Albeit it is a fact that denser liquids are more viscous, these two terminologies are not related in any meaningful way. It has also been seen that equally dense liquids have different levels of viscosity. Viscosity depends upon the friction between the layers of a substance. If the friction is very high, the liquid will tend to flow slowly and has a higher viscosity. The vital difference between density and viscosity is the effects of temperature. A substance’s viscosity can dramatically change when heated, whereas its density remains the same. Viscosity is mostly referred to define the movements of liquids or solids in molten form.
Image Courtesy: zeitnews.org
Higher density of a liquid certainly increases its viscosity but this resistance to flow is susceptible to change at different temperatures. Density of a substance doesn’t change with rising temperature but viscosity can change significantly. Density is not referred to liquids only but to solids and gases as well. This attribute of a substance remains the same, regardless of the physical state.
Image Courtesy: spacegrant.montana.edu