Published: June 03, 2011 r2011 American Chemical Society 13041 dx.doi.org/10.1021/jp203544k | J. Phys. Chem. C 2011, 115, 13041–13046 ARTICLE pubs.acs.org/JPCC Polarization Mediated Chemistry on Ferroelectric Polymer Surfaces Zhengzheng Zhang, † Rosette Gonz  alez, †,‡ Gerson Díaz, †,‡ Luis G. Rosa, †,‡, * Ihor Ketsman, † Xin Zhang, † Pankaj Sharma, † Alexei Gruverman, †, * and Peter A. Dowben* ,† † Department of Physics and Astronomy, Nebraska Center for Materials and Nanoscience, University of Nebraska—Lincoln, Theodore Jorgensen Hall, 855 North 16th Street, Lincoln Nebraska 68588-0299, United States ‡ Department of Physics and Electronics, University of Puerto Rico—Humacao, 100 Road 908 CUH Station, Humacao, Puerto Rico 00791, and the Institute for Functional Nanomaterials, University of Puerto Rico, Facundo Bueso Building, Rio Piedras, Puerto Rico 00931 ’ INTRODUCTION Reversible adsorption of weakly adsorbed molecules has been shown to depend on the polarization ferroelectric domain orientation of both organic 1À4 and inorganic ferroelectrics. 5À10 Such studies have largely investigated polar adsorbate molecules, 1À10 with the tacit assumption that nonpolar molecules should be insensitive to the ferroelectric polarization domain orientation. 5À7 The chemistry of the surface can play a role and it would be rare, if not unusual, for the surface chemistry of positive and negative ferroelectric domains to be identical. 11,12 In this sense, nonpolar molecules would not be immune from the surface dipole direc- tion of a ferroelectric surface. Not only would the nonpolar molecule respond to the dipole direction, as all molecules have a finite polarizability, but surface termination, stoichiometry, and defect densities can differ with different dipole (polarization) directions. This interplay between the surface chemical interactions and the electrostatic dipolar interactions can be explored by compar- ing adsorption of isomeric molecules that are both polar and nonpolar. The investigation of molecular isomeric effects on the adsorption of different diiodobenzene isomers on molecular zwitterion films demonstrated that the frontier orbital symmetry can play a dominant role in the adsorption process. 13 For a stronger substrateÀadsorbate interaction, particularly reaction chemistry, 8,9 it remains unclear whether it is the differences in the static surface dipole or the differences in the surface chemistry that dominates. For ferroelectrics, the reaction chemistry sug- gests that it is the surface dipoles that matter, but there is no clear delineation of surface chemistry and surface dipoles where the surface chemistry is photoactivated. 14À26 Here we investigated diiodobenzene adsorption/absorption on crystalline copolymers of polyvinylidene with trifluoroethy- lene (PVDF-TrFE), a molecular ferroelectric. As with some prior studies of adsorption on ferroelectric substrates, 5 we compare a polar and nonpolar species, but by investigating two different isomers of diiodobenzene, we compare molecules with far more similar surface chemistry. If dipoles alone matter, and pyroelec- tricity and surface chemistry can be excluded, then it is difficult to see how an “up” or “down” poled ferroelectric should matter in an adsorption experiment, as dipole interactions hold regardless of the dipole orientation. Chemically similar adsorbate test species that have different static dipoles should show a preference for surfaces with the same or similar chemical termination (the same dipole direction preference) if surface chemistry alone matters. Thus key to any fundamental understanding is perform- ing the experiments at constant temperature, to eliminate pyro- electric contributions to the surface charge, a complication common to ferroelectric materials. To be sure as a ferroelectric, PVDF-TrFE is also a pyroelectric so surface charge can accumu- late with changes in temperature. 27 At 150 K, the initial adsorption of all three isomers of diiodobenze is found to be similar on a conducting but chemi- cally inert substrate like graphite, 28 although a number of isomer specificeffects have been identified for the halogenated and substituted benzenes. 13,28,29 Such small simple molecules pro- vide a clear test of preferential isomer adsorption, particularly as Received: April 15, 2011 Revised: May 31, 2011 ABSTRACT: We have investigated the chemisorption of two isomers of diiodobenzene on the molecular ferroelectric copolymer poly(vinylidene fluoride) with trifluoroethy- lene (70:30) as a function of the polymeric ferroelectric domain orientation. We find that the 1,4-p-diiodobenzene adsorption at 150 K strongly favors a positive ferroelectric domain orientation while the 1,2-o-diiodobenzene adsorption at 150 K strongly favors a negative ferroelectric domain orientation. Both polar and nonpolar adsorbates are influenced by the substrate dipole direction. Because a nonpolar isomer is also affected by the surface dipole direction, and hence the surface chemical termination, it is clear that surface chemistry and not simply surface dipoles matter in the chemisorption process.