Effect of Additives on Surfactant Micelle Shape Transformation

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C: Surfaces, Interfaces, Porous Materials, and Catalysis

Effect of Additives on Surfactant Micelle Shape Transformation: Rheology and Molecular Dynamics Studies Qi Liu, Xiaoyu Ji, Suxu Wang, Wenjing Zou, Jing Li, Dongmei Lv, Yin Baolin, Hui Yan, and Xilian Wei J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b10495 • Publication Date (Web): 15 Jan 2019 Downloaded from http://pubs.acs.org on January 15, 2019

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The Journal of Physical Chemistry

Effect of Additives on Surfactant Micelle Shape Transformation: Rheology and Molecular Dynamics Studies Qi Liu,1 Xiaoyu Ji,1 Suxu Wang,1 Wenjing Zou,1 Jing Li,1 Dongmei Lv,1 Baolin Yin,1 Hui Yan,2* Xilian Wei1*

1 Shandong

Provincial Key Laboratory of Chemical Energy Storage and Novel Cell

Technology, College of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng, Shandong 252059, P. R. China 2 College

of Pharmacy, Liaocheng University, Liaocheng, Shandong 252059, P. R.

China

1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT: Several additives (NaSal, 1SHNC and 2SHNC) were added into aqueous solutions of a cationic surfactant, 3-tetradecyloxy-2-hydroxy-propyl trimethyl ammonium bromide (R14HTAB). The mixed solutions were investigated using rheological measurements, molecular dynamics (MD) simulations, cryo-TEM, 1H NMR, and FTIR spectroscopy. The results demonstrated that the zero-shear viscosity (0) increased with increasing salt concentrations until reaching a maximum and then decreased. The variations in viscosity were related to transformation of the micellar configuration and were confirmed by cryo-TEM and MD simulations. The ability of the three organic salts to enhance the viscoelasticity of R14HTAB solutions is in the order of NaSal < 1SHNC < 2SHNC. The synergistic interaction between counterions and surfactant molecules was analyzed using 1H NMR spectrograms, FTIR spectroscopy and MD simulations. These findings provide new insight into understanding the self-assembly and bulk properties of ionic surfactant/organic salt mixtures.

2


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1. INTRODUCTION At appropriate concentrations and/or upon addition of salts, surfactant molecules can form various self-aggregates in aqueous media, such as rod-like and wormlike micelles, vesicles and liquid crystals (lamellar, hexagonal and cubic structure). Among these various microstructures, wormlike micelles have attracted much interest in fundamental research and practical applications over the past several decades

1-4.

Wormlike micelles can be formed by individual amphiphilic surfactants, with a certain concentration or by adding additives, such as inorganic salts (NaCl and NaBr), strongly binding organic salts (aromatic compounds) and oppositely charged surfactants to dilute solutions of the surfactants. From a practical point of view, the application of a single surfactant or two surfactants is not economical due to the high cost of their mass production and purification. Therefore, to achieve equivalent efficacy, it is often possible to mix a surfactant with various additives in different proportions. As a consequence, surfactant/counterion salt mixtures are often used to construct wormlike micellar systems in many practical applications. It is well known that adding salts can screen the electrostatic repulsion between the charged head groups and induce a shape transition from spherical to cylindrical micelles by decreasing the effective cross-sectional area of the head group surfactant molecules. With increasing salt concentration, micelles further grow in one dimension to yield wormlike micelles. In contrast, organic salt additives are much more effective in inducing wormlike micelle formation of cationic surfactants in aqueous solutions, such as the mixed solutions of cetyltrimethylammonium chloride (CTAC) or bromide 3



(CTAB) and aromatic salts

5-12.

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In addition to the capacity of aromatic anions to

charge or neutralize head groups which brings them closer together, the additive salts could penetrate deeper into the hydrophobic interior of micelles as a result of favorable hydrophobic forces, thus increasing the molecular packing parameter, P (P=v/al

13,

where v and l are the volume and length of the hydrophobic chain,

respectively, and a is the effective head group area of the surfactant) more efficiently compared to inorganic salts by affecting both V and a. To understand how wormlike micellar structures are related to the chemical composition of surfactant solutions, and in turn, how the structural characteristics of aggregates can be adjusted by specific control parameters, and how these characteristics influence the bulk properties, constitute a considerable research subject. Experimentally, many techniques, such as rheological measurements neutron scattering (SANS)

11-12,

dynamic light scattering (LS) (cryo-TEM)

17,

and rheo-NMR

microrheology 16, 18,19

14

4-10,

neutron spin-echo

small-angle

15,

static and

cryogenic transmission electron microscopy or rheo-SANS

20,

which prove direct links

between the microstructure and rheology, have been used to investigate the macroscopic and microscopic features of wormlike micelles. Among the features, the rheology is widely used to investigate the impact of changes in the structure of aromatic compounds on the formation and characteristics of wormlike micelles. Theoretically, certain simulation methods have also been proposed to project the structure–property relationships

21-24.

Molecular dynamics (MD) simulations can

reveal and predict the microstructure of various aggregates at the molecular level and 4


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explain certain experimental phenomena, and are an efficient method for investigating the structural and dynamic properties of micelles of various shapes. For complex systems of surfactants/additives, the combination of theory and experimentation will be more comprehensive to understand and interpret the relationship between the detailed chemical structures and their macroscopic rheological properties 25. In this paper the cationic surfactant 3-tetradecyloxy-2-hydroxy-propyl trimethyl ammonium bromide (R14HTAB, Figure 1), in which a 2-hydroxy-propoxy group is inserted at the junction between the head-group and the alkyl chain of tetradecyltrimethylammonium bromide (TTAB)

26,

is mixed with different aromatic

cosolutes (sodium salicylate, NaSal; sodium 1-hydroxynaphthalene-2-carboxylate, 1SHNC; and sodium 2-hydroxynaphthalene-3-carboxylate, 2SHNC, Figure 1) as additives to deveop a series of solutions containing wormlike micelles. The effects of three aromatic salts on the morphological transformation of R14HTAB micelles in solution were investigated by rheology, MD simulation, cryogenic transmission electron microscopy (cryo-TEM), 1Hnuclear magnetic resonance (1H NMR), and Fourier transform infrared (FTIR) spectroscopy. We observed that all three aromatic cosolutes induced the growth of globular micelles in the 100 mmolL-1R14HTAB solution into wormlike structures, and this phenomenon was accompanied by an increase in the apparent viscosity, and a maximum viscosity was observed simultaneously in the curve of the zero-shear viscosity (0) as a function of the added salt concentration. According to the molecular structure of the added salts, the influence of the substituent position on the formation and growth of surfactant 5



micelles was discussed by the rheological parameters and the calculated results. The change in the micellar structure resulting from increasing the additive concentrations was observed using cryo-TEM. The interaction mechanism between the counterions and surfactant molecules was analyzed using

1H

NMR spectrograms, FTIR

spectroscopy and the MD configurations. The main objectives of this study were to understand the differences in the self-assembly of R14HTAB into wormlike micelles in the presence of different salts, and to examine how the properties and molecular structures of the added salts, in particular the different substituent positions in the organic salts, impacted the rheological responses of the resulting materials. The new system adopts surfactant synthesized by our laboratory, which shows low toxicity and good antibacterial activity, and provides theoretical support for practical application of this surfactant in daily chemistry. In addition, these investigations would provide this research will provide experimental data that could to facilitate the application of ionic surfactant /salts mixtures for their application, the microscopic mechanism proposed by MD simulations to provide deeper insights into the structure transformations in ionic surfactant /salt mixtures. We also expect that these new results and data will hopefully play important roles in the building of novel self-assembled structures of surfactants and satisfy specific applications in the field of daily chemical industry.

6


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Figure 1. Chemical structures of R14HTABr, NaSal, 1SHNC and 2SHNC.

2. EXPERIMENTAL 2.1.

Materials.

Surfactant

3-tetradecy-2-hydroxypropyltrimethyl-ammonium

bromide (R14HTAB) was synthesized according to the literature in the laboratory

26.

The product was purified three or four times using ethyl acetate. NaSal, 1SHNC, and 2SHNC were purchased from Aldrich Chemical Reagent Co. (purity>99 %). The deionized water was redistilled from alkaline potassium permanganate to ensure that the surface tension was 72.0 mN· m-1 at 25 °C. 2.2.

Methods.

2.2.1 Rheological Measurements. For the experiments the required amounts of R14HTAB and additives were weighed and homogenized using a stirrer at 25 °C. The substances were then stored in a thermostat for at least 5 days to reach equilibrium. Rheological measurements were carried out by a stress-controlled rheometer (AR2000ex, TA instruments, USA, and MCR-302, Anton Paar, Austria). Dynamic frequency spectra were measured at a fixed stress σ (selected at the linear range). All sample measurements were repeated two times to confirm the repeatability.

7



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2.2.2 Molecular Dynamics Simulation Sphere to rod transition of micelles. The effect of the organic salts on inducing the wormlike micelle formation was evaluated from preassembled long cylindrical micelles using molecular dynamics (MD) simulations. The initial coordinates and bonded parameters for the cationic surfactant R14HTAB and additives were generated from the Automated Topology Builder (ATB) server

27.

The charge groups were

defined according to the functional groups involved in the two molecules, and atomic charges were assigned using the ATB server. The atom types and nonbonded parameters were assigned according to the GROMOS 53a6 force field 28, which was validated by the good agreement of the simulation results with experimental data as presented in the following section. The preassembled cylindrical micelle was built following methods reported by previous studies

23, 29.

The obtained cylindrical micelle consisting of 108 R14HTA+

molecules was placed in a rectangular box of dimensions 27 × 27 × 6 nm3 with its central axis along the z-axis of the box, which was used for all the subsequent simulations. Four simulated systems (Table 1) were developed to study the spherical-to-rod-like micelle shape transition in the presence of additives. Thirty-three molecules of each kind of additive were placed near the cylindrical micelle randomly. After the water molecules and bromine ions were added, the concentration values of the surfactants and additives in each system were approximately 100 and 30 mmolL-1 respectively, which were comparable with the experimental conditions.

8


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Table 1 Simulated Systems: Numbers of Each Component in Different Systems Systems NR14HTAB NNaSal N1SHNC N2SHNC Nwater R14HTAB 108 0 0 0 55528 R14HTAB+NaSal 108 33 0 0 55252 R14HTAB+1SHNC

108

0

33

0

55120

R14HTAB+2SHNC

108

0

0

33

55155

Wormlike to branching transition of micelles. The branching transition of the wormlike micelle was simulated by using the R14HTAB/2SHNC system as an example. The initial configuration of this system was built based on the final structure of the above mentioned simulated system. First, the cylindrical micelle was extended three times along the z-axis to represent an infinitely long micelle. Then, another short cylindrical micelle was placed perpendicular to the long micelle at a certain distance. Thereafter, two more simulated systems were employed. One system was built by adding 33 additional NaSal molecules to simulate the increased concentration of the additives, and the other system was constructed without any additional Sal- ions. Finally, corresponding quantities of water molecules and Br- ions were added similarly to the above four systems. All the simulations were performed using the GROMACS 4.6.3 package 30, and a 20 ns MD simulation under an NPT ensemble at 1 atm and 298 K was carried out for each system following a minimization using the steepest descent method. The V-rescale thermostat algorithm 31was used to maintain the pressure and temperature. During the simulation, the LINCS algorithm 32 was used to constrain the bond length and the Lennard-Jones interactions were adopted for the nonbonded potential. The

9



particle mesh Ewald method

33

was employed for the long-range electrostatic

interactions with a cutoff of 1.2 nm. 2.2.3. Cryogenic Transmission Electron Microscopy (cryo-TEM). Approximately 2 μL of the sample solution was coated onto a TEM copper grid, and the grid was blotted with two pieces of filter paper for approximately 6 seconds, leading to the formation of a solution thin film. Then, the grid was plunged into a reservoir containing liquid ethane (at -165 °C, cooled by liquid nitrogen) and was kept in liquid nitrogen until observation. After transferring the grid to a cryogenic sample holder (Gatan 626, USA) and placing it into a JEOL JEM-1400 Plus TEM (120KV) instrument at approximately -174 °C, the microstructures were observed. 2.2.4. NMR Measurements.

1H

NMR spectra for the R14HTAB/NaSal/D2O

(containing the internal reference of TMSP) solution were measured using a 400-MHz NMR spectrometer (Varian Company, U.S.). 2.2.5. Fourier Transform Infrared (FTIR) Spectroscopy Measurements. The FTIR spectra of sample were performed with a Nicolet-6700 infrared spectrometer (Thermo Fischer Scientific Co., USA) at 25 °C. R14HTAB or R14HTAB/additive mixed samples were dissolved in CDCl3 to prepare the liquid sample. The infrared spectra were recorded in the 4000-500 scanning range.

3. RESULTS AND DISCUSSION 3.1. Rheological Behaviors of Wormlike Micellar Solutions 3.1.1. Steady Rheological Characteristics of the Mixed System. First, we explored 10


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the steady-state viscosity of the R14HTAB/additives mixed solutions. The R14HTAB concentration was fixed at 100 mmol·L

− 1.

Figure 2 shows the steady-state shear

viscositiy  of the mixed aqueous solutions of R14HTAB/additives (NaSal, 1SHNC, and 2SHNC) at different salt concentrations. In the salt-free system, the viscosity of the 100 mmol·L-1R14HTAB solution was found to be independent of the shear rate, and exhibited a Newtonian-fluid-like behavior. This result indicates that the system was composed of spherical micelles with very low viscosity (0.0019 Pa.S). The addition of salts increased the viscosity of the R14HTAB solution. However, when the concentrations of added salts were lower than 10 mmol·L-1, the viscosity of the systems did not increase very much. The curves still exhibited Newtonian fluid-like characteristics, which indicated that the spherical micelles were present in the mixed systems or that only a small amount of flat spherical micelles had formed in the R14HTAB/2SHNC system. In contrast, the solution viscosity increased rapidly at a value of Cadditives greater than 20 mmol·L-1 for R14HTAB/NaSal, 15 mmol·L-1 for R14HTAB/1SHNC and 10 mmol·L-1 for R14HTAB/ 2SHNC systems. The notable increase in the viscosity of the solution indicated that the micellar shape had changed, which was induced by the salt addition; the micellar shape was transformed from a sphere to rod-like and even wormlike. These findings could be proved by the obvious shear thinning behavior of the steady-state shear viscosity above the critical shear rate

&c (at which shear thinning appeared). Shear thinning is a classical behavior observed, in most cases, for mixed micellar solutions of surfactants/additives, and is generally attributed to surfactant aggregates, including wormlike micelles, lamellar liquid 11



crystals or rod-like micelles, being destroyed to form aggregations of small structures or the micelle alignment in the flow direction with increasing shear rate, thus leading to a decrease in the viscosity of the system

4, 8, 20

and becoming a non-Newtonian

fluid. Figure 2 shows a distinct power law behavior, with an exponent close to above and within the range of approximately -0.4 - -1 reported for polymer solutions at different concentrations and molecular weights34,

35;

thus, the wormlike micelles

appeared similar to “living” polymers. As a result, shear thinning is also taken as evidence for the formation of rod-like micelles or network structure. From Figure 2, we can observe that the critical shear rate decreased with increasing additive concentrations, i.e., the Newtonian plateau become shorter as the apparent viscosity of the solution increased, indicating that the more concentrated system, the higher the apparent viscosity of system, the greater the influence of the shear rate on the structure, and the smaller the shear capacity. In other words, the longer the micellar length was, the poorer was the micellar structural stability. Using the Carreau or Cross model, the zero-shear viscosity ( 0 ) of the systems was determined by extrapolating the shear-rate to zero. The η0 data of the R14HTAB/additives mixed solutions as a function of the additive concentrations are shown in Figure 3. We see that η0 increased continuously with increasing aromatic salt concentrations (Cadditives) until reaching a maximum value at 40 mmol·L-1 and 50 mmol·L-1 for the R14HTAB/NaSal mixed system. The maximum 0 increased by six orders of magnitude for the three mixed systems compared to the pure R14HTAB solution, indicating the generation of entangled wormlike micelles. Beyond the 12


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maximum, 0 quickly decreased until a plateau region with a poor viscoelastic behavior was reached. The increase in the viscosity of solution before the maximum was due to the counterions of the added salt screening the electrostatic repulsion between the surfactant head groups; the counterions could sometimes be inserted deep into the micellar core. This phenomenon caused an increase in the surfactant packing parameter (P), and facilitated the one-dimensional growth of micelles to yield wormlike micelles in the solution. These phenomena were similar to the results of most mixed systems of cationic surfactant/additive solutions 4-10.

100

CNaSal /mmolL-1

a

0, 20, 30, 50, 70,

10

 Pa.S

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


10 25 40 60 80

1 0.1 0.01 1E-3 0.01

0.1

1 

10

 / s 1 

 / s 1

13


100

1000


10000

C1SHNC /mmolL-1

b

5, 15, 25, 40, 50, 60，

1000

Pa.S

100 10

10 20 30 45 55

1 0.1

0.01 1E-3

10000 1000

0.01

0.1

1

/s

c

10

100

1000

1

C2SHNC /mmolL-1 5, 20, 28, 40, 50, 70

100

 Pa.S

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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10

10 25 30 45 60

1 0.1

0.01 1E-3

0.01

0.1



1

10

100

1000

 / s 1 Figure 2. Steady-state shear viscosity () of the 100 mmol·L−1 R14HTAB solution 

versus shear rate (  ) as a function of the additive concentrations at 25 °C, (a) R14HTAB/NaSal; (b) R14HTAB/1SHNC and (c) R14HTAB/2SHNC mixed solutions

14


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2000

R14HTAB=100 /mmolL



 C

-1

NaSal 1SHNC 2SHNC

1500 

1000

 Pa.S

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


 C

500



 C

0 0

20

40

Cadditave

60 -1 /mmolL

80

Figure 3. Zero-shear viscosity of the 100 mmol·L−1 R14HTAB solution as a function of the additive concentrations at 25 °C. From Figure 3 we see that the mixed solutions became notably more viscous at or above a salt concentrations of 25 mmol·kg-1, and this concentration resulting in a sudden increase in viscosity is called the overlap (or threshold) concentration (CS*) 2. Above CS*, cylindrical micelles begin to entangle with each other as the additive concentrations increased further. The power law function of the zero-shear viscosity and

salt

concentration

are0  C 6.23 ,0  C 47.72

and

0  C 127.22 for

the

R14HTAB/NaSal, R14HTAB/1SHNC, and R14HTAB/2SHNC solutions, respectively. The last two solutions had exponents that went far beyond the range of exponents (1.5–8.5) reported for viscoelastic micellar surfactant systems 18, which indicates that there was a strong interaction between the surfactant and SHNC salts. Notably, the threshold concentration i.e, the concentration at which the cylindrical micelles began 15



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to entangle, was approximately 25 mmol·L-1 for the three mixed systems. The dispersed rod-like micelles existed at the concentration value of 25 mmol·L-1 at which the shear thinning phenomenon appeared. After the maximum viscosity, the reduction in viscosity with further addition of salts was usually ascribed to branching of the 36-41

wormlike micellar induced by an increase in the end-cap energy, Ec,

or

shortening of the mean micelle size 42-46. In general, in cationic surfactant/salt mixture solutions, the micellar branching could take place more easily when the electrostatic interactions were adequately screened, because the branching point of micelles represented a delicate balance in the electrostatic property of the solution. The formation of a 3-fold micellar junction was greatly more favorable compared to the end-cap of a micelle 47. At this point, the free energy cost associated with cross-link formation could be comparable to that for end caps

48.

Micellar branching has been

further confirmed through theoretical predictions with the reptation model molecular-thermodynamic model

22

and through cryo-TEM observations

49,

and

50, 51.

A

theory was proposed that described two different mechanisms of the effect of specific counterions on the viscosity via micellar growth and branching and via the reduction in the aggregate size52. Generally, for a system with branching micelles, the plateau modulus G' is independent of the concentration at which the additives are present or increases monotonically with increasing Cadditives, after the maximum viscosity has been reached

48.

For systems that exhibit a decrease in the mean micellar length,

however, this decrease is usually ascribed to a decrease in G' maximum peak (we will discuss this phenomenon separately) 44. 16


following the

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The physical appearance of several typical samples of the R14HTAB/2SHNC solutions with different 2SHNC concentrations and the schematic presentation of the micellar aggregation morphology in different C2SHNC ranges are depicted in Figure 4. Pure R14HTAB and binary mixtures with a low C2SHNC had a low viscosity, which corresponded to spherical and discrete rod-like micelles. The rod-like micelles were formed below a concentration of 25 mmol·L-1. At the maximum viscosity or in the range of 25-40 mmol·L-1, the appearance of a gel-like state corresponded to entangled wormlike micelles. Finally, the solution turned to a viscous state, resulting in branched micelle connections.

Figure 4. Appearance of several typical samples and the diverse aggregation morphology of R14HTAB/2SHNC mixed systems with different C2SHNCranges. In addition, the three mixed systems were compared under the same conditions (Figure 3) and although the change trend of 0 with increasing CSHNC was the same, i.e., there was only one maximum viscosity in each system, the positions of the extreme values shifted to the direction of lower SHNC concentrations. The absolute 17



maximum value of 0 was relatively large, indicating a stronger interaction between R14HTAB and SHNCs. Why were the R14HTAB micelles so sensitive to SHNCs? In comparing their molecular structure (see Figure 1), NaSal was analogous to SHNC, however a key difference between the two molecules was the presence attendance of an extra benzene ring. The latter suggest that the hydrophobicity of NaSal was lower compared to the SHNCs; thus the SHNC counterions would gather on the R14HTAB micellar surface at lower concentrations, and showed a stronger interaction compared with NaSal. This inference explained the results shown in Figure 3. Moreover, the influence of 2SHNC on the viscosity of the R14HTAB solution was much stronger than that of 1SHNC, implying that the hydroxyl group in the molecule on the outer side of the naphthalene rings was more conducive for generating viscoelastic worm-like micelles than on the inner side. This finding may be related to their molecular structure. Compared with 2SHNC, the hydroxyl group of the 1SHNC molecule was located on the inner side of the benzene ring and occupied a larger cross-sectional area. The steric hindrance was significantly higher compared to the former and led to the low viscosity of the 1SHNC/R14HTAB mixed solution. To verify the difference in interaction between R14HTAB and the three hydrotropes, 1H NMR spectroscopy was used to explore the solubilization state of the hydrotropes in the micelle. The chemical shift changes could provide insight into the microenvironment of the nuclei. Table 2 shows the 1H NMR chemical shifts surveyed for the key resonances in the mixed systems containing R14HTAB (100 mmol·L-1) and added salts (30 mmol·L-1) in D2O, (all proton 1H NMR spectra of mixed solutions are 18


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shown in S1 in the Supporting Information). Figure 5 shows the numbers in the structural drawing correspond the position of hydrogen in the Table 2. From Table 2, it is clear that the 3,5H, 4H and 3-6H proton signals associated with NaSal and 1SHNC and the approximately 4-8 proton signals arising from 2SHNC resulted in an upfield shift relative to their location in free anions, whereas the 6H and 1H signals associated with NaSal and 2SHNC shifted downfield. Clearly, the most obvious shift occurred in the 2SHNC molecule. For each additive molecule, the movement of the proton signals away from the polar groups was the most prominent, such as 4H in NaSal, 5H in 1SHNC and 5H, 6H and 7H in 2SHNC molecules However, for the R14HTAB molecule in all three mixed systems, the resonances associated with all of the 1’H (i.e., the methyl protons located at the end of the hydrocarbon chain), 2H’and 7H’ protons shifted downfield relative to their location in the pure R14HTAB molecule, while the resonances arising from the 5’H and 6’H protons shifted upfield. This observation indicated that the region of solubilization of the hydroxyl benzoates was close to the hydroxyl group of the polar head group of R14HTAB, while the tail of the surfactant was situated in the hydrophobic part of the aromatic ring. Among the systems examined, the resonance arising from the 1’H proton in the R14HTAB /2SHNC mixed system exhibited the most obvious shift changes among the three mixed systems. This result indicates that the strongest hydrophobic action occurred in the R14HTAB /2SHNC mixed system which exhibited the highest viscosity, while the weakest interaction was observed in the R14HTAB/NaSal mixed solution. These results indicate that the interaction formed between R14HTAB and additives involved 19



Page 20 of 43

not only hydrophobic and electrostatic interactions but also the formation of hydrogen bonds because both surfactant and added salt molecules contained hydroxyl groups. Table 2 1H NMR Chemical Shifts (δ, ppm, or δ) of R14HTAB (100 mmol∙L−1) in the Presence of Different Additives (30 mmol∙L−1) at 25 °C chemical shifts (δ or δ, ppm ) NaSal

R14HTAB

4H

3,5H

6H

1'H

2'H

5'H

6'H

7'H

pure δ

7.44

6.94

7.82

0.82

1.260

4.36

2.85

3.23

mixedδ

-0.280

-0.190

0.010

0.080

0.050

-0.060

-0.046

0.040

1SHNC pure δ

3H

4H

5H

7.84

7.430

7.910

-0.120

-0.250

mixedδ

R14HTAB

6H

7H

8H

1'H

2'H

5'H

6'H

7'H

7.610

7.650

8.300

0.820

1.260

4.360

2.850

3.230

-0.130

-0.09

0.140

0.080

-0.040

-0.100

0.010

2SHNC

R14HTAB

1H

4H

5H

6H

7H

8H

1'H

2'H

5'H

6'H

7'H

pure δ

8.440

7.390

7.800

7.430

7.580

7.960

0.820

1.26

4.36

2.85

3.23

mixedδ

0.06

-0.200

-0.29

-0.27

-0.34

-0.11

0.180

0.120

-0.060

-0.090

0.010

Figure 5. The numbers in the structural drawing correspond the position of hydrogen in the table 2.

To further verify whether hydrogen bonds were formed we conducted infrared (IR) spectroscopy determinations. Figure 6 shows the IR spectra of 2800-4000 cm-1 for R14HTAB and additives /R14HTAB mixed solutions. As shown in Figure 6 only a broad peak was observed at 3448 cm-1 in the 100 mmol·L-1 R14HTAB solution in 20


Page 21 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


CDCl3(black line) which was lower than the common values of 3580-3650 cm-1 of the free hydroxyl group 40, 53. This result should be indicative of the hydroxyl group in the associated state due to the IR peak corresponding to the connection state of hydroxyl groups in the 3200-3400 cm-1 range. The latter implies the existence of intermolecular hydrogen bonding among the R14HTAB molecules, which had also been confirmed from measurements of the crystal structures in previous reports

26.

In the three

additive solutions in CDCl3, a broad peak was also observed, but the peak value occurred at 3471 cm-1, indicating intramolecular hydrogen bond formation. When the three additives were added at a concentration of 30 mmol·L-1 to the CDCl3 solution of 100 mmol·L-1 R14HTAB (the top three lines in the figure), the absorption peaks of all three mixed solutions were blueshifted to 3448 cm-1. These results imply that the intramolecular hydrogen bonding in the molecules of the three added salts was destroyed and converted into intermolecular hydrogen bonds with surfactants due to the strong synergy between the additives and R14HTAB. The formation of such intermolecular hydrogen bonds could also be confirmed by the following MD results.

21



80

R HTAB， 14

NaSal

1SHNC，

2HSNC

R HTAB+NaSal 14

60 I/a.u.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 43

40

R HTAB+1SHNC 14

R14HTAB+2SHNC

R HTAB+2SHNC 14

R14HTAB+1SHNC R14HTAB+NaSal R14HTAB

20

3448

2SHNC

3471

1SHNC

0 4000

NaSal

3800

3600 3400 3200 Wavenumber/cm-1

3000

2800

Figure 6. FTIR spectra of the different samples: from bottom to top, 30 mmol·L-1NaSal, 1SHNC and 2SHNC; 100 mmol·L-1 R14HTAB, 30 mmol·L-1 NaSal, 1SHNC and 2SHNC were separately added into 100 mmol·L-1 R14HTAB in CDCl3.

3.1.2. Dynamic Rheological Characteristics of the Mixed System. To discuss the kinetic behavior of the mixed solutions, oscillatory measurements were performed for the three mixed systems under suitable stress conditions where the elasticity modulus G'

(or storage modulus) and viscous modulus G " (or loss modulus) were

independent of the applied stress. Figure 7 shows a plot of G ' and G " versus the dynamic frequency () for the mixed systems of the 100 mmol·L-1 R14HTAB solution containing 30 mmol·L-1 of different additives. For a Maxwell fluid with a single stress relaxation time (R) at low shear frequencies, the following equations can be used to describe the relationship between G ' and G " :

22


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G 

( R ) 2 G 1  ( R ) 2

(1)

G  

 R G 1  ( R ) 2

(2)

Where G' is the plateau modulus and  is the frequency. At high  values, G ' remain constant and is equal to G' . The relaxation time (R) is estimated from

1 / c , at which the two module curves cross. In Figure 7, the complete lines corresponded to the results of fitting with a Maxwell evolution. Except for the R14HTAB/NaSal system, the elastic ( G ' < G " ) and viscous ( G " < G ' ) behaviors were observed at low and high frequencies, respectively. The variations in G " and G ' were analogous to those observed in Maxwell fluids at low  values, indicating that the two systems obeyed Maxwell’s fluid model with a single stress relaxation time

43, 48-49.

However, the rheological behavior significantly diverged

from that of a Maxwell fluid in the high-frequency region, and an upturn in G " could be observed, which could be ascribed to a transformation of the relaxation from reptation-scission to the Rouse mode. This characteristic has been found in many micellar solutions of surfactants and is also a feature of viscoelastic wormlike micelles 9, 36, 48. For the R14HTAB/NaSal system, both the G ' and G " curves continuously sloped upward with increasing frequency, which deviated from Maxwell behavior at most values in the frequency range; the dynamic rheological curve as a function of the angular frequency exhibited rheological characteristics of cylindrical micelles

26.

Furthermore, it can be observed from

Figure 7 that the cross point of the curves of G ' and G " moved to a lower 23



frequency for two R14HTAB/hydroxyl naphthalate systems. The lowest was the 2HSNC/R14HTAB solution, which corresponded to a long relaxation time, and the system showed very high viscoelasticity.

100 10

G',G"/Pa

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 43

1 0.1

-1

Cadditives=30mmolL G', fitG', G', fitG', G', fitG',

0.01 1E-3 1E-4 0.01

0.1

1

G" NaSal, fitG" G"1SHNC, fitG" G"2SHNC, fitG"

10  rads-1

100

1000

Figure 7. Variations in G ' (filled symbols) and G " (open symbols) with the shear frequency  for mixed solutions of R14HTAB (100 mmol·L-1) and different additives (30 mmol·L-1)

G' and  R

are two characteristic parameters for describing the dynamic

rheological properties of wormlike micelles. In all theoretical approaches, the plateau modulus G' was shown to be proportional to the number density of the elastically effective chains in the case of networks, or it depended on the number of crosslinking points per unit volume, and therefore reflected the mesh size of the network. The values of G' can be obtained from the Cole-Cole (G” vs G') plot (not shown). The increase in the plateau modulus G' with 24


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increasing salt concentrations corresponded to an increase in the degree of connection and could simultaneously be regarded as evidence of dimensional micellar growth.  R is relevant to the length of the wormlike micellar system undergoing stress relaxation by reptation, as indicated by the Maxwellian fluid behavior. An increase in these quantities may be relevant to the micellar growth to longer micelles and an increased number of entanglements that result in the system becoming more viscoelastic. In other words, the larger the R value is, the slower the diffusion of wormlike micelles is because of the larger micellar size. Figure 8 shows the changes in G' and  R with increasing Cadditives. The plateau modulus

G'

(Figure 8a) continuously increased with increasing

Cadditives until a relatively high value was reached (which corresponded to the viscosity maximum), while beyond these values, the variation in G' nearly constant. The increase in

G'

was

is usually regarded as evidence of

one-dimensional micellar growth. The relationship between additive concentration followed the power law,

G'

and the

G'  C 2.3 , for R HTAB/NaSal, 14

G'  C 2.2 for R HTAB/1SHNC, and G'  C 2.0 for R HTAB/2SHNC mixed 14 14

systems below the platform values. The exponents of the power law were close to the theoretical value of 2.3  0.2 by Cates and coworkers for entangled wormlike micelles 54. After the viscosity maximum, G' did not depend on the additive concentration indicating that the micellar microstructure did not change in this concentration range. Hence, according to the above discussion and experimental results, micellar shortening could be ruled out as a possible 25



reason. After the maximum was reached, the decrease in viscosity may be relevant with micellar branching. The variation in  R with Cadditives (Figure 8b) was very similar to that observed for0 , as shown in Figure 3, which strongly indicates that a structural transformation occurred with the increase in Cadditives. These results are similar to the behavior of many mixed systems of surfactants and additives 2-8.

160 CR14HTAB /mmolL

40

a

-1

-1

100/NaSal 100/1SHNC 100/2SHNC

30

'

R s

80

b

CR14HTAB /mmolL

100/NaSal 100/1-SHNC 100/2-SHNC

120

G  Pa

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 43

20 10

40

0

0 20

40

60

-1

80

0

Cadditives/mmolkg

20

40

60

-1

80

Cadditives/mmolL

Figure 8 Variation in the plateau modulus G' (a) and relaxation times  R (b) of R14HTAB /additive mixtures as a function of C additives for a 100 mmolL-1 R14HTAB solution

3.2 Cryo-TEM of Wormlike Micelles The rheological measurements revealed the variation in macroscopic properties for the R14HTAB /additive mixtures, while cryo-TEM could provide a clearer observation of the micellar microstructure. In addition, it is also the most reliable way to confirm the branching of wormlike micelles 50, 51, 55. Figure 9 shows a set of cryo-TEM micrographs of 100 mmolL-1 R14HTAB solutions containing no additives, 30 26


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mmol·L-1 NaSal and 2HSNC, and 60 mmol·L-1 2HSNC. The spherical micelles predicted by rheological measurements are shown in Figure 9A. When salts (NaSal and 2HSNC) were added to the system (Figure. 9B and C), wormlike micelles were formed in two solutions. Figure 8B shows that as the length of wormlike micelles was varied, no apparent micellar branching or entanglement was observed. However, very long wormlike micelles are observed in Figure 9C, which overlapped and became entangled; the beginnings and ends of the micelles could not be distinguished. Because of the difficulty of performing cryo-TEM on samples with a very high viscosity that could not be thinned easily, we did not complete cryo-TEM measurements of those samples at the peaks. In Figure 9D, a typical network structure or three-way connections caused by branched micelles is observed. The results from the cryo-TEM measurement are in good consistent with the predictions from the steady-state shear measurements, in which the decrease in viscosity after the maximum was found to be the result of a shift from linear wormlike micelles to branched wormlike micelles.

27



Page 28 of 43

Figure 9. Cryo-TEM micrographs of wormlike micelles formed by R14HTABwith (A) no additives, (B) 30 mmol·L-1NaSal, (C) 30 mmol·L-1 2SHNC, and (D) 60 mmol·L-1 2SHNC. Scale bar 200 nm. 3.3. Molecular Dynamics Simulation. In this section, the MD simulation method was used to investigate the self-assembly behavior of the R14HTAB/additive mixture systems with different mixture proportions. Figure 10 shows the simulated configurations of the four R14HTAB/additives mixture systems. It can be seen that the preassembled rod-like micelle broke into a spherical micelle in the absence of any additive salts, while the straight rod-like micelle remained stable in the presence of additive organic salts after the simulation. These observations coincide well with experimentally observed phenomena and are similar to previous MD studies

23, 28.

Most of the additive

salts (Sal-, 1SHNC, and 2SHNC) penetrated into the interior region of the 28


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rod-like micelles. Figure 11 shows the binding structures of the additive molecules with the surrounding surfactants, formed through electrostatic, van der Waals and H-bonding interactions (the other two mixed system are shown in S2 in the Supplementary Information). Thus, the strong association between the additive ions and R14HTAB can effectively shield the electrostatic repulsion between the surfactant head-groups, which benefitted the formation of long rod-like micelles.

Figure 10. Configurations of R14HTAB micelles in the presence of different additive salts: (a) without salts, (b) NaSal, (c) 1SHNC, and (d) 2SHNC. Only the R14HTAB and additive salts are displayed for clarity. The blue dotted lines represent the edges of the simulation box. The additive salts Sal-, 1SHNC, and 2SHNC are displayed in red, blue, and orange, respectively. In each panel, the left snapshot is the initial configuration and the right one is the configuration after 20 ns of simulation.

29



Figure 11.

Bond

structure of the surfactant head-group with the adjacent 2SHNC

molecules inside the rod-like micelle.

The branched wormlike micelle was simulated from two individual preassembled rodlike micelles, which were arranged in cross type. The branching of the wormlike micelle was due to the increasing additive salt concentration, as mentioned above. To verify our speculation, in the low additive concentration system (30 mmol·L-1 2HSNC), the 2SHNC ions located near the junction of two cylindrical micelles were removed (indicated by the red circle in Figure 12a). The simulation results showed that the branched micelle was separated from the long rod-like micelle after 20 ns of simulation, and the fracture occurred only in the region where the quantity of 2SHNC was lower. The branched wormlike micelle remained stable as more and more 2SHNC ions were solubilized into the micelle in the system with 60 mmol·L-1 2HSNC (Figure 12b). This result suggests that the formation of branched wormlike micelles was promoted by the additive salts in the high 2HSNC concentration solution. Likewise, the bridging action of the penetrated salts also played an important role in the branching process, as shown in Figure 13. 30


Page 30 of 43

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Figure 12. Configurations of the simulated branched wormlike micelles in the (a) 30 mmol·L-1 and (b) 60 mmol·L-1 2SHNC solution. In each panel, the left snapshot is the initial configuration and the right snapshot is the configuration after 10 ns of simulation.

Figure 13. The bridging structure of 2SHNC with the surfactant molecules inside the 31



branched micelles. In summary, by combining the MD simulation configurations with observations and analyses of rheological parameters, such as the chemical shift indicated by 1H NMR spectra of each group and FTIR spectra, we could conclude that the counterions penetrated into the interior region of the micelle and interacted with the surrounding surfactant molecules through electrostatic interactions, hydrogen bonds, and hydrophobic forces or Van der Waals forces. These synergistic effects were the root cause of the increase in the viscosity of the rod-shaped micelles and their enhanced stability.

4. CONCLUSIONS The experimental results show that all three organic salts (NaSal, 1SHNC and 2SHNC) induce the transition from spherical micelles to wormlike micelles in100 mmol·L-1R14HTAB solutions. The rheological behavior presented is controlled by the additive concentration and the zero-shear viscosity (0) as a function of the added salt concentration shows a maximum viscosity. As indicated by the Cryo-TEM observations and MD calculations, the increase in the zero shear viscosity before the maximum was attributed to the formation of wormlike micelles and the decrease in viscosity observed after reaching the maximum viscosity is mainly caused by wormlike micellar branching. The mechanism of the change in micellar structure with increasing additive concentration was revealed through MD simulations. Under 32


Page 32 of 43

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exactly the same conditions, the influence of SHNC on the viscoelastic behavior of R14HTAB solutions was much stronger compared to NaSal. This finding can be attributed to the strong hydrophobic properties of SHNC molecules. For both 1SHNC and 2SHNC, the hydroxyl group in the molecule on the side of the naphthalene rings (1SHNC) can produce an unfavorable environment for micellar growth owing to the steric hindrance effect. The interaction between the surfactant and added salts comes from synergistic effects, such as electrostatic interactions, hydrogen bonds and hydrophobic (Van der Waals forces). These results will facilitate the selection of appropriate surfactants with different additives for practical applications.

Supporting Information The following Supporting Information is available:

1H

NMR spectra for

R14HTAB/additive systems and typical binding structure of the surfactant with Sal-, 1SHNC and 2SHNC inside the rod-like micelles. This material is available free of charge online at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author H. Yan and X.L Wei contributed equally. *E-mail: [email protected](X.L.W.). Tel: +86-635-8230613; *E-mail: [email protected] (H.Y.). ORCID Xilian Wei: 0000-0002-0212-8986 33



Page 34 of 43

Hui Yan: 0000-0002-9843-0601 Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (grant nos. 21473084 and 21203084), Focus Scientific (318011402), Natural Science Foundation of Shandong Province (ZR2017BB035) and Experimental Technology Research Project of Liaocheng University (LDSY2014008).

REFERENCES (1) Yang, J. Viscoelastic Wormlike Micelles and Their Applications. Curr. Opin. Coll. Inter. Sci. 2002, 7, 276-281. https://doi:10.1016/S1359-0294(02)00071-7. (2) Ezrahi, S.; Tuval, E.; Aserin, A. Properties, Main Applications and Perspectives of Worm

Micelles.

Adv.

Colloid

Interface.

2006,

128,

77-102.

https://doi:10.1016/j.cis.2006.11.017. (3) Hellsten, M.; Harwigsson, I. Environmentally Acceptable Drag-reducing Surfactants for District Heating and Cooling. J. Am. Oil. Chem. Soc. l996, 73, 921-928. https://doi.org/10.1007/BF02517996 (4) Wei, X. L.; Wang, X. H.; Sun, D. Z.; Liu, J. F.; Liu, J.; Sha, Y. H.; Wang, Z. N. Phase and Rheological Behavior of a Gemini Cationic Surfactant Aqueous System. Soft Matter. 2012, 8, 10115-10122. https://doi:10.1039/ c2sm26346g. 34


Page 35 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(5) Kern, F.; Cates, M. E.; Sauveur, C.; Lemarechal, P. Rheological Properties of Semidilute and Concentrated Aqueous Solutions of Cetyltrimethylammonium Bromide in the Presence of Potassium Bromide. Langmuir 1992, 2, 437–440. https://doi:10.1021/la00038a020. (6) Davies, T. S.; Ketner, A. M.; Raghavan, S. R. Self-assembly of Surfactant Vesicles that Transform into Viscoelastic Wormlike Micelles upon Heating. J. Am. Chem. Soc. 2006, 128, 6669-6675. https://doi:10.1021/ja060021e. (7) Lin, Y. Y.; Huang, J. B.; Fu, H. L.; Yu, C. L. A Facile Route to Design pH-responsive Viscoelastic Wormlike Micelles: Smart Use of Hydrotropes. J. Colloid Interface. Sci. 2009, 330, 449–455. https://doi:10.1016/j.jcis.2008.10.071. (8) Ketner, A. M.; Kumar, R.; Davies, T. S.; Elder, P. W.; Raghavan, S. R. A Simple Class of Photorheological Fluids: Surfactant Solutions with Viscosity Tunable by Light. J. Am. Chem. Soc. 2007, 129, 1553-1559. https://doi:10.1021/ja065053g. (9) Inoue, T.; Inoue, Y.; Watanabe, H. Nonlinear Rheology of CTAB/NaSal Aqueous Solutions: Finite Extensibility of a Network of Wormlike Micelles. Langmuir 2005, 21, 1201-1208. https://doi:10.1021/la048292v. (10)Ito, T. H.; Miranda, P. C. M. L.; Morgon, N. H.; Heerdt, G.; Dreiss, C. A.; Sabadini, E. Molecular Variations in Aromatic Cosolutes: Critical Role in the Rheology of Cationic Wormlike Micelles. Langmuir 2014, 30, 11535–11542. https://doi:10.1021/la502649j. (11)Chen, W. R.; Butler, P. D.; Magid, L. J. Incorporating Intermicellar Interactions in the Fitting of SANS Data from Cationic Wormlike Micelles. Langmuir 2006, 35



Page 36 of 43

22, 6539–6548. https://doi:10.1021/la0530440. (12)Das, N. C.; Cao, H.; Kaiser, H.; Warren, G. T.; Gladden, J. R.; Sokol, P. E. Shape and Size of Highly Concentrated Micelles in CTAB/NaSal Solutions by Small Angle Neutron Scattering (SANS). Langmuir 2012, 28, 11962−11968. https://doi:10.1021/la2022598. (13)Israelachvili, J. N.; Mitchell, D. J.; Ninham, B. W. Theory of Self-assembly of Hydrocarbon Amphiphiles into Micelles and Bilayers. J. Chem. Soc. 1976, 72, 1525-1568. https://doi:10.1039/f29767201525. (14)Hassan, P. A.; Bhattacharya, K.; Kulshreshtha, S. K.; Raghavan, S. R. Microrheology of Wormlike Micellar Fluids from the Diffusion of Colloidal Probes. J. Phys. Chem. B 2005, 109, 8744–8748. https://doi:10.1021/jp0442807. (15)Nettesheim, F.; Wagner, N. J. Fast Dynamics of Wormlike Micellar Solutions. Langmuir 2007, 23, 5267–5269. https://doi:10.1021/la0635855. (16)Long, M. A.; Kaler, E. W.; Lee, S. P.; Wignall, G. D. Characterization of Lecithin-taurodeoxycholate

Mixed

Micelles

Using

Small-angle

Neutron

Scattering and Static and Dynamic Light Scattering. J. Phys. Chem. 1994, 98, 4402–4410. https://doi:10.1021/j100067a031. (17)Danino, D.; Talmon, Y.; Levy, H.; Beinert, G.; Zana, R. Branched Threadlike Micelles in an Aqueous Solution of a Trimeric Surfactant. Science 1995, 269, 1420-1421. https://doi:10.1126/science.269.5229.1420. (18)Callaghan, P. T.

Rheo-NMR and Velocity Imaging. Curr. Opin. Colloid

Interface Sci. 2006, 11, 13–18. https://doi:10.1016/j.cocis.2005.10.003. 36


Page 37 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(19)López-González, M. R.; Holmes, W. M.; Callaghan, P. T. Rheo-NMR Phenomena

of

Wormlike

Micelles.

Soft

Matter

2006,

2,

855–869.

https://doi:10.1039/b600978f. (20)Croce, V.; Cosgrove, T.; Dreiss, C. A.; King, S.; Maitland, G.; Hughes, T. Giant Micellar Worms under Shear: A Rheological Study Using SANS. Langmuir 2005, 21, 6762–6768. https://doi:10.1021/la0479410. (21)Padding, J. T.; Boek, E. S.; Briels, W. J. Rheology of Wormlike Micellar Fluids from Brownian and Molecular Dynamics Simulations. J. Phys. Condens. Matter. 2005, 17, S3347–S3353. https://doi:10.1088/0953-8984/17/45/021. (22)Andreev, V. A.; Victorov, A. I. Molecular Thermodynamics for Micellar Branching in Solutions of Ionic Surfactants. Langmuir 2006, 22, 8298–8310. https://doi:10.1021/la061087q. (23)Yan, H.; Han, Z.; Li, K. M.; Li, G. Y.; Wei. X. L. Molecular Dynamics Simulation of the pH-induced Structural Transitions in CTAB/NaSal Solution. Langmuir 2018, 34, 351-358. https://doi:10.1021/acs.langmuir.7b03715. (24)Huang, C. C.; Ryckaert, J. P.; Xu, H. Kinetics and Dynamic Properties of Equilibrium Polymers. J. Chem. Phys. 2006, 125, 1094900-1094901. https://doi:10.1063/1.2346670. (25)Zhang, J.; Zhang, Y.; Li, J. W.; Wang, P.; Sun, X. L.; Yan, Y. G. Effect of Organic Salt on the Self-assembly of Ammonium Gemini Surfactant: An Experiment and Simulation Study. Coll and Surf. A 2018, 548, 198-205. https://doi:10.1016/j.colsurfa.2018.01.048. 37



(26)Malde, A. K.; Zuo, L.; Breeze, M.; Stroet, M.; Poger, D.; Nair, P.; Oostenbrink, C.; Mark, A. E. An Automated Force Field Topology Builder (ATB) and Repository: Version 1.0. J. Chem. Theory Comput. 2011, 7, 4026-4037. https://doi:10.1021/ct200196m. (27)Oostenbrink, C.; Soares, T. A.; Vegt, N. F. A. V. D.; Gunsteren, W. F. V. Validation of the 53A6 GROMOS Force Field. J. Eur. Biophys. 2005, 34, 273-284. https://doi:10.1007/s00249-004-0448-6. (28)Wang, Z.; Larson, R. G. Molecular Dynamics Simulations of Threadlike Cetyltrimethylammonium Chloride Micelles: Effects of Sodium Chloride and Sodium Salicylate Salts. J. Phys. Chem. B 2009, 113, 13697-13710. https://doi:10.1021/jp901576e. (29)Hess, B.; Kutzner, C.; Spoel, D. V. D.; Lindahl, E. GROMACS 4: Algorithms for Highly Efficient, Load-balanced, and Scalable Molecular Simulation. J. Chem. Theory Comput. 2008, 4, 435-447. https://doi:10.1021/ct700301q. (30)Bussi, G.; Donadio, D.; Parrinello, M. Canonical Sampling through Velocity Rescaling. J. Chem. Phys. 2007, 126, 014101. https://doi:10.1063/1.2408420. (31)Hess, B.; Bekker, H.; Berendsen, H. J. C.; Fraaije, J. G. E. M. LINCS: A Linear Constraint Solver for Molecular Simulations. J. Comput. Chem. 1997, 18, 1463-1472. https://doi:

10.1002/ (sici) 1096-987 x (199709)18:123.0.co; 2-h. (32)Essmann, U.; Perera, L. M.; Berkowitz, L.; Darden, T.; Lee, H.; Pedersen, L. G. A Smooth Particle Mesh Ewald Method. J. Chem. Phys. 1995, 103, 8577-8593. 38


Page 38 of 43

Page 39 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


https://doi: 10.1063/1.470117. (33)Raghavan, S. R.; Kaler, E. W.; Highly Viscoelastic Wormlike Micellar Solutions Formed by Cationic Surfactants with Long Unsaturated Tails. Langmuir 2001, 17, 300- 306. https://doi: 10.1021/la0007933. (34)Makhloufi, R.; Cressely, R. Temperature Dependence of the Non-Newtonian Viscosity of Elongated Micellar Solutions, Coll. Poly. Sci. 1992, 270, 1035-1041. https://doi: 10.1007/BF00655973. (35)Kulicke, W. M.; Kniewske, R. The Shear Viscosity Dependence on Concentration, Molecular Weight, and Shear Rate of Polystyrene Solutions, Rheol Acta. 1984, 23, 75-83. https://doi: 10.1007/BF01333878. (36)Rehage, H.; Hoffmann, H. Viscoelastic Surfactant Solutions: Model Systems for Rheological

Research.

Mol.

Phys.

1991,

74,

933–973.

https://doi:

10.1080/00268979100102721. (37)Kern, F.; Zana, R.; Candau, S. J. Rheological Properties of Semidilute and Concentrated Aqueous Solutions of Cetyltrimethylammonium Chloride in the Presence of Sodium Salicylate and Sodium Chloride. Langmuir 1991, 7, 1344-1351. https://doi: 10.1021/la00055a010. (38)In, M.; Warr, G. G.; Zana, R. Dynamics of Branched Threadlike Micelles. Phys. Rev. Lett. 1999, 83, 2278–2281. http://dx.doi.org/10.1103/PhysRevLett.83.2278. (39)Ping, A. L.; Geng, P. P.; Wei, X. L.; Liu, J.; Zhang, J. H.; Sun, D. Z.; Guo, X. D.; Yang, M. Rheological Properties of Wormlike Micelles Formed in Aqueous Systems of 3-alkoxy-2-hydroxypropyl Trimethyl Ammonium Bromides in the 39



Page 40 of 43

Presence of Sodium Octanoate. J. Surfact. Deterg. 2015, 18, 1117-1126. https://doi: 10.1007/s11743-015-1724-4. (40)Wei, X. L.; Geng, P. P.; Han, C. H.; Guo, Y.; Chen, X. X.; Zhang, J. H.; Zhang, Y. T.; Sun, D. Z.; Zhou, S. Y. Rheological Properties of Viscoelastic Solutions in a Cationic Surfactant-organic Salts-water System. Ind. Eng. Chem. Res. 2016, 55, 5556-5564. https://doi: 10.1021/acs.iecr.6b00238. (41)Imae, T.; Kohsaka, T. Size and Electrophoretic Mobility of C14TASalmicelles in Aqueous Media. J. Phys. Chem. 1992, 96, 10030–10035. https://doi: 10.1021/j100203a081. (42)Ziserman, L.; Abezgauz, L.; Ramon, O.; Raghavan, S. R.; Danino, D. Origins of the

Viscosity

Peak

Catanionicsurfactants.

in A

Wormlike

Micellar

Cryo-transmission

Solutions.

Electron

1.

Mixed

Microscopy

Study.

Langmuir 2009, 25, 10483–10489. https://doi: 10.1021/la901189k. (43)Cappelaere, E.; Cressely, R. Influence of NaClO3 on the Rheological Behaviour of a Micellar Solution of CPCl. Rheol. Acta. 2000, 39, 346–353. https://doi: 10.1007/s003970000095. (44)Guo, Y.; Chen, X. X.; Sang, Q.; Han, C. H.; Lv, D. M.; Zhang, Q. R.; Liu, M.; Wei, X. L. Comparative Study of the Viscoelastic Micellar Solutions of R16HTAC and CTAC in the Presence of Sodium Salicylate. J. Molecular Liquids. 2017, 234, 149–156. https://doi: 10.1016/j.molliq.2017.03.060. (45)Magid, L. J. The Surfactant-polyelectrolyte Analogy. J. Phys. Chem. 1998, 102, 4064–4074. https://doi: 10.1021/jp9730961. 40


Page 41 of 43 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(46)Raghavan, S. R.; Fritz, G.; Kaler, E. W. Wormlike Micelles Formed by Synergistic Self-assembly in Mixtures of Anionic and Cationic Surfactants. Langmuir 2002, 18, 3797-3803. https://doi: 10.1021/la0115583. (47)Koehler, R. D.; Raghavan, S. R.; Kaler, E. W. Microstructure and Dynamics of Wormlike Micellar Solutions Formed by Mixing Cationicand Anionic Surfactants. J. Phys. Chem. B 2000, 104, 11035–11044. https://doi: 10.1021/jp0018899. (48)Wei, X. L.; Wang, X. H.; Liu, J.; Sun, D. Z.; Yin, B. L.; Wang, X. J. Adsorption Kinetics of 3-alkoxy-2-hydroxypropyl Trimethyl Ammonium Chloride at Oil-water

Interface.

Appl.

Surf.

Sci.

2012,

261,

237-241.

https://doi:

10.1016/j.apsusc.2012.07.151. (49)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. https://doi: 10.1021/la0345800. (50)Swanson-Vethamuthu, M.; Almgren, M.; Karlsson, G.; Bahadur, P. Effect of Sodium Chloride and Varied Alkyl Chain Length on Aqueous Cationic Surfactant-bile Salt Systems. Cryo-TEM and Fluorescence Quenching Studies. Langmuir 1996, 12, 2173-2185. https://doi: 10.1021/la950964h. (51)Colthup, N. B.; Daly, L. H.; Wiberly, S. E. Introduction to Infrared and Raman Spectroscopy.

Academic

Press,

Inc.

1964,

87,

1155-1156.

https://doi:

10.1021/ja01083a063. (52)Koroleva, S. V.; Victorov, A. I. The Strong Specific Effect of Coions on Micellar 41



Page 42 of 43

Growth from Molecular-thermodynamic Theory. Phys. Chem. Chem. Phys. 2014, 16, 17422-17425. https://doi: 10.1039/c4cp02178a. (53)Wei, Z. B.; Wei, X. L.; Wang, X. H. Wang, Z. N. Liu, J. Ionic Liquid Crystals of Quaternary Ammonium Salts with a 2-hydroxypropoxy Insertion Group. J. Mater. Chem. 2011, 21, 6875–6882. https://doi: 10.1039/c1jm10236b. (54)Cates, M. E.; Candau, S. J. Statics and Dynamics of Worm-like Surfactant Micelles.

J.

Phys.

Con.

Matter.

1990,

2,

6869-6892.

https://doi:

10.1088/0953-8984/2/33/001. (55)Lin, Z. Branched Worm-like Micelles and Their Networks. Langmuir 1996, 12, 1729–1737. https://doi: 10.1021/la950570q.

42


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Effect of Additives on Surfactant Micelle Shape Transformation

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