Disperse Systems Flashcards
When is the term “surface” used?
When talking about gases.
When is the term “interface” used?
When talking about solids and liquids.
What does heterogenous mean?
Not all units are the same throughout
What does homogenous mean?
When each unit of a system is looked at under a microscope, it is completely the same as another unit of the system.
How many phases does an emulsion have?
2 or 3
What types of phases are found in suspensions?
A solid and a liquid phase.
What are some examples of heterogenous mixtures?
- blood
- salad dressing
- Tylenol suspension
When is a unit called the dispersed, discontinuous, or internal phase?
- in a suspension–when the solid phase is discrete units
* one homogenous phase
What is a dispersion?
An emulsion is a dispersion. It is a liquid in a liquid–one liquid is discrete units that are immiscible in the liquid medium.
Disperse system encompass a variety of…
…heterogenous, multiphase systems in which one homogenous phase is intimately distributed, in discrete units, within the second phase.
What is the second phase called in a dispersion?
Dispersing or continuous
What is a solution?
A liquid preparation when the drug or AI is in a molecular form dissolved in the solvent system.
What is a two phase system or dispersion?
Liquid preparations when the drug or AI is undissolved, insoluble, or immiscible and is distributed throughout the vehicle.
What is the dispersed phase?
The AI or drug
What is the dispersing phase or medium?
The vehicle
What a dispersion?
The dispersed phase and the dispersing phase or medium mixed together.
Are solutions dispersions?
NO–they are not. They are liquid dosage forms and are homogenous systems with the dissolved solid ingredient in molecular form.
Describe the AI in dispersions.
It is not dissolved or it is immiscible–not in molecular form.
What are some examples of dispersions?
- suspensions
* emulsions
To act in the body, what does a drug and dosage form need to be?
Both physically and chemically stable–distributed uniformly throughout
What is the dispersed phase and dispersing phase of a liquid aerosol?
dispersed phase: liquid
dispersing phase: gas
What is the dispersed phase and dispersing phase of a solid aerosol?
dispersed phase: solid
dispersing phase: gas
What is the dispersed phase and dispersing phase of an emulsion?
dispersed phase: liquid
dispersing phase: liquid
What is the dispersed phase and dispersing phase of a suspension?
dispersed phase: solid
dispersing phase: liquid
What is the most common way to classify dispersions?
Based on the particle size of the dispersed phase (varied particle size to large visible particles to colloidal dimension)
What size are coarse dispersions? What are some examples of dosage form?
- 10 to 50 um
* suspensions and emulsions
What size are fine dispersions? What are some examples of dosage form?
- 0.5 to 10 um
* magmas and gels
What size are colloidal dispersions?
1 nm to 0.5 um
Describe a successful and proper dispersion.
Upon moderate agitation, they result in a uniform and complete redistribution of the dispersed phase throughout the dispersion
What size dispersion has a greater tendency to separate from the dispersing medium? Why?
- Coarse dispersions
- suspensions: denser than water, solids tend to settle down
- emulsions: less dense than water, oils tend to float or cream on top
Lyophobic dispersions are…
…solvent fearing.
Lyophilic dispersions are…
…solvent loving.
What type of dispersion system has greater stability?
Lyophilic dispersions
What is a molecular dispersion?
Units of dispersed phase are composed of single macromolecules (drug exists in molecular form, but is really a solution)
What are micellar dispersions?
Units of dispersed phase are composed of micelles or association of several molecules (surfactant is more concentrated, thus a micelle is formed–not a true dispersion, usually has AI of surface active agent)
What are the 5 principles of surface phenomena?
- surface and interface
- surface tension and interfacial tension
- electrical properties at the interface
- surfactants
- wetting and contact angle
How would a boundary between two homogenous phases be described as?
As a film of a characteristic thickness (NOT as a simple geometric plane)
What is a surface, or an interface?
The boundary of separation of two phases
What is a phase?
A mass of substance (solid, liquid, gas) that possesses a well defined boundary.
Describe the molecules on the surface of a liquid.
The potential energy of the molecules on the surface have a net force that pulls towards the bulk.
Describe the molecules in the bulk of a liquid.
The molecules are being pulled in all directions with a net force of ZERO
Why do droplets want to have a spherical shape?
Because a sphere has the minimum surface area possible–all other shapes have a larger surface area. (the molecules on the outer edge are being pulled towards the bulk to make it smaller)
What does interfacial tension cause in a suspension?
caking
What happens when you decrease the interfacial tension?
increase stability
How do you decrease interfacial tension?
Surfactant binds to the solid internal phase and has association with the dispersion medium (solid in a suspension has a coating that interacts with the liquid medium)
Molecules forming the surface of a liquid behave differently from those in the bulk of each phase. This is manifested in what 3 ways?
- capillary action
- wetting
- adsorption
Describe the binding forces in the bulk of the phase.
The binding forces between molecules are equivalent in all directions. (decreases surface area)
What are molecules on the surface subjected to?
Intermolecular forces in the direction of the interface and towards the bulk (decreases surface area)
What is required to bring molecules from the bulk to the surface?
- work
* think about grinding powder in a mortar–you have to put energy into the grinding
What is surface tension, or surface free energy per unit area?
It is the amount of work required to bring the molecules from the interior to the surface (to expand by unit area)
When you reduce the drop size of an oil to make an emulsion…
…you are increasing the surface area.
What liquid has the highest surface tension?
Water
What describes the interface between two liquids or a solid and a liquid?
Interfacial tension
What is present at the interface between two condensed matters (ex: liquid-liquid interface)?
Tension or excess energy
Which is greater, the interfacial tension between two liquids or a solid and a liquid? Why?
The solid and liquid have a greater interfacial tension because the adhesive forces between the two liquid phases forming the interface are greater than when a liquid and a gas phase or a solid and a liquid exist together.
What is cohesion?
The force of attraction between like molecules.
What is adhesion?
The force of attraction between different molecules.
What force of attraction does a suspension have?
adhesion
True/False
The adhesive forces between a liquid and a liquid are stronger than the adhesive forces with a solid in a liquid.
True
When adhesive forces are stronger, the tension is…
…weaker.
True/False
In an emulsion, the adhesive forces are stronger than in a suspension so the adhesive forces cause the tension to be weaker in an emulsion.
True
What needs to be applied to a system to make a dispersion make states of matter coexist?
Energy needs to be provided–mixing in a mortar and pestle.
True/False
Within the same same of matter, adhesive forces are stronger.
True
Different states of matter have weaker adhesion forces
How is interfacial tension defined?
The force per unit length existing at the interface between two liquid immiscible phases or between solid and liquid phase. (units: dyne/cm)
What are the units for surface tension?
dyne/cm (same as interfacial tension)
What is an important part of the surface’s physical chemistry?
Knowing the influence of electrical charges on a surface. Aqueous suspensions are not only influenced by the interfacial properties, but also by attraction and repulsion caused by electrostatic charges.
What can happen when a particle is dispersed in a surrounding liquid environment? (like in suspensions)
The dispersed particles in the liquid may become charged. (ion adsorption, ionization, and ion dissolution)
The net charge at the particle surface affects what?
It affects the ion distribution in the nearby region, increasing the concentration of counter-ions close to the surface.
What is formed in the region of the particle-liquid interface?
an electrical double layer
Assume a CaCO3 particle is positively charged. As soon as you add a neutral molecule to water or any liquid, it can obtain a charge based on what?
- ion adsorption
- ionization
- ion dissolution
(CaCO3 can adsorb ions from water/liquid medium or undergo ionization and get a charge)
As soon as you put a positive charge on a drug particle in water, what happens?
The positive particle will combine with the anions in the water.
(vice versa: if you have a negative charged drug particle, it will have cations gather around it–these are counter ions)
What is a counter ion?
When the charge is opposite to that of the drug particle.
