Construction of a Different Polymer Chain Structure to Study π-π Interaction between Polymer and Reduced Graphene Oxide

Microwave-Assisted Self-Healable Biovitrimer/rGO Framework for Anticorrosion Applications

Microwave-stimulated smart self-healable polymeric coatings with significant protective technology against corrosion have been developed in this work. Herein, a generous approach is strategized to generate linseed oil-derived epoxy composites embedded with reduced graphene oxide (rGO) as a nanofiller in the shielding network. The composite showed excellent self-healing and shape memory properties when irradiated with microwaves due to the dynamic reversible nature of the disulfide covalent bond exchange mechanism. The network also has improved thermomechanical properties and thermal stability, with a storage modulus of 20.8 GPa and a low activation energy of 79 kJ/mol, indicating a fast disulfide dynamic exchange reaction. The amine functionality in the composite contributes to excellent corrosion protection, with 99.9% protection efficiency, as validated via a Tafel plot. The composite also showed excellent hydrophobicity, with a 131° contact angle. This study provides insights into the engineering and application of smart materials as anticorrosive coatings.

From waste to energy storage: post-consumer waste expanded polystyrene/rGO composite as a high performance self-standing electrode for coin cell supercapacitors

This research work aims to explore the potential usage of post-consumer waste expanded polystyrene (EPS) for the fabrication of self-standing electrodes by incorporating reduced graphene oxide (rGO) into it via a facile cost-effective mechanical mixing process. The π-π interaction between the expanded polystyrene and rGO is evidenced from FT-IR and Raman analysis. The elevated thermal stability of the EPS/rGO composite from thermogravimetric analysis (TGA) further confirms the interconnection between the rGO and EPS. This π-π stacking interaction between the rGO and the polystyrene molecules present in the polymer matrix enable the composite material to be interconnected throughout which is beneficial for the charge transport process. The symmetric coin cell supercapacitor fabricated using the EPS/rGO composite electrode can be operated with a high operating voltage of 1.6 V in aqueous KOH and Na2SO4 electrolytes. The devices fabricated with KOH and Na2SO4 electrolytes deliver an areal capacitance of 11.9 mF cm-2 and 10 mF cm-2 at the discharge current density of 0.1 mA cm-2. Further, the devices fabricated with the KOH and Na2SO4 electrolytes demonstrated remarkable rate capability of 87.1% and 99.5% after 10 000 continuous charge discharge cycles. This facile method of preparation without consuming energy or polluting the environment is a novel approach which can be scaled-up to large-scale fabrication of self-standing plastic electrodes for low-cost energy storage applications.

Luminescent Hybrid BPA.DA-NVP@Eu2L3 Materials: In Situ Synthesis, Spectroscopic, Thermal, and Mechanical Characterization

A series of homogeneous hybrid BPA.DA-NVP@Eu2L3 materials were obtained through an in situ approach where the luminescent dopant was formed at the molecular level with different contents (0.1; 0.2; 0.5; 1; and 2% by weight). A Europium(III) complex (Eu2L3) with quinoline-2,4-dicarboxylic acid was applied as a luminescence additive while a polymer matrix consisted of a combination of bisphenol A diacrylate (BPA.DA) and N-vinylpyrrolidone (NVP) monomers. Synthesis steps and the final materials were monitored by NMR and Fourier transform infrared spectroscopy (FTIR). The emission, excitation spectra, lifetime, and quantum yield measurements were applied for the determination of the photophysical characteristics. The thermal and mechanical properties of the obtained materials were tested via thermal analysis methods (TG/DTG/DSC and TG-FTIR) in air and nitrogen atmospheres, dynamic mechanical analysis (DMA), and hardness and bending measurements. Generally, even a small addition of the metal complex component causes changes in the thermal, mechanical, and luminescent properties. Hybrid materials with a greater europium complex content are characterized by a lower stiffness and hardness while the heterogeneity and the flexibility of the samples increase. A very small amount of an Eu2L3 admixture (0.1% wt.) in a hybrid material causes an emission in the red spectral range and the luminescence intensity was reached for the BPA-DA-NVP@1%Eu2L3 material. These materials may be potentially used in chemical sensing, security systems, and protective coatings against UV.

Fabrication of high strength and functional GO/PVA/PAN ternary composite fibers by gel spinning

Polyacrylonitrile (PAN) fiber is soft and comfortable, but its poor strength compared to other synthetic fibers has limited it wide range of applications. This study effectively improved the strength of PAN fibers by adding graphene oxide (GO) and polyvinyl alcohol (PVA) during PAN spinning. The composite fibers were prepared via gel spinning and subsequent hot drawing process. The results show that the PVA molecular chains embedded into the PAN molecular chain significantly improved the mechanical properties of the hybrid fiber. At the same time, the defect reduced the UV resistance and thermal stability of the hybrid fibers only when the PVA molecular was introduced in the PAN. Surprisingly, after the recomposition of GO in the above mixed polymer system, the interaction between the GO and matrix not only improved the mechanical properties of the fiber, but also enhanced the UV resistance and thermal stability. In addition, when the amount of GO was 0.3 wt%, the crystallinity of the GO/PVA/PAN composite fiber reached the maximum and the tensile strength was the highest. This strategic approach suggests an effective method to prepare graphene-based ternary composites fibers with high strength and novel functional characteristics.

Vertical Alignment of Liquid Crystal on Sustainable 2,4-Di-tert-butylphenoxymethyl-Substituted Polystyrene Films

We synthesized sustainable 2,4-di-tert-butylphenoxymethyl-substituted polystyrenes (PDtBP#, # = 88, 68, 35, and 19, where # is molar percent contents of 2,4-di-tert-butylphenoxymethyl moiety), using post-polymerization modification reactions in order to study their liquid crystal (LC) alignment behaviors. In general, LC cells fabricated using polymer film with higher molar content of 2,4-di-tert-butylphenoxymethyl side groups showed vertical LC alignment behavior. LC alignment behavior in LC cell was related to the surface energy of the polymer alignment layer. For example, when the total surface energy value of the polymer layer was smaller than about 29.4 mJ/m2, vertical alignment behaviors were observed, generated by the nonpolar 2,4-di-tert-butylphenoxymethyl moiety with long and bulky carbon groups. Orientation stability was observed at 200 °C in the LC cells fabricated using PDtBP88 as the LC alignment layer. Therefore, as a natural compound modified polymer, PDtBP# can be used as a candidate LC alignment layer for environmentally friendly applications.

Hyaluronic Acid and Graphene Oxide-incorporated Hyaluronic Acid Hydrogels for Electrically Stimulated Release of Anticancer Tamoxifen Citrate

Transdermal drug delivery is the transport of drug across the skin and into the systemic circulation. Patch is a one of transdermal device that is used to attach on skin and contains drug. The drug matrices from hyaluronic acid (HA) and graphene oxide (GO) incorporated HA hydrogel were fabricated for the release of tamoxifen citrate (TMX) as the anticancer drug under applied electrical field. The pristine HA hydrogels as the matrix and GO as the drug encapsulation host were fabricated for transdermal patch by the solution casting using citric acid as the chemical crosslinker. In vitro drug release experiment was investigated by utilizing the modified Franz-diffusion cell under the effects of crosslinking ratio, electric potential, and GO. The TMX release behaviors from the hydrogels were found to be from the three mechanisms: the pure Fickian diffusion; the anomalous or non-Fickian diffusion; and Super case II transport depending on the crosslinking conditions. The TMX diffusion and release amount from the pristine HA hydrogels were increased with smaller crosslinking ratios. With applied electrical potential, the enhanced TMX diffusion and release amount were observed when compared to that without due to the electro-repulsive force. Furthermore, the TMX diffusion from the HA hydrogel with GO as the drug encapsulation host was higher by two orders of magnitude than without GO.

Controlling Graphene Wrinkles through the Phase Transition of a Polymer with a Low Critical Solution Temperature

A novel method for controlling reduced graphene oxide (rGO) wrinkles through a phase transition in a solution using a low critical solution temperature (LCST) polymer dispersant has been developed. The polymer dispersant is designed by control of architecture and composition using reversible addition-fragmentation chain transfer polymerization. Synthesized poly(2-(dimethylaminoethyl) methacrylate-block-styrene) (PDbS) can be successfully functionalized on the rGO surface via noncovalent functionalization. PDbS-functionalized rGO (PDbS-rGO) exhibits good dispersibility in an aqueous phase at room temperature and forms wrinkles on the PDbS-rGO surface because of phase transition at the LCST of the polymer dispersant. The formation of PDbS-rGO wrinkles is controlled by varying the aggregation number of the polymer dispersant on the PDbS-rGO surface that strongly depends on temperature. This is confirmed by transmission electron microscopy, scanning electron microscopy, and Raman spectroscopy (I_D' /I_G ratios are 0.560, 0.579, and 0.684, which correspond to 45, 70, and 95 °C, respectively). In addition, the mechanism of wrinkle control is proved by gold nanoparticles that are grown in polymer dispersant on the PDbS-rGO surface.

The Role of Interfacial Adhesion in Polymer Composites Engineered from Lignocellulosic Agricultural Waste

This paper presents a comprehensive study about the application of a lignocellulosic agricultural waste, sunflower husk in different polymer composites. Two types of milled sunflower husk with different geometrical factors were incorporated into polypropylene, low-density and high-density polyethylene, polystyrene (PS), glycol-modified polyethylene terephthalate (PETG) and polylactic acid (PLA). The filler content of the composites varied between 0 and 60 vol%. The components were homogenized in an internal mixer and plates were compression molded for testing. The Lewis-Nielsen model was fitted to the moduli of each composite series, and it was found that the physical contact of the filler particles is a limiting factor of composite modulus. Interfacial interactions were estimated from two independent approaches. Firstly, the extent of reinforcement was determined from the composition dependence of tensile strength. Secondly, the reversible work of adhesion was calculated from the surface energies of the components. As only weak van der Waals interactions develop in the interphase of polyolefins and sunflower husk particles, adhesion is weak in their composites resulting in poor reinforcement. Interfacial adhesion enhanced by specific interactions in the interphase, such as π electron interactions for PS, hydrogen bonds for PLA, and both for PETG based composites.

Insights from modeling into structure, entanglements, and dynamics in attractive polymer nanocomposites

Conformations, entanglements and dynamics in attractive polymer nanocomposites are investigated in this work by means of coarse-grained molecular dynamics simulation, for both weak and strong confinements, in the presence of nanoparticles (NPs) at NP volume fractions φ up to 60%. We show that the behavior of the apparent tube diameter dapp in such nanocomposites can be greatly different from nanocomposites with nonattractive interactions. We find that this effect originates, based on a mean field argument, from the geometric confinement length dgeo at strong confinement (large φ) and not from the bound polymer layer on NPs (interparticle distance ID <2Rg) as proposed recently based on experimental measurements. Close to the NP surface, the entangled polymer mobility is reduced in attractive nanocomposites but still faster than the NP mobility for volume fractions beyond 20%. Furthermore, entangled polymer dynamics is hindered dramatically by the strong confinement created by NPs. For the first time using simulations, we show that the entangled polymer conformation, characterized by the polymer radius of gyration Rg and form factor, remains basically unperturbed by the presence of NPs up to the highest volume fractions studied, in agreement with various experiments on attractive nanocomposites. As a side-result we demonstrate that the loose concept of ID can be made a microscopically well defined quantity using the mean pore size of the NP arrangement.