Advanced Materials — Composites, Alloys, Polymers, Bio-mimicry, Nano-manufacturing

Smart materials (SMs) are defined as the materials that change their behavior in systematic manner as a response to specific stimulus (Rogers, 1989) which could be alter in magnetic or/and electric fields, stress, acoustic, temperature, nuclear radiation, or/and chemical properties (Fig. 1). They are superior to other materials with five characteristics: selectivity, directness, immediacy, self-actuation, and transiency

There is growing interest toward production and development of SMs. They show significant merits in various areas especially the medical, electronic applications. The analyses of the smart material around the world refer to 13% annual increment in growth rate and by 2023; it is expected to reaches 73.9 billion dollar. All of these led to the appearance of the SM next generation. The next generation of these materials is usually involving composites of at least two materials. The main reason for this is to minimize the cost, mass and the duration of the active material.

The aim of this article is to provide future vision for SMs in the different applications. This article mentions composition and properties and synthesis process of the next generation of SMs. The article also mentions the research on different smart structures that can be used for various construction and building, electronic and medical applications among others.

Abstract

Smart materials technology enables us to adapt to environmental changes by activating its functions. Multifunctional materials, sort of smart materials, can be activated by electrical stimuli so as to produce its geometry change or property change. There are many multifunctional materials available by the advent of nanotechnology, ranging from carbon nanotubes, graphene, inorganic nanoparticles, conducting polymers, and so on. However, future multifunctional smart materials should be harmonized with our living environment. Thus, it is natural to develop smart materials that can be renewable in the nature. Biopolymers are renewable materials that harmonize with environment.

This chapter introduces multifunctional smart biopolymer composites and their actuator applications. Raw materials of biopolymers including cellulose, bacterial cellulose, chitosan, gelatin, starch, polylactic acid, and polyglycolic acid are introduced and their active behaviors are reviewed in terms of electronic and ionic working behaviors. Polymer films and gels are also taken into account in the review. Recently, cellulose has been rediscovered as an active material, namely electroactive paper (EAPap). This chapter explains the fabrication and actuation principle of EAPap and its three subareas in terms of piezoelectric EAPap, ionic EAPap, and hybrid EAPap along with their applications. 

To further improve functionality of biopolymers, hybrid composites of inorganic functional materials are introduced by incorporating carbon nanotubes, graphene, titanium dioxide, tin oxide, and metal nanoparticles with biopolymers. Their active behaviors in the presence of electrical or pH stimuli are also illustrated. Since biopolymers are biocompatible, biodegradable, capable of broad chemical modification, various actuator applications of multifunctional smart biopolymer composites are possible such as artificial muscles, biomimetic robots, reconfigurable lens systems, and so on.

Development of smart materials for active coating

Smart materials for active coating are mostly active materials which transport the sensing and responding properties to textiles by traditional coating technologies (Singha, 2012). Adaptive polymers can exhibit distinct and great changes when responding to a small stimulus. Accordingly, adaptive coating textiles have preprogrammed responses to small environmental changes. Different stimulations of active materials are listed; these have been applied in active coating textiles:

A number of active materials exist for textile coating, such as smart and polymeric hydrogels, memory polymers, phase-change materials, color-change materials, and functional nanomaterials.

Smart or polymeric hydrogels as a special classification of hydrogels display different changes under specific stimuli such as temperature, pH sensitivity, light, salt, and stress. Responses include swelling/collapsing and hydrophilic/hydrophobic changes in shape. The most commonly used hydrogels in active coating are temperature-active hydrogels with a transition temperature adjusted by additives, a modifying monomer structure, or copolymerization. The widely applied and known hydrogel active coating application is temperature-dependent water vapor permeability textiles, based on their swelling and integrity characteristics below and above the switch temperature.

Memory polymers can sense thermal, mechanical, electric, and magnetic stimuli and respond by changing shape, position, stiffness, and other static and dynamical characteristics. Memory polymers have found wide applications in textiles and other fields. Their low cost, good processing ability, and controllable responses make them more suitable for industrial production than memory alloy (Maria Rosa Aguilar, 2014; Hu, 2010). The functions of memory polymers can be achieved in many systems such as a molecular structure with covalent and noncovalent bonding or a supramolecular structure with novel quadruple hydrogen bonding. As a group of the most applicable smart materials, memory polymers have developed rapidly in both academics and industry areas in past decades.

Adaptive polymeric particles include nanoparticles and microcapsules. The benefits of smart materials combined with particle materials give an integrated and unique property to textile coating owing to their tiny forms and responsive characteristics, which are different from normal particles. The morphology, shape, size, light reflection/diffraction, and solvent ability are the important chemical and physical parameters of adaptive polymeric particles. The surface properties of nanoparticles are more essential than those of microcapsules. The surface energy, surface structure, and reaction ability can be modified to serve the active requirements of coating textiles. There are different methods for obtaining adaptive polymer particles, such as the core–shell structure microencapsulation technique and surface modification. Applications of active coating of these particles include self-cleaning textiles, phase-change microencapsulation textiles, and hydrophilic/hydrophobic textiles.

Conclusions

Smart materials are opening new possibilities for PPE to better respond to users’ needs, act as global systems, and alleviate the effects of severe environmental conditions. For example, responsive barriers based on smart materials can limit or block the passage of chemical and biological hazardous species while preserving most of the wearer’s comfort and functionality. Solutions that are looked at for PPE are based on shape memory polymers, polymer gels, superabsorbent polymers, grafted polymer brushes, and polymeric ionic liquids. A few products using membranes with adjustable breathability are already on the market.

Self-decontaminating membranes provide one step further in smart protection against chemical and biological hazards. Technologies based on N-halamines, quaternary ammonium groups, bioengineered enzymes, metals and metal oxides, nanomaterials, and light-activated compounds have demonstrated some potential for PPE applications. Most self-decontaminating commercial PPE products currently available are based on the antibacterial action of silver and silver salts.

Another application of smart materials for PPE concerns thermoregulating phase change materials. Based on microencapsulation, macroencapsulation, or solid–solid transition, this technology allows a certain level of on-demand, immediate, and powerless cooling and warming with possible recharge at room temperature. Several fiber, textile, and PPE products are already commercially available, with the addition of a fire-resistant functionality soon to come.

The last example of application of smart materials to PPE described in this chapter deals with shock absorbers. With shear thickening fluids, complete flexibility is maintained in static conditions while the material instantaneously hardens upon impact at high rate. Products based on elastomer foam and 2D and 3D impregnated fabrics are already on the market, with a particular target at sports, defense, and law enforcement applications.

Finally, as these new materials progressively enter the PPE market, adjustments in the portfolio of performance specifications and standard test methods is required to take into account their specific properties, the time-dependent nature of their response, and any unintended side effect generated by their presence in the PPE. Work to that extent has been initiated with the creation of the smart textile workgroup in the textiles and textile products committee of the European Committee for Standardization as well as the funding of a research project aimed at developing tools for improving the integration of standardization issues into research projects to help further exploitation and commercialization of resulting innovations, in particular in PPE.

Introduction

Smart materials have been under immense investigation in all fields of science and in all corners of the world over the past decades. Smart materials consist of materials which respond to changes in their environment, thus rendering them stimuli-responsive. This work focuses on use of environmentally responsive hydrogels, essentially polymer networks which are capable of retaining large amounts of water without altering their structure. Many hydrogels possess the ability to undergo reversible changes in phase transition, from a solution-to-gel or gel-to-solution, depending on their chemical properties as well as the type of stimulus they are subjected to. The array of stimuli observed to trigger such changes includes temperature, electric field, pH, light, pressure, magnetic field, and ionic strength. Additionally, other hydrogels have been shown to be responsive to biomolecules including antigens, glucose, enzymes and thrombin.

There is demand for more effective, localized, and need-based systems, which can be used in a plethora of biomedical applications, such as cancer targeting, controlled drug delivery, tissue engineering or biosensors. By developing injectable hydrogels which can respond to variations in their environment and which can achieve the desired outcome (releasing a drug or biological molecule, targeting cancerous cells, or cell differentiation in scaffolds), better medical techniques can be attained.

Stimuli Representative Polymer

Smart materials that are able to respond to an external stimulus have received great attention, especially in last two decades. These bioinspired materials can change their dimensions, solubility, color, and shape, etc., upon a specific trigger. A wide range of smart materials including alloys, composites, gels, and polymers have been investigated for various applications from aerospace industry to medical technologies. Smart materials can be designed with various responses and actuation mechanism based on the requirements of applications.

Shape memory materials are able to memorize their “permanent shape” after being deformed to a “temporary shape”, under specific conditions. Polymers are one of the most widely used materials for novel shape memory applications due to advantages they offer, as tunability, lower density, easier processing, lower cost, and larger attainable strains. Also, they can be easily combined with various types of fillers to overcome the limitations or to combine multiple stimuli. Shape memory polymers (SMPs) are the networks that consist of two components: a hard segment formed by chemical or physical crosslinks that constitutes the permanent shape and a soft segment that maintains the temporary shape. Shape memory behavior can be considered as a functionality arising from the combination of polymer composition, topology, and processing.

Polyvinylidene fluoride (PVDF) is a well-known engineering polymer that posses partially fluorinated, semi-crystalline structure with outstanding physico-chemical and electrical properties. PVDF has a lower melting temperature (170 °C) compared to the other fluorinated polymers, which makes it easier to process by traditional processing methods. Five different polymorphs (α, β, γ, δ, ɛ; Fig. 9.2) can be observed in the crystalline phase of PVDF depending on the processing and conformation of the chains. The β and γ are mostly investigated phases due to their highest dipolar moment while other three phases α, δ, ɛ are apolar as a result of antiparallel packing of the dipoles within the unit cell.

Take Your Website to Next
Level Right Now!

Start Now