ABSTRACT
Long-term stability and long-term performance of thermal storage media are a key issue that should be thoroughly analysed when developing storage systems. However, no testing protocol or guideline exists up to now for validating storage media, so that authors apply their own criteria, not only for designing testing procedures but also for predicting the material behaviour under long-term operation. This paper aims to cover this gap by proposing a methodology for validating thermal storage media; in particular, phase change materials (PCMs). This methodology consists of different stages that include PCM characterization, preliminary assessment tests, and accelerated life testing. For designing the accelerated life tests, lifetime relationship models have to be obtained in order to predict PCM long-term behaviour under service conditions from shorter tests performed under stress conditions. The approach followed in this methodology will be valid for materials to be used as sensible or thermochemical storage media, too.
ABSTRACT
Rodlike gold(I) complexes, [Au(C6F4OCmH2m+1)(C(triple bond)NC6H4C6H4OCnH2n+1)] (m=2, n=4, 10; m=6, n=10; m=10, n=6, 10), display interesting features. They are liquid crystals and show photoluminescence in the mesophase, as well as in the solid state and in solution. The single-crystal, X-ray diffraction structure of [Au(C6F4OC2H5)(C(triple bond)NC6H4C6H4OC4H9)] confirms its rodlike structure, with a linear coordination around the gold atom, and reveals the absence of any Au...Au interactions (such interactions are often present in luminescent gold complexes). Well-defined, intermolecular Fortho...Fmeta interactions, with remarkably short intermolecular FF distances (2.66 A), are observed; these interactions seem to be responsible for the crystal packing, which consists of an antiparallel arrangement of molecules. Experiments under different conditions support the explanation that the photoluminescence has an intramolecular origin.
ABSTRACT
Rodlike gold(I) and gold(III) complexes [AuR(C&tbd1;N(C(6)H(4))(m)()OC(n)()H(2)(n)()(+1)-p)] (m = 1, n = 10, R = C(6)F(5); m = 2, n = 4, 6, 8, 10, 12, R = C(6)F(5), C(6)F(4)Br-o, C(6)F(4)Br-p), [(&mgr;-4,4'-C(6)F(4)C(6)F(4)){AuC&tbd1;N(C(6)H(4))(m)()OC(n)()H(2)(n)()(+1)}(2)] (m = 1, 2; n = 4, 6, 8, 10, 12), [AuRI(2)(C&tbd1;NC(6)H(4)C(6)H(4)OC(n)()H(2)(n)()(+1)-p)] (R = C(6)F(5), n = 8; R = C(6)F(4)Br-o, n = 10), and [(&mgr;-4,4'-C(6)F(4)C(6)F(4)){AuX(2)C&tbd1;N(C(6)H(4))(m)()OC(n)()H(2)(n)()(+1)}(2)] (m = 1, 2; n = 4, 6, 8, 10, 12) have been prepared and their liquid crystal behavior has been studied. The gold(III) compounds are not mesomorphic, but all the perhalo-gold(I) derivatives described are liquid crystals except the phenyl isocyanide gold(I) derivative [Au(C(6)F(5))(C&tbd1;NC(6)H(4)OC(10)H(21)-p)]. The mononuclear derivatives show only a nematic (N) phase when the isocyanides have a short tail (n = 4), N and smectic A phases (S(A)) when the isocyanides have an intermediate tail (n = 6, 8), and only S(A) phases for longer chains. Their thermal stability is high, even in the isotropic state. The variation in transition temperatures is as follows: C(6)F(4)Br-p >/= C(6)F(5) > C(6)F(4)Br-o when n C(6)F(4)Br-o > C(6)F(5) for n >/= 8. This behavior is understood on the basis of electronic and steric factors. The dinuclear compounds [(&mgr;-4,4'-C(6)F(4)C(6)F(4)){AuC&tbd1;N(C(6)H(4))(m)()OC(n)()H(2)(n)()(+1)}(2)] display only N mesophases and all the biphenylisocyanide derivatives and phenyl isocyanide compounds with n
