Advanced Smart and Multifunctional Materials Volume 2: Advanced Processing, Polymers, Ceramics, and Related Functional Materials

Porous ceramics are known for their low density, high surface area, good mechanical properties, and excellent temperature and corrosion resistance, rendering them vital in various advanced fields like biomedical engineering, environmental management, and aerospace. This chapter examines recent advancements in the principal processing techniques for porous ceramics: partial sintering, direct foaming, replica methods, sacrificial pore formers, gel-casting, freeze-casting, and additive manufacturing. Each technique is analyzed for its fundamental principles, recent advancements, and advantages and disadvantages particular to its applications. The chapter delineates prospective trajectories, highlighting sustainable processing, multifunctional ceramics, and intelligent materials with adaptive characteristics. These advancements illustrate the evolving function of porous ceramics as versatile materials capable of fulfilling the growing needs of advanced technological development.

Composite materials offer improved properties over their constituents. However, conventional composites are insufficient when a variation in properties at different regions within a material is required. Functionally graded composite materials (FGMs) are a relatively novel class of materials with a tailored variation of the composition, microstructure, and properties along at least one direction. The combination of properties achieved with the graded structure is not possible with monolithic composites. Accordingly, much research has recently been dedicated to developing FGMs. Several processing techniques have been developed for their fabrication, and FGMs have already been established in a wide range of advanced application domains such as defence, aerospace, automobile, biomedical, etc. This chapter aims to provide a concise review of the fundamental theory of FGMs, a brief description of the different FGM processing techniques with representative examples, and an up-to-date discussion of their different application domains.

Smart polymers, also referred to as intelligent polymers, have become a focal point of research due to their versatile and adaptive properties, which make them ideal for a wide range of applications. These polymers can undergo reversible changes in response to external stimuli such as temperature, pH, light, electric or magnetic fields, and mechanical stress, allowing them to change their structure, properties, or behavior. This responsiveness demonstrates the inherent adaptability of smart polymers, which makes them highly versatile for numerous innovative uses. As a result, smart polymers are increasingly explored for applications in sensors, self-healing materials, shape-memory devices, flexible electronics, water treatment, and agricultural and food packaging. Additionally, their ability to respond dynamically to environmental conditions makes them valuable in biomedical fields, particularly in drug delivery systems, tissue engineering, and cell culture applications. With continued advancements in smart polymer technologies, these materials hold significant promise for transforming industries, offering more efficient, adaptive, and sustainable solutions across technological and healthcare sectors.

Mechanically responsive materials, i.e. materials that can move macroscopically in response to external stimuli, are at the forefront of material science research. Combining chemical, physical and mechanical properties, they create a new generation of smart materials with predictable behaviors in applications ranging from biomedicine to aerospace. This chapter discusses how force fields can function as both stimuli (mechanoresponsive) and responses (mechanoadaptive) from a rheological perspective. The first section addresses mechanoresponsive smart materials, considering their viscoelastic properties as key to their predictable response. Modulating the elasticity enables control over the strain-stiffening behaviour of hydrogel-based systems, while modulating the viscosity allows prediction of the strain-thinning behavior of structured 3D printable systems and the shear-thickening behavior of smart fluids. The second section introduces shape memory polymers (SMP) as the most representative example of mechanoadaptive smart materials. This section provides a brief overview of SMPs and explains why they have received significant attention in recent years. Finally, some of the most relevant applications of mechanoresponsive and mechanoadaptive materials are reviewed, providing up-to-date coverage of the latest advances.

In this chapter, stimulus-responsive shape memory polymer aerogels (SMPAs) are introduced. Shape memory materials (SMMs), including their definition, classification and characteristics, are first briefly introduced. Shape memory polymers (SMPs) are summarized in terms of their deformation characteristics, programming process, structural composition (composed of a stationary phase and a reversible phase) and characterization methods. With respect to shape memory polymer aerogels (SMPAs), three categories, namely, bio-based, synthetic polymer-based, and polymer-derived carbon-based aerogels, are reviewed according to their composition. The conclusion and outlook aim to inspire scientists to further explore the fundamentals and applications of SMPAs.

Sensing technology has made tremendous progress in the last few years due to the increasing demands for real-time monitoring systems within the healthcare, environmental protection, food safety, and industrial sectors. Among the diverse materials researched as being potentially suitable for sensing, ethyl cellulose (EC)-based hybrid films have shown great promise due to their exciting properties such as flexibility, biocompatibility, film-forming ability, and miscibility with a wide range of functional nanomaterials. This exhaustive review delves into the building blocks, fabrication processes, sensing mechanisms, and applications of EC-based hybrid films, emphasizing the latest developments that have brought these materials to the cutting edge of sensing technology. The incorporation of nanomaterials like carbon nanotubes, graphene, metal nanoparticles, and conductive polymers into EC matrices has greatly improved their sensing capabilities for the detection of gases, volatile organic compounds, humidity, temperature, pH, and biomolecules. Hybrid films have excellent sensitivity, selectivity, and stability towards various sensing applications with advantages in sustainability, cost-effectiveness, and probable biodegradability. Future prospects point to substantial potential for these materials in wearable electronics, implantable devices, Internet of Things applications, and green sensing technologies, putting EC-based hybrid films at the vanguard of next-generation sensing platforms.

This article presents a literature review on polymer blends based on thermosetting resins (thermosets) and thermoplastic polymers. The focus is placed on analyzing component compatibility, as well as their mechanical, thermal, and functional properties. The mechanisms of chemical and physical reactions occurring during the mixing process are discussed, including curing, diffusion, and interfacial interactions. The roles of individual components within the composite structure are characterized, along with the most commonly used processing methods, such as melt extrusion and high-shear mechanical mixing. The main limitations of such material systems are identified, including phase separation, low chemical compatibility, and the lack of recyclability. Nevertheless, it is shown that through property hybridization, it is possible to obtain materials with a desirable balance of strength, flexibility, and chemical resistance. The importance of compatibilizers and the role of reactive modifiers in enhancing interfacial adhesion are also highlighted.

The development of functional 2D inks, particularly those based on two-dimensional (2D) materials, has revolutionized the additive manufacturing and advanced printing technologies for flexible electronics and micro/nanodevices. This chapter emphasizes the critical role of rheology in the formulation of functional inks, as it determines their behavior during printing processes and directly influences the quality and resolution of printed patterns. Key physical properties, such as viscosity, surface tension, wettability, and electrical conductivity, are explored, highlighting their relevance across various printing techniques, including screen printing, gravure, inkjet, electrohydrodynamic jet (EHD-jet), and aerosol jet printing. The chapter delves into steady shear, thixotropic, oscillatory, and extensional rheological behaviors of inks, detailing how these properties affect droplet formation, filament thinning, and substrate adhesion. Additionally, the impact of electric fields on rheological responses, particularly in EHD-jet printing, is discussed, underscoring the need for further experimental and theoretical research to optimize ink formulations.

Fluorinated graphene nanosheets, a rising star among graphene derivatives due to its remarkable chemical reactivity, intrinsic hydrophobicity, and simple integration with other materials besides dispersion processability in multiple solvents has witnessed rapid strides in self-cleaning technologies in the last decade. The rise of fluorinated graphene (FG) nanosheet hybrids integrated with polymers, metal organic frameworks (MOF) and macrostructures display outstanding physio-chemical properties, hierarchical porosities, mechanical/chemical stabilities and super-wetting functions. In this chapter, we highlight the multi-facetted features of fluorinated graphene hybrid coatings displaying self-cleaning action chiefly directed toward oil-water/emulsion separation, anti-corrosion protection, electrical insulation, superior thermal conductivity and low dielectric constant structures. The future of FG hybrid coatings foresees on scalability and large area production, environmental compatibility, durable special-wettability towards water/fog harvesting devices, desalination membranes and liquid-liquid separation.

The increasing resistance of microbial pathogens to new antibiotics or antimicrobial agents raises the possibility of a return to the no-antibiotic era, and some other materials for the treatment of infections will be needed. In facing this complicated public health problem, scientists are directing their research toward sources of alternative materials as antimicrobials. The past decade has witnessed a significant increase in the global use of nanomaterials as innovative compounds to combat the high rates of antibiotic resistance. Nanomaterials have emerged as promising antimicrobials that can act at several cellular levels and block defined bacterial resistance mechanisms. Among them, metal (silver, copper, zinc, etc.) nanoparticles and their oxides, which possess antimicrobial effects through nonspecific activity alone or in combinations with other materials as nanocomposites, can achieve high efficacy against resistant microbes due to their high surface area, sorption capacity, and selectivity for target microbes. Although yet to be advanced in the clinic, these nanomaterials are vast and underexplored compounds that could lead to a much-needed new class of antimicrobials. This chapter summarizes the progress in countering antimicrobial resistance and their cytotoxicity through published data. It also discusses innovative approaches and challenges to the future application of such materials for the treatment of infectious diseases.