Disperse Systems: Colloids 5/6

Question 1

Molecular Dispersion

Answer 1

Less Than < 1nm (10A*)

Invisible by electron microscopy

Pass through ultrafilter/semipermeable membrane

Rapidly diffuse through medium

Question 2

Colloidal Dispersion

Answer 2

1-500nm

Visible by electron microscopy (but not light)

pass through filter paper (not semipermeable)

Diffuse slowly through medium

*APPEAR transparent to the eye by transmitted light

Question 3

Coarse Dispersion

Answer 3

500nm - 1mm

Visible by microscopy or even naked eye

do not pass through normal filter paper

Do not diffuse through medium

–> aerosols

Question 4

Cow’s Milk

Answer 4

EMULSION

not a colloid

although it passes through coarse filter paper

globules are not a uniform size, some are greater than the right size range

Question 5

What Do Colloids look like?

Answer 5

Many different shapes

Threads –> entagled

Form structure –> Gels

JELLY = colloidal dispersion

Question 6

Lyophilic Collods

(solvent Loving)

Answer 6

• Consist of porticles that have HIGH AFFINITY for the dispersion medium
• Disperse to form SOLS with ease
  
  • (acacia / gelatin in water)
• Usually large organic molecules
  
  • proteins / nucleic acids / carbs
• Molecules are Solvated
• Viscosity of dispersion medium Increased greatly
  
  • –> can form gels
• Stable to all but very high conc of electrolytes

Question 7

LyoPHOBIC Colloids

(solvent-hating)

Answer 7

• Consist of particles that have poor afinity for dispersion medium
• Disperse with relative difficulty & consist of inorganic particles
  
  • Gold/silver/sulfur​
• Viscocity does not change much
• Unstable in presence of even small amounts of electrolytes

Question 8

Association Colloids

Answer 8

• Consist of particles formed by amphiphilic substances
  
  • SURFACTANTS
  • Aggregate to form MICELLES when CMC is exceeded
    
    • ~5nm (50A*) so it is a COLLOID
• ​​Surface tension changes abruptly @ CMC
• Electrical conduction and osmotic pressure also change @CMC
  
  • –> how you distinguish between SOLUTION and COlloidal DISPERSION

Question 9

Faraday Tyndall Effect

Answer 9

When light passes through a COLLOIDAL SOLUTION

some light is scattered by invisible pathway so you can see the light

Reveals that they are not completely transparent

Exhibit TURBIDITY

turbidity can be measured and is related to partcle size

Question 10

Raleigh Light Scattering

Answer 10

arises from the interaction of light with individual atomsof small-scale

like the faraday-tyndall scattering but with light not colloids

gives atmosphere its blue color

Question 11

Brownian Motion

Answer 11

Describes the random movement of particles dispersed in a medium

due to the bombardment of particles by thermally agitated molecules in the dispersion medium

~5um diameter particles

Explains how particles spontaneously diffuse through the medium

Question 12

Fick’s First Law

Answer 12

Applies to the diffusion of colloidal particles through the dispersion medium

Mass flow per unit area per unit time

Question 13

Stokes-Einstein Equation

D

Answer 13

• Studies the diffusion particles of colloidal dispersion
  
  • Viscosity
  • Absolute temp
  • particle weight
• ​Increase diffusion by:
  
  • Increasing temp
  • decreasing VISCOCITY

Question 14

Osmotic Pressure (pi)

Answer 14

Increasing Temperature –> Increases Osmotic Presure

Is effected by colloidal dispersions

Question 15

Stoke’s Law

Answer 15

Higher gravitational force is needed to cause colloidal particles to SEDIMENT

velocity density viscocity in a gravitational field

Question 16

Sedementation

in colloidal dispersions

Answer 16

Ultracentrifuge can be used to generate the High gravitational fields needed to sedement the particles

Heavier/larger => sedement faster

High Viscoscity => slow sedementation

Question 17

Viscoscity

Answer 17

Critical to controlling sedementation rate

Particle Shape influences Viscosity

-rod/thread shaped particles INCREASE VISCOSITY

sphericle particles have little effect on viscosity

Making a colloidal dispersion of something –> INCREASES VISCOSITY

Question 18

Viscosity can help determine what?

Answer 18

Molecular weight of molecules that form LYOPHILIC colloidal dispersions

Question 19

Electric Double Layer

Answer 19

• POSITIVE CATIONS (1st line) OFFSETTED by:
  
  • 2nd Layer of NEGATIVE ANIONS
    
    • –> edge (shear plane) comes after that
• Tightly bound layer containing tightly bound solvent molecules
  
  • • off-setting anions
• Also a looseley defined region containing the rest of the off-setting anions
  
  • +extra anions/cations
• Thermal energy keeps the bulk solution well mixed
  
  • Charge balance with the surface –> electroneutrality

Question 20

Zeta Potential

Answer 20

Potential @ the Shear (Edge) Plane

• Net Positive or Negative Zeta Potential
  
  • –> Repel Each other
  • Colloidal dispersions will stay dispersed
  • ~coarse dispersions will sediment slowly
• ​Zeta potential ~ ZERO
  
  • ​–> no repulsive forces
  • particles can FLOCCULATE (coalesce)
    
    • ​due to brownian motion

Question 21

Flocculation

= Coalescense / clump

Answer 21

• Occurs when Zeta Potential is LOW (close to zero)
  
  • Coagulation becomes easier
  • since there are less repulsive forces to overcome attractive forces
• Colloidal dispersions might sediment
  
  • ​You do not want flocculation in colloidal dispersion
  • hard to redisperse
• Coarse dispersions will too, but will easily disperse with agitation
  
  • Flocculation is a Good thing for coarse dispersions

Question 22

Electrokinetic Phenomena

Answer 22

Movement of a charged surface w/ respect to a bulk liquid

underlies 4 related phenomena:

Electrophoresis

ElectroOSMOSIS

Sedementation Potential

Streaming Potential

Question 23

Electrophoresis

Answer 23

Involves the movement of charged particles through a liquid

under the influence of an applied electrical potential difference

Technique to Seperate macrromolecules (lyophilic colloids)

Rate determining potential is ZETA POTENTIAL of particle

Question 24

Electroosmosis

Answer 24

Opposite of electrophoresis

Solid is IMMOBILIZED and the fluid is allowed to flow through a

membrane/porous structure

Can be used to obtain Zeta Potential measurements

Question 25

**Sedementation Potential**

Answer 25

**Backwards of electrophoresis** When **charged particles** **sediment** in a gravitational field, the movement of the charges **creates an electrical potential difference**

Question 26

**Streaming Potential**

Answer 26

Potential created when **external pressure** is used to force a liquid containing charged particles through a **semipermeable membrane** to **allow only the passage of the liquid** **Electric Potential Difference = Streaming Potential**

Question 27

**Donnan Membrane Equilibrium**

Answer 27

Used experimentally as a way to enhance absorption of **permeable drugs across GI tract membrane** by co-administering an **impermeable charged excipient**

Question 28

**Physical Stability of Colloids**

Answer 28

* Presence/absensce of **Charge** on sthe surface of colloidal particles is a key factor * **Brownian motion** will result in **flocculation** * if LOW/Zero Zeta potential * Expecially problomatic for **Lyophobic colloids** * **​****Ions disrupt the electric double layer** * **Salts** will reduce zeta potential * --\> agglomeration/precipitation * **Mixing two EQUAL AMOUNTS of colloidal dispersions w/ OPPOSITE charged particles** * **​--\>** leads to **COAGULATION =** a **COACERVATE** * **​​**physical incompatibility * *if not equal, LARGE EXCESS --\> stablize some formulations*

Question 29

**Solubilization of Drugs by Surfactants**

Answer 29

Three distinct regions within micelles that solubilize drugs: * **Hydrophobic core** * **​** --\> dissolves NONPOLAR DRUGS * **Region closer to polar heads** * **​** --\> SEMIPOLAR drugs are attracted to this region * **Palisade Region** (polar head group themselves) * --\> POLAR DRUGS adsorb to this area

Question 30

**Factors affecting solubilization by surfactants**

Answer 30

* Solubilization capacity varies with: * **Type of Surfactant** * **Location within the micelle of the dissolved drug** * **​Long hydrocarbon chains** in **Anionic Surfactants (up to C16)** * ​promote solubilization of non-polar drugs * non-ionic surfactants are less effective * **Solution pH** effect ionization state * **Uncharged form** is **More** readily solubilized * in interior hydrophobic part of micelle

Question 31

**Kraft Point**

Answer 31

**Critical temperature** that a solution has to reach for **micelle formation by surfactants** * **Above krafft temperature:** * **​**solubility of surfactant rises sharply * excess dissolved surfactant --\> **forms Micelles** * **​***Below Kraft temp:* * *​excess solid crytalline remains in equilibrium*

Question 32

**Cloud Point**

Answer 32

*many NONIONIC surfactants decrease in solubility as solutions are heated* As temperature rises to CLOUD POINT**,** **phase seperation --\> 2 immiscible liquid phases begin** 1 phase is **mostly solvent** Other phase is **mostly liquid surfactant**

Question 33

**Liposomes**

Answer 33

* Artificial cells consisting of: * **Lipid Bilayers** * **​****aphoteric lipids (**lecethins) that are found in cell membranes * Most liposomes are the **same size range as colloids** * have same usual properties

Question 34

**Micelle Delivery Systems**

Answer 34

* Most common systems are based on **Nonionic Surfactants** * **Pluronic Block Copolymers** * Widely used to deliver poorly soluble small molecule drugs * As well as to stabilize/solubilize macromolecules * such as proteins and nucleic acids

Question 35

**Nanoparticles**

Answer 35

* Colloidal particles consisting of a **thin polymer film surrounding a liquid/solid core** * **Solid lipid nanoparticles** * deliver drugs topically or cosmetics * size is similar to **viruses** * Been tested as **gene delivery systems**