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DF21 - 23
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1Examples of colloidal dispersions:
• Used as drug-delivery systems, for example
– [blank_start]Liposomes[blank_end] (0.15 – 0.5 µm)
– [blank_start]Micelles[blank_end] (<100 nm)
– Nanoparticles [blank_start]2 –100 nm[blank_end]- ALiposomes
- BMicelles
- C(2 –100 nm)
- D(1 - 2 µm)
- ERibosomes
23 kinds of colloids:
1. Lyophilic colloids
- Dispersed phase is [blank_start]solvent loving[blank_end] (‘hydrophilic’ if water)
- Significant [blank_start]interaction between[blank_end] the dispersed and the continuous phase
– Form [blank_start]spontaneously[blank_end]
– Thermodynamically [blank_start]stable[blank_end]
2. Lyophobic colloids
- Dispersed phase is [blank_start]solvent hating[blank_end] (‘hydrophobic’)
- [blank_start]Minimal interaction[blank_end] between the dispersed and the continuous phase
– Do [blank_start]not[blank_end] form spontaneously
– Thermodynamically [blank_start]unstable[blank_end] (tendency to aggregate)
3. Association colloids
- Dispersed phase has [blank_start]both solvent hating and solvent loving[blank_end] characteristics
- Form spontaneously (e.g. micelles)
- Individual surfactant molecules are [blank_start]smaller[blank_end] than colloids, but [blank_start]micelles[blank_end] are association colloids- Asolvent loving
- Bsolvent hating
- Cboth solvent hating and solvent loving
- Dinteraction between
- EMinimal interaction
- Fspontaneously
- Gstable
- Hnot
- Iunstable
- Jsmaller
- Kmicelles
3Colloids display the [blank_start]F-T effect[blank_end], meaning you can see a [blank_start]beam of light[blank_end] if you were to shine one through it, whereas coarse dispersions appear [blank_start]opaque or turbid[blank_end] due to [blank_start]scattered[blank_end] light.
- AF-T effect
- Bbeam of light
- Copaque or turbid
- Dscattered
4Colloidal kinetic properties:
– Thermally induced
• [blank_start]Brownian motion and diffusion[blank_end]
– Gravitationally induced
• [blank_start]Sedimentation[blank_end]
– Induced by external application
• [blank_start]Viscosity[blank_end]- ABrownian motion and diffusion
- BSedimentation
- CViscosity
5The velocity, [blank_start]ν[blank_end], of sedimentation of spherical particles (radius, [blank_start]r[blank_end]) having a density, [blank_start]ρ[blank_end], in a medium of density [blank_start]ρ0[blank_end], and a viscosity, [blank_start]η0[blank_end], is given by Stokes’ Law.
- Aη0
- Bρ0
- Cρ
- Dr
- Eν
6Stokes’ law holds for particle sizes < 0.5 µm.
- AVerdadeiro
- BFalso
7Factors affecting the creaming rate in emulsions:
– Droplet [blank_start]size[blank_end]
– Difference in [blank_start]density[blank_end] between the dispersed and continuous phase
– Gravitational [blank_start]force[blank_end]- Asize
- Bdensity
- Cforce
8Stokes’ Law holds exactly only for:
• Spherical particles
– Must [blank_start]not be aggregated[blank_end] or clumped
• Influence of gravity
– [blank_start]Lower size limit: 0.5 µm[blank_end]
• Free fall at constant rate
– Particles must [blank_start]not interfere[blank_end] with one another
• Laminar or streamline flow around particles
– Sedimentation [blank_start]must not cause turbulence[blank_end]- Anot be aggregated
- BLower size limit: 0.5 µm
- CUpper size limit: 0.5 µm
- Dnot interfere
- Emust not cause turbulence
9The drive to aggregate is because molecules of the dispersed phase at their core stable have [blank_start]strong cohesive forces[blank_end] with each other and are at a [blank_start]low energy state[blank_end], while molecules at the interface have [blank_start]low strength adhesive forces[blank_end] between the opposing molecules of the continuous phase. Aggregation makes the dispersed molecules [blank_start]more stable[blank_end].
- Astrong cohesive forces
- Blow energy state
- Clow strength adhesive forces
- Dmore stable
10As surface area increases, Gibb's free energy increases.
- AVerdadeiro
- BFalso
11The DLVO theory applies strictly to [blank_start]hydrophobic colloids[blank_end] only, but helps us understand the stability of [blank_start]coarse dispersions[blank_end].
- Ahydrophobic colloids
- Bcoarse dispersions
12The Electrical Double Layer (EDL) is a model used to understand the electrical behaviour of colloids in contact with solutions. A particle with a [blank_start]charged surface[blank_end] eg positive will be in contact with the first layer, the [blank_start]stern layer[blank_end], which consists of ions of [blank_start]opposite charge[blank_end] eg negative. The second layer is the [blank_start]diffuse layer[blank_end], with ions predominantly still of opposite charge but [blank_start]some[blank_end] of the original charge of the surface which are [blank_start]attracted to[blank_end] ions in the stern layer. The boundary between the diffuse layer and the bulk electroneutral region is called the [blank_start]slipping or shear plane[blank_end].
- Acharged surface
- Bstern layer
- Copposite charge
- Ddiffuse layer
- Esome
- Fattracted to
- Gslipping or shear plane
13Zeta potential decreases as distance from the particle surface decreases.
- AVerdadeiro
- BFalso
14DLVO Theory graphL
• Repulsion curve, VR
– Dependent on [blank_start]ζ-potential and distance[blank_end] (thickness of the double layer) of the particles
• Attraction curve, VA
– [blank_start]Independent[blank_end] of surface charge
– Dependent on [blank_start]chemical nature, size and distance[blank_end] of the particles
• Composite curve, VT
– Net interaction energy = [blank_start]sum of VR and VA[blank_end]- Aζ-potential and distance
- BIndependent
- Cchemical nature, size and distance
- Dsum of VR and VA
15The primary maximum on the DLVO graph:
– double-layer [blank_start]repulsion[blank_end] between particles dominates
– point of [blank_start]maximum[blank_end] repulsive energy
• In the secondary minimum:
– Particles are held together by [blank_start]weak attraction forces[blank_end] (‘Flocs’)
Therefore by changing the [blank_start]zeta-potential[blank_end] (or better: the repulsive forces in
general) it is possible to influence the [blank_start]stability[blank_end] of the dispersion.- Arepulsion
- Bmaximum
- Cweak attraction forces
- Dzeta-potential
- Estability
16We can manipulate the zeta potential with a) [blank_start]electrolyte concentration[blank_end] and b) [blank_start]valency[blank_end] of the counterion. The higher the electrolyte concentration present in
the system, the higher the [blank_start]screening effect[blank_end] of the counterions. The [blank_start]higher[blank_end] the valency of the counterion (eg Na+ vs Mg2+ at a constant total electrolyte concentration) the higher the screening effect.
A higher screening effect means a [blank_start]lower[blank_end] the zeta potential due to [blank_start]double layer compression[blank_end], making agglomeration [blank_start]more[blank_end] probable.- Aelectrolyte concentration
- Bvalency
- Cscreening effect
- Dhigher
- Elower
- Fdouble layer compression
- Gmore
- Hless
17Select all the forces which are non-DLVO.
- AHydration forces
- BVan der waals
- CSteric forces
18• [blank_start]Lyophilic colloids[blank_end] are stabilised by hydration layer → do not tend to aggregate
• [blank_start]Lyophobic colloids[blank_end] are thermodynamically unstable → do tend to aggregate- ALyophilic colloids
- BLyophobic colloids
19Suspensions are thermodynamically stable systems
- AVerdadeiro
- BFalso
20Deflocculated systems:
- [blank_start]Discrete individual[blank_end] particles
- Sediment [blank_start]more slowly[blank_end] and cake [blank_start]irreversibly[blank_end]
Flocculated systems:
- Particles form [blank_start]flocs[blank_end]
- Flocs sediment [blank_start]quickly[blank_end]
- Sediment [blank_start]redisperses[blank_end] easily
- [blank_start]Cost effective[blank_end] in munafacture- ADiscrete individual
- Bmore slowly
- Cirreversibly
- Dflocs
- Equickly
- Fredisperses
- GCost effective
21Properties under control of formulator of suspensions:
– State of [blank_start]flocculation[blank_end]
– [blank_start]Particle size[blank_end] of the dispersed phase
– [blank_start]Viscosity[blank_end] of the continuous phase- Aflocculation
- BParticle size
- CViscosity
22Methods to improve the properties of a suspension:
– Inclusion of viscosity inducing agents ([blank_start]suspending agents[blank_end]) to retain deflocculated particles in suspension
– Encourage [blank_start]flocculation[blank_end]
– Use of [blank_start]viscosity inducing agents[blank_end] to retain flocculated particles in suspension
– Particle [blank_start]size reduction[blank_end] by milling- Asuspending agents
- Bflocculation
- Cviscosity inducing agents
- Dsize reduction
23Which components would you need in the dispersed phase of a suspension? Select all.
- AInsoluble drug
- BWetting agent
- CFlocculating agent
- DSuspending agent
- EPreservatives
- FVehicle
24Surfactants HLB 6-9, alcohol and glycerin are all examples of:
- ALubricants
- BWetting agents
- CPreservatives
- DSuspending agents
25Choose the correct statement.
- AA wetting agent is a compound that when dissolved in water increases the contact angle between the particle surface and the liquid.
- BTweens and spans are surfactants for external use.
- CSodium lauryl sulfate and sodium dioctyl sulphosuccinate are surfactants for oral use.
- DLecithin, poloxamer, and tweens can be used parenterally.
26Controlled flocculation is the state in which attractive and repulsive forces are [blank_start]balanced[blank_end]. Attractive forces must be [blank_start]large enough[blank_end] to cause flocculation. Repulsive forces must be sufficiently high enough to [blank_start]prevent close contact[blank_end] (aggregation), but low enough so that attractive force is [blank_start]dominant[blank_end]
- Abalanced
- Blarge enough
- Cprevent close contact
- Ddominant.
27Which of these is not a flocculating agent?
- ASurfactants
- BPolymers (hydrophilic colloids)
- CElectrolytes
- DAlcohols
28Ionic and non-ionic agents can act as flocculating agents, which [blank_start]adsorb[blank_end] onto the surface of [blank_start]hydrophobic dispersed particles[blank_end]. Non-ionic flocculating agents (eg [blank_start]Hydrophilic colloids[blank_end]) may adsorb on to more than one particle, and [blank_start]link[blank_end] them together in a [blank_start]loosely[blank_end] arranged structure. Ionic flocculating agents (eg [blank_start]Electrolytes[blank_end]) alter the [blank_start]zeta-potential[blank_end]. If sufficiently [blank_start]lowered[blank_end], flocculation occurs.
- Aadsorb
- Bhydrophobic dispersed particles
- CHydrophilic colloids
- DElectrolytes
- Elink
- Floosely
- Glowered
- Hzeta-potential
29Select all the hydrophilic polymers that can aid aggregation and are suspending agents.
- AStarch
- BTragacanth
- CAlginates
- DCellulose derivatives
- EMagnesium stearate
- FPropylene glycol
- GEthanol
30Too much or too little electrolyte will lead to caking.
- AVerdadeiro
- BFalso
31Examples of Natural Suspending Agents:
- Tragacanth
- Sodium [blank_start]Alginate[blank_end]
- Acacia
- [blank_start]Xantham[blank_end] Gum
- [blank_start]Bentonite[blank_end] (aluminium silicate)
- [blank_start]Veegum[blank_end] (magnesium aluminium silicate)
(Above two are clay minerals, which are readily [blank_start]hydrated[blank_end] — absorb up to 12 times their weight of water. Risk of [blank_start]microbial contamination[blank_end].)- AAlginate
- BXantham
- CBentonite
- DVeegum
- Ehydrated
- Fmicrobial contamination
32Examples of Semi-Synthetic Suspending Agents:
Semi-synthetic:
– [blank_start]Methyl cellulose[blank_end]
• Nonionic
• Viscosity increases with molecular weight
– [blank_start]Sodium carboxymethyl cellulose[blank_end]
• Degree of substitution affects solubility
• Viscosity depends on molecular weight
– [blank_start]Microcrystalline cellulose (Avicel)[blank_end]
• Cellulose crystals in colloidal size range
• Disperses readily in water but not water-soluble
• Widely used- AMethyl cellulose
- BSodium carboxymethyl cellulose
- CMicrocrystalline cellulose (Avicel)
33Choose the incorrect statement about the ideal suspending agent.
- AMost suspending agents are either neutral or positively charged.
- BGenerally effective in a concentration range of 1 to 5%
- CEasily and uniformly incorporated into the formulation
- DEasily dissolved or dispersed in water without the need to resort to specialised mixing techniques
- EInert
- FNon-toxic
34Ideal rheological properties of suspensions: high apparent viscosity at [blank_start]low[blank_end] rates of shear, and sufficiently low apparent viscosity at [blank_start]higher[blank_end] rates of shear to allow the suspension to be poured from the bottle. It is important that we get reformation of [blank_start]initially high apparent viscosity[blank_end] after a short time to maintain adequate physical stability.
- Alow
- Bhigh
- Chigher
- Dlower
- Ehigh apparent viscosity
- Flow apparent viscosity
Informações
- Descrição
- PHCY211 (Formulation) Quiz sobre DF21 - 23, criado por Mer Scott em 02-05-2018.
- Autor
- Mer Scott
- Idioma
- English
- Visualizações
- 15
- Etiquetas
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