Abstract
Here are described the dilution-driven gel-sol-gel-sol transitions in aromatic hydrotrope/zwitterionic surfactant bi-component aqueous mixtures. Long and entangled wormlike micelles (WLMs) of concentrated erucyl dimethyl amidopropyl betaine (EAPB) solutions sequentially transform into hexagonal liquid crystal phase (H1), highly concentrated spherical micelles (HCSMs), and finally hexagonal close packed micellar phase (HCP) upon gradual introducing an aromatic hydrotrope, sodium salicylate (NaSal). The HCP then successively converts into HCSMs, WLMs, and spherical micelles (SMs) upon further dilution with water, corresponding to a gel-sol-gel-sol transition. This dilution-induced HCSMs to WLMs transition results in an interesting thickening process, which is caused by a slow kinetic process, from the agglomeration and recombination of SMs to long and rigid WLMs via the intermediately formed rodlike micelles. In this work, the sustained adjustment of the competitive self-sorting and co-assembly between hydrotropes and surfactants by dilution was identified, benefitting the creation and application of WLMs fluids with switchable viscosity.
Introduction
Self-assembly is an important characteristic of surfactants. As such molecular self-assembly at the mesoscale is essential for materials and life1,2,3,4,5. In the semi-dilute solutions surfactants form primary molecular aggregates, i.e., spherical micelles (SMs), rodlike micelles (RMs), wormlike micelles (WLMs) and vesicles. In concentrated surfactant phases three-dimensional cubic and hexagonal liquid crystals may form, corresponding to higher-level assemblies of SMs and WLMs, respectively6,7,8,9,10,11. The inherent aggregate morphology is mainly determined by molecular structure, however, it can be regulated further by extra-environmental factors such as temperature, light, pH, and electrolytes, and so forth12,13,14,15,16,17,18. Nowadays, stimuli-responsive aggregates are widely studied due to their application potential in catalysis, medicine, biomaterials, and petroleum reservoir exploitation for example19,20,21,22,23,24. In the latter case viscoelastic WLMs are excellent substitutes of polymeric fracturing fluids and oil-displacing agents, which can avoid the irreversible shear-thinning of polymers and reduce the crude oil/water interfacial tension simultaneously25,26. However, because of the high viscosity of WLMs this approach still has challenges in terms of diluting and waterflooding. Ideally, these fluids should be initially of low viscosity for easier injection, but then spontaneously thicken in situ under reservoir conditions. Undoubtedly, dilution-induced formation of WLMs in situ would be desirable.
The dilution-induced morphological variation of surfactant aggregates is obvious, which often results in the formation of aggregates with the smaller sizes, i.e., the transitions from WLMs to SMs, vesicles to WLMs, and so forth27,28. Battaglia and Ryan reported the evolution of amphiphilic block copolymer vesicles from water-poor planar lamellae by dilution, which went through the intermediate water-rich interconnected sponge phase and the gel-like hexagonally packed vesicles phase29. However, the reverse transitions from small aggregates to large ones by dilution are much rarer. One of the most studied SMs to vesicles transition induced by dilution is with lipid/surfactant mixtures30, and in this case, the use of surfactants with a high critical micelle concentration (cmc) is the most important. A high cmc endows surfactants with strong tendency to partition from surfactant-rich SMs into water, favoring the formation of lipid-rich vesicles. In fact the desired dilution-induced thickening process in situ is very difficult to achieve, especially under the restrictive conditions, although it can be conveniently triggered by numerous other stimuli31,32,33,34,35,36,37,38,39. This is because high-viscosity liquid crystal phases are often formed in the concentrated solutions11. Recently, Meijer and coworkers reported the dilution-induced gel-sol-gel-sol sequential transitions in aqueous mixtures of supramolecular amphiphile benzene-1,3,5-tricarboxamide (BTA-EG4) and surfactants at a specific molar ratio, which formed nano-fibers and SMs alone, respectively40. During the process, the initially formed densely packed networks of fused hybrid SMs were dissociated into separated SMs, and then transferred into entangled BTA-EG4 fiber networks, and finally individual fibers upon continuously diluting. The phenomena were mainly caused by the competitive co-assembly and self-sorting in these multicomponent mixtures, under concentrated and diluted conditions, respectively.
In surfactant science, aromatic hydrotropes are often employed to regulate surfactant aggregate morphology, typically with the opposite charged mixtures such as sodium salicylate/alkyltrimethylammonium bromide (NaSal/CnTAB)35,41,42,43,44,45,46. In these mixtures micellar morphology is primarily controlled by the molar ratio R between hydrotrope and surfactant. The synergistically co-assembly based on a fine balance between electrostatic and hydrophobic interactions is thought to be the main cause. For example, introduction of p-toluidine hydrochloride induced micellar growth of sodium dodecyl sulfate (SDS), which gradually transfer into WLMs and vesicles upon increasing R to about 147,48,49. Indeed, similar hydrotrope-induced micellar growth has commonly been observed in the hydrotrope-poor regions41,42,43,44,45,46. However, the opposite transitions might also happen in hydrotrope-rich regions, i.e., hydrotrope-induced vesicles or WLMs to SMs transitions. Raghavan et al. noticed the formation of SMs through introducing excessive sodium 3-hydroxy naphthalene 2-carboxylate (NaNHC) into the semi-dilute erucyl dimethyl amidopropyl betaine (EAPB) WLMs50. Moreover, the hydrotrope-rich aggregates might show unusual self-assembly behaviors such as the dilution-induced WLMs to vesicles or RMs to WLMs transitions51,52. The dilution-driven release of hydrotropes in the hybrid micelles was considered as the main cause, corresponding to the self-sorting process between different components. The adjustment of competitive interactions between hydrotropes and surfactants by dilution might endow the bi-component systems with special self-assembly behaviors. Here is reported an unusual dilution-driven gel-sol-gel-sol transition in aromatic hydrotrope/zwitteronic surfactant binary aqueous mixtures, attributed to a morphological evolution from the initial hexagonal close packed micellar phase (HCP)53,54,55 to highly concentrated spherical micelles (HCSMs), WLMs and finally to SMs, where the hydrotrope-induced formation of HCP phase is critical.
Results
Hydrotrope-induced gel-sol-gel transitions
Zwitterionic surfactants EAPB and EHSB (Fig. 1a) prefer to form WLMs in the bulk owing to the ultra-long hydrophobic chain50,56. Concentrated EAPB solutions are gel-like with high viscosity (Supplementary Fig 1), showing birefringence under polarized light (The inset image in Fig. 1c), i*.*e., that at cEAPB = 625 mmol/kg (ratio between the molar quantity of surfactant and the mass of the mixture). The introduced aromatic hydrotropes (Fig. 1b), such as NaSal, can dramatically change the properties of the concentrated EAPB aqueous solution, mainly depending on the molar ratio R between NaSal and EAPB. To demonstrate the effect of R on the self-assembly of concentrated EAPB aqueous mixtures, EAPB, NaSal and water were mixed directly and stirred at 60 °C until homogeneous, and then equilibrized at 25 °C for 1 month.
Fig. 1: Hydrotrope-induced morphological transition.
figure 1
Molecular structures of (a) surfactants and (b) hydrotropes. c The zero-shear viscosity (η0) vs the NaSal and EAPB molar ratio R plot of NaSal/EAPB mixtures (red square) where the concentration of EAPB (cEAPB) is fixed as 625 mmol/kg at 25 °C. The inset images show photographs and polarized light microscopy (POM) image of the NaSal/EAPB mixtures at certain R. d The SAXS profiles of NaSal/EAPB mixtures at different R, the reflections (hkl) of different Bragg peaks index well to the hexagonal liquid crystal phase and hexagonal close packed micellar phase at R = 0.5 and 2.5, respectively. e Illustration of R-induced morphological transition from wormlike micelles (WLMs) to hexagonal liquid crystal phase (H1), highly concentrated spherical micelles (HCSMs), and finally to hexagonal close packed micellar phase (HCP).
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This R-induced morphological evolution of aggregates (Fig. 1c) was subsequently studied by rheology and small angle X-ray scattering (SAXS, Fig. 1d). At low R below 0.75, all mixtures are gel-like with high zero-shear viscosity (η0) around 106–107 mPa·s. The scattering of pure EAPB aqueous solution is complex, showing a strong peak at q = 0.0822 Å−1, and a weak shoulder comprising multiple sharp peaks at q = 0.112, 0.117 and 0.124 Å−1 (Supplementary Fig 2a). The electrostatic interactions between WLMs contribute to the strong scattering, whereas the weak features can be attributed to the kinetically trapped ordered metastable structures of partially-aligned WLMs, consistent with the observed birefringence. In contrast, two prominent peaks at q = 0.109 and 0.189 Å−1 and two smaller ones at q = 0.218 an 0.289 Å−1 appear in the SAXS profile of NaSal/EAPB aqueous mixture at R = 0.5 (Supplementary Fig 2b). The q values match the proportional relation of 1: 31/2: 2: 71/2 well as indexed by the (100), (110), (200), and (210) reflections, respectively, indicating the formation of hexagonal liquid crystal phase (H1) with the micellar cross-section dimension of 66.5 Å11. The characteristic reflections (100) and (110) of H1 at q = 0.102 and 0.176 Å−1 were still visible at R = 0.75. Accordingly, the R-induced shift of the (100) reflection of H1 from q = 0.109 to 0.102 Å−1 was observed upon increasing R from 0.5 to 0.75 as indicated, corresponding to the enlarged micellar dimension.
With an equimolar composition of NaSal and EAPB (R = 1) the viscosity decreases markedly. All NaSal/EAPB aqueous mixtures became fluids for R in the region 1.25–1.75: the viscosities reduce by 5 orders of magnitude to lower than 100 mPa·s. The transparent and isotropic NaSal/EAPB aqueous mixtures at R = 1.25 and 1.5 were further studied by SAXS. The resulting SAXS profiles were analyzed using the core-shell sphere model well (Supplementary Fig 3 and Tab 1), consistent with the formation of SMs at high-volume fraction (ϕvol) ~ 0.4, corresponding to a highly concentrated spherical micelles (HCSMs) phase. The fitted core radius (Rc) and shell thickness (Ts) of HCSMs are 25.2 Å and 8.0 Å, respectively. When R was increased to above 2, isotropic gels with very high viscosities were reformed. In the SAXS curve at R = 2.5, multiple reflections at q = 0.109, 0.116, 0.124, 0.159, and 0.188 Å−1 can be observed. The scattering peaks perfectly match the reflection indexed (100), (002), (101), (102), and (110) as expected for hexagonal close packed micellar phase (HCP)53,54,55, respectively. The gel-sol-gel transition caused by the R-induced morphological evolution from WLMs to H1, HCSMs, and the final HCP is illustrated by Fig. 1e.
Similar morphological transitions are also presented in other aromatic hydrotrope/zwitterionic surfactant two-component systems such as concentrated NaSal/EHSB and NaBen/EAPB aqueous mixtures. With NaSal/EAPB aqueous mixtures at specific compositions, the intermediate HCSMs formed are rarely reported. In addition, introducing NaSal facilitates the alignment and dense packing of WLMs and HCSMs to form H1 and HCP, respectively. The NaSal-induced sequential gel-sol-gel transition was not found at the slightly lower cEAPB of 573 mmol/kg, whereas the R-induced gel-sol transition was observed instead (Supplementary Fig 4), assigned to the WLMs to HCSMs transition. For NaSal/EAPB aqueous mixtures at cEAPB = 573 mmol/kg, HCSMs instead of HCP was commonly formed even at the solubility limit of NaSal. However, HCP could be formed at R > 2 at cEAPB = 625 mmol/kg. Closely packed SMs in HCP at R = 2 were dissociated into HCSMs when cEAPB was decreased, suggesting a dilution-induced HCP to HCSMs transition.
Dilution-induced gel-sol-gel-sol transitions
The gel-sol-gel-sol sequential transition occurs upon continuously diluting the NaSal/EAPB HCPs at R = 2 with water as suggested by the η0 vs R plot (Fig. 2a). The η0 vs R variation tendency for the NaSal/EAPB mixtures at R = 5 is the same but the curve shifts toward the bottom-right slightly, where no gel-like HCP can be obtained because of the solubility limit of components at 25 °C. For NaSal/EAPB HCPs at cEAPB above 625 mmol/kg at R = 2, η0 are very high because of densely packed SMs (Fig. 2c). The η0 of the NaSal/EAPB mixture at cEAPB = 594 mmol/kg decreases sharply about 7 orders of magnitude, and the mixture arrives the minimum η0 of 2.9 mPa·s at around cEAPB of 300 mmol/kg. The unexpected low viscosities are attributed to the formation of HCSMs as confirmed by cryo-TEM (Fig. 2d). The SAXS profiles of NaSal/EAPB HCSMs in the cEAPB region from 313 to 573 mmol/kg can be fitted well by the core-shell sphere model (Fig. 2b). All Rc keep nearly constant at ~22.8 Å, whereas the corresponding Ts are reduced gradually from 14 Å to 9.9 Å at the higher cEAPB along with the enlarged ϕvol of SMs (Supplementary Tab 2). The decrease in Ts can be attributed to the compressed double layers of SMs in the presence of NaSal.
Fig. 2: Characterization of dilution-induced morphological transition.
figure 2
a The zero-shear viscosity (η0) vs the concentration of EAPB (cEAPB) plots of NaSal/EAPB binary mixtures at constant R of 2 (red square) and 5 (blue circle). The inset images represent photographs of NaSal/EAPB mixtures at R = 2 at different cEAPB. b The corresponding SAXS profiles of HCSMs at cEAPB of 313 (red square), 365 (blue circle), 417 (vermilion rhombus), 469 (green triangle), 521 (orange inverted triangle), and 573 (purple hexagon) mmol/kg, respectively. The solid lines were fitted using the core-shell sphere model associated with the Hayter-Penfold Rescaled Mean Spherical Approximation (RMSA) structure factor (the inset image). Rc and Rm represent the radii of core and micelle, Ts is the shell-thickness. Cryo-TEM images of NaSal/EAPB binary mixtures at R = 2 at cEAPB of c 625, d 417, e 250, f 50, g 10 and h 2 mmol/kg, respectively. i Illustration of dilution-induced morphological transition from hexagonal close packed micellar phase (HCP) to highly concentrated spherical micelles (HCSMs), wormlike micelles (WLMs), and finally to spherical micelles (SMs).
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Interestingly, η0 begins to increase upon further dilution. The η0 is 338 mPa·s at cEAPB = 200 mmol/kg that is far larger than that at cEAPB = 300 mmol/kg, in which the connected networks of SMs are predominant (Fig. 2e). When cEAPB is lowered to 100–50 mmol/kg, the hybrid mixtures become gel-like again and achieve the maximum η0 about 2 × 105 mPa·s. This is mainly caused by the formation of very long and entangled WLMs (Fig. 2f, g). Once cEAPB is below 5 mmol/kg, the NaSal/EAPB aqueous mixtures become Newtonian fluids with very low viscosities, i.e., the η0 of 1 mPa·s at cEAPB = 1 mmol/kg. The cryo-TEM image shows that SMs are re-formed at the low cEAPB (Fig. 2h). This is also supported by the corresponding SAXS profiles as analyzed by the core-shell ellipsoid and cylinder models (Supplementary Fig 5, Tab 3 and Tab 4). Specifically, ellipsoidal micelles with Rc, Ts, and axial ratio uc of about 25.5 Å, 10.5 Å, and 0.7, respectively, are formed at cEAPB of 250–200 mmol/kg. However, cylindrical micelles with the cross-section radii Rm about 35 Å are formed in the cEAPB region from 100 to 10 mmol/kg. Dynamic rheological responses show that mainly elastic WLMs are formed at R = 2 when cEAPB is below 100 mmol/kg, and the elasticity is essentially positively correlated with cEAPB (Supplementary Fig 6a). The NaSal/EAPB HCSMs are also elastic but much weaker than that of WLMs, which are also significantly different from the viscous connected networks of SMs formed at cEAPB of 200 mmol/kg (Supplementary Fig 6b). The corresponding microstructures in this dilution-induced gel-sol-gel-sol transition based on the sequential morphological evolution from HCP to HCSMs, WLMs and SMs is illustrated in Fig. 2i.
General characteristics of intermediate HCSMs
Both the R-induced gel-sol-gel and dilution-induced gel-sol-gel-sol transitions present an important intermediate HCSMs state. To improve understanding, the effect of R on HCSMs was studied in a wide region of cEAPB by viscosity and cryo-TEM measurements. All η0 vs R plots show similar variations regardless of cEAPB (Fig. 3a). For a given cEAPB, η0 changes a little when R is relatively low. Then, η0 begins to decrease sharply around a critical R (Rc1), and arrives the minimum value at another one (Rc2). In general, the whole η0 vs R plots shift down-right at the lower cEAPB, resulting in the larger Rc1 and Rc2. For example, the Rc1 and Rc2 are about 0.75 and 1.25, 10 and 40 at cEAPB of 417 and 10 mmol/kg, respectively. Cryo-TEM images show that very long and entangled WLMs were formed in the absence of NaSal in the semi-dilute EAPB region (Fig. 3c), i*.*e., at cEAPB = 10 mmol/kg, which transfer into rigid WLMs at R = 2 (Fig. 3d) and SMs at R = 40 (Fig. 3e), respectively. The formation of SMs at high R is commonly presented in the NaSal/EAPB mixtures at different cEAPB such as those at cEAPB = 50 mmol/kg and R = 10 (Fig. 3f) and at cEAPB = 417 mmol/kg and R = 2 (Fig. 2d), respectively. In this case, NaSal/EAPB hybrid SMs are formed at the lower R at the higher cEAPB. Therefore, the R-induced viscosity decrease is attributed to the WLMs to SMs transition.
Fig. 3: Effects of R and cEAPB on the WLMs to SMs transitions.
figure 3
a The zero-shear viscosity (η0) vs the NaSal and EAPB molar ratio R plots at constant concentration of EAPB (cEAPB) of 417 (red square), 100 (blue circle), 50 (vermilion rhombus), 25 (green triangle) and 10 (orange inverted triangle) mmol/kg at 25 °C, respectively. b The η0 vs the molar ratio R between different hydrotropes and EAPB plots of NaBen/EAPB (red square), NaOTs/EAPB (blue circle), NaHNC/EAPB (vermilion rhombus), 4NaMS/EAPB (green triangle) and 5NaMS/EAPB (orange inverted triangle) mixtures at cEAPB of 417 (solid) and 10 (blank) mmol/kg. Cryo-TEM images of NaSal/EAPB mixtures at cEAPB = 10 mmol/kg at R of c 0, d 2, and e 40, and f at cEAPB = 50 mmol/kg and R = 10, respectively.
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Other aromatic hydrotropes such as NaBen and NaOTs showed the same general behavior as for NaSal (Fig. 3b), and similar η0 vs R relationships were also observed in the NaSal/EHSB systems (Supplementary Fig 7). Thus, the R-induced transitions from WLMs to HCSMs or SMs are universal in such hydrotrope/zwitterionic surfactant mixtures. The major characteristics of the intermediate HCSMs is the presence between the liquid crystal phase H1 and HCP at such high concentrations (Fig. 1c), and surprisingly no such observation was reported previously in similar hydrotrope/surfactant binary systems57,58,59,60,61,62. Noticeably, the morphological difference of WLMs formed at cEAPB = 10 mmol/kg at R = 0 and 2 comes from the stronger rigidity. Dynamic rheological responses show that elastic WLMs are formed in the presence of NaSal instead of predominantly viscous WLMs of pure EAPB (Supplementary Fig 8a). The introduced NaSal endows WLMs with more negative charges gradually, and achieves the maximum zeta potential (ζ) of −61 mV at about R = 8–10 (Supplementary Fig 8b). Upon further increasing R, the value of ζ begins to decrease, and the WLMs to SMs transition occurs simultaneously (Fig. 3a). This suggests that more Sal- counterions are bound and co-assembled in the hybrid micelles at the higher R. Therefore, the intensified elasticity or rigidity of WLMs can be attributed to the strong electrostatic interaction between them27,44,50.
Moreover, NaSal/EAPB HCSMs were often formed at relatively low R and high cEAPB, whereas WLMs remain over a wide region of R at the lower cEAPB. Thus, the dilution-induced thickening based on HCSMs to WLMs transitions is essential at the constant R. When the NaSal/EAPB HCSMs at cEAPB = 417 mmol/kg and R = 2 were diluted directly by water to cEAPB = 10 mmol/kg at 25 °C, a slow thickening in situ can be observed. The initial η0 of the diluted solution is very low ~1 mPa·s, whereas the equilibrium η0 of 2800 mPa·s is attained after about 7 days (Fig. 4a). Alternatively, the equilibrium η0 can be achieved rapidly at 80 °C or in the presence of 100 mmol/L CaCl2 at 25 °C (Supplementary Fig 9). This is because the removal of NaSal from the aggregates is enhanced by the increased temperature and CaCl2 is more effective in screening the surfactant electric double layer56.
Fig. 4: The growth of the diluted HCSMs over time.
figure 4
a The zero-shear viscosity (η0) of the diluted NaSal/EAPB mixture at different aging time at the constant concentration of EAPB (cEAPB) of 10 mmol/kg and 25 °C. The inset image is the corresponding shear viscosity at aging intervals, 0.75 (square), 4.65 (circle), 16.5 (rhombus), 40.4 (triangle), 88.4 (inverted triangle), and 112 (hexagon) hours, respectively. Cryo-TEM images at the aging time of b 0 h, c 2 h, d 6 h, e12 h and f 168 h, respectively. g Illustration of growth kinetic in situ of the diluted highly concentrated spherical micelles (HCSMs), transforming from spherical micelles to connected networks of agglomerated spherical micelles, rodlike micelles, and finally into wormlike micelles.
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To gain a better understanding about the growth over time, the thickening process of the diluted NaSal/EAPB HCSMs at cEAPB = 10 mmol/kg and 25 °C was monitored by cryo-TEM. At the very beginning, once the NaSal/EAPB HCSMs system is diluted, mainly separated SMs are visible (Fig. 4b). Two hours later, connected networks of agglomerated SMs are observed (Fig. 4c). Then, RMs appear after 6 h (Fig. 4d), which are grown from the agglomerated SMs by fusion. The tendency is strengthened along with the aging time, and more RMs with the longer lengths are observed after 12 h (Fig. 4e). A week later, very long and rigid WLMs become the major morphology (Fig. 4f). Thus, the growth kinetic in situ of the diluted HCSMs is represented by Fig. 4g, which ultimately transfer to WLMs go through the connected networks of SMs and the sequentially formed RMs.
Mechanism of R- and dilution-induced transitions
For further understanding, the molecular interactions between NaSal and EAPB were investigated by 1H NMR. In NaSal aqueous solutions, the cNaSal-dependent chemical shifts δ of aromatic protons show similar variation tendency as for surfactants during micellization (Supplementary Fig 10). The δ of protons apparently shift toward upfield when cNaSal is above a critical value, indicating the micellization of NaSal. The obtained cmc of NaSal is 298 ± 21 mmol/kg based on the δ vs 1/cNaSal plot, one way to think about this is as NaSal being an amphiphile with very large cmc63. Similar apparent δ changes were also observed in the 1H NMR spectra of NaSal/EAPB mixtures at R = 2 and different cEAPB (Fig. 5a). The δ of H3, H4, and H5 shift toward upfield significantly at the higher cEAPB, whereas the shift for H6 is much less. This is evidence for co-assembly of NaSal with the hydrophobic aromatic ring inserting into micellar cores and polar section in the micellar palisade layer27,44,50. To quantitatively distinguish the difference between NaSal in NaSal/EAPB mixtures and NaSal alone in water, the chemical shift change (Δδ) vs cEAPB plots were investigated (Fig. 5b), where Δδ (Δδ = δNaSal/EAPB mixture − δNaSal) is the difference between the apparent chemical shift of NaSal in the mixture and that of NaSal at the same cNaSal. The absolute values of Δδ of all protons decrease upon lowering cEAPB. This suggests that the micro-environment of NaSal in the mixtures is significantly distinguished from that of NaSal alone at high cEAPB.
Fig. 5: Molecular interactions between surfactants and hydrotropes.
figure 5
a 1H NMR spectra of NaSal/EAPB mixtures in D2O at the NaSal and EAPB molar ratio R of 2 at different concentration of EAPB (cEAPB). b The corresponding chemical shift change (Δδ) vs cEAPB plots of protons H6 (red square), H4 (blue circle), H3 and H5 (green triangle). The inset image shows the relevant protons in the aromatic ring of NaSal as signed by H3, H4, H5, and H6, respectively. c 1H NMR spectra of NaSal/EAPB mixtures in D2O at cEAPB = 10 mmol/kg at different R and d the corresponding Δδ vs R plots of protons H6 (red square), H4 (blue circle), H3 and H5 (green triangle).
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In NaSal/EAPB aqueous mixtures, NaSal molecules are present both in water and in the hybrid micelles simultaneously. At the constant R = 2, the higher cEAPB results in the lower mass fractions of water in the bulk, which promotes the actual concentration of NaSal. For example, the fractions of water are 0.88, 0.67, and 0.5 at cEAPB of 100, 417, and 625 mmol/kg with the nominal cNaSal in the mixtures of 200, 834, and 1250 mmol/kg, respectively. However, the actual cNaSal in water are 218, 1043, and 1786 mmol/kg, respectively, which are far larger than the nominal cNaSal. The difference between the actual and nominal cNaSal is enlarged significantly at the higher cEAPB. Noticeably, NaSal will arrive its cmc in the mixture at the critical cEAPB of 140 mmol/kg. Thus, the actual cNaSal is far larger than cmc in the formation region of NaSal/EAPB HCSMs. Undoubtedly, the high cNaSal would facilitate the co-assembly of NaSal in micelles to favor the formation of NaSal/EAPB SMs.
During the process, the binding degree between NaSal and EAPB in micelles is enhanced, resulting in the compressed electric double layers of SMs. Accordingly, the micellar shell thickness (Ts) decreases as confirmed by SAXS (Supplementary Tab 1). The effect of R on Δδ at the constant cEAPB (Fig. 5c, d) is similar with that of cEAPB (Fig. 5b). For one thing, the enlarged R is certainly beneficial to the transfer of NaSal from water into micelles, and thereby enhancing the binding degree between NaSal and EAPB (Supplementary Fig 8b). On the other hand, the reduced content of water at the higher cEAPB is advantageous to increase the binding degree of Sal- counterions in micelles, favoring the formation SMs at the lower R. Accordingly, the WLMs to SMs transitions at the higher cEAPB happens at the relatively smaller R. It is obvious that the competitive self-sorting and co-assembly between hydrotropes and surfactants in water and in aggregates can be adjusted sustainedly by both R and dilution, which is also the main driving force in the R-induced gel-sol-gel and dilution-induced gel-sol-gel-sol transitions.
Discussion
In summary, adding NaSal can induce the gradual transitions from WLMs to HCP via H1 and sequential HCSMs in concentrated EAPB aqueous solutions by continuously increasing R. More importantly, NaSal/EAPB HCPs show dilution-driven gel-sol-gel-sol sequential transitions. In general, the closely packed SMs in HCPs were dissociated into low-viscosity HCSMs directly by slight dilution, i.e., lowering cEAPB from 625 to 594 mmol/kg. This corresponds to the first dilution-induced gel-sol process. Further decreasing cEAPB, the HCSMs were transferred into viscoelastic gels due to the formation of very long and entangled WLMs at the intermediate cEAPB, i.e., between 100 and 50 mmol/kg, showing a dilution-induced sol-gel transition. It would appear that this is universal in aromatic hydrotrope/zwitterionic surfactant two-component systems, and WLMs are gradually grown from connected networks of SMs and the sequential RMs. Upon continuous dilution, a second dilution-induced gel-sol transition was observed due to the formation of SMs via long and rigid WLMs in the semi-dilute solutions. During this process, the sustained adjustment of the competitive self-sorting and co-assembly between hydrotropes and surfactants in water and in aggregates by dilution is the most important. This work provides a general way to create dilution-driven gel-sol-gel-sol transitions in surfactant WLMs systems, which will in turn benefit the application of WLMs fluids with switchable viscosity in fields for metal cleaning, personal care products, drug delivery and enhanced oil recovery technologies.
Methods
Materials
Erucyl dimethyl amidopropyl betaine (EAPB) and erucyl dimethyl amidopropyl hydroxysulfobetaine (EHSB) were synthesized and purified according to the reported procedure64, which were described in the Supplementary material. Aromatic hydrotropes including sodium salicylate (99%, NaSal), sodium benzoate (99%, NaBen), sodium p-toluenesulfonate (99%, NaOTs), 3-hydroxy-2-naphthoic acid (99%, HNC), 4-methylsalicylic acid (99%, 4MS) and 5-methylsalicylic acid (99%, 5MS) were all purchased from Aladdin and used as received. The corresponding sodium salts such as NaHNC, 4NaMS and 5NaMS were obtained by the neutralization method using equimolar NaOH from HNC, 4MS and 5MS, respectively. N-(3-(dimethylamino) propyl) erucamide (Winsono New Material Technology Co. Ltd, China) and other chemicals from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China) were used as received. The resistance of the ultrapure water produced by Millipore-Q was 18.2 MΩ·cm at 25 °C.
Preparation of hydrotrope/zwitterionic surfactant aqueous mixtures
The required amount of surfactant, hydrotrope, and water was weighed and then mixed in vials to obtain hydrotrope/zwitterionic surfactant aqueous mixtures. All mixtures were stirred at 60 °C until transparent and homogeneous, and then equilibrated at 25 °C. Samples for NMR measurements were prepared in D2O (99.8 atom% D).
Rheology measurements
Steady and dynamic rheological measurements were performed on a HAAKE MARS 60 rheometer (ThermoFisher Scientific, Germany) by employing a Couette geometry DG 41, a cone & plate geometry CP 35 (diameter 35 and cone angle 1°) or CP 60 (diameter 60 mm and cone angle 1°) at 25 °C. The dynamic rheological responses were measured in the linear viscoelastic region as measured by the stress sweeps at a fixed frequency of 1 Hz. All samples were equilibrated at least 3 h under the required conditions before each measurement except the time-dependent experiments, which were performed immediately. In addition, a solvent trap was used to minimize the water evaporation.
Polarized optical microscopy measurements
Polarized optical microscopy (POM) images were obtained on a polarized optical microscopy (Olympus BX51, Japan), in which the sample was dropped on a slide and covered by a glass slip.
Cryogenic transmission electron microscopy (cryo-TEM) measurements
The specimens of aggregates in the aqueous solutions for cryo-TEM observation were prepared according to the reported procedure65. Typically, 2 µL sample was deposited on the surface of a TEM copper grid covered by a holey carbon film, and the excess solution was blotted away to form a thin liquid film. Then, the grid was immediately plunged into liquid ethane cooled by liquid nitrogen, and the obtained specimen was maintained at approximately −173 °C before observation. The specimen of the NaSal/EAPB HCP was prepared by the cryo-focused-ion-beam (cryo-FIB) technique66, the cryo-FIB (Aquilos 2, Thermo Fisher) milling was used to carve (micromachining) out a 100–250-nm-thin lamella for cryo-TEM observation. Cryo-TEM images were performed on a transmission electron microscope (Glacios, Thermo Fisher) at an accelerating voltage of 200 kV under low dose conditions.
Small angle X-ray scattering (SAXS) measurements
SAXS measurements were carried out by Anton Paar SAXSpoint 2.0 (Anton Paar, Austria) equipped with an EIGER R 1 M detector (Dectris, Switzerland). The radiation was produced from Cu/Mo double micro focal spot, and the wavelength (λ) was 0.1542 nm. Aqueous samples were sealed in a quartz capillary with thickness and external diameter of 10 μm and 1 mm, respectively. Experiments were performed by applying a fixed sample-detector distance of 350 mm at 25 °C under vacuum, and the exposure time was 30 min. The raw data were reduced into one-dimensional form using SAXS analysis software (Anton Paar, Austria), and the influence of solvent was eliminated for subsequent analysis. The scattering vector q is q = (4π sin θ)/λ, where θ is half of the scattering angle. The SAXS data were fitted by employing SasView software (http://www.sasview.org/, version 5.0.6). SMs were analyzed by the core-shell sphere or ellipsoid model associated with the Hayter-Penfold Rescaled Mean Spherical Approximation (RMSA) structure factor67, in which the electric double layer repulsion between colloidal particles was expressed by means of a screened Coulomb potential. Alternatively, the core-shell cylinder model was employed for WLMs. The scattering length densities of core and solvent employed were 7.73 × 10-6Å−2 and 9.43 × 10-6Å−2, respectively, which were estimated using 1-docosene and water. The scattering length density of shell employed was 10.02 × 10−6Å−2 65.
Proton nuclear magnetic resonance (1H NMR) measurements
1H NMR spectra were recorded on a Bruker Avance 400 at 25 °C. All chemical shifts were measured from the internal residual proton of HOD in D2O, and the solvent effects on the shifts were negligible.
Zeta potential measurements
Zeta potential measurements were performed on a Zetasizer ZEN 3600 (Malvern, UK) with a 173° back scattering angle and He-Ne laser (λ = 633 nm) at 25 °C.
Data availability
The data supporting the findings of this study are available within the article and the supplementary file. All data are available from the corresponding author upon request. Source data are provided with this paper.
References
Lombard, J. et al. The early evolution of lipid membranes and the three domains of life. Nat. Rev. Microbiol. 10, 507–515 (2012).
CASPubMedMATHGoogle Scholar
Levin, A. et al. Biomimetic peptide self-assembly for functional materials. Nat. Rev. Chem. 4, 615–634 (2020).
CASPubMedPubMed CentralMATHGoogle Scholar
Jordan, S. F. et al. Promotion of protocell self-assembly from mixed amphiphiles at the origin of life. Nat. Ecol. Evol. 3, 1705–1714 (2019).
PubMedMATHGoogle Scholar
Chagri, S. et al. Designing bioresponsive nanomaterials for intracellular self-assembly. Nat. Rev. Chem. 6, 320–338 (2022).
PubMedPubMed CentralGoogle Scholar
Das, K. et al. Chemically fueled self‐assembly in biology and chemistry. Angew. Chem. Int. Ed. 60, 20120–20143 (2021).
CASMATHGoogle Scholar
Gonçalves, R. A. et al. Cationic surfactants: a review. J. Mol. Liq. 375, 121335 (2023).
MATHGoogle Scholar
Long, P. & Hao, J. Phase behavior and self-assembly aggregation of hydrocarbon and fluorocarbon surfactant mixtures in aqueous solution. Adv. Colloid Interface Sci. 171–172, 66–76 (2012).
PubMedMATHGoogle Scholar
Ghosh, S. et al. Self-assembly of surfactants: an overview on general aspects of amphiphiles. Biophys. Chem. 265, 106429 (2020).
ADSCASPubMedMATHGoogle Scholar
Greavesa, T. L. & Drummond, C. J. Ionic liquids as amphiphile self-assembly media. Chem. Soc. Rev. 37, 1709–1726 (2008).
Google Scholar
Lu, Y. et al. Self-assembly of copolymer micelles: higher-level assembly for constructing hierarchical structure. Chem. Rev. 120, 4111–4140 (2020).
CASPubMedMATHGoogle Scholar
Kekicheff, P. & Cabane, B. Crystallography of systems with long periods: a neutron-scattering study of sodium dodecyl sulfate/water mesophases. Acta Crystallogr. 44, 395–406 (1988).
Google Scholar
Chen, S. et al. Self-assembly of photoresponsive molecular amphiphiles in aqueous media. Angew. Chem. Int. Ed. 60, 11604–11627 (2021).
ADSCASMATHGoogle Scholar
Liu, Q. et al. Temperature-responsive self-assembly of single polyoxometalates clusters driven by hydrogen bonds. Adv. Funct. Mater. 31, 2103561 (2021).
CASGoogle Scholar
Dowlati, S. et al. Advances in CO2-switchable surfactants towards the fabrication and application of responsive colloids. Adv. Colloid Interface Sci. 315, 102907 (2023).
CASPubMedMATHGoogle Scholar
Dai, L. et al. All-lignin-based hydrogel with fast pH-stimuli responsiveness for mechanical switching and actuation. Chem. Mater. 32, 4324–4330 (2020).
CASMATHGoogle Scholar
Brown, P. et al. Magnetic control over liquid surface properties with responsive surfactants. Angew. Chem. Int. Ed. 51, 2414–2416 (2012).
CASMATHGoogle Scholar
Yang, Y. et al. Micelle to vesicle transitions of N-dodecyl-1, ω-diaminoalkanes: effects of pH, temperature and salt. J. Colloid Interface Sci. 380, 83–89 (2012).
ADSCASPubMedMATHGoogle Scholar
Heuser, T. et al. Biocatalytic feedback‐driven temporal programming of self‐regulating peptide hydrogels. Angew. Chem. Int. Ed. 54, 13258–13262 (2015).
CASMATHGoogle Scholar
Huang, Y. Y. et al. Self‐assembly of multi‐nanozymes to mimic an intracellular antioxidant defense system. Angew. Chem. Int. Ed. 55, 6646–6650 (2016).
CASMATHGoogle Scholar
Liu, Y. et al. Switchable surfactants. Science 313, 958–960 (2006).
ADSCASPubMedMATHGoogle Scholar
Weingarten, A. S. et al. Self-assembling hydrogel scaffolds for photocatalytic hydrogen production. Nat. Chem. 6, 964–970 (2014).
CASPubMedPubMed CentralMATHGoogle Scholar
Grzelczak, M. et al. Stimuli-responsive self-assembly of nanoparticles. Chem. Soc. Rev. 48, 1342–1361 (2019).
CASPubMedMATHGoogle Scholar
Hu, J. et al. Development of highly efficient oil–water separation carbon nanotube membranes with stimuli-switchable fluxes. ACS Omega 3, 6635–6641 (2018).
CASPubMedPubMed CentralMATHGoogle Scholar
Lu, C. & Urban, M. W. Stimuli-responsive polymer nano-science: Shape anisotropy, responsiveness, applications. Prog. Polym. Sci. 78, 24–46 (2018).
CASGoogle Scholar
Lu, Y. et al. Advanced switchable molecules and materials for oil recovery and oily waste cleanup. Adv. Sci. 8, 2004082 (2021).
CASGoogle Scholar
Omari, A. et al. A comprehensive review of recent advances on surfactant architectures and their applications for unconventional reservoirs. J. Petrol. Sci. Eng. 206, 109025 (2021).
CASMATHGoogle Scholar
Lu, Y. et al. Light-responsive viscoelastic fluids based on anionic wormlike micelles. J. Colloid Interface Sci. 412, 107–111 (2013).
ADSCASPubMedMATHGoogle Scholar
Silva, B. F. B. et al. Unusual vesicle-micelle transitions in a salt-free catanionic surfactant: temperature and concentration effects. Langmuir 24, 10746–10754 (2008).
CASPubMedMATHGoogle Scholar
Battaglia, G. & Ryan, A. J. The evolution of vesicles from bulk lamellar gels. Nat. Mater. 4, 869–876 (2005).
ADSCASPubMedMATHGoogle Scholar
Taguchi, S. et al. A novel method of vesicle preparation by simple dilution of bicelle solution. Biochem. Eng. J. 162, 107725 (2020).
CASMATHGoogle Scholar
Davies, T. S. et al. Self-assembly of surfactant vesicles that transform into viscoelastic wormlike micelles upon heating. J. Am. Chem. Soc. 128, 6669–6675 (2006).
CASPubMedMATHGoogle Scholar
Zhang, Y. et al. Bell-shaped sol–gel–sol conversions in pH-responsive worm-based nanostructured fluid. Soft Matter 11, 2080–2084 (2015).
ADSCASPubMedMATHGoogle Scholar
Zhang, Y. et al. CO2-switchable wormlike micelles. Chem. Commun. 49, 4902–4904 (2013).
ADSCASGoogle Scholar
Jia, K. et al. Thermal, light and pH triple stimulated changes in self-assembly of a novel small molecular weight amphiphile binary system. RSC Adv. 5, 640–642 (2015).
ADSCASMATHGoogle Scholar
Dehmoune, J. et al. Shear thickening in three surfactants of the alkyl family CnTAB: Small angle neutron scattering and rheological study. Langmuir 25, 7271–7278 (2009).
CASPubMedMATHGoogle Scholar
Wojciechowski, J. P. et al. Kinetically controlled lifetimes in redox-responsive transient supramolecular hydrogels. J. Am. Chem. Soc. 140, 2869–2874 (2018).
CASPubMedMATHGoogle Scholar
Hermans, T. M. & Singh, N. Chemically fueled autonomous sol–gel–sol–gel–sol transitions. Angew. Chem. Int. Ed. 62, e202301529 (2023).
CASGoogle Scholar
Panja, S. et al. Controlling syneresis of hydrogels using organic salts. Angew. Chem. Int. Ed. 61, e202115021 (2022).
ADSCASMATHGoogle Scholar
Shintani, Y. et al. Oxidation‐responsive supramolecular hydrogel based on a simple fmoc‐cysteine derivative capable of showing autonomous gel–sol–gel transitions. Adv. Funct. Mater. 34, 2312999 (2024).
CASGoogle Scholar
Su, L. et al. Dilution-induced gel-sol-gel-sol transitions by competitive supramolecular pathways in water. Science 377, 213–218 (2022).
ADSCASPubMedMATHGoogle Scholar
Eastoe, J. et al. Action of hydrotropes and alkyl-hydrotropes. Soft Matter 7, 5917–5925 (2011).
ADSCASMATHGoogle Scholar
Kunz, W. et al. Hydrotropes. Curr. Opin. Colloid Interface Sci. 22, 99–107 (2016).
CASGoogle Scholar
Lin, Y. et al. A facile route to design pH-responsive viscoelastic wormlike micelles: smart use of hydrotropes. J. Colloid Interface Sci. 330, 449–455 (2009).
ADSCASPubMedMATHGoogle Scholar
Jia, K. et al. Light-responsive multillamellar vesicles in coumaric acid/alkyldimethylamine oxide binary systems: effects of surfactant and hydrotrope structures. J. Colloid Interface Sci. 477, 156–165 (2016).
ADSCASPubMedGoogle Scholar
Lu, S. et al. Molecular origin for pH-responsive wormlike micelles of zwitterionic surfactants triggered by aromatic acid derivatives. ChemPhysMater 3, 230–238 (2024).
MATHGoogle Scholar
Mushi, S. J. et al. Viscoelasticity and microstructural properties of zwitterionic surfactant induced by hydroxybenzoate salt for fracturing. J. Mol. Liq. 301, 112485 (2020).
CASMATHGoogle Scholar
Zhang, J. et al. Dilution or heating induced thickening in a sodium dodecyl sulfate/p-toluidine hydrochloride aqueous solution. RSC Adv. 6, 39016–39023 (2016).
ADSCASGoogle Scholar
Hassan, P. A. et al. Microstructural changes in SDS micelles induced by hydrotropic salt. Langmuir 18, 2543–2548 (2002).
CASMATHGoogle Scholar
Hassan, P. A. et al. Small angle neutron scattering study of sodium dodecyl sulfate micellar growth driven by addition of a hydrotropic salt. J. Colloid Interface Sci. 257, 154–162 (2003).
ADSCASPubMedMATHGoogle Scholar
Kumar, R. et al. Wormlike micelles of a C22-tailed zwitterionic betaine surfactant: from viscoelastic solutions to elastic gels. Langmuir 23, 12849–12856 (2007).
CASPubMedGoogle Scholar
Verma, G. et al. Dilution induced thickening in hydrotrope-rich rod-like micelles. J. Colloid Interface Sci. 359, 163–170 (2011).
ADSCASPubMedMATHGoogle Scholar
Verma, G. et al. Transition from long micelles to flat bilayers driven by release of hydrotropes in mixed micelles. Soft Matter 9, 4544–4552 (2013).
ADSCASMATHGoogle Scholar
Zeng, X. et al. Hexagonal close packing of nonionic surfactant micelles in water. J. Phys. Chem. B 111, 5174–5179 (2007).
CASPubMedMATHGoogle Scholar
Park, M. J. et al. Epitaxial transitions among FCC, HCP, BCC, and cylinder phases in a block copolymer solution. Macromolecules 37, 9064–9075 (2004).
ADSCASGoogle Scholar
Chen, L. et al. Close-packed block copolymer micelles induced by temperature quenching. Proc. Natl. Acad. Sci. USA 115, 7218–7223 (2018).
ADSCASPubMedPubMed CentralGoogle Scholar
Ji, X. et al. Effects of calcium ions on the solubility and rheological behavior of a C22-tailed hydroxyl sulfobetaine surfactant in aqueous solution. Langmuir 34, 291–301 (2018).
CASPubMedMATHGoogle Scholar
Ghosh, S. K. et al. Structure of mesh phases in a cationic surfactant system with strongly bound counterions. Langmuir 23, 3606–3614 (2007).
CASPubMedMATHGoogle Scholar
Ghosh, S. K. et al. Re-entrant phase behavior of a concentrated anionic surfactant system with strongly binding counterions. Langmuir 25, 8497–8506 (2009).
CASPubMedMATHGoogle Scholar
Krishnaswamy, R. et al. Phase behavior of concentrated aqueous solutions of cetyltrimethylammonium bromide (CTAB) and sodium hydroxy naphthoate (SHN). Langmuir 21, 10439–10443 (2005).
CASPubMedMATHGoogle Scholar
Pal, A. et al. Defect-mediated lamellar–isotropic transition of amphiphile bilayers. Soft Matter 8, 9069–9072 (2012).
ADSCASMATHGoogle Scholar
Kamal, M. A. & Pal, A. Topological changes accompanying the phase transitions in AOT-water binary system in the presence of a strongly binding counter-ion. Colloids Surf. A 611, 125788 (2021).
MATHGoogle Scholar
Abdel-Rahem, R. The influence of hydrophobic counterions on micellar growth of ionic surfactants. Adv. Colloid Interface Sci. 141, 24–36 (2008).
CASPubMedGoogle Scholar
Balasubramanian, D. et al. Aggregation behavior of hydrotropic compounds in aqueous solution. J. Phys. Chem. 93, 3865–3870 (1989).
CASMATHGoogle Scholar
Wang, Y. et al. Effect of a hydrophilic head group on Krafft temperature, surface activities and rheological behaviors of erucyl amidobetaines. J. Surfactants Deterg. 17, 295–301 (2014).
CASMATHGoogle Scholar
Lu, S. et al. Gradual transformation of anionic/zwitterionic wormlike micelles from viscous to elastic domains: unravelling the effect of anionic surfactant chain length. J. Colloid Interface Sci. 641, 319–328 (2023).
ADSCASPubMedMATHGoogle Scholar
Wagner, F. R. et al. Preparing samples from whole cells using focused-ion-beam milling for cryo-electron tomography. Nat. Protoc. 15, 2041–2070 (2020).
CASPubMedPubMed CentralMATHGoogle Scholar
Hayter, J. B. & Penfold, J. An analytic structure factor for macroion solutions. Mol. Phys. 42, 109–118 (1981).
ADSCASMATHGoogle Scholar
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Acknowledgements
We acknowledge support from the National Natural Science Foundation of China [NSFC 22372125 and 22072109]. We are grateful to the Core Facility of Wuhan University for the cryo-TEM measurements, Xi’an Jiaotong University and University of Science and Technology of China for the SAXS measurements.
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Engineering Research Center of Organosilicon Compounds & Materials, Ministry of Education, College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, 430072, PR China
Shuo Lu, Yashuang Liu, Jinfeng Dong & Xuefeng Li
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Shuo Lu
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S.L.: Investigation, data curation, Formal analysis. Y.L.: Investigation. J.D.: Project administration, Methodology, Writing—review & editing. X.L.: Conceptualization, Methodology, Formal analysis, Validation, Project administration, Funding acquisition, Writing—original draft.
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Lu, S., Liu, Y., Dong, J. et al. Dilution-driven gel-sol-gel-sol transitions by the sequential evolution of surfactant micelles. Nat Commun 16, 2314 (2025). https://doi.org/10.1038/s41467-025-57686-w
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Received:04 July 2024
Accepted:27 February 2025
Published:08 March 2025
DOI:https://doi.org/10.1038/s41467-025-57686-w
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