Mohsen Moazzami Gudarzi

Self-alignment and high electrical conductivity of ultralarge graphene oxide–polyurethane nanocomposites

Polyurethane (PU)-based composite films containing highly aligned graphene sheets are produced through an environmentally benign process. An aqueous liquid crystalline dispersion of graphene oxide (GO) is in situ reduced in PU, resulting in a fine dispersion and a high degree of orientation of graphene sheets. The PU particles are adsorbed onto the surface of the reduced graphene oxide (rGO), and the rGO sheets with a large aspect ratio of over 10 000 tend to self-align during the film formation when the graphene content is high enough, say more than 2 wt%. The resulting composites show excellent electrical conductivity with an extremely low percolation threshold of 0.078 vol%, which is considered one of the lowest values ever reported for polymer composites containing graphene. The electrical conductivity of the composites with high graphene contents presents significant anisotropy due to the preferential formation of conductive networks along the in-plane direction, another proof of the existence of the self-aligned, layered structure.

Self assembly of graphene oxide at the liquid–liquid interface: A new route to the fabrication of graphene based composites

Dispersion of graphene in a polymer matrix as mono layers is an important step towards fabricating high performance polymer–graphene nanocomposites. In this paper, a novel method based on Pickering emulsion polymerization has been introduced that assures fine dispersion and enhances loading. The major idea is to use a high affinity of graphene oxide (GO) for assembly at the liquid–liquid interface for Pickering emulsion polymerization. A guideline for ensuring stable hybrid colloids of polymer–graphene oxide with an appropriate polymer particle size has been introduced. Then a system of poly (methyl methacrylate) (PMMA)–GO has been selected and the nanocomposites have been made by Pickering emulsion polymerization to examine the theory. TEM studies of the products show various interesting arrangements of PMMA and GO for a different size ratio of nanolayers to polymer particles. The new method paves the way for an environmentally benign process for the production of high quality polymer graphene nanocomposites as it is water-based (no organic solvent is employed) and soap free. Furthermore, resulting hybrid particles were melt mixed with PMMA as a master batch. The resulting nanocomposites with 0.3 wt% graphene showed improved thermal stability and stiffness.

Molecular level dispersion of graphene in polymer matrices using colloidal polymer and graphene.

A novel and environmentally friendly method based on mixing of colloidal polymer particles and graphene sheets has been developed. It is found that colloidal polymers can be employed to stabilize graphene oxide (GO) sheets during reduction to graphene. Adsorption of polymer particles at the surface of graphene layers seems to be underlying mechanism of stabilization of graphene sheets. Surface polarity of the polymer particles is crucial for the successful stabilization of graphene layers. Presence of colloidal particles at the surface of graphene prohibits restacking and agglomeration of nanolayers, resulting in fine dispersion of graphene throughout the polymeric matrix. Formation of strong bond between polar segments of the polymer chain and oxygen groups of graphene sheets generates a strong interface improving final properties of the composites. Inclusion of merely 2 wt% of graphene into an acrylic resin resulted in an increase of 522% and 242% in modulus and hardness, respectively.

Characteristics of polymers that stabilize colloids for the production of graphene from graphene oxide

There is an increasing interest to find cost-effective methods to produce graphene. It is common to produce graphene from the reduction of graphene oxide colloids. The key to this methods success and producing graphene layers is having stable colloids of graphene and graphene oxide. The objective of this paper is to study the characteristics of a polymeric stabilizing agent that ensures stabilization of both graphene and graphene oxide. After providing a theoretical basis for selecting a proper polymer, experimental evaluations are performed to show that only proper polymers with the right molecular weight can serve as the stabilizing agent for both graphene and graphene oxide.

Lightweight flexible polyurethane/reduced ultralarge graphene oxide composite foams for electromagnetic interference shielding

Multifunctional flexible polyurethane (PU)/reduced ultralarge graphene oxide (rUL-GO) composite foams with low density in the range of ∼53–92 kg m−3 were fabricated through the in situ polymerization of PU in the presence of rUL-GO. The incorporation of 1 wt% rUL-GO gave the insular flexible PU composite foams a high electrical conductivity of 4.04 S m−1, and an excellent electromagnetic interference (EMI) shielding efficiency of ∼253 dB (g−1 cm−3) at 8–12 GHz. Achieving such a high specific EMI shielding efficiency as well as a low percolation threshold, combined with the method of foam preparation, results in a uniform dispersion and very high aspect ratio (>20 000) for the rUL-GO nanosheets. Furthermore, by the introduction of rUL-GO, the Young’s modulus and tensile strength of the PU composite foams also improved significantly without reducing the flexibility. TGA experiments also indicated the enhanced thermal stability of the composite foams.

A new approach to using submicron emeraldine-base polyaniline in corrosion-resistant epoxy coatings

The present work reports on a new approach to the preparation of special corrosion-resistant epoxy coatings. The aminic hardener of these coatings contained emeraldine-base polyaniline (EB-PANi). The aminic hardener was prepared by dispersion of EB-PANi in 3-(aminomethyl)-3,5,5-trimethylcyclohexan-1-amine employing sonication, centrifuging and submicron filtering methods. The state of dispersion and dissolution of these coating materials, during different stages of preparation, were characterized by optical microscopy and scanning electron microscopy. The corrosion resistances of resulting coatings were measured by electrochemical impedance spectroscopy (EIS) and salt spray methods. As little as 0.5% EB in initial mixture of EB-hardener compositions led to relatively better corrosion protection of resulting coating compared with neat resin coating. Presence of initial 2.5% of EB in the hardener and its processing through our approach resulted in the formulation of an epoxy coating with superior corrosion protection properties.

Using of p-Phenylenediamine as Modifier of Montmorrilonite for Preparation of Epoxy-Clay Nanocomposites: Morphology and Solvent Resistance Properties

In this article, modification of clay surfaces with an aromatic amine for the increment of dispersion and exfoliation into the epoxy matrix has been investigated. In the solvent media, slurry of hydrophilic clay was mixed and treated with p-phenylenediamine. Structure of the modified clay and the microstructure of the resultant nanocomposite were studied by optical microscopy, X-ray diffraction, transmission electron microscopy and Fourier-transform infrared spectroscopy. Also solvent resistance of resultant nanocomposite evaluated via standard method and compared with which of neat resin. The resultant nanocomposite exhibited a substantial dramatic decrease in solvent uptake compared to the neat resin system.

The Impact of Organoclay on the Physical and Mechanical Properties of Epoxy-Clay Nanocomposite Coatings

Nanocomposite coatings have recently been of interest because of their superior technical, environmental and economical advantages. Some new solvent free nanocomposite coatings were formulated using epoxy resin and montmorillonie (MMt) nanoclay. The organomodified MMt was well dispersed and partially exfoliated in the epoxy resin. The dispersion process comprised high-shear mixing and ultrasonication. The structure of the resultant coatings was characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses. The effect of the clay content on the physical and mechanical properties of the resultant coatings, such as abrasion and impact resistance, hardness, and flexibility were measured and compared with unmodified coatings. The introduction of organoclay up to 4 wt% in coating systems resulted in improvement in the physical and mechanical properties such as hardness (micro and König) and abrasion resistance. Also an increment of up to 3 wt% of organoclay leads to an increase in the impact resistance and flexibility of resultant coating films. On the other hand, flexibility and impact resistance of the coatings containing more than 3 wt% of clay was decreased. The main reason for these observations was agglomeration of the clay particles for high clay-loading compositions.

Enhancement of Nanoclay Dispersion and Exfoliation in Epoxy Using Aminic Hardener Treated Clay

Exfoliation and dispersion of nanoclays in epoxy matrices plays an important role in achieving better physical and mechanical properties of resultant nanocomposites. In this article, modification of clay with an aminic hardener for the increment of dispersion and exfoliation into the epoxy matrix has been investigated. In the solvent media, a slurry of hydrophilic Na-Montmorrilonite was mixed and treated with isophoronediamine (IPDA). The nanocomposites containing epoxy and IPDA-modified clay were produced through a recently developed “slurry compounding” method. Dispersion and exfoliation of the modified clay and the microstructure of the resultant nanocomposite were studied by optical microscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier-transform infrared (FTIR) spectroscopy. The samples were then compared with the high shear mixed and sonicated nanocomposites containing commonly used quaternary ammonium modified clays. The comparison showed that dispersion and exfoliation of hardener-modified organoclays in epoxy have been improved due to the treatment of clay and the compounding method.

Comment on “Colloidal stability of reduced graphene oxide materials prepared using different reducing agents” by Y. Qi, T. Xia, Y. Li, L. Duan and W. Chen, Environ. Sci.: Nano, 2016, 3, 1062

The colloidal stability of graphene oxide (GO) and its reduced forms can be described using classical DLVO theory. This contradicts the claims by Qi et al. (Environ. Sci.: Nano, 2016, 3, 1062–1071). Lower colloidal stability of reduced GO is caused by changes in surface charging and optical properties of GO upon reduction which leads to the suppression of double layer forces but enhancement of van der Waals forces, respectively.