فصلنامه بسپارش
سال هشتم شماره 4 (پیاپی 29، زمستان 1397)

Self-healing materials with repair or healing ability of damages can be used with high reliability under service conditions. Approaches to the creation of a self-healing phenomenon in materials include: healing without or with internal or external interferences, which are referred to autogenic and autonomic repair, respectively. The most important self-healing mechanisms in polymer based composites are: the release of healing agent, reversible cross-links, electrohydrodynamics, conductivity, shape memory effect, nanoparticle migration and co-deposition. Since the production and use of self-healing materials is in its early stage, the use of nanoparticles in polymer-based composites can provide a great opportunity to create self-healing capabilities and improve properties. In this paper, the results of theoretical studies and models are considered in order to fully understand the self-healing behavior of nanocomposites and then various polymer- based composites such as hydrogels (containing nanoclay, gold nanoparticles, carbon nanomaterials) and composites (containing carbon nanomaterials and other nanoparticles) are introduced and investigated as the most important nanocomposites with self-healing capabilities. The most widely used nanoparticles in self-healing polymers include carbon nanotubes, graphene oxide, organoclay, halloysite nanotubes, gold and silver.

In the past decades, the solar cells based on regioregular poly(3-hexylthiophene) (P3HT) and phenyl-C-butyric acid methyl ester (PCBM) have attracted a large attention among the polymeric photovoltaics. Although the P3HT:PCBM solar cells possess some advantages such as low-weight, low-cost and flexibility, their power conversion efficiency (PCE) is relatively less than other types of photovoltaic systems. Thereby, the researchers from various fields have focused on different methodologies to increase the PCE by manipulating the active layer morphology, which plays a substantial role in the efficacy of polymeric solar cells. A morphology with the pure phase separated donor (P3HT) and acceptor (PCBM) components which are connected to each other is an optimized morphology. The solar cells demand the pathways of interconnected donors and acceptors to reach an appropriate function, which could be originated from the crystallization and nanoscale phase separation in the active layer. This work is devoted to review the effective procedures to enhance the PCE of P3HT:PCBM photovoltaics including preparation and annealing methods, use of distinct polymeric and non-polymeric additives, some particular methods such as developing the core-shell nanofibers and nanospheres and anodic patterns as well as controlling the crystallinity and orientation of the donor chains.

Designing materials with a non-oxide structure with a fine porosity and nanoscale porosity are attractive because they are not generally limited to four-dimensional spatial networks of zeolites. The internal space of these types of nanoporous solids can be completely different in polarity, spatial position, performance, and reactivity, quite different from that of conventional aluminum silicate zeolites. Nanoporous coordination polymer or metal-organic framework (MOFs), are among the newest range of crystalline nanoporous materials, which have attracted wide attention to these days. The framework of these materials usually consists of metal ions and polydentate organic connectors. MOFs have unique properties such as low density, extremely high and tunable surface area, high porosity, high cavity volume, good thermal stability and easy synthesis, resulting in their widespread use in storage and separation of gases, as the drug delivery carrier, sensors, GC columns adsorbent, and etc. Each MOF-based composite shows a new material with particular functional properties. The remarkable new feature and the multi-purpose nature of the emerging MOF composites stimulate the emergence of innovative industrial applications in a wide range of important technological fields. In recent years, the research and use of a variety of nanocomposites based on MOF compounds have been improved for many uses of this material, for example in the storage and separation of gases, as heterogeneous catalysts, as membranes and sensors, and many other applications.

Interest in CO2-responsive systems has received significant research attention in recent years. CO2, which is a benign, inexpensive, abundant, and non-toxic gas, could be used as a green trigger for CO2 responsive materials. Among the CO2-responsive materials that have been developed, polymer-based materials are of particular interest. To have CO2-responsivity in polymers, CO2-responsive moieties in the structure of polymer are required; these moieties can be originated from a surfactant, monomer and initiator. These polymers exhibit reversible changes in chemical structures and/or physical properties in response to the addition or removal of CO2, and are being considered for application in a variety of fields including controlled drug delivery, reversible cells capture, catalysis, switchable latexes, and oil/water separation. CO2 responsive polymers have been used in the form of latexes, solvents, gels, surfactants, and electrospun nanofibrous membranes. This review article focuses on applied aspects of CO2-responsive materials by emphasizing on polymeric materials. In this review paper, first, we present the general aspects of CO2-responsivity, and then provide numerous examples of applying the chemistry of CO2-responsivness to the preparation of CO2-responsive polymers. We intend to highlight those applications which are more promising commercially.

Recently the use of acrylic-based polymers has attracted many industries specially construction, sealing and adhesives due to special and useful features. These polymers in combination with cement structures in form of composites and or nanocomposites could eliminate many existing defects of cement and concrete structures. In this study, a variety of cement-acrylic composites and nanocomposites and their properties are introduced and the bonding mechanism of hydrated cement with acrylic latex particles is presented. The results illustrate that using acrylic latex in cement mortar leads to modify the pore structure in cement and reduce water requirement. Mechanical properties like flexural strength and toughness have been dramatically improved. But it does not have a good effect on the compressive strength of the cement. Furthermore, corrosion resistance and weathering resistance have also been increased. Polyacrylics are resistant to discoloration and degradation due to low ultraviolet radiation absorption that leads to improvement of durability of the polyacrylic-cement composites. Addition of silica nanoparticles to acrylic-cement composites accelerates the hydration of the cement and reduces the amount of pores in the structure. However, because of the hydrophilic nature and the high surface area of the nanoparticles, the liquidity of the cement mortar decreases.

Human need for energy is an inevitable necessity, which is increasing day by day. The reason for this is the need for technological change and the development of various human societies around the world. There are limited sources of energy available on the earth, while solar energy is abundantly available at the surface of the earth. The polymers normally used in organic solar cells are often made of aromatic heterocyles structures which contain heteroatoms such as oxygen, nitrogen and sulfure. These structures form a resonating network which leads to closing together HUMO and LOMO which results in small energy gaps. Polymers are normally used as donors and other molecules are used as acceptors to conduct electrons towards anode. Activities on different technologies are underway to collect and store solar energy, and some of them have grown well. Polymer solar cells are one of these technological branches, which have many advantages due to their low energy consumption in their production and the rapid roll-to-roll production process. On the other hand, due to the flexibility and lightness of the polymeric solar cells, there are many developing applications for this type of solar cells. Thus, in the near future, by increasing the efficiency and longevity, polymer solar cells grow rapidly and take on dominant positions in areas such as building integrated photovoltaics (BIPVs).