» 剪切稀化(假塑性)

剪切稀化(假塑性)

1925
  • Wilhelm Ostwald
在实验室用番茄酱演示剪切稀化行为。

Shear-thinning, or pseudoplasticity, is a 非牛顿 behavior where a fluid’s 粘度 decreases with an increasing rate of shear stress. Many common substances, like ketchup or paint, exhibit this property. At rest, they are thick, but they flow more easily when shaken, stirred, or spread. This is often modeled by the Ostwald–de Waele power-law relationship.

Shear-thinning behavior is typically caused by the alignment of the fluid’s internal structure under shear. In polymer solutions, for instance, long-chain molecules are randomly coiled and entangled at rest, leading to high viscosity. When shear is applied, these chains begin to untangle and align in the direction of flow. This alignment reduces the interactions and friction between the molecules, causing a decrease in the apparent viscosity. The more the fluid is sheared, the more aligned the molecules become, and the lower the viscosity gets, until it potentially reaches a lower plateau.

This property is highly desirable in many applications. For example, paint should be thick enough in the can to prevent pigments from settling and to avoid dripping from the brush (low shear), but it must flow easily when brushed onto a surface (high shear). Similarly, printing inks need to flow from the printing press onto the paper but then stay put without smudging. In the food industry, products like yogurt and cream are designed to feel thick in the mouth (low shear) but be easy to swallow (higher shear). The opposite of shear-thinning is shear-thickening, where viscosity increases with shear rate.

UNESCO Nomenclature: 2210
- 机械

类型

物理特性

中断

实质性

使用方法

广泛使用

前体

  • 胶体和聚合物溶液中异常粘度的观察
  • 开发能够测量不同剪切速率下粘度的粘度计
  • Newton’s law of viscosity as a baseline for comparison

应用

  • 罐中很厚但用刷子很容易涂抹的油漆
  • 摇晃后番茄酱很容易从瓶子里流出来
  • 指甲油涂抹顺滑,但不会脱落
  • 血液循环,因为血液是一种剪切稀化流体
  • 易于泵送但可以悬浮静止岩屑的钻井泥浆

专利:

NA

潜在的创新想法

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Related to: shear-thinning, pseudoplastic, viscosity, rheology, polymer solutions, ketchup, paint, power-law fluid.

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