Pulse width modulation (PWM) control of the bending displacement and force generation of ionomer‐based polymer actuators

This paper discusses results of the pulse width modulation (PWM) control of the bending displacement and force generation of ionomer‐based polymer actuators. The idea of PWM control for polymer actuators is based on the frequency dependence on relaxation processes of the bending motion of the actuator. The actuators were fabricated by electroless plating of platinum on a perfluorinated sulfonated polymer (i.e. Nafion). It was noted that the duty cycles of PWM can smoothly control both the displacement and force generated by the actuator. The performance of the actuator was evaluated under 40%RH and 90%RH conditions because of the moisture sensitivity of the actuators. Copyright © 2013 John Wiley & Sons, Ltd.     

Molecule motion at polymer brush interfaces from single‐molecule experimental perspectives

Polymer brushes have been widely used as functional surface coatings for broad applications including antifouling, energy storage, and lubrications. Understanding the molecule dynamics at polymer brush interfaces is important in unraveling the structure–property relationships in these materials and establishing a new materials design paradigm of novel functional polymer thin films with efficient interfacial transport. By applying modern fluorescence‐based single‐molecule spectroscopic and microscopic techniques, molecule dynamics at varied polymer brush interfaces have been experimentally investigated in recent years. New insights are given to the understandings of some unique and unusual materials properties of polymer brush thin films. This review summarizes some recent studies of molecular diffusion at polymer brush interfaces, highlights some new understandings of the interfacial properties of polymer brushes, and discusses future research opportunities in this field. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014 , 52, 85–103     

A proposal for a novel evaluation method of the bending velocities of polymer actuators

This paper proposes a novel evaluation method for three types of velocities of the bending processes of polymer actuators. These velocities are the initial, bending, and backtracking velocities, and the method considers three processes of the bending motion. By calculating the time–width differentiation of the displacement of each process, the initial, bending, and backtracking velocities can be evaluated. Δt of 0.1, 1.0, and 10.0 s were considered to be the differentiations of bending displacement, and the initial, bending, and backtracking velocities were calculated to be 2.15, 0.46, and 0.002 mm/s, respectively. By using the method proposed here, we found that the initial velocity at 75%RH is 2.5 times faster than it was at 45%RH by increasing the adsorption of water. Copyright © 2013 John Wiley & Sons, Ltd.     

The effects of the potential and polarization time on the performance of ionic polymer metal composite actuators: a control of forward and reverse displacements

This paper focuses on the dependence of various waveforms of the potential on the displacement of Nafion‐platinum based IPMC actuators at 40 and 90% relative humidity (RH). In comparison with simpler square waveforms, a waveform that is being composed by inclusion of a rest potential of 0 V has given a longer displacement. This benefit was effective at lower humidity conditions. By a polarization, the actuators show three major displacement processes of maximum forward displacement, steady forward displacement, and maximum reverse displacement. Here, the dependence of the potential and polarization time on these displacements has been carefully examined. An increase in the forward displacement by the potential does not strongly affect a slower reverse relaxation. To give a suitable relaxation period before a polarity switching of the potential seems effective to release the internal stress of the actuator. An elevated drive potential has decreased in the bending speed apparently. Finally, it has been noted that the ‘recovery’ of the maximum displacement is possible if a suitable waveform is applied to the actuator. This recovery effect is more remarkable at higher dive potential. Copyright © 2007 John Wiley & Sons, Ltd.     

Effects of d.c. potential patterns on the performance of ion‐exchange polymer based molecular actuators

The dynamic performance (i.e. displacement, current, velocity, and force) of ion‐exchange polymer based actuators (the Nafion?/platinum electrodes) have been examined by developing instrumentation. The CCD imaging technique was examined to evaluate the displacement under the various d.c. potential patterns. Two different d.c. potential patterns with or without a rest were applied to the electrodes at 0.1 Hz. It was better to take a rest at 0 V for the polarization back and forth between +2 and ?2 V to give lower current consumption and longer displacement. The actuator produced the force of ca. 0.95 g at 3.25 V in air. The result also demonstrated that higher overpotential has to be avoided to maintain the maximum force. The generative force is in inverse proportion to the length of the actuators. The dimension of the film strongly governs the force production and its performance. Copyright © 2006 John Wiley & Sons, Ltd.     

A regenerable pseudo-reagentless glucose biosensor based on Nafion polymer and l,1''-dimethylferricinium mediator

Glucose oxidase was immobilized onto electrodes by co-deposition from an aqueous solution containing the diluted ion-exchange polymer Nafion. The cationic exchange property of the polymer was used to provide high local concentrations of l,1'-dimethylferricinium (DMFc⁺) mediator in the film by exchange from solution. The mediated electrodes were operated at +200 mV (vs. ), and the Nafion film was shown to reduce interfering current from ascorbate anion. Cyclic voltammetric analysis revealed a fourteen-fold increase in the effective DMFc⁺ activity at the electrode after extraction into the film. The sensitivity to glucose was 52 μA/cm²/mM in a solution containing 0.09 mM DMFc⁺, which is at least three-fold greater than reported for similar electrodes using hydrogen peroxide detection at +650 mV, with a response time of less than 1 min for a 10 μm thick membrane. Oxygen interference was significant, requiring deaeration of the solution before analysis. The electrodes exhibited no significant decrease in sensitivity for more than 50 days on storage in acetate buffer. Electrodes covered with 8000 MWCO dialysis membrane slowed the exchange of DMFc⁺ with the solution such that the Nafion film functioned as a mediator reservoir. This permitted reagentless analysis of glucose, typically capable of twenty assays when measuring concentrations between 0.1 and 1 mM. The sensitivity for glucose was 7.85 μA/cm²/mM, which is 15% of the sensitivity for the electrode without the dialysis membrane. The detection limit was 20 μM, with a linear range extending to about 3 mM, giving a dynamic range of over two orders of magnitude. Thus where some sacrifice of sensitivity and response rate may be made, the dialysis membrane cover enables multiple analyses in a reagentless biosensor scheme.     

Temperature and pressure dependence of the free volume in the perfluorinated polymer glass CYTOP: A positron lifetime and pressure‐volume‐temperature study

The microstructure of the free volume was studied for an amorphous perfluorinated polymer (T_g = 378 K). To this aim we employed pressure–volume–temperature experiments (PVT) and positron annihilation lifetime spectroscopy (PALS). Using the Simha‐Somcynsky equation of state the hole free volume fraction h and the specific free and occupied volumes, V_f = hV and V_occ = (1 ? h)V, were determined. Their expansivities and compressibilities were calculated from fits of the Tait equation to the volume data. It was found that in the glass V_occ has a particular high compressibility, while the compressibility of V_f is rather low, although h (300 K) = 0.108 is large. In the rubbery state the free volume dominates the total compressibility. From the PALS spectra the hole size distribution, its mean, 〈v_h〉, and mean dispersion, σ_h, were calculated. From a comparison of 〈v_h〉 with V_f a constant hole density of N_h′ = 0.25 × 10²¹ g^?1 was estimated. The volume of the smallest representative freely fluctuating subsystem, 〈V_SV〉 ∝ 1/σ_h², is unusually small. This was explained by an inherent topologic disorder of this polymer. 〈v_h〉 and σ_h show an exponential‐like decrease with increasing pressure P at 298 K. The hole density, calculated from N_h′ = V_f/〈v_h〉, seems to show an increase with P which is unexpected. This was explained by the compression of holes in the glass in two, rather than three, dimensions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2519–2534, 2007     

Temperature dependence of the fluorescence quantum yields of diphenylsiloxane‐based copolymers in dilute solutions

The monomer and excimer fluorescence quantum yields of well‐defined poly(dimethylsiloxane‐co‐diphenylsiloxane)s with different diphenylsiloxane (Ph₂SiO) contents have been determined, along with those of 1,1,3,3‐tetraphenyl‐1,3‐dimethyldisiloxane and 1,1,3,3,5,5‐hexaphenyltrisiloxane‐1,5‐diol used as model compounds, in a dilute organic solvent at different temperatures. The measured fluorescence quantum yields of the copolymers are correlated with the fraction of the ? (CH₃)₂SiO? (Ph₂SiO)_n? (CH₃)₂SiO? structures. The monomer fluorescence yield for copolymers with low Ph₂SiO contents is dominated mainly by the isolated ? (CH₃)₂SiO? (Ph₂SiO)? (CH₃)₂SiO? unit, and the apparent mean binding energy of the excimer does not increase significantly with increasing Ph₂SiO content. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 854–861, 2002     

Semi‐micro reversed‐phase liquid chromatography for the separation of alkyl benzenes and proteins exploiting methacrylate‐ and polystyrene‐based monolithic columns

Monolithic columns were synthesized inside 1.02 mm internal diameter fused‐silica lined stainless‐steel tubing. Styrene and butyl, hexyl, lauryl, and glycidyl methacrylates were the functional monomers. Ethylene glycol dimethacrylate and divinylbenzene were the crosslinkers. The glycidyl methacrylate polymer was modified with gold nanoparticles and dodecanethiol (C₁₂). The separation of alkylbenzenes was investigated by isocratic elution in 60:40 v/v acetonitrile/water. The columns based on polystyrene‐co‐divinylbenzene and poly(glycidyl methacrylate)‐co‐ethylene glycol dimethacrylate modified with dodecanethiol did not provide any separation of alkyl benzenes. The poly(hexyl methacrylate)‐co‐ethylene glycol dimethacrylate and poly(lauryl methacrylate)‐co‐ethylene glycol dimethacrylate columns separated the alkyl benzenes with plate heights between 30 and 60 μm (50 μL min^?1 and 60°C). Similar efficiency was achieved in the poly(butyl methacrylate)‐co‐ethylene glycol dimethacrylate column, but only at 10 μL min^?1 (0.22 mm s^?1). Backpressures varied from 0.38 MPa in the hexyl methacrylate to 13.4 MPa in lauryl methacrylate columns (50 μL min^?1 and 60°C). Separation of proteins was achieved in all columns with different efficiencies. At 100 μL min^?1 and 60°C, the lauryl methacrylate columns provided the best separation, but their low permeability prevented high flow rates. Flow rates up to 500 μL min^?1 were possible in the styrene, butyl and hexyl methacrylate columns.     

Time dependence of piezoresistance for the conductor‐filled polymer composites

The piezoresistance and its time dependence of conductor‐filled polymer composites have been investigated. To reveal the origin of the time dependence of piezoresistance, the creep of the polymer matrix is also studied. Based on the interparticle separation change under the applied stress, a model has been developed to predict the piezoresistance and its time dependence. By analyzing this model, the influences of applied stress, filler particle diameter, filler volume fraction, matrix compressive modulus, potential barrier height, and the matrix creep behavior on the piezoresistance and its time dependence are interpreted quantitatively. These predicted results are compared with the experimental data obtained on the polymer composites filled with conductor fillers, and good agreements were obtained. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2739–2749, 2000     

Film thickness dependence of the domain size in weakly incompatible thin polymer blend films

The surface morphology of thin polymer blend films of deuterated polystyrene (dPS) and polyparamethylstyrene (PpMS) is investigated with scanning force microscopy (SFM) and optical microscopy. From a statistical analysis of the data the most prominent in-plane length picturing the domain size as a function of the blend film thickness is determined. In ultra-thin films surface patterns directly after preparation are absent, whereas for thicker films a linear dependence is observed. After a relaxation towards equilibrium, resulting from annealing or storage under toluene vapor, the power law observed changes for ultra-thin films and remains unchanged for thicker films. Received: 27 July 2000 Accepted: 30 October 2000     

Development of an online solid‐phase extraction with liquid chromatography method based on polymer monoliths for the determination of dopamine

Porous polymer monoliths have been used to develop an online solid‐phase extraction with liquid chromatography method for determination of dopamine in urine as well as for a continuous monitoring of dopamine in flowing system. A polymerization mixture containing 4‐vinylphenylboronic acid monomer has been used to prepare a trapping column based on specific ring formation reaction with dopamine cis‐diol functionality. Additionally, a monolithic stationary phase with zwitterion functionality has been used to prepare capillary column for the separation of dopamine. Experimental conditions including molarity, pH, and flow rate of the loading buffer together with a valve switching time have been optimized to provide the highest recovery for dopamine. Experimental setup has been used to determine dopamine in a urine. By using both calibration curve and standard addition method, the dopamine level was determined to be 1.19 and 1.28 mg/L, respectively. Further, we have used experimental design to optimize coupling of two extraction monolithic loops to separation capillary column with monolithic phase for a comprehensive monitoring of dopamine. After multivariate analysis, sample loading flow‐rate and a flow‐rate of flushing buffer were selected as the most significant variables. Optimized experimental setup was applied to continuously monitor dopamine degradation.     

Molecular dynamics study of the cations,water molecules,and polymer chains in Nafion type membranes

The structure and dynamics of the hydrated cationic complexes in Nafion type membrane pores has been studied by the molecular dynamics approach. The mechanism of the cationic transport has been examined. The dependence of the cationic transport coefficients on temperature and the number of water molecules has been investigated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1233–1236, July, 1995.The present work was made possible in part by financial support of the International Science Foundation (Grant MPG000) and the Russian Foundation for Basic Research (Grant 93-03-4205).     

Voltammetric Studies of Cadmium‐ and Zinc‐Containing Metallothioneins at Nafion‐Coated Mercury Thin Film Electrodes

Voltammetric studies of rabbit liver metallothioneins (MTs, containing both Zn and Cd ions) and Zn₇‐MT were carried out at Nafion‐coated mercury film electrodes (NCMFEs). The accumulation of MT molecules into the NCMFEs enhances the voltammetric signals and the electrostatic interaction between the Nafion membrane and MT facilitates facile electron transfer reactions. Two well‐defined redox waves, with reduction potential (E_pc) values at ?0.740 and ?1.173 V, respectively, were observed. The peak at E_pc =?0.740 V is attributable to the reduction of the Cd‐MT complex, whereas that at E_pc=?1.173 V was assigned to the reduction of the Zn‐MT complex. Zn₇‐MT exhibits only one redox wave with E_pc=?1.198 V. The NCMFE was found to be more advantageous than thin mercury film electrode (MFE), because the pristine metal ions in MTs (e.g., Cd²⁺ and/or Zn²⁺) are not significantly replaced by Hg²⁺. The NCMFE is also complementary to Nafion‐coated bismuth film electrode in that it has a greater hydrogen overpotential, which allows the reduction of the Zn‐MT complex to be clearly observed. Moreover, intermetallic compound formation between Cd and Zn appears to be less serious at NCMFEs. Consequently, the amounts of Cd and Zn deposited into the electrode upon the reduction reactions can be quantified more accurately.     

Influence of thermal history and humidity on the ionic conductivity of nanoparticle‐filled solid polymer electrolytes

The crystallinity and conductivity of nanoparticle‐filled solid polymer electrolytes (SPEs) are investigated as a function of thermal history and water content. Our objective is to evaluate how performance is affected by the conditions under which the SPEs are handled and tested. The samples consist of polyethylene oxide (PEO), LiClO₄, and Al₂O₃ nanoparticles. At low humidity, SPEs at ether oxygen to lithium ratios of 8:1 do not crystallize immediately; instead, 3 days are required for crystallization to occur, and this does not depend strongly on the presence of nanoparticles. The conductivity is improved by the addition of nanoparticles at low humidity, but only at an ether oxygen to lithium ratio of 10:1, which corresponds to the eutectic concentration. At high humidity, the recrystallization time is delayed for 3 weeks, and the conductivity increases in both filled and unfilled SPEs beyond that of the low humidity samples. Although we observe that water amplifies the influence of nanoparticles on conductivity, we also find that nanoparticles inhibit water uptake—but only in the presence of lithium. Because Li⁺ strongly absorbs water, this result suggests that nanoparticles may interact directly with Li⁺ ions to prevent water uptake. In filled samples at the eutectic concentration (10:1), more water is absorbed compared to the nanoparticle‐filled 8:1 samples, even though less lithium is present. This suggests that nanoparticles may segregate to lithium‐poor regions in the 10:1 samples, and this scenario is supported by the morphology that would be expected at the eutectic concentration. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1496–1505, 2011     

Determination of Patent Blue V (E131) at a Nafion‐Modified Glassy Carbon Electrode

Patent Blue V was determined in aqueous solutions at a Nafion‐coated glassy carbon electrode using a DPV technique. Preliminary cyclic voltammetric studies allowed to choose the most sensitive peak and a further DPV study allowed determining the analyte in the 10^?7–10^?6 M range, with a detection limit equal to 7.6×10^?8 M, two orders of magnitude lower than at a bare GC electrode. The modified electrode was applied to the analysis of matrices of alimentary concern in presence of tartrazine. Thanks to the method high sensitivity, very diluted samples can be analyzed minimizing the matrix effects.     

Temperature dependence of strain energy and thermodynamic properties of V2O5‐based single‐walled nanotubes: Zone‐folding approach

A zone‐folding approach is applied to estimate the thermodynamic properties of V₂O₅‐based nanotubes. The results obtained are compared with those from the direct calculations. It is shown that the zone‐folding approximation allows an accurate estimation of nanotube thermodynamic properties and gives a gain in computation time compared to their direct calculations. Both approaches show that temperature effects do not change the relative stability of V₂O₅ free layers and nanotubes derived from the α‐ and γ‐phase. The internal energy thermal contributions into the strain energy of nanotubes are small and can be ignored. © 2016 Wiley Periodicals, Inc.