نشریه مطالعات در دنیای رنگ
سال ششم شماره 3 (پیاپی 22، پاییز 1395)

Supercritical fluids have found numerous promising applications due to its excellent properties. A number of research groups have also investigated the application of scCO2 to textile dyeing. Dyeing in supercritical fluids has been identified as a new and acceptable method that has been replaced with conventional dyeing methods of not discharging waste aqueous effluent containing colored compounds and concentrated electrolytes. Today, there is a need to reduce the amount of wastewater containing dye, chemical agents, and the like in the conventional method for the dyeing of textiles from the viewpoints of the cost of wastewater treatment and environmental pollution. In this way, a new dyeing method using supercritical CO2 fluid, supercritical fluid dyeing, has been developed. Dyeing in supercritical CO2 is carried out analogous to aqueous systems. Both decisive tasks of water at dyeing, which means the transport of dyestuff and heat to the fibre, are in the new dyeing process replaced with supercritical fluids. The new dyeing method is particularly attractive as it is non-toxic, non-flammable, and cheap. In addition CO2 has mild critical conditions and can easily be recovered and recycled after use. The aim of this paper is to provide the reader with an up-to-date overview of this subject. Wool and silk fibers have found several applications in textile industry especially in hand-knotted carpets. In this paper, various methods for the dyeing of these fibers in supercritical CO2 has been investigated, which is, at the moment, the limiting step of this technology.

We live in a nature full of different colors around us. Different areas of science were interested understanding the means of colors been produced in nature. Three main sources have been identified for nature’s colors: pigments, structural colors and bioluminescence. Structural colors are a different way in producing color which is not based on pigments. Many various types of creatures such as beetles, butterflies and peacock feather show bright and attractive colors based on structural colors. Structural color is a special one, which is the color produced from complex interaction between light and sophisticated nano- or micro-structures. The most common mechanisms of structural colors are film interference, diffraction grating, scattering and photonic crystals. Film interference is the mostly used one. The mechanisms mentioned are used independently or combined with each other in nature. Along with animals which are best known for structural colors, there are many examples of plants in case too. This paper presents an overview of various relevant mechanisms in nature and focus on diffraction grating in details. Diffraction gating is rare than other methods and produces iridescent colors. Some examples of it have been recognized in opals, beetles, butterflies and some plants like hibiscus and tulip flowers.

In nanostructured solar cells, sensitizers are responsible for light absorption. A quarter century after the birth of this kind of solar cells, different types of sensitizers, containing dyes, quantum dots and perovskites have been introduced and used in solar cells. One of the most important features of a sensitizer is its band gap, optical properties and ability of light absorption. In each kinds of sensitizers, molecular structure determinds optical properties. In this paper the relation between structure and optical properties of different sensitizers were discussed.

Graphene is a monolayer two-dimensional material in which the carbon atoms form a honeycomb lattice. The outstanding electrical, thermal, optical and mechanical properties of graphene due to its electronic structure have made graphene a promising nanostructure for vast range of applications. In this zero-gap semiconductor material, electron/ hole carriers concentration is around 〖10〗^13 cm^(-2) and it possesses high electron mobility (500000 s^(-1) V^(-1) cm^2) at room temperature. Adding graphene to a polymeric matrix enhances the polymer properties noticeably, various researches have been devoted to studying the fabrication methods of polymer/graphene coatings and achieving the optimum properties in them. In this paper, the general structure, properties and various procedures of graphene production are briefly investigated. Then the fabrication methods of polymer/graphene coatings are studied. The main part of this paper has focused on electrical conductivity of various coatings based on epoxy, polyurethane, polypropylene, polystyrene, polyester and etc. In which achieving the lowest possible electrical percolation threshold (minimum amount of graphene required to convert an insulator coating to a conductor), finding and controlling the factors that affect the percolation threshold are discussed.

The results of different studies showed that there is a strong relation between microstructure and mechanical, electrical and optical properties of coatings. For microstructural studies of nanostructured coatings we need electron microscopies that can work and detect in nano scale or even less. The purpose of using electron microscopy is finding the relationship between microstructure and different properties of coatings. In current paper working principles and sample preparation method for electron microscopy observation with focus on transmission electron microscopy as an effective way for microstructure analysis of nanostructured coatings is discussed. Finally, in order to give better understanding of using electron microscopies in microstructural analysis of nanostructured coatings, microstructural change of CrAlN and TiAlN/a-C coatings with chemical composition studied using electron microscopy instruments.

Consumers increased expectations of high quality food products as well as stringent regulations has increased the need for an accurate and fast method for quality assessment and control of the products in food industries. Machine vision with the aid of various image processing methods has been introduced as an objective, automate, and non-destructive approach capable for food quality control. Texture as one of the most important image's features has been used extensively in food quality monitoring applications. Generally, quantitative texture assessment methods are divided into four groups: statistical, structural, model-based, and transform-based methods. In the first part of this research (part A), the statistical methods are reviewed and in the second part (part B) the model-based and transform-based methods will be presented. Statistical methods work based on statistical quantities that obtained from image pixel's intensities, while structural methods operate based on texture primitives (a group of pixels with almost the same intensities). In the present paper, the applications of statistical image texture evaluation methods in food industries were investigated. Therefore, at first mechanisms of different statistical texture evaluation methods have been presented. Then, examples of recent studies related to employments of statistical image texture in quality control of food products have been reviewed. The results of the previous studies indicate that statistical methods are the most popular texture evaluation methods in food industries. This popularity is due to their highly accurate performances.