화학공학소재연구정보센터
Journal of Non-Newtonian Fluid Mechanics, Vol.54, 109-120, 1994
SHEAR AND NORMAL STRESSES OF A POLY(VINYL ALCOHOL) SODIUM BERATE AQUEOUS-SOLUTION AT THE START OF SHEAR-FLOW
The shear stress, sigma, and the first normal stress difference, N-1, at the start of shear flow with various rates of shear, gamma, were measured for a 2% aqueous poly(vinyl alcohol) solution containing 1% sodium berate (PVA/B). Reduced stresses, sigma/gamma and N-1/gamma(2), increased slightly with gamma and leveled off to steady values when gamma was less than a certain critical value, gamma(c). At very high rates of shear, the reduced stresses increased significantly with gamma and kept on increasing with time until the flow became unstable. At moderate gamma just above gamma(c), the reduced stresses exhibited a tendency to level off over quite a long period and then started to increase again. At any rate of shear, the stress relaxed rapidly on cessation of the flow. This observation may be interpreted by the assumption of enhanced rate of Borax-ol complex formation in highly oriented PVA chains in flow, and the slowing down of the relaxation of chain orientation trapped in the temporarily crosslinked network formed by the complex of finite lifetime.