TAILIEUCHUNG - Thermal Analysis of Polymeric Materials Part 4

Tham khảo tài liệu 'thermal analysis of polymeric materials part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 166 2 Basics of Thermal Analysis Fig. Fig. changes in entropy which are coupled with the disordering are listed. Details about these data are presented in Sect. . Usually these transitions are first-order transitions see Sect. . All mesophases when kept for structural or kinetic reasons from full crystallization on cooling display in addition a glass transition as is indicated on the left-hand side of Fig. . The glass transition leads to a glass Phases and Their Transitions 167 Summary of Possible Condensed Phases Fig. with mesophase order but without the large-amplitude motion. The recognition of mesophases and mesophase glasses as states of intermediate order and their study by thermal analysis has become of great importance for the understanding of the multitude of materials. The empirical rule of change of the heat capacity when going through a glass transition is described in Sect. . Phases of Different Sizes It was noted about 150 years ago that the properties of phases change when their dimensions decrease to the micrometer scale. This observation was first made after the discovery of colloids. Today such small phases are better called microphases 27 . In microphases the effect of the surfaces cannot be neglected. Surface free energies and charges surface potentials govern the properties and stability or metastability of the microphases. Similarly in Fig. it is shown that molecules may be classified into three types small large and flexible and large and rigid. In this section the changes of phase size and molecular size are analyzed briefly. When forming a crystal via nucleation and growth as described in Sects. and the linear growth rates in the various crystallographic directions determine the initial usually metastable crystal shape. Linear flexible macromolecules for example chain-fold to lamellar crystals with much faster growth in the crystallographic a- and b-directions than in direction c .

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