فصلنامه دنیای نانو
پیاپی 57 (زمستان 1398)

Particles in the size between 1-100 nm are called nanoparticles whose surface-to-volume ratio is greater than the bulk. The term of colloid is applied if the particles have larger surface and smaller volume, so nanoparticles can produce colloid. The study of colloid phenomena is known as colloid science, leading to technological advances including ceramic processing, coating, pharmaceuticals, and etc. Due to antibacterial properties, silver nanoparticles are used in medical equipment and textiles fabrics, as well as in cosmetics, hygiene and plastics. Due to its widespread use, silver nanoparticles may be released to the environment when they are being built and used by consumers or after wearing out. The main concern for the release of silver nanoparticles in environment is due to their effect on the ecosystem and microorganisms. The bioavailability and toxicity of silver nanoparticles in each ecosystem is highly dependent on the stability of silver colloid. Factors that prevent the agglomeration of nanoparticles are considered to be stabilizing. The stability of colloids depends on many factors, including the type of covering agent, environmental conditions including pH and ionic strength. There are three types of nanosilver stability mechanisms that include electrostatic repulsion, spatial repulsion, and electrostatic and spatial repulsion simultaneously. Considering the importance of stabilizers in the synthesis of nanoparticles, in this study the stability of nanoparticles and the stability mechanisms of nanoparticles were investigated.

<![CDATA[Heat transfer fluids must have high thermal stability to be used at high temperatures. Ionic fluids are suitable for heat transfer due to their unique properties. These fluids are a good choice for use in solar collectors. Ionic fluids have recently been studied by researchers.In this paper, an overview of nanoparticles incorporating thermophysical properties including: thermal conductivity, viscosity and thermal capacity of ionic fluids and models presented so far to measure thermal conductivity of nanofluids has been investigated.The results show that increasing the concentration of nanoparticles increases the thermal conductivity and increases the thermal capacity of ionic nanofluids relative to the ionic fluids, as well as the effect of increasing temperature on the thermophysical properties of the investigated ionic nanofluids so that the thermal conductivity and thermal capacity of the ionic nanofluids relative to the fluid The base ionic fluids increases with increasing temperature, and viscosity decreases.Some papers have investigated the effect of nanoparticle shape on thermal conductivity and have shown that the addition of non-spherical nanoparticles has a greater effect on increasing the thermal conductivity of ionic fluid than spherical particles]]>

In this paper, we design the temperature and strain nanosensors using fiber Bragg gratings. Bragg wavelengths for temperature and strain nanosensors are 1555 and 1549 nm, respectively. The design of strain and temperature nanosensors has been investigated by using barium impurity and its injection into silica fiber core as well as by using methyl methacrylate polymer fiber. Temperature changes in the Bragg grating nanosensors change the modulation depth of the refractive index and consequently change the Bragg wavelength. As a result, by using polymer fiber and impurity injection such as benzophenone into the polymer fiber core, the thermo-optical parameters are increased and as a result the temperature sensitivity of the designed nanosensor is greatly enhanced. The sensitivity obtained for the temperature nanosensor was obtained using polymer fiber -0.3223nm /°C. Also, strain changes in Bragg gratings in addition to changing the depth of refractive index modulation also cause changes in the periodicity of gratings. By injecting barium impurities into the silica fiber core, the strain-optical parameters were increased and due to the strain relationship with the Bragg wavelength variations, the strain sensitivity of the designed nanosensor increased. The sensitivity obtained for the designed strain nanosensor was 0.0019nm/μ. Also, due to the proper selection of grating parameters, the reflectance intensity at the Bragg wavelength of the designed nanosensors is approximately 100, and the transmission intensity at the Bragg wavelength is reduced, thereby reducing the intensity, losses of the designed nanosensors, significantly Acceptance has declined.

Nanoparticles have a wide variety of physical, electrical, and chemical properties due to their small size and surface-to-volume ratio. These properties have made them widely used in a wide range of applications from medical engineering to aerospace and electronics. In nano devices usable in the electronics industry, the bonding of the particles used, such as gold, to the space symmetrically is important. In recent years, there have been extensive international efforts to study the arrangement of nanoparticles as 2D and 3D crystals in nanotechnologies, which has led to good achievements in the field, and in particular to the development of nanotechnologies for internal solutions. It is important to establish an ohmic connection of network components. In this paper, we have tried to introduce different methods of bonding materials and structures to bond the mentioned nanoparticles, especially gold and platinum.

Some of the biological processes, such as mutation, protein misfolding and/or partially unfolding may cause the formation of amyloid fibrils, which have a diameter of nanometer range and a length up to many microns. Extensive studies have demonstrated that the formation of fibrils is associated with a variety of human disorders, such as Alzheimer’s disease, Parkinson’s disease, Huntington’s diseases, type II diabetes, and so on. Therefore, inhibiting fibril formation or disrupting preformed mature fibrils could be beneficial strategies for the treatment of fibril-related diseases. Other investigations have revealed that fibrils feature several fundamental properties, including high structural stability. Thus, they are increasingly exploited for a broad range of applications in Nano biotechnology, such as nanotubes and nanowires. In these cases, materials and compounds that stimulate the in vitro formation of fibrils may contribute to the development of these applications.

Today, metal matrix nanocomposites are widely used in many industries, including aerospace and automotive, due to their extraordinary properties such as hardness, strength to weight ratio and high modulus. But the high cost of manufacturing is one of the major challenges. Stir casting is recognized as one of the most cost-effective and simplest ways to fabrication of these materials. Recent progresses, such as the use of ultrasonic waves in stir casting or two-step stir casting, have led to the production of metal matrix nanocomposites with enhanced mechanical and tribological properties. In this paper, after classifying nanocomposites according to the type of reinforcement and matrix, different manufacturing methods are investigated. Among the available methods, stir casting process because of its simplicity, flexibility and availability as a cost-effective process of production metal-based nanocomposites, have been studied in detail. Finally, the effect of new techniques on improving the properties of metallic nanocomposites and challenges were evaluated.

Today, nanotechnology has wide application potential in various fields. The use of nanomaterials and nanostructures has been expanded due to their small size, high surface area, distinct properties and unique advantages in orthopedics. Implantable nanoscale biomaterials as essential components of orthopedic surgery have led to the development of this field. Recent advances in this technology have become important in orthopedics with bone tissue engineering, implantable materials, diagnosis and treatment. The application of nanotechnology in orthopedic implants can be extremely useful in improving the treatment of many types of bone defects and orthopedic injuries. Application of biocompatible nanomaterials to implants with the ability to promote cell growth, tissue regeneration, mimic cellular environment, better extracellular adhesion, bone formation and better fusion is important given their potential need and efficacy. Hydroxyapatite is one of the most important minerals and bio-ceramics of bone in orthopedic surgery due to its unique properties in recent years. This article reviews the preparation, application and benefits of nanotechnology in orthopedic implants based on hydroxyapatite.