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As an emerging area in organic electronics, polymer memories have become an active research topic in recent years. Polymer memories based on bistable electrical switching are likely to be an alternative or supplementary technology to the conventional memory technology facing the problem in miniaturizing from micro- to nano-scale. In this article, an account of our recent work on bistable electrical switching in a series of processable electroactive polymers is given. The polymers can provide the required electronic properties within a single macromolecule for memory device applications. Bistable electrical switching phenomena arising from four processes, viz., trappingedetrapping, charge transfer, conformational change and nanocomposite redox effects, in electroactive polymers are described. In each case, three aspects of the memory effect, viz., (i) materials and structural features, (ii) conductance switching and currentevoltage characteristics, and (iii) operating mechanism and electronic transitions are emphasized. Finally, the performance of these polymer memories is summarized. 2007 Elsevier Ltd. All rights reserved.

Surface modification of polypyrrole (PPY), polyaniline (PAN) and poly(3-alkylthiophene) films by ozone was studied by angle-resolved x-ray photoelectron spectroscopy (XPS). In the case of the N-containing polymers, oxidation occurs readily and mainly at the carbon atoms, resulting in the formation of C-O, C=O, COOH and even O-COOH (especially for PAN) species. The carbon atoms of doped PPY and PAN films are significantly more resistant to ozone oxidation, but the samples suffer some loss of the dopant in the surface region. Ozone treatment does not involve the direct oxidation of the nitrogen heteroatoms to form the - NO x species, even at high extent of carbon oxidation. In addition, a substantial decrease in the intrinsic oxidation state ([=N-]/[-NH-] ratio) was observed in the 25% deprotonated PPY (DP-PPY) base, the 50% intrinsically oxidized emeraldine (EM) base and the 75% intrinsically oxidized nigraniline (NA) base after ozone treatment and subsequent atmospheric exposure. In the case of the S-containing polymers, ozone treatment results predominantly in the oxidation of sulphur heteroatoms to give rise to the sulphone and peroxide species. The oxidized sulphur species, however, are readily reduced or consumed in a photochemical reaction.

Surface thermal graft copolymerization with concurrent lamination was carried out between an Ar plasma pretreated poly(vinyh'dene fluoride) (PVDF) film and a copper foil in the presence of a small quantity of a N-containing monomer, such as 4-vinyl pyridine (4-VPN) and acryloyl morpholine (ACMO), under atmospheric conditions and in the complete absence of an added polymerization initiator and system degassing. The adhesion strength, as reported by T-peel strength, was dependent on the argon plasma pretreatment time of the PVDF film, the thermal lamination temperature and the type of monomer. An optimum T-peel adhesion of about 10 N/cm was readily achieved in the Cu/PVDF laminate for grafting and lamination carried out in the presence of 4-VPN. A lower adhesion strength was obtained using ACMO and other N-containing monomers. The chemical compositions of the graft copolymerized and delaminated sample surfaces were studied by X-ray photoelectron spectroscopy (XPS). The failure mode of the Cu/4-VPN/...

Controlled grafting of polybetaine brushes onto hydrogen-terminated Si(100) substrates (Si−H substrates) was carried out via surface-initiated reversible addition−fragmentation chain-transfer (RAFT) polymerization. The azo initiator was immobilized on the Si−H surface through a three-step process: (i) coupling of an ω-unsaturated alkyl ester to the Si−H surface under UV irradiation, (ii) reduction of the alkyl ester into a hydroxyl group by LiAlH4, and (iii) esterification of the hydroxyl group with the initiator 4,4‘-azo-bis(4-cyanopentanoic acid) after acid chlorination. In the presence of the chain-transfer agent, RAFT-mediated polymerization of the sulfobetaine monomer N,N‘-dimethyl(methylmethacryloyl ethyl) ammonium propane sulfonate (DMAPS) was initiated from the surface-immobilized azo initiator to produce DMAPS polymer (PDMAPS) brushes on the silicon substrate (Si-g-PDMAPS). X-ray photoelectron spectroscopy (XPS) analysis indicated that the PDMAPS brushes had been successfully grafted onto the si...

Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) film were carried out via near-UV light-induced graft copolymerization with acrylic acid (AAc), Na salt of styrenesulfonic acid (NaSS) and N,N-dimethylacrylamide (DMAA). The structure and chemical composition of each copolymer surface and interface were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). For each PTFE substrate with a substantial amount of grafting, the hydrophilic graft penetrated or became partially submerged beneath a thin surface layer of dense substrate chains to form a stratified microstructure. This surface microstructure was further confirmed by the water contact angle results. In all cases, the concentration of surface grafted polymer increased with the plasma pretreatment time and monomer concentration. Adhesive-free adhesion studies revealed that the AAc graft copolymerized PTFE surface adhered strongly to another similarly modified surface (homo-interface) or to a DMAA graft copolymeri...

Surface modification of ozone-pretreated low-density polyethylene (LDPE) films were carried out via a novel technique of UV-induced graft copolymerization with acrylamide (AAm), Na salt of styrenesulfonic acid (NaSS), 3-dimethyl(methacryloylethyl)ammonium propanesulfonate (DMAPS), acrylic acid (AAc), N,N-dimethylacrylamide (DMAA), and 2-(dimethylamino)ethyl methacrylate (DMAEMA) under atmospheric conditions and in the complete absence of an added initiator or oxygen scavenger. Photografting with concurrent photolamination in assemblies containing a monomer solution sandwiched between two LDPE films was demonstrated. The chemical composition and microstructure of the graft copolymerized surfaces were studied by angle-resolved X-ray photoelectron spectroscopy. For LDPE films with high graft concentrations, such as those graft copolymerized with AAm, DMAA, and DMAEMA, surface chain rearrangement to form a stratified surface microstructure with a higher substrate to graft chain ratio at the outermost surface ...

Surface modifications of emeraldine base (EB) films have been carried out via thermally induced graft copolymerization with acrylic acid (AAc), sodium salt of styrenesulfonic acid (NaSS), N,N‘-dimethyl(methacryloylethyl)ammonium propanesulfonate (DMAPS), and acrylamide (AAm). The structure and chemical composition of each graft-copolymerized surface were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). In all cases, the concentration of grafting increases with monomer concentration. Surface grafting with the four functional monomers also leads to a more hydrophilic EB film surface. Two graft-copolymerized EB film surfaces are capable of exhibiting adhesive-free adhesion when brought into direct contact in the presence of water and subsequently dried. This adhesive-free adhesion also exists between a surface-modified EB film and a similarly modified polytetrafluoroethylene (PTFE) film from graft copolymerization. The development of the lap shear adhesion strength depends on the concentrati...