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Ceutics Midterm 2 > Interfacial Phenomena & Surfactants 3/4 > Flashcards

Interfacial Phenomena & Surfactants 3/4 Flashcards

1
Q

Types of Interfaces

Gas-Liquid

Gas-Solid

A

Immicible phases in pharmaceutical systems

Gas-liquid

-solutions exposed to air = Liquid Aerosols

Gas-solid

-solid dosage forms exposed to air = Solid Aerosols

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2
Q

Liquid Liquid

Interfaces

A

Immicible phases in pharmaceutical systems

Emulsions

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3
Q

Liquid-Solid

Interafaces

A

Immicible phases in pharmaceutical systems

Suspensions

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4
Q

Solid-Solid

Interfaces

A

Immicible phases in pharmaceutical systems

Dry powder particles in

tablets/capsule/other dosage forms

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5
Q

Surface Tension

A

When one phase is a liquid and the other is a

GAS

the net force is called Surface Tension

Cohesive (like molecules) forces

PARALLEL force per unit to measure

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6
Q

Interfacial Tension

*Analagous to surface tension @ gas-liquid or gas-solid interafaces

A

If the two faces are:

both immiscible liquids

both solids

liquid/solid

the force is called interfacial tension

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7
Q

Phases combine (mix together)

WHEN?

A

When

ADHESION > COHESION

dissimilar forces > like forces

then the two phases will combine

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8
Q

Surface Tension

determinants

A

More Polar = Greater Surface Tension

ex. Water / Glycerine

Determined by the degree to which molecueles of the liquid attract to one another (cohere)

Electrostatic interactions

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9
Q

Interfacial Tension vs WATER

determinants

A

MERCURY IS THE HIGHEST

the less the molecule wants to interact with water = greater interfacial tension

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10
Q

Increasing Temperature

effect on

Surface Tension

A

Increasing Temperature

v

decreasing surface tension

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11
Q

Surface Free Energy

A

Potential energy of moving a molecule from the interior of a phase to the surface

work is done against the force of surface tension

Proportional to total surface area

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12
Q

Spreading

A

When you drop a Liquid on a horizontal flat surface

(solid or immiscible liquid)

Extent of spreading depends on the balance between

Adhesive forces & Cohesive forces

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13
Q

Wetting

A

= Spreading but only if the flat surface is

SOLID

if adhesive forces > cohesive forces within the droplet

droplet will spread(wet) the solid surface

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14
Q

Spreading Coefficient = S

A

= Difference between

Work of Adhesion - Work of Cohesion

if POSITIVE (S>0), droplet will spread over the surface

if negative, droplet will remain intact as a lens-shaped globule

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15
Q

Spreading Coefficient

determinants

A

High spreading coefficients (+) on water

Completely/patially miscible w/ water

ex. ethyl alcohol / ethyl ether
* Substances with low or NEGATIVE coefficients*
* are poorly soluble in water*

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16
Q

Contact Angle

What Degrees are more spreading vs less spreading

A

Angle between a tagent to the droplet and the surface @ the point of contact.

Contact Angle > 90* = More Spreading

Contact Angle < 90* = Less spreading

17
Q

Scrupulously Clean Glass

A

= Very High surface free energy

in respect to water

is high enough to overcome internal cohesive forces in a water droplet

–>Water will completely wet clean glass surface

18
Q

Adsorption

A

refers to migration towards or away from a interface (surface)

ALWAYS a surface phenomenon

~sticking to surfaces

tend to spontaneously toward/away from the interface

19
Q

Absorption

A

penetraion of 1 substance into the interior of the bulk phase

through physical pores or dissolution in the phase

20
Q

Positive Adsorbtion

A

Molecules that move TOWARD the interface

Reduce interfacial tension

++++++

surfactants

21
Q

Negative Adsorption

A

Molecules that move AWAY from the interface

INCREASE the interfacial tension

——-

22
Q

Surfactants

Surface Active Agents

A

Chemical substances, due to molecular properties,

that tend to migrate interfaces between liquids/surrounding other phases = Positively Adsorbed to surface

Ampiphiles / small polar group attached to a long non-polar group

there are four categories of surfactants

23
Q

Soaps

A

first form of surfactant

Animal Fats / Vegetable oils + Hot Water

(in presensce of Alkali metal hydroxides / carbonite salts)

Produce–> SOAPS (free glycerol)

through hydrolysis = saponification

ex. Potassium oleate (from olive oil)

Sodium stearate (from beef tallow)

24
Q

Anionic Surfactants

-

A

Highly water soluble surfactants that promote solubilization/suspension of oily/greasy materials in water

Soaps made from natural fats & Oils

Detergents (synthetic, not soaps)

Have NEGATIVE charges (sulfate-tail)

Ex. SDS, sodium alkyl benzensulfonic acid

25
Q

Cationic Surfactants

++++

A

Used primarily as antiseptic / antimicrobial preservative

has POSITVE CHARGE (nitrogen w/ ch3’s in tail)

ex. CTAB, cetylphyridinium chloride

26
Q

Zwitterionic Surfactants

A

Have both + and -

ex. Alyl bentaines / Lecithin

27
Q

Nonionic Surfactants

A

most commonly used in pharmaceutical surfactants

ex. alcohol ethyoxylate, poloxyethylene

Tween / Span

28
Q

Hydrophilic-Lipophilic Balance

HLB

A

Scale that compares surface-active properties of various surfactants as they relate to use

Greater (18) = detergents/solubizing agents

Middle (6-12) = wetting/spredding agents

Low (0-3) = antiFoaming agents

29
Q

Critical Micelle Concentration

A

Adding surfactant to a aquious solution results in an accumulation of suractant –> Reduces Surface tension

Once surface is Completely Saturated & surface tension can no longer be reduced.

Micelles are formed @ this concenctration

30
Q

Determining the size of a surfactant molecule

A
  1. Use Gibbs adsorption equation
    1. calculate area occupied by a single molecule
    2. –> calculate molecular surface area
  2. Generate a mololayer film (layer 1 molecule thick) on the surface
    1. ​done by ben Franklin, 1 tsp of fatty acid over a pond
31
Q

Solid Adsorption

A

Both gases & liquids can adsorb to solids.

Physical Adsorption is reversible

  • by changing external conc/pressure
32
Q

Gas Adsorption

A

dependedent on Gas pressure & Temperature

5 Types of adsorption isotherms

depend on:

conditions used & gas/solid studied

33
Q

Type 1 Isotherm

A

Observed when only a monolayer of gas can be adsorbed onto the solid surface

FREUNDLICH ISOTHERM

LANGMUIR ISOTHERM

(regular curve, y limit)

34
Q

Type 2 / 3 Isotherm

A

observed when gases adsorb to the surface of

nonporous solids

but condense to form multiple layers after the initial monolayer has saturated the surface

BET MODEL

(s-looking curve and regular curve w/ x-limit)

35
Q

Type 4/5 Isotherms

A

Arise when gas adsorbs onto a

Porous solid

where condensation inside the pores can occur

36
Q
A

Ceutics Midterm 2 (7 decks)

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