Self-assembled full nanowire P(VDF-TrFE) films with both anisotropic and high bidirectional piezoelectricity.

With the explosive growth of flexible electronics, the prototype piezoelectric polymer poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] has gained tremendous attention due to potential applications in flexible sensors, energy harvesters, and new smart devices. However, full realization of these applications is still challenging due to the lack of high quality films with strong piezoelectricity, which requires tailored molecular organization. Here we report unique 'full nanowire' P(VDF-TrFE) films with substantially enhanced bidirectional performance by a simple self-assembly via selective vapor annealing. Structural analysis showed that the solvent molecules significantly enhanced the copolymer chain mobility, giving highly ordered nanowires, whose quantity increased with time and finally formed a full flat-on lamellar nanowire array with backbones highly aligned along the film plane, leading to high lateral piezoelectricity as revealed by vector piezoresponse force microscopy and confirmed by electrical measurements. Surprisingly, the nanowire films also showed a much higher vertical piezoelectric coefficient (-35.2 pC N-1 directly measured by using a Berlincourt meter) than that of usually crystallized films owing to simultaneously enhanced molecular order and dipole switching ability. The scalability of the new method might boost industrial applications, and the findings may provide hints on new routes to nanostructured polymers with novel functionalities and deepen our understanding of the self-assembly of random copolymers.

A Numerical Simulation of Cell Separation by Simplified Asymmetric Pinched Flow Fractionation.

As a typical microfluidic cell sorting technique, the size-dependent cell sorting has attracted much interest in recent years. In this paper, a size-dependent cell sorting scheme is presented based on a controllable asymmetric pinched flow by employing an immersed boundary-lattice Boltzmann method (IB-LBM). The geometry of channels consists of 2 upstream branches, 1 transitional channel, and 4 downstream branches (D-branches). Simulations are conducted by varying inlet flow ratio, the cell size, and the ratio of flux of outlet 4 to the total flux. It is found that, after being randomly released in one upstream branch, the cells are aligned in a line close to one sidewall of the transitional channel due to the hydrodynamic forces of the asymmetric pinched flow. Cells with different sizes can be fed into different downstream D-branches just by regulating the flux of one D-branch. A principle governing D-branch choice of a cell is obtained, with which a series of numerical cases are performed to sort the cell mixture involving two, three, or four classes of diameters. Results show that, for each case, an adaptive regulating flux can be determined to sort the cell mixture effectively.