Condensed-Matter and Materials Physics Basic Research for Tomorrow's Technology (1999) / Chapter Skim
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5 Soft Condensed Matter: Complex Fluids, Macromolecular Systems, and Biological Systems
5 Soft Condensed Matter: Complex Fluids, Macromolecular Systems, and Biological Systems
Pages 194-224
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From page 194... ...
Chemical synthesis using biological methods will create huge classes of materials amenable to physical experiments. Physical techniques and principles will come to be applied to biological materials in unexpected ways.
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From page 195... ...
Our effort to see what is common and mutually constructive in working with diverse soft materials immediately encounters cultural differences between physicists, engineers, and biologists. Particularly at the intersection between biology and physics, barriers to learning from each other are daunting.
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From page 196... ...
The gelation of fat globules and proteins, the distribution of gel networks, and the size of nano-droplets of dispersions which change the texture, taste, and feel of food are in fact physical properties amenable to systematic physical investigation. in fields that traditionally disdain each other.
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From page 197... ...
Liquid Crystals and Microemulsions Most large asymmetric molecules, viruses, and lipids assemble spontaneously into ordered structures whose dimensions and macroscopic properties vary dramatically with small changes in the conditions under which they are formed. The statistical mechanics of these assemblies challenges the best theorists, and measurements of macroscopic behavior and microscopic structure are a primary activity in materials research.
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From page 198... ...
, and the pair distribution function of the resulting structure is in good agreement with experiment. Although this approach comes closer than any to defining a structural paradigm, more work is clearly needed, such as an extension to larger clusters and the detailed study of the defect lines their identification in computer models, their systematic enumeration and statistical mechanics, and a demonstration of their role in atomic diffusion and viscous flow.
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From page 199... ...
From the observed structure of these phases, experimentalists construct materials of controlled microscopic structure, symmetry, density, and thermal conductivity. For example, the fragile cubic lattice of a lipid-water microemulsion can be perfused by water-soluble monomers that are then polymerized to create a hardened tortu
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From page 200... ...
At more than nanometer separations, there are clearly defined electrostatic double layer interactions; at smaller distances, salvation and the properties of the restructured solvent often dominate intermolecular forces. Taken together, this body of measurements introduces us to a new physics of the forces that act to organize biological macromolecules and colloidal suspensions.
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From page 201... ...
All the usual difficulties that impede understanding of highly structured liquids are amplified by the minute details of macromolecular structure. Still, the empirical facts speak for themselves, telling us how to think more logically about molecular organization.
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From page 202... ...
For colloids, practical applications will probably come sooner than fundamental theories. New ways to position materials to effect force measurements are also new ways to organize those materials for practical use.
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From page 203... ...
At present, modifications in chemistry and physical processing are creating new research questions and many practical applications, from the design of new paper currencies to the creation of industrial fibers to cosmetics to artificial food and blood thickeners. It has recently become possible to measure equations of state of several polysaccharide systems, a development that should demand better theories of polymer assembly.
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From page 204... ...
MACROMOLECULES AND MACROMOLECULAR FILMS Phase Separation and Ordering in Thin Polymer Films Because diffusion is so slow in molten polymer systems, physicists have been able to observe the very early stages of phase separation stages in which change is so slight that simplified, linear theories can be applied. It is possible to see the importance of polymer chain length on the kinetics and evolution of chain
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From page 205... ...
Structured films of synthetic and of natural polymers can be used as substrates to host and guide the growth of biological tissues. New processing treatments of surfaces for medical implants might follow from fundamental discoveries on thin polymer films.
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From page 206... ...
The periodicity scales with the thickness of the polymer film and disappears if the SiOx capping layer is very thick; in this case the film consists of a uniform, five-layer sandwich, SlOx/ PMMA/PS/PMMA/SiOx. The structure comes from a balance between the free energy associated with forming the interfaces between PS- and PMMA-rich domains and the free energy increase associated with the elastic bending of the silicon oxide capping layer.
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From page 207... ...
These cylinders may find uses as engineered channels through cell membranes. Because they can be engineered so reliably and because of their rigidly simple spherical shape, dendrimers are a powerful research tool.
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From page 208... ...
208 CONDENSED-MATTER AND MATERIALS PHYSICS BOX 5.5 Continued 'it ~ <~9, ~ \ 1 _ cow Am,` ~ / 1 I ~ ~ ~ \~ ~ i' I ~ WN~
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From page 209... ...
The possibility of learning from the properties of these molecules leads naturally to related phenomena, such as protein folding and the organization of polymer systems of increasing but controlled "randomness." Polymers associated into gels will hold drugs whose diffusive release into the body can be controlled by gel compactness. These gels can be placed in a particular
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From page 210... ...
Processing methods such as fiber spinning, blow molding, injection molding, extrusion, film blowing, solution casting (for adhesives and coatings) , and reactive blending subject the molten polymer or polymer solution to a flow field that strongly distorts or aligns the molecular conformations.
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From page 211... ...
The aim is to be able to screen polymers for desired properties with the same efficiency that is achieved for developing and producing biological polymers by the natural checks of evolution and growth. BIOLOGICAL SYSTEMS Biological molecules are substances that have evolved to do highly specific jobs on highly specific timescales.
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From page 212... ...
It will be built on a developed respect for the very different thinking and experimental methods used by the two "sides." This point is far more pertinent than any review of particular systems or prediction of future events. A 1996 study on self-assembling biological materials2 nicely summarizes the current state of learning about molecular organization and provides many examples of doing physics with biomaterials, including: · New paths for synthesis of peptide (proteinaceous)
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From page 213... ...
Synchrotrons, neutron sources, laboratory x-ray generators, and NMR machines, with their ancillary detectors and computation algorithms, are practical microscopes whose success can be measured in the number of publications involving their use, number of students studying and using them, and numbers of dollars expended on them. Increasingly precise molecular structures, frequently with better than 1 A resolution, are the product of strong light sources as well as better handling of delicate materials.
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From page 214... ...
214 CONDENSED-MATTER AND MATERIALS PHYSICS FIGURE 5.3 Quick clicks. High-power x-ray sources provide successive pictures of a protein process.
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From page 215... ...
Energy storage and energy flow through this nanometer-sized machine still deserve the attention of molecular biologists and biophysicists, who still have difficulty conversing. Molecular Conformation and Protein Folding The protein-folding problem attracts some of the best minds in biological physics and statistical mechanics, but it will require much more effort to reach satisfactory results.
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From page 216... ...
The actual values of these material properties still often surprise us and require new thinking. Force microscopes can be used to break bonds, stretch molecules, or observe spontaneous changes in macromolecular conformation.
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From page 217... ...
There is already a small literature on the spectroscopy of single proteins trapped in small spaces and illuminated by narrowly focused laser light. Through the combined efforts of structural biologists, muscle biophysicists, and statistical physicists, force generation in muscle and in transport within cells is being seen as the combination of stochastic events and directed response.
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From page 218... ...
We can now expect the design of new mechanical transduction systems. Single ionic channels show electrically detectable transitions between "open" and "closed" configurations, whose probabilities are a function of solution conditions as well as the applied transmembrane electric fields.
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From page 219... ...
Molecular Association There is justified pride in modern polymer synthesis, by which stretches of one or another kind of monomer allow polymers to associate in parts to multimolecular arrays of specific symmetry, packing, and material properties. Yet this kind of packing is rough compared to that of proteins or DNA, whose every monomer has functional consequence.
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From page 220... ...
For example, biosensors are being designed with biological materials for contact with the species to be detected and electrodes with integrated circuitry for amplified response.
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From page 221... ...
It is probably pointless even to speculate about what we will be able to do with all these new techniques and manipulations. There is already a National Research Council study on new technology based in molecular biology.4 Natural polymers such as silk and collagen will sooner or later be produced synthetically.
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From page 222... ...
Mechanical properties and biological functions such as information transmission are increasingly discussed in terms of molecular structure. A science of single molecules or similarly small objects as mechanical objects, as functioning machines, as interacting bodies can be expected to have a large impact on biological science and on the development of artificial materials.
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From page 223... ...
Even if there were time in school, subject matter changes too fast to rely only on what is learned in school. Several strategies can be tried: Interdisciplinary workshops; Summer schools with laboratories, for scientists at all career stages; New courses for biologists in elementary physics and for physicists in wet chemistry, biochemistry, and molecular biology; · Introductory physics instruction that emphasizes soft systems; and · Bilingual texts e.g., in biology and physics that teach the vocabulary and basic phenomena of particular systems.
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From page 224... ...
Research Facilities For structure determination, neutron sources in particular are urgently needed. Synchrotron x-ray, ion beam, transmission electron microscope, and surface probe facilities are high on the list.
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