Poly(vinylidene fluoride) (PVDF) nanofibers were prepared by electrospray deposition (ESD). To control the diameter, morphology, and structure of PVDF nanofibers, some parameters were investigated, such as polymer concentration, nozzle‐to‐ground collector distance, feeding rate of the polymer solution, and applied voltage. The fabricated fiber was 80–700 nm in diameter. The increase in the polymer concentration caused an increase in the polymer viscosity and fiber diameter. At low polymer concentration (5 wt %), polymer nanoparticles were formed. An increase in applied voltage will increase the fiber diameter. Variation in the nozzle‐to‐ground collector distance did not result in significant changes in the fiber diameter. Increase in the feeding rate of the polymer solution decreased the fiber diameter. Differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD) measurements showed that the melting point and total crystallinity were decreased. Fourier transform infrared spectroscopy (FTIR) measurement revealed that ESD process induced the formation of the oriented β‐phase PVDF structures. It was also demonstrated that the addition of hydrofluorocarbon solvent to polymer solution remarkably enhanced the formation of β‐phase crystalline structure of PVDF nanofiber. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 779–786, 2006

Fracture behavior of amorphous poly(ethylene terephthalate) (PET) films added multiwalled carbon nanotube (MWCNT) has been compared with that of the PET films added with carbon black (CB) to elucidate the effects of the large aspect ratio of MWCNT. Fracture toughness has been evaluated using the essential work of fracture tests. Evolution of the crazes has been analyzed by conducting time-resolved small-angle X-ray scattering measurements during tensile deformation of the films at room temperature using synchrotron radiation. CB and MWCNT increased the fracture toughness of the PET film by increasing the plastic work of fracture. This resulted from the effects of the fillers to prevent the localization of deformation upon the crazes formed at earlier stages of tensile deformation and to retard the growth of the fibrils in the crazes to a critical length. The CB particles provided a number of sites where the crazes were preferably formed due to stress concentration. In the case of MWCNT, on the other hand, the widening of the crazes formed at earlier stages was suppressed due to the bridging effect arising from the large aspect ratio of MWCNT.

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A twisted polymeric fiber (TPF) actuator often referred to as a fishing line/sewing thread artificial muscle, is one of the soft actuators which is made by twisting and heating a nylon fishing line. There are mainly two types of the TPF actuator, one is to make a contraction motion, which is sometimes called a twisted and coiled polymeric fiber actuator, and the other is to make a rotational motion, called simply a TPF actuator. This letter focuses on the latter one and proposes an estimated temperature feedback control method to regulate a torsional angle of the TPF actuator. The TPF actuator is very lightweight and low cost, but the advantage would be lost if some external sensors, such as a thermal sensor or encoder is used. In order to control the torsional angle without the use of the external sensors, a temperature of the actuator is estimated by measuring the change in the Ohm resistance of a heater wrapping around the actuator. By feedbacking the estimated temperature, the torsional angle can be regulated indirectly. First, the two types of models are proposed. One is to derive a desired temperature of the actuator from the desired angle. The other is to estimate the actuator's temperature from a change of the resistance of the actuator's heater. Next, the temperature feedback control law is composed using these two models. Finally, experiments of the torsional angle regulation are conducted using a prototype of the actuation module, which consists of antagonistically embedded two TPF actuators to demonstrate the usefulness of the proposed controller.