فصلنامه بسپارش
سال چهارم شماره 1 (پیاپی 10، بهار 1393)

It is often disputed if nanoclay enhances the thermal properties of polymer nanocomposites. Scientists all over the world have reported different and some times contradictory results concerning this issue. There are papers suggested that nanoclay is a factor in improving the thermal properties، while there are other reports on its reducing effect on thermal resistance. It seems that nanoclay has two opposite actions. The barrier effect which should improve the thermal stability of a blend by char formation and the promoter effect which may encourage the degradation process and reduce the thermal stability of the system. Therefore it is important to focus on this subject in order to study the conditions affecting thermal stability of nanocomposites and the mechanism by which nanoclays improve the thermal properties of a blend.

Dendrimers are a relatively new class of materials with unique molecular architectures and dimensions in comparison to linear polymers. Dendritic macromolecules containing several types of functional groups can be successfully synthesized through divergent or convergent method. The functional surface groups make them very hydrophilic and highly water soluble. Dendrimer diameters increase with generations in increments of up to 1 nm per generation، while molecular weight and number of functional surface groups increase exponentialy. An ideal dendritic drug-carrier must be non-toxic، non-immunogenic، and preferably biodegradable and present an adequate biodistribution. This review investigates recent advances in the application of drug-conjugated PAMAM dendrimers in drug delivery and finally، molecular dynamics simulations of PAMAM structures and their properties are discussed

Electro-optical devices are composed of various components and flexibility in such devices depends on two major parts: substrate and transparent conducting anode electrode which is deposited on the substrate. Since polymers have many advantages such as light weight، low price، flexibility as well as suitable chemical and mechanical properties، so they can be used as appropriate materials in different parts of flexible electronic devices. In this study، deposition techniques of various conducting polymers including soluble and insoluble conducting polymers on polymeric substrates and their characteristics requirements in order to use these polymers in different parts of flexible electronic devices are described.

Common elastomers exhibit similar behaviors in solvents of those for gums under normal condition، but when cured with curing agents they tend to swell in solvents، which is due to different behaviors of rubbery networks in solvents. Studying the thermodynamics of these materials in different solvents and investigating their physico-chemical properties is very important in their molecular design and final applications. Usually the thermodynamics of swollen polymeric materials are defined by Flory-Rehner equation. The most important parameter that has influence on thermodynamics of polymer-solvent interaction is a parameter designated as. Although this parameter is the key to better understanding of thermodynamical swelling of rubbery networks but the number of articles which have studied its concept with deeper understanding is few. Therefore، the uncertainty over the determination of this parameter is one of the most crucial problems to evaluate the physic- chemical properties of polymeric networks.

In order to control microbial growth in foods and improve their shelf-life and safety، the actions of different antimicrobial agents were studied by mixing them with food formulations، or they were applied onto food surface by spraying. Incorporation of antimicrobial agents directly into food is appropriate when there is a risk of microbial growth at both surface and internal parts of final food products. However، when the main cause of spoilage of food is microbial growth at its surface، the use of excessive amounts of chemical additives into food would be necessary. Thus، this traditional strategy does not fit into the current trend of food technology to develop healthier processed foods by using minimum amounts of chemical additives. The use of polymers as packaging materials containing antimicrobial agents is an alternative to overcome these limitations. Antimicrobial food packaging is based on controlled release of antimicrobial agents on packed food surfaces to maintain a predetermined concentration of the active compound for a determined period of time to reduce، inhibit or retard the growth of pathogenic microorganisms. In this article، different types of food packaging with controlled release properties of antimicrobial agents are studied and some mathematical models are presented to describe the release kinetics of active compound.

The Monte Carlo simulation method and its mode of actions in different processes are introduced. This article addresses some answers to some frequent questions raised by students of chemical and polymer engineering on Monte Carlo simulation methods. The interesting name on this method and the extraordinary developments in both soft and hardware facilities in computer world encourage the researchers to explore and solve complex problems using this method. Consequently، the increase in the number of research areas in academic centers focuses on the stochastic and especially on the Monte Carlo methods. The fundamental issues and requirements are presented for how to begin the Monte Carlo simulation method. A little historical origin and a detailed example are given as standard reference for students who are willing to pursue their research on Monte Carlo simulation methods.

An introduction to polymer structure and morphology will be followed by a brief review of the structural parameters that are commonly measured using X-ray scattering techniques. New measurement capabilities and their relevance for understanding the structural basis of performance will be discussed. Two techniques، microdiffraction and surface-enhanced scattering، two areas of investigation، crystallization kinetics and polymer deformation، and two examples of analysis of data، complete analysis of 2-D wide-angle pattern and analysis of 2-D small-angle X-ray scattering patterns in elliptical coordinates will be highlighted to illustrate the recent developments in polymer X-ray diffraction.