(Midterm) INTERFACIAL TENSION AND COLLOIDS Flashcards by Monica Anne Colina

Boundary between two phases

Interface

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Boundaries of solids, liquids, or gases with
other solids, liquids or gases.

Interface

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force that pulls the molecules at the
interface together, which results to the
contraction of the surface.

Surface tension

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Boundaries of solids or liquids with air

Surface

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Is the force per unit length that must be
applied parallel to the surface so as to
counterbalance the net inward pull

Surface tension

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Dynes/cm or N/m

Surface tension

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force per unit length existing at the interface
between two immiscible liquid phases.

Interfacial tension

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Attractive forces between immiscible liquids

Interfacial tension

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Capillary rise:

γ = 1⁄2 hgrρ

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Molecules or ions that are adsorbed at
interfaces.

Surface Active Agents

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It has a certain affinity for both polar and
nonpolar solvents, depending on the
number and nature of the polar and
nonpolar groups present

Surface Active Agents

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Maybe predominantly hydrophilic, lipophilic
or reasonably well-balanced between these
two extremes.

Surface Active Agents

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Without surfactants

higher meniscus

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With surfactants

Lower Meniscus

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Types ofSurfactants

● Anionic Surfactants
● Cationic Surfactants
● Non-ionic surfactant
● Zwitterionic Surfactants

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In solution, the head is negatively charged.

Anionic surfactants

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These surfactants are the most widely used
type of surfactant for preparing shampoos
because of its excellent cleaning properties
and high hair conditioning effects.

Anionic surfactants

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But they have unpleasant taste and have
skin irritation potential.

Anionic surfactants

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particularly effective at oil cleaning and oil/clay suspension.

Anionic surfactants

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They are incompatible with cationic
surfactants but compatible with other type of
surfactants.

Anionic surfactants

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are quaternary ammonium compounds and
they are mostly used for their disinfectant
and preservative properties as they have
good bactericidal properties.

Cationic surfactants

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They are used on skin for cleansing wounds
or burns.

Cationic surfactants

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They are also used as hair conditioners
and fabric conditioners.

Cationic surfactants

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They are also electrolytes like anionic
surfactants and that are incompatible with
anionic surfactants.

Cationic surfactants

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Those surfactants do not have any electrical charge, which makes them resistant to water hardness deactivation.

Non-Ionic Surfactants

They are not affected by presence of salts or changes in pH.

Non-Ionic Surfactants

They are less irritant than other anionic or cationic surfactants.

Non-Ionic Surfactants

They are mainly used as cosurfactants.

Amphoteric/Zwitterionic Surfactants

InterfacialPhenomenon- Applications:

● Improve drug dissolution rate in solid dosage forms. ● They act as lubricants or glidants. ● Suppository base ● Solubilizing agents to aid in solubility. ● Preparation of mouthwashes. ● Cerumenolytic ● In cosmetics, improve penetration and cleaning purposes. ● Biologically important.

These surfactants are very mild, making them particularly suited for use in personal care preparations over sensitive skins.

Amphoteric/Zwitterionic Surfactants

They can be anionic (negatively charged), cationic (positively charged) or non-ionic (no charge) in solution, depending on the acidity or pH of the water. hence surfactants have excellent dermatological properties.

Amphoteric/Zwitterionic Surfactants

They are frequently used in shampoos and other cosmetic products, and also in hand dishwashing liquids because of their high foaming properties.

Amphoteric/Zwitterionic Surfactants

They are systems where one substance is dispersed within another substance.

Pharmaceutical Dispersions

Components of pharmaceutical Dispersions

- Internal / Noncontinuous / Dispersed phase components - External / Continuous / Dispersion medium

It includes homogenous dispersions and heterogenous dispersions.

Pharmaceutical Dispersions

ex. of Sol (S&L)

gels, paints, fruit jellies, dyes

ex. of Emulsion (L&L)

mayonnaise, cream, milk

ex. of Solid Sol (S&S)

Alloys, gems

ex. of Foam (G&S)

Beer froth, soap suds, whipped cream

ex. of Solid foam (G&S)

pumice, marshmallow, meringue

ex. of Solid Emulsion (L&S)

Butter, cheese

ex. of Solid Aerosol (S&G)

smoke, dust and bacteria in air

ex. of Liquid Aerosol (L&G)

Fog, mist, cloud, spray

Types of dispersion

1. Molecular dispersion 2. Colloidal Dispersion 3. Coarse Dispersion

- <1 nm - Invisible on EM - Dialysable/Ultrafiltration - Rapid diffusion - ex. Glucose, oxygen, ions

Molecular Dispersion

- 1 nm to 0.5 um - Visible on EM - Pass filter paper - Slow diffusion/ Brownian motion - Higher surface area - Light scattering (Tyndall Effect) - Unlikely to settle (no Stokes Law) - ex. Colloidal silver, polymers, milk

Colloidal dispersion

Systems in which the size of the dispersed phase is 1nm – 500 nm (5 micrometer) or from the previous slide.

Colloids or Colloidal Systems Dispersions

- >0.5 um - Fine (0.5 - 10) - Coarse (10-50) - Visible under OM - Do not pass filter paper - Do not diffuse - ex. Grains of sand, emulsions/suspensions, RBCs

Coarse Dispersion

The dispersion medium can be liquid, solid or gas.

Colloids or Colloidal Systems Dispersions

It can Hydrophilic or Lipophilic colloidal dispersions

Lyophilic Colloids

Types of Colloids

● Lyophilic Colloids ● Lyophobic Colloids ● Association Colloids

They have polar regions that enable them to become hydrated in contact with aqueous environments.

Hydrophilic Colloidal Dispersions

Examples of LyophilicColloids

● Hydrophilic Colloidal Dispersions ● Lipophilic Colloidal Dispersions

Examples of Hydrophilic Colloidal Dispersions

a. Macromolecules b. true solutions c. colloid solutions

such as proteins (albumin and gelatin) and polysaccharides (natural gums and semisynthetic cellulose derivatives)

Macromolecules

since they are solvated by their medium but their size makes them in the colloidal size ranges

true solutions

Usage of Hydrophilic Colloidal Dispersions

Plasma Volume expansion

to distinguish them from crystalloid solutions

colloid solutions

They don’t have sufficient surface hydrophilicity to enable them to interact well with water.

Lipophilic Colloidal Dispersions

They have the tendency to form aggregates.

LipophilicColloidal Dispersions

Examples of Lipophilic Colloidal Dispersions

- Milk, - Lipid emulsions, - Nanocrystal suspensions

Colloidal systems in which the dispersed phase has little affinity towards the dispersed medium.

Lyophobic Colloidal SYSTEM

They require more time to prepare than lyophilic colloidal systems because the dispersion process is not spontaneous.

Lyophobic Colloidal SYSTEM

Examples of Lyophobic Colloidal SYSTEM

- Hydrophobic polymers, - Ethylcellulose - Inorganic particles such as gold, silver and sulfur.

Properties of colloids:

- Optical Properties - Kinetic Properties

Optical Properties

1. Faraday-Tyndall Effect 2. Turbidity

the formation of a highly visible cone of light when a strong beam of light is allowed to pass through a colloidal sol.

Faraday-Tyndall Effect

fractional decrease in the intensity of light due to scattering as the incident light passes through 1 cm of the dispersion.

Turbidity

3 Kinetic Properties:

1. Brownian movement 2. Sedimentation 3. Viscosity

Method of Preparing Colloids

1. Dispersion method 2. Peptization 3. Condensation method

coarse particles are reduced in size achieved by using mechanical disintegration devices.

Dispersion method

This is the breaking up of aggregates or secondary particles into smaller aggregates in the colloidal size range.

Peptization

colloidal dispersion is achieved by allowing materials of subcolloidal dimensions to aggregate into particles within colloidal size range

Condensation method

Method of Separation

1. Ultrafiltration 2. Dialysis 3. Electrodialysis

a technique of separation where semi-permeable membrane will prevent the passage if colloidal particles yet will permit small molecules and ions to pass through

Dialysis

a method which uses negative pressure through the dialysis membrane thus separating colloidal particles from the filtrate.

Ultrafiltration

The presence or absence of charge on a colloidal particle may affect the stability of the system. For stabilization to be accomplished, we may provide the dispersed particles with an electric charge and surround the particle with a protective sheath to prevent the adhesion of particles as they due to Brownian movement.

Stability of Colloids

Lyophilic colloids are stable, forms a true solution, addition of small amount of electrolyte may not result in precipitation of the colloid but this may be possible at higher electrolyte concentration.

Stability of Colloids

a dialysis and ultrafiltration method which makes use of an electric potential to hasten the removal of ionic contaminants.

Electrodialysis

Hofmeister series – lyotropic series, lists of cations and anions in their rank as precipitant of hydrophilic sols (decreasing order) - Citrate, tartrate, sulfate, acetate, Cl, NO3, Br, I - Li, Na, NH4, K, Rb, Cs

Stability of Colloids

Alcohols and other semi polar solvents may decrease solubility of hydrophilic colloids thus increasing the possibility of precipitation.

Stability of Colloids

usual expression for the protective property of colloid.

Gold number

Minimum weight in mg of the protective colloid (dry weight) required o prevent a color change from red to blue in 10 mL of gold sol on the addition of 1 mL of a 10% solution of sodium chloride.

Gold number

Examples of Gold number

- Gum Arabic and Egg albumin:0.15 – 0.25 - Gelatin: 0.005 – 0.01 - Starch: 25 - Hemoglobin: 0.03 - Caseinate: 0.01 - Sodium oleate: 0.4 - Dextrin: 6 -20

Surfactant micelle:

2 – 5 nm in diameter

These are colloids formed by the association of dissolved molecules of a substance to create particles of colloidal dimensions, most commonly termed as micelles.

Association Colloids

Microemulsion:

10 – 100 nm in diameter

Classification of Association Colloids

- Surfactant micelle - Microemulsion - Liposome

Liposome:

50 – 100 nm

They contain larger particles than colloidal dispersions (1 – 200 um)

Coarse Dispersions

They include emulsions and suspensions.

Coarse Dispersions

They are mixtures of immiscible liquids in which one phase is dispersed as droplets within the other phase

Emulsions