Abstract
Self assembled nanofibers derived from donor-acceptor (D-A) pair of dodecyl methyl viologen (DMV) and potassium salt of coronene tetracarboxylate (CS) is an excellent material for the development of organic electronic devices particularly for ultrafast response to relative humidity (RH). Here we have presented the results of in-situ grazing incidence small angle x-ray scattering (GISAXS) measurements to understand aridity dependent self reorganization of the nanofibers. The instantaneous changes in the organization of the nanofibers was monitored with different equilibrium RH conditions. Additionally formation of nanofibers during drying was studied by GISAXS technique – the results show two distinct stages of structural arrangements, first the formation of a lamellar mesophase and then, the evolution of a distorted hexagonal lattice. The RH dependent GISAXS results revealed a high degree of swelling in the lattice of the micelles and reduction in the distortion of the hexagonal structure with increase in RH. In high RH condition, the nanofibers show elliptical distortion but could not break into lamellar phase as observed during formation through drying. This observed structural deformation gives insight into nanoscopic structural changes of the micelles with change in RH around it and in turn explains ultrafast sensitivity in its conductivity for RH variation.
Highlights
An ultrafast relative humidity (RH) sensor with these fibers
We have indicated in this figure the expected Yoneda peak (YP) positions of water, dodecyl methyl viologen (DMV) and silicon-substrate calculated from the known electron densities
The expected YP positions of water, DMV and silicon-substrate calculated from the known electron densities are marked here. (c) RH dependent grazing incidence small angle x-ray scattering (GISAXS) data of DMV-CS nanofibers on Si substrate
Summary
An ultrafast RH sensor with these fibers. Using UV-Vis, XRD and AFM measurements, it has been found that the π-π interaction length - the d spacing (refer Fig. 1(d)) corresponding to the π-π bond of DMV-CS moieties shortens with increasing RH giving a significant change (refer Fig. 1(e)) in the conductivity[37]. The large variation in the diameters of the nanofibers resulted in a very rough film of about 2 micron thickness and the measured Yoneda peak (YP in Fig. 2(b)) and diffused scattering was found to be sensitive to the position of the footprint of the x-ray beam. It is apparent in the cut along the qz direction of the YP shown in Fig. 2(b) that in high humid condition the film become smoother and the Yoneda peak becomes well defined. The (0, 0, 2) peak is apparent in qz data and qy data reveals presence of two peaks, first peak correspond to a lamellar structure and second peak is the (0, −1, 1) reflection
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