Deformation and Breakup of Viscoelastic Drops

Emulsion microrheology predicts that in a Newtonian system a drop will break when the deformabUity exceeds D /2, that is, when the reduced capillarity number 1 k = k/kct 2 (Eq. (2.21)). Most experimental data for viscoelastic systems indicate that the drop elasticity has a stabilizing effect thus, that Ko- and the minimum drop diameter for drop break increase with drop elasticity [284-286]. When conditions are identical for Newtonian and viscoelastic drops, the latter fibrillate easier and upon cessation of flow the filament breakup and formation of satellite drops are retarded by elasticity [287]. 

In a subsequent publication the authors concentrated on the transient rheology/ morphology response to flow [262]. For affine deformation at k 2Kcnt the authors 

The relations well described the experimental stress growth data for slightly viscoelastic PIB/PDMS blends containing 10% of either component Since the scaling relationships in Eq. (2.43) have been preserved, the authors recommended that Eq. (2.46) be used for the affine polymer blends as a substitute for the original Doi-Ohta expressions. Furthermore, recent numerical analysis of the T(y) function for y = 10-500 is well approximated by T(y) IjyX 

In the next paper, Vinckier et aL [279] fitted the viscosity and the first normal stress difference of the model PIB/PDMS emulsions to Eq. (2.18). A reasonable description of the rheological behavior was obtained for the diluted and semi-diluted concentrations with the viscosity ratios A = 1.5—4. The experiments were carefiilly conducted within the range of the capillarity numbers (k Kcr) and  

While the Choi and Schowalter [113] theory is fundamental in understanding the rheological behavior of Newtonian emulsions under steady-state flow, the Palierne equation [126], Eq. (2.23), and its numerous modifleations is the preferred model for the dynamic behavior of viscoelastic liquids under small oscillatory deformation. Thus, the linear viscoelastic behavior of such blends as PS with PMMA, PDMS with PEG, and PS with PEMA (poly(ethyl methacrylate))at 0.15 followed Palierne s equation [129]. From the single model parameter, R = R/vu, the extracted interfacial tension coefficient was in good agreement with the value measured directly. However, the theory (developed for dilute emulsions) fails at concentrations above the percolation limit, 0 (p rc 0.19 0.09. 

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