No abstract

Morphology, molecular weight, polydispersity, functionality, and thermal properties are important characteristics when using polyglycerol as a building block in the development of materials for industrial applications such as hydrogels, surfactants, asphalts additives, cosmetics, pharmaceutical, biomedical, and drug delivery systems. In this study several experimental techniques are used to understand the effect of process variables during synthesis in the catalyzed etherification of glycerol, a coproduct of biodiesel industry. Biobased polyglycerol is a high-valued product, which is useful as building block material because of its remarkable features, for instance, multiple hydrophilic groups, excellent biocompatibility, and highly flexible aliphatic polyether backbone. A connection between polyglycerol characteristics and process variables during synthesis allows the control of glycerol polymerization through reaction conditions. We show that temperature and catalyst concentration can be tuned with the aim of tailoring fundamental polyglycerol parameters including molecular weight, polydispersity, morphology, and functionality.

In the current study, we present the synthesis of novel low cost bio‐polyurethane compositions with variable mechanical properties based on castor oil and glycerol for biomedical applications. A detailed investigation of the physicochemical properties of the polymer was carried out by using mechanical testing, ATR‐FTIR, and X‐ray photoelectron spectroscopy (XPS). Polymers were also tested in short term in‐vitro cell culture with human mesenchymal stem cells to evaluate their biocompatibility for potential applications as biomaterial. FTIR analysis confirmed the synthesis of castor oil and glycerol based PU polymers. FTIR also showed that the addition of glycerol as co‐polyol increases crosslinking within the polymer backbone hence enhancing the bulk mechanical properties of the polymer. XPS data showed that glycerol incorporation leads to an enrichment of oxidized organic species on the surface of the polymers. Preliminary investigation into in vitro biocompatibility showed that serum protein adsorption can be controlled by varying the glycerol content with polymer backbone. An alamar blue assay looking at the metabolic activity of the cells indicated that castor oil based PU and its variants containing glycerol are non‐toxic to the cells. This study opens an avenue for using low cost bio‐polyurethane based on castor oil and glycerol for biomedical applications.

Density functional theory is used to investigate the interaction between Pt (111) surfaces, clean and in the presence of atomic and molecular oxygen, as a function of the distance between the two surfaces. It is found that the confinement effect produces a series of new physicochemical phenomena, including changes in the surface−subsurface distance between the approaching surfaces, variations in the adsorption energy of O and O2, and dissociation of molecular oxygen when the separation between surfaces becomes lower than particular threshold distances. It is suggested that these findings may be useful for designing novel devices for catalysis and sensors, and to elucidate the role of cracks in surface degradation behavior.

Density functional theory is used to evaluate activity and stability properties of shell-anchor-core structures. The structures consist of a Pt surface monolayer and a composite core having an anchor bilayer where C atoms in the interstitial sites lock 3d metals in their locations, thus avoiding their surface segregation and posterior dissolution. The modified subsurface geometry induces less strain on the top surface, thus exerting a favorable effect on the surface catalytic activity where the adsorption strength of the oxygenated species becomes more moderate: weaker than on pure Pt(111) but stronger than on a Pt monolayer having a 3d metal subsurface. Here we analyze the effect of changing the nature of the 3d metal in the subsurface anchor bilayer, and we also test the use of a Pd monolayer instead of Pt on the surface. It is found that a subsurface constituted by two layers with an approximate composition of M(2)C (M = Fe, Ni, and Co) provides a barrier for the migration of subsurface core metal atoms to the surface. Consequently, an enhanced resistance against dissolution in parallel to improved oxygen reduction activity is expected, as given by the values of adsorption energies of reaction intermediates, delayed onset of water oxidation, and/or low coverage of oxygenated species at surface oxidation potentials.

Density functional theory (DFT) calculations show changes in geometric and electronic properties of an ethylene molecule confined between two metal surfaces and its conversion into a radical anion monomer ready to react, forming a polymer chain. Here we demonstrate the evolution of the molecular properties under confinement, as well as that of the metal surfaces, and the optimum range of surface−surface separation that allows the production of the radical anion and the dimerization reaction. The effect of an electron donor surface on the already known confinement effect on reactivity is useful not only in many applications where a controlled polymerization is desired but also where specific chemical reactions are sought.

No abstract

Previous work has shown that unusual chemistry can be induced inside metallic slit nanopores. This phenomenon has been attributed to the presence of an enhanced electronic density within the pore. Here we use ab initio density functional theory and post-Hartree− Fock correlated methods to characterize the electronic density in the gap defined by two parallel metallic surfaces. In the first part of this work, the electronic density of states of several transition metal nanopores is calculated for different pore sizes (i.e., surface−surface separations). Results show the existence of a critical surface−surface separation below which electronic states corresponding to the gap between surfaces become populated at energies below the Fermi level of the metal, leading to the presence of electrons in the pore. Further reduction in the nanopore size increases the number of states corresponding to the gap, which agrees with the increasingly higher electronic densities found in the gap for smaller surface−surface separations. In the second part of this work, the presence of electrons in the gap between two finite platinum layers (each layer composed of 4−13 atoms) is assessed using density functional theory and correlated ab initio methods, to analyze the dependence of the electronic density observed in these nanopores on the computational method employed.