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Questions and Answers
If a formulation requires an emulsifier with a required HLB of 7, which range of HLB in emulsifiers should be considered for optimal performance?
If a formulation requires an emulsifier with a required HLB of 7, which range of HLB in emulsifiers should be considered for optimal performance?
Which of the following ranges corresponds to surfactants that would show poor solubility?
Which of the following ranges corresponds to surfactants that would show poor solubility?
What is the total mass of the non-ionic surfactant C10H21(OCH2CH2)6OH as calculated?
What is the total mass of the non-ionic surfactant C10H21(OCH2CH2)6OH as calculated?
Which of the following HLB values corresponds to emulsifiers that are readily soluble and capable of solubilization?
Which of the following HLB values corresponds to emulsifiers that are readily soluble and capable of solubilization?
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What is the significance of the critical micelle concentration (cmc) in surfactant solutions?
What is the significance of the critical micelle concentration (cmc) in surfactant solutions?
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How does the presence of surfactants affect surface tension as their concentration increases?
How does the presence of surfactants affect surface tension as their concentration increases?
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What does the equation Γ = −(Cb/RT)(dγl/v/dCb) represent in the context of surfactants?
What does the equation Γ = −(Cb/RT)(dγl/v/dCb) represent in the context of surfactants?
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Which statement accurately describes the difference between surfactant monomers and micelles?
Which statement accurately describes the difference between surfactant monomers and micelles?
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What is the available surface area per molecule when the bulk concentration (p) is known?
What is the available surface area per molecule when the bulk concentration (p) is known?
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What happens to surfactant molecules when the solution is full or unavailable?
What happens to surfactant molecules when the solution is full or unavailable?
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In which condition do micelles tend to form?
In which condition do micelles tend to form?
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What role does stirring play in the formation of micelles?
What role does stirring play in the formation of micelles?
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What is the effect of high concentration of surfactants on surface tension?
What is the effect of high concentration of surfactants on surface tension?
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Which factor leads to the coalescence of micelles?
Which factor leads to the coalescence of micelles?
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What happens to surfactant droplets in water when they reach a certain concentration?
What happens to surfactant droplets in water when they reach a certain concentration?
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What characteristic of micelles is highlighted by their formation in a continuous phase?
What characteristic of micelles is highlighted by their formation in a continuous phase?
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How do micelles interact with water molecules in their formation?
How do micelles interact with water molecules in their formation?
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What happens to the critical micelle concentration (cmc) when the polyoxyethylene chain length increases for non-ionic surfactants?
What happens to the critical micelle concentration (cmc) when the polyoxyethylene chain length increases for non-ionic surfactants?
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How does the size of ionic micelles change when electrolytes are added?
How does the size of ionic micelles change when electrolytes are added?
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What is unique about the solubility behavior of ethoxylate surfectants when the temperature is increased?
What is unique about the solubility behavior of ethoxylate surfectants when the temperature is increased?
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Which factor leads to the decrease of charge repulsion in surfactants?
Which factor leads to the decrease of charge repulsion in surfactants?
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At what point does the solubility of ionic surfactants significantly increase?
At what point does the solubility of ionic surfactants significantly increase?
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What is the effect of increasing the length of the polyoxyethylene chain on the aggregation number of surfactants?
What is the effect of increasing the length of the polyoxyethylene chain on the aggregation number of surfactants?
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What occurs when plotting conductivity versus surfactant concentration at the critical micelle concentration?
What occurs when plotting conductivity versus surfactant concentration at the critical micelle concentration?
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What is the expected behavior of oil droplets in relation to micelles during solubilization?
What is the expected behavior of oil droplets in relation to micelles during solubilization?
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Which factor will lead to an increase in critical micelle concentration (cmc)?
Which factor will lead to an increase in critical micelle concentration (cmc)?
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What is the primary reason non-ionic surfactants can form micelles at lower concentrations compared to ionic surfactants?
What is the primary reason non-ionic surfactants can form micelles at lower concentrations compared to ionic surfactants?
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In a dynamic equilibrium of micelles, what is primarily happening with the surfactant molecules?
In a dynamic equilibrium of micelles, what is primarily happening with the surfactant molecules?
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What describes the shape of non-ionic micelles compared to ionic micelles?
What describes the shape of non-ionic micelles compared to ionic micelles?
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How does an increase in chain length of a surfactant's hydrophobic group affect micelle properties?
How does an increase in chain length of a surfactant's hydrophobic group affect micelle properties?
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Which statement is true regarding ionic micelles?
Which statement is true regarding ionic micelles?
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What role does the hydrophobic group play in surfactant functionality?
What role does the hydrophobic group play in surfactant functionality?
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What is a key characteristic of non-ionic surfactants compared to ionic surfactants regarding aggregation number?
What is a key characteristic of non-ionic surfactants compared to ionic surfactants regarding aggregation number?
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What happens to the conductivity of a solution with ionic surfactants like SDS as micelles form?
What happens to the conductivity of a solution with ionic surfactants like SDS as micelles form?
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How does the viscous drag of the solvent affect the movement of ions in solutions containing micelles?
How does the viscous drag of the solvent affect the movement of ions in solutions containing micelles?
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What role do bound counter ions play in the conductivity of ionic micelles?
What role do bound counter ions play in the conductivity of ionic micelles?
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Why does the formation of a micelle reduce the drag compared to monomers?
Why does the formation of a micelle reduce the drag compared to monomers?
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What counter-intuitive effect does the ionic atmosphere around a micelle have on its conductivity?
What counter-intuitive effect does the ionic atmosphere around a micelle have on its conductivity?
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How does the number of micelles relate to the overall electrical conductivity of the solution?
How does the number of micelles relate to the overall electrical conductivity of the solution?
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What is primarily responsible for the retardation of ion movement in solutions with ionic micelles?
What is primarily responsible for the retardation of ion movement in solutions with ionic micelles?
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What effect does micellization have on the overall charge of the micelles?
What effect does micellization have on the overall charge of the micelles?
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Study Notes
Surfactant Activity & Application
- Surfactants are amphipathic molecules, possessing both hydrophobic and hydrophilic groups.
- Hydrophobic groups (usually carbon chains) repel water, while hydrophilic groups attract water.
- Water's high structure due to hydrogen bonding is disrupted by ionic or strongly polar solutes.
- Surfactants compensate for this disruption by forming bonds with water molecules.
- This allows ionic and polar materials to dissolve in water.
- Non-polar molecules do not compensate, resulting in resistance.
- Water molecules cluster around non-polar regions, causing a negative entropy change.
- Surfactants increase solubility depending on whether polar groups sufficiently hydrogen bond with water to overcome repulsive forces from water molecules around the hydrophobic region.
- Surfactant molecules orientate themselves at the surface/interface with hydrophobic tails away from the aqueous phase.
- Longer surfactant chains increase the energy favorability for adsorption at the surface/interface, leading to higher concentrations of surfactant at the surface/interface and lowering of surface tension.
- Adsorption lowers surface tension, as water-water forces are reduced by water-hydrocarbon attractive forces and hydrocarbon-hydrocarbon attractive forces.
- These actions cause the water-water bonding to disrupt, leading to a reduced contractile nature and, therefore, surface tension.
HLB (Hydrophilic-Lipophilic Balance)
- HLB determines surfactant partition between phases (oil/water).
- Low HLB = oil-soluble, high HLB = water-soluble.
- HLB = percentage hydrophilic part / 5.
- Formula for calculating total mass and then hydrophilic part is provided.
- Different HLB values correspond to distinct uses (solubilization, emulsification, wetting, antifoaming).
Solubilization
- Although there is excess surfactant on the surface, it accounts for a very small proportion.
- The majority of surfactant molecules are in the bulk, leading to the application of solubilization.
- Adding surfactant causes a sharp reduction in surface tension followed by a slight decrease over a narrow concentration range.
- This slight decrease occurs at a critical micelle concentration (CMC).
- Below CMC, surfactants exist as monomers in solution.
- Above CMC, surfactants aggregate to form micelles, which are in dynamic equilibrium with monomers.
- Monomer concentration remains constant.
Micelle Formation
- Micelle formation minimizes free energy, with structuring of water around hydrophobic groups creating negative entropy.
- At high concentrations, surfactants get packed at the surface, where self-aggregation and freedom of movement within the micelle occur.
- There is dynamic equilibrium with monomers, involving continual breaking and reforming.
- Non-ionic surfactants form micelles at lower concentrations than ionic surfactants, related to repulsion of charged head groups.
Micelles
- Non-ionic micelles are larger than ionic micelles and have asymmetrical shapes.
- Oxyethylene chains in non-ionic surfactants can entrap water molecules.
Factors Affecting CMC & Micellar Size
- Factors influencing critical micelle concentration and micellar size include hydrophobic group structure (increasing chain length decreases CMC and increases micellar size) and hydrophilic group structure (increasing hydrophilic portion increases CMC).
Non-ionic Surfactants
- These have lower CMCs and higher aggregation numbers compared to ionic surfactants with similar hydrocarbon chains.
- Increasing polyoxyethylene chains enhances hydrophilicity, increasing CMC.
- Examples of non-ionic surfactants and their corresponding CMCs and aggregation numbers are provided.
The Counter Ion
- A more weakly hydrated counter ion (with larger mass) can absorb into the micellar surface, reducing repulsion between head groups.
Effect of Temperature
- Heating aqueous solutions of many non-ionic surfactants may cause cloudiness at a cloud point temperature.
- Ethoxylate surfactant solubility decreases with increasing temperature (unusual).
- This effect is reversible.
- Experiments should be conducted below the cloud point.
- Ionic surfactants' solubility significantly increases above the Krafft point.
Sites for Solubilization
- Different types of surfactants have different solubilization sites.
- Water-soluble surfactants are found within the micelles, while polar solubilizers are distributed between micelles and oil droplets.
- Non-polar solubilizers dissolve in oil droplets.
Electrical Conductivity of Ionic Micelles
- The movement of ions is impeded by solvent viscosity. Micelle formation reduces viscous drag.
- Ionic atmospheres surrounding micelles exert breaking effects because unbound counter ions exert attractive forces, carrying water and countering micelle movement, resulting in decreased conductance.
- Bound counter ions reduce overall charge and exert opposing forces, primarily contributing to decreased conductance.
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Description
Test your knowledge on non-ionic surfactants, their HLB values, and the critical micelle concentration. This quiz covers essential concepts related to emulsifiers, surface tension, and solubility in surfactant solutions. Understand the significance of HLB values and their practical implications in formulations.
