TOPIC 9A Colloidal Systems Flashcards
macroemulsion particle size
0.2-50 mm
microemulsion particle size
0.01-0.2 mm
emulsion type depends on
nature of emulsifying agent
type of emulsifier for O/W
hydrophilic (high HLB 8-18)
type of emulsifier for W/O
hydrophobic (low HLB 3-6)
type of emulsifier for W/Si
hydrophobic (low HLB) 3-6)
advantages of O/W emulsion (4)
● good skin spreadability and penetration with active hydration by water
● non-greasy, light feel, easily removable
● cooling effect (water evaporation)
● easy to formulate and low cost
disadvantages of O/W emulsion (3)
● not as effective for dry skin bc less emolliency and nourishment delivered
● not water-resistant
● lesser active concentration
advantages of W/O emulsion (3)
● most effective for dry skin bc more emolliency and nourishing purposes
● water-resistant
● precisely tailored to needs with wide choice of ingredients
disadvantages of W/O emulsion (4)
● greasy, oily, tacky feel
● not washable with water
● less stable due to lack of double layer effect
● more expensive ingredients, harder to manufacture and clean up
clear micro-emulsions are called solubilised systems because …
macroscopically they behave like true solutions
they have globule radius within 10-50 nm
three (3) tests for emulsion types
- dilution test
- dye test
- conductivity measurement
dilution test
water added slowly into emulsion
● if distributed uniformly, water is cont. phase (O/W)
● if separate out as a layer, water is dispersed phase (W/O)
dye test
malachite (green, water-soluble) and sudan III (red, oil-soluble) dyes added
● if readily coloured by green, water is cont. phase (O/W)
● if readily coloured by red, oil is cont. phase (W/O)
conductivity measurement
apply small electrical charge between 2 terminals immersed in emulsion connected to light bulb
● if bulb glows, water is cont. phase (O/W)
● if bulb does not glow, oil is cont. phase (W/O)
characteristics of effective emulsifiers (3)
● good surface activity
● able to form condensed interfacial film
● rate of adsorption to interface comparable to emulsion forming time
rules (2) in choosing emulsifier
- RHLB-HLB matching: RHLB (required HLB) should approximate HLB value
- surfactant blends
● blends give better interface coverage = better stability
● blends from same parent chain = best synergy
● chemical type of surfactant
why pair emulsifiers
allows more surfactants to pack at oil-water interface and lower interfacial tension for more stable emulsion
chemical type of surfactant is related to
attraction of lipophilic group in emulsifier to lipophilic material with which emulsifier is being used
emulsifiers with unsaturated alkyl chains eg. oleyl chains have an increased affinity for …
oils with unsaturated bonds eg. vegetable oils
emulsifiers with saturated alkyl chains have an increased affinity for …
oils with saturated bonds eg. mineral oil
four (4) stages in emulsifier selection
- select required HLB range by calculating RHLB value for oil-phase components
- select emulsifier systems and consider chemical type
- select blending ratio to match HLB
- prototyping stage: make a series of formulations varying total emulsifier dosage (using same blending ratio)
two (2) steps in emulsification process
- rapid breaking of internal phase into droplets by agitation
- stabilisation of droplets
for hot process, why must oil and water phases be heated to same temperature (what happens if not)
to ensure stability
● if not, emulsifiers / co-emulsifiers may solidify when it meets lower temperature and precipitate out
● results in particulates in formulation and affects stability
high energy method (hot process) of emulsification (O/W macroemulsion) (5)
- both oil and water phases heated to around 75-80 deg C
- oil mixed into water
- energy supply breaks down both phases and disperses oil into water in fine droplets
- (opt) homogenisation for 1-3 min to achieve finer droplets
- cool down under slower speed to eliminate air entrapment
physical parameters affecting droplet size distribution, viscosity, and emulsion stability (6)
● agitation speed and time
● location of emulsifier
● quantity of total emulsifiers used
● method of incorporation of phases
● rate of addition
● temperature of each phase and rate of cooling after mixing phases
what to watch out for with agitation speed and time
long enough for sufficient breakdown into smaller droplets but avoid over-agitation during and after emulsion formation as it may cause coalescence
three (3) options to incorporate emulsifier in formulation
● all emulsifiers in oil phase
● divide 2/3 in oil phase and 1/3 in water-phase
● high HLB in water-phase, low HLB in oil-phase (most common)
smaller droplets need _____ total dosage of emulsifiers
higher dosage of emulsifiers
(to ensure sufficient encapsulation)
two (2) methods of incorporation of phases for O/W emulsion
- standard: addition of internal oil phase to external water phase
- phase inversion by volume technique: add water to oil first (lesser mechanical action)
advantage (1) of phase inversion technique
allows formation of smaller droplets with lesser mechanical action
limitation (1) of phase inversion technique
production equipment limitation
important thing to note about rate of addition of water phase into W/O emulsions
water phase must be added slowly for better stabilisation of emulsion
common temperature heated to in hot process
75-80 deg C
how does cooling rate (hot process) affect emulsion
gradual cooling gives time for better alignment of emulsifier; sudden cooling can result in low viscosity
what is phase inversion
phenomenon where phases of W/O dispersion interchange spontaneously from W/O to O/W
two (2) approaches to phase inversion
- by volume
- by temperature (typically for ethoxylated non-ionic emulsifiers)
what happens near / at inversion point for phase inversion by volume
water droplets begin to coalesce and emulsion inverts upon any small further addition, entrapping oil phase
where does viscosity peak during phase inversion by volume
inversion point
phase inversion by temperature emulsification can be used when
● O/W emulsion
● stabilised by ethoxylated non-ionic surfactant
phase inversion by temperature emulsification process (4)
- when temp increases, water solubility of O/W emulsifier decreases = CMC and HLB decreases
- when temp increases beyond cloud point, emulsifier precipitates, causing separation with now insoluble emulsifier and water into oil phase
- low-viscosity W/O emulsion is formed containing water droplets in continuous oil phase
- during cooling stage, HLB of O/W emulsifier increases as water solubility increases back. once phase inversion temperature is attained, W/O inverts back to O/W
what is phase inversion temperature?
PIT is the temperature at which the emulsion inverts from water-in-oil to back to oil-in-water. It is the temperature at which the hydrophilic and lipophilic properties of the emulsifier are in balance and is therefore also called HLB temperature.
what is observed at phase inversion temperature
viscosity increases
advantage of phase inversion by temperature emulsification method
smaller droplet O/W emulsion formed
what to note for phase inversion by temperature method
must heat to ABOVE phase inversion temperature so it can cool down to phase inversion temperature
process (3) for determining phase inversion temperature experimentally
- weigh 200g of emulsion in beaker and heat it at 1°C / min
- adjust stirring speed to get a 1cm deep vortex
- record the temperature at which vortex disappears
how does phase inversion temperature affect stability
PIT is inversely proportional to rate of droplet coalescence
(so if PIT is high, rate of coalescence is low = more stable!)
ideal PIT
20 deg C higher than storage temperature
properties of W/Si emulsion (2)
● silicone emulsifiers only (high or low shear)
● water phase added slowly into oil phase
why is low shear emulsifier preferred for W/Si emulsions
lesser energy required for dispersion
what to note for formulating with silicone emulsifiers (2)
● silicone emulsifiers are nonionic
● silicone emulsifiers have optimum range for silicone oil content
cetyl dimethicone copolyol (Abil EM 90) (silicone emulsifier) optimum oil-phase content range
22-35%
Lauryl PEG-10 Tris(trimethylsiloxy)silylethyl Dimethicone (Dowsil ES-5300) optimum oil-phase content range
min. 5% (can take high level of water phase to form HIPE)
properties of W/O emulsion
● oil phase is mixture of oil and silicones
● emulsifier can be silicone or non-silicone
for W/O, increasing water phase ratio will (2)
● increase viscosity
● decrease gloss
how to increase viscosity of W/O cream (3)
● increase water phase ratio
● incorporating occlusive emollients eg. petrolatum, DISM, DISD
● incorporate emulsion stabilising waxes eg. hydrogenated castor oil, beeswax, hydrocarbon waxes
examples of occlusive emollients (3)
● petrolatum
● DISM
● DISD
what should be added to stabilise W/Si or W/O (2)
and exceptions!
● 2-5% w/w glycerine
● 0.5% w/w NaCl or MgSO4 (heptahydrate)
except for
● Dowsil 5225C and ES5300: 1-2% w/w NaCl
● EasyNov no need NaCl
key ingredients of hyper internal phase emulsion (HIPE) using geltrap technology (2)
● non-silicone W/O emulsifier (EasyNov)
● Sepiplus 400 (emulsifier + thickener for water phase)
advantage of HIPE emulsion
rich sensory feel without heavy or greasy afterfeel
how to increase viscosity of HIPE (geltrap) (2)
● increase dispersion speed
● replace lower viscosity oils with higher viscosity oils
what is liquid crystal emulsion (LCE) (3)
● O/W emulsion
● 3D association structures that stabilise emulsions
● can refract and reflect polarised light and hence exhibit birefringence under polarised light microscope (looks like cabbage)
impact of increasing surfactant concentration on LCE
formation of larger aggregates (liquid crystals)
lamellar gel network effect on stability of emulsion (2)
● barrier to coalescence and prevents emulsion breakdown
● when liquid crystals extend from surface of droplets to bulk of external phase, viscosity increases
advantages of liquid crystal emulsion (2)
● enhanced stability
● prolonged moisturisation effect
how does liquid crystal emulsion provide prolonged moisturisation effect (2)
● structure of LCE is similar to skin = enhanced affinity with skin
● offers better absorption and counters water evaporation
how to achieve liquid crystal emulsion in formulation (3 ingredients)
● nonionic emulsifier pair
● fatty alcohol (co-emulsifier)
● fatty acid (optional co-emulsifier)
ingredient: Brij S2
low HLB nonionic emulsifier
ingredient: Brij S721
high HLB nonionic emulsifier
ingredient: Lubrizol Chemonic OE-2
low HLB nonionic emulsifier
ingredient: Lubrizol Chemonic OE-20
high HLB nonionic emulsifier
ingredient: Glucate SS
low HLB nonionic emulsifier
ingredient: Glucamate SSE
high HLB nonionic emulsifier
things to note during heating and cooling to form LCE (3)
● water and oil phase should be heated to same temperature and must be fully melted
● maintain temperature for 10-15 min after mixing
● gradual cooling down
key benefits of LCE in cosmetic formulation (6)
● increased stability against coalescence and creaming
● prolonged skin hydration
● varying skin feel due to structuration of emulsion
● enhanced water resistance
● controlled release of actives
● pH flexibility and salt tolerance (since emulsifiers are nonionic)
benefits of multiple emulsions (2)
● controlled / sustained release of actives
● protection of sensitive actives from external phase
process of preparation of W/O/W emulsion (4)
- prepare primary W/O emulsion: add water phase dropwise to oil phase with lipophilic (low HLB, W/O) emulsifier.
- homogenise at high shear rate (8000-10000 rpm)
- pour primary W/O emulsion into another aqueous solution containing hydrophilic (high HLB, O/W) emulsifier
- homogenise at low shear (to obtain larger droplet)
problems with multiple emulsion (2)
● settling, coalescence bc of large droplets
● phase separation
