Calorimetric measurements of adsorption for the surfactant (benzyldimethyldodecylammonium bromide) and its polar head-group
(benzyltrimethylammonium bromide) from aqueous solutions on two different silica surfaces (hydrophilic and hydrophobic one)
allow a more detailed picture of the subsequent stages of the adsorption process to be drawn. It is possible to determine
more precisely a boundary between the adsorption of individual molecules and the formation of surface aggregates. The local
disruption of the structure of the interfacial water molecules by surfactant cations gives an endothermic contribution to
the total enthalpy of displacement. This contribution depends on the length of alkyl chain as well as on the type and the
origin of solid surface.
The importance of calorimetric methods in studies of colloidal phenomena is illustrated by the analysis of the experimental
enthalpies of dilution and adsorption for aqueous solutions of three zwitterionic surfactants: 1–12 betaine, 3–12 betaine,
and 3–12 sulfobetaine. The batch microcalorimeter ‘Montcal 3’, used to obtain these data, is described. The molar enthalpies
of micellization and the differential molar enthalpies of adsorption onto silica gel are shown to be functions of the headgroup
hydrophilicity, fixed by the type of negatively charged center and the number of methylene groups separating the charged sites.
An amide-type local anesthetic drug, bupivacaine hydrochloride (BupiHCl), in the form of racemate is listed in the European and American pharmacopoeias and continues to be used in medicine. Thermal and X-ray analysis of commercial BupiHCl monohydrate was performed by differential scanning calorimetry with thermogravimetry, hot stage microscopy, and X-ray diffraction. Endothermic dehydration occurs at the temperature range of 73–130 °C for DSC–TG 111 (Setaram) and at 83–150 °C for DSC 404 (Netzsch). Both curves at 2 and 10 °C min−1 clearly reflect phase transformation of anhydrous Form I into II before reaching the melting point. A well-defined exothermic phase transition of BupiHCl was detected at a lower heating rate. Temperature-resolved X-ray diffraction in conjunction with DSC led to determining a similarity between the obtained thermal events. Microscopic investigation also confirmed the above-mentioned transformations.