Tham khảo tài liệu 'thermal analysis of polymeric materials part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 526 5 Structure and Properties of Materials Fig. Change of Gauche Cone. with Temperature _ 14 average between simulation time 5-10 ps 0 o 0 data from simulation data from IR experiments Kim Strauss Snyder J. Phys Chem. 93 7520 1989 1 00 0- 80 160 240 320 400 440 Temperature K Fig. By inspection one can see that the kink is the result of the collision of a transverse A torsional B and longitudinal vibration C between and ps see also Fig. . After formation this particular kink defect had a life time of about 2 ps. The mechanism of twisting of a single chain is illustrated in Fig. . One can see a very gradual twist starts at about ps and is completed after ps. After this Defects in Polymer Crystals 527 Fig. Fig. twist the whole chain has been rotated by about 90o. It remains with minor fluctuations in this position until 7 ps when the rotation reverses. The twist is so gradual that no gauche conformations are necessary for its occurrence. The sequence of Figs. illustrates the details of the diffusion of a chain through the crystal. The figures refer to a chain that was driven into the direction of 528 5 Structure and Properties of Materials Lifetime of a Gauche Defect in Polyethylene 19 mobile chains 1g surrounded JJ by 18 312 stationary 0 chains E T 350 K Gradient 20 40 60 80 100 Defect Position Fig. Motion of the Central Chain Positions of the Upper and Lower 12 Chain Ends 10 Z-Distance 8 nm 6 4 Gradient 2 2 0 100 chain -2 ---1--1---1----1---1-----1--1---1-----1- atoms 350 K 0 2 4 6 8 10 12 14 16 18 20 gradient Time ps Fig. the indicated gradient by application of an external force. Figure illustrates the gauche conformations that appear during the diffusion compare to Fig. . There is no direct involvement of the gauche defects in the motion. At later time the increase in gauche bonds is connected with the chain having moved out of the crystal in the
