Cross-polarization with magic-angle spinning kinetics and impedance spectroscopy study of proton mobility,local disorder,and thermal equilibration in hydrogen-bonded poly(methacrylic acid)

The ¹H–¹³C cross-polarization with magic-angle spinning (CP MAS) kinetics was studied in poly(methacrylic acid) (PMAA) having the purpose to track the links between the local order in the main chain and the proton dynamics in peripheral hydrogen bond networks. The experimental CP MAS kinetic curves were analyzed applying the models of isotropic and anisotropic spin-diffusion with thermal equilibration. The fractal dimension D_p ≈ 3 was deduced that indicates that PMAA behaves as an isotropic 3D-system. No proton conductivity in the neat PMAA was deduced from the impedance spectroscopy data analyzing the frequency dependences of the complex dielectric permittivity. The value of local order parameter S = 0.70 for CH₂ in PMAA occupies an intermediate position between 0.63 and 0.85 deduced for CH₂ sites in the main chains of poly(vinyl phosphonic acid) and poly(2-hydroxyethyl methacrylate), that is, the true proton conductor and the polymer that contains the H-bond network, however, no proton conductivity, respectively.     

Development of a new ultrasonic actuator based on Langevin bending transducer

A new ultrasonic actuator based on a bending-type Langevin piezoelectric transducer has been developed. An actuator consists of a half-wavelength Langevin transducer and an aluminum plate that is mounted in the middle of the transducer. The driving tip is located at the bottom of the aluminum plate. Piezoceramic rings with opposite polarity within each half of the ring are divided into two groups. Two harmonic signals with shifted phases by π/2 are used to excite the first bending mode of the Langevin transducer and aluminum plate. Elliptical trajectory of the contact point motion is obtained by combining these two bending modes. Numerical modelling was carried out to analyze harmonic response of the actuator and to investigate the trajectories of the contact point motion. Optimization of the aluminum plate design was performed to maximize the parameters of elliptical motion of the driving tip. A prototype actuator was fabricated, and output characteristics were measured. The results of numerical and experimental study are discussed.