Rheology and Viscosity Overview
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Questions and Answers

What does rheology primarily study?

  • The chemical reactions of pharmaceutical products
  • The flow properties of matter (correct)
  • The interactions between drugs and biological systems
  • The structural design of pharmaceutical packaging

How does viscosity affect a fluid's behavior?

  • It determines the internal friction and resistance to flow (correct)
  • It completely prevents flow under any conditions
  • It increases the speed of flow in all cases
  • It has no effect on the molecular makeup of the fluid

What defines a Newtonian fluid?

  • It does not exhibit any flow resistance
  • It behaves differently under varying shear conditions
  • It has a viscosity that increases with temperature
  • It has a constant viscosity regardless of shear rate (correct)

In which pharmaceutical dosage form is rheology particularly important?

<p>Liquid and semisolid forms like creams and emulsions (C)</p> Signup and view all the answers

What is the relationship between shearing stress and viscosity in a Newtonian fluid?

<p>They are directly proportional regardless of the area of contact (D)</p> Signup and view all the answers

What does the reciprocal of viscosity represent?

<p>Fluidity (D)</p> Signup and view all the answers

What does a high viscosity fluid do in terms of flow?

<p>Resists motion and has high internal friction (C)</p> Signup and view all the answers

Why is rheology significant in the formulation of lotions and creams?

<p>It influences the flow, stability, and acceptance by the patient (D)</p> Signup and view all the answers

In terms of flow, how are non-Newtonian fluids characterized?

<p>Their viscosity changes with varying shear rates (A)</p> Signup and view all the answers

What aspect of rheology can affect the bioavailability of drugs?

<p>Rate of drug absorption from the gastrointestinal tract (D)</p> Signup and view all the answers

What characterizes a Newtonian fluid?

<p>The relationship between shear stress and rate of shear is directly proportional. (B)</p> Signup and view all the answers

What occurs in pseudoplastic flow when shearing stress is increased?

<p>Macromolecules align with flow direction, leading to decreased viscosity. (A)</p> Signup and view all the answers

What is an example of dilatant flow?

<p>Suspension of corn starch in water. (A)</p> Signup and view all the answers

How does the coefficient of viscosity (η) relate to shear stress and shear rate?

<p>η is the ratio of shear stress to shear rate. (C)</p> Signup and view all the answers

What is a characteristic of dilatant fluids under increasing shearing stress?

<p>They show increased viscosity and resistance to flow. (C)</p> Signup and view all the answers

What happens to macromolecules in a pseudoplastic fluid when shearing stress is applied?

<p>They become oriented along the flow direction. (C)</p> Signup and view all the answers

What is the effect of decreasing shearing stress on a pseudoplastic fluid?

<p>Viscosity increases due to frictional resistance. (D)</p> Signup and view all the answers

Which of the following describes the relationship of shearing stress to viscosity in dilatant flow?

<p>Increasing shear stress increases viscosity. (D)</p> Signup and view all the answers

In the equation η = F/A/(dv/dx), what does F/A represent?

<p>Shear stress. (D)</p> Signup and view all the answers

Flashcards

Newtonian Fluid

The relationship between shear stress and shear rate is directly proportional, meaning the force needed to deform the fluid increases linearly with the rate of deformation.

Viscosity

The resistance of a fluid to flow. The higher the viscosity, the more force is needed to make it flow.

Non-Newtonian Fluid

A fluid that does not follow a linear relationship between shear stress and shear rate. Its viscosity changes with the applied force.

Pseudoplastic Flow (Shear-thinning)

A type of non-Newtonian fluid where the viscosity decreases as the shear rate increases. Examples: paints, emulsions, and certain polymers.

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Dilatant Flow (Shear-thickening)

A type of non-Newtonian fluid where the viscosity increases as the shear rate increases. Examples: cornstarch and water mixtures.

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Plastic Flow

A non-Newtonian fluid that initially behaves like a solid and requires a certain amount of force (yield stress) to start flowing. Examples: toothpaste, mayonnaise.

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Shear stress

The force per unit area required to deform a fluid. It's a measure of the internal resistance to flow.

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Shear rate

The rate at which a fluid is deformed. It's a measure of how fast the fluid is flowing.

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Molecular alignment

The arrangement of molecules in a fluid, which affects its viscosity. In pseudoplastic fluids, molecules align with flow, reducing friction and viscosity.

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Shear-thinning

The property of some fluids where the viscosity decreases with increasing shear rate. This is characteristic of pseudoplastic flow.

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What is Rheology?

The study of how materials flow and deform under stress. It's especially important for liquid and semi-solid dosage forms like solutions, suspensions, and creams.

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What is Viscosity?

The resistance of a liquid to flowing when a force is applied. Imagine how thick or thin a liquid feels when you try to stir it.

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What is a Newtonian Fluid?

A fluid where the viscosity stays constant regardless of how fast it's moving. Think of water - it's always the same consistency, no matter how hard you stir it.

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What is Velocity Gradient?

The change in velocity of a liquid over a small distance. It describes how quickly the liquid is moving compared to its surroundings.

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What is Shearing Stress?

The force applied per unit area to make a liquid flow. It's how much force is needed to make the liquid move.

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What is a Non-Newtonian Fluid?

Fluids where the viscosity changes depending on how fast they are moved. Think of ketchup - it's thick when it's sitting in the bottle, but flows more easily when you shake it.

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What is Fluidity?

The reciprocal of viscosity, meaning it describes how easily a fluid flows. A higher fluidity means the liquid flows more freely.

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How does Rheology Impact Product Manufacturing?

Mixing, packaging, and removal of dosage forms are directly influenced by the rheological properties of the substance, making it crucial to the production and use of pharmaceuticals.

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How does Rheology Affect Product Stability and Bioavailability?

Rheology affects the stability of the product, ensuring it maintains its desired consistency over time. It can also impact bioavailability through its effect on drug absorption.

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How does Rheology Impact Patient Acceptability?

The rheological properties of a product affect how well patients accept or reject it, influencing the overall success of the pharmaceutical product.

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Study Notes

Rheology Overview

  • Rheology is the science of flow properties of matter under stress
  • Originates from Greek words "rheo" (flow) and "logos" (science)
  • Helps understand fluid-type preparations' flow in pharmaceutical and related areas (e.g., pouring, extrusion, spreading)
  • Important for measuring the ease of pouring, extruding semisolid dosage forms, spreading on skin, and passage through needles

Viscosity

  • Viscosity is the resistance of a liquid to flow
  • High viscosity = resists flow due to high internal friction
  • Low viscosity = flows easily due to low internal friction
  • Determines how a liquid behaves under stress or force

Types of Viscosity

  • Kinematic Viscosity: Calculated by dividing Newtonian viscosity by density, denoted by (u)
  • Relative Viscosity: Ratio of dispersion viscosity (η) to solvent viscosity (ηo), denoted by (nr)

Types of Fluids

  • Newtonian Fluids: Flow properties are directly proportional to the applied stress and the rate of shear (e.g., water, some thin liquids)

  • Force required for one layer to slip past another depends on viscosity, exposed areas, and distance between surfaces

  • Shear stress (force/unit area) needed increases with viscosity

  • Formula: F/A = η (dv/dx) where F/A = shearing stress, dv/dx = rate of shear, η = viscosity

  • Non-Newtonian Fluids: Flow properties are not directly proportional to the applied stress and rate of shear (e.g., many foods, paints, suspensions)

  • Plastic Flow: Flow doesn't occur until a certain yield value (f) or stress is reached; the viscosity is defined as (F - f)/G

  • Pseudoplastic Flow (Shear-thinning): Viscosity decreases with increasing shear; molecules align with flow and reduces friction (e.g., paints, some polymers)

  • Dilatant Flow (Shear-thickening): Viscosity increases with increasing shear; particles rearrange and increase friction during flow; (e.g., concentrated suspensions, some doughs)

Additional Notes

  • Corn starch suspension is a real-world example of a dilatant fluid
  • Different flow behaviors (Newtonian, plastic, pseudoplastic, dilatant) are represented by different graphical relationships between shear stress and shear rate
  • Flow characteristics are crucial in pharmaceutical and cosmetic product development and application.

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PHAR 305 Rheology Lecture 4 PDF

Description

This quiz delves into the principles of rheology, the science of matter flow under stress. It covers various types of viscosity, fluid behavior, and the importance of these concepts in pharmaceutical applications. Test your understanding of these critical topics in the field of fluid mechanics.

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