Surfactant-aided dispersion of polystyrene-functionalized carbon nanotubes in a nanostructured poly(styrene-b-isoprene-b-styrene) block copolymer

The synergistic effect of using polystyrene-grafted multi-walled carbon nanotubes (PSgMWCNT) and a surfactant in the dispersion of MWCNT in a self-assembled poly(styrene-b-isoprene-b-styrene) (SIS) block copolymer is reported. The functionalization of MWCNT with polystyrene achieved by the grafting-from approach is not enough to disperse them in the SIS block copolymer. However, a high dispersion of PSgMWCNT in SIS is achieved when dodecanethiol (DT) was added through composite preparation, without affecting the SIS capacity to self-assemble in ordered cylinders. Suspensions of PSgMWCNT without DT and not functionalized MWCNT with DT presented low stability forming aggregates in less than 10 min. On the contrary, the stability of PSgMWCNT suspension in the presence of DT was dramatically enhanced to more than two weeks. This synergistic effect is due to interactions between PSgMWCNT and DT molecules, as proved by UV-Vis spectroscopy.     

Mapping of carbon nanotubes in the polystyrene domains of a polystyrene-b-polyisoprene-b-polystyrene block copolymer matrix using electrostatic force microscopy

Electrostatic force microscopy (EFM) was used to localize and characterize conducting nanofillers inside the domains of a block copolymer matrix. The confinement of carbon nanotubes into polystyrene-b-polyisoprene-b-polystyrene block copolymer (SIS) matrix was investigated. The EFM technique provided information with unprecedented imaging of octadecylamine functionalized single-walled carbon nanotubes, sequestered in the self-assembled lamellar polystyrene domains of the SIS block copolymer matrix.     

Viscoelastic and photo-actuation studies of composites based on polystyrene-grafted carbon nanotubes and styrene-b-isoprene-b-styrene block copolymer

Photoactuating composites based on the linear triblock copolymer polystyrene-b-polyisoprene-b-polystyrene (SIS) were prepared by incorporation of polystyrene-modified multiwalled carbon nanotubes (MWCNT–PS). Modification of MWCNT was performed by surface-initiated atom transfer radical polymerization (SI ATRP) of styrene. The presence of the polystyrene chains on the MWCNT surface facilitated their dispersion in the SIS matrix. Improved interactions of the modified MWCNT–PS compared to neat MWCNT were confirmed by dynamic mechanical analysis. The activation energy of glass transition of the polystyrene phase in the MWCNT–PS/SIS composite increased significantly compared to the neat SIS matrix, while the incorporation of neat MWCNT to the SIS matrix disturbed the physical cross-linking of the SIS and degraded its elastic properties. The photo-actuation ability of the MWCNT–PS/SIS composite was proved using atomic force microscopy.     

Dispersion of carbon nanotubes in nanostructured epoxy systems for coating application

This study about the dispersion of carbon nanotubes into an epoxy matrix can be considered as a first approach to investigate a potential industrial coating. In order to well disperse carboxylic acid-modified multiwalled carbon nanotubes (a-MWCNT) in a commercial epoxy-based resin, its nanostructuring with an amphiphilic epoxidized styrene-b-butadiene-b-styrene triblock copolymer that also acts as surfactant was carried out. In order to determine if coating performance is suitable for industrial applications, morphologies generated for copolymer-modified coating and the dispersion of a-MWCNT was characterized by atomic force microscopy. Contact angle measurements, Taber abrasion testing and thermogravimetric analysis were also performed. A tailor-made coating was developed with improved a-MWCNT dispersion and hydrophobicity due to the effect of block copolymer. System modified with 5 wt% of block copolymer and filled with 1 wt% a-MWCNT present the lowest value in weight loss in the wear test, while systems filled with 0.2 wt% of a-MWCNT showed increased thermal stability. Coating properties analyzed depend largely on the amount of components and a-MWCNT dispersion level, thus adding new application possibilities to the coatings, while most of the conventional epoxy-coating advantages are retained.     

The structure and electro‐mechanical properties of novel hybrid CNT/PANI nanocomposites

Electrically conductive elastomeric nanocomposites containing carbon nanotubes (CNT) and polyaniline (PANI) are reported in the present investigation. The synthesis procedure included an in situ inverse emulsion polymerization of aniline doped with dodecylbenzene sulfonic acid (DBSA) in the presence of CNT and dissolved styrene‐isoprene‐styrene (SIS) block copolymer. The PANI synthesis step was carried out by applying ultrasonic energy. The dispersions obtained were processed by two methods: a recently developed precipitation‐filtration procedure, and a conventional drop‐cast procedure. The techniques developed resulted in homogeneous exfoliated PANI coated nanotubes within the elastomeric matrix. The presence of CNT/PANI in the SIS elastomeric matrix affects thermal, mechanical, and electrical properties of the nanocomposites. The formation of continuous three‐dimensional CNT/PANI networks prepared via the precipitation‐filtration method enhances the nanocomposite properties. Contrarily, the intermittent three‐dimensional network prepared by conventional drop‐cast method leads to inferior properties. Nanocomposites produced by both techniques are observed by HRSEM. The two processing techniques result in different structures, which affect the physical properties of the materials produced. A relatively low percolation threshold for both methods was determined. The Young's modulus of the SIS/CNT/PANI significantly increased in the presence of CNT. The precipitation‐filtration technique yields an improved nanocomposite product compared to the drop‐cast route. POLYM. COMPOS., 35:788–794, 2014. © 2013 Society of Plastics Engineers     

Compatibilization of epoxidized triblock copolymer on the generation of self-assembled nanostructured epoxies and their surface wettability

In this work, we have successfully synthesized epoxidized poly(styrene-block-butadiene-block-styrene) with the highest epoxidation degree (55 mol%) for the first time by using metachloroperbenzoic acid method. This highly epoxidized styrene-butadiene-styrene (eSBS) block copolymer exhibited good compatibility with the epoxy (diglycidylether of bisphenol-A)/ eSBS block copolymer- 4,4′-diamino diphenyl methane blend. Transmission electron microscope images showed that the eSBS block copolymer formed spherical nanostructure morphology within the blend due to reaction induced phase separation. The addition of eSBS block copolymer in the system significantly improved the wetting parameters such as hydrophilicity, surface free energy, work of adhesion, spreading coefficient and Girifalco-Good's interaction parameter values, which are discussed in detail. The as-prepared self-assembled nanostructured epoxy system will be useful in highly toughened coating applications such as aircraft, automobile, and flooring industries.     

Nanostructured thermosetting epoxy systems modified with poly(isoprene‐b‐methyl metacrylate) diblock copolymer and polyisoprene‐grafted carbon nanotubes

Nanostructured thermosetting composites based on an epoxy matrix modified with poly(isoprene‐b‐methyl methacrylate) (PI‐b‐PMMA) block copolymer were prepared through PI block segregation. Morphological structures were examined by means of atomic microscopy force microscopy. As epoxy/pristine multi‐walled carbon nanotubes (MWCNT) systems were found to present big agglomerations, with a very poor dispersion of the nanofiller, epoxy/PI‐b‐PMMA/MWCNT systems were prepared by using polyisoprene‐grafted carbon nanotubes (PI‐g‐CNT) to enhance compatibility with the matrix and improve dispersion. It was found that the functionalization of MWCNT with grafted polyisoprene was not enough to totally disperse them into the epoxy matrix but an improvement of the dispersion of carbon nanotubes was achieved by nanostructuring epoxy matrix with PI‐b‐PMMA when compared with epoxy/MWCNT composites without nanostructuring. Nevertheless, some agglomerates were still present and the complete dispersion or confinement of nanotubes into desired domains was not achieved. Thermomechanical properties slightly increase with PI‐g‐CNT content for nanostructured samples, whereas for nonnanostructured epoxy/PI‐g‐CNT composites they appeared almost constant and even decreased for the highest nanofiller amount due to the presence of agglomerates. Compression properties slightly decreased with block copolymer content, while remained almost constant with nanofiller amount. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Processing dependency of percolation threshold of MWCNTs in a thermoplastic elastomeric block copolymer

We prepared carbon nanotube thermoplastic elastomeric block copolymer nanocomposites using a commercial styrene-ethylenebutylene-styrene (SEBS) block copolymer and multiwall carbon nanotubes (MWCNTs) at different filler concentrations. Hereto we applied two different processing strategies, namely direct melt mixing and solution-precipitation. We observe that the mechanical and electrical properties such as storage module and electrical percolation threshold are clearly affected by the processing approach. We studied these effects in detail by means of dielectric spectroscopy, which provided important information about the dispersion state of the MWCNT filler network. It revealed a fractal filler behaviour of the samples independent of the processing method. However, in samples prepared by melt mixing an additional dielectric response related to nanoscopic gap junctions of 1.5 nm was identified. This response was not present in solution-mixed samples, which are characterized by improved polymer wetting. We discuss how the interactions between CNTs and the two phases of the block copolymer matrix are affected by the processing conditions resulting in the important differences in the filler network structure, which directly influence the final electrical and mechanical properties of the composite.     

Selective self-assembly of surface-functionalized carbon nanotubes in block copolymer template

Microphase-separated styrene-butadiene-styrene (SBS) triblock copolymer was utilized as a template for the selective self-assembly of polystyrene (PS)-functionalized carbon nanotubes (CNTs) in the PS phase. It was also found that PS-functionalized CNTs could be accommodated in the PS phase of SBS regardless of the molecular weight of the PS ligand. This is different from the case for assembling nanoparticles or nanorods with a block copolymer, in which the ligand should be shorter than the corresponding block such that the nanoparticles or nanorods can be incorporated into that block. This phenomenon is explained based on the different chain morphologies of the ligands functionalizing the CNTs, nanoparticles and nanorods.     

SWCNT PEG-eggs: Single-walled carbon nanotubes in biocompatible shell-crosslinked micelles

Pristine, individualized single-walled carbon nanotubes (SWCNTs) have been noncovalently captured within PEG-terminated block copolymer amphiphiles. Two cross-linkable amphiphiles were evaluated: polyethylene glycol-polyacrylic acid-polystyrene (PEG-PAA-PS) and polyethylene glycol-polybutadiene (PEG-PB). The resulting self-assembled PEG-PAA-PS structures, called PEG-eggs, are freely soluble in water and stable in physiological media. SWCNTs in PEG-eggs retain their intrinsic near-infrared fluorescence, resist exchange with serum proteins, and are non-cytotoxic to mouse macrophage and human renal cells based on in vitro viability assays.     

Silicon and carbon substrates induced arrangement changes in poly(styrene-b-isoprene-b-styrene) block copolymer thin films

Poly(styrene-b-isoprene-b-styrene) (SIS) block copolymer ordering in thin films was studied using two selective substrates as carbon and silicon. Atomic force microscopy (AFM) and contact angle measurements were employed to examine the affinities between domains and surrounding interfaces. The surface morphology was examined by AFM using different amplitude ratios. Results showed polyisoprene (PI) domain layer formation in the outermost film layer. On the other hand, the layer close to substrate adopted different arrangements on silicon and carbon substrates. Topographical and phase images revealed that in both substrates with the thickest films, the interactions between substrate and block domains were not enough to induce surface ordering being the morphology independent of employed substrate. However, decreasing film thickness, SIS thin films displayed a variety of arrangements such as perforated lamellae and cylindrical morphologies. Depending on substrate, these morphologies were achieved in different film thicknesses. Finally, the thinnest film did not adjust to characteristic domain spacing commensurability and terraces formation was observed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Alignment and orientational proliferation of HEX cylinders in a polystyrene-block-polyisoprene-block-polystyrene copolymer in the presence of clay

We investigated the effect of an anisotropic silicate layer on the alignment and orientational proliferation of hexagonally packed cylinder microdomains of a block copolymer in the presence of a clay by using synchrotron small angle X-ray scattering (SAXS), rheology, and transmission electron microscopy (TEM). The block copolymer employed in this study was polystyrene-block-polyisoprene-block-polystyrene copolymer (SIS). The degree of intercalation of the clay in the presence of SIS was examined by wide angle X-ray diffraction (WAXD).Almost all of the HEX cylinders in neat SIS are aligned toward the flow direction after large amplitude oscillatory shearing is applied to the specimens. However, some tactoids in nanocomposites are not aligned, although most tactoids are also aligned to the flow direction. Due to HEX cylinders near tactoids, which are not aligned to the flow direction, the orientational factor of HEX cylinders in SIS/clay nanocomposites is smaller than that of neat SIS. However, once HEX cylinders in SIS/clay nanocomposites are degenerated after experiencing body-centered cubic microdomains, the decrease in the orientational factor from original aligned HEX is smaller compared with neat SIS.     

Large strain and toughness enhancement of poly(dimethyl siloxane) composite films filled with electrospun polyacrylonitrile-graft-poly(dimethyl siloxane) fibres and multi-walled carbon nanotubes

Unfilled cross-linked poly(dimethyl siloxane) (PDMS) is a weak material and is generally filled with high levels of particulate fillers such as silica, calcium carbonate and carbon black to improve its mechanical properties. The use of fibrous fillers such as electrospun nanofibres and multi-walled carbon nanotubes as fillers for PDMS has not been widely studied. In this study anew copolymer, polyacrylonitrile-graft-poly(dimethyl siloxane) (PAN-g-PDMS), is used as fibrous filler for PDMS. The graft copolymer is electrospun to produce the fibre filler material. It is shown how the PDMS content of the graft copolymer provides increased compatibility with silicone matrices and excellent dispersion of the fibre fillers throughout a silicone matrix. It is also shown that it is possible to include multi-walled carbon nanotubes in the electrospun fibres which are subsequently dispersed in the PDMS matrix. Fibre mats were used in the non-woven and the aligned forms. The differently prepared fibre composites have significantly different mechanical properties. Conventional composites using fibrous fillers usually show increased strength and stiffness but usually with a resultant loss of strain. In the case of the composites produced in this study there is a dramatic improvement in the extensibility of the non-woven PAN-g-PDMS fibre mat filled silicone films of up to 470%.     

Reinforcement of polymers with carbon nanotubes. The role of an ordered polymer interfacial region. Experiment and modeling

Significant increases in the Young's modulus of nanotube–polymer composites have been associated with the formation of an ordered polymer layer coating the nanotubes. Polyvinyl alcohol (PVA) is known to display nanotube-induced ordering. It is used here as a model matrix to investigate how the polymer coating influences the mechanical reinforcement of the composite material. Young's modulus and calorimetry measurements were carried out on films of PVA-based composites reinforced with different types of nanotubes. An unmistakable correlation between polymer ordering and reinforcement was found. This is supported by the introduction of a model capable of establishing, on quantitative grounds, how the ordered phase affects the increase in the Young's modulus. Rather than acting as intrinsically stiffer reinforcing agents, our results suggest that the major role played by the nanotubes in improving the mechanical properties of composites is to nucleate an ordered polymer coating. It is the presence of this stiff ordered phase that dominates the reinforcement mechanism.     

Conductive polymer blends with low carbon black loading: High impact polystyrene/thermoplastic elastomer (styrene-isoprene-styrene)

Electrical resistivity and morphology of high impact polystyrene (HIPS)/styrene-isoprene-styrene copolymer (SIS)/carbon black (CB) blends were studied. Conductive CB particles locale preferentially within the HIPS phase of the HIPS/SIS blends. The blends studied remain conductive as long as HIPS maintains a continuous phase and the effective CB concentration within HIPS surmounts its percolation threshold. Thus, blends containing 2 phr CB depict significant changes in resistivity with the HIPS/SIS composition, transforming from insulative to conductive. SIS/CB mixtures exhibit an unusual behavior, explained by a physical model suggested in this paper and extended to the HIPS/SIS/CB systems.     

有序介孔聚合物的研究进展

综述了以自组装法、硬模板法和软模板法合成有序介孔聚合物及介孔碳的研究进展。对上述3种制备方法及原理进行了比较,指出目前以嵌段共聚物进行自组装以及采用软模板法制备介孔聚合物的途径更有利于制备有序的介孔聚合物及介孔碳。讨论了采用自组装法及软模板法时,嵌段共聚物的种类、模板剂的类型、聚合物前躯体的结构等对所制备的介孔聚合物以及介孔碳的形貌、介孔结构、骨架结构以及介孔材料的物理化学性能的影响。指出目前在介孔聚合物以及介孔碳的研究中,主要问题是如何提高介孔聚合物的有序性以及其介孔结构的稳定性。最后对有序介孔聚合物及介孔碳的发展方向及应用领域进行了展望。     

Large-scale synthesis of ordered mesoporous carbon fiber and its application as cathode material for lithium–sulfur batteries

A novel type of one-dimensional ordered mesoporous carbon fiber has been prepared via the electrospinning technique by using resol as the carbon source and triblock copolymer Pluronic F127 as the template. Sulfur is then encapsulated in this ordered mesoporous carbon fibers by a simple thermal treatment. The interwoven fibrous nanostructure has favorably mechanical stability and can provide an effective conductive network for sulfur and polysulfides during cycling. The ordered mesopores can also restrain the diffusion of long-chain polysulfides. The resulting ordered mesoporous carbon fiber sulfur (OMCF-S) composite with 63% S exhibits high reversible capacity, good capacity retention and enhanced rate capacity when used as cathode in rechargeable lithium–sulfur batteries. The resulting OMCF-S electrode maintains a stable discharge capacity of 690 mAh/g at 0.3 C, even after 300 cycles.     

A mesoporous composite template composed of self-assembled silica nanotube and multi-walled carbon nanotube

The multi-walled carbon nanotubes (MWNTs) were successfully embedded in the hexagonally-arranged silica tubular structure by the self-organization of two surfactant systems providing a MWNT-incorporated silica nancomposite template. The anionic surfactant (sodium dodecyl sulfate, SDS) adsorbed on the MWNT surfaces allowed the MWNTs to interact with the outer surface of the self-assembled non-ionic surfactant, poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer. Due to the hydrophilic–hydrophilic interaction between the PEO blocks and the sulfate group of SDS, the MWNTs were most possibly surrounded by the outer wall of the SBA-15 hexagonal tubes aligning in the longitudinal and transverse directions to the silica tube direction. According to the interplanar distances, electron microscopy images, and N₂ adsorption–desorption isotherms, the synthesized SBA-15/MWNT system exhibited the structural integrity of silica-tube arrangement and structural characteristics of MWNTs in terms of BET surface area and micropore volume. This work made it clear that the developed SBA-15/MWNT template could be used to synthesize various MWNT-incorporated 2-D replicas.     

High-performance poly(butylene oxide)/poly (ethylene oxide) block copolymer surfactants for the preparation of water-in-oil high internal phase emulsions

High-performance surfactants have been developed for the preparation of water-in-oil high internal phase emulsions (HIPE), particularly for the preparation of polymerized HIPE foams. High-efficiency surfactants with poly(butylene oxide)/poly(ethylene oxide) (BO/EO) block copolymer backbones have been developed that can stabilize an HIPE through polymerization at concentrations as low as 0.006 wt% based on total emulsion weight. Polymerizable versions have been developed that bind into the polymeric foam backbone. BO/EO block copolymer surfactants also allow preparation of polymerized HIPE foams without salt in the aqueous phase. HIPE with the BO/EO surfactants have been prepared at room temperature and polymerized at temperatures exceeding 90°C. By minimizing the required amount of surfactant, allowing the surfactant to react during HIPE polymerizations, eliminating the need for salt, and stabilizing over a broad range of temperatures, BO/EO block copolymer surfactants have demonstrated their place as high-performance HIPE surfactants.     

Control over the surface plasmon band of block copolymer/Ag/Au nanoparticles composites by the addition of single walled carbon nanotubes

In this study, we demonstrate control over the localized surface plasmon band (SPB) of a micellar poly(styrene-block-4vinylpyridine) (PS-b-P4VP) copolymer thin film composite that includes Ag and Au nanoparticles (NPs) in the presence of single walled carbon nanotubes (SWCNTs). Ag and Au NPs are preferentially located in the P4VP core and the PS corona of ordered spherical PS-b-P4VP copolymer micelles, respectively. This structure gave rise to a single SPB due to the coupling of Ag and Au SPBs. The non-covalent addition of SWCNTs in the block copolymer micelles shifts the coupled SPB to a lower wavelength. The maximum shift in the coupled SPB of approximately 30 nm was achieved in the PS-b-P4VP/Ag/Au NPs composite. The carbon nanotube induced modulation of the coupled SPB stems from the charge accumulation effect of the SWCNTs placed between the two types of nanoparticles.