Polymer Science and Engineering The Shifting Research Frontiers (1994) / Chapter Skim
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2. Advanced Technology Applications
2. Advanced Technology Applications
Pages 32-64
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From page 32... ...
DNA directs the assembly of about 20 amino acids in complex sequences that become the proteins. These proteins are polypeptide polymers that differ from one another only in the sequence of their constituent amino acids.
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From page 33... ...
Sutures, which were made of cat gut for over 2,000 years, are now made of synthetic polymers. Hard and soft lenses required after cataract surgery, artificial corneas, and other ocular materials are all polymers.
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From page 34... ...
The synthetic nondegradable materials needed in such products as orthopedic joints, heart valves, vascular prostheses, heart pacemakers, neurostimulators, and ophthalmic and cochlear implants must meet many technical requirements, including being stable and biocompatible in the host environment for moderate to long lifetimes. However, the fact that most of the polymers currently used in implants were not initially designed for medical use means that those polymers may not meet such requirements.
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From page 35... ...
It seems likely that synthetic polymers will eventually come into use, although to date they do not have the proper combination of properties. Dental materials are dominated by polymers to an increasing extent.
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From page 36... ...
~~ ~~ ~~ dent~ sdbesives. Flubber advances in dental matedals can be expected as polymer systems He designed and engineered to sagest He complex needs of He Lea.
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From page 37... ...
or a soft hydrogel lens. The hydrogel lens may be inserted through a smaller incision, but it has a smaller refractive index than that of PMMA, requiring a greater thickness.
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From page 38... ...
Delivery to difficult-to-reach areas such as the brain is desirable, and progress is being made in the area through the use of polyanhydrides, as is discussed in the vignette "Implanted Polymers for Drug Delivery." Success in this area will be rewarded with improved quality of life and longevity. Several drug release technologies have become clinically and commercially important.
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From page 39... ...
Recently, more sophisticated technologies have emerged, such as electrotransport systems, whereby the drug is driven from a reservoir under the influence of an electric field. Such systems are being developed predominantly for transdermal drug delivery.
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From page 40... ...
~~ ~~ ~~ Stales, and ~ lager number me in developmeDL Tale 2.1 lists a ~w of [be avaN~le products as examples of dam delved systems, along wig the mechanisms of Please and polymers used as major components of me rate-con~olUng element.
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From page 42... ...
Except in special cases, synthetic polymer science does not yet have the precision to create specific monomer sequences: polymers can be synthesized as homopolymers, chains composed of only a single type of monomer, or simple block copolymers, where the monomers repeat only in the simplest patterns, AAA BBB AAA Bl3B, or random sequences. But the ability to synthesize specific monomer sequences by a linear process would have extraordinary potential.
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From page 43... ...
The study of informational polymers aims to determine the specific shapes of biological polymers at atomic and nanometer resolution, the relationship between structure and function, and how the structure and function arise from the underlying interatomic forces of nature. Because these are the same goals as in the study of synthetic polymers, the topics of biomaterial-related polymer science and engineering cut across all the areas of this report.
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From page 44... ...
If we had nature's ability to control network structure, it would be possible for us to design materials with better mechanical properties. For example, many bioelastomers have relatively high efficiencies for storing elastic energy through the precise control of cross-link structure.
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From page 45... ...
This approach is yet another opportunity to exploit nature's ideas. Overlap Between Structural Biology and Polymer Science The above exciting areas involve considerable overlap between biomaterials and polymer science.
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From page 46... ...
In these applications, polymers offer ease and economy of manufacture, tough, durable mechanical properties, and excellent dielectric properties (i.e., low dielectric constant and loss)
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Polymer Dielectrics for Electronics Organic polymers play a crucial role as insulating materials in electronics. The most visible applications are in silicon chip encapsulation and in dielectric layers for printed circuit boards (PCBs)
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From page 49... ...
The dielectric constants may be compared as follows: alumina 9 glass ceramics 4-5 fused silica polyimides triazine BCB 4 3-4 2.8 2.7 In the final analysis, the choice of materials will be based on the sum of property advantages and processing practicality. Polymers offer the lowest dielectric constants and the thinnest "wires." Lithographic processes and associated technologies have advanced to the point that semiconductor device cells and conductor lines (i.e., the on-chip "wires")
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From page 50... ...
Conducting Polymers and Synthetic Metals Organic materials are generally insulators or, in other words, poor conductors of electricity compared with metals and semiconductors. Electrical conductivity in metals and semiconductors arises from the delocalized electrons of the system, and they are best described by "band theory." In these terms, the organic materials have localized electrons because there is a large energy gap between the most energetic electrons and the conduction band.
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From page 51... ...
In addition, pure conducting polymers and their blends can be oriented by stretching to produce highly anisotropic electrical and optical properties. The thermal, hydrolytic, and oxidative stability of doped forms of pure conducting polymers varies enormously from the e-doped form of polyacetylene, which undergoes instant decomposition in air, to polyaniline, which has suffi
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From page 52... ...
Clearly, research to improve the stability of conducting polymers is essential to commercial applications in the future. Polyaniline is currently the leading conducting polymer used in technological applications and is commercially available in quantity.
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From page 53... ...
A related sensor type in the chemical and biomedical fields is the microsensor based on integrated solid-state electronic devices, for example, CHEMFETS. These sensors incorporate chemically sensitive polymer films placed in contact with the gate of a field effect transistor on a transducing silicon chip.
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From page 54... ...
, can be poled by applying a strong electric field, and then used to construct acoustic, pressure, or thermal sensors. They are applied in pyroelectric detectors, hydrophores, ultrasonic transducers, shock wave sensors, and tactile sensors for robotics.
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From page 55... ...
Pattern-wise exposure of the resist to radiation of the appropriate wavelength results in a radiation-induced chemical reaction in the resist film, which renders the exposed areas more soluble in some developer solvent (positive tone imaging) or less soluble (negative tone imaging)
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From page 56... ...
This is a very demanding requirement that will require a significant advance in resist technology. One promising approach to the production of high-aspect-ratio imaging at small dimensions is "top surface imaging." In this process the resist film is formulated to be opaque to the exposure radiation, and chemical transformation occurs only on the top surface of the resist.
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From page 57... ...
The aspect ratio of the image produced by this process is dependent on the anisotropy of the oxygen etching process. Aspect ratios exceeding five in polymer relief images have been achieved by this method.
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From page 58... ...
These optical circuits can be created today by means of a photolithographic procedure in which lines of high refractive index are formed in thin polymer films by photochemical techniques. The circuit pattern is defined by irradiating a photoresist through a mask.
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From page 59... ...
based on conducting polymers have been achieved in a number of laboratories around the world. The active element is a thin film structure based on a modified poly~phenylene vinylene)
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From page 60... ...
The latent electrostatic image is formed by first depositing a layer of ionic charge from a corona discharge onto the photoreceptor surface. This induces an equal but opposite charge on the metal layer below, resulting in the formation of an electric field within the photoconductor layers.
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From page 61... ...
When such a hologram is illuminated with the reference beam, it produces a light beam that appears to come from the solid object used in its recording. Holograms can also be made from light beams produced by conventional optical elements such as lenses and mirrors.
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From page 62... ...
The chemical and physical changes associated with monomer polymerization preserve the interference pattern created during exposure as a corresponding pattern of refractive index variation. Numerous and diverse chemical and physical requirements greatly limit monomer choice.
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From page 63... ...
· Electromagnetic shielding will become increasingly necessary, and conducting polymers offer solutions that are conveniently fabricated in complex shapes.
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From page 64... ...
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