RISS 검색 - 국내학술지논문

무료
기관 내 무료
유료

내보내기
내책장담기
한글로보기

정확도순

내림차순

내림차순

10개씩 출력

1
Kinematics of filament stretching in dilute and concentrated polymer solutions

McKinley, Gareth H.,Brauner, Octavia,Yao, Minwu The Korean Society of Rheology 2001 Korea-Australia rheology journal Vol.13 No.1
- 원문보기
The development of filament stretching extensional rheometers over the past decade has enabled the systematic measurement of the transient extensional stress growth in dilute and semi-dilute polymer solutions. The strain-hardening in the extensional viscosity of dilute solutions overwhelms the perturbative effects of capillarity, inertia & gravity and the kinematics of the extensional deformation become increasingly homogeneous at large strains. This permits the development of a robust open-loop control algorithm for rapidly realizing a deformation with constant stretch history that is desired for extensional rheometry. For entangled fluids such as concentrated solutions and melts the situation is less well defined since the material functions are governed by the molecular weight between entanglements, and the fluids therefore show much less pronounced strain-hardening in transient elongation. We use experiments with semi-dilute/entangled and concentrated/entangled monodisperse polystyrene solutions coupled with time-dependent numerical computations using nonlinear viscoelastic constitutive equations such as the Giesekus model in order to show that an open-loop control strategy is still viable for such fluids. Multiple iterations using a successive substitution may be necessary, however, in order to obtain the true transient extensional viscosity material function. At large strains and high extension rates the extension of fluid filaments in both dilute and concentrated polymer solutions is limited by the onset of purely elastic instabilities which result in necking or peeling of the elongating column. The mode of instability is demonstrated to be a sensitive function of the magnitude of the strain-hardening in the fluid sample. In entangled solutions of linear polymers the observed transition from necking instability to peeling instability observed at high strain rates (of order of the reciprocal of the Rouse time for the fluid) is directly connected to the cross-over from a reptative mechanism of tube orientation to one of chain extension.
2
비평형 표면사이의 유체전이 거동 분석

문혁균(Hyeokgyun Moon),조규진(Gyoujin Cho),Gareth H. McKinley,이진기(Jinkee Lee) 대한기계학회 2023 대한기계학회 춘추학술대회 Vol.2023 No.11
- 원문보기
3
Capillary breakup extensional rheometry of a wormlike micellar solution

Nahn Ju Kim,Christopher J. Pipe,Kyung Hyun Ahn,Seung Jong Lee,Gareth H. McKinley 한국유변학회 2010 Korea-Australia rheology journal Vol.22 No.1
The behaviour of a cetylpyridinium chloride/sodium salicylate wormlike micellar system undergoing capillary breakup is investigated experimentally. The transient elongational flow induced in a thinning thread is used to study the apparent viscosity and effective relaxation time of the micellar network in extension. The sensitivity of the material response to initial conditions and deformation history is explored by varying the endplate diameter of the capillary breakup rheometer and the initial step strain imposed on the sample. Local regimes in which the extensional viscosity shows constant (Newtonian), weak extensional thinning and strong extensional thickening are observed depending on the accumulated strain and strain rate. For this concentrated micellar network, the relaxation time determined in extension was found to be independent of the initial configuration and in close agreement with the value measured in shear flow.