Investigation of Active-Inactive Material Interdigitated Aggregates

Aug 31, 2018 - B: Fluid Interfaces, Colloids, Polymers, Soft Matter, Surfactants, and Glassy ... Investigation of Active-Inactive Material Interdigita...
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B: Fluid Interfaces, Colloids, Polymers, Soft Matter, Surfactants, and Glassy Materials

Investigation of Active-Inactive Material Interdigitated Aggregates Formed by Wormlike Micelles and Cellulose Nanofiber Mingwei Zhao, Zhibin Gao, Caili Dai, Yue Zhang, Xin Sun, Mingwei Gao, Yongping Huang, Long He, and Yining Wu J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.8b06440 • Publication Date (Web): 31 Aug 2018 Downloaded from http://pubs.acs.org on September 2, 2018

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Investigation of Active-Inactive Material Interdigitated Aggregates Formed by Wormlike Micelles and Cellulose Nanofiber Mingwei Zhao,a Zhibin Gaoa Caili Dai,a,* Yue Zhang,a, Xin Sun,a Mingwei Gao,a Yongping Huang,a Long He,b Yining Wua,* a

School of Petroleum Engineering, State Key Laboratory of Heavy Oil Processing, China University of Petroleum (East China), Qingdao, Shandong 266580, China

b

Petroleum Engineering Institute, Northwest Branch of Sinopec, Urumchi, Xinjiang 830000, China

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ABSTRACT: In this work, a novel active-inactive material interdigitated aggregates (AIMIAs) structure was constructed by self-assembled wormlike micelles (WLMs) and one-dimensional cellulose nanofiber (CNF). The rheological behaviors and microstructures of AIMIAs systems with different CNF concentrations were investigated by rheometer, cryogenic transmission electron microscopy and environmental scanning electron microscope. Some key parameters including zeroshear viscosity (η0), relaxing time (τR) and contour length (L) were calculated to analyze the changes in properties of different systems. Meanwhile, a proper mechanism describing the interaction between CNF and WLMs was proposed. Through this work, we expect to deepen the understanding of AIMIAs structure and widen its application.

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1. INTRODUCTION

In recent years, the aggregation behavior of surfactant in aqueous solution has been a research focus1,2. As the concentration of surfactant increases, surfactant molecules gradually aggregate to form spherical micelles, rod micelles, wormlike micelles (WLMs), vesicles and lamellar crystals3. Herein, WLMs have attracted much attention because of the unique viscoelastic network structure4-7. In general, WLMs can be formed by self-assembled surfactant molecules based on the non-covalent bonds8. This assembled process is always in a dynamic equilibrium of reassemble-dissociate, which determines the distinctive properties of WLMs. As a result, WLMs are also called “living polymer”9. Generally, the length of WLMs can be promoted by adding counter ions, which can screen the electrostatic repulsion between the surfactant molecules10,11. Once the WLMs grow to a certain length, they can overlap and entangle with each other12,13. Then, a complex network with viscoelasticity occurs in solution, which is the fundamental component of viscoelastic surfactant (VES) fracturing fluid14-16. However, the network structure of WLMs developed by adding surfactants or counter ions is easy to be destroyed, leading to a significant reduction in viscoelasticity of system, and this phenomenon limits the application of VES fracturing fluid17. How to strengthen the network structure of wormlike micelles becomes an urgent problem3. At present, many groups have made effective efforts to improve the viscoelasticity of WLMs. Kumar et al. studied the rheological behavior of erucyl dimethyl amidopropyl betaine with C22-carbon-tail at different temperatures18. They found that 3

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WLMs conformed to the characteristic of Maxwell model, maintaining an obvious viscosity even at 60 °C. Mao et al. synthesized a new Gemini surfactant which can enhance the network of WLMs, resulting in a remarkable improvement of viscoelasticity14. However, the branched chain was detrimental to the entanglement of WLMs as it increased the steric hindrance and stiffness of surfactant. Unfortunately, it may be difficult to satisfy the demand for higher viscoelasticity in WLMs system by designing and synthesizing new surfactant molecules. Another effective method, adding certain amounts of nanoparticles, was proposed as these new materials can strengthen the network structure of WLMs19. Helgeson et al. proposed a “double networks” model, which revealed a physical cross-link structure between micelles and nanoparticles20. We analyzed the changing in the parameters of nanoparticle-enhanced wormlike micellar system formed in a surfactant aqueous with different concentrations of silica nanoparticles3,21. A bilayer circular structure consisting of micelles and nanoparticles was formed under the combined effects of electrostatic force and hydrophilic interaction, resulting in a larger length and more complex entanglement of micelles. Therefore, in contrast to the network structure with bilayer nodes composed of nanoparticles and micelles, we wandered whether one-dimensional nanofibers can construct a more complex and stable network by intertwining WLMs, making a fascinating advance in enhancing the viscoelasticity of WLMs system, which can speed up the application of VES fracturing fluid. In fact, cellulose nanofiber (CNF), also called nanofibrillated cellulose or microfibrillated cellulose, as a new one-dimensional nanomaterial, has many special properties22-25. The diameter of CNF is only a few 4

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nanometers, which is about the same as that of WLMs. Its aspect ratio usually ranges from 100 to 1000, providing CNF flexibility and large specific surface area26. More importantly, CNF tends to overlap and interweave, resulting in an active-inactive material interdigitated aggregates (AIMIAs) structure between WLMs and CNF, which may greatly enhance the viscoelasticity of WLMs27,28. In this work, the AIMIAs system was prepared by sodium oleate (NaOA) and potassium chloride (KCl) with the addition of CNF. Some equipments, including rheometer,

cryogenic

transmission

electron

microscopy

(Cryo-TEM)

and

environmental scanning electron microscope (ESEM), were employed to investigate the rheological properties and microstructure of AIMIAs system. Furthermore, the mechanism describing the effects of CNF on WLMs was also proposed. Compared with the network formed by WLMs, the AIMIAs system has a more complex and stable structure, demonstrating it can enhance the stability of network at high shear frequency. As a result, the AIMIAs structure can help to accelerate the popularization and application of viscoelastic surfactant fracturing fluid.

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2. MATERIALS AND METHODS 2.1. Materials. Sodium oleate (NaOA) and potassium chloride (KCl) were prepared (both were analytical purity and bought from Sinopharm Chemical Reagent Co., Ltd.), and cellulose nanofiber (CNF) was premium grade (obtained from Chemkey Advanced Materials Technology Co., Ltd.). The main chain of cellulose nanofiber was shown in Fig. 1. The reagents were used without further purification. Samples were prepared using deionized water. AIMIAs system was prepared with the following steps. First, solutions of 200 mM NaOA and 600 mM KCl were prepared separately. Then, two equal cellulose nanofibers (CNFs) were added to the solutions with shaking mildly for a few minutes. After that, AIMIAs samples were prepared by mixing KCl solution and NaOA solution and stirred slightly at 25 °C. Finally, samples were stored for at least 24 h prior to further testing after prepared. In addition, the solution without CNF was used as a contrast sample.

Fig. 1 The main chain of cellulose nanofiber

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2.2 Rheological Measurements. Rheological measurements were carried out on a Haake RS6000 rheometer with a cone-and-plate sensor system (C35 2°/Ti). The test temperature was fixed at 25.00 ± 0.05 °C with the help of Peltier-based temperature control. In steady shear measurement, the shear rate ranged from 0.01 to 100 s-1. In oscillatory measurements, dynamic oscillation shear measurements were employed to investigate the storage modulus and loss modulus of system. During this measurement, frequency sweep was performed at a special stress (σ) which was determined in linear viscoelastic stress zone of system, so that the frequency sweep can be guaranteed in linear viscoelastic domain. The frequency was set up from 0.01 to 100 rad/s. 2.3 Cryogenic Transmission Electron Microscopy (Cryo-TEM). AIMIAs sample was prepared in a controlled environment vitrification system (CEVS) at 25 °C. The 5-μL solution was taken by a micropipette and spread on a TEM copper grid. The excess solution was blotted by filter paper, leading to a thin film on the mesh holes. After waiting for about 5 s, the copper grid adhering with AIMIAs sample was put into liquid ethane at -165 °C, resulting a vitrified sample. Then, a JEOL JEM-1400 TEM (120 kV) was employed to detect the processed sample at -174 °C. The images were kept on Gatan Multiscan CCD and managed by Digital Micrograph.

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2.4 Environmental Scanning Electron Microscope (ESEM). An environmental scanning electron microscope (ESEM, FEI Quanta 650) was employed to investigate the microstructure of dried AIMIAs samples. The images of system were measured by using an accelerating voltage of 20 kV and the operating pressure was 3-5 torr of water vapor. All samples were fractured in liquid nitrogen. In order to improve the quality of images, the surface of fracture was sputter-coated with gold by using a Denton sputter coater.

3. RESULTS AND DISCUSSION

3.1 Rheological Properties of WLMs.

Rheological measurements were

employed to explore the viscosity of surfactant solutions with 100 mM NaOA and 300 mM KCl. The results are shown in Fig. 2a. At low shear rates, the value of viscosity in solution keeps constant with the increasing shear rates, showing the characteristic of typical Newtonian behaviors. At high shear rates, the viscosity decreases with the increasing shear rates, indicating the shear thinning phenomenon29. These phenomena are supposed to be the evidence of WLMs existing30,31. Cryo-TEM technique was carried out to detect the formation of WLMs. As shown in Fig. 2b, WLMs are long but hard to be measured because of the limit of instrument, and the complex network structure formed by flexible micelles contributed to the viscosity of system32.

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Fig. 2. (a) Steady rheology plots for solutions with 100 mM NaOA and 300 mM KCl at 25 °C. (b) Cryo-TEM image of solution with 100 mM NaOA and 300 mM KCl at 25 °C.

3.2 Formation of AIMIAs.

In order to investigate the effect of CNFs on WLMs,

steady shear measurement was employed. The results are shown in Fig. 3a and Fig. 3b. As shear rates increase, the viscosity of solutions with different CNF concentrations keep constant at low shear rates while decrease at high shear rates, showing the features of WLMs33. As can be seen in Fig. 3b, with the increasing of CNF addition, the zeroshear viscosity (the viscosity plateau value of solution at low shear rates, η0) increases sharply until the CNF concentration comes up to 0.03 wt%, demonstrating that CNF can strengthen the network of WLMs34. Then, the value of η0 declines gradually with the further addition of CNF, indicating the break of AIMIAs. The viscoelastic properties of three typical solutions were investigated by oscillatory measurements at 25 °C. The viscoelastic modulus curves are presented in Fig. 3c. For the solution without CNF, at low frequencies, both storage modulus G’ and loss modulus G” increase with frequency. The value of G” is higher than that of G’, showing the system was dominated by viscous properties. At high frequencies, G’ is 9

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higher than G”, meaning the elastic properties made a major contribution to the system35. Meanwhile, with the increasing in frequencies, G’ tends to remain growing while G” prefers to keep constant, indicating the viscoelastic properties of system deviate from Maxwell model36. This phenomenon occurs on account of the rouse motion which is caused by rapid breaking of WLMs at high frequencies37. Compared with pure WLMs, the storage modulus G’ and loss modulus G” of solution with 0.03 wt% CNF are separately higher, indicating CNF can strengthen the network of WLMs. Furthermore, in order to eliminate the misunderstanding of viscoelastic fluid by the one-dimensional structure of CNF itself, steady shear measurement was applied to CNF aqueous solution. Obviously, from the curve showed in Fig. 3d, it can be asserted that the CNF aqueous solution belongs to Newtonian fluid because of the linear function relations between shear stress and shear rate. Therefore, CNF cannot offer the viscoelastic properties of AIMIAs immediate assistance. It can strengthen the network of WLMs in a special way according to the rheological behaviors of different AIMIAs systems.

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Fig. 3. (a) Steady-shear viscosities for 100 mM NaOA/300 mM KCl with different CNF concentrations at 25 °C. (b) Variations in zero-shear viscosity (η0) as a function of different CNF concentrations for 100 mM NaOA/300 mM KCl at 25 °C. (c) Variations of G’ and G’’ with shear frequency for 100 mM NaOA/300 mM KCl with different CNF concentrations (0 wt%, 0.03 wt%, 0.3 wt%). (d) Rheological curve of 0.03 wt% CNF aqueous solution. In order to detect the microstructure of AIMIAs, ESEM technique was carried out. The images of three typical solutions are presented in Fig. 4. For the WLMs without CNF, a three-dimensional network with thin walls and several gaps formed by WLMs can be observed clearly from Fig. 4a, which shows a destructible structure, corresponding to the low G’ and G’’ of system. Compared with the pure WLMs, the network formed in solution with 0.03 wt% CNF is more complex and stable. As shown in Fig. 4b, the microstructure of AIMIAs seems to be aggregates of various “dead caves”. Unlike the chemical bonds of CNF molecule, the non-covalent bonds among surfactant molecules tend to be destroyed, meaning the structure of pure WLMs was weaker than that of AIMIAs. Compared with the pure wormlike micelles network which is weak in the disordered and fragmented 11

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structure, “dead caves” have bottom caps and enclosed walls. They can separate aqueous solution into independent spaces, preventing water from moving once the shear force is applied. In addition, from Fig. 3c, the G’ and G’’ of the AIMIAs system are larger than those of WLMs system at same shear frequency, demonstrating the network formed by AIMIAs is harder to be destroyed. When more CNF is added to the solution, the microstructure of AIMIAs changes significantly. As can be seen in Fig. 4c, the grid of network grows larger while the number of grids decreases. The thicker walls with thinner joints are presented in network as well. Under the combined effect of two factors, water is hard to be trapped in original position once there is a disturbance. More deeply, as the concentration of CNF increases, WLMs get closer as the result of the lager electrostatic repulsion, which causes the appearing of branched joints38. Differing from the grafting point in polymer, the branched joints can slide freely along the outline of WLMs, resulting in a brittle network.

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Fig. 4. ESEM images of the AIMIAs with 100 mM NaOA/300 mM KCl and different CNF concentrations (a-0 wt%, b-0.03 wt%, c-0.3 wt%). In order to quantitatively analyze the interaction between WLMs and CNF, some basic parameters which can describe the rheological properties of WLMs were calculated according to the following equations: 1

𝜏𝑅 = 𝜔

(1)

𝑐𝑜

The value of ωco is the frequency of the crossing point when G’ equals G”. The relaxing time τR can reflect the complexity of network formed by WLMs. The contour length L can be calculated by Eq. 3 and Eq. 512: ′ ′′ 𝐺∞ = 2𝐺𝑚𝑎𝑥

(2)

𝑘 𝑇

𝜉𝑀 = ( 𝐺𝐵′ )

(3)



5/3

𝑙𝑒 = ′ 𝐺∞ ′′ 𝐺𝑚𝑖𝑛

𝜉𝑀

(4)

2/3

𝑙𝑝

𝐿

(5)

≈𝑙

𝑒

′′ Here, 𝐺𝑚𝑎𝑥 is the modulus when the G’ is same as the G’’. kB is the Boltzmann

constant (kB = 1.38×10-23 J/K) and the test temperature T is 298.15 K. According to the ′′ previous studies, the persistence length lp is set 15-25 nm39. 𝐺𝑚𝑖𝑛 is the minimum

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value of G’’ at high frequencies. The mesh size ξM and the entanglement le are also figured out. The key parameters of AIMIAs are listed in Table 1. Table 1. Rheological Parameters of Solutions with 100 mM NaOA/300 mM KCl and Different CNF Concentrations (0 wt%, 0.03 wt%, 0.3 wt%) at 25 °C CCNF(wt%) 0 0.03 0.3 η0(Pa·s) 2.83 8.48 4.83 ′′ 𝐺𝑚𝑖𝑛 (Pa) 5.1 4.0 3.5 ′ 𝐺∞ (Pa) 11.9 8.0 5.1 -1 ωco(rad·s ) 8.5 3.3 4.2 τR(s) 0.118 0.306 0.238 L(nm) 325.9-458.1 347.9-489.1 330.4-464.4 As can be seen in Table 1, with the increasing concentration of CNF, the contour length increases initially and decreases afterwards with a demarcation point of 0.03 wt%. The extent of variation is small, showing the CNF contributes less to the growth of WLMs. Simultaneously, the zero-shear viscosity and relaxing time vary with the addition of CNF, showing a similar trend as the contour length, which indicates the structure formed by AIMIAs is more complicated than the network of WLMs. In conclusion, CNF is mainly used to intertwine the WLMs instead of growing it, causing a significant increase in the viscosity of AIMIAs. 3.3 Mechanism Discussion. Based on the experiment results, the network structure formed by WLMs can be strengthened by a moderate amount of CNF while the excess CNF will destroy it. The mechanism which describes how the CNF changes the network structure formed by WLMs is presented in Fig. 5. For the surfactant solution, potassium ions screen the electrostatic repulsion among the surfactant headgroups, promoting the growth of WLMs40. Then, the long micelles begin to intertwine and entangle to form a network structure, which contributes 14

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to the viscoelasticity of the system. After adding CNF, these soft macromolecules with abundant hydroxyls are first gathered together by hydrogen bonding. The potassium ions decrease the electrostatic repulsion between WLMs and CNF, resulting in a special structure. Here, as the selfassembled wormlike micelle is in a dynamic equilibrium of reassemble-dissociate and CNF is relatively rigid and lack in growth, we called this novel structure formed by living wormlike micelles and inelastic CNF active-inactive material interdigitated aggregates (AIMIAs). In addition, the surface of CNF is negatively charged and it may contribute to the slight growth of WLMs. Apparently, the electrostatic repulsion between CNF and WLMs increases with the addition of CNF, pushing the WLMs intertwine and surround together. As a result, the branched WLMs appear in solution, leading to a significant decrease in the viscosity of system. Meanwhile, in this work, experiments confirmed that the CNF solution belongs to Newtonian fluid, which cannot directly contribute to increasing the viscoelasticity of AIMIAs. As a result, the G’ and G’’ of system decline.

Fig. 5. Illustration of the mechanism of AIMIAs structure formed by CNF and WLMs. 15

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4. CONCLUSIONS

In this work, we reported a special AIMIAs structure formed by CNF and WLMs. CryoTEM image of system without CNF confirmed the formation of WLMs. Rheological properties indicated that the viscoelastic properties of WLMs were promoted effectively by certain amount of CNF, and ESEM image of system with 0.03 wt% CNF also proved it. Moreover, an appropriate explanation was provided to describe the effect of CNF on WLMs. It is the potassium ion bridging and hydrogen bonding that contribute greatly to the formation of AIMIAs structure, leading to a remarkable increasing in the viscoelasticity of AIMIAs system. However, with the further increasing of CNF concentration, the viscosity of system decreases, corresponding to the smaller relaxing time as well as the lower zero-shear viscosity. In conclusion, the AIMIAs structure can be supposed to enrich some relevant fields, such as viscoelastic surfactant fracturing fluid, functional materials and so on.

Author Information Corresponding Author Caili Dai* email: [email protected]. Yining Wu* email: [email protected]. ORCID Zhao Mingwei: 0000-0002-9671-8206. Notes 16

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The authors declare no competing financial interest. Acknowledgments This work was financially supported by the Natural Science Fund of Shandong Province (ZR2018QEE003); the National Natural Science Fund (51874337, 51425406); the Chang Jiang Scholars Program (T2014152); Climb Taishan Scholar Program in Shandong Province (tspd20161004) and the Fundamental Research Funds for the Central Universities (14CX02184A, 16CX02056A).

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reduction mechanism in high temperature of a Gemini viscoelastic surfactant (VES) fracturing fluid and effect of counter-ion salt (KCl) on its heat resistance. J. Pet. Sci. Eng. 2018, 164, 189-195. (16) Sullivan, P. F.; Panga, M. K. R.; Lafitte, V. Wormlike micelles: advances in systems, characterisation and applications. R. Soc. Chem. 2017, 330-352. (17) Crews, J.; Huang, T. Internal breakers for viscoelastic surfactant fracturing fluids. J. Pet. Technol. 2007. (18) Rakesh Kumar; G. C. K.; Lior Ziserman; Dganit Danino, A.;S. R. R. Wormlike micelles of a C22-tailed zwitterionic betaine surfactant:  From viscoelastic solutions to elastic gels. Langmuir 2007, 23, 12849-12856. (19) Fan, Q.; Li, W.; Zhang, Y.; Fan, W.; Li, X.; Dong, J. Nanoparticles induced micellar growth in sodium oleate wormlike micelles solutions. Colloid Polym. Sci. 2015, 293, 2507-2513. (20) Helgeson, M. E.; Hodgdon, T. K.; Kaler, E. W.; Wagner, N. J.; Vethamuthu, M.; Ananthapadmanabhan, K. P. Formation and rheology of viscoelastic "double networks" in wormlike micelle-nanoparticle mixtures. Langmuir 2010, 26, 8049-60. (21) Zhao, M.; Zhang, Y.; Zou, C.; Dai, C.; Gao, M.; Li, Y.; Lv, W.; Jiang, J.; Wu, Y. Can more nanoparticles induce larger viscosities of nanoparticle-enhanced wormlike micellar system (NEWMS)? Materials 2017, 10. (22) Chen, J.; Huang, X.; Zhu, Y.; Jiang, P. Cellulose nanofiber supported 3D interconnected BN nanosheets for epoxy nanocomposites with ultrahigh thermal management capability. Adv. Funct. Mater. 2017, 27, 1604754. 20

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(23) Suzuki, K.; Homma, Y.; Igarashi, Y.; Okumura, H.; Yano, H. Effect of preparation process of microfibrillated cellulose-reinforced polypropylene upon dispersion and mechanical properties. Cellulose 2017, 24, 3789-3801. (24) Na, S.; Jiao, D.; Cui, S.; Hou, X.; Peng, D.; Shi, L. Highly anisotropic thermal conductivity of layer-by-layer assembled nanofibrillated cellulose/graphene nanosheets hybrid films for thermal management. ACS Appl. Mater. Interfaces 2017, 9, 2924-2932. (25) Gourlay, K.; Zwan, T. V. D.; Shourav, M.; Saddler, J. The potential of endoglucanases to rapidly and specifically enhance the rheological properties of micro/nanofibrillated cellulose. Cellulose 2018, 25, 977-986. (26) Gopakumar, D. A.; Manna, S.; Pasquini, D.; Thomas, S.; Grohens, Y. 19– Nanocellulose: Extraction and application as a sustainable material for wastewater purification. New Polymer Nanocomposites for Environmental Remediation 2018, 469486. (27) Arjmandi, R.; Hassan, A.; Eichhorn, S. J.; Haafiz, M. K. M.; Zakaria, Z.; Tanjung, F. A. Enhanced ductility and tensile properties of hybrid montmorillonite/cellulose nanowhiskers reinforced polylactic acid nanocomposites. J. Mater. Sci. 2015, 50, 31183130 (28) Spagnol, C.; Fragal, E. H.; Witt, M. A.; Follmann, H. D. M.; Silva, R.; Rubira, A. F. Mechanically improved polyvinyl alcohol-composite films using modified cellulose nanowhiskers as nano-reinforcement. Carbohydr. Polym. 2018, 191, 25-34. (29) Walker, L. M. Rheology and structure of worm-like micelles. Curr. Opin. Colloid Interface Sci. 2001, 6, 451-456. 21

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(30) Wang, D.; Dong, R.; Long, P.; Hao, J. Photo-induced phase transition from multilamellar vesicles to wormlike micelles. Soft Matter 2011, 7, 10713-10719; (31) Croce V.; Cosgrove T.; Maitland G.; Hughes, T.; Karlsson, G. Rheology, cryogenic transmission electron spectroscopy, and small-angle neutron scattering of highly viscoelastic wormlike micellar solutions. Langmuir 2003, 19, 8536-8541. (32) Zhao, M.; Gao, M.; Dai, C.; Du, M.; Liu, Y.; Zou, C.; Tao, J.; Wang, X.; Wang, T. Investigation on a novel photo-responsive system formed by N-methyl-N cetylpyrrolidinium bromide and ortho-methoxycinnamic. J. Mol. Liq. 2016, 223, 329334. (33) Dreiss, C. A. Wormlike micelles: where do we stand? Recent developments, linear rheology and scattering techniques. Soft Matter 2007, 3, 956-970. (34) Pei, X.; Xu, Z.; Song, B.; Cui, Z.; Zhao, J. Wormlike micelles formed in catanionic systems dominated by cationic Gemini surfactant: Synergistic effect with high efficiency. Colloids Surf., A 2014, 443, 508-514. (35) Yin, H.; Lin, Y.; Huang, J. Microstructures and rheological dynamics of viscoelastic solutions in a catanionic surfactant system. J. Colloid Interface Sci. 2009, 338, 177-183. (36) Raghavan S. R.; Kaler E. W. Highly viscoelastic wormlike micellar solutions formed by cationic surfactants with long unsaturated tails. Langmuir 2001, 17, 300-306. (37) Granek, R.; Cates, M. E. Stress relaxation in living polymers: Results from a Poisson renewal model. J. Chem. Phys. 1992, 96, 4758-4767. (38) Wang, P.; Pei, S.; Wang, M.; Yan, Y.; Sun, X.; Zhang, J. Study on the transformation 22

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from linear to branched wormlike micelles: An insight from molecular dynamics simulation. J. Colloid Interface Sci. 2017, 494, 47-53. (39) Zhao, M.; Yuan, J.; Zheng, L. Spontaneous formation of vesicles by N-dodecyl-Nmethylpyrrolidinium bromide (C12MPB) ionic liquid and sodium dodecyl sulfate (SDS) in aqueous solution. Colloids Surf., A 2012, 407, 116-120. (40) Zhao, L.; Zhang, H.; Wang, W.; Wang, G. Effects of sodium salicylate on didecyldimethylammonium formate properties and aggregation behaviors. J. Mol. Liq. 2017, 225, 897-902.

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