Rheology and Pharmaceutical Applications

Flashcards about Rheology and its Pharmaceutical Applications

What is Rheology?

The study of the deformation of materials, including flow, encompassing solids, semi-solids, liquids, and gases.

What are the ways stress may be applied to a material?

Elongation, compression, bending, twisting, and shearing.

Why is rheology important to physiologists?

It governs the circulation of blood and lymph, flow of mucous, bending of bones, stretching of cartilages, and contraction of muscles.

Why is rheology important to pharmacists?

Flow of emulsions through colloid mills and pumps, working ointments, and triturating suspensions.

What is the elastic modulus?

A measure of the difficulty in obtaining a deformation when stress is applied to a material.

What is Compliance?

The reciprocal of the modulus of elasticity, indicating the ease of deformation.

What is Viscosity?

An expression of the resistance of a fluid to flow.

How does the velocity of liquid layers change with distance from the moving plate?

The velocity of the liquid layers increases in the direction X perpendicular to the direction of flow y, leading to a velocity gradient.

How is shear stress calculated?

The applied force divided by the area of the upper layer, measured in Nm-2.

What is a Pascal (Pa)?

Force per unit area (Nm-2), which is used to measure viscosity in the SI system.

What is Fluidity?

The reciprocal of viscosity.

What is Kinematic Viscosity?

Dynamic viscosity divided by the density of the fluid.

What happens when a Newtonian fluid is subjected to an increasing rate of shear?

A linear relationship is produced, with the line passing through the origin.

What is Plastic Flow?

The rheogram does not pass through the origin but intersects with the shear stress axis at the yield value.

What is Pseudoplastic Flow?

The rheogram arises at the origin, and the slope of the curve gradually increases with increasing rate of shear.

What is Dilatant Flow?

Viscosity increases with an increase in shear rate.

What is Thixotropy?

The reversible time-dependent decrease in apparent viscosity of a material.

What is Rheopexy?

A time-dependent gain and loss of structure in a dilatant system.

How does temperature affect the viscosity and fluidity of a liquid?

The viscosity of a liquid decreases, and the fluidity increases.

What additional requirement is needed for time-dependent flow measurements?

The ability to control the duration of the experimental determinations.

When is it sufficient to measure the flow rate at a single stress?

It is adequate to measure the flow rate at a single stress.

What are the types of Viscometers?

Capillary and Rotational Viscometers.

What does 'A' stand for in the equation n = Ae^(Ev/RT)?

Dependent on the molecular weight and molar volume of the liquid.

What does Ev stand for in the equation n = Ae^(Ev/RT)?

An activation energy required to initiate flow between the molecules.

In what processes is rheology involved?

Mixing and flow of materials, packaging, and removal prior to use.

What aspects of a pharmaceutical product does rheology affect?

Patient acceptability, physical stability, and biologic availability.

How are materials used to increase the viscosity of water-based formulations classified?

Natural, semisynthetic, synthetic, and mineral materials.

What formulations is Thixotropy useful for?

Suspensions and Emulsions.

How are vaccines prepared?

Viscosity of the emulsion and other liquids.

What is the mixed emulsifier system?

Combination of surfactants with cetostearyl alcohol.

What is the spreadability of ointments and creams related to?

Shear stress, and the stickiness to the time required separating finger and skin with the product between.