Spinning of Polysulfone Hollow Fiber Membranes Using Constant Dope Solution Composition: Viscosity Control via Temperature

The dope solution viscosity is an important parameter that largely determines the properties of hollow fiber membranes. In the literature available today, the change in viscosity is carried out only by changing the quantitative and/or qualitative dope solution compositions. However, such an important spinning parameter as temperature should significantly affect the dope solution viscosity. For the first time, the influence of the dope solution viscosity of a constant composition on polysulfone hollow fiber membrane properties was studied. The hollow fiber membranes were obtained by the phase separation method induced by a non-solvent (NIPS). The change in the dope solution temperature was carried out in the temperature range of 17-27 °C, providing a dope solution viscosity range of 34.3-21.6 Pa∙s. This work shows that even in such a narrow temperature range, the properties of polysulfone hollow fiber membranes change significantly. With a decrease in the viscosity in this temperature range, the wall thickness of the hollow fiber membrane decreases by 2.8 times; the permeance for the individual gases He and CO₂ increases by 1.6-1.8 times, respectively; the ideal selectivity decreases by 1.12 times; the mean flow pore size increases by 1.63 times; and the surface porosity increases about 3 times.

Finite element simulation for the effect of loading rate on visco-hyperelastic characterisation of soft materials by spherical nanoindentation

Nanoindentation test performed by atomic force microscopy is highly recommended for the characterisation of soft materials at nanoscale. The assumption proposed in the characterisation is that the material is pure elastic with no viscosity. However, this assumption does not represent the real characteristics of soft materials such as bio tissue or cell. Therefore, a parametric finite element simulation of nanoindentation by spherical tip was carried out to investigate the response of cells with different constitutive laws (elastic, hyperelastic and visco-hyperelastic). The investigation of the loading rate effect on the characterisation of cell mechanical properties was performed for different size of spherical tip. The selected dimensions of spherical tips cover commercially available products. The viscosity effects are insensitive to the varied dimensions of spherical tip in this study. A limit loading rate was found above which viscous effect has to be considered to correctly determine the mechanical properties. The method in this work can be implemented to propose a criterion for the threshold of loading rate when viscosity effect can be neglected for soft material characterisation.

The Effect of Viscosity on the Diffusion and Termination Reaction of Organic Radical Pairs

The effect of viscosity on the diffusion efficiency (F_dif ) of an organic radical pair in a solvent cage and the termination mechanism, that is, the selectivity of disproportionation (Disp) and combination (Comb) of the geminated caged radical pair and the diffused radicals encountered, were investigated quantitatively by following the photolysis of dimethyl 2,2'-azobis(2-methylpropionate) (V-601) in the absence and presence of PhSD. F_dif and Disp/Comb selectivity outside the cage [Disp_(dif) /Comb_(dif) ] are highly sensitive to the viscosity. In contrast, the Disp/Comb selectivity inside the cage [Disp_(cage) /Comb_(cage) ] is rather insensitive. The difference in viscosity dependence between Disp_(cage) /Comb_(cage) and Disp_(dif) /Comb_(dif) is explained by the spin state of the radical pair inside and outside the cage and the spin state dependent configurational changes of the radical pair upon their collision. Given that the configurational change of the radicals associates the displacement and reorganization of solvents around the radicals, the termination outside the cage, which requires larger change than that inside the cage, is highly viscosity dependent. Furthermore, while the bulk viscosity of each solvent shows good correlation with F_dif and Disp/Comb selectivity, microviscosity is the better parameter predicting F_dif and Disp_(dif) /Comb_(dif) selectivity regardless of the solvents.