新型開式砂帶振動(dòng)磨削頭架的設(shè)計(jì)

新型開式砂帶振動(dòng)磨削頭架的設(shè)計(jì),新型開式砂帶振動(dòng)磨削頭架的設(shè)計(jì),新型,開式砂帶,振動(dòng),磨削,設(shè)計(jì) DOI: 10.1126/science.1075707 , 976 (2002); 297Science et al.Robert R. Matheson, Jr., Soft Coatings 20th- to 21st-Century Technological Challenges in This copy is for your personal, non-commercial use only. . clicking herecolleagues, clients, or customers by , you can order high-quality copies for yourIf you wish to distribute this article to others . herefollowing the guidelines can be obtained byPermission to republish or repurpose articles or portions of articles (this information is current as of March 23, 2010 ): The following resources related to this article are available online at www.sciencemag.org http:/www.sciencemag.org/cgi/content/full/297/5583/976 version of this article at: including high-resolution figures, can be found in the onlineUpdated information and services, found at: can berelated to this articleA list of selected additional articles on the Science Web sites http:/www.sciencemag.org/cgi/content/full/297/5583/976#related-content 7 article(s) on the ISI Web of Science. cited byThis article has been http:/www.sciencemag.org/cgi/collection/mat_sci Materials Science : subject collectionsThis article appears in the following registered trademark of AAAS. is aScience2002 by the American Association for the Advancement of Science; all rights reserved. The title CopyrightAmerican Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by theScience on March 23, 2010 www.sciencemag.org Downloaded from where R is the reflectance of the sample, H9270 is the distance on the surface between two points, H9275 is the angular frequency, k is the wave number, f is the focal length of the incident radiation, and H9268 is the rms height of the surface. A 2D analysis of the optics has been carried out by Ogilvy (35). Whitehouse concluded (34) (for undulations with length scale greater than the wavelength of the incident radiation) that the surface appeared glossy if the probability density of the slopes on the surface was strictly confined to a narrow angle. Biocompatibility. Finally, biological interac- tions with a surface have also been found to depend on its topography. A good review of the topological control of cell adhesion and activity on a surface has been made by Curtis and Wilkinson (36), and a more general review of the role of polymer biomaterials may also be found (37). Such considerations are relevant for a number of in vivo and in vitro applications, such as biological sensors, hip replacements (38), and more complex tissue implants such as replacement bone, where the growth of cells within the artificial structure is to be encour- aged. For example, the size and morphology of crystals at the surface of octacalcium phos- phatecoated collagen have been shown to af- fect the interaction of cells with the surface, as illustrated in Fig. 4. The larger scale topography was found to lead to less favorable spheroidal cells that formed fewer intercellular connections (39). In some cases, the topography of a surface may be carefully controlled to promote cell adhesion (40, 41). Conclusion The topography of a surface is a direct result of the nature of the material that defines it. The analysis of the topography of a sample, made possible on the nanoscale by the devel- opment of AFM techniques, needs to be care- fully considered in order to relate the com- plexity of a 2D surface to the materials properties. The result will be the better con- trol of a number of properties, such as optical finish, and of the interaction of a surface with a secondary material, whether that be an ad- hesive, a secondary component of a compos- ite, or a biological species. References and Notes 1. J. D. Afnito et al., Thin Solid Films 291, 63 (1996). 2. J. A. DeAro, K. D. Weston, S. K. Buratto, U. Lemmer, Chem. Phys. Lett. 277, 532 (1997). 3. Y. Nabetani, M. Yamasaki, A. Miura, N. Tamai, Thin Solid Films 393, 329 (2001). 4. M. Sferrazza et al., Phys. Rev. Lett. 78, 3693 (1997). 5. E.Schaffer,T.Thurn-Albrecht,T.P.Russell,U.Steiner, Europhys. Lett. 53, 218 (2001). 6. D. G. Bucknall, G. A. D. Briggs, MRS Symp. Ser.: Nanopatterning: Ultralarge-Scale Integration Bio- technol. 705, 151 (2002), L. Merhari, K. E. Gonsalves, E. A. Dobisz, M. Angelopulss, D. Herr, Eds. 7. S. Walheim, E. Schaffer, J. Mlynek, U. Steiner, Science 283, 520 (1999). 8. J. Heier, E. Sivaniah, E. J. Kramer, Macromolecules 32, 9007(1999). 9. T. Thurn-Albrecht, J. DeRouchey, T. P. Russell, Mac- romolecules 33, 3250 (2000). 10. A. Karim et al., Macromolecules 31, 857(1998). 11. X. P. Jiang, H. P. Zheng, S. Gourdin, P. T. Hammond, Langmuir 18, 2607(2002). 12. G. Goldbeck-Wood et al., Macromolecules 35, 5283 (2002). 13. V.N.Bliznyuk,K.Kirov,H.E.Assender,G.A.D.Briggs, Polym. Preprints 41, 1489 (2000). 14. F. Dinelli, H. E. Assender, K. Kirov, O. V. Kolosov, Polymer 41, 4285 (2000). 15. C. Rauwendaal, Polymer Extrusion (Hanser, Munich, 1985). 16. S.-J. Liu, Plast. Rubber Composites 30, 170 (2001). 17. B. Monasse et al., Plast. Elastomeres Mag. 53,29 (2001). 18. Y. Oyanagi, Int. Polym. Sci. Technol. 24, T38 (1997). 19. A. Guinier, X-ray Diffraction in Crystals, Imperfect Crystals, and Amorphous Bodies (W.H.Freeman,San Francisco, 1963). 20. V.N.Bliznyuk,V.M.Burlakov,H.E.Assender,G.A.D. Briggs, Y. Tsukahara, Macromol. Symp. 167,89 (2001). 21. W. M. Tong, R. S. Williams, Annu. Rev. Phys. Chem. 45, 401 (1994). 22. P. Meakin, Fractals, Scaling and Growth Far from Equilibrium (Cambridge Univ. Press, Cambridge, 1998). 23. C. M. Chan, T. M. Ko, H. Hiraoka, Surf. Sci. Rep. 24,3 (1996). 24. E.M.Liston,L.Martinu,M.R.Wertheimer,J. Adhesion Sci. Technol. 7, 1091 (1993). 25. Q. C. Sun, D. D. Zhang, L. C. Wadsworth, Tappi J. 81, 177 (1998). 26. V. Bliznyuk et al., Macromolecules 32, 361 (1999). 27. N.Zettsu,T.Ubukata,T.Seki,K.Ichimura,Adv.Mater. 13, 1693 (2001). 28. R. S. Hunter, R. W. Harold, The Measurement of Appearance (Wiley, New York, ed. 2, 1987). 29. H. Davies, Proc. Inst. Electr. Eng. 101, 209 (1954). 30. F. M. Willmouth, in Optical Properties of Polymers, G. H. Meeten, Ed. (Elsevier, Amsterdam, 1986). 31. D. Porter, Group Interaction Modelling of Polymer Properties (Marcel Dekker, New York, 1995). 32. P. Beckmann, A. Spizzichino, The Scattering of Elec- tromagneticWaves from Rough Surfaces (Pergamon, New York, 1987). 33. K. Porfyrakis, N. Marston, H. E. Assender, in preparation. 34. D. J. Whitehouse, Proc. Inst. Mech. Eng. B: J. Eng. Manuf. 207, 31 (1993). 35. J. A. Ogilvy, Theory of Wave Scattering from Random Rough Surfaces (Adam Hilger, Bristol, UK, 1991). 36. A. Curtis, C. Wilkinson, Biomaterials 18, 1573 (1997). 37. L. G. Grifth, Acta Mater. 48, 263 (2000). 38. T. M. McGloughlin, A. G. Kavanagh, Proc. Inst. Mech. Eng. Part HJ. Eng. Med. 214, 349 (2000). 39. A. C. Lawson et al., MRS Symp. Ser.: Biomed. Mater.: Drug Delivery, Implants Tissue Eng. 550, 235 (1999), T. Neenan, M. Marcolongo, R. F. Valentini, Eds. 40. C. S. Ranucci, P. V. Moghe, J. Biomed. Mater. Res. 54, 149 (2001). 41. P. Banerjee, D. J. Irvine, A. M. Mayes, L. G. Grifth, J. Biomed. Mater. Res. 50, 331 (2000). 42. The authors acknowledge contributions to this work from A. Briggs, D. Bucknall, V. Burlakov, J. Czernuska, and S. Wilkinson from Oxford University; N. Marston and I. Robinson from Lucite International; and Y. Tsukahara from the Toppan Printing Company. VIEWPOINT 20th- to 21st-Century Technological Challenges in Soft Coatings Robert R.Matheson Jr. Coatings are among the most ancient technologies of humankind. Rela- tively soft coatings comprising organic materials such as blood, eggs, and extracts from plants were in use more than 20,000 years ago, and coating activityhasbeencontinuouslypracticedsincethenwithgraduallyimprov- ing materials and application techniques. The fundamental purposes of protecting and/or decorating substrates have remained ubiquitous across all the centuries and cultures of civilization. This article attempts to extrapolate the long tale of change in soft coating technology from its current state by identifying some key problems that attract research and development efforts as our 21st century begins. Humans have been decorating and protecting various surfaces for many thousands of years. One very useful way of accomplishing either or both of those tasks is to apply a thin layer of some new material with appropriate char- acteristics (of appearance, durability, adhe- sion, and application requirements) directly onto the surface of interest. That new material is a coating. Understandably, the early history of coatings is a story of very specialized, often unique material combinations, as trial and error achieved goals with only the mate- rials at hand in nature. This heritage of cus- tomization is still detectable in the modern coatings world, which demands a tremendous amount from the materialsoften synthetic but some still containing or made of natural productsto be thinly applied on a surface. They need to be easily and uniformly applied; set up within a reasonable amount of time and process constraints; have a minimal environ- mental impact in their synthesis, combina- DuPontPerformanceCoatings,950StephensonHigh- way,Troy,MI48083,USA.E-mail:robert.r.matheson 9 AUGUST 2002 VOL 297SCIENCE www.sciencemag.org976 M ATERIALS S CIENCE:SOFT S URFACES on March 23, 2010 www.sciencemag.org Downloaded from tion, and application; resist the effects of environmental assault; and provide good eco- nomic value. I examine five important forces that are driving how such coatings are made and improved today. Nomenclature The long, decentralized, and empirical evo- lution of coating materials and processes has left behind an arcane and frequently confus- ing vocabulary (1). It will be helpful to define three terms that are frequently used but also are indiscriminately interchanged. A lacquer (from the Arabic word lakk) is a coating that forms on a surface (frequently by evaporation of solvents) without the intervention of cova- lent bonds forming between the film-forming ingredients. In contrast, a varnish (from the Medieval Latin vernice) is a coating that essentially requires chemical reactions be- tween film-forming ingredients during a cur- ing process after its application to a substrate. Enamels (from the Germanic esmail) are a very common subset of varnishes, which use a heating (stoving) step to carry out the cur- ing process. These classifications were sharp and distinct in the past, but current develop- ments are beginning to weaken their clarity. However, they will be useful here in high- lighting the particular challenges facing coat- ing development. Minimizing the Environmental Footprint One of the most commonly recognized chal- lenges is the reduction or elimination of vol- atile organic compounds (VOCs) from the formulations of modern coatings (2). In the quantities generated by todays population and particularly in the concentrations pro- duced in industrialized urban environments, VOC emissions contribute to air pollution problems. Clearly, this problem is most acute for lacquers. The mutually unreactive com- ponents of a lacquer absolutely depend on some processing aid (commonly a solvent) to make them malleable enough for applica- tion, and those aids must then be removed to leave the coating robust enough to protect and decorate. Solvent minimization finds its ultimate expression in lacquer versions of powder coatings, where solvents are replaced with heat, which is used to apply the coating. Upon cooling, the properties that develop can sometimes be adequate to the task at hand. However, these products are limited in that if the coating is heated to a temper- ature where its application is possible, then it will soften and deform once again. More- over, because most coating films are either amorphous or semicrystalline, their ability to retain a minimum hardness and to resist sustained loads begins to fall off quite no- ticeably at temperatures well below those where rapid flow and leveling are achieved (3). Acceptable solvent substitution basically amounts to using the liquid form of substanc- es that are naturally present as gases in the atmosphere (such as water and carbon diox- ide). Liquid or supercritical carbon dioxide is limited to industrial applications because of the requirements for high pressure. Water is easier to use widely as a coating solvent, but it is not a panacea. One example of a problem that comes with water is the inevitably wide variation in drying times that accompanies application in environments of different rel- ative humidity. Because relative humidity can change almost hourly, this is a serious complication. In fact, virtually all waterborne coatings today contain quite substantial levels of organic “cosolvents.” The VOC content of waterborne coatings is greatly reduced as compared to that of older, conventional solvent-borne coatings, but it is not fully eliminated. A major activity in modern coat- ing development is the search for balanced chemistry that will push back these limits on environmentally more favorable lacquers while retaining the attractive simplicity, the synthetic control, and the low cost of the technology. VOC release is not the only environmen- tal impact factor that is important for driving change in coating technology. In the United States, regulations on so-called hazardous air pollutants (HAPs) are important (4). This is an explicit list of solvents, typically aromatic, that are used in large quantities and are either known to cause or suspected of causing hu- man health problems with chronic exposure. A variety of other, similarly local constraints for particular ingredients exist around the globe. One very widely experienced restric- tion is that on heavy metals. There are many historical examples where fairly large amounts of particular metals have found use in soft coatings (5). Some examples are the use of lead for anticorrosion in cathodic elec- trocoat coatings, of hexavalent chromium in metal coatings, of both lead and cadmium in various pigments, of divalent tin in antifoul- ing marine coatings, and even of mercury as an antifungal agent for some interior paints. In common with other areas of materials processing, coating technology now has to look for alternative ingredients without un- controllable, long-term environmental conse- quences. No similarly general technical solu- tions have yet been found, although progress is being made, particularly with respect to anticorrosion coatings. Beating Back the Environment Chemical and mechanical resistance to envi- ronmental insult is a common feature of many coating systems and a key reason for their application. Biological attacks are clas- sic problems encountered over the years, and their catalog defines the current frontier. Un- derwater coatings that can resist the attach- ment and degradation of aqueous organisms (such as worms and barnacles) are needed for shipping and for structures. Exterior coatings that can resist particular insect, bird, and plant excretions are frequently needed in lo- cal geographies. Interior coatings that can resist mildew, other fungal damage, molds, and bacteria are frequently desired. The gen- eral challenge is nearly always the same: specific resistance to a defined class of bio- logical insult without nonspecific toxicity or irritation. It is natural to work toward this set of objectives with additives tailored to each task. Experience shows this natural path to be expensive and usually imperfect, but occa- sionally fruitful. Still, it is probably fair to say that no examples exist where the performance of the broadly toxic, heavy metalbased ad- ditives has been achieved with the more spe- cific modern tools. A new idea is to produce counteragents in situ by tapping the chemical reactions that must accompany biological attack or even simple weathering in the active environments near Earths surface (6). For example, bio- logical damage may be accompanied by hy- drolytic scission of coating components. If those can be designed to hydrolyze into anti- septic, antifouling, or anti-whatever products tailored to the task, then perhaps an effective solution can be found. Maximizing Control Through Molecular Architectures It is important to look beyond environmental attack on the coating itself. The classical role of coatings is to protect something else from the environment. This protection can be me- chanical or chemical in nature. Varnishes have been developed particularly for these purposes, because in situ or “on the work” cross-linking is a very effective technique for augmenting the coatings material properties while avoiding compromises in application. An extremely active area of development in modern coatings is directed to improving the control of such reactions. Inevitably, these must be carried out in a variety of work environ- ments. Near one extreme are coatings used in controlled chambers, as for the radiation or thermal curing of a coating used to seal a connection between electronic components. The variables of concern may be film thickness at various points, surface cleanliness, and small temperature gradients arising from materials of different thermal conductivity. Near the other extreme are the grossly fluctuating environ- ments that can be found in a railroad locomo- tive shed, where humidity, temperature, air flow, application rate, surface preparation, and maybe even surface material are all variables. One idea for meeting these challenges is www.sciencemag.org SCIENCE VOL 2979 AUGUST 2002 977 M ATERIALS S CIENCE:SOFT S URFACES on March 23, 2010 www.sciencemag.org Downloaded from to take great care in synthesizing the var- nish ingredients so that no especially trou- blesome reactions can ever occur. Some side reactions are understandably more del- eterious than others, and the goal is to leave no opportunity for the most troublesome, no matter what conditions might appear. This leads to the use of controlled polymer- ization techniques exemplified but certain- ly not limited to group transfer polymeriza- tion (7) for acrylic materials, rigorous exclusion of nonfunctional (unable to par- ticipate in curing) matrix materials, and optimizing molar mass distributions to avoid untimely immiscibility during cure and similar strategies. The specific field of automotive coating has been in the fore- front of this activity because of the ex- tremely high performance standards and powerful economic incentives found in mass-producing automobiles. Some of the new synthetic and analytical techniques be- ing introduced for controlling and monitor- ing automotive enamels have been de- scribed (8). Decorative coatings in particular need to incorporate pigments, dyes, reflective metal, and mica flakes for many applications. One common technique for effectively distribut- ing such particles is to cover their surfaces with dispersants that aid in their dispersion in the bulk of the coating and prevent reagglom- eration under the variety of circumstances that might arise later. Exquisite control of the molecular structure is needed in order to achieve good distribution of the particles, minimal mobility once applied to a surface, the ability to resist forces that drive re- agglomeration, and compatibility with the bulk coating and yet not induce problems with adhesion, application, or long-term per- formance. Because pigments are very fre- quently the most expensive ingredients in a decorative coating, it is important to use them efficiently. Additionally, as solvent concen- tration and variety are decreased because of the environmental pressures previously cited, opportunities for managing dispersion prob- lems by modifying the coating medium (the coating vehicle) decrease. Small wonder that the chemistry used to make modern dispers- ants provides an exceptionally clear picture of the sta