Swelling-diffusion-interfacial polymerized core-shell typed polystyrene/poly(3, 4-ethylenedioxythiophene) microspheres and their electro-responsive characteristics

Cross-linked polyelectrolyte microspheres: preparation and new insights into electro-surface properties

Polyelectrolyte microspheres find applications in many fields such as ion exchange columns, fuel cell membranes, and catalysis, to name a few. Synthesis of these microspheres by inverse emulsion polymerization offers various advantages due to the increased specific surface area and high surface charge density. The surface charge density of the obtained polyelectrolyte microspheres is a hundred times higher than that of either particles obtained by dispersion copolymerization of styrene and styrenesulfonic acid or sulfonated microspheres. The morphology, chemical structure, and electro-surface properties of the synthesized microspheres were studied by transmission and scanning electron microscopy, FTIR-spectroscopy, and conductometric and potentiometric titrations, respectively. Using the potentiometric titration it is possible to characterize the structure of the surface layer of polyelectrolyte microspheres as entirely as possible. The study of the ion-exchange capacity of polyelectrolyte microspheres shows that ion-exchange capacity is 2.1 meq g-1 in this case, which is more than 2 times higher than that of sulfonated microspheres, and 20 times higher than that of particles obtained by dispersion copolymerization.

Nanoparticles Functionalized by Conducting Polymers and Their Electrorheological and Magnetorheological Applications

Conducting polymer-coated nanoparticles used in electrorheological (ER) and magnetorheological (MR) fluids are reviewed along with their fabrication methods, morphologies, thermal properties, sedimentation stabilities, dielectric properties, and ER and MR characteristics under applied electric or magnetic fields. After functionalization of the conducting polymers, the nanoparticles exhibited properties suitable for use as ER materials, and materials in which magnetic particles are used as a core could also be applied as MR materials. The conducting polymers covered in this study included polyaniline and its derivatives, poly(3,4-ethylenedioxythiophene), poly(3-octylthiophene), polypyrrole, and poly(diphenylamine). The modified nanoparticles included polystyrene, poly(methyl methacrylate), silica, titanium dioxide, maghemite, magnetite, and nanoclay. This article reviews many core-shell structured conducting polymer-coated nanoparticles used in ER and MR fluids and is expected to contribute to the understanding and development of ER and MR materials.

Smart and Functional Conducting Polymers: Application to Electrorheological Fluids

Electro-responsive smart electrorheological (ER) fluids consist of electrically polarizing organic or inorganic particles and insulating oils in general. In this study, we focus on various conducting polymers of polyaniline and its derivatives and copolymers, along with polypyrrole and poly(ionic liquid), which are adopted as smart and functional materials in ER fluids. Their ER characteristics, including viscoelastic behaviors of shear stress, yield stress, and dynamic moduli, and dielectric properties are expounded and appraised using polarizability measurement, flow curve testing, inductance-capacitance-resistance meter testing, and several rheological equations of state. Furthermore, their potential industrial applications are also covered.

Active control of properties of concrete: a (p)review

Concrete properties to a large extent depend on mix design and processing, currently leaving only limited options to actively modify concrete properties during or after casting. This paper gives a (p)review on a more advanced active control of properties of concrete, based on the application of external signals to trigger an intended response in the material, either in fresh or hardened state. Current practices in concrete industry that could be considered as active control are briefly summarized. More advanced active control mechanisms as studied in other fields, e.g. based on hydrogels and other functional polymers, are reviewed and some principles are listed. A specific focus is further given on potential methods for active rheology control. Based on the concepts developed in other fields, substantial progress could be made in order to achieve active control of fresh and hardened concrete properties. However, several challenges remain, like the stability and functioning of the responsive material in a cementitious environment, the applicability of the control signal in a cementitious material, and the economy, logistics and safety of a control system on a construction site or in precast industry. Finding solutions to these challenges will lead to marvelous opportunities in general, and for 3D and even 4D printing more particularly.

Polyaniline Coated Core-Shell Typed Stimuli-Responsive Microspheres and Their Electrorheology

Functional core-shell-structured particles have attracted considerable attention recently. This paper reviews the synthetic methods and morphologies of various electro-stimuli responsive polyaniline (PANI)-coated core-shell-type microspheres, including PANI-coated Fe₃O₄, SiO₂, Fe₂O₃, TiO₂, poly(methyl methacrylate), poly(glycidyl methacrylate), and polystyrene along with their electrorheological (ER) characteristics when prepared by dispersing these particles in an insulating medium. In addition to the various rheological characteristics and their analysis, such as shear stress and yield stress of their ER fluids, this paper summarizes some of the mechanisms proposed for ER fluids to further understand the responses of ER fluids to an externally applied electric field.

Smart Fluid System Dually Responsive to Light and Electric Fields: An Electrophotorheological Fluid

Electrophotorheological (EPR) fluids, whose rheological activity is dually responsive to light and electric fields (E fields), is formulated by mixing photosensitive spiropyran-decorated silica (SP-sSiO₂) nanoparticles with zwitterionic lecithin and mineral oil. A reversible photorheological (PR) activity of the EPR fluid is developed via the binding and releasing mechanism of lecithin and merocyanine (MC, a photoisomerized form of SP) under ultraviolet (UV) and visible (VIS) light applications. Moreover, the EPR fluid exhibits an 8-fold higher electrorheological (ER) performance compared to the SP-sSiO₂ nanoparticle-based ER fluid (without lecithin) under an E field, which is attributed to the enhanced dielectric properties facilitated by the binding of the lecithin and SP molecules. Upon dual application of UV light and an E field, the EPR fluid exhibits high EPR performance (ca. 115.3 Pa) that far exceeds its separate PR (ca. 0.8 Pa) and ER (ca. 57.5 Pa) activities, because of the synergistic contributions of the PR and ER effects through rigid and fully connected fibril-like structures. Consequently, this study offers a strategy on formulation of dual-stimuli responsive smart fluid systems.

Enhanced Electrorheological Performance of Mixed Silica Nanomaterial Geometry

The mixed geometrical effect on the electrorheological (ER) activity of bimodal ER fluids was investigated by mixing SiO₂ spheres and rods of different dimensions. To gain an in-depth understanding of the mixed geometrical effect, 12 bimodal ER fluids were prepared from 4 sizes of SiO₂ spheres (50, 100, 150, and 350 nm) and 3 types of SiO₂ rods with different aspect ratios (L/D = 2, 3, and 5). Five concentrations of SiO₂ spheres and rods were created for each bimodal ER fluid, resulting in a total of 60 sets of comprehensive ER measurements. Some bimodal ER fluids exhibited enhanced ER performance, as high as 23.0%, compared to single SiO₂ rod-based ER fluids to reveal the mixed geometrical effect of bimodal ER fluids. This interesting experimental result is based on the structural reinforcement provided by spheres to fibrillated rod materials, demonstrating the mixed geometrical effect on ER activity.