Overview on conducting polymer in energy storage and energy conversion system

Polymer-based electrochemical devices such as supercapacitor, battery, and fuel cell have been developed and advanced for energy related application. In this regard, conducting polymers own several tunable characteristics for energy conversion and energy storage relevance. Consequently, efficient, reliable, low cost, conducting, stable, and environment friendly energy systems have been developed using conducting polymers. To enhance the efficiency and commercialization of energy systems, design, structure, composition, and fabrication technique used for conducting polymers and related composite have been focused. Challenges and future trend associated with current state of the art conducting polymer materials in supercapacitor, battery, and fuel cell are highlighted.     

Nanostructured polymer gels

A brief review of our recent work on polymer gel opals is given in memory of late Professor Tanaka. The central idea is to first synthesize monodisperse polymer gel nanoparticles, then self-assemble them into a 3D network, and eventually covalently bond them. The covalent bonding contributes to the structural stability, while self-assembly provides them with crystal structures that diffract light, resulting in colors. N-isopropylacrylamide (NIPA) gel has been used as a model system for this study. The nanostructured NIPA gel, which contain up to 97 wt% water, displays a striking iridescence like precious opal but are soft and flexible like gelatin.     

Smart nanocomposite polymer gels

The combination of polymers with nanomaterials displays novel and often enhanced properties compared to the traditional materials. They can open up possibilities for new technological applications. The magnetic polymer gel represents a new type of composites consisting of small magnetic particles, usually from the nanometer range to the micron range, dispersed in a highly elastic polymeric gel matrix. Combination of magnetic and elastic properties leads to a number of striking phenomena that are exhibited in response to impressed magnetic fields. Giant deformational effects, high elasticity, anisotropic properties, temporary reinforcement and quick response to magnetic field open new opportunities for using such materials for various applications.     

Osmotic deswelling of polymer gels

The osmotic deswelling of polymer networks swollen in a good solvent by transferring it into a solution of a linear polymer in the same solvent is investigated using the modified Flory model proposed previously. The predicted results obtained using this simple model are compared to the experimental data available in the literature. We further examine the variation of the degree of deswelling, the degree of swelling and the partition coefficient with the molecular weight, and the volume fraction of the linear polymer chains in the surrounding polymer solution. Also, the role of the packing factor is briefly discussed.© 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2525–2535, 1998     

Magnetic applications of polymer gels

In this paper we report results of both, material preparation and magnetic characterisation, on CoFe₂O₄ particles of nanometric size formed by in‐situ precipitation within polymer gels. The size of the particles was controlled within a very narrow volume distribution and its average value was shifted from 2 to 10 nm. The existence of nanoparticles showing, at room temperature, coercive field values between 500 and 900 Oe and saturation magnetisations of about 500 emu/cm³, suggest to use these systems to get magnetic recording media with ultra high density. Poly(vinyl alcohol) (PVA) and Polystyrene (PS) films were prepared from this nanocomposite material. After a magnetic field treatment nanoparticles within the PVA films are free to rotate in response to an applied magnetic field. This PVA based nanocomposite film portends a new class of magnetic material with very little or no electrical and magnetic loss.     

Viscoelastic scaling in polymer gels

New scaling laws for chain networks are derived to describe the fundamental relationships between the viscosity exponent (k), viscoelastic exponent (m), stretched exponent (β), spatial dimension (d). fractal dimension (d_f), and a universal constant (γ). The scaling of the total number of monomers and the radius of gyration is defined by d_f. We have discovered γ = m/β to be a universal constant which relates the shear modulus of a polymer gel melt to the shear modulus near the glass transition. Analyzing the size-dependent shear viscosity, we have determined γ = 3d_fcd/(7d−5d_fc) = 2.647 for d = 3 where d_fc is the fractal dimension of critical clusters at the gel point. By using γ, the present theory extends previous work pertaining to systems near the sol-gel transition, and shows how properties far from the critical point can be explained. The theoretical prediction is in good agreement with viscoelastic measurements.     

Inhomogeneity control in polymer gels

Inhomogeneities, that is, nonrelaxing frozen concentration fluctuations, are inevitably present in polymer gels because they are introduced during the crosslinking of the constituent polymer chains in a solvent. Therefore, inhomogeneities increase as the number of crosslinks increases in a gel. The ionization of polymer gels is one of the methods used to suppress inhomogeneities. However, because crosslinking also means a freezing‐in of the conformation and topology of polymer chains in a solvent according to the chemistry of crosslinking, inhomogeneity control is quite sophisticated. In this article, we discuss the relationship between the inhomogeneities and the molecular/environmental parameters of polymer gels, such as the polymer concentration, the degree of crosslinking, the degree of ionization, and the interaction parameter, by considering the memory effect of gels. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 617–628, 2005     

Liquid flow through polymer gels

Slow neutron transmission technique was applied to investigate features of the solvent flow through quasi-porous matrices of gelatin, poly (acrylamide) and silica gels of different concentration/mesh sizes. We find the macromolecular friction coefficient for all gels to be proportional to the concentration of polymer network which correlates well with the predictions of the effective medium approach under the condition of negligible impact of hydrodynamic self-interactions. Determined values of the friction coefficient are used for evaluating the effective mesh sizes, which are in good agreement with the appropriate results of quasi-elastic light scattering for homogeneous poly (acrylamide) gels.     

Concentration polydispersity in polymer gels

For swollen polymer networks there is no generally accepted relation between the macroscopic osmotic properties and the scattering behaviour. Detailed information on the relationship between these properties can, however, be deduced from complementary measurements of osmotic and elastic behaviour, small angle neutron and X-ray scattering (SANS and SAXS) and quasi-elastic light scattering. We describe such an investigation in two types of networks, differing in the mechanism of cross-linking. The SANS spectra yield information on the structure, which is generated both by the dynamics of the system and by long range static constraints. The former, arising from thermodynamic concentration fluctuations, governs the macroscopic osmotic and elastic moduli of the swollen network. The static superstructure in the gel reflects local variations in the cross-link density. The resulting concentration polydispersity, <δφ²>/φ², is determined by the details of the cross-linking procedure. Its concentration dependence as a function of gel swelling can be expressed in terms of the same macroscopic osmotic and elastic variables as those that govern the thermodynamic properties of the gel.     

Ion aggregation in polymer gels

This brief review deals with our early experimental studies of ion aggregation in polymer gels proceeding via the condensation of counterions on the oppositely charged monomer units of the network with the formation of ion pairs and their clustering into multiplets. The two particular cases of the emergence of ion aggregates are considered: (a) for monovalent counterions in media of low polarity and (b) for multivalent counterions in water.     

Mechanochemical synthesis of mixed-ligand europium β-diketonates with nitrogen-containing neutral ligands

The solid-phase reaction between europium salts of β-diketones and nitrogen-containing neutral ligands in a planetary mill produces luminescent mixed-ligand compounds Eu(β-dic)₃ · D, where β-dic stands for dibenzoylmethane (DBM), benzoylacetone (BA), thenoyltrifluoroacetone (TTA), or benzoyltrifluoroacetone (BTFA); and D stands for 1,10-phenanethroline (Phen), 2,2-dipyridyl (Dipy), or diphenylguanidine (DPG). The mechanosynthesis and yield of lanthanide β-diketonates are studied as affected by the treatment parameters and the nature of the reagents. Powder X-ray diffraction demonstrates a staged course of the mechanochemical synthesis. Examination of formation-rate curves shows that grinding/stirring is the rate-controlling stage of the process. Thermogravimetric analysis (TGA) shows that the mechanosynthesis can proceed in the self-propagation mode. The relative luminescence intensity is determined as a function of treatment time. Particles of the mechanically activated mixture have sizes of 10–100 μm.     

Self-oscillatory systems based on polymer gels

Chemical and mechanical oscillations arising when the Belousov-Zhabotinsky reaction is performed in composite gels based on polyacrylamide and silica gel and gels of poly(acrylamide-co-sodium acrylate) have been investigated. The catalyst of the reaction can be incorporated into a gel through electrostatic interactions. Mechanical and absorption properties of polymer matrices are characterized, and the periods and amplitudes of mechanical oscillations arising in them are estimated. The mechanism of the phenomenon under consideration is advanced.     

Self-oscillating swelling and deswelling of polymer gels

Novel gel systems demonstrating rhythmically pulsatile mechanical motion similar to that of a heartbeat were developed. Self-oscillations of swelling and deswelling for the polymer hydrogels were realized by coupling pH and temperature sensitive hydrogels with a non-linear chemical reaction in the external solution media. The novel gel dynamics exhibiting cyclic and rhythmical oscillations may establish a new concept for functional materials that work under dynamic oscillating states.     

Dynamic scaling of polymer gels comprising nanoparticles

We present dynamic light scattering (DLS) measurements of soft poly(methyl-methacrylate) (PMMA) and polyacrylamide (PA) polymer gels prepared with trapped bodies (latex spheres or magnetic nanoparticles). We show that the anomalous diffusivity of the trapped particles can be analyzed in terms of a fractal Gaussian network gel model for the entire time range probed by DLS technique. This model is a generalization of the Rouse model for linear chains extended for structures with power law network connectivity scaling, which includes both percolating and uniform bulk gel limits. For a dilute dispersion of strongly scattering particles trapped in a gel, the scattered electric field correlation function at small wavevector ideally probes self-diffusion of gel portions imprisoning the particles. Our results show that the time-dependent diffusion coefficients calculated from the correlation functions change from a free diffusion regime at short times to an anomalous subdiffusive regime at long times (increasingly arrested displacement). The characteristic time of transition between these regimes depends on scattering vector as approximately q(-2), while the time decay power exponent tends to the value expected for a bulk network at small q. The diffusion curves for all scattering vectors and all samples were scaled to a single master curve.     

Study of life time and energy conversion efficiency in bi-layer and tri-layer polymer actuators

Devices based on bi-layer and tri-layer conducting polymer-polyethylene glycol (PEG) composite films of electrochemically synthesized polypyrrole-PEG/non-conducting adhesive polymer and polypyrrole-PEG/non-conducting adhesive polymer/polypyrrole-PEG were constructed. The bending motions of bi-layer and tri-layer composite films were investigated in 1.0 M LiClO₄ aqueous solution. The movement rate (rad s^?1), consumed electrical energy, consumed electrical charge and mechanical output energy of actuation of the bi-layer and tri-layer composite films both in free or in loading state were studied and compared with those of bi-layer and tri-layer prepared in the absence of PEG. At a given driving potential or driving current, the movement rates of bi-layer and tri-layer composite films in free and loading states are higher than those of bi- and tri-layer films synthesized without PEG respectively. The energy consumed per degree for bending actuation increases with the increase of loading weight and driving potential. The energy conversion efficiency decreases with the increase of driving potential. It was observed that the polypyrrole films prepared at low temperature with the optimized thickness in the presence of PEG plasticizer have shorter response time and longer cycle life than those of prepared without PEG. Study of Fatigue and training in the prepared artificial muscles reveals that the presence of PEG has considerable influence on the response of fabricated muscles.     

Platinum-acetylide polymer based solar cells: involvement of the triplet state for energy conversion

Relatively efficient photovoltaic devices were fabricated using blends of a phosphorescent platinum-acetylide polymer and a fullerene (PCBM); involvement of the triplet excited state of the platinum-acetylide polymer in photoinduced charge transfer is believed to contribute to the device efficiency.     

Construction of biomimetic smart nanochannels with polymer membranes and application in energy conversion systems

Learning from nature has inspired the creation of intelligent devices to meet the increasing needs of the advanced community and also to better understand how to imitate biology. As one of biomimetic nanodevices, nanochannels or nanopores aroused particular interest because of their potential applications in nanofluidic devices, biosensing, filtration, and energy conversions. In this review we have summarized some recent results mainly focused on the design, construction and application in energy conversion systems. Like biological nanochannels, the prepared smart artificial nanochannels fabricated by ion track-etched polymer membranes and smart molecules show a great potential in the field of bioengineering and biotechnology. And these applications can not only help people to know and understand the living processes in nature, but can also inspire scientists to study and develop novel nanodevices with better performance for the mankind.     

Intelligent polymer gels controlled by magnetic fields

 In this paper we summarise the effects induced by electric and magnetic fields on the mobility and shape of polymer gels containing a complex fluid as a swelling agent. Magnetic-field-sensitive gel beads and monolith gels have been prepared by introducing magnetic particles of colloidal size into chemically cross-linked poly(N-isopropylacrylamide) and poly(vinyl alcohol) hydrogels. The influence of uniform and nonuniform fields has been studied. In uniform magnetic fields the gel beads form straight chainlike structures, whereas in nonhomogeneous fields the beads aggregates due to the magnetophoretic force directed to the highest field intensity. The ability of magnetic-field-sensitive gels to undergo quick, controllable changes in shape can be used to mimic muscular contraction. Received: 26 July 1999/Accepted: 27 August 1999