Thermally Induced Phase Transitions and Morphological Changes in Organoclays GelferM. BurgerC. FadeevA. SicsI. ChuB. HsiaoB. S. HeintzA. KojoK. HsuS-L. SiM. RafailovichM. 2004 Thermal transitions and morphological changes in Cloisite organoclays were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and in situ simultaneous small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) over the temperature range of 30−260 °C. On the basis of DSC and FTIR results, the surfactant component in organoclays was found to undergo a melting-like order−disorder transition between 35 and 50 °C. The transition temperatures of the DSC peaks (<i>T</i><sub>tr</sub>) in the organoclays varied slightly with the surfactant content; however, they were significantly lower than the melting temperature of the free surfactant (dimethyldihydrotallowammonium chloride; <i>T</i><sub>m</sub> = 70 °C). FTIR results indicated that within the vicinity of <i>T</i><sub>tr</sub>, the gauche content increased significantly in the conformation of surfactant molecules, while WAXD results did not show any change in three-dimensional ordering. Multiple scattering peaks were observed in SAXS profiles. In the SAXS data acquired below <i>T</i><sub>tr</sub>, the second scattering peak was found to occur at an angle lower than twice that of the first peak position (i.e., nonequidistant scattering maxima). In the data acquired above <i>T</i><sub>tr</sub>, the second peak was found to shift toward the equidistant position (the most drastic shift was seen in the system with the highest surfactant content). Using a novel SAXS modeling technique, we suggest that the appearance of nonequidistant SAXS maxima could result from a bimodal layer thickness distribution of the organic layers in organoclays. The occurrence of the equidistant scattering profile above <i>T</i><sub>tr</sub> could be explained by the conversion of the bimodal distribution to the unimodal distribution, indicating a redistribution of the surfactant that is nonbounded to the clay surface. At temperatures above 190 °C, the scattering maxima gradually broadened and became nonequidistant again but having the second peak shifted toward a scattering angle higher than twice the first peak position. The changes in SAXS patterns above 190 °C could be attributed to the collapse of organic layers due to desorption and/or degradation of surfactant component, which was supported by the TGA data.