Search results for "Surfaces"
showing 10 items of 2837 documents
Magnetic molecular nanostructures: Design of magnetic molecular materials as monolayers, multilayers and thin films
2007
In this paper we summarize the importance and versatility of the molecular approach in the design and development of novel magnetic molecular materials. These materials processing, in order to obtain controlled molecular structures at the nanoscale, will also be remarked.
Second harmonic generation in self-assembled alternating multilayers of hemicyanine containing polymers and polyvinylamine
1995
Abstract Assembly of noncentrosymmetric multilayers is a facile technique for preparing noncentrosymmetric films avoiding electrical poling procedures and problems from subsequent relaxation of the induced orientational order. A maximum Xzzz of 13 × 10−9 esu was achieved for the assembly of up to six layers. Current problems are the long-term hydrolysation of the hemicyanine nonlinear optical chromophores and the reduction of polar orientation with increasing layer thickness.
Influence of processing conditions on some properties of anionically synthesized polycaprolactam in presence of lithium chloride
1980
Nylon 6–LiCl systems of various concentrations were prepared by anionic polymerization of caprolactam in the presence of salt. A depression of both crystallization rate and melting temperature was evidenced through x-ray, density, and DSC analyses. Such a preliminary characterization allowed for choosing the proper conditions in order to obtain amorphous fibers from a spinning operation which was performed at a temperature lower than the pure polymer melting point. These results are of technological relevance, especially in view of obtaining, as in similar cases, large amorphous orientations through a spinning–drawing process and high-modulus fibers after subsequent crystallization. Also, t…
Influence of plasticizers suggests role of topology in polymer solidification at high cooling rates
2012
Although solidification in processing deter- mines short- and long-term properties, methods for under- standing polymer crystallization mostly rely on real time experiments. Their evidences being drawn on time scales farther apart with respect to those experienced in process- ing. Nor significant outcomes have been so far drawn with approaches mimicking the typical processing times, the Continuous Cooling Transformation methods. Use of these techniques has indeed been limited to a heuristic interpretation of the structure developed under extreme solidification conditions without suggesting alternative routes to the understanding or even clues to the many open questions on polymer crystalliz…
Relative strength of H-bonding groups on biodegradable polymer-based blends in solution
2006
The intermolecular hydrogen bonding interactions between poly(3-hydroxybutyrate) and poly(styrene-co-vinyl phenol) copolymers with mutual solvent epichlorohydrin were thoroughly investigated by steady-state fluorescence and viscosity techniques. Fluorescence spectroscopy along with viscosity technique was used to asses the intermolecular hydrogen bonding between poly-(3-hydroxybutyrate) and its blends with five copolymer samples of styrene–vinyl phenol, containing different proportions of vinyl phenol but similar average molecular weight and polydispersity index. In the case of very low OH contents (2–4 mol %), as expected, both components of poly(3-hydroxybutyrate) and poly(styrene-co-4-vi…
Liquid crystal polymer-based blends: “Universal grade” polymers?
1992
Polymeric materials can be easily processed with different processing operations thanks to suitable rheological properties. Melt flow index, or grade, which is a measure of the fluidity of the polymers, is the most commonly parameter used to characterize the polymers from the point of view of their melt viscosity. Injection molding requires high grade materials, whereas low grade values are best suited for extrusion. Of course, it would be no doubt of interest if single “universal grade” materials could be used for all processing operations. In this paper it is demonstrated that the blends of low grade polymers with small amounts of liquid crystal polymers can be conveniently used for all p…
Mechanical behavior and structure of single beads of homogeneous and macroporous styrene–divinylbenzene copolymers
1982
The stress–stain and ultimate behavior in compression of homogeneous and macroporous beads of styrene–divinylbenzene copolymers has been investigated in the dry state or in equilibrium with toluene, acetone, methanol, and water. The penetration modulus A indicates sensitively the transition from the glassy into the rubbery state induced by an increase in temperature or swelling. For macroporous copolymers, A of the glassy polymers is mainly determined by the porosity P, while in the rubbery region it primarily depends on the matrix structure (degree of crosslinking and concentration and composition of the diluent). The high value of the slope s of the A vs. P dependence (s ∼ −3) for macropo…
The role of the disposition of the recycled polymer on the properties of films for greenhouses coverage
2010
Multilayer films, by using postconsumer materials in the central layer, i.e., multilayer composition: virgin polyethylene/postconsumer polymer/virgin polyethylene, allows to get a film for greenhouses coverage with good mechanical properties and photo-oxidation resistance, similar to that of the films made from virgin material and certainly better than the photo-oxidation resistance of the film made melt blending the virgin polyethylene and the postconsumer polymer. Moreover, the disposition of the postconsumer polymer containing oxygenated groups only in the central layer determines a significant slowdown of the photo-oxidation process of the multilayer film although faster than of the pri…
Indentation test as a tool for monitoring the solidification process during injection molding
2003
An inline method for monitoring the solidification process during the injection molding of semicrystalline polymers is demonstrated. The method has been applied to various poly(ethylene terephthalate) (PET) and poly(buthylene terephthalate) (PBT) samples. The technique is based on a simple device by which an additional ejector pin is pushed onto the injection-molded part with a fixed force at different times during the solidification phase while the mold remains closed. The residual deformation (the so-called indentation depth) due to the applied load is measured offline after ejection. By the performance of indentation at different times during the cooling phase, an indentation depth profi…
Architecture, self-assembly and properties of well-defined hybrid polymers based on polyhedral oligomeric silsequioxane (POSS)
2013
Abstract Well-defined hybrid polymers based on polyhedral oligomeric silsequioxane (POSS) with a variety of architectures have been developed, including telechelic polymers, block copolymers and star-shaped polymers. The synthesis, self-assembly and properties of this kind of materials are reviewed. Well-defined POSS-containing hybrid polymers can be constructed by living polymerization techniques, such as ring-opening polymerization and living free-radical polymerization or the combination of living polymerization and coupling reactions, such as click chemistry and hydrosilylation. The self-assembly behavior of well-defined POSS-containing hybrid polymers is also described in detail. The P…