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Crystallization and second-order transitions in silicone rubbers

1950; US government; Volume: 44; Issue: 4 Linguagem: Inglês

10.6028/jres.044.032

2376-5305

C. E. Weir, W. H. Leser, Lawrence A. Wood,

Force Microscopy Techniques and Applications

In t he course of an investigation to determine which rubbers might be suitable fo r usc at low temperatures, interferometric m eas urem e nts of the length-temp erature relat ionships of silicone rubbers have been made .C rystall ization was found between -60° a nd -67° C in Dow-Corning SiJastic X -6160 and in Ge neral E lectric 9979G sili co ne ru bber, thc lattcr of wh ich co nta in s no fi llcr.Crystallizat ion between -75° and -85 ° C \\"as found in Silast ic 250.~1elting occurred ovcr a range of tempcrat ure above t he temperaturc of c rystalli zation .Th e volume change on crystalli zation vari cd from 2.0 to 7.8 pcrcent.Xo crystall izatio n PI' melt in g ph enom cn a were obscrvcd in Sil a st ic X-6073 between -180 ° and + 100° C .All types of silico ne rubbcr ex h ibited a scco nd-order t rans ilion at about -123° C, t hc lowcs t tcmpcraturc at which s uc h a tra ns it ion has been obscrv cd in a polymer.The coc ffi cic nt of lin car thcrmal expan sion of s ilicone rubbcrs contai nin g no fillf'l" wa' 3 fo und to be about 40 X 10-5 /dcg C bctween -35 ° a nd 0 ° C.