulsion before and after the heat treatment were recorded to analyze its thermal stability.

[0040] 3. The verification method for the freeze-thaw stability of the oil-water two-phase emulsion without surfactant is as follows: The freshly prepared emulsion was placed at -18 °C and frozen for 24 h, then taken out and thawed at 25 °C for 24 h. The phase state changes, layering degree and uniformity of the emulsion were observed, and the appearance and physical property changes before and after freeze-thaw were recorded in time to evaluate the influence of freeze-thaw on the emulsion.

[0041] 4. Verification method for the storage stability of an oil-water two-phase emulsion without surfactant, the specific steps are as follows: The freshly prepared emulsion is stored at room temperature. At fixed time intervals (1 week), observe the appearance change of the emulsion and observe the internal situation using an optical microscope, and record the results of each observation to evaluate the stability of the emulsion.

[0042] In this embodiment, 3 kinds of oil-water two-phase emulsions without surfactant were prepared for testing. The preparation methods of the 3 kinds of oil-water two-phase emulsions without surfactant are as follows:

[0043] a) Add 1 mL of pure water into a glass bottle, and then add 2 mL of dioctyl phthalate into the glass bottle; The obtained mixed solution is treated with an ultrasonic power of 100 W for 15 s to prepare an oil-water two-phase emulsion without surfactant with an oil-water volume ratio of 2:1.

[0044] b) Add 1.5 mL of pure water into a glass bottle, and then add 1.5 mL of dioctyl phthalate into the glass bottle; The obtained mixed solution is treated with an ultrasonic power of 100 W for 15 s to prepare an oil-water two-phase emulsion without surfactant with an oil-water volume ratio of 1:1.

[0045] c) Add 2 mL of pure water into a glass bottle, and then add 1 mL of dioctyl phthalate into the glass bottle; The obtained mixed solution is treated with an ultrasonic power of 100 W for 15 s to prepare an oil-water two-phase emulsion without surfactant with an oil-water volume ratio of 1:2.

[0046] The structure of the oil-water two-phase emulsion without surfactant was observed using an optical microscope. It can be seen that the oil-water two-phase emulsions without surfactant with three different oil-water volume ratios all exhibit a stable spherical structure. However, the microstructure of the emulsion with an oil-water volume ratio of 2:1 is denser and the interfacial stability is stronger, significantly superior to other ratios. Figure 1 It can be seen that the oil-water two-phase emulsions without surfactant with three different oil-water volume ratios all exhibit a stable spherical structure. However, the microstructure of the emulsion with an oil-water volume ratio of 2:1 is denser and the interfacial stability is stronger, significantly superior to other ratios.

[0047] The rheological properties of the oil-water two-phase emulsion without surfactant were tested. It can be seen from Figure 2It can be seen that there are significant differences in the rheological behaviors of emulsions with three different oil-water volume ratios (1:2, 1:1, 2:1). The emulsion with an oil-water volume ratio of 1:2 usually has a lower viscosity and exhibits good fluidity. The emulsion with an oil-water volume ratio of 1:1 has a higher viscosity at low shear rates, and as the shear rate increases, the viscosity decreases significantly, showing strong shear thinning characteristics. While for the emulsion with an oil-water volume ratio of 2:1, the viscosity continuously increases as the shear rate increases, indicating its high shear thickening characteristics. In the frequency sweep experiment, the storage modulus G' reflects the elastic properties of the material, while the loss modulus G'' represents its viscous properties. For the emulsion with an oil-water volume ratio of 1:2, G' rises rapidly under initial shear, indicating its strong elasticity and low loss modulus, showing good stability. The emulsion with an oil-water volume ratio of 1:1 shows relatively stable changes in G' and G'', indicating enhanced fluidity and ductility. The emulsion with an oil-water volume ratio of 2:1 shows strong elasticity, where G' increases significantly with time while G'' decreases, indicating the formation of a stronger elastic network structure under shear. These rheological characteristics reveal that different oil-water volume ratios can affect the properties and microstructure of emulsions, and also illustrate that the emulsion with an oil-water volume ratio of 2:1 has better rheological properties.

[0048] The stability of the surfactant-free oil-water two-phase emulsion was tested, mainly including thermal stability experiment, freeze-thaw stability experiment and storage stability experiment. According to Figure 3 the results, on the 7th day, there was almost no significant change in the emulsion, which indicates that its interfacial film can effectively maintain stability for at least more than 7 days, thus verifying its reliability in short-term storage. Further analysis of Figure 4 and Figure 5 the results shows that although the high-temperature and low-temperature environments have certain adverse effects on the stability of the emulsion, the emulsion still did not show complete breakage.

[0049] The stability principle of the surfactant-free oil-water two-phase emulsion was explored. From Figure 6 the analysis of the simulation results, it can be seen that the initially dispersed dioctyl phthalate molecules showed a tendency to aggregate after a period of time. This aggregation actually marks the formation of the emulsion. At the same time, an important discovery is that almost all of the ester group parts of the dioctyl phthalate molecules are dispersed at the oil-water interface. After in-depth analysis, this phenomenon can be attributed to the partial hydrophilicity of the ester group. If the ester group is located at the oil-water interface, it means that some chemical bonds of the dioctyl phthalate molecule are inserted into the water phase, which is an important reason to prevent the compatibility of two oil droplets.

[0050] This embodiment also explored the preparation of oil-in-water and water-in-oil emulsions in the two-phase emulsion. In the surfactant emulsion system, the formation of oil-in-water and water-in-oil emulsions mainly depends on the hydrophilic-lipophilic balance of the surfactant, which is usually characterized by the hydrophilic-lipophilic balance value of the surfactant. The position and stability of particles with different properties in the emulsion are usually determined by the hydrophilicity or lipophilicity of the particles. Hydrophilic particles tend to form oil-in-water emulsions, while lipophilic particles are more likely to form water-in-oil emulsions. Thus, the amphiphilic design of particles is a key technology for regulating the type of emulsion. However, in the study of oil-water two-phase emulsions without surfactants, the mechanism for regulating the emulsion type is different. The stability and structure of the emulsion system are not only affected by surfactants but also closely related to the adjustment of interfacial energy, the composition and concentration of phases, and the ratio between different substances. By precisely adjusting these factors, effective regulation of the emulsion type can be achieved. In the oil-water two-phase system without surfactants, the ratio of water to oil is an important factor determining the emulsion type. When the proportion of the oil phase greatly exceeds that of the water phase, the system exhibits unique kinetic behavior. Under the action of external forces such as ultrasonic waves, positive waveform motion begins at the oil-water interface. As the external force continues to act, the waveform gradually approaches a circle. In each half cycle of the fluctuation, the two ends of the waveform come into contact with each other, and finally a well-defined structure is formed: the upper layer is a water-in-oil emulsion, and the lower layer is an oil-in-water emulsion.

[0051] The double emulsion in the oil-water two-phase emulsion without surfactant was explored. Figure 7 Figure 0000125 is an optical micrograph of the double emulsion. The most critical step in this process is to use the already formed oil-in-water emulsion as the water phase. Since the interface of this emulsion exhibits excellent stability under repeated ultrasonic conditions and does not easily break, it creates favorable conditions for adding an external oil phase. These external oil phases form a new stable interface in the emulsion, further enhancing the structural integrity of the double emulsion.

[0052] The separation and recovery performance of the oil-water two-phase emulsion without surfactant was explored, and the following experiment was conducted:

[0053] First, the oil phase and the water phase were weighed separately before preparing the emulsion, and then the prepared emulsion was placed at -18 °C for a period of time and then centrifuged. After centrifugation, the oil phase and the water phase were separated and weighed separately, and then the oil-water separation efficiency was calculated. The formula is as follows:

[0054]

[0055] Where F is the efficiency of oil-water separation, m1 is the weight of the oil phase or water phase before preparation, and m2 is the weight of the oil phase and water phase after separation.

[0056] From Figure 8It can be seen that the oil-water separation recovery rate is about 90%, and then 10 cycles were carried out. From Figure 9 It was found that the efficiency of oil-water separation did not decrease. This process also reflects the reversibility of the emulsion. After centrifugal separation, if the emulsion is reheated to room temperature, the ice phase will melt, and the water phase and oil phase can be mixed again to restore the stable emulsion state. The reversible mechanism of this emulsion not only provides flexibility for the application of surfactant-free oil-water two-phase emulsions, but also provides new ideas for their development in the fields of drug delivery, food processing and cosmetics.

[0057] The breaking of emulsions is costly and generates a large amount of waste. Switchable low-molecular surfactants have recently attracted attention because their surface activity can be changed by appropriate stimuli, allowing controlled emulsion breaking. However, their recovery is difficult. The surfactant-free oil-water two-phase emulsions proposed in the present invention are also very promising because they can easily achieve emulsion breaking and can achieve very high oil-water recovery efficiency, which provides unique advantages for their application in various fields. Since no surfactant is used in the preparation process, the characteristics of traditional surfactants cannot be used for demulsification. However, we can achieve emulsion demulsification through the difference in freezing points between the water phase and the oil phase. Specifically, the two-phase emulsion is placed in an environment at -18 °C for a period of time, and the water phase will start to freeze while the oil phase remains liquid. This phase change under such temperature conditions causes a significant change in the composition of the emulsion. The formation of ice crystals causes the volume of the water phase to expand, forcing the originally uniformly dispersed oil phase to separate. At this time, if the emulsion is centrifuged, the frozen water phase and the unfrozen oil phase can be effectively separated, thereby realizing emulsion demulsification. By Figure 8 As a result, it can be seen that the oil-water separation recovery rate is about 90%, and then 10 cycles were carried out. From Figure 9 it was found that the efficiency of oil-water separation did not decline. This reversible demulsification mechanism not only provides flexibility for the application of surfactant-free oil-water two-phase emulsions, but also provides new ideas for their development in the fields of drug delivery, food processing and cosmetics.

[0058] The above schematically describes the present invention and its embodiments. This description is not restrictive, and what is shown in the drawings is only one of the embodiments of the present invention. The actual structure is not limited thereto. Therefore, if those of ordinary skill in the art are inspired by it and design similar structural forms and embodiments without creative work without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. An oil-water two-phase emulsion without surfactant, characterized in that: It includes an oil phase and an aqueous phase. The aqueous phase is ultrapure water, and the oil phase is dioctyl phthalate, without adding any surfactant.

2. The oil-water two-phase emulsion without surfactant according to claim 1, characterized in that: By volume fraction, the emulsion includes 1 / 3 of the aqueous phase and 2 / 3 of the oil phase.

3. The oil-water two-phase emulsion without surfactant according to claim 1, wherein: The emulsion forms a thin film at the oil-water interface. This thin film can prevent the fusion of two oil droplets, and this thin film is spontaneously anchored at the oil-water interface by the ester groups of dioctyl phthalate due to partial hydrophilicity.

4. An oil-water two-phase emulsion without surfactant according to claim 1, characterized in that: The emulsion can separately prepare water-in-oil and oil-in-water two-phase emulsions without surfactant.

5. A method for preparing an oil-in-water two-phase emulsion without surfactants, characterized in that: It uses a two-phase emulsion as described in any one of claims 1-4, and includes the following steps: Add 2 mL of dioctyl phthalate to 1 mL of ultrapure water, and then perform ultrasonic treatment at 100 W for 15 s to obtain an oil-water two-phase emulsion without surfactant.

6. The preparation method of an oil-water two-phase emulsion without surfactant according to claim 5, characterized in that: The emulsion can prepare double emulsions. The specific steps are to first prepare an oil-in-water emulsion, and then add an equal volume of oil phase to the inside on this basis. After ultrasonic treatment, double emulsions are successfully formed.

7. The preparation method of an oil-water two-phase emulsion without surfactant according to claim 5, characterized in that: The emulsion has high separation and recovery characteristics. The method of separation and recovery is to place the emulsion in an environment of -18°C for 30 min. The aqueous phase will start to freeze, while the oil phase remains liquid. Then, the emulsion is centrifuged at 10,000 rpm for 8 min, and the frozen aqueous phase and the unfrozen oil phase can be separated.

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