Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session W4: Industrial Challenges to Polymer Physics |
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Sponsoring Units: DPOLY Chair: Edward Kramer, University of California-Santa Barbara Room: LACC 515A |
Thursday, March 24, 2005 2:30PM - 3:06PM |
W4.00001: Blurring the Line: Polymers and Optics Invited Speaker: Aesthetic considerations are critical in the development of consumer products. Aesthetic defects can be ``lines'' caused by the merging of melt flows in an injection molding process or scratches on an automotive surface or patterns on the light guide in a computer display which may affect uniformity of the image on the screen. It is often unproductive or impossible to eliminate these defects entirely. However the defect needs to be minimized to below a ``threshold'' of acceptability for the consumer. Understanding the optics of a defect and its effect on human perception is critical for designing consumer products. In this talk we present the optical parameters that govern ``perception'' of defects such as scratches or ``lines,'' their relationship to physical parameters of the defect and the implications on polymer design. The sharpness of the optical contrast between the defect and its surroundings will be presented as the metric for ``visibility.'' Empirical models between perceived visibility and defect physical dimensions will be presented as a basis for understanding the desired deformation characteristics of a material under stress. In addition we will discuss the intrinsic optical characteristics and the surface roughness of the product as important parameters in defect perception. [Preview Abstract] |
Thursday, March 24, 2005 3:06PM - 3:42PM |
W4.00002: Scaling down polymer thermomechanics for data storage applications Invited Speaker: The Atomic Force Microscopy based data storage concept [1], called the ``Millipede,'' involves making indents in a thin polymer film using heated cantilever/tips. Using this technique, high areal storage density and a good data rate in a small form factor can be achieved. The underlying technical and scientific questions are related to polymer mobility at small dimensions and various time-scales: First, polymer indentation has to be regarded in a 3D confinement of nanometer size, at time scales down to and below one microsecond and under extreme shear and compressive stresses. The kinetics is found to be a key in understanding the indentation mechanism. Second, for the `reverse' indentation process, both small time scales (in microseconds during erasing) and large time scales (up to 10 years for data lifetime) matter. Finally, tribology issues, in particular polymer wear on nm scale, have to be considered. Experiments are presented shedding light onto the polymer physics related to most of these questions. Some of the technical solutions as well as open questions are addressed. [1] P. Vettiger et al., IEEE Trans. Nanotechnology, 1(1), 39- 55, 2002 [Preview Abstract] |
Thursday, March 24, 2005 3:42PM - 4:18PM |
W4.00003: Polymer thin film transistors - from transport mechanisms to display backplanes Invited Speaker: Organic semiconductors have dramatically improved in performance so that they are now competitive with amorphous silicon thin film transistors (TFT), and may even challenge crystalline silicon for electronic device applications. The research at PARC has focused on polymers which have the advantage of simple deposition from solution. The improvement in electronic transport is largely due to developments in material synthesis and an understanding of how to deposit films with a high degree of structural order. The talk will discuss how the ordering is achieved and describe recent progress toward understanding the relation between structural order and electronic transport in TFTs, as well as other aspects of transistor performance. Solution-based deposition allows conventional photolithography to be replaced by simpler printing processes such as jet-printing, for the fabrication of electronic circuits. Polymer TFT arrays can now be made with jet-printing as the only patterning technique. This is a revolutionary manufacturing approach for flat panel displays, with the opportunity for greatly reduced cost but with many remaining challenges to overcome. [Preview Abstract] |
Thursday, March 24, 2005 4:18PM - 4:54PM |
W4.00004: Controlling Polymer Rheology and Blend Thermodynamics Through Chain Architecture Invited Speaker: David Lohse A great deal of progress has been made in determining how the chemical architecture of macromolecules determines the properties of polymeric materials, but much remains to be done. Central to this effort has been the ability to make polymers where such structure is well controlled and well known, and improvements on this will be key to extending the knowledge of how molecular structure controls performance. I will illustrate the current state of knowledge and suggest where new efforts should be directed in several areas. The melt rheology of linear polymers depends critically on the degree to which the chains entangle, and the state of entanglement has now been shown to depend in a simple way on the dimensions of the molecules, for polymers from polyolefins to acrylates and even to polymeric sulfur. A deeper understanding of the flow of linear polymers will depend on the synthesis of well-characterized polymers with a wider range of stiffness. It is now clear that the miscibility of polyolefins also depends on the size of the chains, and the way this knowledge can be used to design new materials will be illustrated. I will describe the kinds of new polymers that will need to be made to enhance this understanding of structural effects, as well as illustrate how this can be used. [Preview Abstract] |
Thursday, March 24, 2005 4:54PM - 5:30PM |
W4.00005: Lithium and proton conducting membranes: Two sets of challenges for the polymer physicist Invited Speaker: Advanced energy conversion systems are sought actively for chemical to electric transformation, as storage (batteries) or production (fuel cells). Solid-state systems mean higher energy density and safety. Polymers add the extra advantages of mechanical and design flexibility, ease of processing. Lithium is now synonymous for high energy density batteries, while proton-conducting membrane is the motto in fuel cells. Though the two species are kin in the first row of the elements, the requirements for moving the corresponding ions differ considerably in concept and practice. \begin{itemize} \item H$^{+}$ does not exist formally and is always borne by a guest molecule. Its coordination is one, or two when H bonds are present. Proton$^{ }$motion is either that of the guest (vehicular) or from translocation (Grotthus) through a chain of hydrogen bonded relays (tenfold increase in mobility). Water is the ubiquitous guest/relay (H$_{3}$O$^{+})$, as it is the by-product of the electrochemical reaction. In terms of polymer membranes, the need for a chemically robust backbone (fluorinated, electron-depleted aromatics{\ldots}) incompatible with the aqueous proton environment leads to bi-continuous phase-separated systems. The fraction of vehicular process that leads to co-transport of water and the lack of selectivity between water and methanol ---the most practical fuel---, remain the main challenges. Other guests (imidazole, pKa = 7) are also considered. \end{itemize} Li$^{+}$ (6.510$^{{\-}2}$ nm radius) requires a 4 to 6-fold coordination in a water-free environment. When the ligand shell is the polymer [e.g. poly(ethylene oxide)], the motion of Li$^{+ }$is allowed$^{ }$by a solvation/desolvation process. This ``immobile solvent'' conductivity, assisted by the segmental motion, requires (T$_{g}+\approx $100 \r{ }K), i.e. @ 60 \r{ }C. Adding plasticizing discrete molecules lowers T$_{g}$ and ultimately they replace the Li$^{+}$ close$^{ }$environment (gels with liquid-like conductivity). Safety is still an incentive to get a solvent-free electrolyte working at (sub)ambient temperature. Most recent progresses come from establishing some order [(liquid)crystal, chain orientation, chirality{\ldots}]. The conductivity in this case decouples from T$_{g}$, initially thought to be an inevitable barrier. [Preview Abstract] |
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