Authors:Krystyna Cieśla, H. Rahier, and Grażyna Zakrzewska-Trznadel
One to three endothermal peaks atributted to melting of bulk and interfacial water were observed by DSC in the regenerated
cellulose — water system. The profiles of thermal effects depend on water content, time of conditioning, film pretreatment
and the conditions applied during the preceding freezing-thawing cycles. The occurrence might be deduced of melting-crystallisation
processes. A large amount of non-freezable strongly bounded water was also detected.
Although cellulose absorbs water quickly after immersion, the structural changes consisting on ordering of polymer fraction
occur during further conditioning due to increase in strength of water binding. Using the membranes in the separation module
at 90C causes weakening of these bonds. Differences between interaction of particular cellulose films with water can be detected
during the first, the second and the third heating.
Authors:Marta Fernandez-Tarrio, Carmen Alvarez-Lorenzo, and A. Concheiro
comprises X-shaped copolymers formed by four poly(propylene oxide) (PPO) and
poly(ethylene oxide) (PEO) block chains bonded to an ethylene diamine central
group. Micellization behaviour of three representative Tetronics (T304, T904
and T1307) was characterized to gain an insight into the interactions between
the copolymer unimers and the state of water in their solutions. The enthalpy
of demicellization, recorded at 37°C in an isoperibol microcalorimeter,
indicated that the process was in all cases exothermic and the enthalpy ranked
in the order T1307≥T904>>T304. Micellization is entropy-driven owing to
hydrophobic interactions between the PPO chains.
showed that the crystallization and melting peaks of the free water remaining
in T304 and T904 solutions were progressively shifted toward lower temperatures
as the surfactant proportion increased, owing to a colligative effect. Bound
water corresponded to 3 water molecules per EO repeating unit. In the case
of T1307, which has longer PEO chains, a splitting of the melting peak was
observed, one peak appearing around 0°C due to free water and another
at –15°C due to interfacial water. As T1307 proportion raised, the
enthalpy of the former decreased, whilst the enthalpy of the latter increased.
In 40% T1307 solutions, interfacial water overcame the proportion of free
water; there being 1 interfacial and 3 bound water molecules per EO repeating
unit. Gaussian deconvolution of FTIR spectra also enabled to characterize
the evolution of free water as a function of Tetronic proportion. The dependence
of micellization and water interaction behaviour on Tetronics structure should
be taken into account to use these copolymers as drug solubilizers and micellar
The state of water and several transitions were examined in the systemsn-decanephosphonic acid (DPA)—water and the sodium salts of DPA—water. Temperature — composition phase diagrams are reported.
The results show that several liquid crystalline phases plus isotropic liquid, and two solid phases (a waxy solid phase and
a crystalline phase) are formed. Several types of water were detected: bulk-like water, interfacial water and hydration water.
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.