An Electrospun Poly(vinylidene fluoride) Nanofibrous Membrane and Its Battery Applications

Abstract

tained over macroscopic film thicknesses and large surface areas by vapor deposition of a single molecular species on an amorphous substrate. Inducing the non-centrosymmetric order by using selective hydrogen bonding to the substrate and between the molecules leads to a much better molecular ordering than with the technique described by Cai et al., [13] which requires control of the molecular beam direction relative to the substrate. The present technique does not require a well-defined molecular beam, and is also much simpler and faster than the synthetic methods used by Ulman [7] and Marks and Ratner [18] or for LB films.It is important to note that the alignment in our films is critically dependent on the ability of these molecules to selectively hydrogen bond to the surface, in order to begin the alignment process, and selectively hydrogen bond to itself in a unidirectional fashion in order to maintain the alignment over a large thickness. We have carried out preliminary experiments with molecules that only posses hydrogen bond acceptors and, therefore, can form hydrogen bonds to the substrate surface, but which lack hydrogen bond donors thus eliminating the possibility of intra-molecular hydrogen bonding, and have shown that only very thin films (of the order of a few monolayers thickness) with polar ordering perpendicular to the substrate surface can be grown. As the films grow thicker, we see that the ordering cannot be maintained.In conclusion, we have shown a simple and efficient new method to produce supramolecular self-assembled thin films with well-defined polar ordering perpendicular to the substrate surface. The resulting films are homogenous over a large area, and a regular, deterministic molecular ordering can be maintained over a large thickness of the order of 1 lm. The fact that the films were grown on amorphous glass substrates circumvents the need for surface epitaxy. The quality of the films and the simplicity of the fabrication method make this novel technique very attractive for the fabrication of nonlinear optical waveguides for frequency conversion or electrooptic modulation. Despite the relatively low nonlinearity (d 111 = 5 pm V ±1 ) that has been obtained in this first demonstration, the high degree of molecular ordering and the fact that the films consist of only one component make them potentially very interesting when compared to present candidates for organic electro-optic modulators, poled polymers. The higher degree of order and tighter molecular packing in our films should also lead to a better photostability when compared to amorphous systems with embedded chromophores. A further detailed investigation of the mechanism that leads to the molecular ordering and an optimization of the growth conditions should lead to a new generation of organic waveguides for frequency conversion and electro-optic modulation. Experimental.BITINPH was purchased from Opto-Organics Industrial Research Limited and purified by recrystallization from ethanol. The amorphous glass substrates were cl...

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