Viscosity or gel-formation is associated with the ability of dietary fiber to absorb water, which results in the formation of gelatinous mass. Some soluble dietary fiber, such as pectins, gums, psyllium, and β-glucan may form viscous solutions when interact with aqueous phase. Viscosity is one of the significant properties associated with soluble dietary fibers. The droplets are therefore stabilized and tend not to reform into a single bubble.ĭeepak Mudgil, in Dietary Fiber for the Prevention of Cardiovascular Disease, 2017 3.3 Viscosity Emulsification only occurs when this surface energy is reduced by the presence of surfactants. These droplets naturally have higher surface energy and will tend to coalescence back into a single bubble. Technically, dispersion refers to the break up of a large bubble of oil into smaller droplets. “Dispersion” and “emulsification” are terms sometimes used interchangeably. Whether these silicone oils are more stable when used in the eye, is yet to be proven in clinical trials. At the same time, the extensional viscosity can be increased especially when the liquid is subjected to shear stress. 108 By adding 5% or 10% of 423 kD to 1000 cSt SO, the shear viscosity of the mixture can be increased to 2000 cSt and 5000 cSt, respectively. Williams and associates added these high-molecular-weight polymers to low-viscosity SO (1000 cSt), and successfully increased the extensional viscosity to a level equal to that of SO of 5000 cSt. When the strand breaks, satellite droplets tend to form ( Fig. This is a measure of the resistance of the SO to break up, when a globule is drawn into a strand. The second type of viscosity that is important refers to extensional viscosity. It has also been shown that the presence of low-molecular-weight components also increases the readiness of the oil to disperse.
It has been shown that the lower the shear viscosity, the greater the propensity for dispersion this has been demonstrated up to a viscosity of 12 500 cSt. Two kinds of viscosities are involved, namely shear and extensional viscosities. This has practical implications, as ease of injection and removal is directly proportional to viscosity. Generally, SOs with longer chain lengths have higher viscosity.
Higher energy is required to deform a highly viscous liquid, while lower energy is needed when deforming a less viscous fluid. It is caused by the attractive forces between molecules in close contact, and the friction between molecular chains. Hence, it is also known as shear viscosity. Viscosity is a measure of the resistance of a fluid towards being deformed when under shear stress. Wong, David Wong, in Retina (Fifth Edition), 2013 Viscosity