There is a burgeoning interest in the development of geopolymers as sustainable construction materials and incombustible inorganic polymers. However, geopolymers show quasi-brittle behavior. To overcome this weakness, hundreds of research have been focused on development, characterization, and implementation of fiber-reinforced geopolymers for a wide range of applications. This paper discusses the rapidly developing state-of-the-art of fiber-reinforced geopolymer composites, focusing on material and geometrical properties of construction fibers, and underlying mechanisms on fiber-binder interaction at fresh and hardened states, mechanical properties, toughening mechanisms, thermal characteristics, and environmental durability. It is intended to build a strong conceptual and technical background for what is currently understood on fiber-reinforced geopolymers by tying the subject together with knowns for other similar cementitious composites rather than a historical report of literature.

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Fiber-reinforced geopolymer composites: A review

Metal-free carbon materials for persulfate-based advanced oxidation process: Microstructure, property and tailoring

Since the discovery of buckminsterfullerene over 30 years ago, sp2-hybridised carbon nanomaterials (including fullerenes, carbon nanotubes, and graphene) have stimulated new science and technology across a huge range of fields. Despite the impressive intrinsic properties, challenges in processing and chemical modification continue to hinder applications. Charged carbon nanomaterials (CCNs), formed via the reduction or oxidation of these carbon nanomaterials, facilitate dissolution, purification, separation, chemical modification, and assembly. This approach provides a compelling alternative to traditional damaging and restrictive liquid phase exfoliation routes. The broad chemistry of CCNs not only provides a versatile and potent means to modify the properties of the parent nanomaterial but also raises interesting scientific issues. This review focuses on the fundamental structural forms: buckminsterfullerene, single-walled carbon nanotubes, and single-layer graphene, describing the generation of their respective charged nanocarbon species, their interactions with solvents, chemical reactivity, specific (opto)electronic properties, and emerging applications.

Charged Carbon Nanomaterials: Redox Chemistries of Fullerenes, Carbon Nanotubes, and Graphenes

Carbon nanotube dispersion in nematic liquid crystals: An overview

Recent experiments have reported that ferroelectric nanoparticles have drastic effects on nematic liquid crystals---increasing the isotropic-nematic transition temperature by about 5 K, and greatly increasing the sensitivity to applied electric fields. To understand these effects, we develop a theory for the statistical mechanics of ferroelectric nanoparticles in liquid crystals. This theory predicts the enhancements of liquid-crystal properties, in good agreement with experiments. These predictions apply even when electrostatic interactions are partially screened by moderate concentrations of ions.

http://absimage.aps.org/image/MAR09/MWS_MAR09-2008-002758.pdf

Theory of Ferroelectric Nanoparticles in Nematic Liquid Crystals

The present study focuses on the ionic behaviour in nanoparticles (NPs) dispersed nematic liquid crystal. Dielectric spectroscopy has been used to investigate the behaviour of ions in suspension of NPs and liquid crystal (LC). Ionic concentration, diffusion coefficient, activation energy and mobility have been calculated from dielectric data. It is found that ion concentration increases initially and then it decreases with increasing concentration of NPs in suspension. The initial increase in ion concentration is attributed to the insertion of more ions due to impurities of TiO2 NPs and various other reasons. Temperature dependence of diffusion constant for different loading of TiO2 NPs is also investigated. The activation energy of NPs dispersed LC is found to be lower than the pristine one and it decreases with increasing concentration of NPs. The decreasing DC conductivity with increasing NPs concentration is attributed to the hindered or restricted motion of ions in the suspension. It is proposed that...

Effect of TiO2 nanoparticles dispersion on ionic behaviour in nematic liquid crystal

Sign inversion of dielectric anisotropy in nematic liquid crystal by dye doping

10% Cu doped ZnO nanoparticles (NPs) prepared by hydrothermal and solvothermal method have been dispersed to the pure FLC 17/100 in 1% concentration of guest entity. Electro-optical, elastic and dielectric analysis has been made for the FLC-NPs composite system with the variation of temperature. The nature of the composite system clearly shows the alteration in FLC parameters with the dispersion of NPs. The interaction between crystalline NPs and non-crystalline ferroelectric liquid crystal matrix modifies the properties of the pure FLC system. The synthesis method of NPs is also responsible for the changes taking place in physical properties of the pure FLC. The size and surface defects of the NPs amend the FLC parameters like dielectric permittivity, relaxation frequency, relaxation strength, tilt angle, spontaneous polarization and rotational viscosity etc. The coupling of spontaneous polarization and tilting of the FLC molecules are factors responsible for the resultant electro-optical (E-O) parameters of the composite system.

Ferroelectric liquid crystal matrix dispersed with Cu doped ZnO nanoparticles

The ferroelectric liquid crystals (FLCs) displays normally suffer from less contrast ratio and vision angle. To produce high optical contrast and colors in FLC displays, Guest-host mode is widely used. Addition of a small amount of polymer in the pure FLC results in considerable change in its dielectric and electro-optical properties. In the present paper we have investigated the effect of adding polymer (PMMA) on the FLC material (Felix 17/100). Polymer doped FLC composites (FLCPC) has been prepared by the dispersion of 1% wt/wt concentration of polymer in pure FLC. Planar aligned cells have been used to study dielectric and electro-optical properties in SmC* phase of both the samples i.e. pure FLC and FLCPC. Considerable change in various properties like spontaneous polarization, anchoring parameters, Goldstone mode relaxation time and relaxation strength have been noticed for both the samples. These changes have been explained by considering polymer network formed in the FLC matrix.

Satya Prakash Yadav

Papers

Carbon nanotube dispersion in nematic liquid crystals: An overview

Effect of TiO2 nanoparticles dispersion on ionic behaviour in nematic liquid crystal

Sign inversion of dielectric anisotropy in nematic liquid crystal by dye doping

Ferroelectric liquid crystal matrix dispersed with Cu doped ZnO nanoparticles

Comparative study of dielectric and electro-optical properties of pure and polymer ferroelectric liquid crystal composites