Poly(methyl methacrylate) Nanocomposite Foams Reinforced with Carbon and Inorganic Nanoparticles—State-of-the-Art

Thermophysical properties of graphene reinforced with polymethyl methacrylate nanoparticles for technological applications: a molecular model

CONTEXT

"Nanostructure of graphene-reinforced with polymethyl methacrylate" (PMMA-G), and vice versa, is investigated using its molecular structure, in the present work. The PMMA-G nanostructure was constructed by bonding PMMA with graphene nanosheet in a sense to get three different configurations. Each configuration consisted of polymeric structures with three degrees of polymerization (such as monomers, dimers, and trimers polymers, respectively). The results obtained make this new PMMA-G material more reliable and useful for several important technological applications, such as the construction of devices for hydrogen storage, batteries, super-capacitors, sensors and solar cells, and dental materials, among others. The PMMA reinforcement with graphene favors its thermal stability maintaining greater dimensional stability against thermal variations (minimal deformation); this is crucial for electronic devices and for packaging systems that undergo repeated thermal cycles during their manufacture, and also they are good thermal insulators. For microelectronic devices, such as chips and sensors, with low thermal expansion coefficients, it may prevent unwanted deformation. The PMMA density increases when it is reinforced with graphene, the polymers tend to be stiffer and stronger, important for applications where greater structural strength is required, and also become less soluble in solvents than pure PMMA and more resistant to the action of chemicals. Comparing a common polyvinyl chloride (PVC) material with the PMMA-G polymer, we found more advantages, such as the PMMA-G is less expensive, it has improved aesthetics, it is less rigid, it has more stable color, and it is less prone to keeping microorganisms alive, among others advantages.

METHODS

Materials Studio (MS) software is used as the best and most reliable computational tool in the sense of analyzing some thermophysical properties of graphene reinforced with polymethyl methacrylate nanoparticles. The most stable PMMA nanostructures, graphene and PMMA-G, were obtained by applying density functional theory methods implemented by a DMol3 computational code under the MS software. The Synthia computational code, also under MS software, which is based on connectivity indices methods derived from graph theory combined with geometric variables, was also applied, to each polymerized structure, obtaining some of the important thermophysical properties; i.e., Van der Waals volume, molar volume, coefficient of volumetric thermal expansion, density, solid phase molar heat capacity at constant pressure, thermal conductivity, glass transition temperature, secondary relaxation temperature, and half decomposition temperature. The best-used hardware was a T7500 Dell Workstation, with 3.47 GHz Quad-Core Processors, 96 Gb RAM memory, and a perpetual MS software license.

Effect of graphene on the key electrical, optical, and magnetic properties of polymethylmethacrylate: a study based on molecular modeling

CONTEXT

In this work, a new polymeric structure was designed consisting of a nanometric sheet of graphene (G) and a polymethylmethacrylate (PMMA) repeat unit, which was designated as PMMA-G. Three degrees of polymerization of PMMA-G were considered: monomer (PMMA-G1), dimer (PMMA-G2), and trimer (PMMA-G3). The effect of incorporating a nanometric sheet of graphene into the molecular structure of PMMA on the modification of some of its main optical, magnetic, and electrical properties was investigated. Currently, the study presented here is of great relevance since various areas of technology require new materials with specific properties for the development of new devices. The results of our study reveal that the dielectric constant of PMMA is reduced when graphene is incorporated. However, a percentage increase of 14.48% in the refractive index of PMMA when graphene is inserted to form the nanocomposite is observed. It is found that the absolute value of molar magnetic susceptibility of PMMA increases considerably when reinforced with graphene. Finally, when reinforcing PMMA with graphene to obtain the PMMA-G nanocomposite, the electrical resistivity increases by almost an order of magnitude.

METHODS

We used computational tools under Materials Studio (MS) software. We built a PMMA molecule with three degrees of polymerization, graphene sheet, and polymethylmethacrylate-graphene composite (PMMA-G) was built also with three degrees of polymerization using a concentration of 50% graphene over the PMMA polymer. For each structure, we used computational code DMol3 of MS, which is based on the Density Functional Theory, and the geometry optimization process was carried out to obtain the most stable structures. Finally, using the connectivity indices method together with topological properties of the molecular structures, implemented in Synthia computational code of MS software, we calculated the dielectric constant, magnetic susceptibility, refractive index, and electrical resistivity, for pure PMMA and PMMA-G structures for their three degrees of polymerization. The results were analyzed, and the changes in these properties were discussed in terms of the effect of an electric and magnetic field on the molecular structures of PMMA-G with respect to PMMA.

Influence of High Energy Ball Milling and Dispersant on Capacitive Properties of Fe2O3—Carbon Nanotube Composites

This investigation is motivated by increasing interest in ferrimagnetic materials and composites, which exhibit electrical capacitance. It addresses the need for the development of magnetic materials with enhanced capacitive properties and low electrical resistance. γ-Fe2O3-multiwalled carbon nanotube (MWCNT) composites are developed by colloidal processing and studied for energy storage in negative electrodes of supercapacitors. High energy ball milling (HEBM) of ferrimagnetic γ-Fe2O3 nanoparticles results in enhanced capacitive properties. The effect of HEBM on particle morphology is analyzed. Gallocyanine is used as a co-dispersant for γ-Fe2O3 and MWCNTs. The polyaromatic structure and catechol ligand of gallocyanine facilitated its adsorption on γ-Fe2O3 and MWCNTs, respectively, and facilitated their electrostatic dispersion and mixing. The adsorption mechanisms are discussed. The highest capacitance of 1.53 F·cm−2 is achieved in 0.5 M Na2SO4 electrolyte for composites, containing γ-Fe2O3, which is high energy ball milled and co-dispersed with MWCNTs using gallocyanine. HEBM and colloidal processing strategies allow high capacitance at low electrical resistance, which facilitates efficient charge–discharge. Obtained composites are promising for fabrication of multifunctional devices based on mutual interaction of ferrimagnetic and capacitive properties.