Ultrathin Copolymer Films Research Articles

Nanoscale polarization manipulation and conductance switching in ultrathin films of a ferroelectric copolymer

We report the direct observation of induced molecular reorientation on a ferroelectric copolymer with a scanning tunneling microscope (STM). Ultrathin copolymer films of vinylidene fluoride (70%) with trifluoroethylene (30%) revealed a quasihexagonal close-packing structure with long-range polymer chain ordering. By flipping the polarity of the STM tip bias voltage, a reversal of local polarization was observed through an apparent lattice shift and was accompanied by an asymmetric “diode-like” character in tunneling current I(V). These results clearly demonstrated conductance switching behavior on nanoscale with local polarization reversal.

Electrochemical Polymerization of Conducting Polymer Coatings on Neural Prosthetic Devices: Nanomushrooms of Polypyrrole Using Block Copolymer Thin Films as Templates

ABSTRACTWe have demonstrated a method to rapidly and reliably fabricate arrays based on the self-assembled morphology of block copolymer ultra thin films. An ordered, nanoporous structure obtained from the block copolymer thin films is used a template for the subsequent electrodeposition of conducting polymer nanomushrooms of polypyrrole (PPy). The influence of current density, deposition charge and morphology of the templates and nanostructured conducting polymer coatings has been investigated. The electrical properties of the polymer coatings were studied.

Topological coarsening of low-molecular-weight block copolymer ultrathin films by environmental AFM

Topological coarsening of block copolymer ultrathin films is well-understood for copolymers exhibiting intermediate or strong segregation and differing in film thickness or molecular weight at temperatures above the upper glass transition temperature ( T g), but below the order–disorder transition ( T ODT), of the copolymers. More recent studies suggest that the stability and topology of such films differ at temperatures above T ODT. In this work, we use environmental atomic force microscopy to examine the effect of temperature on the coarsening of block copolymer ultrathin films in situ. Films measuring ca. 25 nm thick consist of a low-molecular-weight poly(styrene- b-isoprene) diblock copolymer for which the upper T g and T ODT in the bulk are about 42 and 70 °C, respectively. Time-resolved image sequences illustrating surface reorganization are obtained at temperatures below, above and near 70 °C. At temperatures very close to 70 °C, coarsening is found to slow markedly, by almost an order of magnitude relative to what is observed at higher and lower temperatures, suggesting that thermal factors may provide a means by which to inhibit the dewetting of block copolymer ultrathin films.

Dielectric properties and ferroelectric behavior of poly(vinylidene fluoride‐trifluoroethylene) 50/50 copolymer ultrathin films

Dielectric properties and ferroelectric behavior of poly(vinylidene fluoride‐trifluoroethylene) 50/50 copolymer ultrathin films

Diblock copolymer ultrathin films studied by high resolution electron energy loss spectroscopy

Surface segregation of polymers forming thin films is relevant in several industrial applications. This paper studies the influence of preparation parameters on the surface composition of poly(ethylene oxide)–polystyrene diblock copolymer ultrathin films. Silicon wafers were used as substrates. The film preparation method (spin coating vs. casting followed by solvent evaporation), solvent (THF vs. CCl 4), annealing vs. non-annealing and the substrate nature (native silicon oxide vs. silanized substrate) were analyzed. High resolution electron energy spectroscopy in vibrational energy loss range was used to estimate the extreme surface composition. Generally, THF favors the surface segregation of polystyrene. After annealing, whatever the preparation method, the polystyrene preferentially segregates at the surface without forming a pure overlayer. These results were compared with the surface compositions calculated from X-ray photoelectron spectroscopy spectra of the films.

Dielectric properties and ferroelectric behavior of poly(vinylidene fluoride‐trifluoroethylene) 50/50 copolymer ultrathin films

AbstractUltrathin films of poly(vinylidene fluoride‐trifluoroethylene) copolymer [P(VDF‐TrFE), with a content (mol %) ratio of 50/50 VDF/TrFE] were fabricated on silicon wafers covered with platinum by a spin‐coating technique, ranging in thickness from 20 nm to 1 μm. The effect of thickness on dielectric properties and polarization behavior was investigated. A critical thickness was found to be about 0.1 μm. An abrupt drop of dielectric constant was observed, although there is no significant change in dielectric loss at this thickness. Square and symmetric hysteresis loops were obtained in films thicker than 0.1 μm. However, for films thinner than 0.1 μm, fewer square hysteresis loops were observed. SEM and X‐ray results demonstrate that the effect of thickness on dielectric and ferroelectric properties could be explained by the changes of crystal structure in these films. In addition, the effects of irradiation on dielectric property and polarization response for ultrathin P(VDF‐TrFE) films were also presented. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2259–2266, 2001

Use of an External Electric Field to Convert the Paraelectric Phase to the Ferroelectric Phase in Ultra-thin Copolymer Films of P(VDF-TrFE)

AbstractX-ray diffraction was used to probe the structural changes associated with the conversion of the paraelectric phase to the ferroelectric phase that results from the application of a large external electric field. The samples under study are ultrathin (150 to 250 Å) Langmuir-Blodgett films of the copolymer vinylidene fluoride (70%) with trifluoroethylene (30%) deposited on aluminum-coated silicon. Theta-2theta X-ray diffraction was used to measure the change in inter-layer spacing perpendicular to the film surface. Upon heating at zero external electric field, the crystalline films undergo a structural phase transition, at 100± 5°C, from the all-trans ferroelectric phase to the trans-gauche paraelectric phase. [1,2] Above the phase transition temperature, the non-polar paraelectric phase can be converted back to the polar ferroelectric phase, in a smooth continuous process, using a large external electric field (∼1 GV/m). For example, at 100° C the ferroelectric phase first appears above 0.2 GV/m and increases steadily in proportion while the paraelectric phase decreases until complete conversion to the ferroelectric phase is achieved at approximately 0.6 GV/m.

Time evolution of the free surface of ultrathin copolymer films

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTTime evolution of the free surface of ultrathin copolymer filmsG. Coulon, J. Daillant, B. Collin, J. J. Benattar, and Y. GallotCite this: Macromolecules 1993, 26, 7, 1582–1589Publication Date (Print):March 1, 1993Publication History Published online1 May 2002Published inissue 1 March 1993https://doi.org/10.1021/ma00059a015RIGHTS & PERMISSIONSArticle Views181Altmetric-Citations36LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (5 MB) Get e-Alerts Get e-Alerts

Geometrical constraints on microstructural development in block copolymer ultrathin films

The fact that microstructures form in microphase-separated block copolymers, endowing the materials with unique thermo-mechanical properties, is well-established. However, no thermodynamic theories directly address the problem of microstructural development in ultrathin films, which might be useful as adhesives or resists. To predict the microstructural dimensions in such films, a model based on unit-cell geometries and material/volume balances is developed. Predictions of the ratio of the characteristic length of the domain core to domain repeat distance are obtained for poly (styrene-butadiene) diblock (SB) copolymers at 298 K. The finite interphase region is included in the volume balances with the parameterf, the volume fraction of interphase material, obtained from a modified version of the Leary-Henderson-Williams thermodynamic theory and shown here not to be a strong function of composition. An approach, implementingf, for accurately estimating the critical molecular weight of microphase separation in the strong-segregation limit (Mc), as a function of bulk composition for monodisperse SB copolymers at 298 K, is also presented.