Search results for "FILMS"
showing 10 items of 2839 documents
Study on compatibilization of polypropylene-liquid crystalline polymer blends
1997
The mechanical properties, melt rheology, and morphology of binary blends comprised of two polypropylene (PP) grades and two liquid crystalline polymers (LCP) have been studied. Compatibilization with polypropylene grafted with maleic anhydride (PP-g-MAH) has been attempted. A moderate increase in the tensile moduli and no enhancements in tensile strength have been revealed. Those findings have been attributed to the morphology of the blends, which is predominantly of the disperse mode. LCP fibers responsible for mechanical reinforcement were only exceptionally evidenced. Discussion of PP-LCP interfacial characteristics with respect to mechanical properties-morphology interrelations allowed…
Aqueous Laponite Clay Dispersions in the Presence of Poly(ethylene oxide) or Poly(propylene oxide) Oligomers and their Triblock Copolymers
2008
The effect of polyethylene oxide (PEO) or polypropylene oxide (PPO) oligomers of various molecular weight (Mw) as well as of triblock copolymers, based on PEO and PPO blocks, on aqueous laponite RD suspensions was studied with small-angle neutron scattering (SANS). The radius of gyration (RG) increases for low Mw whereas the opposite occurs for larger Mw. This behavior is explained on the-basis that an effective RG is given by two contributions: (1) the size of the particles coated with the polymer and (2) the interactions between the laponite RD particles which are attractive for small and repulsive for large polymers. The SANS curves in the whole Q-range are well described by a model of n…
Improving the properties of polypropylene–wood flour composites by utilization of maleated adhesion promoters
2007
Polymer composites filled with natural organic fillers have gained a significant interest during the last few years, because of several advantages they can offer compared with properties of inorganic-mineral fillers. However, these composites (based, in most cases, on polyolefins) often show a reduction in some mechanical properties. This is mainly due to the problems regarding dispersion of the polar filler particles in the non-polar polymer matrix and their interfacial adhesion with polymer chains. In this work, polypropylene-wood flour composites were prepared and the effect of the addition of a maleated polypropylene was investigated. The two materials were compounded by an industrial c…
Anisotropic Stick-slip friction of highly oriented thin films of poly(tetrafluoroethylene) at the molecular level
1996
Lateral force microscopy (LFM) studies of poly(tetrafluoroethylene) (PTFE) films with molecular resolution are reported. Thin PTFE layers with a high degree of orientation were obtained by pressing and sliding a block of polymer on a clean, heated muscovite mica substrate. LFM nanographs obtained on these films by scanning at directions between ca. 40 and 90° with respect to the film orientation direction, i.e. with respect to the direction of the polymer chains, showed a “stick-slip” type frictional motion of the LFM probe tip at the molecular level. The friction force observed at constant load decreased with decreasing scan angles. Chain-chain packing distances obtained by LFM and contact…
Enzyme molecular mechanism as a starting point to design new inhibitors: a theoretical study of O-GlcNAcase.
2011
O-Glycoprotein 2-acetamino-2-deoxy-β-d-glucopyranosidase (O-GlcNAcase) hydrolyzes O-linked 2-acetamido-2-deoxy-β-d-glucopyranoside (O-GlcNAc) residues from post-translationally modified serine/threonine residues of nucleocytoplasmic protein. The chemical process involves substrate-assisted catalysis, where two aspartate residues have been identified as the two key catalytic residues of O-GlcNAcase. In this report, the first step of the catalytic mechanism used by O-GlcNAcase involving substrate-assisted catalysis has been studied using a hybrid quantum mechanical/molecular mechanical (QM/MM) Molecular Dynamics (MD) calculations. The free energy profile shows that the formation of the oxazol…
Electronic Perspective on the Electrochemistry of Prussian Blue Films
2009
The derivative of the voltabsommetric scans, together with previous nano-electrogravimetric and X-ray diffraction results, allow different electrochemical processes to be distinguished during the Prussian blue (PB) voltammetric scan. Potassium, proton, and hydrated proton counterions involved in PB electrochemistry are related here to the electrochemical reactions of specific Fe sites. Potassium counterions show two different sites for their insertion: one located in the crystalline framework and another in ferrocyanide vacancies. From the monitoring of electroactive Fe sites, the covalent-exchange model is suggested as one of the first approaches to explain the origin of the PB magnetic or…
Usefulness of F(dm/dQ) Function for Elucidating the Ions Role in PB Films
2007
The conversion process of "insoluble" prussian blue (PB) films into the "soluble" structure has been followed by the simultaneous measurement of current and mass changes during voltammetric experiments and focusing on the possibilities of the use of the instantaneous mass/electrical charge ratio at each potential. A similar procedure was used for the analysis of the mechanism of reduction of PB films to the Everitt's salt form and to follow the partial dissolution of iron species during the oxidation to the prussian yellow form. The possibility of covering PB films by Nafion membranes, which make difficult the transport of anions through it, allows us to discern the role of anions in the so…
Molecular modeling studies of interactions between sodium polyacrylate polymer and calcite surface
2013
Abstract The interactions between calcite pigment and sodium polyacrylate dispersing agent, widely used in papermaking as paper coating components, were investigated using classical force field and quantum chemical approaches. The objective was to understand interactions between the calcite surface and sodium polyacrylate polymer at 300 K using molecular dynamics simulations. A quantum mechanical ab initio Hartree–Fock method was also used to obtain detailed information about the sodium polyacrylate polymer structure. The effect of water molecules (moisture) on the interactions was also examined. Calculations showed that molecular weight, branching and the orientation of sodium polyacrylate…
Photoinduced electron transfer in molecular organizates at the gas-water interface
1994
Abstract The influence of the molecular geometry is of fundamental importance for a better understanding of the photoinduced electron transfer mechanism. Because of their typical molecular structures, cyclophane rings have proved to be suitable for this purpose as electron acceptor molecules adsorbed under an amphiphile monolayer. We used a pyrene-labelled phospholipid derivative both as molecular anchor for the cyclophane ring and electron donor molecule. The co-spreading technique was used to prepare the complex monolayers. Surface pressure and surface potential measurements have indicated similar monolayer behaviour as with dimyristoylphosphatidic acid as anchor molecule, leading to the …
Structure and Yielding of Colloidal Silica Gels Varying the Range of Interparticle Interactions.
2016
The relationship between interaction range, structure, fluid-gel transition, and viscoelastic properties of silica dispersions at intermediate volume fraction, Φv ≈ 0.1 and in alkaline conditions, pH = 9 was investigated. For this purpose, rheological, physicochemical, and structural (synchrotron-SAXS) analyses were combined. The range of interaction and the aggregation state of the dispersions were tuned by adding either divalent counterions (Ca(2+)) or polycounterions (PDDA). With increasing calcium chloride concentration, a progressive aggregation was observed which precludes a fluid-gel transition at above 75 mM of calcium chloride. In this case, the aggregation mechanism is driven by s…