Intelligent wormlike micelle with pH response and preparation method thereof

Abstract

The invention belongs to the technical field of application of surfactants, and particularly relates to a pH response type wormlike micelle and a preparation method thereof. According to the wormlike micelle provided by the invention, a multifunctional reactive surfactant and oxalic acid are utilized to form a quasi-gemini surfactant, and the quasi-gemini surfactant is self-assembled at room temperature to form the wormlike micelle with viscoelasticity. The obtained wormlike micelle has pH stimulation responsiveness, and the viscoelasticity of the system is obviously changed along with the change of pH. Firstly, a certain mass of oxalic acid is dissolved in deionized water, and after the oxalic acid is fully dissolved, the multifunctional reaction type surfactant with the corresponding proportion is added. The preparation method comprises the following steps: completely dissolving at room temperature by utilizing a stirring method, and standing for one night to fully balance, so as to obtain stable wormlike micelles. The wormlike micelle obtained by the invention is simple in preparation method, easy to regulate and control, sensitive to pH change and quick in response.

Description

Technical Field

[0001] The present invention belongs to the technical field of the application of surfactants, and specifically relates to the preparation of a pH-responsive wormlike micelle. Background Art

[0002] The "pseudo" gemini surfactant has a structure and properties similar to those of traditional gemini surfactants. The difference is that the hydrophilic and hydrophobic groups of the "pseudo" gemini surfactant are not connected by a covalent bond, but by intermolecular forces such as hydrogen bonds, electrostatic attractions, or van der Waals forces. A wormlike micelle refers to a flexible, uniform, and slender cylindrical aggregate self-assembled by surfactants with a specific structure under certain conditions. These micelles can entangle and overlap with each other to form a three-dimensional spatial network structure, having good viscoelasticity.

[0003] An intelligent wormlike micelle refers to a wormlike micelle self-assembled by surfactants with intelligent response groups (such as light response, pH response, and light response). Under the change of external conditions (such as surfactant concentration, temperature, pH, light, electric field, etc.), its physicochemical properties (such as surface tension, aggregation structure, etc.) will change significantly. Intelligent wormlike micelles have important applications in these fields such as oil and gas exploitation, drug delivery, environmental governance, and cosmetics. The aggregation structure of surfactants can be predicted and judged by the "packing parameter p". The molecular packing parameter p is defined as:

[0004] p = V / al (1)

[0005] Where V represents the volume of the hydrophobic tail chain of the surfactant, l represents the length when the hydrophobic tail chain of the surfactant is fully extended, and a represents the minimum area occupied by the polar group of the surfactant. When p < 1 / 3, it can be judged that the surfactant self-assembles to form spherical micelles; when 1 / 3 < p < 1 / 2, it can be judged that rod-like or wormlike micelles are formed; when 1 / 2 < p < 1, it can be judged that vesicles or lamellar micelles are formed; when p > 1, the surfactant self-assembles to form an inverse structure.

[0006] In the existing technology, for example, Pei Xiaomei et al. provided a pH-responsive dimeric surfactant wormlike micelle system, which is constructed by electrostatic interactions and has high viscoelasticity and pH responsiveness (CN108837772A). However, the preparation process of this system is relatively complex, involving multiple synthesis and purification steps, and the yield is relatively low (about 20%), increasing the production cost. They also provided a high-temperature resistant wormlike micelle formed by surfactants constructed by acid-base interactions. This system can still maintain a high viscosity in a high-temperature environment (>60 °C) and is suitable for high-temperature application scenarios such as oilfield fracturing fluids (CN114671778B). The viscosity of the existing systems is too high and the response is slow.

[0007] The "quasi" gemini surfactant constructed by the present invention is convenient to synthesize, and the surfactant DMAEDM used has polymerizable double bonds and can be applied in polymerization. The provided wormlike micelles have a viscosity of 25-30 Pa·s and have a more sensitive pH responsiveness. Summary of the Invention

[0008] The object of the present invention is to provide a preparation method of pH-responsive wormlike micelles, and the preparation method is simple and easy to control. The preparation method of the pH-responsive wormlike micelles provided by the present invention is to form a "quasi" gemini surfactant by using a multifunctional reactive surfactant and oxalic acid, and self-assemble at room temperature to form viscoelastic wormlike micelles.

[0009] The structural formula of the intelligent wormlike micelles with pH responsiveness is as follows:

[0010]

[0011] The specific steps of the preparation method of the intelligent wormlike micelles with pH responsiveness are as follows:

[0012] (1) Prepare the multifunctional reactive surfactant by a two-step method. React the acid anhydride compound and dodecanol at 80 °C for 4 hours, cool to room temperature and then separate and purify to obtain intermediate product 1;

[0013] (2) Dissolve intermediate product 1 in chloroform solvent, dissolve potassium carbonate and 18-crown-6 in deionized water, add dropwise, react at 50 °C for 9 hours, then dissolve dimethyl chloroethane hydrochloride in deionized water, add dropwise, react for 24 hours, and treat the product to obtain the final product DMAEDM, which is a transparent oily substance.

[0014] (3) Dissolve oxalic acid in water, after complete dissolution, add the product obtained in step (2), stir to completely dissolve it, let it stand overnight at room temperature, and wait for it to stabilize to obtain pH-responsive wormlike micelles, and the structural formula is as follows:

[0015]

[0016] Preferably, the acid anhydride compound in step (1) is maleic anhydride; the molar ratio of maleic anhydride to dodecanol is 1:1.

[0017] Preferably, the dropping rate of the potassium carbonate and 18-crown-6 aqueous solution and the dimethyl chloroethane hydrochloride aqueous solution in step (2) is one drop every three seconds.

[0018] Preferably, in step (3), the concentration of the multifunctional reactive surfactant DMAEDM is 250 mmol / L to fix the concentration of the surfactant. This surfactant can complex with the dibasic acid to form a "pseudo" gemini surfactant and self-assemble into worm-like micelles. Oxalic acid is selected as the dibasic acid for complexation in the present invention to explore the effect of the concentration of oxalic acid on the formation of worm-like micelles.

[0019] Preferably, in step (3), the concentration of the oxalic acid solution is 87.5 - 125 mmol / L. That is, the molar ratios of DMAEDM to oxalic acid are 1:0.35, 1:0.40, 1:0.45, and 1:0.50 respectively. If the concentration is too low, it is not conducive to the formation of the "pseudo" gemini surfactant and the worm-like micelles are difficult to form. If the concentration is too high, the stability of the worm-like micelles is damaged, the solubility of the surfactant is reduced, resulting in precipitation.

[0020] Preferably, in step (3), the stirring speed is between 1000 - 1500 r / min and the stirring time is about 1 min (40 s - 90 s) to prevent the destruction of the stability of the worm-like micelles and reduce their viscosity.

[0021] Preferably, in step (3), the standing time needs to exceed 8 hours to stabilize the system.

[0022] Preferably, in step (3), the surfactant DMAEDM should be added after the oxalic acid is completely dissolved to prevent their premature complexation.

[0023] Preferably, the pH-responsive worm-like micelles in step (3) are self-assembled from a "pseudo" gemini surfactant composed of one oxalate ion and two protonated surfactants DMAEDM.

[0024] Preferably, the pH-responsive worm-like micelles in step (3) have two pH-responsive groups, namely the tertiary amine group in the surfactant DMAEDM and the oxalate ion.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] The "pseudo" gemini surfactant provided by the present invention has simple and environmentally friendly synthesis steps, a low CMC value, and excellent surface activity. It can form worm-like micelles with good viscoelasticity at a low concentration (250 mmol / L), and when the pH changes, its viscoelasticity also changes rapidly. This characteristic enables the invention to be applied in personal care, cosmetics, drag reducers, etc. Description of the Drawings

[0027] Figure 1 It is the structural diagram of the "pseudo" gemini surfactant prepared in Example 2

[0028] Figure 2 Static rheology curves of different oxalic acid concentrations in Example 3.

[0029] Figure 3 Dynamic rheology curves of different oxalic acid concentrations in Example 3.

[0030] Figure 4 Cole-Cole curve of micelles with an oxalic acid concentration of 112.5 mmol / L in Example 3.

[0031] Figure 5 SEM image of worm-like micelles with an oxalic acid concentration of 112.5 mmol / L in Example 4.

[0032] Figure 6 Surface tension curve and its fitting curve of worm-like micelles with an oxalic acid concentration of 112.5 mmol / L in Example 4.

[0033] Figure 7 Static rheology curves of worm-like micelles with an oxalic acid concentration of 112.5 mmol / L at different pH values in Example 5.

[0034] Figure 8 Dynamic rheology curves of worm-like micelles with an oxalic acid concentration of 112.5 mmol / L at different pH values in Example 5. Detailed implementation manners

[0035] The technical features of the present invention are further illustrated by the following examples, but the protection scope of the present invention is not limited to the following examples.

[0036] Example 1: Synthesis of multifunctional reactive surfactant DMAEDM

[0037] 0.05 mol of maleic anhydride and 0.05 mol of dodecanol were added to a 100 ml flask and reacted at 80 °C for 4 hours. After the reaction was completed and cooled to room temperature, recrystallization was carried out three times, and a white crystalline product 1 was obtained after drying. 0.04 mol of product 1 was dissolved in 100 ml of chloroform and poured into a 500 ml three-necked flask. 0.08 mol of potassium carbonate and 0.004 mol of 18-crown-6 were dissolved in 50 ml of deionized water and added to the reactants at a rate of one drop every three seconds. After reacting at 50 °C for 9 hours, 0.08 mol of dimethyl chloroethane hydrochloride was dissolved in deionized water and added to the reactants at a rate of one drop every three seconds, and the reaction continued for 24 hours. After the reaction was completed, the upper oily substance was separated, and the final product DMAEDM was obtained after dehydration and impurity removal, which was a transparent oily substance.

[0038] Example 2: DMAEDM and oxalic acid form a "pseudo" gemini surfactant

[0039] Prepare 5 mL of aqueous oxalic acid solutions with concentrations of 87.5 mmol / L, 100 mmol / L, 112.5 mmol / L, and 125 mmol / L respectively. After the oxalic acid is completely dissolved, add 0.465 g of the multifunctional reactive surfactant DMAEDM to prepare an aqueous solution with a DMAEDM concentration of 250 mmol / L. Stir and mix evenly at room temperature until the solution becomes transparent, and let it stand at room temperature. After the solution is stable and free of bubbles, micelles with different appearances are obtained.

[0040] Example 3: Rheological property test of micelles with different oxalic acid concentrations

[0041] Perform rheological property tests on the different micelles in Example 2 using a cone-plate (d = 47 mm, 1°) rheometer. Conduct static rheological tests on the micelles at a varying shear rate of 0.001 - 100 s -1 ^(-1). When the oxalic acid concentration is 112.5 mmol / L, the system exhibits obvious shear-thinning behavior, and when the shear rate is small, the viscosity changes little, showing a plateau region. At an angular frequency ranging from 0.03 - 80 rad / s, measure the changes of the elastic modulus G’ and viscous modulus G” of the micelles with the angular frequency, and the Cole-Cole curve can be plotted. When the oxalic acid concentration is 100 mmol / L and 112.5 mmol / L, as the angular frequency increases, the G’ and G” curves intersect, indicating that worm-like micelles are formed in the solution at this time; when the oxalic acid concentration is 125 mmol / L, the two curves are intertwined; when the oxalic acid concentration is 87.5 mmol / L, the two curves show no tendency to intersect within the measurement range. Further, from its Cole-Cole plot, it can be seen that when the oxalic acid concentration is 112.5 mmol / L, the data fits well with the Maxwell model.

[0042] From Figure 2 and Figure 3 it is known that when the oxalic acid concentration is 112.5 mmol / L, the system has a relatively high viscosity of 27.8 Pa·s and is a viscoelastic Maxwell fluid. It can be seen from Figure 5 that the aggregate morphology existing in the solution with a concentration of 112.5 mmol / L is worm-like.

[0043] Example 4: Surface tension test of micelles with an oxalic acid concentration of 112.5 mmol / L

[0044] Prepare micelles with an oxalic acid concentration of 112.5 mmol / L using the method in Example 2. At room temperature, use the pendant drop method to test the surface tension of the worm-like micelles with an oxalic acid concentration of 112.5 mmol / L, obtain its surface tension curve, and calculate the packing parameter p according to formula (1).

[0045] Among them, V and l can be calculated according to the number of carbon atoms n of the surfactant hydrocarbon chain, and the formula is as follows:

[0046] V = (27.4 + 26.9n) × 10 -3 (2)

[0047] l = (0.15 + 0.1265n) (3)

[0048] a can be calculated according to the limiting adsorption amount Γ of the surfactant on the solution surface max calculate

[0049] a = 1 / (N A ·Γ max ) (4)

[0050] N A is the Avogadro constant, and the limiting adsorption amount Γ max can be obtained by fitting the surface tension curve. The Γ of the wormlike micelles with an oxalic acid concentration of 112.5 mmol / L obtained from the fitting curve max is 2.74×10 6 mol / m 2 , and a can be obtained as 0.61 nm from formula (4) 2 , and the number of carbon atoms n of the hydrocarbon chain of the "quasi" gemini surfactant is 42. Therefore, according to formula (3), l can be obtained as 5.46 nm, and according to formula (2), V can be obtained as 1.16 nm 3 . According to formula (1), the packing parameter p value of the wormlike micelles with an oxalic acid concentration of 112.5 mmol / L can be obtained as 0.35, which is between 1 / 3 and 1 / 2, proving that wormlike micelles with excellent surface activity have been successfully obtained in the solution.

[0051] Example 5: Rheological property test of micelles with an oxalic acid concentration of 112.5 mmol / L at different pH values

[0052] Prepare 200 mM / L HCl and NaOH aqueous solutions, and add the acid-base solutions to 1 ml of wormlike micelles with an oxalic acid concentration of 112.5 mmol / L respectively. Micelles with pH values of 4 and 8 are obtained. And their static and dynamic rheological tests are carried out, and compared with the wormlike micelles without adding acid-base solution (pH = 6). It can be found that the viscosity of the micelles with changed pH is significantly reduced, and G' and G" do not intersect in their dynamic rheological curves, indicating that this wormlike micelle has good pH responsiveness.

[0053] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A pH-responsive intelligent worm-like micelle, characterized in that, The structural formula of the pH-responsive intelligent wormlike micelle is as follows:

2. The preparation method of the pH-responsive intelligent worm-like micelle according to claim 1, characterized in that, The preparation method of the pH-responsive intelligent wormlike micelle is as follows: The pH-responsive wormlike micelle is self-assembled from a "pseudo" gemini surfactant composed of one oxalate ion and two protonated surfactants DMAEDM.

3. The preparation method of the pH-responsive intelligent worm-like micelle according to claim 2, characterized in that, Dissolve oxalic acid in water. After complete dissolution, add the multifunctional reactive surfactant DMAEDM and stir until it is completely dissolved. Let it stand at room temperature. After it stabilizes, the pH-responsive wormlike micelle is obtained; the structural formula of DMAEDM is 4. The preparation method of the pH-responsive intelligent worm-like micelle according to claim 3, characterized in that The concentration of the multifunctional reactive surfactant DMAEDM is 250 mmol / L, and the concentration of the oxalic acid solution is 87.5 - 125 mmol / L.

5. The preparation method of the pH-responsive wormlike micelles according to claim 3, characterized in that, The standing time exceeds 8 hours until the system stabilizes.

6. The preparation method of the pH-responsive wormlike micelles according to claim 3, characterized in that, Add the multifunctional reactive surfactant after the complete dissolution of oxalic acid to prevent premature complexation of the two.

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