α-Pyrene polymer functionalized multiwalled carbon nanotubes: Solubility, stability and depletion phenomena

Applications, fluid mechanics, and colloidal science of carbon-nanotube-based 3D printable inks

Additive manufacturing, also known as 3D printing (3DP), is a novel and developing technology, which has a wide range of industrial and scientific applications. This technology has continuously progressed over the past several decades, with improvement in productivity, resolution of the printed features, achievement of more and more complex shapes and topographies, scalability of the printed components and devices, and discovery of new printing materials with multi-functional capabilities. Among these newly developed printing materials, carbon-nanotubes (CNT) based inks, with their remarkable mechanical, electrical, and thermal properties, have emerged as an extremely attractive option. Various formulae of CNT-based ink have been developed, including CNT-nano-particle inks, CNT-polymer inks, and CNT-based non-nanocomposite inks (i.e., CNT ink that is not in a form where CNT particles are suspended in a polymer matrix). Various types of sensors as well as soft and smart electronic devices with a multitude of applications have been fabricated with CNT-based inks by employing different 3DP methods including syringe printing (SP), aerosol-jet printing (AJP), fused deposition modeling (FDM), and stereolithography (SLA). Despite such progress, there is inadequate literature on the various fluid mechanics and colloidal science aspects associated with the printability and property-tunability of nanoparticulate inks, specifically CNT-based inks. This review article, therefore, will focus on the formulation, dispersion, and the associated fluid mechanics and the colloidal science of 3D printable CNT-based inks. This article will first focus on the different examples where 3DP has been employed for printing CNT-based inks for a multitude of applications. Following that, we shall highlight the various key fluid mechanics and colloidal science issues that are central and vital to printing with such inks. Finally, the article will point out the open existing challenges and scope of future work on this topic.

Versatile Multi-Functional Block Copolymers Made by Atom Transfer Radical Polymerization and Post-Synthetic Modification: Switching from Volatile Organic Compound Sensors to Polymeric Surfactants for Water Rheology Control via Hydrolysis

Novel, multipurpose terpolymers based on styrene (PS), tert-butyl methacrylate (tBMA) and glycidyl methacrylate (GMA), have been synthesized via Atom Transfer Radical Polymerization (ATRP). Post-synthetic modification with 1-pyrenemethylamine (AMP) allows non-covalent functionalization of carbon nanotubes, eventually yielding a conductive nanocomposite materials capable of interacting with different Volatile Organic Compounds (VOCs) by electrical resistance variation upon exposure. Moreover, facile hydrolysis of the tBMA group yields polyelectrolytic macrosurfactants with remarkable thickening properties for promising applications in water solution, such as Enhanced Oil Recovery (EOR).

The application of the surface energy based solubility parameter theory for the rational design of polymer-functionalized MWCNTs

The surface energy based solubility parameters theory was applied to model the degree of polystyrene-functionalisation of MWCNTs in six different organic solvents. The experimental characterization of the polymer-functionalized MWCNTs is consistent with the predictions of this model providing a breakthrough towards the rational design of functionalized MWCNTs based on thermodynamic parameters.

Effect of the Polyketone Aromatic Pendent Groups on the Electrical Conductivity of the Derived MWCNTs-Based Nanocomposites

Electrically conductive plastics with a stable electric response within a wide temperature range are promising substitutes of conventional inorganic conductive materials. This study examines the preparation of thermoplastic polyketones (PK30) functionalized by the Paal⁻Knorr process with phenyl (PEA), thiophene (TMA), and pyrene (PMA) pendent groups with the aim of optimizing the non-covalent functionalization of multiwalled carbon nanotubes (MWCNTs) through π⁻π interactions. Among all the aromatic functionalities grafted to the PK30 backbone, the extended aromatic nuclei of PMA were found to be particularly effective in preparing well exfoliated and undamaged MWCNTs dispersions with a well-defined conductive percolative network above the 2 wt % of loading and in freshly prepared nanocomposites as well. The efficient and superior π⁻π interactions between PK30PMA and MWCNTs consistently supported the formation of nanocomposites with a highly stable electrical response after thermal solicitations such as temperature annealing at the softening point, IR radiation exposure, as well as several heating/cooling cycles from room temperature to 75 °C.

An easy synthetic way to exfoliate and stabilize MWCNTs in a thermoplastic pyrrole-containing matrix assisted by hydrogen bonds

MWCNTs were dispersed in a thermoplastic polymer containing pyrrole units in the main chain and hydroxyl pendant groups, affording a well-distributed percolative network. The resulting soft nanocomposite shows stable conductive behavior.

Rational Design of Multiamphiphilic Polymer Compatibilizers: Versatile Solubility and Hybridization of Noncovalently Functionalized CNT Nanocomposites

The design of amphiphilic polymer compatibilizers for solubility manipulation of CNT composites was systematically generalized in this study. Structurally tailored multiamphiphilic compatibilizer were designed and synthesized by applying simple, high-yield reactions. This multiamphiphilic compatibilizer was applied for noncovalent functionalization of CNTs as well as provided CNTs with outstanding dispersion stability, manipulation of solubility, and hybridization with Ag nanoparticles (NPs). With regard to the dispersion properties, superior records in maximum concentration (2.88-3.10 mg/mL in chloroform), and mass ratio of the compatibilizer for good CNT dispersion (36 wt %) were achieved by MWCNTs functionalized with a multiamphiphilic block copolymer compatibilizer. In particular, the solubility limitations of MWCNT dispersion in solvents ranging from toluene (nonpolar) to aqueous solution (polar) are surprisingly resolved by introducing this multiamphiphilic polymer compatibilizer. Furthermore, this polymer compatibilizer allowed the synthesis of the hybrid CNT nanocomposites with Ag nanoparticles by an in situ nucleation process. As such, the multiamphiphilic compatibilizer candidate as a new concept for the noncovalent functionalization of CNTs can extend their use for a wide range of applications.

Non-covalent polymer wrapping of carbon nanotubes and the role of wrapped polymers as functional dispersants

Carbon nanotubes (CNTs) have been recognized as a promising material in a wide range of applications from biotechnology to energy-related devices. However, the poor solubility in aqueous and organic solvents hindered the applications of CNTs. As studies have progressed, the methodology for CNT dispersion was established. In this methodology, the key issue is to covalently or non-covalently functionalize the surfaces of the CNTs with a dispersant. Among the various types of dispersions, polymer wrapping through non-covalent interactions is attractive in terms of the stability and homogeneity of the functionalization. Recently, by taking advantage of their stability, the wrapped-polymers have been utilized to support and/or reinforce the unique functionality of the CNTs, leading to the development of high-performance devices. In this review, various polymer wrapping approaches, together with the applications of the polymer-wrapped CNTs, are summarized.

Morphology control in biphasic hybrid systems of semiconducting materials

Simple blends of inorganic nanocrystals and organic (semiconducting) polymers usually lead to macroscopic segregation. Thus, such blends typically exhibit inferior properties than expected. To overcome the problem of segregation, polymer coated nanocrystals (nanocomposites) have been developed. Such nanocomposites are highly miscible within the polymer matrix. In this Review, a summary of synthetic approaches to achieve stable nanocomposites in a semiconducting polymer matrix is presented. Furthermore, a theoretical background as well as an overview concerning morphology control of inorganic NCs in polymer matrices are provided. In addition, the morphologic behavior of highly anisotropic nanoparticles (i.e. liquid crystalline phase formation of nanorod-composites) and branched nanoparticles (spatial orientation of tetrapods) is described. Finally, the morphology requirements for the application of inorganic/organic hybrid systems in light emitting diodes and solar cells are discussed, and potential solutions to achieve the required morphologies are provided.

Thermoresponsive self-assembly of nanostructures from a collagen-like peptide-containing diblock copolymer

Temperature-triggered formation of nanostructures with distinct biological activity offers opportunities in selective modification of matrices and in drug delivery. Toward these ends, diblock polymers comprising poly(diethylene glycol methyl ether methacrylate) (PDEGMEMA) conjugated to a triple helix-forming collagen-like peptide were produced. Triggered by the collapse of the thermoresponsive domain above its LCST, the conjugate undergoes a reversible transition in aqueous solution to form well-defined nanovesicles with diameters of approximately 100 nm, with a transition temperature of 37 °C. The incorporation of CLP domains in these nanostructures may offer opportunities for the selective targeting of collagen-containing matrices.

Non-covalent and reversible functionalization of carbon nanotubes

Carbon nanotubes (CNTs) have been proposed and actively explored as multipurpose innovative nanoscaffolds for applications in fields such as material science, drug delivery and diagnostic applications. Their versatile physicochemical features are nonetheless limited by their scarce solubilization in both aqueous and organic solvents. In order to overcome this drawback CNTs can be easily non-covalently functionalized with different dispersants. In the present review we focus on the peculiar hydrophobic character of pristine CNTs that prevent them to easily disperse in organic solvents. We report some interesting examples of CNTs dispersants with the aim to highlight the essential features a molecule should possess in order to act as a good carbon nanotube dispersant both in water and in organic solvents. The review pinpoints also a few examples of dispersant design. The last section is devoted to the exploitation of the major quality of non-covalent functionalization that is its reversibility and the possibility to obtain stimuli-responsive precipitation or dispersion of CNTs.

Morphological transformations in a dually thermoresponsive coil-rod-coil bioconjugate

We report the conformational and assembly behavior of a thermoresponsive triblock biohybrid conjugate under aqueous conditions. The triblock comprises of poly(diethylene glycol methyl ether methacrylate) (PDEGMEMA) conjugated to the ends of a triple-helix forming collagen-like peptide. The circular dichroism (CD) experiment confirms the ability of the collagen-like peptide middle block to assemble as a triple helix in the hybrid conjugate. Above the LCST (~35 °C), the collapse of the thermoresponsive PDEGMEMA polymer at the ends of the peptide domain resulted in a concomitant increase in the conformational stability of the peptide domain towards thermal denaturation. Upon cooling back, the kinetic conformational refolding behavior was still observed for the peptide domain in the hybrid conjugate. Static light scattering (SLS) experiments suggested the formation of supramolecular structures upon increasing solution temperatures to above the LCST. The scattering intensity increased with increasing temperature, until at 75 °C then it was found to decrease. Cryogenic scanning electron microscopy and regular transmission electron microscopy suggested the formation of spherical aggregates that increased in size with increasing temperature up to 65 °C and a morphological transformation into fibrils was also observed at 75 °C. The synergistic effect of dual thermoresponsive behavior from the peptide and the polymer block in the triblock hybrid is suggested for the observed conformational and assembly behaviors.

Double Stimuli-Responsive Copolymer Stabilizers for Multiwalled Carbon Nanotubes

A unique copolymer stabilizer is presented that can be used to stabilize multiwalled carbon nanotubes in aqueous solution to form "smart" dispersions. They showed double stimuli-responsive behavior (in dependence of temperature and ionic strength) and allowed for accurate control of the transition (exfoliated → agglomerated) temperature of nanotubes over a wide temperature range. In spite of its effective dispersion strength, the copolymer was easily synthesized in one step via free radical copolymerization of N-isopropylacrylamide and 1-ethyl-3-vinylimidazolium bromide.

Synthesis, characterization, and multilayer assembly of pH sensitive graphene-polymer nanocomposites

pH sensitive graphene-polymer composites have been prepared by the modification of graphene basal planes with pyrene-terminated poly(2-N,N'-(dimethyl amino ethyl acrylate) (PDMAEA) and poly(acrylic acid) (PAA) via pi-pi stacking. The pyrene-terminal PDMAEA and PAA were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization with a pyrene-functional RAFT agent. The graphene-polymer composites were found to demonstrate phase transfer behavior between aqueous and organic media at different pH values. Atomic force microscopy (AFM) analysis revealed that the thicknesses of the graphene-polymer sheets were approximately 3.0 nm when prepared using PDMAEA (M(n): 6800 and PDI: 1.12). The surface coverage of polymer chains on the graphene basal plane was calculated to be 5.3 x 10(-11) mol cm(-2) for PDMAEA and 1.3 x 10(-10) mol cm(-2) for PAA. The graphene-polymer composites were successfully characterized using X-ray photoelectron spectroscopy (XPS), attenuated total reflection infrared (ATR-IR) spectroscopy, and thermogravimetric analysis (TGA). Self-assembly of the two oppositely charged graphene-polymer composites afforded layer-by-layer (LbL) structures as evidenced by high-resolution scanning electron microscopy (SEM) and quartz crystal microbalance (QCM) measurements.

Interactions of phenyldithioesters with gold nanoparticles (AuNPs): implications for AuNP functionalization and molecular barcoding of AuNP assemblies

The interactions of phenyldithioesters with gold nanoparticles (AuNPs) have been studied by monitoring changes in the surface plasmon resonance (SPR), depolarised light scattering, and surface enhanced Raman spectroscopy (SERS). Changes in the SPR indicated that an AuNP-phenyldithioester charge transfer complex forms in equilibrium with free AuNPs and phenyldithioester. Analysis of the Langmuir binding isotherms indicated that the equilibrium adsorption constant, K(ads), was 2.3 +/- 0.1 x 10(6) M(-1), which corresponded to a free energy of adsorption of 36 +/- 1 kJ mol(-1). These values are comparable to those reported for interactions of aryl thiols with gold and are of a similar order of magnitude to moderate hydrogen bonding interactions. This has significant implications in the application of phenyldithioesters for the functionalization of AuNPs. The SERS results indicated that the phenyldithioesters interact with AuNPs through the C=S bond, and the molecules do not disassociate upon adsorption to the AuNPs. The SERS spectra are dominated by the portions of the molecule that dominate the charge transfer complex with the AuNPs. The significance of this in relation to the use of phenyldithioesters for molecular barcoding of nanoparticle assemblies is discussed.