An explicit model of contact-charge exchange in polymers is proposed in which the steady-state exchanged charge resides in intrinsic molecular-ion states. The eigenvalue spectra of these states are inferred from metal/polymer contact-charge measurements using a theoretical formalism constructed for this purpose. This model of metal/polymer contact-charge exchange is extended to encompass the description of polymer/polymer contact-charge exchange as well. Utilizing the metal/polymer contact-charge-exchange spectra as input data, the model predicts correctly both the sign and order of magnitude of measured contact-charge exchange between polystyrene and copolymers of styrene and methyl methacrylate.
Observation of a new phenomenon, the reversible change in sign of charge transferred to a polymer upon sequential contacts with a series of metals, is reported. This observation is interpreted using a model which attributes the polymer charges to the occurrence of local intrinsic molecular-ion states. A phenomenological representation both of these charge states and of the metal/polymer contact charge exchange process is developed. The validity of this phenomenology is tested by comparing its predictions with a systematic study of the contact charging of poly(styrene), poly(methyl methacrylate), and copolymers thereof. Using the contact charge exchange spectra of poly(styrene) and poly(methyl methacrylate) to determine the input parameters, the phenomenological model successfully predicts the contact charge exchange spectra of the copolymers.
Energy loss spectra of 80 keV electrons transmitted through thin films polymethylmethacrylate (PMMA) were measured with a resolution of 0.1 eV for energy losses from 1 to 300 eV. From the loss spectra, the dielectric response function of PMMA was obtained from 1 to 100 eV and compared with recent synchrotron radiation results. The spectrum of valence excitations from 5 to 13 eV is shown to be characteristic of the pendant group and is compared to experimental gas phase spectra and molecular orbital (CNDO/S) calculations of model molecules. The spectrum of core electron excitations above 285 eV provides a measure of the distribution of empty molecular orbitals and, when the carbon 1s binding energies are taken into account, a qualitatively accurate description of the observed spectrum is made from the CNDO ground state calculation. The energy loss spectra of 20, 40, and 100 eV electrons reflected from the surface of PMMA exhibit a triplet excitation at 4.2 eV and indicate the extreme sensitivity of this material to radiation damage. Finally, the spectrum of electron damage is shown to be similar to that reported for uv photolysis but with a strong previously unreported peak at 6.3 eV assigned here to excitation of radiation induced isolated unsaturated bonds.
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