Colloids Flashcards
Define dispersed system
a system in which one substance is distributed as particles throughout another phase
What are the two parts of a dispersed system?
disperse phase
dispersion medium
Define molecular dispersions
also known as true dispersions
solute molecules are homogeneously distributed throughout the solvent
List some examples of dispersed system
colloid
gels
suspensions
emulsion
lotion, ointments and cream
Which physicochemical feature is most important to define the type of the dispersed system?
size of the dispersed particles
What the types of dispersed systems based on?
the physicochemical properties of the dispersed particles and dispersion medium
What are the two classifications?
colloidal dispersions
coarse dispersions (suspensions)
What is the particle size of colloids?
1-500 nm
What is the common use for colloidal systems?
excellent candidate for research regarding novel nano-drug delivery systems
List some unique properties of colloids
Platinum is effective as a catalyst only as platinum black (colloidal form)
Cellular uptake of nanoparticles is different from micro/macroparticles or true molecular dispersions – drug delivery, toxicity
What are some shapes that colloidal systems have?
may can occur as
globules
rods
flakes
threads
branched structure
What factors does shape and size define?
flow
sedimentation
osmotic pressure
Distinguish between solutions as related to particle size and dispersion.
Particle size: < 1 nm
Dispersion: Homogeneous (particles uniformly distributed throughout the mixture)
Examples: Saltwater, sugar water, air
Distinguish between colloids as related to particle size and dispersion.
Particle size: 1-500 nm
Dispersion: Heterogeneous (particles are not uniformly distributed and may settle over time)
Examples: Milk, fog, gelatin
Distinguish between suspensions as related to particle size and dispersion.
Particle size: > 1000 nm
Dispersion: Heterogeneous (particles settle quickly and can be filtered out)
Examples: Muddy water, blood, sand in water
Give examples of colloids in various states of matter
Gas: Smoke, fog, aerosol sprays
Liquid: Milk, blood, ink
Solid: Pearl, opal, cheese
List the key features of lyophilic colloids
Also known as hydrophilic colloids
Can be easily dispersed in a solvent
Have a strong attraction to the solvent molecules
Examples: Starch, proteins, cellulose
List the key features of lyophobic colloids
Also known as hydrophobic colloids
Have little to no affinity for the solvent molecules
Cannot be easily dispersed in a solvent
Require the addition of a stabilizing agent to remain dispersed
Examples: Gold, silver, sulfur
Define gels and give examples
A type of colloid where a solid network is formed throughout a liquid
The solid component is referred to as the gel network or gel phase
Examples: Jell-O, hair gel, toothpaste
Define Magmas/Milks and give examples
A type of colloid where a solid is suspended in a liquid
The solid particles are larger than those in a solution but smaller than those in a suspension
Examples: Concrete, lava, paint
What are colloidal dispersions and how do they differ from coarse dispersions (suspensions)?
Colloidal dispersions are systems in which the particle size ranges from 1-500nm and the particles are too small to see with the naked eye. They have a large surface area and unique properties, and may occur as globules, rods, flakes, threads or branched structures. Coarse dispersions (suspensions), on the other hand, have larger particle sizes and are visible to the naked eye.
What are some examples of colloids in various states of matter?
The components of a colloidal dispersion may be in any of the three states of matter (solid, liquid or gas). Of the 9 possibilities, 8 exist as colloidal dispersions. For example, milk is a colloidal dispersion of fat particles in water (a liquid-liquid colloidal system), while smoke is a colloidal dispersion of solid particles in air (a solid-gas colloidal system).
List some unique properties of colloids
Platinum is effective as a catalyst only as platinum black (colloidal form)
Cellular uptake of nanoparticles is different from micro/macro particles or true molecular dispersions – drug delivery, toxicity
Describe lyophobic colloids
Lyophobic colloids are colloidal dispersions in which the dispersed phase is not attracted to the dispersion medium. This means that the particles of the dispersed phase tend to repel each other and may require the addition of a stabilizing agent in order to prevent them from aggregating or settling out of the dispersion. Some examples of lyophobic colloids include suspensions of metal oxides in water and emulsions of oil in water.
Describe gelling agents and give some examples
Gelling agents are substances that can form a gel-like consistency when mixed with a liquid. Some examples of gelling agents include agar, gelatin, carrageenan, pectin, and xanthan gum.
Some compounding considerations when making the gels in pharmacy
When making gels in pharmacy, there are several compounding considerations to take into account. These may include selecting the appropriate gelling agent for the intended purpose, ensuring that the gelling agent is properly hydrated before mixing it with other ingredients, and maintaining the proper pH and temperature during the compounding process. It is also important to consider factors such as the desired consistency and viscosity of the final product, as well as any potential interactions between the gelling agent and other ingredients.
Why are colloidal dispersions made in pharmacy practice?
increase surface area of absorption
reduce side effects of the drug due to low retention time and exposure to mucosal membrane
stability and solubility enhancement
What does these electrical charges do?
The charge on the particle surface will attract oppositely charged ions (counter ions) to achieve electrical neutrality: this causes the formation of an electrical double layer around the particle
How does the electrical double layer determines the distance between particles in the dispersion?
directly affects the stability of the system
What is an example of protective colloids?
gelatin
methylcellulose
What are some ways to stabilize a dispersed system?
changing the viscosity of the system restricts particles movement
addition of buffer salt to maintain pH required for product stability
addition of electrolytes after compatibility testing for type and concentrations of electrolytes
What is the equations for the DLVO theory?
VT = VA + VR
What are the variables for the DLVO theory?
VT – total potential energy of interaction (attraction or repulsion)
VA – van der Waals attraction
VR – electrostatic repulsion
What does the DLVO theory describe?
a quantitative approach to estimating the stability of hydrophobic sols. This theory reflects a balance between net attractive and repulsive forces.
What are the two systems of gelling agents?
Two phase
One phase
What are some characteristics of colloids?
Small size (invisible)
Filtration not possible
DO NOT SETTLE but sometimes lyophobic colloids show visible sedimentation at bottom merely due to aggregation of colloidal particles
What are some characteristics of suspension?
Large size (visible)
Filtration possible easily
ALWAYS SETTLE at bottom upon standing
Define two phase gelling system
mostly inorganic gels
tendency to cross-link and solidify upon standing and liquefy under stress like staking
Define one phase system
common gels in pharmacy
linear or branched polymer macromolecules that dissolve in water are used as gelling agents
List examples of natural gelling agents
alginic acid
tragacanth
What concentration usually for gelling agents?
between 0.5-5%
List examples of semi-synthetic gelling agents
methylcellulose
hydroxypropyl methylcellulose
List examples of synthetic gelling agents
carbomers
poloxamers
Examples of lyophobic colloids
Colloidal gold (sol)
colloidal sulfur
colloidal silver
