Wanchai Lerdwijitjarud

Influence of weak elasticity of dispersed phase on droplet behavior in sheared polybutadiene/poly(dimethyl siloxane) blends

The contribution of weak droplet-phase elasticity is investigated for blends of polybutadiene in poly(dimethyl siloxane) in a simple shearing flow with droplet-phase Weissenberg number, Wid, up to around unity. The elasticity of the polybutadiene-dispersed phase is varied by adding various amounts of high-molecular-weight polybutadiene into low-molecular-weight polybutadiene Newtonian fluid. To isolate the contribution of elasticity, the experiments are conducted at fixed viscosity ratio by varying the experimental temperature to counteract the small effect of high-molecular-weight polymer on droplet viscosity. Droplet deformation and relaxation are measured using an optical flow cell mounted on an optical microscope. As the droplet-phase elasticity increases, the steady-state shape deformation at fixed capillary number, Ca, decreases and the critical capillary number for droplet breakup increases. For a 20% dispersed phase blend, the steady-state capillary number calculated from the volume-averaged dropl...

Influence of dispersed-phase elasticity on steady-state deformation and breakup of droplets in simple shearing flow of immiscible polymer blends

The effect of dispersed-phase elasticity on steady-state deformation and breakup of isolated droplets for polybutadiene/poly(dimethyl siloxane) blends in simple shearing flow is investigated systematically for values of the dispersed-phase Weissenberg number (Wid) ranging up to around 3, where the Weissenberg number is defined as the ratio of the first normal stress difference to twice the shear stress at the imposed shear rate. The dependence on droplet elasticity of steady-state morphology for 10%-dispersed phase blends is also studied. The polybutadiene droplet phase is an elastic “Boger” fluid prepared by dissolving a high-molecular-weight polybutadiene into a low-molecular-weight Newtonian polybutadiene melt. To isolate the contribution of droplet elasticity, all experiments were done at a fixed viscosity ratio of around unity, achieved by adjusting the temperature appropriately for each blend. When the droplet elasticity increases, the steady-state deformation of isolated droplets decreases for fixe...

Oscillatory shear induced droplet deformation and breakup in immiscible polymer blends

Deformation and breakup of droplets in polybutadiene/polydimethylsiloxane blends subject to oscillatory shear flow were investigated experimentally using an optical shear flow cell. The apparent major axis (a∗) and the minor axis (c) in the vorticity direction of the droplets were measured as functions of time. From the time series of a∗ and c and the deformation parameter, (a∗−c)/(a∗+c), we define the deformation amplitudes as one-half the differences between the maximum and minimum values. The deformation amplitude parameters generally decrease with increasing viscosity ratio, time scale ratio, and droplet elasticity. The dependences of the deformation amplitude parameters on capillary number are generally linear up to a certain value for Newtonian droplets regardless of viscosity ratio and time scale ratio. The dependences become totally nonlinear with increasing droplet elasticity. Droplet viscosity and elasticity generally impede breakup under oscillatory shear. Critical capillary number for breakup,...

Soft poly(2-chloroaniline)/pectin hydrogel and its electromechanical properties

Pectin hydrogels were successfully fabricated with various physical crosslinkers and concentrations for soft actuator applications. A small amount of synthesized P2ClAn was added as a dispersed phase into the pectin matrix. The electromechanical properties of the pectin hydrogels and blends were investigated under the effects of electric field strength, ionic crosslinker type and concentration, and P2ClAn concentration. The electromechanical properties of the pectin hydrogel as crosslinked by Fe2+ were superior to other pectin hydrogels. The pristine pectin hydrogel and the P2ClAn/Pectin hydrogel blended with 0.10%v/v P2ClAn provided the high storage modulus sensitivity values of 8.61 and 14.01, respectively, under the electric field strength of 800 V/mm. The P2ClAn/Pectin hydrogel blend responded to the electric field with higher dielectrophoretic forces, but lower deflections relative to the pristine pectin hydrogel due to the additional P2ClAn polarization and the latter lower rigidity.

Drop deformation and breakup in polystyrene/high-density polyethylene blends under oscillatory shear flow

Drop deformation and breakup in polystyrene/high-density polyethylene viscoelastic melt blends were investigated under the effects of viscosity ratio, the time scale ratio, and droplet elasticity under oscillatory shear flow using an optical flow cell. The deformation was studied in terms of deformation parameters, Def∗=a∗−c/a∗+c, where a∗ and c are the apparent drop principal axes and the minor axes of the droplets as measured from the time series of images. Amplitudes of deformation parameters are defined as the difference between the maximum and minimum values divided by two. The amplitudes increase linearly at small capillary number and nonlinearly at large capillary number, where the capillary is defined as the ratio between the matrix viscous force and the interfacial tension force. The deformation amplitude parameters decrease with increasing viscosity ratio, time scale ratio, and elasticity at any fixed capillary number. Drop breakup patterns observed are the nonsymmetric one-end tearing pattern f...

Influence of carrageenan molecular structures on electromechanical behaviours of poly(3-hexylthiophene)/carrageenan conductive hydrogels

The κ, ι, and λ carrageenans were fabricated by solution casting as soft and electrically responsive actuators. The poly(3-hexylthiophene) (P3HT) was added as a dispersed phase to improve the electrical and electromechanical properties of the pristine carrageenan hydrogels. The electromechanical properties of the carrageenan hydrogels were investigated under the effects of electric field strength, carrageenan type namely κ, ι, and λ, operating temperature, and P3HT concentration. The electromechanical responses of the pristine carrageenans increased with increasing sulfated groups present; the λ-carragenan hydrogel provided the highest storage modulus sensitivity of 4.0 under applied electric field strength of 800 V/mm. With increasing temperature, the double-helical structure of the κ-carrageenan hydrogel changed into a random coil leading to the increase in the storage modulus response. On the other hand, the P3HT/κ-carrageenan hydrogel blend at 0.10%v/v P3HT provided the high storage modulus sensitivity of 2.20 at the electric field strength of 800 V/mm. The higher dielectrophoretic forces were due to the additional P3HT electronic polarization, but lower deflections relative to those of the pristine κ-carrageenan hydrogel. Both κ- and λ-carrageenans with the double helical structures are shown here as possible candidates to be fabricated as electroactive hydrogels for actuator or biomedical applications.