Các chuyên ngành cơ bản của cơ khí bao gồm: động học, tĩnh học, sức bền vật liệu, truyền nhiệt, động lực dòng chảy, cơ học vật rắn, điều khiển học, khí động học, thủy lực, chuyển động học và các ứng dụng nhiệt động lực học. Các kỹ sư cơ khí cũng đòi hỏi phải có kiến thức và năng lực áp dụng những khái niệm trong môi trường kỹ thuật điện và hóa học. Với một mức độ nhỏ, cơ khí còn trở thành kỹ thuật phân tử - một mục tiêu viễn cảnh của nó là tạo. | 330 The Coming of Materials Science for the leading early treatment of the mechanical properties of solid polymers Ward 1971a . . DETERMINING MOLECULAR WEIGHTS At the end of the 1930s the only generally available method for determining mean MWs of polymers was by chemical analysis of the concentration of chain end-groups this was not very accurate and not applicable to all polymers. The difficulty of applying well tried physical chemical methods to this problem has been well put in a reminiscence of early days in polymer science by Stockmayer and Zimm 1984 . The determination of MWs of a solute in dilute solution depends on the ideal Raoult s Law term which diminishes as the reciprocal of the MW but to eliminate the non-ideal terms which can be substantial for polymers and which are independent of MW one has to go to ever lower concentrations and eventually one runs out of measurement accuracy . The methods which were introduced in the 1940s and 1950s are analysed in Chapter 11 of Morawetz s book. In the 1930s one novel method was introduced by a Swedish chemist The Svedberg who invented the ultracentrifuge an instrument in which a solution of colloidal particles proteins or synthetic polymers is subjected to forces many times greater than gravity and the equilibrium distribution of concentration which may take weeks to attain is estimated by measuring light absorption as a function of position along the length of the specimen chamber as the centrifuge spins. It took a long time for this approach to be widely used for polymers because of the great cost of the instrument Du Pont acquired the first production instrument in 1937. Eventually it became a major technique and Svedberg who himself was mainly concerned with proteins earned a Nobel Prize. The theory that related equilibrium concentration gradients to molecular weight is the same as that put forward in Einstein s 1905 paper that was applied to Brownian motion and thus served to cement the atomic hypothesis
