Can the Isothermal Calorimetric Curve Shapes Suggest the Structural Changes in Micellar Aggregates?

Inspired by the unusual shapes of the titration curve observed for many surfactants and mixed colloidal systems, we decided to extend the analysis to isothermal titration calorimetric curves (ITC) by paying special attention to potential structural changes in micellar aggregates. In this paper, we used isothermal titration calorimetry in conjunction with Scanning Transmission Electron Microscopy (STEM), Small-Angle Neutron Scattering (SANS) and X-ray Scattering (SAXS) methods support by Monte Carlo and semiempirical quantum chemistry simulations to confirm if the isothermal calorimetric curve shape can reflect micelle transition phenomena. For that purpose, we analysed, from the thermodynamic point of view, a group of cationic gemini surfactants, alkanediyl-α,ω-bis(dimethylalkylammonium) bromides. We proposed the shape of aggregates created by surfactant molecules in aqueous solutions and changes thereof within a wide temperature range. The results provide evidence for the reorganization processes and the relationship (dependence) between the morphology of the created aggregates and the conditions such as temperature, surfactant concentration and spacer chain length which affect the processes.

Rheological and Calorimetric Characterization of the Role of CaCl2 on Portland Cement Early Hydration

Paper describes a new way how to characterize early hydration and setting of Portland cement pastes with various dosages of setting accelerator CaCl2. The aim was not to characterize the role of well-known setting accelerator CaCl2 but to correlate rheology and calorimetry in view of early hydration of Portland cement. Characterization was based on measurements on rotational rheometer, isothermal calorimeter and semiadiabatic calorimeter. The courses of calorimetric exotherms in time were correlated to the development of the phase angle obtained by rheological oscillation tests. Heat flow peaks can be successfully correlated to rheological processes described by change of storage and elastic moduli up to the time that corresponds to the start of the setting which was found to be the limit for rheological tests. The start of the setting on calorimetric curve belongs to the onset point of the main silicate peak during acceleration period of hydration. The value of phase angle decreases as the setting cement paste changes from liquid to solid-like. Times of low values of phase angle ~ 2.5 (°) can be related to times of onset points of main peak for every dosage of setting accelerator.

Structural and Ferroelectric Properties of NaNO2: PVF Composite Film

The structural and ferroelectric properties of NaNO2: PVF composite film prepared by hot press method have been studied and analyzed. The x-ray diffraction study revealed that the strain is reduced in the composite film. The image of field emission scanning electron microscope shows uniform distribution of NaNO2 grains of 150 nm size in the composite film. The differential scanning calorimetric curve supports the presence of ferroelectric phase. The polarization reversal characteristics were studied with the bipolar square pulse. The application of Ishibashi and Shur’s theory to the experimental switching transients supports needle like domain growth (1D) during switching process. The remanent polarization obtained from the polarization reversal is in agreement with the hysteresis loop value. The composite film shows faster switching time compared to pure NaNO2 film and may be attributed to the reduced strain.