Glass-to-metal seal absorb the stresses from thermal expansion mismatches. Due to its very low vapor pressure, indium finds use in glass-metal seals used in vacuum technology. Gallium is a soft metal with melting point at 30 °C. It readily wets glasses and most metals and can be used for seals that can be assembled/disassembled by just slight heating. It can be used as a liquid seal up to high temperatures or even at lower temperatures when alloyed with other metals (e.g. as galinstan). Mercury is a metal liquid at normal temperature. It was used as the earliest glass-to-metal seal and is still
Liquid crystal Rod-shaped molecules have an elongated, anisotropic geometry which allows for preferential alignment along one spatial direction. • The molecular shape should be relatively thin, flat or bowl-like, especially within rigid molecular frameworks. • The molecular length should be at least 1.3 nm, consistent with the presence of long alkyl group on many room-temperature liquid crystals. • The structure should not be branched or angular, except for the bowlics. • A low melting point is preferable in order to avoid metastable, monotropic liquid crystalline phases. Low-temperature mesomorphic behavior in general is technologically more useful, and alkyl terminal groups promote this. An