Supertoughened Polylactic Acid/Polybutylene Adipate Terephthalate Blends Compatibilized with Ethylene-Methyl Acrylate-Glycidyl Methacrylate: Morphology and Mechanical Properties by the Response Surface Methodology.

Optimized extrusion melt-blending of polylactic acid (PLA) polymer with a minor biopolymeric phase, polybutylene adipate terephthalate (PBAT), and compatibilized with random ethylene-methyl acrylate-glycidyl methacrylate terpolymer (EMA-GMA, Trademark: Lotader AX-8900) led to an outstanding improvement in mechanical properties. At the noncompatibilized PLA-PBAT (80-20) blend point, significant enhancement (∼4500%) in toughness and elongation-at-break was already obtained without compromising any elastic properties. The effect of the compatibilizer content on the mechanical properties of the PLA-PBAT (80-20) blend was investigated by an optimal custom response surface methodology. Thus, 2 wt % Lotader content was determined to be optimal by a numerical optimization methodology with a desirability value, D, of 0.882 to maximize toughness and elongation-at-break. The compatibilization and thermal behavior of the Lotader-modified blends were analyzed by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Upon adding the compatibilizer, the original phase-separated morphology of the blends changed from PBAT quasi-spherical domains to nearly elongated elliptical ones. It was also found that the interfacial boundary line of the domains faded away, which revealed that interfacial compatibility was achieved. The thermostability of the blends remained largely unaltered following the incorporation of PBAT and Lotader. Moreover, while PBAT exhibited a minor influence on the crystallinity of PLA, Lotader had no discernible impact on crystallinity, as evidenced by the DSC thermograms. Thus, the compatibilizer at the optimal point in the optimized blend ratio led to the formation of a phase-separated morphology that combined internal cavitation, interfacial cavitation, and strong adhesion features at the right proportions in the microstructure which underlies the micromechanisms driving the remarkable enhancement of as much as 7100% in toughness and ductility.

Polyurea/Aminopropyl Isobutyl Polyhedral Oligomeric Silsesquioxane-Functionalized Graphene Nanoplatelet Nanocomposites for Force Protection Applications.

Herein, the development of new nanocomposite systems is reported based on one-part polyurea (PU) and aminopropyl isobutyl polyhedral oligomeric silsesquioxane (POSS)-functionalized graphene nanoplatelets (GNP-POSS) as compatible nanoreinforcements with the PU resin. GNP-POSS was effectively synthesized via a two-step synthesis protocol, including ultrasonication-assisted reaction and precipitation, and carefully characterized with respect to its chemical and crystalline structure, morphology, and thermal stability. FTIR and XPS spectroscopy analyses revealed that POSS interacts with the residual oxygen moieties of the GNPs through both covalent and noncovalent bonding. The X-ray diffraction pattern of GNP-POSS further revealed that the crystallinity of the GNPs was not altered after their functionalization with POSS. GNP-POSS was successfully incorporated in PU at contents of 1, 3, 5, and 10 wt % to yield PU/GNP-POSS nanocomposite films. An ATR-FTIR analysis of these films confirmed the presence of strong interfacial interactions between the urea groups of PU and the GNP-POSS functionalities. Moreover, the PU/GNP-POSS nanocomposite films exhibited enhanced thermal stability and mechanical properties compared to those of the neat PU film. The quasi-static tensile testing of the PU/GNP-POSS samples revealed remarkable enhancements in the tensile strength (from 7.9 for the neat PU to 25.1 MPa for PU/GNP-POSS) and Young's modulus (238-617 MPa), while elongation at break and toughness also showed 14 and 125% improvements, respectively. Finally, the effects of GNP-POSS content on the morphological, quasistatic tensile, and high-strain-rate dynamic behavior of the PU/GNP-POSS nanocomposite films were also investigated. Overall, the tests performed using a split-Hopkinson pressure bar setup revealed a large increase in the film strength (from 147.6 for the neat PU film to 199 MPa for the PU/GNP-POSS film) and a marginal increase in the energy density of the film (38.1-40.8 kJ/m3). These findings support the suitability of the PU/GNP-POSS nanocomposite films for force protection applications.

Graphitic Carbon Nitride Quantum Dots (g-C3N4 QDs): From Chemistry to Applications.

Since their emergence in 2014, graphitic carbon nitride quantum dots (g-C3N4 QDs) have attracted much interest from the scientific community due to their distinctive physicochemical features, including structural, morphological, electrochemical, and optoelectronic properties. Owing to their desirable characteristics, such as non-zero band gap, ability to be chemically functionalized or doped, possessing tunable properties, outstanding dispersibility in different media, and biocompatibility, g-C3N4 QDs have shown promise for photocatalysis, energy devices, sensing, bioimaging, solar cells, optoelectronics, among other applications. As these fields are rapidly evolving, it is very strenuous to pinpoint the emerging challenges of the g-C3N4 QDs development and application during the last decade, mainly due to the lack of critical reviews of the innovations in the g-C3N4 QDs synthesis pathways and domains of application. Herein, an extensive survey is conducted on the g-C3N4 QDs synthesis, characterization, and applications. Scenarios for the future development of g-C3N4 QDs and their potential applications are highlighted and discussed in detail. The provided critical section suggests a myriad of opportunities for g-C3N4 QDs, especially for their synthesis and functionalization, where a combination of eco-friendly/single step synthesis and chemical modification may be used to prepare g-C3N4 QDs with, for example, enhanced photoluminescence and production yields.

Introducing photo-crosslinked bio-nanocomposites based on polyvinylidene fluoride/poly(glycerol azelaic acid)-g-glycidyl methacrylate for bone tissue engineering.

As a glycerol-based polyester, poly(glycerol azelaic acid) (PGAz) has shown great potential for biomedical applications, such as tissue engineering. However, it tends to show low mechanical strength and a relatively fast biodegradation rate, limiting its capability of mimicking and supporting a broad range of hard tissues such as bone. Moreover, the typical thermal curing process of poly(glycerol-co-diacids) is one of their drawbacks. To overcome these limitations, glycidyl methacrylate (GMA) moieties were first grafted on the backbone of PGAz herein to achieve a UV-curable PGAz-g-GMA (PGAG) resin. Then polyvinylidene fluoride (PVDF), nano-hydroxyapatite, and Cloisite Na+ nanoclay were used to fabricate photo-crosslinked PGAG/PVDF nanocomposites with efficient properties to mimic various hard tissues. Our results demonstrated that all nanocomposites possessed a semi-crystalline structure with noticeable PVDF ß-phase fraction. The scaffolds yielded Young's modulus, ultimate tensile strength, and elongation at break of 15-24 MPa, 13-15 MPa, and 50-65%, respectively that could meet the requirements for supporting cancellous bone tissue. The presence of nanofillers improved the hydrophilicity and slightly accelerated the biodegradation rate of the scaffolds. Additionally, it was illustrated that the scaffolds had no noticeable in vitro cytotoxicity, and mouse fibroblast L929 cells and osteoblast MG-63 cells attached to and proliferated on their surface desirably. Our findings indicate that the PGAG/PVDF blend and its nanocomposites could be high-potential candidates for a range of hard tissues, specifically cancellous bones.

Highly antifouling polymer-nanoparticle-nanoparticle/polymer hybrid membranes.

We introduce highly antifouling Polymer-Nanoparticle-Nanoparticle/Polymer (PNNP) hybrid membranes as multi-functional materials for versatile purification of wastewater. Nitrogen-rich polyethylenimine (PEI)-functionalized halloysite nanotube (HNT-SiO2-PEI) nanoparticles were developed and embedded in polyvinyl chloride (PVC) membranes for protein and dye filtration. Bulk and surface characteristics of the resulting HNT-SiO2-PEI nanocomposites were determined using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). Moreover, microstructure and physicochemical properties of HNT-SiO2-PEI/PVC membranes were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), and attenuated total reflectance (ATR)-FTIR. Results of these analyses indicated that the overall porosity and mean pore size of nanocomposite membranes were enhanced, but the surface roughness was reduced. Additionally, surface hydrophilicity and flexibility of the original PVC membranes were significantly improved by incorporating HNT-SiO2-PEI nanoparticles. Based on pure water permeability and bovine serum albumin (BSA)/dye rejection tests, the highest nanoparticle-embedded membrane performance was observed at 2 weight percent (wt%) of HNT-SiO2-PEI. The nanocomposite incorporation in the PVC membranes further improved its antifouling performance and flux recovery ratio (96.8%). Notably, dye separation performance increased up to 99.97%. Overall, hydrophobic PVC membranes were successfully modified by incorporating HNT-SiO2-PEI nanomaterial and better-quality wastewater treatment performance was obtained.

Hyperbranched polyethylenimine functionalized silica/polysulfone nanocomposite membranes for water purification.

Hyperbranched polyethyleneimine functionalized silica (PEI-SiO2) nanoparticles with considerable hydrophilicity were synthesized and incorporated into a polysulfone (PSF)/dimethylacetamide (DMA)/polyvinylpyrrolidone (PVP) membrane casting solution in five different ratios to fabricate PEI-SiO2/PSF nanocomposite membranes using nonsolvent-induced phase separation. The hydrophilic PEI-SiO2 nanoparticles were characterized by TEM, FTIR, TGA, and XPS analyses. Morphology, water contact angles, mean pore sizes, overall porosity, tensile strengths, water flux, antifouling and the dye separation performances of the PEI-SiO2/PSF membranes were also studied. The PEI-SiO2 nanoparticles were uniformly dispersed in the PSF-based membranes, where a fall in the water contact angle was observed from 65.4° to 49.7° by addition of 2 wt% nanoparticles. The fouling resistance parameters of the PEI-SiO2/PSF membranes were declined with an increase in the nanoparticle concentration, suggesting the superior hydrophilic nature of the PEI-SiO2 nanoparticles. The permeability of the nanocomposite membranes was increased from 38.5 to 70 L m-2 h-1 bar-1 by incorporation of 2 wt% PEI-SiO2. Finally, improvements were observed in the flux recovery ratio (95.8%), Reactive Green 19 dye rejection (99.6%) and tensile strengths of the PEI-SiO2/PSF membranes over the neat PSF and SiO2/PSF membranes, which were used as controls. The results of this study demonstrate the promising application of PEI-SiO2 nanoparticles in improving the separation and antifouling performances of the PSF membranes for water purification.

Effects of Ionic Liquid Nanoconfinement on the CO2/CH4 Separation in Poly(vinylidene fluoride)/1-Ethyl-3-methylimidazolium Thiocyanate Membranes.

A combined experimental and molecular dynamics (MD) simulation approach was used to investigate the effects of the nanoconfinement of a highly CO2/CH4-selective ionic liquid (IL), 1-ethyl-3-methylimidazolium thiocyanate ([EMIM][SCN]), in porous poly(vinylidene fluoride) (PVDF) matrices on the gas separation performance of the resulting membranes. The observed experimental CO2/CH4 permselectivity increased by about 46% when the nominal pore diameter in PVDF, which is a measure of nanoconfinement, decreased from 450 to 100 nm, thus demonstrating nanoconfinement improvements of gas separation. MD simulations corroborated these experimental observations and indicated a suppression in the sorption of CH4 by [EMIM][SCN] when the IL nanoconfinement length decreased within the nonpolar PVDF surfaces. This is consistent with the experimental observation that the CH4 permeance through the IL confined in nonpolar PVDF is significantly less than the CH4 permeance through the IL confined in a water-wetting polar formulation of PVDF. The potential of mean force calculations further indicated that CO2 has more affinity to the nonpolar PVDF surface than CH4. Also, a charge/density distribution analysis of the IL in the PVDF-confined region revealed a layering of the IL into [EMIM]- and [SCN]-rich regions, where CH4 was preferentially distributed in the former and CO2 in the latter. These molecular insights into the nanoconfinement-driven mechanisms in polymer/IL membranes provide a framework for a better molecular design of such membranes for critical gas separation and CO2 capture applications.

Molecular Insights into the Loading and Dynamics of Doxorubicin on PEGylated Graphene Oxide Nanocarriers.

Molecular dynamics (MD) simulations were performed to investigate the loading and dynamics of doxorubicin (DOX) anticancer drug on graphene oxide (GO) and poly(ethylene glycol) (PEG) decorated GO (PEGGO) nanocarriers in an aqueous environment at human body temperature (310 K) and physiological pH level of 7.4. Mechanisms of DOX adsorption on PEGGO as a function of PEG chain length were revealed. While the total DOX-nanocarrier interaction energy was the same for the DOX/GO (control), DOX/Sh-PEGGO (short PEG chains consisting of 15 repeat units), and DOX/L-PEGGO (long PEG chains consisting of 30 repeat units) within the margin of error, the PEG-DOX interactions increased with an increase in the PEG chain length. At the same time, the PEG-DOX solvent-accessible contact area almost doubled going from the short to long PEG chains. PEGylation of the GO effectively causes an increase in the average water density around the nanocarrier, which can act as a barrier, leading to the DOX migration to the solvated PEG-free part of the GO surface. This effect is more pronounced for shorter PEG chains. The DOX-DOX solvent-accessible contact area is smaller in the DOX/GO system, which means the drug molecules are less aggregated in this system. However, the level of DOX aggregation is slightly higher for the PEGGO systems. The computational results in this work shed light on the fact that increasing the PEG chain length benefits DOX loading on the nanocarrier, revealing an observation that is difficult to acertain through experiments. Moreover, a detailed picture is provided for the DOX adsorption and retention in PEGGO drug delivery systems, which would enable the researchers to improve the drug's circulation time, as well as its delivery and targeting efficiency.

Doxorubicin Stability and Retention on PEGylated Graphene Oxide Nanocarriers Adjacent to Human Serum Albumin.

Drug stability and retention on nanocarriers is essential for maximizing the drug targeting and therapeutic efficiency. PEGylation of graphene oxide (GO) as a drug nanocarrier is widely known to prolong its circulation time in the body, thereby increasing the probability of drug delivery system interactions with the proteins in the blood stream. Herein, molecular dynamics (MD) simulations were performed to investigate the interactions between doxorubicin (DOX)-loaded GO and PEGylated GO (PEGGO) nanocarriers with human serum albumin (HSA), a prevalent human blood protein and among the first to be adsorbed on the DOX-loaded nanocarriers. The results indicate that drug stability and retention on PEGGO nanocarriers are far more superior to the GO nanocarriers (control) when in contact with HSA. It is also demonstrated in this work that the PEGGO nanocarriers retain the DOX molecules irrespective of the HSA Sudlow site I and II orientations, thereby revealing their robustness in DOX loading.

Reactive Molecular Simulation of the Damage Mitigation Efficacy of POSS-, Graphene-, and Carbon Nanotube-Loaded Polyimide Coatings Exposed to Atomic Oxygen Bombardment.

Reactive molecular dynamics simulation was employed to compare the damage mitigation efficacy of pristine and polyimide (PI)-grafted polyoctahedral silsesquioxane (POSS), graphene (Gr), and carbon nanotubes (CNTs) in a PI matrix exposed to atomic oxygen (AO) bombardment. The concentration of POSS and the orientation of Gr and CNT nanoparticles were further investigated. Overall, the mass loss, erosion yield, surface damage, AO penetration depth, and temperature evolution are lower for the PI systems with randomly oriented CNTs and Gr or PI-grafted POSS compared to those of the pristine POSS or aligned CNT and Gr systems at the same nanoparticle concentration. On the basis of experimental early degradation data (before the onset of nanoparticle damage), the amount of exposed PI, which has the highest erosion yield of all material components, on the material surface is the most important parameter affecting the erosion yield of the hybrid material. Our data indicate that the PI systems with randomly oriented Gr and CNT nanoparticles have the lowest amount of exposed PI on the material surface; therefore, a lower erosion yield is obtained for these systems compared to that of the PI systems with aligned Gr and CNT nanoparticles. However, the PI/grafted-POSS system has a significantly lower erosion yield than that of the PI systems with aligned Gr and CNT nanoparticles, again due to a lower amount of exposed PI on the surface. When comparing the PI systems loaded with PI-grafted POSS versus pristine POSS at low and high nanoparticle concentrations, our data indicate that grafting the POSS and increasing the POSS concentration lower the erosion yield by a factor of about 4 and 1.5, respectively. The former is attributed to a better dispersion of PI-grafted POSS versus that of the pristine POSS in the PI matrix, as determined by the radial distribution function.

Interatomic Potential for Hydrocarbons on the Basis of the Modified Embedded-Atom Method with Bond Order (MEAM-BO).

In this paper, we develop a new modified embedded atom method (MEAM) potential that includes the bond order (MEAM-BO) to describe the energetics of unsaturated hydrocarbons (double and triple carbon bonds) and also develop improved parameters for saturated hydrocarbons from those of our previous work. Such quantities like bond lengths, bond angles, and atomization energies at 0 K, dimer molecule interactions, rotational barriers, and the pressure-volume-temperature relationships of dense systems of small molecules give a comparable or more accurate property relative to experimental and first-principles data than the classical reactive force fields REBO and ReaxFF. Our extension of the MEAM potential for unsaturated hydrocarbons (MEAM-BO) is a step toward developing more reliable and accurate polymer simulations with their associated structure-property relationships, such as reactive multicomponent (organic/metal) systems, polymer-metal interfaces, and nanocomposites. When the constants for the BO are zero, MEAM-BO reduces to the original MEAM potential. As such, this MEAM-BO potential describing the interaction of organic materials with metals within the same MEAM formalism is a significant advancement for computational materials science.

Molecular simulation of pH-dependent diffusion, loading, and release of doxorubicin in graphene and graphene oxide drug delivery systems.

In this study, the adsorption of doxorubicin (DOX), an anticancer drug, on pristine graphene (PG) and graphene oxide (GO) nanocarriers with different surface oxygen densities and in an aqueous environment with varying pH levels was investigated using molecular dynamics (MD) simulation. The drug loading and release on the GO nanocarrier was also simulated using pH as the controller mechanism. Overall, the DOX/nanocarrier interactions become stronger as the graphene surface oxygen density increases. Although pH has a negligible effect on the single-molecule drug adsorption on the GO surfaces under acidic and neutral conditions, significantly stronger DOX/nanocarrier interactions occur for the GO nanosheet with a lower surface oxygen density (GO-16, with an O/C ratio of 1 : 6) at basic pH levels. Moreover, the DOX/nanocarrier interactions are greatly weakened in the GO nanosheet with higher surface oxygen density (GO-13, with an O/C ratio of 1 : 3) under basic conditions. These observations are partly attributed to a more favorable geometry of the DOX molecule on the GO-16 surface as opposed to a loosely attached DOX molecule on the edges of the GO-13 nanosheet. When comparing the adsorption kinetics and transport properties of the DOX molecule in different GO systems, the drug diffusion coefficient increases with decreasing pH value (going from basic to neutral to acidic) due to the reduced total water-nanocarrier interactions. The latter observation is an indication of the more facilitated transport of the DOX molecule in an aqueous medium towards the nanocarrier surface at lower pH levels. Finally, we have confirmed the loading and release of the DOX molecules on the GO nanocarrier under neutral (pH = 7) and acidic (pH = 5) conditions, respectively. The former signifies the blood pH level, whereas the latter is reminiscent of the pH of a tumorous cell. The computational results presented in this work reveal the underlying mechanisms of DOX loading and release on PG and GO surfaces, which may be used to design better graphene-based nanocarriers for the DOX delivery and targeting applications.