Smart material

About: Smart material is a research topic. Over the lifetime, 3704 publications have been published within this topic receiving 74280 citations. The topic is also known as: intelligent material & responsive material.

Nanodielectrics: an emerging sector of polymer nanocomposites

Abstract: tance of nanostructured materials is worldwide understood and recognized, giving rise to expectations for materials with superior or unique performance and properties. The term nanodielectrics is rather new and refers to dielectric materials, which comprise entities with dimensions (at least one) at the nanometric scale. Two are the basic categories of nanodielectrics: (a) polycrystalline semiconducting or insulating materials, with grain diameter at the nanoscale level and (b) polymer composites incorporating nanoinclusions. The second category displays a number of advantages, e.g. easy processing and thermo-mechanical stability. Moreover the dielectric behaviour can be tailored by simply controlling the type and the amount of the nanofiller. Under this point of view, polymer matrix nanocomposites are expected to replace conventional insulating materials in a variety of applications. Capacitance the fundamental quantity in dielectrics, in contrary with other physical quantities, is increasing as the dimension of width in nanoinclusions is decreasing. This fact gives the possibility to exploit nanoinclusions as an inherent system of nanocapacitors. The charging and discharging of nanocapacitors defines an energy storing process, at the nanoscale level, introducing a new type of nanodevices. Nanofillers are frequently used as structural elements in nanocomposite systems. In some cases, the same elements could be able to act as nanocapacitors or ‘structural batteries’. Furthermore, the presence of ‘active dielectrics’ (i.e. piezo/ferroelectric or polar oxides nanoparticles) within the polymer matrix could provide functionality to the nanocomposite, through the conditionally variable electrical polarization. Combining mechanical and electrical reinforcement with energy storing procedure and functionality leads to a significant approach to the concept of ‘smart materials’, where structural elements should also play the roles of sensing, actuating and energy storing subsystems. Finally, the importance of studying conduction mechanisms in polymer matrix – conductive nanoinclusions composites should be noted. The insulator to conductor transition is expected to occur at a low content of the conductive phase, while the temperature and field dependence of conductivity can be exploited for the development of self-current regulators, selfheating systems, memory switches and other applications. Definitely a lot should be expected from this field in the near future.

Responsive Polymers as Smart Nanomaterials Enable Diverse Applications.

Abstract: Responsive polymers undergo reversible or irreversible physical or chemical modifications in response to a change in environment or stimulus, e.g., temperature, pH, light, and magnetic or electric fields. Polymeric nanoparticles (NPs), which constitute a diverse set of morphologies, including micelles, vesicles, and core-shell geometries, have been successfully prepared from responsive polymers and have shown great promise in applications ranging from drug delivery to catalysis. In this review, we summarize pH, thermo-, photo-, and enzymatic responsiveness for a selection of polymers. We then discuss the formation of NPs made from responsive polymers. Finally, we highlight how NPs and other nanomaterials are enabling a wide range of smart applications with improved efficiency, as well as improved sustainability and recyclability of polymeric systems.

Multistable actuator based on magnetic shape memory alloy..

Abstract: Magnetic Shape Memory Alloys (MSMs) are attractive smart materials because they exhibit, at the same time, a large strain (10 %) and a short time response (100 microns s). In this paper, we propose a novel MSM based actuator exploiting the characteristics of MSMs. This device is a push-pull actuator where two pieces of MSM act in an opposite way. The magnetic fields are created by two magnetic coils supplied by current pulses. The hysteretic behaviour of the MSM permits to keep a stable position when no current is applied and so limits heat losses in the coils. A model of this actuator is proposed and validated by experiments. A precise position feedback control of the actuator is then achieved using a displacement laser sensor.

Superelastic stress–strain behavior in ferrogels with different types of magneto-elastic coupling

Abstract: Colloidal magnetic particles embedded in an elastic polymer matrix constitute a smart material called a ferrogel. It responds to an applied external magnetic field by changes in elastic properties, which can be exploited for various applications such as dampers, vibration absorbers, or actuators. Under appropriate conditions, the stress–strain behavior of a ferrogel can display a fascinating feature: superelasticity, the capability to reversibly deform by a huge amount while barely altering the applied load. In previous work, using numerical simulations, we investigated this behavior assuming that the magnetic moments carried by the embedded particles can freely reorient to minimize their magnetic interaction energy. Here, we extend the analysis to ferrogels where restoring torques by the surrounding matrix hinder rotations towards a magnetically favored configuration. For example, the particles can be chemically cross-linked into the polymer matrix and the magnetic moments can be fixed to the particle axes. We demonstrate that these systems still feature a superelastic regime. As before, the nonlinear stress–strain behavior can be reversibly tailored during operation by external magnetic fields. Yet, the different coupling of the magnetic moments causes different types of response to external stimuli. For instance, an external magnetic field applied parallel to the stretching axis hardly affects the superelastic regime but stiffens the system beyond it. Other smart materials featuring superelasticity, e.g. metallic shape-memory alloys, have already found widespread applications. Our soft polymer systems offer many additional advantages such as a typically higher deformability and enhanced biocompatibility combined with high tunability.