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เปลี่ยนรูป การผ่อนคลาย การแตกตัว การรวมตัวในพอลิเมอร์ผสมแบบไม่เข้ากัน

หน่วยงาน สำนักงานกองทุนสนับสนุนการวิจัย


ชื่อเรื่อง : เปลี่ยนรูป การผ่อนคลาย การแตกตัว การรวมตัวในพอลิเมอร์ผสมแบบไม่เข้ากัน
นักวิจัย : อนุวัฒน์ ศิริวัฒน์
คำค้น : -
หน่วยงาน : สำนักงานกองทุนสนับสนุนการวิจัย
ผู้ร่วมงาน : -
ปีพิมพ์ : 2550
อ้างอิง : http://elibrary.trf.or.th/project_content.asp?PJID=BRG4680015 , http://research.trf.or.th/node/1929
ที่มา : -
ความเชี่ยวชาญ : -
ความสัมพันธ์ : -
ขอบเขตของเนื้อหา : -
บทคัดย่อ/คำอธิบาย :

Deformation and breakup of droplets in polybutadiene/polydimethysiloxane blends subject to oscillatory shear flow were investigated experimentally using an optical shear flow cell. The apparent major axis (a*), the minor axis (c) in the vorticity direction of the droplets were measured as functions of time. From the time series of the deformation parameters, (a* -c)/(a8 +c), we can define the deformation amplitudes as one halves differences between the maximum and minimum values. The deformation parameters generally decreased with increasing viscosity ratio, time scale ratio and droplet elasticity. The dependence of the deformation parameters on capillary number is generally linear up to a certain value for Newtonian droplets, regardless of viscosity ratio and time scale ratio. The dependence becomes totally nonlinear with increasing droplet elasticity. Droplet viscosity and elasticity generally impede breakup under oscillatory shear. Critical capillary number for breakup, the number of resultant daughter droplets, and the number of cycle required for breakup to occur increase with time scale ratio. The apparent breakup pattern changes from the dumbbell type to the end-pinching type as time scale ratio increases. Drop deformation and breakup in PS/HDPE 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 term of deformation parameters, Def*=a*-c/a8+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 increased 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 decreased with increasing viscosity ratio, time scale ratio, and elasticity at any fixed capillary number. Drop breakup patterns observed were the non symmetric one-end tearing pattern for the system with a lower viscosity ratio, and the two-ends stretching and twisting for the system with a higher viscosity ratio. The critical capillary number increased with viscosity ratio but varied slightly with the time scale ratio. The effect of droplet elasticity on transient deformation of isolated droplets in immiscible polymer blends of equal viscosity was investigated. In terms of the deformation parameter, Def*=a*-c/a*+c where a* and c are apparent drop principle axes, it undergoes two cycles of positive oscillations before reaching a negative value, followed by one cycle of oscillation before attaining a steady state negative value. This behavior was observed when Capillary number, Ca, was varied between 3 and 9 at a fixed Weissenberg number( ___) of 0.31, and when Ca number was held fixed at 8 and Wi number was varied between 0.21 and 0.40. In another blend of relatively lower Wi number of 0.21, one cycle of oscillation inn Def* was observed before reaching steady state negative values when Ca number was varied between 3 and 14. The steady state Def* varies inversely with Ca number, with a stronger dependence for the blend with higher Wi number. The magnitude of oscillation increases with increasing Ca and Wi number. The critical Ca was found to be 12 and 14 for the two blends studied; these values are about 30 times greater than that of Newtonian blends. Transient and steady-state deformation and breakup of viscoelastic polystyrene droplets dispersed in viscoelastic high density polyethylene matrices were observed in a simple steady shear flow between two transparent parallel disks. By separately varying the elasticities of the individual blend components, the matrix shear viscosity, and the viscosity ratio, their effects on the transient deformation, steady-state droplet size, and the breakup sequence were determined. After the startup of a steady shear flow, the viscoelastic droplet initially exhibits oscillations of its length in the flow diection, but eventually stretches preferentially in the vorticity direction. We find that at fixed capillary number, the oscillation amplitude decreases with, increasing droplet elasticity, while the oscillation period depends primarily on, and increases with the viscosity ratio. At steady-state, the droplet length along the vorticity direction increases with increasing capillary number, viscosity ratio, and droplet elasticity. Remarkably at a viscosity ratio of unity, the droplets remain in a nearly undeformed state as the capillary number is varied between 2 to 8, apparently because under these conditions a tendency for the droplets to widen in the vorticity direction counteracts their tendency to stretch in the flow direction. When a critical capillary number, Cac,is exceeded, the droplet finally stretches in the vorticity direction and forms a string which becomes thinner and finally breaks up, provided that the droplet elasticity is sufficiently high. For a fixed matrix shear stress and droplet elasticity, the steady-state deformation along the vorticity direction and the critical capillary number for breakup both increase with increasing viscosity ratio. 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 low-molecular-weight Newtonian polybutadiene. To isolate the contribution of droplet elasticity, all experiments were done on 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 fixed capillary number. The critical capillary number for breakup (Ca_) increases linearly with the Weissenberg number of the droplet phase (Wid) up to a value of Wid of around unity. When Wid is greater than unity, Ca_ seems to approach an asymptotic value of 0.95 for high volume-averaged droplet diameter is less than the Ca_ for isolated droplets for the same blend. Ca_ increases monetonically with the first normal stress difference of the droplet phase (Nld). Droplet widening in the vorticity direction is not observed even at droplet Weissenberg number much in excess of those for which widening is observed in blends of melts, suggesting that widening is strongly influenced by factors other than the first normal stress difference, such as shear thinning or second normal stress differences.

บรรณานุกรม :
อนุวัฒน์ ศิริวัฒน์ . (2550). เปลี่ยนรูป การผ่อนคลาย การแตกตัว การรวมตัวในพอลิเมอร์ผสมแบบไม่เข้ากัน.
    กรุงเทพมหานคร : สำนักงานกองทุนสนับสนุนการวิจัย.
อนุวัฒน์ ศิริวัฒน์ . 2550. "เปลี่ยนรูป การผ่อนคลาย การแตกตัว การรวมตัวในพอลิเมอร์ผสมแบบไม่เข้ากัน".
    กรุงเทพมหานคร : สำนักงานกองทุนสนับสนุนการวิจัย.
อนุวัฒน์ ศิริวัฒน์ . "เปลี่ยนรูป การผ่อนคลาย การแตกตัว การรวมตัวในพอลิเมอร์ผสมแบบไม่เข้ากัน."
    กรุงเทพมหานคร : สำนักงานกองทุนสนับสนุนการวิจัย, 2550. Print.
อนุวัฒน์ ศิริวัฒน์ . เปลี่ยนรูป การผ่อนคลาย การแตกตัว การรวมตัวในพอลิเมอร์ผสมแบบไม่เข้ากัน. กรุงเทพมหานคร : สำนักงานกองทุนสนับสนุนการวิจัย; 2550.