Lanthanum laurate

Keywords fullerenes, nanovoid, positronium, liquid crystal, lanthanum laurate... 

Lanthanum laurate La(Ci2H25COO)3 exemplifies ionic metal mesogenes, which are known to form thermotropic and liotropic liquid crystals [1], Anisotropy and high molecular mobility are essential properties of liquid crystals, which ensure the fast rate of information processing systems on their base. Molecular mobility is also known to depend on the presence of the free-volume defects. These are intermolecular cavities (nanovoids) or atomic-size vacancies. 

Lanthanum laurates in crystalline (powder) and liquid-crystalline states, as well as after dissolution of Cgo fullerenes were studied by means of the positron annihilation technique which is extremely sensitive to the free-volume defects. 

Lanthanum laurates were prepared as in Ref. [2]. The spectra of the angular correlation of annihilation photons (ACAP) were measured in a standard long-slit geometry using 22Na radioactive isotope as a positron source. 

Positronium (Ps) annihilation probability in the nanovoids of the samples in initial state is found to be 11.13 %, whereas the mean nanovoid radii for the crystalline and liquid-crystalline samples are 0.33 and 0.28 nm, respectively. After dissolution of Cgo fullerenes probability of Ps annihilation in nanovoids is decreased by the factor of 2.7. The general spectrum of lanthanum laurate initial pattern is presented in the Fig. 1. The calculated parameters of the investigated patterns are resulted in the Table 1. 

Figure 1. Lanthanum laurate angle correlation of annihilation photons spectra in slowly cooled from melted state ( ) and it s expansion to narrow (NG), mean (MG) and broad (BG) Gaussians.

TABLE 1. Parameters of ACAP spectra and the calculated sizes of nanovoids in lanthanum laurate patterns... 

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