Solid polymorphism of 4-alkyl-4'-cyanobiphenyl (nCB) was studied so far as a function of thermal history. In this paper we show that metastable solid phases of 4-octyl-4'-cyanobiphenyl (8CB) are also formed when the mesogens are confined in porous silica matrices and we study their structure by neutron diffraction and by Raman spectroscopy. Three metastable solid states are identified : one crystalline phase K', two frozen-in smectic-like phases Ks and K s . We discuss the relation between the

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... tructure of the metastable solid phases and that of the mesomorph phases. PACS . 61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems -61.12.Ld Neutron diffraction -78.30.-j Infrared and Raman spectra (condensed matter) -64.60.My Metastable phases 2220 2240 2260 ν (cm -1 ) Raman scattering