Term
| Define interfacial tension |
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Definition
| Interfacial phenomenon deals with the behavior of molecules at the boundaries of phases (interface). The term ‘phase’ here refers to solid, liquid or gaseous phase. The behavior of molecules at the boundaries is different from their behavior in the bulk of the phase. |
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Term
| What types of surface interfaces exist? |
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Definition
| solid-solid (powder particles in contact), solid-liquid (suspension), liquid-liquid (emulsion) etc |
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Term
| Is there interfacial tension with the gas phase? |
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Definition
| Yes, but when dealing with solid-gas or liquid-gas boundaries, we use the term ‘surface’ instead of interface. Gas-gas interface is non-discernible. |
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Term
| If a wire frame with a length L is exposed to a liquid and changes its area by length F, what is the formula for surface area? |
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Definition
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Term
| What are the units for surface area? |
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Definition
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Term
Give the formula for work.
How could you change this formula for the wire-square example? |
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Definition
W=force x distance
W = γ x A
W= γ x 2 x L x d |
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Term
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Definition
| The device which measures interfacial tension |
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Term
| What is a Du Nouy Ring? What is the formula for surface tension to be calculated from it? |
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Definition
A tensiometer that consists of a hanging platinum-iridium ring.
γ = k x F where k is a proportionality constant that depends on the geometry of the ring.
[image] |
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Term
| What is a capillary tube? How is surface tension calculated from it? |
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Definition
γ = h r g d /( 2cosθ)
r is the radius of capillary tube, d is the density of liquid, g is the acceleration of gravity, and θ is the contact angle
[image]
Can NOT be used for interfacial tension |
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Term
| Define Wihemny plate. How is it used to calculate surface tension? |
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Definition
Similar to the ring method, but uses a thin plate suspended from a balance
F = 2(L + T)γ cos θ where L is the length of the plate, and T is the thickness of the plate.
If T is much less than L, γ= F/2L
[image] |
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Term
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Definition
The angle between the surface of liquid (at the contact point) and the tangent to the solid particle.
Measures the tendency of a liquid to wet the solid particle (smaller the contact angle, greater is the wetting and vice-versa). |
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Term
| Define surface active agents/surfactants |
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Definition
Surface active molecules have two parts: one part is hydrophilic and the other part lipophilic.
Lower the interfacial tension and contact angle.
Aid in drug solubilization, mixing, stabilizing suspension/emulsion etc.
Can be synthetic or natural and are classified as anionic, cationic, nonionic , and zwitterionic |
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Term
| Define zwitterionic surfactant |
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Definition
| Their surface active portions have both negative and positive charges. Depending on the pH of the medium they are in, they can be anionic, cationic, or zwitterionic. These agents are compatible with all types of surfactants. |
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Term
| Are nonionic and ionic surfactants compatible? |
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Definition
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Term
| What is the surface tension of water at 20 degrees C? |
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Definition
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