Colloidal Wormlike Micelles with Highly Ferromagnetic Properties

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Colloidal Wormlike Micelles with Highly Ferromagnetic Properties Wenrong Zhao, Shuli Dong, and Jingcheng Hao* Key Laboratory of Colloid and Interface Chemistry & Key Laboratory of Special Aggregated Materials, Shandong University, Ministry of Education, Jinan 250100, P. R. China S Supporting Information *

ABSTRACT: For the first time, a new fabrication method for manipulating the ferromagnetic property of molecular magnets by forming wormlike micelles in magnetic-ionic-liquid (magIL) complexes is reported. The ferromagnetism of the mag-IL complexes was enhanced 4-fold because of the formation of wormlike micelles, presenting new evidence for the essence of magnetism generation at a molecular level. Characteristics such as morphology and magnetic properties of the wormlike micelle gel were investigated in detail by cryogenic transmission electron microscopy (Cryo-TEM), rheological measurements, circular dichroism (CD), FT-IR spectra, and the superconducting quantum interference device method (SQUID). An explanation of ferromagnetism elevation from the view of the molecular (ionic) distribution is also given. For the changes of magnetic properties (ferromagnetism elevation) in the wormlike micelle systems, the ability of CTAFe in magnetizing AzoNa4 (or AzoH4) can be ascribed to an interplay of the magnetic [FeCl3Br]− ions both in the Stern layer and in the cores of the wormlike micelles. Formation of colloidal aggregates, i.e., wormlike micelles, provides a new strategy to tune the magnetic properties of novel molecular magnets.

1. INTRODUCTION Magnetic media such as ferrofluids have attracted extensive research interest because of their potential use in microfluidics, catalysis, targeted drug delivery,1 and controlled conjugation2 and migration3 of magnetic surfactants to DNA and/or biomolecules by regulating the magnetic field. Scientists have found that plate-shaped magnets in a liquid crystal have been produced to exhibit ferromagnetism.4 Recently, a new class of surfactants with the chemical structures characteristic of ionicliquids (ILs), which are responsive to a magnetic field, has been reported.5 Except for the amphiphilic characteristics, these transition metal-based ILs with halide anions, such as [FeCl4]−, [CoCl4]2−, [MnCl4]2−, and [GdCl6]3−,6 display simple paramagnetic behavior over most of the temperature range of 50 to 350 K. As one kind of liquid molecular magnet, these mag-ILs behave differently compared with typical magnetic fluids (ferrofluids) which contain magnetic colloidal particles (larger than 10 nm) dispersed in a carrier fluid. Being paramagnetic and accompanied by a weak ferromagnetism, the nanoparticlefree mag-ILs comprise highly effective concentrations of metal centers and magnetoresponsive physicochemical properties. In our previous work,3 we reported that magnetic gold nanoparticles were prepared via one-step modification with a paramagnetic cationic surfactant. Considering novel molecular magnets,7 interspin coupling of these new surfactants could be regulated through the manipulation of molecular architecture, such as the species of transition metal ion and the aggregation behavior.1 Given that these molecular magnets self-assemble into colloidal aggregates, various surfactant aggregates may provide a feasible way to manipulate the magnetic behavior. In this paper, we report a new and convenient strategy to regulate the magnetic behavior (ferromagnetism) of mag-IL © XXXX American Chemical Society

complexes by forming wormlike micelles, in which the formation of self-assembled aggregates, such as micelles, vesicles, and discs, involves no convalent bonds between spin sites1 of the magnetic materials. J. Eastoe et al. elucidated whether the formation of micelles at the critical micelle concentration (cmc) gives rise to any additional magnetic effects by investigating the susceptibility of micellar solutions.1 The additional magnetic effects of wormlike micelle formation on the molecular magnets remain unexploited to date. It should be groundbreaking progress to manipulate the magnetic behavior by the formation of colloidal wormlike micelles, and in our strategy the magnetic behavior of these molecular magnets might be controlled through noncovalent interactions. In our previous work,8 we demonstrated that an achiral azobenzene gelator combined with CTAB could self-aggregate into chiral wormlike micelles in the presence of acid. Now we design and synthesize a magnetoresponsive cationic surfactant, cetyltrimethylammonium trichloromonobromoferrate (CTAFe),2 which is based on a common cationic surfactant with transition metal-based coordinated anions (Figure 1a, CTAFe is also a magnetic ionic liquid surfactant on account of its special [FeCl3Br]− anion5) and an effective gelator AzoNa49 to investigate the formation of colloidal wormlike micelles for further control of magnetic behavior. As shown in Figure 1b, the mag-IL surfactant5 was facilely incorporated into the wormlike micelles comprising a pH-responsive supramolecular magnet switch. Via intermolecular H-bonds, AzoH4 within the wormlike micelles will connect to a chiral helix,8 with the head Received: August 23, 2015 Revised: September 24, 2015

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DOI: 10.1021/acs.langmuir.5b03148 Langmuir XXXX, XXX, XXX−XXX

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KOH (the calculated amount of KOH was weighed to add into the viscoelastric gel) was added to 1.0000 g of the above gel (60 mmol·L−1 CTAFe/15 mmol·L−1 AzoNa4/ 60 mmol·L−1 HCl). Upon the addition of the KOH, gel was destroyed and turned into sol. 2.3. Rheological Measurements. Rheological measurements were carried out on a HAAKE RS6000 rheometer with a coaxial cylinder sensor system (Z41 Ti) for lower viscosity samples and a cone−plate system (C35/1° Ti L07116) for samples with high viscosity. 2.4. Cryogenic (cryo)-TEM Observations. Cryo-TEM samples were prepared in a controlled environment vitrification system (CEVS) at 25 °C. That is, 5 μL of sample solution sucked by a micropipette was cast onto a TEM copper grid with carbon supporting film and then quickly plunged into a reservoir of liquid ethane (cooled by nitrogen) at −165 °C. The vitrified samples were then examined with a JEOL JEM-1400 TEM (120 kV) at about −174 °C. The phase contrast was enhanced by underfocus. The images were recorded on a Gatan multiscan CCD and processed with Digital Micrograph. 2.5. Superconducting Quantum Interference Device Magnetometry. Frozen dried samples (60 mmol·L−1 CTAFe/15 mmol· L−1 AzoNa4/60 mmol·L−1 HCl) were placed in sealed polypropylene tubes and mounted inside a plastic straw for measuring in a magnetometer with a superconducting quantum interference device (SQUID, MPMSXL, Quantum Design, San Diego, CA) and a reciprocating sample option (RSO). The experiment is conducted at 300 K. 2.6. Spectroscopic Measurements. Fourier transform infrared (FT-IR) spectra were obtained on a VERTEX-70/70v FT-IR spectrometer (Bruker Optics, Germany). Circular dichroism (CD) measurement was performed on a JASCO J-810 spectropolarimeter, which was flushed with constant nitrogen flow during operation to purge the ozone generated by the light source of the instrument. The spectra were smoothed by using the noisereducing option in the operating software of the instrument. Three scans were averaged per spectrum to improve the signal-to-noise ratio. Wavelength scans were recorded at 1 nm intervals from 700 to 200 nm. The wormlike micellar solution was determined using a 0.1 mm path-length quartz cuvette at 25 °C. The possible influence of linear dichroism (CD) was excluded by measuring the spectra of xerogels cast on a quartz slide with solvents evaporated under vacuum. During the measurement of CD spectra, the slides were kept perpendicular to the light direction and rotated within the film plane to keep out polarization-dependent reflections and exclude the possible angle-dependent CD signals.

Figure 1. (a) Chemical structures of the achiral gelator azobenzene, AzoNa4, and CTAFe. (b) A scheme illustrating the ferromagnetism elevation by the formation of wormlike micelles. The molecules are simplified for better view: the green balls are the hydrophobic anions [FeCl3Br]− of CTAFe, and the purple-red balls indicate the +N(CH3)3 group of CTAFe.

groups of CTAFe binding strongly to AzoH4. Except for the chiral characteristics ascertained previously,8 the observed remarkable magnetic behavior also revealed that the ferromagnetism of the molecular magnet system by forming colloidal wormlike micelles can be largely enhanced by 4-fold. To the best of our knowledge, it is the first report of manipulation of the ferromagnetic property of molecular magnets by forming wormlike micelles in magnetic-ionic-liquid (mag-IL) complexes.

2. EXPERIMENTAL SECTION 2.1. Chemicals and Materials. Cetyltrimethylammonium trichloromonobromoferrate (CTAFe) was synthesized by mixing equal molar amounts of cationic surfactant CTAB and FeCl3 in methanol and stirring overnight at room temperature; then the solvent was removed, and the product was dried at 80 °C, yielding brown/red solids.2 Cetyltrimethylammonium bromide (CTAB) was purchased from J&K CHEMICA Company (China), purity >99%. Iron trichloride (FeCl3) was purchased from Sinopharm Chemical Reagent Co. Ltd., China. The gelator, 4,4-bis(2,3-dicarboxylphenoxyl)azobenzene (AzoNa4) was synthesized according to our earlier study.8 2.2. Gel Regulation with HCl/KOH. Typically, 0.3160 g of CTAFe and 0.0950 g of AzoNa4 were dissolved in 8.0 mL of distilled H2O to form the stock solution of 75.00 mmol·L−1 CTAFe and 18.75 mmol·L −1 AzoNa 4 mixtures. HCl solution with an accurate concentration of 300 mmol·L−1 was prepared. A 0.2000 g amount of the HCl solution (300 mmol·L−1) was added dropwise into 0.8000 g of the above stock solution to be 60 mmol·L−1 CTAFe/15 mmol·L−1 AzoNa4/60 mmol·L−1 HCl. Upon the addition of the HCl, the gel was formed instantly. The samples of the varied HCl concentration were prepared by changing the amount of the HCl solution and distilled water. To list an example, 0.1000 g of HCl solution (300 mmol·L−1) and 0.1000 g of distilled H2O were mixed and then added to 0.8000 g of the stock solution to be 60 mmol·L−1 CTAFe/15 mmol·L−1 AzoNa4/30 mmol·L−1 HCl. Accordingly, a series of sols/gels with different ratios, namely solutions of 60 mmol·L−1 CTAFe/15 mmol· L−1 AzoNa4/60 mmol·L−1 HCl, 60 mmol·L−1 CTAFe/15 mmol·L−1 AzoNa4/45 mmol·L−1 HCl, 60 mmol L−1 CTAFe/15 mmol·L−1 AzoNa4/30 mmol·L−1 HCl, and 60 mmol·L−1 CTAFe/15 mmol·L−1 AzoNa4/ 15 mmol·L−1 HCl were prepared, respectively. For comparison, a solution without HCl was also prepared, i.e., 0.2000 g of distilled water was added to 0.8000 g of the stock solution to form a solution of 60 mmol·L−1 CTAFe/15 mmol·L−1 AzoNa4/0 mmol·L−1 HCl.

3. RESULTS AND DISCUSSION 3.1. Wormlike Micelles and Their pH-Responsiveness. As shown in Figure 2 (a and b), with the addition of HCl, the

Figure 2. (a) Steady shear measurements for the solutions (60 mmol· L−1 CTAFe/15 mmol·L−1 AzoNa4) with different cHCl (0, 15, 30, 45, 60 mmol·L−1). (b) The sample photographs of the solution at cHCl = 0 mmol·L−1 and the gel at cHCl = 60 mmol·L−1. B

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Figure 3. Stress sweep rheogram (a), oscillatory shear rheogram (b), and Cole−Cole plots (c) for the samples of 60 mmol·L−1 CTAFe/15 mmol· L−1 AzoNa4/60 mmol·L−1 HCl.

viscosity of the micelle solution of 60 mmol·L−1 CTAFe/15 mmol·L−1 AzoNa4 in water increases largely. It turned out to be a viscoelastic gel with a low shear Newtonian plateau and a shear thinning phenomenon. This is clearly predictive of wormlike micelles because the alignment of wormlike micelles under the direction of flow could be attributed to the shear thinning behavior.10 It is interesting that the pH-induced gel can turn back to flowing solution upon introducing a stoichiometric amount of OH− (the calculated amount of KOH was weighed to add to the viscoelastric gel, Figure S1, Supporting Information (SI)). This thereof constitutes a pHresponsive viscoelastic fluid11 by the combination of H+sensitive gelator AzoNa4 and a magnetic cationic surfactant CTAFe. To further confirm the existence of wormlike micelles, the rheological properties of the selected gel sample (60 mmol·L−1 CTAFe/15 mmol·L−1 AzoNa4/60 mmol·L−1 HCl) were measured in stress sweep mode and oscillatory shear (dynamic shear) mode. The stress sweep data (Figure 3a) revealed an elastic-dominant response with a linear viscoelastic region (yield stress 15.27 Pa), in which the storage modulus G′ and the loss modulus G″ are parallel. In Figure 3b, curves of the elastic modulus G′ and viscous modulus G″ agree well with Maxwell’s model,12 which is characteristic to describe the wormlike micelle solution with high viscoelasticity. To further confirm whether the dynamic plots fit the Maxwell mode, the Cole−Cole13 plots model was employed, which is a semicircular form. The Cole−Cole plots (Figure 3c) originated from Figure 3b fitted the semicircle well, which can act as a primary tool in ascertaining whether the dynamic plots fit the Maxwell mode. All the rheological data correspond well to the characteristics of wormlike micelles.14 All of the rheological data of samples exhibited above led us to postulate that the H+-

induced gel sample corresponds well to the characteristics of wormlike micelle solution. Cryo-TEM images give the direct visual confirmation of wormlike micelle structures.15 In Figure 4 (a and b), a typical wormlike micellar network showing

Figure 4. Cryo-TEM images for the sample of 60 mmol·L−1 CTAFe/ 15 mmol·L−1 AzoNa4/60 mmol·L−1 HCl.

overlap is observed, which accounts for the high viscoelasticity of the gel. The long, entangled wormlike micelles can be clearly observed, having 5 to 6 nm in diameter and several hundreds or even thousands of nanometers in length. 3.2. Supramolecular Chirality of Wormlike Micelles. Though the gelator AzoNa4 is achiral, its supramolecular structures could exhibit chiral sense via nonsymmetrical arrangements connected by intermolecular H-bonds.8−10 Gelation-induced chirality phenomena were observed in many previous works;10,16 herein we present more evidence from circular dichroism (CD) spectra (Figure S2, SI). For the gel phase, a positive and a negative Cotton Effect (CE) appeared at 364 and 340 nm, respectively. Because the CEs appeared at the corresponding absorption maxima of the gel in the UV−vis spectra,8−10 we suggest that the CD signals are derived from the chromophores (AzoH4) in the gel.8 It is very rare for an C

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3.3. Ferromagnetic Properties of Wormlike Micelle Gels. The solution of AzoNa4/CTAFe complexes (60 mmol· L−1 CTAFe/15 mmol·L−1 AzoNa4/0 mmol·L−1 HCl) was not stable and produced macroscopic phase separation in 1 day. The strong electrostatic screening interactions between AzoNa4 and CTAFe account for the formation of overcharged aggregates in the precipitates. The addition of acid (HCl) to the AzoNa4 and CTAFe complexes (60 mmol·L−1 CTAFe/15 mmol·L−1 AzoNa4/60 mmol·L−1 HCl) not only transforms the aggregates to wormlike micelles but also widens their stable period to over 30 days, followed by a gradual phase separation. As shown in Figure 6a, for the samples with a macroscopic phase separation, by vertically applying a weak external magnet (1 T), the micelle cluster could be manipulated and even overcome the gravity to migrate to the water interface, which definitely demonstrates the ferromagnetic property of the gel samples of wormlike micelles induced by paramagnetic counterions, [FeCl3Br]−. Referring to the magnetic property, most compounds do not have ferromagnetism; for example, AzoNa4 and AzoNa4 mixed with HCl, as shown in Figure S4 (SI), show strong diamagnetism17 by using the superconducting quantum interference device (SQUID) method. The CTAFe molecules possess typical paramagnetic behavior with a very small hysteresis loop as well as an effective magnetic moment of about 0.01756 emu·g−1 (Figure 6b), indicating weak ferromagnetism.18 Interestingly, the combination of AzoNa4 or AzoH4 and cationic CTAFe micelles resulted in the formation of ferromagnetic wormlike micelles with a typical “hysteresis loop” as shown in Figure 6c. The effective magnetic moment was measured to be 0.05538 emu·g−1. Accordingly, though the specific weight ratio of CTAFe decreases to 0.77 in the gel sample compared with the pure CTAFe, the saturation magnetism of the gel sample was improved 4.1-fold (acquired by 3.15/0.77). The binding with CTAFe micelles can turn the diamagnetic AzoNa4 or AzoH4 to ferromagnetic and be controlled by external magnetic force. The formation of wormlike micelles

observation in the isotropic gel phase to exhibit CD signals. To exclude the linear dichroism (LD) artifact derived from the linear dichroism (LD) in the partially aligned gel solution,8,10 the CD spectra of the xerogel film with freeze-drying were measured by rotating the angles (Figure 5) between light path

Figure 5. CD spectra of the gel sample (60 mmol·L−1 CTAFe/15 mmol·L−1 AzoNa4/60 mmol·L−1 HCl) depending on different rotating angles between light path and quartz slide.

and quartz slide. The obtained CD spectra shapes of the xerogels nearly stay the same and are independent from the rotating angles. Thus, the CD spectra of the gel are authentic. FT-IR measurements (Figure S3, SI) were performed to identify the intermolecular H-bond between hydrotrope AzoH4 molecules. The asymmetric stretching vibrations of CO at 1571.23 cm−1 shifted from 1718.62 cm−1 after the addition of HCl on account of the formation of intermolecular H-bond of AzoH4 molecules.8,10 Accordingly, combined with the CD results and the chiral inducting nature of the molecule AzoH4,8−10 we speculated that AzoH4 also keeps a helical arrangement within the wormlike micelles by intermolecular Hbonds like in our previous work,8 as shown in Figure 1b. In other words, because of the strong electrostatic screening interactions and hydrophobicity, +N(CH3)3 groups of CTAFe are distributed tightly around H-bonded AzoH4 molecules. On the basis of the above results, we concluded that wormlike micelles with chiral nature were formed.

Figure 6. (a) Photographs of the samples responding to a magnet (1 T). The magnet was smoothly moved up by hand, and more details are shown in a video in Supporting Information. Hysteresis plots for samples formed by pure CTAFe (b) and a gel sample of wormlike micelles (c). Details are presented in Figure S5 (SI). D

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Langmuir led to a fantastic ferromagnetism enhancement of about 4-fold. The magnetism change of the complexes implies the potential and possibility of magnetism regulation by forming colloidal aggregates. The question remains as to why the ferromagnetism can be improved. Considering the molecular packing theory, because of the electrostatic screening interactions of AzoH4 or AzoNa4 and the +N(CH3)3 group of CTAFe molecules, the complexes of CTAFe and AzoH4 or AzoNa4 can self-assemble more tightly to wormlike micelles with stronger long-range structural ordering and long-range interactions. In our previous work, we demonstrated that the paramagnetic azoTAFe micelles could magnetize diamagnetic DNA to ferromagnetic DNA by classical models to describe colloid aggregates.19 Herein, although the magnetic [FeCl3Br]− ions in the diffuse layer will be released by the charge competition of AzoNa4 or AzoH4, those [FeCl3Br]− ions in the Stern layer19 remain unchanged (Figure 1b), which could bind and magnetize the AzoNa4 or AzoH4 within the wormlike micelles. J. Eastoe et al. demonstrated that as counterions, [FeCl3Br]−, because of the hydrophobic interaction between it and the alkyl chains of cationic surfactants,5 is a relatively hydrophobic anion that can be partitioned into the micellar core.1 Besides, a certain coupling effect may exist between the anionic metallic centers,1 and thus the anionic metallic centers retain long-range ordering (Figure 1b) instead of being disorderly dispersed in solution. With the combination of AzoNa4 or AzoH4 to the Stern layer of the wormlike micelles, the magnetic [FeCl3Br]− ions in the core of CTAFe micelles also contribute to the magnetization of AzoNa4 or AzoH4. In conclusion, the ability of CTAFe in magnetizing AzoNa4 or AzoH4 can be ascribed to an interplay of the magnetic [FeCl3Br]− ions both in the Stern layer and in the cores of the wormlike micelles. For the first time, colloidal wormlike micelles having chirality provide a fantastic platform to arrange molecular magnets and regulate magnetic properties such as ferromagnetism.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel: +86-531-88366074. Fax: +86531-88564750. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was funded by the National Natural Science Foundation of China (grant nos. 21420102006 and 21273134).

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REFERENCES

(1) Brown, P.; Bushmelev, A.; Butts, C. P.; Eloi, J. C.; Grillo, I.; Baker, P. J.; Schmidt, A. M.; Eastoe, J. Properties of new magnetic surfactants. Langmuir 2013, 29, 3246−3251. (2) Brown, P.; Khan, A. M.; Armstrong, J. P. K.; Perriman, A. W.; Butts, C. P.; Eastoe, J. Magnetizing DNA and proteins using responsive surfactants. Adv. Mater. 2012, 24, 6244−6247. (3) Xu, L.; Feng, L.; Dong, S.; Hao, J. Magnetic controlling of migration of DNA and proteins using one-step modified gold nanoparticles. Chem. Commun. 2015, 51, 9257−9260. (4) Clark, N. A. Ferromagnetic ferrofluids. Nature 2013, 504, 229− 230. (5) Brown, P.; Bushmelev, A.; Butts, C. P.; Cheng, J.; Eastoe, J.; Grillo, I.; Heenan, R. K.; Schmidt, A. M. Magnetic control over liquid surface properties with responsive surfactants. Angew. Chem. 2012, 124, 2464−2466. (6) Del Sesto, R. E.; McCleskey, T. M.; Burrell, A. K.; Baker, G. A.; Thompson, J. D.; Scott, B. L.; Wilkes, J. S.; Williams, P. Structure and magnetic behavior of transition metal based ionic liquids. Chem. Commun. 2008, 447−449. (7) Blundell, S. J.; Pratt, F. L. Organic and molecular magnets. J. Phys.: Condens. Matter 2004, 16, 771−828. (8) Zhao, W.; Wang, D.; Lu, H.; Wang, Y.; Sun, X.; Dong, S.; Hao, J. Self-assembled switching gels with multiresponsivity and chirality. Langmuir 2015, 31, 2288−2296. (9) Zhao, W.; Feng, L.; Xu, L.; Xu, W.; Sun, X.; Hao, J. Chiroptical vesicles and disks that originated from achiral molecules. Langmuir 2015, 31, 5748−5757. (10) Trickett, K.; Eastoe, J. Surfactant-based gels. Adv. Colloid Interface Sci. 2008, 144, 66−74. (11) Chu, Z.; Feng, Y. pH-switchable wormlike micelles. Chem. Commun. 2010, 46, 9028−9030. (12) Chu, Z.; Dreiss, C. A.; Feng, Y. Smart wormlike micelles. Chem. Soc. Rev. 2013, 42, 7174−7203. (13) Acharya, D. P.; Kunieda, H. Wormlike micelles in mixed surfactant solutions. Adv. Colloid Interface Sci. 2006, 123−126, 401− 413. (14) Dreiss, C. A. Wormlike micelles: where do we stand? Recent developments, linear rheology and scattering techniques. Soft Matter 2007, 3, 956−970. (15) Feng, Y.; Chu, Z.; Dreiss, C. A. Smart wormlike micelles: design, characteristics and applications. SpringerBriefs in Molecular Science; Springer: New York, 2015; pp 1−103 10.1007/978-3-662-45950-8_1 (16) Duan, P.; Cao, H.; Zhang, L.; Liu, M. Gelation induced supramolecular chirality: chirality transfer, amplification and application. Soft Matter 2014, 10, 5428−5448. (17) Zaghib, K.; Ravet, N.; Gauthier, M.; Gendron, F.; Mauger, A.; Goodenough, J. B.; Julien, C. M. Optimized electrochemical performance of LiFePO4 at 60 °C with purity controlled by SQUID magnetometry. J. Power Sources 2006, 163, 560−566.

4. CONCLUSIONS In summary, a new paradigm for manipulating the magnetic property via constructing colloidal wormlike micelles was reported, by employing paramagnetic mag-IL CTAFe and diamagnetic AzoH4. Formation of wormlike micelles elevates the ferromagnetism of Mag-IL complexes about 4-fold. Our results suggest a strategy that can be applied in attempts to optimize and regulate the magnetic properties of mag-ILs via forming colloidal aggregates. Besides manipulation of the aggregation type, our results also provide new evidence for better understanding the essence and origin of magnetism generation and the mechanism of magnetic property variation. These magnetic wormlike micelles could enable efficient magnetic control over the migration property for targeted drug delivery and effective photocontrolled drug release for cancer therapy.

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and hysteresis plots for pure AzoNa4 combined with HCl and for gel samples (PDF) Movie of magnetic chiral gel (AVI)

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.langmuir.5b03148. Steady shear measurements and photos for the gel upon introducing OH−, CD spectra of the samples, FT-IR spectra of stock solution before and after adding acid, E

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Langmuir (18) Ohno, Y.; Young, D. K.; Beschoten, B.; Matsukura, F.; Ohno, H.; Awschalom, D. D. Electrical spin injection in a ferromagnetic semiconductor heterostructure. Nature 1999, 402, 790−792. (19) Xu, L.; Feng, L.; Hao, J.; Dong, S. Controlling the capture and release of DNA with a dual-responsive cationic surfactant. ACS Appl. Mater. Interfaces 2015, 7, 8876−8885.

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