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DP 2: Exam 2 Interfacial Phenomena Chapter
Terms in this set (45)
What are the properties related to interfacial phenomena?
the properties of molecules situated at the boundary between immiscible phases
List the types of boundaries between immiscible phases
The term surface is used to denote either a _____/_____ or ______/______ interface.
In class, Dr. Jay gave more specific boundaries for the surface and for interface. What are these boundaries?
Interface: Liquid/liquid = emulsions
Solid/liquid = suspensions
There is a significant intermolecular attraction between the molecules in a ______ liquid.
Image of Surface boundary and Interface boundary
In the example of water, any given molecule in the bulk of the water is __________ attracted to those molecules surrounding it and is being pulled equally in all ____________.
Water molecules at the surface (at the air-liquid interface) are only attracted to the molecules of water which are _______ and _________ to them.
Would water molecules at the surface have a significant attraction or interaction with the air? Why or why not
No because air is very hydrophobic to the water
Image of surface tension (boundary) of air and water
Image of surface tension with water (and with mercury) when placed in test tube
Why do water molecules assume a spherical shape when sprayed in the air?
the inward force causes a contraction of the surface of the liquid since water molecules have an inward pull towards the bulk of the liquid
A __________ has the smallest surface area to volume ratio of all possible shapes.
Define surface tension
Surface tension is the force which must be applied to the surface of the liquid to exactly counterbalance the inward pull
The stronger the intermolecular forces of the liquid, the stronger the pull on the surface molecules by the molecules in the bulk of the liquid and the ________ the surface tension.
As the amount of H-bonding decreases the strength of the intermolecular interactions ___________.
An increase in temperature results in a ___________ in surface tension.
What will happen when two pure immiscible liquids are placed in a beaker?
the liquids will quickly separate into two layers
Why do immiscible liquids form two separate layers when put together?
the cohesional forces between the identical molecules in each phase being greater than the adhesional forces
Rank cohesional forces of water to oil
water > oil
The greater the difference in the cohesional forces of the molecules in each phase, the __________ the interfacial tension and the __________ the resistance to mixing.
What will happen to the interfacial tension if there is some attraction between the molecules in two phases?
the interfacial tension is much lower
What will happen to the surface tension if there is significant attraction between the two phases?
the liquids are miscible and there is no interface or interfacial tension
Describe the process that occurs when a liquid is dispersed throughout another liquid in which it is insoluble in
the dispersed oil droplets naturally assume a spherical shape as the oil molecules pull away from the water molecules in an effort to minimize their contact with each other
What happens if two dispersed oil spheres touch while in an immiscible system
when the two spheres touch, they immediately coalesce to form a larger sphere
What is coalescence and why does it occur?
Coalescence is the fusion between two dispersed oil spheres upon touching and it occurs to increase particle size to decrease surface area or interfacial area
Coalescence continues until there is a complete ______________ of the liquids into two layers.
Coalescence becomes faster as the difference in density between the two phases __________.
If a slightly polar liquid is used rather than a non-polar liquid, the downward pull on a water molecule at the interface into the bulk is partially offset by its attraction to the OH group on the polar liquid and the interfacial tension is ________.
slightly polar liquids can act as _______________ agents.
Surface Active Agents are also known as ___________________.
What are surface active agents?
surface active agents are molecules that naturally migrate to interfaces because they are amphiphilic
liquids that are amphiphilic have some affinity for both polar and nonpolar solvents
Most commonly, surfactants are of what general structure
Long chain hydrocarbons with a polar functional group on one end
Give an example of a amphiphilic surface active agent
Image of water alone vs water with a surfactant depicting a decrease in surface tension
As the concentration of surfactant increases, more of the surface of the water is covered, so there is less air/water contact, so the surface tension becomes lower until it reaches a minimum value. What must the minimum value always be greater than?
minimum value is always greater than zero
At what point will the surface tension reach a minimum?
The surface tension reaches a minimum when enough surfactant is added to form a complete monolayer of surfactant covering the surface of the water
What happens if we continue to add surfactant after this minimum is reached?
Once there is no more room at the surface monolayer, the additional surfactant molecules become trapped in the water (the bulk) where they form micelles
Critical Micelle Concentration (CMC)
Which part of the micelle forms the interior and which part of the micelle forms the exterior if the solvent is water?
Lipophilic tails form the interior
Polar heads from the exterior
To form an emulsion, you need surfactant concentration above...
the Critical Micelle Concentration (CMC)
Surfactants can act as _______________ agents.
Micelles that will serve as a host for lipophilic molecules/drugs are of what size typically?
What would happen if the same surfactant is placed in a beaker of oil, rather than water, at a concentration greater than the CMC?
the formation of Reverse Micelles, this is not very common
Give one reason for the addition of emulsifiers to pharmaceutical products?
For easier blending
THIS SET IS OFTEN IN FOLDERS WITH...
DP 2: Exam 2 Interfacial Properties Part…
DP 2: Exam 2 Suspensions
DP 2: Exam 2 Liposomes and Nanomedicines
DP 2: Exam 2 Rheology
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