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Ceutics Midterm 2 > Disperse Systems: Colloids 5/6 > Flashcards

Disperse Systems: Colloids 5/6 Flashcards

1
Q

Molecular Dispersion

A

Less Than < 1nm (10A*)

Invisible by electron microscopy

Pass through ultrafilter/semipermeable membrane

Rapidly diffuse through medium

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2
Q

Colloidal Dispersion

A

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

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3
Q

Coarse Dispersion

A

500nm - 1mm

Visible by microscopy or even naked eye

do not pass through normal filter paper

Do not diffuse through medium

–> aerosols

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4
Q

Cow’s Milk

A

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

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5
Q

What Do Colloids look like?

A

Many different shapes

Threads –> entagled

Form structure –> Gels

JELLY = colloidal dispersion

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6
Q

Lyophilic Collods

(solvent Loving)

A
  • 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
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7
Q

LyoPHOBIC Colloids

(solvent-hating)

A
  • 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
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8
Q

Association Colloids

A
  • 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
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9
Q

Faraday Tyndall Effect

A

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

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10
Q

Raleigh Light Scattering

A

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

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11
Q

Brownian Motion

A

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

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12
Q

Fick’s First Law

A

Applies to the diffusion of colloidal particles through the dispersion medium

Mass flow per unit area per unit time

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13
Q

Stokes-Einstein Equation

D

A
  • Studies the diffusion particles of colloidal dispersion
    • Viscosity
    • Absolute temp
    • particle weight
  • ​Increase diffusion by:
    • Increasing temp
    • decreasing VISCOCITY
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14
Q

Osmotic Pressure (pi)

A

Increasing Temperature –> Increases Osmotic Presure

Is effected by colloidal dispersions

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15
Q

Stoke’s Law

A

Higher gravitational force is needed to cause colloidal particles to SEDIMENT

velocity density viscocity in a gravitational field

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16
Q

Sedementation

in colloidal dispersions

A

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

Heavier/larger => sedement faster

High Viscoscity => slow sedementation

17
Q

Viscoscity

A

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

18
Q

Viscosity can help determine what?

A

Molecular weight of molecules that form LYOPHILIC colloidal dispersions

19
Q

Electric Double Layer

A
  • 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
20
Q

Zeta Potential

A

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
21
Q

Flocculation

= Coalescense / clump

A
  • 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
22
Q

Electrokinetic Phenomena

A

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

underlies 4 related phenomena:

Electrophoresis

ElectroOSMOSIS

Sedementation Potential

Streaming Potential

23
Q

Electrophoresis

A

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

24
Q

Electroosmosis

A

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

25
Q

Sedementation Potential

A

Backwards of electrophoresis

When charged particles sediment in a gravitational field,

the movement of the charges creates an electrical potential difference

26
Q

Streaming Potential

A

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

27
Q

Donnan Membrane Equilibrium

A

Used experimentally as a way to enhance absorption

of permeable drugs across GI tract membrane

by co-administering an impermeable charged excipient

28
Q

Physical Stability of Colloids

A
  • 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
29
Q

Solubilization of Drugs by Surfactants

A

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
30
Q

Factors affecting solubilization by surfactants

A
  • 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
31
Q

Kraft Point

A

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
32
Q

Cloud Point

A

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

33
Q

Liposomes

A
  • 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
34
Q

Micelle Delivery Systems

A
  • 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
35
Q

Nanoparticles

A
  • 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
36
Q
A

Ceutics Midterm 2 (7 decks)

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