The role of organically modified silicate (OMS), Lucentite STN on the formation of beta-crystalline phase of poly(vinylidene fluoride) (PVDF) is investigated in the present study. The OMS was solution blended with PVDF and cast on glass slide to form PVDF-OMS nanocomposites. Solution cast samples were subjected to various thermal treatments including annealing (AC-AN), melt-quenching followed by annealing (MQ-AN), and melt-slow cooling (MSC). Fourier-transform infrared spectroscopy (FT-IR), wide angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC) were used to investigate the crystalline structure of thermally treated samples. As a special effort, the combination of in situ thermal FT-IR, WAXD, and DSC studies was utilized to clearly assess the thermal properties. FT-IR and WAXD results of MQ-AN samples revealed the presence of beta-phase of PVDF. Ion-dipole interaction between the exfoliated clay nanolayers and PVDF was considered as a main factor for the formation of beta-phase. Melt-crystallization temperature and subsequent melting point were enhanced by the addition of OMS. Solid beta- to gamma-crystal phase transition was observed from in situ FT-IR and WAXD curves when the representative MQ-AN sample was subjected to thermal scanning. Upon heating, beta-phase was found to disappear through transformation to the thermodynamically stable gamma-phase rather than melting directly. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2173-2187, 2008