Rational Design and Synthesis of Carboxylate Gemini Surfactants with

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Rational Design and Synthesis of Carboxylate Gemini Surfactants with Excellent Aggregate Behaviour for Nano-La2O3 Morphology-controllable Preparation Xueming Liao, Zhinong Gao, Yan Xia, Fei Niu, and Wenzhong Zhai Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b00096 • Publication Date (Web): 02 Mar 2017 Downloaded from http://pubs.acs.org on March 11, 2017

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Rational Design and Synthesis of Carboxylate Gemini

Surfactants

with

Excellent

Aggregate

Behavior for Nano-La2O3 Morphology-controllable Preparation Xueming Liao,† ‡ Zhinong Gao,*†‡ Yan Xia,† ‡ Fei Niu, † ‡ Wenzhong Zhai† ‡ †College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, Hubei, PR China ‡Key Laboratory of Biomedical Polymers, Ministry of Education, Wuhan 430072, Hubei, PR China KEYWORDS: Carboxylate Gemini Surfactants, Diphenyl Ketone Spacer Group Aggregate Behavior, Nano-La2O3, Morphology ABSTRACT: A series of carboxylate gemini surfactants (CGS, Cn-Φ-Cn, n=12, 14, 16, 18) with diphenyl ketone as spacer group were prepared by a simple and feasible synthetic method. These CGS exhibited excellent surface activity with extremely low critical micelle concentration (CMC) value (about 10-5 mol/L), good performance in reducing surface tension (nearly 30 mN/m), and the ability of molecular self-assembly into different aggregate morphologies via adjusting the concentrations, which is attributed to the introduction of diphenyl ketone and carboxylic acid ammonium salt in the molecular structure. Moreover, the surface activity and self-assembly ability of CGS were further optimized by tuning the length of tail chain. These excellent properties imply

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that CGS can be a soft template to prepare nanomaterials, especially in morphology-controllable synthesis. Through adjusting the concentration of one of CGS (C12-Φ-C12), nano-La2O3 particles with diverse morphologies were obtained, including spherical shape, bead-chain shape, rod shape, velvet-antler shape, cedar shape and bowknot shape. This work offers a vital insight into the rational design of template agents for the development of morphology-controllable nanomaterials. 1. INTRODUCTION Gemini surfactants1,2 are known as a classic of the latest "industrial monosodium glutamate", and have aroused great interest due to a promising application in fields of new materials,3-5 biotechnology,6,7 medicine,8,9 oil and gas exploitation.10,11 Gemini surfactants are amphiphilic compounds, containing two hydrophilic head groups, two hydrophobic tail chains and a spacer group. As reported, both CMC value and exchange rate (between surfactants in the bulk and in the micelles) depend critically on the size of hydrophobic tail chain.12 Soon afterwards, Zana13-15 and other researchers 16-24 have studied the effect of the spacer group on the CMC and the aggregate morphology. Our laboratory25-27 focuses on the property of gemini surfactants that is affected by the head group type, the tail chains length and the spacer groups ranging from flexible to rigid chains. However, in the past decades, relevant research focused mainly on the cationic gemini surfactants,28-32 and little attention was paid to the study on anionic gemini surfactants, especially CGS, which resulted mainly from complex synthesis process, fussy purification, and low production.33-36 To date, the reported CGS generally contain carboxylic acid sodium or carboxylic acid potassium as hydrophilic head groups. However, these CGS show poor properties in hard water resistance, aggregate behavior, etc.37-41 Therefore, developing of novel CGS with good performance, and understanding the relationship between the molecular structures and their properties, are a great challenge.


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Over the past decades, nano-rare earth oxide compounds had raised wide attention because of their unique photoelectric and catalytic properties 42-46. Nano-La2O3 is one of the most important rare earth oxides and widely used as battery materials,47,48 hydrogen storage materials,49 catalytic materials50 and optical materials51 in industry. As is well known, different morphologies of nanomaterials have different performance and application. Taking catalytic materials as an example, micromorphology greatly affects their specific surface area, and thereby the catalytic efficiency.52-54 Currently, template synthesis is found to be a feasible way to prepare nanomaterials,55,56 but there are still some issues to solve, such as morphology inhomogeneity, poor controllability, low yield or higher cost.57-59 Herein, we report an effective strategy for developing morphology-controllable nano-La2O3 particles through rational design of CGS as template agents. In these structures, we intentionally introduced carboxylic acid ammonium salts as hydrophilic head groups and diphenylketone as spacer group, to create proper conditions for the formation of hydrogen bonds between molecules. The presence of intermolecular hydrogen bonds is beneficial for molecules to aggregate closely and form small micelles. Meanwhile, considering that the tail chain length has great influences on the aggregate properties of the corresponding surfactants, tail chains with different length (-C12H25, -C14H29, -C16H33 and -C18H37) were adopted to further optimize the aggregate behaviors of CGS. After carefully designing CGS, C12-Φ-C12 exhibited excellent surface activity and selfassembly ability, implying that it could be an ideal template agent to prepare nanomaterials. As a result, nano-La2O3 particles using C12-Φ-C12 as template were successfully prepared. Moreover, through adjusting C12-Φ-C12 concentration, diverse morphologies of nano-La2O3 particles were obtained, including spherical shape, rod-shape, bead chain shape and velvet antler shape. The


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results offer an insight into rationally designing template agents for the development of morphology-controllable nanomaterials. 2. EXPERIMENTAL SECTION 2.1 Materials 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA, CP) was purchased from Beijing Tianyi Xionghui Tech. Co. Ltd. Octanol (CP), decyl alcohol (CP), lauryl alcohol (CP), tetradecyl alcohol(CP), palmitoyl alcohol (CP), octadecyl alcohol (CP), N,N-dimethylacetamide (AR), ptoluenesulfonic acid (AR), trimethylamine (TEA, AR), absolute ethyl alcohol (AR), lanthanum chloride (AR) and dichloromethane (AR) were purchased from Sinopharm Chemical Reagent Co. Ltd. Water was redistilled in all experiments (conductivity was less than 1.3 μS·cm–1 at 298 K). The chemicals listed above were of analytical grade and used without further purification. 2.2 Synthesis and Characterization of CGS The CGS, 3,3'-dicarboxylic acid ammonium salt-4,4'-dialkyl esters-diphenyl ketone (referred to as Cn-Φ-Cn, n= 12, 14, 16, 18), were synthesized in our laboratory. As a representative sample, Scheme 1 describes the synthesis route of CGS. Synthesis of the target gemini surfactants was detailed below: BTDA (16.1 g) was reacted with lauryl alcohol (18.6 g) in the solution of N,N-dimethylacetamide (DMAc, 81 g) at room temperature for 4 h to form 3,3’-dicarboxylic acid-4,4’-dialkyl esters-diphenyl ketone (DADEK). Then, p-toluenesulfonic acid (0.17 g) was added into the reaction solution and this mixture was stirred at 140 °C for 4 h, followed by the addition of xylene to separate azeotropic water. After keeping stirred at 160 °C for 4 h, the mixture was poured into deionized water. The precipitation


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was filtered off, washed with deionized water for three times. The raw product was subsequently dissolved into anhydrous ethanol, and finally purified by recrystallization with deionized water to obtain DADEK as white solid (yield: 95.8%). The obtained product was further reacted with triethylamine to form the target gemini surfactants C12-Φ-C12, the pH of gemini surfactants aqueous solution is between 7 to 8. Other gemini surfactants (C14-Φ-C14, C16-Φ-C16 and C18-ΦC18) were synthesized through the same route and method. The corresponding spectral data, including FTIR, 1H NMR, ESI-MS are provided in shown in Figure S1, Figure S2 and Figure S3 in the Supporting Information (SI), respectively. 2.3 Preparation of Nano-La2O3 Using gemini surfactants as soft template, nano-La2O3 was prepared with hydrothermal method. 15 mL of lanthanum chloride aqueous solution (1 wt.%) and 20 mL C12-Φ-C12 aqueous solution (0.05 mmol/L, 0.1 mmol/L, 0.5 mmol/L, 1 mmol/L, 5 mmol/L and 10 mmol/L respectively) were added into polytetrafluoroethylene (PTFE) tank with ultrasonic dispersion. Then, the solution of NaOH (0.01 mol/L) was dropped into the solution to adjust the pH value in between 9 to 11 to form La(OH)3 colloid, and followed by the addition of hexamethylenetetramine (0.2 g) into the system with ultrasound for 1 h. Next, the tank was put into hydrothermal synthesis reactor and reacted at 100 °C for 2 h, 160 °C 4 h and 200 °C at least 4 h in the oven, respectively. After cooling down to the room temperature, the nano-La2O3 particles were collected by centrifugation and washing with deionized water. The synthetic route is shown in Scheme 2. The structure and the morphologies for nano-La2O3 were characterized by XRD, SEM and TEM, respectively. 2.4 Measurements


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2.4.1 Surface Tension Measurement. The surface tension was measured with a Fangrui tensiometer (type QBZY-2) through plate method. The plate and glassware used in the measurements were scrupulously clean. To verify cleanness of the plate and glassware, the surface tension of bidistilled water was measured regularly. Measurements were made in beakers thermostatted by means of a constant-temperature bath (Fangrui DC0506). Surface tensions from aged samples were obtained by allowing solutions to stand in covered beakers for 12 h at room temperature. Care was taken not to agitate the samples as they were uncovered and placed in the tensiometer. 2.4.2 Electrical Conductivity Measurement. The WTW conductivity meter (model inoLab Cond 730) was used to conduct the experiments. A cell with 30 mL bidistilled water was dipped in thermostatic water bath. A dip-type conductivity cell with a cell constant of 1.47 cm–1 was inserted into the water. A known volume of a concentrated solution of CGS (200 μL) was then added into the water with a microliter syringe (accuracy of 10 μL) and was fully mixed, followed by the measurement of the conductance. In the course of conductivity testing, the temperature of the aqueous solution was maintained at 298.15±0.1 K of the desired temperature. 2.4.3 Resistance to Hard Water Measurement. Sample preparation and testing are in accordance with QB/T 2485-2485 (liquid soap 0.20%, 50.0 mL, 40±2 °C/mL). 50 mL CaCl2 aqueous solution was prepared (75 mmol/L), then 0.2% gemini surfactants solution (50 mL, 40 ±2 °C) was titrated by CaCl2 aqueous solution, which was added 0.2 mL each time, until floccules or precipitate was generated. The volume (mL) of CaCl2 consumption is the hard water resistance degree of gemini surfactants.


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2.4.4 Dynamic Light Scattering (DLS). DLS measurements were performed with Malvern Instruments Zetasizer Nano (ZEN 3600). Light of λ = 632.8 nm from a solid-state He-Ne laser was applied as the incident beam. The measurement was conducted at a scattering angle of 173°. The measured autocorrelation function was analyzed with the CONTIN method. The effective hydrodynamic radius (Rh) is calculated according to the Einstein–Stokers equation Rh = kBT/(6πηD), where D is the diffusion coefficient, kB is the Boltzmann constant, T is the absolute temperature, and η is the solvent viscosity. The diffusion coefficient was measured three times for each sample, and all measurements were performed at 298.15 ±0.1 K. 2.4.5 Tyndall Effect. Solution concentrations of CGS are 25 times and 50 times to the CMC, which were prepared respectively. Meanwhile, deionized water sample was taken as a reference. Irradiation with a laser beam was employed to observe the Tyndall phenomenon. 2.4.6 Scanning Electron Microscopy (SEM). Micelle/aggregate morphologies of CGS were observed by SEM (QUANTA 200, Holland). Samples preparation process is as follows: different concentrations of samples were put in a vacuum before spray gold processing was taken place. Then micelle/aggregate morphologies were observed, and the accelerating voltage was 30 KV. 2.4.7 Transmission Electron Microscopy (TEM). Micrographs were obtained with a JEOL JEM2100 (HR) transmission electron microscope at a working voltage of 200 kV. The TEM samples were prepared through the negative-staining method. Phosphotungstic acid solution (2 wt.%) was employed as the staining agent. A carbon formvar-coated copper grid (200 mesh) was placed on one drop of the sample solution for 5 min, and the excess CGS solution was wiped away with filter paper to form a thin liquid film on the copper grid. Afterwards, the copper grid was placed onto


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one drop of phosphotungstic acid solution. The excess liquid was also wiped away with filter paper, and then the samples were dried in air. 2.4.8 Powder X-ray diffraction (XRD). XRD pattern was observed on a PANalytical X'pert Pro X-ray diffractometer at a voltage of 40 kV, and a current of 40 mA and at a scanning rate of 10°min-1 in the 2θ range from 10°to 80°with Cu-Kα radiation (λ = 0.15405 nm). 2.5 RESULTS and DISCUSSION 2.5.1 Synthesis and surface active properties of CGS We designed a series of novel CGS (Cn-Φ-Cn, n=12, 14, 16, 18) with diphenyl ketone as spacer group and carboxylic acid ammonium salt as hydrophilic head group. CGS were prepared through two steps (Scheme 1): the intermediates of DADEK were obtained by ring-opening esterification reaction of BTDA and long chain alkyl alcohol, and followed by neutralization reaction with DADEK and TEA to attain target products. Both reactions occurred naturally and the yields of CGS were over 95 %, indicating that this synthesis method is effective. Chemical structure and purification of CGS were confirmed by FTIR, 1H NMR and ESI-MS, provided in Figure S1, Figure S2 and Figure S3 in the SI.

Scheme 1. Synthetic route of CGS. To study the surface-active properties, certain amount of CGS (Cn-Φ-Cn, n=12, 14, 16, 18) were dissolved in deionized water respectively, then colloid solutions were obtained. Taking C12-Φ-C12 as an example, when the concentration of C12-Φ-C12 increased to 0.02 mmol/L (pH=7.5), the solution turned bluish, suggesting that the molecular aggregation had happened. Tyndall


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phenomenon appeared obviously in the first (0.02 mmol/L) and the second sample (0.05 mmol /L) in a left-to-right order, but there was no Tyndall effect in the third sample which was filled with deionized water (Figure S4a in the SI). This phenomenon indicates that the aggregate behavior of the CGS happens at very low concentration. Meanwhile, DLS was employed to study the colloid particle size distribution of C12-Φ-C12 at the concentration of 0.02 mmol /L. Figure S4b (in the SI) shows the narrow size distributions (10 - 100 nm) in the DLS plots. Colloid particle size mainly distributes from 20 to 40 nm, and most particle size distribution is around 30 nm. This phenomenon suggests that this kind of CGS tends to form small micelles at low concentration. To study the relationship between surface tension and CGS concentration, the surface tension was measured with a Fangrui Tensiometer through plate method at 25°C (shown in Figure 1). The value of surface tension is found to decrease dramatically at first and then come to a balance state with the increase of concentration. The reason for the decrease of surface tension at first may be that the molecules of CGS could arrange orderly on the interface of water and gas when the concentration is low. With the increase of the concentration, the molecules arrange closely on the interface and the surface tensions fall sharply. When the concentration increases to a certain extent, molecular arrangement tends to be saturated on the interface, and the surface tension goes down to the minimum, and the corresponding concentration is CMC. Afterwards, even if the concentration further increases, molecules can form micelles or large aggregation in aqueous solution, and the surface tension tends to balance.


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Figure 1. The relationship between surface tension and concentration of CGS.

As can be seen from Table S1 in the SI, the CMC values of CGS are from 10-5 mol/L to 10-4 mol/L, the surface tension of CGS is no more than 34.6 mN /m, and the CMC of C12-Φ-C12 is as low as 2.2x10-5 mol/L. Data show that these novel CGS display good surface properties, which excel the corresponding single chain surfactant (sodium dodecanoate)60. The surface tension of sodium dodecanoate is as high as 37.2 mN /m, and the CMC value is up to 2.5x10-2 mol /L. Moreover, the CMC value of a reported61 anionic gemini surfactants is 8.9x10-4 mol/L, which is the further evidence to demonstrate that CGS have far more excellent surface performance than anionic surfactants reported before. Additionally, CMC value was found to increase sharply as the tail chain grew, implying that the CMC value is affected by the length of tail chain. The explanation may be that the extension of hydrophobic tail chains can increase hydrophobicity of gemini surfactants, and thereby enhance


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diffusion of gemini surfactants molecules on the interface between water and gas. Comparing the four types of CGS, longer tail chain increases the space steric hindrance, which could greatly influence the close arrangement of molecules, and therefore, its ability to aggregate into micelle is reduced. Under CMC condition, we also found that surface tensions of all CGS are around 30 mN /m, showing that although the influence of tail chain length on the surface tension is not obvious, CGS perform excellent in reducing the surface tension. Additional experiments of C10-Φ-C10 show that the CMC value is 5.9 x10-5 mol/L and the surface tension is 30.6 mN /m respectively. All data above prove that the tail chain length of –C12H25 is appropriate, which has the lowest CMC value and with the strongest ability to form micelles.

Figure 2. The relationship between electrical conductivity and the concentrations of CGS.


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The electrical conductivities were determined under 25 °C, and the relationship between conductivity and concentration is shown in Figure 2. The conductive capability of CGS solution is connected with the concentration of CGS solution, and apparent inflection point of conductivity appeared when the concentration increased to a certain degree. The corresponding concentration was CMC, and the lowest CMC was 7.4 x10-5 mol /L. Then, the conductivity continued to rise with the increase of concentration, but slowly. These changes imply that ion-pair of carboxylic acid ammonium salt increase gradually with the increase of CGS concentration, resulting in the improvement of conductivity. This suggests that the electrical conductivity is greatly affected by hydrophilic head groups. Further research of CGS find that the resistance degree to hard water is from 2.5 to 3.4, more strikingly, the C12-Φ-C12 is up to 3.4. As can be seen from Table S2 in the SI, the single carboxylic acid sodium is poor in hard water resistance. Though the sodium laurate is the highest one, the resistance degree to hard water only reaches 2.0, and the others are even lower. The industrial standard on the resistance degree to hard water is 3 in China (QB/T 24872008). It means that the performance of CGS with carboxylic acid ammonium salt as head groups are more advantageous than with carboxylic acid sodium. So it is confirmed that the resistance to hard water is greatly influenced by the hydrophilic head group. Interestingly, Table S3 (in the SI) shows that the CMC value is different from the surface tension measurement. The obvious decrease of CMC with the extension of tail chains is originated from the increased hydrophobicity of gemini surfactants, and thereby the CGS comprising longer hydrophobic parts gather easily and the solubility reduce dramatically. More interestingly, the CMC values between C16-Φ-C16 and C18-Φ-C18 are very close, indicating that the influence of tail chain length on the CMC has reached the maximum value, and the CMC would stay stable despite the further increase of the tail chain length. Test measurements probably cause the difference of CMC values between surface tension


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and electrical conductivity, but it is by no means an order of magnitude. Therefore, the surfaceactive properties indicate that C12-Φ-C12 has the most excellent surface-active properties among all four kinds of CGS. 2.5.2 Aggregate behaviour of CGS In order to study the aggregate behaviours of CGS in deionized water, the samples were prepared at the same concentration and stored at 25 °C for 4 hrs by negative staining (using 2 wt.% phosphotungstic acid sodium). The aggregate behaviours of CGS were investigated through the aggregation morphologies (characterized by SEM and TEM). When the concentration of CGS were increased to more than 0.02 mmol /L, spherical micelles could be distinguished clearly, which corresponds to the narrow distributions in the DLS plots and Tyndall effect. As is shown in Figure 3(i), the sizes of spherical micelles are less than 100 nm. According to the theory of the same charges repelling each other, the ionic head groups increase the distance between the molecules when they gathered into micelles in solution. However, in our study, we chose trimethylamine as the neutralizer to react with carboxyl, resulting in the formation of carboxylic acid ammonium salt. Unlike carboxylic acid sodium salt, a weak ionization carboxylic acid ammonium salt enables the head groups to carry small amounts of charges and hereby reduces the intermolecular repulsion, facilitating close arrangement for the gemini surfactants. Moreover, the existence of the diphenyl ketone spacer group fails to rotate and stretch, which limits the distance increase between the two head groups and the two tail chains intramolecular. That is to say, within the gemini surfactants, intramolecular charge repulsion extends the distance in head groups or tail chains, while the rigid spacer group restrains it, which helps them aggregate tightly. Furthermore, the carbonyls in diphenyl ketone and ester groups can form hydrogen bonds with hydrogen atoms on the coordination bond in head groups, the structure diagram of hydrogen bonds is presented in Figure


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3(ii). This kind of hydrogen bonding interaction between molecules can facilitate molecular aggregation. The synergistic effect enables the molecules to pack tightly and easier to form micelles.

Figure 3. (1) The TEM images about the aggregation morphologies of CGS at CMC (a, b, c and d are represented C12-Φ-C12, C14-Φ-C14, C16-Φ-C16 and C18-Φ-C18, respectively); (2) The hydrogen bond structure diagram of CGS. Further research was carried out to adjust aggregate morphologies through changing the concentration of C12-Φ-C12. When the colloidal concentration of C12-Φ-C12 reached 0.05 mmol/L, 0.1 mmol/L, 0.5 mmol/L, 1 mmol/L, 5 mmol/L and 10 mmol/L, spherical shape, bead-chain, rod


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like, velvet-antler shape, cedar shape and bowknot shape were formed respectively. SEM and TEM images show that the micelles are gradually self-assembled into various aggregations with the change of colloidal concentration (Figure 4 (i) and (ii)). For example, the micelles self-assemble into spherical aggregation when the colloidal concentration is 0.02 mmol/L, and the vesicles form at the concentration of 0.5 mmol/L. The results imply that CGS aggregate into micelles with the increase of concentration, then self-assemble into different aggregate morphologies under higher concentration. The diphenyl ketone as rigid spacer group favours to form hydrogen bond with head groups, facilitating molecular aggregation and self-assembly. The rigid spacer group with hydrogen bond together as skeleton provides the necessary conditions for the stability of the various aggregate morphologies. The good aggregate behaviour of CGS suggests that this kind of CGS can be used as template agent in morphology controllable synthesis of nanomaterials. 2.5.3 Morphology-controllable preparation of nano-La2O3 CGS perform excellent in surface-active properties and aggregate behaviour, and C12-Φ-C12 comes out as particularly prominent. Its ability of self-assembly into different aggregate morphologies, by means of concentration adjustment, inspires us to choose it as the soft template in morphology-controllable synthesis of nanomaterials. A series of La2O3 nanomaterials were prepared using different concentration solution of C12-Φ-C12 as template and were shown in Figure S6(i) in the SI. The SEM and TEM images show that the particles with diverse morphologies are obtained, including spherical shape, rod-shape, bead chain shape, velvet antler shape, cedar shape and bowknot shape, indicating that C12-Φ-C12 is a promising template agent for developing morphology-controllable nanomaterials. Remarkably, the morphologies of bead chain shape, velvet antler shape, cedar shape and bowknot shape were rarely reported before. As can be seen from Figure 4(iii), The morphology of nano-La2O3 is highly consistent with the aggregate


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morphology of C12-Φ-C12 (Figure 4(ii)). It means that molecules can form into micelles through concentration increase, and the molecular arrangement changes with the further increase of concentration, and then self-assembles into different aggregate morphologies. This should result from the directional arrangement of the molecules in aggregation. Therefore, the template-induced growth can be used to prepare nano-La2O3 particles, and finally we got several different morphologies of the nano-La2O3. Additionally, nano-La2O3 was confirmed by XRD measurement, (shown in Figure S6(ii) and summarized in Table S4). It can be observed that the diffraction peaks at 2θ = 6.08°, 29.12°, 29.92°, 39.48°, 46.01°, 52.16°, 55.42° and 55.90°are identical with diffraction data of the JCPDS standard card (card No. 5-602), and the particles belong to hexagonal system.41

Scheme 2. Preparation route of nano-La2O3.


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Figure 4. The relationship among CGS C12-Φ-C12, aggregation of colloid and the morphologies of nano-La2O3. (Among them, spherical shape of nano-La2O3 is SEM image, the other shapes of nano-La2O3 and aggregate morphologies of C12-Φ-C12 are TEM images) 3. CONCLUSION In summary, a kind of novel and promising CGS containing the carboxylic acid ammonium salt and the diphenyl ketone were successfully synthetized and characterized. The introduction of the carboxylic acid ammonium salt as hydrophilic head groups and the diphenyl ketone as spacer group in the molecular structures of CGS, could create proper conditions for the formation of hydrogen bonds between molecules, leading to low CMC value, good performance in reducing surface tension, and the ability of molecular self-assembly into different aggregate morphologies. Additionally, the existence of tight ion pair on the head groups is favorable for improving its


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resistance to hard water, and the resistance degree to hard water is up to 3.4, which is over the industry standard 3.0. Moreover, the surface activity and self-assembly ability of CGS were further enhanced by molecular modification of tail chain. These excellent properties for CGS, especially for C12-Φ-C12 imply that it can be an ideal template agent to synthesize nanomaterials with different morphologies. The expected results showed that a diversity of nano-La2O3 morphologies, including spherical shape, rod shape, bead chain shape and velvet antler shape, could be achieved. The work represents a breakthrough in the development of nanomaterials through rational design of template agents and demonstrates the effect of molecular structures on their properties of template agents and thereby nanomaterials. We believe that this synthetic strategy has guiding significance for developing morphology-controllable nanomaterials. AUTHOR INFORMATION Corresponding Author: Zhinong Gao * E-mail: [email protected]

Tel: (+86) 027-68754067

Present Addresses: College of Chemistry and Molecular Science, Wuhan University, Wuhan 430072, Hubei, PR China Funding Sources: Fundamental Research Funds for the Chinese Central Universities. (2012203020211). ACKNOWLEDGMENT This work was supported by the Fundamental Research Funds for the Chinese Central Universities. (2012203020211). The author is grateful to Doctor Zhengran Yi at Huazhong University of Science and Technology (PRC), and Professor Li Zhou at Hubei University of Chinese Medicine (PRC) for their contribution to this work.


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ABBREVIATIONS 1）CGS: carboxylate gemini surfactants； 2）CMC: critical micelle concentration; 3）BTDA: 3,3',4,4'-benzophenonetetracarboxylic dianhydride; 4）DADEK :3,3’-dicarboxylic acid-4,4’-dialkyl esters-diphenyl ketone; 5）Cn-ϕ-Cn: 3,3'-dicarboxylic acid ammonium salt-4,4'-dialkyl esters-diphenyl ketone (n=12,14,16,18) 6）SI: Supporting Information. REFERENCES 1 Menger, F. M.; Littau, C. A. Gemini Surfactants: Synthesis and Properties. J. Am. Chem. Soc.1991,113,1451-1452. 2 Menger, F. M.; Keiper, J. S. Gemini Surfactants. Angew. Chem. Int. Edit., 2000, 39, 19071920. 3 Meier, W. Nanostructure Synthesis Using Surfactants and Copolymers. Curr. Opin. Colloid. In., 1999, 4, 6-14. 4 Fluegel, E. A.; Aronson M. T.; Junggeburth, S. C.; Chmelka B. F.; Lotsch, B. V. SurfactantDirected Syntheses of Mesostructured Zinc Imidazolates: Formation Mechanism and Structural Insights. Crystengcomm., 2015, 17, 463-470. 5 Huo, Q. S.; Leon, R.; Petroef, P. M. Mesostructure Design with Gemini SurfactantsSupercage Formation in a 3-Dimensional Hexagonal Array. Science., 1995, 268, 13241327. 6 Kirby, A. J.; Camilleri, P.; Engberts, J.B.F.N. Gemini Surfactants: New Synthetic Vectors for Gene Transfection. Angew Chem Int Edit., 2003, 42, 1448-1457.


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Table of content (TOC)

Well-designed carboxylate gemini surfactants can self-assemble into different aggregate morphologies via adjusting the concentration, which enables it to be used to prepare nanoLa2O3 particles with diverse morphologies.


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Rational Design and Synthesis of Carboxylate Gemini Surfactants with

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