Materials Chemistry and Physics 99 (2006) 61–65 Bis-(4-stearoylaminophenyl)methane asse tio Xi and T ience ber 20 Abstract Gelator, b ize s so on. TEM wer which in tur g fo hydrogen bo eract as templates ke ag SiO2 nanow that s 200–500 nm © 2005 Else Keywords: Si 1. Introduction In the recent years, much attention has been paid to the aggregation and water. of gelators interaction phobic effe water have Nanowi Also, many nanowires chemical an nanowires chemical v past decade ing carbon templates i a variety o by using te ∗ Correspon E-mail ad at Mobil demonstrated mesoporous silicate and alminosilicate materials (M41S) [7]. Comparing with conventional methods for preparation of nano-materials, such as carbon nanotubes, 0254-0584/$ doi:10.1016/j and self-assembly of gelators in organic solvents The gelation of media through the self-assembly into supramolecular systems is formed by physical s, including hydrogen bonding, �–� stacking, solvo- cts and so on. Many types of organic liquids and been gelatinized by different gelators [1,2]. re is an important member of nano-materials family. studies have been concerned with preparation of in the recent years because of its fantastic physical, d mechanical properties. The preparation methods of usually include arc discharge, laser ablation, catalytic apor deposition (CVD) growth and so on [3]. In the , template synthesis was attracted attention in prepar- nanotubes and nanowires [4]. One of the attractive s anodic aluminum oxide (AAO) [5,6]. In addition, f non-carbon nano-materials have been synthesized mplates of surfactant aggregates since researchers ding author. Tel.: +86 27 87547141; fax: +86 27 87543632. dress:
[email protected] (Y. Yang). which is usually synthesized by high temperature techniques, the conditions of template synthesis are mild and the efficiency is higher. Recently, the synthesis and modification of SiO2 nanowires becomes an active area of nano-materials because of host–guest interaction inside nano-structure. This kind of novel porous materials exhibits potential wide-ranging applications in catal- ysis, adsorption and nanotechnology. The synthesis of SiO2 nanowires is rather easy comparing the synthesis of carbon nanotubes. Briefly, TEOS, a precursor compound, was adsorbed onto the surface of the templates and then preceded sol/gel polymerization at room temperature. Sil- ica nanowires can be obtained after calcinations for the removal of templates. Most of inorganic oxide nano-materials can be effi- ciently prepared by using two types of templates that is surfactant and gelator aggregates. Typical example is M41S mentioned above and huge length silica nanotubes were synthesized by using surfactant aggregates [7,8]. Another typical example is sil- ica nanotubes synthesized by using sugar-appended azonaphthol gelator assemblies [9]. Interestingly, most of silica nanotubes reported recently were twisted and entangling [10], even some – see front matter © 2005 Elsevier B.V. All rights reserved. .matchemphys.2005.09.081 and used as templates for prepara Chang Xueling b, Li Wang a, Yajiang Yang a,∗, a Department of Chemistry, Huazhong University of Science b School of Life Science and Technology, Huazhong University of Sc Received 29 March 2005; received in revised form 7 Septem is-(4-stearoylaminophenyl)methane (BSAPM), can be used to gelatin images of n-butanol gel indicate that BSAPM can self-assembled at lo n form an extended three-dimensional network structure. The drivin nding, �–� stack interaction and other non-covalent intermolecular int , tetraethoxysilane (TEOS) can be adsorbed onto the surfaces of fiber-li ires were formed after calcinations. SEM and AFM images indicate and lengths of 2–18�m. vier B.V. All rights reserved. O2 nanowires; Gelator; Sol/gel polymerization mbles in organic solvents n of SiO2 nanowires angliang Yang b, Huibi Xu a echnology, Wuhan 430074, China and Technology, Wuhan 430074, China 05; accepted 29 September 2005 ome organic solvents, such as benzene and n-butanol and concentration (less than 3 wt.%) into fiber-like aggregates, rce for BSAPM assembling in organic solvent is mainly ion. Using the fiber-like aggregates assembled by BSAPM gregates and then polymerized by sol–gel polymerization. ilica consisted of nanowires structures with diameters of 62 C. Xueling et al. / Materials Chemistry and Physics 99 (2006) 61–65 of them was helical [11,12] and left- and right-handed structure [13]. In the present work, we described the gelation of n- butanol and other solvents by gelator bis-(4-stearoylaminoph- enyl)methane (BSAPM), which exhibits versatile gelation prop- erties at room temperature. The formation of straight silica nanowires by using BSAPM assemblies as templates was also discussed. The morphology and size of BSAPM assemblies and silica nanowires were characterized by TEM, SEM and AFM. 2. Experimental 2.1. Synthesis of bis-(4-stearoylaminophenyl)methane (BSAPM) Gelator BSAPM was synthesized according to a method described previ- ously and identified by IR, 1H NMR and elemental analysis [14]. Scheme 1 shows the molecular structure. 2.2. Gelation test The gelator and the solvent were placed in a test tube and the solution was heated until the solid completely dissolved. The solution was then slowly cooled at room temperature until gel formed. If the gel was stable, it was designated as “G” in Table 1. If gel was formed but not stable at the room temperature, it was designated as “GN”. If gelator was not soluble in the solvent, it was designated as “I”. Table 1 Gelation ability of BSAPM in organic solvents Solvents The minimum gelation concentration (wt.%) Gelation state Stability at RT Ethanol Acetone Toluene Cyclohexanol 1,2-Dichloroe Chlorobenzen Cyclohexane p-Xylene Carbon tetrac Chloroform Benzene N,N-dimethyl Soybean oil n-Butanol Dimethyl sulf Styrene Diphenyl ethe G: gel formed insoluble in th 2.3. TEM for n-butanol gel formed by BSAPM A piece of n-butanol gel formed by BSAPM was placed on a carbon coated copper grid (200 mesh) and removed after 1 min, leaving some small patches of the gel on the grid. After specimens had been dried under vacuum, they were shadowed with OsO4 (10 mg, 2% of aqueous solution). Then they were dried for 1 h under vacuum. The specimens were examined with JEM-100CX II microscope with an accelerating voltage of 80 kV. 2.4. Preparation of SiO2 nanowires using template of BSAPM aggregates TEOS (41 another 10 ml solution (70 m in an ice bath. BSAPM. The completely. The hot m to the room te at room temp organic mass and 500 ◦C fo obtained. 2.5. SEM fo SEM mea white powder palladium–pla 2.6. AFM fo AFM mea little white po The Sample w freshly cleave tion o easure ingle- ults elati gela ts. In ts at g. seen tic so fter f the s ben of hyd – I – – I – 0.9 GN 1 day 0.8 GN 2 days thane 0.5 G 7 days e 1.5 G 7 days 2.5 G 8 days 1.0 G 14 days hloride 0.8 G 15 days 0.4 G 17 days 0.7 G 2 months formamide 1.0 G 4 months 1.0 G 4 months 2.0 G 6 months oxide 0.8 G 6 months 0.7 G 1 year r 0.8 G 1 year and stable; GN: gel formed but not stable at room temperature; I: e medium. evapora AFM m by the s 3. Res 3.1. G The solven solven heatin As alipha even a point o such a Scheme 1. Molecular structure of BSAPM and schematic diagram mg) and n-butanol (429.5 mg) were added into a 10 ml beaker. In beaker, n-butanol (429.5 mg) and 7.5% of hydrochloride aqueous g) were added. Both solutions were then mixed together by stirring The mixed solution was poured into a test tube containing 30 mg of test tube was heated slowly with stirring until BSAPM dissolved ixture was added dropwise on a clear glass plate. After cooling mperature, formed gel was placed in a desiccator for 7–10 days erature for sol/gel polymerization. Then, the BSAPM and other was removed by calcinations at 100 ◦C for 4 h, at 200 ◦C for 2 h r 1.5 h under vacuum, respectively. White powder product was r the SiO2 nanowires surements were carried out with an NEC-5510 microscope. A little of SiO2 nanowires was placed on a glass plate and coated with tnium. The accelerating voltage was 30 kV. r the SiO2 nanowires surements were carried out with a Seiko SPA400 microscope. A wder of SiO2 nanowires was dispersed in ethanol by sonicating. as prepared by spreading one drop of ethanol suspension onto a d surface of highly oriented pyrolytic graphite (HOPG). After the f ethanol, the sample was placed in the AFM chamber for imaging. ments were tapping mode to minimize damage of the soft surface crystal silicon probe. and discussion on ability of BSAPM tion ability of BSAPM was tested in various organic fact, BSAPM is almost insoluble in most organic room temperature, but it gradually dissolves upon in Table 1, BSAPM did not dissolve at all in some lvents with lower polarity, such as ethanol or acetone, prolonged heating at the temperature of the boiling solvents. But BSAPM can gelatinize many solvents, zene, chloroform and n-butanol and so on. rogen bonds and �–� stack interaction. C. Xueling et al. / Materials Chemistry and Physics 99 (2006) 61–65 63 Fig. 1. TEM images of fiber-like assemblies of BSAPM obtained from xerogel of n-butanol. Magnifications for left: 1400× and for right: 10,000×. From T vents seem such as po of gel stab as dimethy diphenyl e assembly o centration higher stab some relati gelation ab the concen given gelat specific sol gel. Regard vent, a com fiber-like a dimensiona action and Excellen to speciall BSAPM pr matic benz vided �–� aggregation 3.2. The m and acting Conside n-butanol s obtain furth BSAPM re the g wor ictu el o l exh ly o ther s d pr in a stribu sho ires in Fi The n-bu ated pres urthe e su ril is TE ggre ntera grou . Th out ropa mov he m mo able 1, gelation ability of BSAPM in organic sol- s to be no regularity on the properties of solvent, larity, aromaticity, etc. But, based on the viewpoint ility, higher polarity and aromatic solvents, such l sulfoxide, N,N-dimethylformamide, benzene and ther, were more preferable for the aggregation and f BSAPM. On the other hand, lower gelation con- of BSAPM (less than 1 wt.% for some solvents) and ility of gels (more than 6 months) also implied that onship could exist between polarity, aromaticity and ility, although gel stability is directly proportional to tration of gelator [1,2]. Nevertheless, it is a fact that a or can gelatinize certain solvents, in other word, the vent strongly influences the physical properties of the ing the driving force for the gelation of organic sol- mon viewpoint is that gelator self-assembles into ggregates, which in turn form an extended three- l network by hydrogen bonding, �–� stack inter- other non-covalent intermolecular interaction [1,2]. t gelation ability of BSAPM could be attributed y designed molecular structure. Amide groups of ovided sites of hydrogen bonding formation. Aro- ene ring and long aliphatic chains of BSAPM pro- stack interaction and molecular flexibility for the and assembly in organic media. orphology of BSAPM assemblies in n-butanol as template for TEOS adsorption ring TEOS sol/gel polymerization is carried out in olution for the preparation of silica nanowires, to er evidence that the fiber-liked assemblies of gelator silica, in this TEM p dried g butano random It is ra reporte gelator and di As nanow trated plate. gel of aggreg in the gates f onto th ent fib rate of fibril a static i amide groups carried This p after re 3.3. T The ally acting as a template for the creation of fiber by SEM an Fig. 2. Schematic illustration of silica nanowires synthesized by using elation of n-butanol was carried out by using BSAPM k. Fig. 1 shows lower and higher magnifications of res of the BSAPM assemblies obtained from a freeze- f n-butanol. The TEM pictures of the xerogel of n- ibit a dense three-dimensional pattern consisted of riented fibrous bundles with diameters of 50–200 nm. imilar to the assemblies of BSAPM in other solvents eviously [14]. Since the aggregation and assembly of medium is a spontaneous process, the size control tion of these fibrous is still a research subject. wn in Fig. 1, the formation processes of silica in the BSAPM/TEOS system are schematically illus- g. 2 using fiber-like assemblies of BSAPM as tem- formation mechanism of silica nanowires from the tanol could be proposed that the gelator BSAPM and assembled into the incipient fibril aggregates ence of TEOS, whereas the incipient fibril aggre- r grow into the bundled fibrils. TEOS was adsorbed rface of the fibril structure as the growth of incipi- relatively slow in comparison to the polymerization OS. The adsorption of TEOS on the surface of the gates could be, more or less, attributed to the electro- ction between partial electropositive of BSAPM with ps and partial electronegative of TEOS with ethoxy us, the sol/gel polymerization of TEOS was further along these fibrous bundles by the catalysis of HCl. gation mode eventually yields the silica nanowires al of fibril aggregates by calcination. orphology of silica nanowires rphology of the silica nanowires was characterized d AFM techniques. Fig. 3 shows the SEM pictures template of aggregates of BSAPM. 64 C. Xueling et al. / Materials Chemistry and Physics 99 (2006) 61–65 Fig. 3. SEM images of the silica nanowires obtained from n-butanol gel after calcinatio of the silica nanowires obtained from n-butanol gel formed by BSAPM after calcination. The overlapped silica nanowires feature a straight rod-like structure, which was similar to fiber- like structures obtained from BSAPM assemblies in the gel phase. As shown in the left image of Fig. 3 (9500×), the silica nanowires clearly exhibit a relatively smooth surface and straight rod-like structure without any twisted and entangling although the nanowires randomly stacked. The shape and appearance of nanowires with diameters of 200–500 nm and a few microm- eters length silica nanow vation of l color in bo low nanow assemblies Fig. 4 is that the mo also straigh of 15�m. I comparing cated that silica nano BSAPM ag Floccule ica un-tran Fig. 4. AFM nations. SEM gel af not mati arting material of SiO2 nanowires, the quantity of TEOS match to the quantity of template. If TEOS was excess, it not be completely transcribed into the form of nanowires. case, excess TEOS exists in amorphous form. There- he mass ratio of TEOS and BSAPM plays an important r the transcription of TEOS. For the preparation of silica ires, the hydrochloric acid also plays an important role catalysis of sol/gel polymerization. In general, TEOS be hydrolyzed into the anionic oligomeric silica species the sol–gel polymerization is carried out in acidic solu- hen a little amount of acid exists in the sol–gel medium, ide groups of BSAPM are also protonated. Consequently, ionic fibril aggregates would be formed by BSAPM self- bly. Contrastively, the product of sol/gel polymerization OS only showed the conventional granular structure in the e of the acid (Fig. 5). Therefore, electrostatic interaction were also clearly shown in Fig. 3. Obviously, the ires seem to be semi-transparent based on the obser- ight white color in the center part and bright white th edges of nanowires, which implied a possible hol- ires structure and the previous existence of gelator inside the silica fibers. the AFM image of the silica nanowire. It can be found rphology of selected large-scale SiO2 nanowire was t rod-like with a diameter of about 500 nm and length t further confirmed the formation of silica nanowire with the SEM images in Fig. 3. These results indi- the organogel was successfully transcribed into the wires by the intermolecular interaction between the gregates and silica particles. s mass appeared in Fig. 3 could be amorphous sil- scribed into the nanowires because all organic mass Fig. 5. butanol could the for As a st should could In this fore, t role fo nanow for the would when tion. W the am the cat assem for TE absenc images of silica nanowire obtained from n-butanol gel after calci- between th species is a onto the su can eventu 4. Conclu Gelator, can be use zene and n n. Magnifications for left: 9500× and for right: 9000×. picture of granular silica structure in the absence of acid for n- ter calcinations. exist after calcinations at 500 ◦C. It suggested that on of SiO2 nanowires is dependent on the template. e cationic templates and the anionic oligomeric silica driving force for the adsorption of oligomeric silica rface of BSAPM aggregates. This propagation mode ally yield the formation of fibrous silica (Fig. 3). sion bis-(4-stearoylaminophenyl)methane (BSAPM), d to gelatinize some organic solvents, such as ben- -butanol and so on. TEM images of n-butanol gel C. Xueling et al. / Materials Chemistry and Physics 99 (2006) 61–65 65 indicate that BSAPM can self-assembled at lower concentration (less than 3 wt.%) into fiber-like aggregate, which in turn form an extended three-dimensional network structure. The driving force for the gelation of organic solvent is mainly hydrogen bonding, �–� stack interaction and other non-covalent inter- molecular interaction. Using the fiber-like aggregates assem- bled by BSAPM as templates, tetraethoxysilane (TEOS) can be adsorbed onto the surfaces of fiber-like aggregates and then polymerized by sol–gel polymerization. SiO2 nanowires were formed after calcinations. SEM and AFM images indicate that silica consisted of nanowires structures with diameters of 200–500 nm and lengths of 2–18�m. Acknowledgement This work is financially supported by Natural Science Foun- dation of China (Grant No. 20474022). References [1] P. Terech, R.G. Weiss, Chem. Rev. 97 (1997) 3133. [2] D.J. Abdallah, R.G. Weiss, Adv. Mater. 12 (2002) 1237. [3] W.-B. Zhao, J.-J. Zhu, H.-Y. Chen, J. Cryst. Growth 258 (2003) 176. [4] A. Huczko, Appl. Phys. A 70 (2000) 365. [5] C.R. Martin, Chem. Mater. 8 (1996) 1739. [6] X.-Y. Wang, W.-G. Huang, P.J. Sebastian, S. Gamboa, J. Power Sources 140 (2005) 211. [7] C.T. Kresge, M.E. Leonowicz, W.J. Roth, J.C. Vartuli, J.S. Beck, Nature 359 (1992) 710. [8] M. Adachi, T. Harada, M. Harada, Langmuir 16 (2000) 2376. [9] J.H. Jung, S. Shinkai, T. Shimizu, Nano Letters 2 (1) (2002) 17. [10] J.H. Jung, Y. Ono, S. Shinkai, Langmuir 16 (2000) 1643. [11] J.H. Jung, S. Shinkai, T. Shimizu, Chem. Mater. 15 (2003) 2141. [12] J.H. Jung, K. Yoshida, T. Shimizu, Langmuir 18 (2002) 8724. [13] J.H. Jung, Y. Ono, K. Hanabusa, S. Shinkai, J. Am. Chem. Soc. 122 (2000) 5008. [14] W.-J. Cui, Y.-J. Yang, J. Huazhong Univ. Sci. Technol. 29 (8) (2001) 96. Bis-(4-stearoylaminophenyl)methane assembles in organic solvents and used as templates for preparation of SiO2 nanowires Introduction Experimental Synthesis of bis-(4-stearoylaminophenyl)methane (BSAPM) Gelation test TEM for n-butanol gel formed by BSAPM Preparation of SiO2 nanowires using template of BSAPM aggregates SEM for the SiO2 nanowires AFM for the SiO2 nanowires Results and discussion Gelation ability of BSAPM The morphology of BSAPM assemblies in n-butanol and acting as template for TEOS adsorption The morphology of silica nanowires Conclusion Acknowledgement References