Our research in the first year focuses on probing the structures of polymer synthesized with ionic liquids. Previously, we have observed novel morphologies of polyurea induced by uniform electric fields of various intensities and orientations via interfacial polymerization between a dielectric organic solvent (n-hexane) and IL (1-octyl-3-methylimidazolium tetrafluoroborate, [omim][BF₄]). The reaction cell and experiment configuration is shown in Figure 1.  A uniform electric field was generated between two large parallel aluminum plates connected to a high-voltage DC power supply.  A cylindrical reaction cell was placed at the center between the two large plates. The parallel plates were made inclined against the horizontal liquid interface.  Since ionic liquid is conductive, the surface boundary of the liquid is of equipotential and the field inside the bulk is zero (shielding effect). The ion distribution and the molecular orientations at the interface will respond to the external field. Small angle neutron scattering (SANS) was employed to probe the structure of such polyurea films. The SANS experiment was performed at Chalk River Lab, Ontario, Canada.  The wavelength of neutrons was l = 2.37 Ĺ, chosen by pyrolitic graphite monochromator at (0,0,2) Bragg reflection.  The collected scattering intensities were then corrected from the scattering of empty cell, background and transmission and plotted as a function of the scattering vector, q.    Figure 2 shows the neutron scattering data of the polymer samples synthesized in absence of the electric field (E=0) and in a constant field, E=5x10⁴ V/m, at theta = 0^o and 90^o.  The common feature of these scattering curves is a nearly q^-4 dependence at q £ 0.04 Ĺ^-1, presumably contributed from the tail of surface scattering of large clusters (Porod's law).  The main difference among the three samples is in the mid-q range (0.05 Ĺ^-1 < q < 0.1 Ĺ^-1).  In the case of E=0, the intensity is nearly a plateau indicating that another structure with a much smaller length scale also exists in the system.  In comparison of the SEM result, it is presumed the skeleton of the porous structure is made of such small particles.  In the case of E=5x10⁴ V/m and theta = 0^o, the intensity follows approximately q^-1, representing the characteristic scattering from long objects.  This is consistent with the observation in SEM, where the morphology is possibly composed of bundles of long polymer particles.  As for E=5x10⁴V/m and theta=90^o, the q-dependence of intensity at this mid-q range increases to almost q^-2, which usually represents the scattering from layered structures. 

Previously, Baldelli et al. reported that excess ions at IL/Pt electrode interface will not form a diffuse double layer but a Helmholtz layer.  Sum-frequency generation spectroscopy results suggested the cations of [bmim][BF₄] and [bmim][PF₆] near a platinum electrode tipped with the imidazolium rings aligning along the interface normal when the potential was higher than the potential of zero charge (PZC). When the potential was below PZC, cations formed a Helmholtz layer with the ring planes parallel to the electrode surface. Such property changes corresponding to the external fields could affect the kinetics of phase separation.  In summary, different morphology and microstructures of polyurea can be induced by an external electric field via a non-charge-transfer polymerization reaction at the interface between a dielectric organic liquid and a room-temperature ionic liquid.  The observations could be attributed to the following reasons. 1. The induced surface ions at the liquid membrane that affect the molecular orientations of ionic liquid.  2. The aggregation and coarsening of polymer precipitates affected by the external field via interactions between polymer and ionic liquid. Further investigation of the response of liquid/ionic liquid interface to external field is underway.

Figure 1 Configuration of the reaction cell and the electric field.   Theta is defined as the angle between the negatively charged plate and the horizontal plane.  The ionic liquid phase is in the lower phase where excess charges (ions) are induced at the boundaries. 

Figure 2 The neutron scattering results of the polyurea synthesized at the IL/n-hexane interfaces in absence of electric field (red triangles) and under an electric field (E=5x10⁴V/m) at theta = 0^o (blue circles) and 90^o (green squares).