Pharmacy 431 Midterm 2 Study Material - Key Concepts and Definitions

Example of a Gas-Liquid immiscible medication

solutions exposed to air, liquid aerosols

Examples of gas-solid immiscible medications

solid dosage exposed to air, solid aerosols

Examples of liquid-liquid medications

Emulsions (fish oil)

Examples of liquid-solid immiscible medications

suspensions

Examples of solid-solid immiscible medications

Dry powder particles in tablets, capsules and other dosage forms

What is surface tension defined as?

the net force when one phase is liquid and the other is a gas

What is the unit used to measure surface tension?

force per unit length

What is interfacial tension?

when two phases are both immiscible liquids, both solids, or both gases

When will two phases mix together?

when adhesion > cohesion

Do polar molecules or non-polar molecules have stronger surface tension?

polar. Caused by stronger cohesion and thus stronger

What is surface free energy?

quantifies the disruption of intermolecular bonds that occurs when a surface is created

What is surface free energy proportional to?

total surface area

What does surface free energy change with?

Temperature and Pressure

What is surface tensions relationship with temperature

As temperature increases, surface tension decreases. Reaches zero at critical temperature

What is wetting?

when the spreading occurs on a flat surface that is a solid

How do adhesive/cohesive tensions relate to each other when wetting

when adhesive forces are greater than cohesive forces there is complete wetting

What is the work of adhesion?

the work required to separate the droplet from the surface. The difference between the before and after surface tensions

What is the work of cohesion?

The work required to seperate the droplet into two smaller droplets

What does a positive and low/negative spreading coeffiecient relate to?

positive = droplet will spread over the surface

Negative = no spreading

How do molecules with positive absorption interact with interfaces?

Molecules that move toward the interface are said to positively absorb to the interface and REDUCE interfacial tension

How do molecules with negative absorption interact with interfaces?

Molecules that move away from the interface are said to negatively absorb to the interface and INCREASE surface tension

What is adsorption?

the migration of molecules towards or away from an interface

What is absorption?

Refers to penetration of one substance into the interior of the bulk phase, either through physical pores (as in a sponge) or through dissolution in the phase (as in gases dissolving in water).

What is a surfactant?

Chemical substances that (due to their molecular properties) tend to migrate to interfaces between liquids and surrounding solid, liquid, or gas phases

How do surfactants interact with their interfaces?

polar orients towards other polar molecules while non-polar goes more inward, decreasing surface tension

What is the structure of a soap?

polar head with long non-polar tail

What are the four different categories of surfactants?

Anionic, Cationic, Zwitterionic and Nonionic

What is a detergent?

highly water-soluble surfactants that promote solubilization and suspension of oily, greasy material in water

Examples of Anionic surfactants

SDS, Sodium, Alkyl Benzene

What are cationic surfactants?

surfactants with a positive charge. usually having bacteriocidal properties. CTAB and Cetylpyridinium chloride

What are zwitterionic surfactants?

Positive and negative charged functional groups (net charge=0). Alkyl betaines and Lechitin

What are non-ionic surfactants?

detergents with no charge. Most commonly used in pharmaceutics. Ex: polyethylene glycol, Pluronic surfactants, Sorbitan Monolaurate (polar -OH groups)

What is HLB?

hydrophilic-lipophilic balance

What does a higher and lower HLB correspond to?

higher = more hydrophilic surfactant (used as detergent or solubilizing agents)

Lower = more lipophilic surfactant (most antifoaming agents)

What is a micelle?

a particle formed when surfactant is added to a saturated surface.

What is the shape of a micelle?

small spherical aggregates in which hydrophobic portions of the surfactant occupy the interior and hydrophilic portions form the outside surface

What is CMC?

critical micelle concentration. The concentration at which micelles begin to form

What types of surfactants form micelles?

Phospholipids and PEGylated phospholipids (poly(ethylene)glycol: PEG)

What are SSM's?

Sterically Stabilized Micelles (SSM) - made up of PEGylated phospholipid monomers

What is Gibbs absorption equation?

equations used to calculate the surface area taken up by a single molecule

What is chemisorption?

when the adsorbed substance becomes chemically bonded to the solid surface. This process is irreversible

What is gas pressure?

The amount (x) of gas adsorbed per unit mass (m) of the solid

How is gas adsorption related to temperature and pressure

As temp and pressure increase, gas adsorption also increases

What is the Type 1 Isotherm?

isotherms are observed when only a monolayer of gas can be absorbed onto the solid surface. Usually a plateuing line

What are Type 2 and 3 isotherms?

observed when gases adsorb to the surface of nonporous solids but condense to form multiple layers after initial monolayer has saturated the surface. Looks exponential

What are type 4 and 5 isotherms?

Isotherms arise when the gas adsorbs onto a porous solid (not flat solid with porous notch), where condensation inside the pores can occur

What is a dispersed system?

consist of particulate matter, known as the dispersed phase, distributed throughout a continuous or dispersion medium

Particle size of molecular dispersion

<1 nm

Particle size of Colloidal dispersion

1-500nm

Particle size of Coarse dispersion

>500 nm - 1mm

Characteristics of a molecular dispersion?

Visible by TEM, passes through ultrafilter and semipermeable membrane, rapid diffusion

Characteristics of a colloidal dispersion

Visible by SEM, not vidible by Light Miscroscope, passes through filter paper, diffuses very slowly

Characteristics of Coarse dispersion

visible by light microscope or naked eye, does NOT diffuse

Is cows milk a colloid?

Yes

What is the visual test for colloids in water?

transparent = dissolves in water

precipitates = insoluble in water

What is true in regards to colloids and semi-permeable paper?

colloids will not pass through semi-permeable membranes

What is a sol?

a solid dispersed in a liquid

What is a gel?

a solid network distributed throughout a liquid

What is a liquid emulsion?

liquid dispersed in a liquid

What is a solid emulsion?

liquid dispersed in a solid

What is a foam?

Gas dispersed in a liquid

What is a solid foam?

gas in solid (insulation)

What is a solid aersol?

solid dispersed in gas

What is a liquid aersol?

liquid dispersed in gas

What are the three types of colloidal systems?

Lyophilic Colloids

Lyophobic Colloids

Association Colloids

What is a lyophilic colloid?

consist of particles that have high affinity for the dispersion medium

Properties of a lyophilic colloid

Dispersed to form sols easily. viscosity increases with concentration. stable in the presence of electrolytes

What is a lyophobic colloid?

consist of particles that have poor affinity for the dispersion medium. Gold, silver, silver iodide. Unstable in the presence of electrolytes

Typical surface diameter of micelles?

50 Angstroms

Typical shape of micelles?

spherical normally and rod-shaped at high concentrations

What can be used to calculate CMC?

mole fractions of molecules

What is the Faraday-Tindall effect?

Light is not scattered by the pure solvent or a solution containing a molecular dispersion

What is turbidity defined as?

fractional decrease in light intensity (l) as the light passes through 1 cm of solution.

What is Rayleigh scattering?

Special form of scattering that occurs when the structure's dimensions are much smaller than the beam's wavelength

What is brownian motion?

random movement of particles suspended in a fluid

What is fick's first law?

applies to the diffusion of colloidal particles through the dispersion medium. Based on Mass flow per unit time and concentration gradient

What is the Stokes Einstein equation?

diffusion properties are decided by the average radius of colloid particles and average particle weight

What is osmosis?

diffusion of water

What is osmotic pressure?

minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable

What is stoke's law?

velocity of a sedimentation particle is decided by radius and denisty of the particle along with gravity

How does rate of particle settling increase?

higher particle size and higher particle density increase settling

How does viscosity relate to sedimentation?

Sedimentation becomes a problem for formulating disperse systems with larger, heavier particles as found in coarse dispersions.