- Open Access
Porous POSS-PANI nanofibre from interfacial polymerization and hydrothermal approach
© Liu and Xu. 2015
- Received: 28 August 2015
- Accepted: 10 November 2015
- Published: 25 November 2015
Nowadays, novel applications for polyaniline (PANI) make new demands on its morphology controlling, and designing novel PANI or PANI composite polymeric materials has been more and more attractive. In this work, octaaminophenyl polyhedral oligomeric silsesquioxane (POSS) was employed to prepare nanostructured PANI composites via controlled fabrication. By interfacial copolymerization, fibrous nanostructure was obtained. The size and morphology of this structure was adjusted by changing POSS to OAPS ratio: the size increased from about 20 to 200 nm when the molar ratio of POSS in the composites increased from 0.5 to 2.0 mol %. More importantly, further hydrothermal treatment for the samples with higher POSS concentration resulted in mesoporous structure on a more microscopic scale, which helps to improve the thermal stability. In the total synthesis, POSS played an important role in the morphology controlling of the composites.
- Polymeric composites
- Thermal properties
As one kind of conjugated polymers, PANI can be easily obtained via oxidative polymerization in various organic solvents or aqueous system. Because of its good environmental stability under normal processing conditions, excellent physical and chemical properties, adequate level of electrical conductivity and unique doping mechanism, it has been incorporated more and more widely in many applications (Dhand et al. 2010), such as batteries (Li et al. 2014), electro-magnetic interference (EMI) shielding (Teotia et al. 2014) and solar cells (Han et al. 2014). Recent research work has shown that nanostructured PANI can play an important role in sensor applications for its greater sensitivity and faster response time due to its higher effective surface area and shorter penetration depth for target molecules. The developments of PANI in molecular sensors have made new demands on its morphology controlling. Existed work shows that PANI based micro/nanostructures with different dimensions and morphologies can be obtained by template methods (Vijayakumar et al. 2013; Hu et al. 2012), template free methods (Du et al. 2008) and electro-spinning technology (Wanna et al. 2006). For example, zero-dimensional and one-dimensional nanostructures of polyaniline (PANI) can be achieved by using swollen liquid crystals as “soft” templates (Dutt and Siril 2014). PANI micro/nanostructures featuring square nanosheets, microspheres and microdisks are successfully synthesized via hydrothermal method (Zhu et al. 2015). By taking advantage of a microfluidic technology and employing organic soluble acid labile t-Boc-protected PANI as precursor, fabrication of PANI microfibres in a size-controlled manner is possible (Yoo et al. 2015).
On the other hand, the synthesis, characterization and application nanoporous or mesoporous materials have been more and more important in material research field due to their attractive features such as high pore volume, large surface area. Among lots of members in mesoporous family, silica based nanoporous or mesoporous materials have been widely studied for their pore size distribution, regular pore structure and other attractive properties. The can be used in catalyst, separation and purification, drug delivery, gas sensing and other fields. Generally speaking, typical silica based mesoporous materials, such as hexagonal MCM-41, cubic MCM-48, lamellar M41S, and cubic octamer [(CTAB)SiO2.5]8, can be prepared by silica and surfactant via template-directed synthesis following co-operative assembly pathways. In these preparations, surfactant works as soft template to induce the self-assembly, while silica works as framework in building mesoporous structure. The recent development of silicon chemistry provides us novel choice for selecting silica based framework, such as POSS. POSS are one type of hybrid materials with the general formula (RSiO3/2)n, whose organic substituents are connected with a silicon-oxygen core. The sizes POSS cages range from 1 to 3 nm, which can be regarded as the smallest possible units of silica (Agaskar and Klemperer 1995; Anderson et al. 2006; Li et al. 2001). Obviously, certain POSS cages with special substituted groups can be used to design novel materials with defined mesoporous structure. In this work, we introduce octaaminophenyl POSS into PANI chains to get nanostructured PANI composites with improved properties by controlled fabrication.
Synthesis of OPS and OAPS
FTIR, NMR and MALDI-TOF characterizations and for OPS are listed as followings: FTIR (cm−1) with KBr powder: 3072 (H-Ar), 1594 (C–C), 1112 (Si–O–Si); 29Si NMR (ppm): −76.5, MALDI-TOF (m/z): 77, 399, 400, 401, 876, 877, 878, 954, 955, 956, 1031, 1032, 1033 [C48H40Si8O12 = 1032 amu].
FTIR and NMR characterizations for OAPS are listed as followings: FTIR (cm−1) with KBr powder: 1134 (Si–O–Si), 3383 (N–H), 1488 (C–N), 29Si NMR (ppm): −73.3, −77.4; 1H NMR (ppm): 7.8–6.2 (4.0H), 5.2–3.7 (2.0H).
Fibrous POSS-PANI composites
Detailed POSS-PANI composite samples
OAPS concentration (mol %)
Interfacial polymerization, 25 °C, pH = 3.0
24-h hydrothermal treatment
48-h hydrothermal treatment
96-h hydrothermal treatment
Porous POSS-PANI composite fibres
Due to the organic–inorganic hybrid structure of POSS-PANI, the dense packing structures of rigid PANI arms are prohibited, instead of loosely packing structures. These structures can convert into stable mesoporous structures by hydrothermal treatments. As we know, the size of octafunctional POSS cage in this experiment is about 1.2 ~ 1.4 nm, which have functional groups in each octant in Cartesian space, either opposite or completely orthogonal to each other. PANI chains that linked in the corner of POSS cages can be regarded as flexible connections among POSS cages. The final morphologies of the POSS-PANI mesostructure after hydrothermal treatments will be affected by many factors, such as conformational energy of flexible PANI chains, van der Waals forces and the interactions between POSS cages, and electrostatic interaction. In POSS-PANI composites, POSS can be regarded as a head-group area, which plays a governing role in works as in building the mesoporous framework and selecting the mesophases. The favored mesoporous structures can permit the area of POSS cage to be closest to the most optimal value, while maintaining favorable packing mode of the hydrophobic PANI chains. In this case, the total energy of the composite tends to minima and the system is most stable.
In summary, nanostructured POSS-PANI composite fibres have been successfully prepared by using aniline and octaaminophenyl POSS through copolymerization and hydrothermal approaches. The morphology of fibrous POSS-PANI composites can be adjusted by changing POSS concentrations. Further hydrothermal treatment can result in mesoporous structure, which helps to improve its thermal stability. Detailed studies on other properties of nanostructured POSS-PANI composites are now in progress.
Materials and techniques
Aniline, tetramethylammonium hydroxide (Me4NOH), phenyltrichlorosilane, triethylamine, ethylacetate, toluene, ammonium peroxydisulfate and fuming nitric acid were bought from Shanghai Experiment Reagent Co., Ltd. and they were of analytical grade.
XRD patterns were obtained by using a Rigaku K/max-γA X-ray diffractometer with a Cu Ka (λ = 1.5415 Å) at the scanning rate of 0.02°/s; Infrared spectra were obtained by using a MAGNA-IR 750 spectrometer. Thermal gravimetric analysis (TGA) was performed on a Netzsch STA-409c Thermal Analyzer under a 50 × 103 mm3/min nitrogen or air flow with the heating rate of 10 °C/min; TEM images were obtained from JEOL2010 Transmission Electronic Microscope system. MALDI-TOF data was acquired on a GCT gas chromatography time-of-flight mass spectrometer at the pressure of 0.280 Pa under a certain heating program. NMR spectra were acquired using a Bruker AVANCE 400 spectrometer. The hydrothermal synthesis reactor used in our experiments is made up of two parts: the inner part is a pot with a lid made of polytetrafluoroethylene; the outer part is a stainless-steel kettle, which can play a sealing role by tightening its lid. Hydrothermal synthesis reactor can provide a sealing reaction environment under high temperature and high pressure.
Synthesis and preparations
Interfacial polymerization was performed in an aqueous/organic biphasic system containing aniline and OAPS mixture dissolved in toluene together with ammonium peroxydisulfate dissolved in an aqueous acid solution. The experiments for interfacial polymerization were carried out in a room with constant temperature and humidity, where the temperature was controlled at (25 ± 1 °C). For sample POPA-4 with higher POSS concentration, further hydrothermal treatments (PH = 8~9, 120 °C) were carried out after 20-min ultrasonic dispersion. Detailed composite samples are listed in Table 1.
LL carried out the experimental design and result analysis, part of the experimental work and drafted the manuscript. XXX carried out part of the experimental work. Both authors read and approved the final manuscript.
This work is financially supported by the Natural Science Foundation of China (U1332134), the Natural Science Foundation of Suzhou (SYG201329), the Fundamental Research Funds for the Central Universities, the Qing Lan Project and the International Foundation for Science, Stockholm, Sweden, the Organization for the Prohibition of Chemical Weapons, The Hague, Netherlands, through a grant to Lei Liu (F/4736-2).
Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, School of Mechanics, Southeast University, Nanjing 210096, People’s Republic of China. Zhengde Polytechnic College, Nanjing 211106, People’s Republic of China
The authors declare that they have no competing interests.
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