فصلنامه بسپارش
سال پنجم شماره 1 (پیاپی 14، بهار 1394)

Understanding the mechanism underlying the behavior of polymer-based nanocomposites requires investigations at molecular level that challenge experimental techniques. Molecular dynamic (MD) simulation as one of the most commonly used computation methods is being increasingly partnered with experiments. In the present work، we study some properties of polymer-based nanocomposites including carbon nanotube، boron nitrides nanotube، functionalized carbon nanotube and several polymers and copolymers. Radial distribution function، diffusion and radius of gyration are some physical chemistry properties that have been calculated for different polymerbased nano composites using MD simulation. Also، the interface of nanotube-polymer of polymeric nanocomposites is studied. The intermolecular interaction energy between carbon nanotubes and polymer molecules is computed and the morphology of polymers physisorbed to the surface of nanotubes is investigated by the radius of gyration and the dihedral angle. Our results show that the intermolecular interaction in our systems is strongly influenced by the specific monomer structure of polymer. The high values of intermolecular interaction energy of such composites suggest to us that an efficient load transfer would exist in the interface between nanotube and conjugated polymer، which is of a key role in the composite reinforcement practical applications.

Chemical reactions on the structure of polymers، especially natural polymers result in production of new properties. One of these cases is chitin deacetylation reaction for production of chitosan. Property and application of chitosan with extensive uses in food، cosmetic، healing and drug industries depend on the degree and percent of acetyl groups or in other words the degree deacetylation (DDA). Proton nuclear magnetic resonance spectroscopy (1HNMR) is the simplest، most accurate and fastest method for quantitative determination of the degree of deacetylation in chitosan and its salts. In this method، the degree of deacetylation، ranging from 50 to 100%، with acceptable accuracy and repeatability is determined by a small amount of material without undergoing degradation and simple calculation. In addition، if the molecular weight of polymer is low، this test method can determine the number average degree of polymerization (DPn) in chitosan and chitosan salts for use in biomedical and pharmaceutical applications.

Nowadays polymeric materials are an important part of human life around the world. Polymer materials are used to manufacture different substances from commonly used instruments to complex and precise scientific tools. Additives are commonly used in polymer industry to improve the properties of polymer materials and reduce their costs. Nano-scaled additives، due to their small dimensions and enormous surface area، produce improved properties compared to larger structures. Zinc oxide (ZnO) is an n type inorganic semiconductor with a band gap energy of 3. 37 eV which due to good stability، environmental friendly feature، high ultraviolet absorption and low cost are commonly used in polymer industry as inorganic additive. Therefore، ZnO nanostructures can produce various hybrid، blends or combination of composite materials in polymer matrixes and improve their properties. In this study، applications and the role of various nanostructures of zinc oxide in polymer productions are reviewed.

From the first discovery of Phillips catalysts، extensive investigations have been conducted to explore the effect of catalyst textural properties on the kinetic control of polymerization and the obtained polymer properties. The findings have confirmed that both catalyst chemical structure and support porosity have great influence on the catalyst activity and the obtained polymer properties. Based on catalyst activity، control of molecular weight and its distribution، the degree of branching and its type، different commercial Phillips catalysts have been introduced until now. Furthermore، high sensitivity of polymer properties towards the process، especially activation methods and polymerization reaction conditions، has led to many variations of catalytic system and polymer grade diversity. This diversity is the main reason for credibility of the Phillips catalyst، CrOx/SiO2، in 40–50% of current world production of high-density polyethylene (HDPE). The largest fraction of HDPE is used for manufacturing bottles، drums، fuel tanks and other containers، film and pipe extrusion، cable and so on. Because of special importance of Phillips catalyst in polyethylene production، history، chemistry of this important catalyst، type and structure of catalytic system، different polymerization methods and produced polymer properties are reviewed here.

The accidental discovering of semiconductive polyacetylene by Heeger، MacDiarmid and Shirakawa – who were granted the Nobel Prize – a new field arised in the class of polymers that is called “conducting polymers”. In this paper we discuss conjugated polymers which are semiconductors and become conducting polymers by doping that، conductivity of some of them are as good as copper. Conducting polymers، due to unique conductivity and electroactivity properties and optical properties (in some)، have several applications. For example they can be used in medical industries، military industries، electronics and etc. In this paper it was attempted to briefly describe the history of synthesis of these polymers، their structures، ways of doping and some of their applications.

Epoxy resins as one of the most important thermoset materials have shown various applications in production of composites، adhesives and surface coatings. Due to formation of the network structure، the cured epoxy resin shows brittleness and low impact resistance. The mechanical properties in the epoxy resin (especially the fracture toughness) can be modified by adding a softer phase preferably the rubber phase، thermoplastic fillers and even rigid particles. In comparison with other methods، the inclusion of rigid particles into epoxy resin improved the fracture toughness of epoxy resin without sacrificing the other main properties of epoxy resin such as the modulus (E) and glass transmission temperature (Tg). In recent years، the introduction of nanotechnology has shown some possibilities in toughening improvement of nanomaterials. Due to the special properties and different types of nanoparticles، a review study on effective nanoparticles would be useful in utilizing nanomaterials in toughening of the epoxy resin.

Aerogels are nanostructured materials with the lowest density compared to other materials and according to their composition; they have special applications in different fields. Aerogels are synthesized in a first step by low-temperature traditional solgel chemistry. While in the final step most wet gels are dried by evaporation to produce xerogels، aerogels are dried by other techniques، essentially supercritical drying. These materials with bulk density of 0. 003-0. 35 g/cm3 are known as the lightest solid materials. Also، aerogels have the lowest thermal conductivity in comparison with other solid materials. Some polymeric nanoaerogels are: resorcinol-formaldehyde، polyurethane، cellulosic، cross-linked polymer and biopolymer-containing aerogels. Depending on the synthesis process، structure، physical and mechanical properties، these nanomaterials can be used in various industries including electronics، optics، mechanics، aerospace، medical، pharmaceutical and etc. In this paper، the aerogel production procedure is briefly reviewed and then types of polymeric aerogels، their synthesis، properties and special applications are summarized.