Rheology in Pharmacy and Fluid Dynamics
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Questions and Answers

What does viscosity measure in a fluid?

  • Resistance to flow (correct)
  • Density of the fluid
  • Temperature variation
  • Molecular weight

Higher viscosity liquids flow more easily than lower viscosity liquids.

False (B)

Name two examples of high viscosity liquids.

Castor oil and honey

The main factor affecting the flow of materials is _____ .

<p>viscosity</p> Signup and view all the answers

Match the following features with their corresponding terms:

<p>Flow resistance = Viscosity Injection ability = Syringe needle passage Liquid flow through containers = Ease of pouring Tablet surface application = Coating</p> Signup and view all the answers

Which factor does NOT influence the flow of a material?

<p>Color of the material (B)</p> Signup and view all the answers

Emulsions should not flow easily from their containers.

<p>False (B)</p> Signup and view all the answers

What term describes the ability of a material to exist in various arrangements and characteristics?

<p>Molecular chain characteristics</p> Signup and view all the answers

What does the Greek term 'rheo' mean?

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

Rheology is concerned solely with solid materials.

<p>False (B)</p> Signup and view all the answers

How can rheological properties affect pharmaceutical products?

<p>They can affect formulation, drug absorption and bioavailability, and patient acceptability.</p> Signup and view all the answers

Rheology is the study of the flow and __________ of matter under stress.

<p>deformation</p> Signup and view all the answers

Match the following terms with their definitions:

<p>Rheology = Study of flow and deformation of matter Viscosity = Resistance of a liquid to flow Formulation = Designing various dosage forms Bioavailability = Rate at which a drug is absorbed in the body</p> Signup and view all the answers

Which of the following areas is NOT impacted by the rheological properties of pharmaceutical products?

<p>Drug stability (A)</p> Signup and view all the answers

Studying flow properties is essential for all pharmacists.

<p>True (A)</p> Signup and view all the answers

The term 'logos' in Greek means __________.

<p>study</p> Signup and view all the answers

What is the equivalent dynamic viscosity of 1 mPa·s?

<p>1 centipoise (cP) (B)</p> Signup and view all the answers

The dynamic viscosity of olive oil at 20 °C is lower than that of glycerol.

<p>True (A)</p> Signup and view all the answers

What is the SI unit for kinematic viscosity?

<p>m2s-1</p> Signup and view all the answers

Kinematic viscosity is defined as dynamic viscosity divided by the __________ of the fluid.

<p>density</p> Signup and view all the answers

Which fluid has the highest dynamic viscosity at 20 °C?

<p>Glycerol (A)</p> Signup and view all the answers

Relative viscosity has units.

<p>False (B)</p> Signup and view all the answers

What is the kinematic viscosity in Stokes for a fluid with dynamic viscosity of 1.002 cP and a density of 1 g/mL?

<p>0.001002</p> Signup and view all the answers

Match the following fluids with their corresponding dynamic viscosity at 20 °C.

<p>Chloroform = 0.58 cP Water = 1.002 cP Ethanol = 1.20 cP Olive oil = 84.0 cP Glycerol = 1490 cP</p> Signup and view all the answers

What does the specific viscosity (ηsp) equation represent?

<p>ηsp = ηr - 1 (A)</p> Signup and view all the answers

Intrinsic viscosity is also known as limiting viscosity number.

<p>True (A)</p> Signup and view all the answers

Define specific viscosity.

<p>Specific viscosity (ηsp) is defined as ηr - 1.</p> Signup and view all the answers

The volume fraction (Ø) in the equation η = ηs(1 + 2.5Ø) represents the _______ of the dispersed phase.

<p>volume</p> Signup and view all the answers

According to the equation ηr = 1 + 2.5Ø, what happens to ηr if the volume fraction (Ø) increases?

<p>ηr increases (B)</p> Signup and view all the answers

In a colloidal dispersion, the mean particle diameter is up to _____ µm.

<p>1</p> Signup and view all the answers

The equation η = ηs(1 + 2.5Ø) can be used for both colloidal dispersions and solutions.

<p>False (B)</p> Signup and view all the answers

What is the unit for viscosity (η)?

<p>dL/g (B)</p> Signup and view all the answers

Newtonian fluids do not obey Newton's law of viscosity.

<p>False (B)</p> Signup and view all the answers

What type of fluids are most pharmaceutical fluids classified as?

<p>Non-Newtonian fluids</p> Signup and view all the answers

The relationship between shear stress (τ) and shear rate (γ) for Newtonian fluids is expressed as τ = η______.

<p>γ</p> Signup and view all the answers

Match the following types of fluid with their characteristics:

<p>Newtonian = Obeys Newton's law of viscosity Plastic = Flow only after a certain stress is applied Pseudoplastic = Viscosity decreases with increasing shear rate Dilatant = Viscosity increases with increasing shear rate</p> Signup and view all the answers

Which of the following best describes the slope of a flow curve for a Newtonian fluid?

<p>It gives the viscosity of the fluid (C)</p> Signup and view all the answers

Non-Newtonian fluids maintain a constant viscosity regardless of shear stress.

<p>False (B)</p> Signup and view all the answers

Write the equation representing the relationship between shear stress (τ), viscosity (η), and shear rate (γ) for Newtonian fluids.

<p>τ = ηγ</p> Signup and view all the answers

Which of the following materials is NOT mentioned as an example of a hydrocolloid or gum?

<p>Alginate (C)</p> Signup and view all the answers

Dilatant flow is characterized by a decrease in viscosity with an increase in shear rate.

<p>False (B)</p> Signup and view all the answers

What happens to the molecules in a solution under shear in terms of their alignment?

<p>They become disentangled and align in the direction of flow.</p> Signup and view all the answers

Under the influence of shear, molecules in a solution tend to become ______ and align themselves in the direction of flow.

<p>disentangled</p> Signup and view all the answers

Match the following terms with their correct descriptions:

<p>Dilatant Flow = Increases in viscosity with shear rate Pseudoplastic Flow = Decreases in viscosity with shear rate Newtonian Flow = Viscosity remains constant regardless of shear rate Shear Thickening = Volume increases during shearing</p> Signup and view all the answers

What behavior do dilatant systems exhibit when stress is removed?

<p>They return to their original state of fluidity (C)</p> Signup and view all the answers

Aqueous dispersions of hydrocolloids are examples of materials that exhibit pseudoplastic behavior.

<p>True (A)</p> Signup and view all the answers

At high shear stresses, the flow curve tends towards what behavior?

<p>Linearity.</p> Signup and view all the answers

Flashcards

Viscosity

The resistance of a fluid to flow. Higher viscosity means greater resistance.

Factors affecting flow

A material's ability to flow depends on its viscosity, applied stress, temperature, composition, and molecular structure.

Rheology

The study of the flow of matter, particularly its deformation and flow under stress.

Simple liquid flow

The flow property of a simple liquid.

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Why is rheology important in pharmacy?

Important for development, preparation, evaluation, and performance of pharmaceutical dosage forms.

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Rheology in pharmaceutical formulation

Stiff creams might be difficult to use and cause pain. Suspensions and emulsions should flow easily for dosing. Pastes should be squeezeable but form a string.

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Rheology in injections

Fluidity is important for injection through a syringe needle.

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Rheology in tablet coating

Rheology influences coating tablets for better performance and appearance.

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Newton's Law of Flow

A fundamental relationship in fluid mechanics that states that the shear stress in a fluid is proportional to the rate of shear strain.

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Newtonian Fluids

A category of fluids that follow Newton's Law of Flow. Their viscosity is constant regardless of shear stress.

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Non-Newtonian Fluids

Fluids that don't follow Newton's Law of Flow. Their viscosity changes depending on the applied force.

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Shear-thinning (Pseudoplastic)

How the viscosity of a fluid changes when the shear stress is applied. A common example is the consistency changing with force.

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Shear-thickening (Dilatant)

The ability of a fluid to become thicker/more viscous with increased shear stress.

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Why Is Rheology Important for Pharmacists?

The study of rheology is vital for pharmacists because the flow properties of formulations can impact: 1. Formulation of different dosage forms. 2. Drug absorption and bioavailability. 3. Patient acceptability and compliance.

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Dynamic Viscosity

A measure of a fluid's resistance to flow. It is a critical factor in the manufacturing and dispensing of pharmaceuticals.

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Centipoise (cP)

1 mPa·s (millipascal-second) is equivalent to 1 cP (centipoise).

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Relative Viscosity

The viscosity of a solution compared to its solvent. It's a ratio, so it has no units.

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Kinematic Viscosity

Dynamic viscosity divided by the fluid's density. It describes how easily a fluid moves.

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Stoke (St)

The SI unit of kinematic viscosity. 1 St (Stoke) = 10⁻⁴ m²s⁻¹

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Dynamic Viscosity at 20°C

The viscosity of a fluid at a specific temperature. It's often measured at 20°C for reference.

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Fluid

A substance in which the molecules are arranged in a non-crystalline pattern and can move freely, resulting in a flow property.

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Glycerol

Glycerol is a highly viscous fluid with applications in pharmaceuticals, cosmetics and food production.

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Relative Viscosity (ηr)

The ratio of the viscosity of a solution (η) to the viscosity of the solvent (ηs).

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Specific Viscosity (ηsp)

The difference between the relative viscosity (ηr) and 1.

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Einstein's Equation (η = ηs(1+2.5Ø))

The viscosity of a colloidal dispersion, related to the volume fraction of the dispersed phase.

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Volume Fraction (Ø)

The volume fraction occupied by the dispersed phase in a colloidal dispersion.

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Intrinsic Viscosity Equation (ηsp = kC)

The relationship between specific viscosity (ηsp) and concentration (C) of a polymer solution.

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Intrinsic Viscosity ([η])

A constant that represents the intrinsic viscosity of a polymer at infinite dilution.

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Intrinsic Viscosity Plot

A plot of specific viscosity (ηsp) divided by concentration (C) against concentration (C).

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Colloidal Dispersion

A type of dispersion where small particles are distributed throughout a continuous medium.

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Flow Curve

The relationship between shear stress and shear rate for a fluid, plotted as a graph.

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Plastic Fluid

A non-Newtonian fluid that exhibits a yield stress. It requires a certain amount of force to start flowing.

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Pseudoplastic Fluid

A non-Newtonian fluid whose viscosity decreases with increasing shear rate. They become thinner as they move faster.

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Dilatant Fluid

A non-Newtonian fluid whose viscosity increases with increasing shear rate. They become thicker as they move faster.

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Pseudoplastic Flow

The viscosity of a fluid decreases with increasing shear rate. Imagine squeezing a tube of toothpaste - the more you squeeze (shear stress) the easier it flows (lower viscosity).

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Newtonian Flow

A fluid's viscosity is constant regardless of the applied shear stress. Imagine honey - it flows at the same rate whether you stir it gently or vigorously.

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How do long chains of molecules influence flow?

This flow behavior typically occurs in solutions with high molecular weight polymers. These molecules unravel and align with the direction of flow, making the substance thinner.

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Dilatant Flow

The viscosity of a material increases with increasing shear rate. Imagine cornstarch and water. It flows normally when stirred gently but becomes almost solid when stirred quickly.

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Why do dilatant materials thicken under stress?

Dilatant materials have a unique property of increasing in volume during shearing. This is because the molecules pack closer together under stress, making the fluid thicker.

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What happens to the flow curve at high shear stresses?

The flow curve of a material transitions to a linear relationship at higher shear stresses. This indicates that the molecules have reached their maximum orientation.

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What happens to a dilatant material when stress is removed?

The viscosity of a dilatant material returns to its original state when the shear stress is removed. This means the fluid 'thins out' again.

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How common is dilatant flow in pharma?

Dilatant flow is less common compared to pseudoplastic and plastic flow in pharmaceutical systems.

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Study Notes

Viscosity and Rheology

  • Rheology is the study of flow and deformation of matter under stress.
  • It's important for pharmacists to understand how formulations, like suspensions, gels, creams, and pastes, flow and deform under stress.
  • Rheological properties impact dosage form design, drug absorption/bioavailability, and patient acceptance/compliance.
  • Viscosity is the resistance of a fluid to flow.
  • Higher viscosity means greater resistance.
  • Example: Castor oil, honey, and syrups flow slower than water or alcohol.
  • Viscosity affects mixing energy requirements for viscous materials.
  • Viscosity modification can improve product characteristics, but needs care to avoid unwanted effects.
  • Example: decreasing suspension viscosity to reduce solids sedimentation in a suspension.

Introduction/Definitions

  • Rheology is a Greek word, coined by Bingham.
  • "Rheo" means "to flow" and "Logos" means "study of".
  • Deformation is how matter changes shape or size.
  • Flow behaviour of formulations changes with stress.

Types of Flow Systems

  • Newtonian Fluids:

    • Simple fluids that follow the law of τ = ηγ.
    • Viscosity is constant and independent of shear stress.
    • Plot of shear rate against shear stress is a straight line through the origin.

  • Non-Newtonian Fluids:

    • Most pharmaceutical fluids don't follow Newton's law.
    • Viscosity changes with shear stress.
    • Includes plastic, pseudoplastic, and dilatant fluids.

Plastic Fluids

  • Flows only above a yield stress(value).
  • Flow behaviour is similar to a Newtonian fluid above the yield value.
  • The examples of these are concentrated suspensions.

Pseudoplastic Fluids

  • Shear thinning.
  • Viscosity decreases with increasing shear rate.
  • The plot of shear stress vs. shear rate is characteristic of a curve decreasing as shear rate increaes.
  • Example: aqueous dispersions of natural and chemically modified hydrocolloids, like acacia, tragacanth, methylcellulose, and carmellose.

Dilatant Fluids

  • Shear thickening
  • Viscosity increases with increasing shear rate.
  • The opposite of pseudoplastic.
  • Shear thickening behaviour where suspensions act like solids at high shear stresses.
  • Example: dispersions containing a high concentration of small, unflocculated particles.

Thixotropy

  • Time-dependent viscosity change in some non-Newtonian fluids.
  • Recovers consistency gradually on standing after breakdown.
  • Distinguished by hysteresis loops.
  • Example: gels and some colloidal preparations.

Viscosity Coefficients

  • Dynamic viscosity (η): Resistance to flow.
  • Kinematic viscosity (ν): Dynamic viscosity divided by density.
  • Specific viscosity (ηsp): A measure of the increase in viscosity of a solution relative to the solvent.
  • Intrinsic viscosity ([η]): A measure of the viscosity contribution per unit concentration of a polymer solution.
  • Pharmaceutics: The Science of Dosage Form Design
  • Martin's Physical Pharmacy and Pharmaceutical Sciences
  • Remington: Essentials of Pharmaceutics

Important Values of Viscosity

  • Chloroform - 0.58 cP
  • Water - 1.002 cP
  • Ethanol - 1.20 cP
  • Olive oil - 84.0 cP
  • Glycerol - 1490 cP

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SOPH 231 Rheology 2 PDF

Description

Explore the fascinating world of rheology and its significance in fluid dynamics, especially within the pharmaceutical industry. This quiz covers key concepts such as viscosity, flow properties, and the impact of rheological properties on pharmaceutical products. Test your knowledge on the terms and definitions related to the study of flow and deformation of matter.

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