Anna Kozina

Influence of Water/Alkoxide Ratio in the Synthesis of Nanosized Sol—Gel Titania on the Release of Phenytoin

The sol-gel method was used to synthesize inorganic reservoirs with encapsulated antiepileptic drug phenytoin. The drug release profile was shown to depend on the morphology and surface properties of the matrix. A parameter of the synthesis such as water/alkoxide ratio r(w) was varied in order to investigate its influence on the matrix properties and as a result on the drug release profile. It was found that the specific surface area and crystallization degree decrease with an increase of r(w), whereas the hydroxyl group coverage increases with an increase of r(w). Drug release kinetics studies revealed that the initial release rate increases with an increase of water content in the reaction, whereas the long time release rate first slightly increases with an increase of water content from 4 to 8 and then decreases for r(w) = 16. The interplay of different parameters of the matrix is shown to be responsible for such a dependence and is discussed in the Article.

Structural and dynamical evolution of colloid-polymer mixtures on crossing glass and gel transition as seen by optical microrheology and mechanical bulk rheology

We present a study of the evolution of structural properties and dynamical behaviour of colloidal complex systems, as seen by two techniques working on two different length scales. Our system consists of a binary mixture at high volume fraction of internally crosslinked polystyrene microgels dispersed in an organic solvent. In this colloidal binary mixture the total polydispersity of the system has been artificially increased in order to “tentatively” suppress crystallization. We have studied concentrated repulsive and attractive systems. In the first case, the colloidal particles have a ‘nearly’ hard sphere interaction. In latter case, we have introduced an attractive interaction via Asakura-Oosawa potential using free linear polymer added to this system. We characterize the mechanical properties applying dynamic light scattering based optical microrheology at the microscopic level, and mechanical bulk rheology at the macroscopic level. We compare the results obtained by both techniques finding, under certain conditions, discrepancies attributed to existing heterogeneities. Analyzing the observed discrepancies, we propose a qualitative model of structural and dynamical evolution of the studied systems.

Influence of aggregation on characterization of dilute xanthan solutions

Xanthan is an extracellular polysaccharide of polyanionic nature widely used in industrial processes as flow modifier. Its characterization in dilute solutions is complicated by the strong tendency to aggregation. We explore the possibility to obtain dilute xanthan solutions without aggregates. We applied some steps of the sample preparation procedures from previous works on xanthan, such as ultrasonication, heating and micro filtration. The influence of this type of treatment on the observed properties of xanthan 0.1M NaCl aqueous solutions is studied. Renaturalization of xanthan solutions above the overlap concentration does not break the aggregates but, on the opposite, produces the ones that are more resistant to ultrasound. Ultrasonication breaks only large aggregates and at long sonication times brings the risk of the single chain degradation. The best results are provided by a procedure that combines a short ultrasonication time followed by micro filtration but it is impossible to obtain a solution completely free of small aggregates by conventional sample preparation methods. Nevertheless, a significant reduction of large aggregates results in a linear concentration dependence of xanthan reduced viscosity, which allows more confident determination of the intrinsic viscosity. Another advantage of large aggregates removal is a possibility of physical interpretation of xanthan molecular parameters by static light scattering, taking into account its association tendency.