Interfacial Phenomena Overview
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Questions and Answers

What defines an interface between two phases?

  • The average temperature of the two phases
  • The similarity of molecular properties in adjacent phases
  • The boundary where two phases meet (correct)
  • The pressure exerted by the phases

Which of the following best describes surface tension?

  • Force per unit volume required to maintain a stable droplet
  • Force per unit length counterbalancing the inward pull at a surface (correct)
  • Pressure difference across a liquid interface
  • The energy required to create a new surface

What is one key role of surface active agents in the body?

  • To create a solid interface between tissues
  • To increase the viscosity of liquids
  • To stabilize suspensions and emulsions (correct)
  • To reduce the temperature of liquid surfaces

Which scenario would result in a lack of interfacial tension?

<p>Two miscible liquids combining (C)</p> Signup and view all the answers

How does surface tension influence the shape of liquid droplets?

<p>It results in droplets forming a spherical shape (A)</p> Signup and view all the answers

What is the primary reason that interfacial tension is often less than surface tension?

<p>Adhesive forces at the interface weaken the inward pull (A)</p> Signup and view all the answers

In the context of surface and interfacial tension, what is a dyne?

<p>A unit of force (A)</p> Signup and view all the answers

What effect does increasing the length of a liquid surface have on surface tension?

<p>Surface tension increases (D)</p> Signup and view all the answers

What role do functional groups on the surface of a solid play in relation to adsorbate molecules?

<p>They facilitate bonding with adsorbate molecules. (A)</p> Signup and view all the answers

What effect does a wetting agent have on the contact angle?

<p>It decreases the contact angle. (B)</p> Signup and view all the answers

Which of the following describes the composition of the tightly bound layer in the electric double layer?

<p>It contains less counter ion charge than the adsorbed layer. (B)</p> Signup and view all the answers

What is zeta potential an indicator of?

<p>The charge at the interface between a solid surface and its liquid medium. (B)</p> Signup and view all the answers

Which process can result in particles obtaining a charge when dispersed in a liquid medium?

<p>Selective adsorption of specific ions from the solution. (D)</p> Signup and view all the answers

What does the symbol $γ$ represent in the equation $γ = \frac{F_b}{2L}$?

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

What happens to the pressure difference ($ΔP$) in a soap bubble as the radius ($r$) increases?

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

Which method is specified for the determination of surface tension only?

<p>Capillary rise method (C)</p> Signup and view all the answers

How does the surface tension of water change as temperature increases?

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

In the equation for work done, $dW=F*ds= γ 2Lds$, what does $dW$ represent?

<p>Work done to increase surface area (B)</p> Signup and view all the answers

What happens to the surface tension of water at 75˚C compared to its surface tension at 0˚C?

<p>It is lower at 75˚C (A)</p> Signup and view all the answers

What is the equation that expresses the relationship between pressure difference and the radius of a bubble?

<p>$ΔP = \frac{2γ}{r}$ (B)</p> Signup and view all the answers

Which method is NOT suitable for interfacial tension determination?

<p>Capillary rise method (D)</p> Signup and view all the answers

Which surfactant is completely miscible with water and has no effect at the interface?

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

What does a higher HLB value indicate about a surfactant?

<p>It is more hydrophilic. (C)</p> Signup and view all the answers

What is required HLB (RHLB) primarily used for?

<p>To obtain an o/w emulsion or w/o emulsion. (D)</p> Signup and view all the answers

In the mixture containing Tween 80 and Span 80, what percentage of the surfactant is Span 80?

<p>41% (A)</p> Signup and view all the answers

What characterizes amphiphilic molecules?

<p>They are insoluble or slightly soluble in water. (D)</p> Signup and view all the answers

What is the basis for calculating the Required HLB (RHLB) for a mixture of oily materials?

<p>Proportions and individual RHLB values. (B)</p> Signup and view all the answers

How is surface excess or surface concentration (Γ) defined?

<p>As the amount of surfactant per unit area exceeding the bulk amount. (D)</p> Signup and view all the answers

Which of the following statements regarding insoluble films is correct?

<p>They are often made from amphiphilic molecules. (A)</p> Signup and view all the answers

What is the primary factor causing the rise of liquid in a capillary tube?

<p>Adhesive forces between the liquid and the capillary surface (B)</p> Signup and view all the answers

Which formula represents the equilibrium condition when a liquid rises in a capillary tube?

<p>γ = (1/2) r h ρ g (B)</p> Signup and view all the answers

What does a positive spreading coefficient, S, indicate?

<p>The adhesive forces are greater than cohesive forces (B)</p> Signup and view all the answers

In the DuNouy ring method, what does the force reading measure?

<p>The force required to detach a ring from a liquid's surface (B)</p> Signup and view all the answers

What property of surfactants allows them to accumulate at liquid interfaces?

<p>Amphiphilic nature of their molecules (C)</p> Signup and view all the answers

Under what conditions does spreading occur between two liquids?

<p>When the spreading coefficient is positive (A)</p> Signup and view all the answers

What role does the radius of the capillary play in the liquid's height in the capillary tube?

<p>It is inversely proportional to the height of the liquid (C)</p> Signup and view all the answers

Which factor does NOT affect the spreading of a liquid on the surface of water?

<p>Density of the spreading liquid (C)</p> Signup and view all the answers

What does the film thickness formed by oils on water surface represent?

<p>The length of the molecules in a vertical position (A)</p> Signup and view all the answers

What is surface or film pressure, π, defined as?

<p>The difference between the pure substrate and the film spread on it (B)</p> Signup and view all the answers

What factors affect the degree of gas adsorption on a solid surface?

<p>Chemical nature of adsorbent and adsorbate (A)</p> Signup and view all the answers

What is the difference between physical sorption and chemi-sorption?

<p>Physical sorption is a physical bond, while chemi-sorption is a chemical bond. (C)</p> Signup and view all the answers

Which equation is often used to describe adsorption isotherms?

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

What does the term 'desorption' refer to in the context of adsorption?

<p>The removal of adsorbate from the surface of adsorbent (D)</p> Signup and view all the answers

What role does activated charcoal play in relation to poisoning?

<p>It acts as an antidote due to its large surface area. (D)</p> Signup and view all the answers

What does an adsorption isotherm plot represent?

<p>The relationship between the amount of adsorbate and the partial pressure of the gas (C)</p> Signup and view all the answers

Flashcards

Interface

The boundary between two different phases, like liquid and gas. Molecules at the interface have different properties than those in the bulk.

Surface tension

The force per unit length acting parallel to the surface of a liquid, arising from the inward pull towards the bulk. It's what makes droplets spherical.

Interfacial tension

The force per unit length acting at the interface between two immiscible liquids. Typically lower than surface tension due to adhesive forces.

Cohesive forces

The forces of attraction between molecules of the same type. These forces are stronger in the bulk of a liquid, creating the inward pull.

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Adhesive forces

The forces of attraction between molecules of different types. At the interface, adhesive forces can be stronger than cohesive forces.

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Surface tension origin

The inward pull towards the bulk caused by the differences in cohesive and adhesive forces at the interface. This leads to contraction of the surface and surface tension.

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Units of surface and interfacial tension

The unit of measurement for both surface and interfacial tension. It represents the force per unit length required to overcome the inward pull.

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Liquids as elastic surfaces

The property of a liquid where the molecules at the surface are more attracted to each other than to the air, creating a thin, flexible, and elastic surface.

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DuNouy Ring Method

The force required to detach a ring from a liquid surface, measured using a DuNouy tensiometer. It's related to the surface tension of the liquid.

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Surfactant (Amphiphile)

A molecule with both polar (hydrophilic) and nonpolar (hydrophobic) parts. These molecules tend to accumulate at liquid interfaces.

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Spreading Coefficient

The ability of a liquid to spread on a surface, depending on the balance between cohesive and adhesive forces.

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Surface Active Agent (Surfactant)

A substance that lowers the surface tension or interfacial tension of a liquid. These molecules tend to accumulate at the interface.

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Capillary Rise

The upward force exerted on a liquid contained in a narrow tube (capillary) due to the surface tension of the liquid and the adhesive force between liquid and the capillary wall.

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Adsorption at Liquid Interfaces

The process where molecules of a liquid or gas concentrate at the interface, influenced by the balance of forces between the molecules of the different phases.

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Surface Tension (γ)

The force per unit length required to break a film of liquid, measured in units like dynes per centimeter.

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Work Done (W)

The work done to increase the surface area of a liquid, proportional to the change in surface area.

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Pressure Difference (ΔP)

The pressure difference across a curved liquid surface like a soap bubble, caused by surface tension. Higher pressure inside the bubble compared to outside.

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Young-Laplace Equation

The pressure difference across a curved surface is directly proportional to the surface tension and inversely proportional to the radius of the curved surface.

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Effect of Temperature on Surface Tension

Surface tension usually decreases as the temperature of the liquid increases. For example, water's surface tension changes at various temperatures.

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Capillary Rise Method

A method for determining surface tension of a liquid using the height of a liquid column within a narrow capillary tube, based on the balance between surface tension and gravity.

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Hydrophilic-Lipophilic Balance (HLB)

A number system that classifies surfactants based on their hydrophilic/lipophilic balance (HLB). Higher values mean more hydrophilic, and lower values mean more lipophilic.

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Required HLB (RHLB)

The HLB value required for a surfactant to create a stable oil-in-water (o/w) or water-in-oil (w/o) emulsion.

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Soluble Monolayer

A monolayer formed at the surface of a liquid, where the surfactant molecules are soluble in the liquid.

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Insoluble Film

A monolayer formed at the surface of a liquid, where the surfactant molecules are insoluble or slightly soluble in the liquid.

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Surface Excess or Surface Concentration (Γ)

The amount of surfactant per unit area of the surface, exceeding the concentration in the bulk liquid.

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dγ/dc (Change in Surface Tension with Concentration)

The change in surface tension as the concentration of a surfactant in the bulk solution changes.

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Gibbs Adsorption Equation

A relationship that describes the relationship between the surface excess and the change in surface tension with concentration.

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B Point (Complete B-C Linear Region)

A point on the surface tension vs. concentration graph where the surface concentration becomes constant.

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Contact Angle

The angle formed between a liquid droplet and a solid surface, indicating how well the liquid spreads on the surface. A smaller angle indicates better wetting.

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Wetting Agent

A substance that reduces the contact angle between a liquid and a solid, promoting better spreading of the liquid.

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Electric Properties of Interfaces

Particles dispersed in a liquid can acquire an electrical charge due to the adsorption of specific ions, the ionization of surface groups, or differences in dielectric constants between the particle and the liquid.

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Electric Double Layer

A structure formed at the interface between a solid and its liquid environment, consisting of two layers: a tightly bound layer and a diffuse layer. The tightly bound layer has adsorbed ions, while the diffuse layer contains more counter-ions.

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Zeta Potential

The electrical potential at the boundary between the tightly bound layer and the diffuse layer of an electric double layer. It represents the charge difference at the interface.

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Monolayer Film

A single layer of molecules formed when an oil spreads on a water surface. The thickness of this film is determined by the length of the molecules standing vertically and packed tightly.

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Adsorption

The process of a substance accumulating on the surface of a solid or liquid. It's driven by the attraction between the substance and the surface.

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Desorption

The process of removing an adsorbed substance from a surface, often achieved by increasing temperature or reducing pressure.

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Physical Adsorption

The bonding between an adsorbate (the substance being adsorbed) and an adsorbent (the surface) due to weak forces, like van der Waals forces. This is a reversible process.

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Chemisorption

The chemical bonding between an adsorbate and an adsorbent, forming a stronger, often irreversible attachment.

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Adsorption Isotherm

A graph showing the relationship between the amount of adsorbate adsorbed on a surface and the partial pressure of the adsorbate gas at a constant temperature.

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Study Notes

Interfacial Phenomena

  • An interface is the boundary between phases.
  • Properties of interface molecules differ from bulk molecules.
  • Interface type depends on adjacent phase states.
  • "Surface" refers to gas-liquid or gas-solid interfaces.

Classification of Interfaces

  • Gas-Gas: No interface possible.
  • Gas-Liquid: YLV (liquid surface)
  • Gas-Solid: Ysv (solid surface)
  • Liquid-Liquid: YLL (liquid-liquid interface)
  • Liquid-Solid: YLS (liquid-solid interface)
  • Solid-Solid: Yss (solid-solid interface, touching particles)

Importance of Interfacial Phenomena

  • Drug absorption and penetration through membranes.
  • Emulsion and suspension stability.
  • Surface-active agent function (e.g., in lungs).

Liquid Interfaces

  • Liquid-gas
  • Liquid-liquid
  • Liquid-solid

Surface and Interfacial Tension

  • Cohesive forces act between similar molecules.
  • Adhesive forces act between dissimilar molecules.
  • Interfacial tension results from the unsimilarity of bulk and interface forces.
  • Liquid droplets are spherical due to minimizing surface area.

Surface and Interfacial Tension Units

  • Force per unit length (dyne/cm or Newton/meter)
  • 1 Newton = 100,000 dynes
  • 1 dyne = 0.00001 Newton

Interfacial Tension Compared to Surface Tension

  • Interfacial tensions are usually lower than surface tensions due to adhesive forces.
  • Miscible liquids have no interfacial tension.

Measurement of Surface and Interfacial Tension

  • Capillary rise method (for surface tension—not interfacial)
  • Du Noüy ring method
  • Drop weight method
  • Bubble pressure method
  • All experiments should be performed at constant temperature.

Capillary Rise Method

  • Liquid rises in a capillary due to adhesive and wetting forces.
  • Depends on surface tension, liquid density, and capillary radius.
  • Rise continues until upward force equals downward gravity force.(upward force= down ward force)

Surface Tension and Bubbles

  • Young-Laplace equation: ΔP = 2γ/r ( ΔP is pressure difference, γ is surface tension, and r is radius)
  • Pressure inside a curved surface is higher than outside.

Effect of Temperature

  • Surface tension of most liquids decreases with increasing temperature.

Adsorption at Liquid Interfaces

  • Adsorption occurs at liquid surfaces where molecules prefer the surface.
  • Surface-active agents, or surfactants, exhibit this preference.

Surfactant Molecules

  • Amphiphilic molecules (polar and nonpolar parts)
  • Polar (hydrophilic): Water-loving
  • Nonpolar (lipophilic): Oil-loving

Hydrophilic-Lipophilic Balance (HLB)

  • Classification system for surfactants based on their optimum use.
  • Higher HLB values = more hydrophilic.
  • Lower HLB values = more lipophilic.

Types of Monolayers at Liquid Surfaces

  • Soluble monolayers (e.g., amyl alcohol in water—dissolves)
  • Insoluble films (e.g., cetyl alcohol in water—does not dissolve)
  • Surface excess (Γ) is amount of surfactant per unit surface area exceeding the bulk

Adsorption Isotherms

  • Isotherms are plots showing the relationship between adsorbed amount and partial pressure at a constant temperature.

Adsorption of Gases on Solids

  • Adsorption degree depends on adsorbent and adsorbate chemical nature, surface area, partial pressure, and temperature.
  • Desorption is adsorbate removal from surface via elevating temperature or reducing pressure.
  • Physical sorption and chemical sorption (reversible/irreversible).

Adsorption at Solid-Liquid Interfaces

  • Solutes from solutions adsorb onto solid surfaces (e.g., charcoal).
  • Similar to solid-gas isotherms.
  • Langmuir equation can be used (C/(x/m) = 1/(Ym b) + C/ Ym)

Activated Charcoal

  • Used as antidote for poisoning.
  • High surface area (e.g., 3000 m²/g)
  • Surface functional groups facilitate adsorbate molecule bonding.
  • Adsorption of gases on solid materials

Wetting

  • Contact angle: Angle between liquid and solid surface
  • Wetting agent: surfactant that lowers the contact angle.

Electric Properties of Interfaces

  • Particles in liquid media can gain a charge due to selective adsorption, ionization of surface groups, or differences in dielectric constants.

Electric Double Layer

  • Tightly bound layer contains less counter ion charge than the adsorbed layer.
  • Diffuse layer has more negative charge; equal negative and positive charges.

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Interfacial Phenomena PDF

Description

Explore the fascinating world of interfacial phenomena and learn about the properties of molecules at the interface between different phases. This quiz covers various types of interfaces, their classifications, and the significance of interfacial tension in real-world applications such as drug absorption and emulsion stability.

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