Rheological behaviour of poly(vinyl alcohol) (PVA) aqueous systems was systematically investigated at 30 C for different concentrations, molecular weights and hydrolysis degrees. The viscosity of very dilute polymer solutions was studied by means of viscometry, while the concentrated solutions were analyzed by steady shear flow measurements. The limit between the entangled and non-entangled states of PVA aqueous solutions was determined as the crossover of two scaling laws describing the dependence of specific viscosity as a function of coil overlap parameter, c[h]. Then, physical gels with good elastic properties were prepared in situ by freezing/thawing/ageing (200 min per cycle) of entangled PVA solutions. The influence of each stage of the applied cryogenic treatment on the gel formation and elastic properties of the final network was followed by means of dynamic rheological measurements at low strain, in the linear domain of viscoelasticity. It was shown that the gel properties largely depend on the initial state of PVA solutions, as described by the c[h] value, and on the degree of hydrolysis, as well as on the thermal history, i.e., the number of cryogenic cycles, thawing rate, and ageing step. For a given coil overlap parameter, the elastic modulus of cryogels tends to a limiting value, which can be reached faster by adding an ageing sequence to the classical freezing/thawing cryogenic cycles. This maximum value of the elastic modulus increases with increasing the coil overlap value of the initial solution.

International audienceThis work presents an in situ experimental investigation of the shear-induced coalescence mechanism in low concentration polymer blends (1%-10%). An original sizing method based on small-angle light scattering and optical microscopy were used to determine the evolution of the drop size distributions as a function of time. In order to study the pure coalescence mechanisms, measurements were conducted according to a specific flow protocol. The influences of the shear rate, initial morphology, concentration of the polymer blend and phase inversion on the coalescence kinetics were investigated. The investigated blends are mixtures of polydimethylsiloxane and polyisobutene. The amount of strain, the step-down rate ratio and the concentration squared are identified as relevant parameters to describe the coalescence kinetics. The dependence of the steady state drop sizes on the applied shear rate is well described by a coalescence model considering partially mobile interfaces