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skincare > Viscosity Control > Flashcards

Viscosity Control Flashcards

1
Q

Two primary purposes of adding thickeners

A
  • Enhancement of product form/aesthetics/application properties
  • Product Stability
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2
Q

Flow properties are determined by

A
  • particle-particle interaction
  • association structure disturbances
  • polymer behavior in solution
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3
Q

Define rheology

A

How materials deform or flow in response to external forces

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4
Q

Define shear stress

A

External force applied over area

Pa = N/m^2

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5
Q

Define shear rate

A 
velocity gradient (1/sec) 
HOW FAST
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6
Q

Define shear strain

A

Relative displacement

HOW FAR

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7
Q

Define viscosity

A

Measure of a material’s resistance to flow

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8
Q

Newtonian shear

A

linear response of flow rate to shear stress

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9
Q

Pseudoplastic refers to ______ rheology

A

Shear thinning

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10
Q

Dilatant refers to _________ rheology

A

Shear thickening

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11
Q

Thixotropic refers to _______ rheology

A

Shear thinning with time dependence

Slower return to original state

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12
Q

Thickening agents in external water phase in O/W emulsions

A

Hydrocolloids

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13
Q

Thickening agents in lipid phase in O/W emulsions

A
  • Co-emulsifiers

- Solid amphiphiles that form liquid crystalline gel networks

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14
Q

Factors governing O/W emulsion viscosity

A
  • Thickeners in water phase
  • Thickeners in lipid phase dispersed in water phase
  • Phase volume (Ratio—-Volume of dispersed phase: volume of continuous phase)
  • Lipid composition of internal phase
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15
Q

Examples of synthetic polymer thickeners

A
  • acrylates
  • carbomers
  • polyurethanes
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16
Q

Carbohydrates/plant/algal thickeners

A
  • Xanthan gum
  • Alginates
  • Scleroglucan
  • Carrageenan
  • Guar
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17
Q

Example of fermentation derived microbiological by-product thickeners

A

Gellan-exopolysaccharide from Sphingomonas elodea

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18
Q

Cellulose derivative thickeners

A

Carboxymethylcellulose

Hydroxyethylcellulose

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19
Q

Examples of smectite clay thickeners

A
  • Bentonites

- Hectorites

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20
Q

Dramatic viscosity increase occurs past the Critical Overlap Concentration due to

A

interaction of polymer molecules to form interpenetrating networks in the solvent

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21
Q

Associative rheology modifiers control rheology by

A

Association with:

  • itself
  • surfactant micelles
  • water dispersible clays
  • emulsified solvent phase
  • dispersed solids
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22
Q

Nonassociative rheology modifiers control rheology by

A

chain entanglement of lightly cross-linked polymer molecules

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23
Q

Liquid Dispersion polymers used as self-emulsifying system consist of

A

Polymer thickener (anionic/cationic/nonionic)
Emollient Solvent
Nonionic emulsifier

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24
Q

What portion of Agar is Agarose

A

neutral gelling portion separated from sulfate non-gelling portion

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25
Q

What is agarose polymer made of

A

galactose and anhydrogalacose

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26
Q

Agarose gels are ___________ and are hydrated at _____ temperatures

A

thermoreversible

high

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27
Q

Agarose is derived from

A

Rhodophycae

28
Q

Alginic Acid is derived from

A

Laminaria, Macrocystis, brown seaweeds

29
Q

Acid sugars making up algal polysaccharides

A

Mannuronic, Guluronic

30
Q

Form of alginic acid that acts as thickener

A

Sodium/Potassium alginate

31
Q

Algin-derived thickeners exhibit __________ rheology, _____ sensitivity to heat, and _______ yield value

A

pseudoplastic shear thinning
high
little

32
Q

Anionic forms of alginic acid complex with _______ to form _________

A

Divalent calcium ions

rigid gels

33
Q

Having a high yield value leads to

A

increased stability at room temperature

34
Q

Water swellable clays have ______ rheology

A

thixotropic

35
Q

High solids dispersions tend to have ______ rheology

A

dilatant

36
Q

What type of measurements does a viscometer give

A

Single point

37
Q

What do rheometers measure

A

Give shear stress at a controlled shear rate

38
Q

_______ phase is most important in finished product viscosity

A

Outer

39
Q

Co-emulsifiers give

A

liquid gel network

40
Q

Silicas work as thickeners by

A

hydrogen bonding

41
Q

Hydrophobically modified polymers will act as thickeners by

A

associating with other hydrophobic materials OR have intermolecular bonding with other ingredients in solution

42
Q

Which inorganic rheology modifier can also work in organic media

A

silica

43
Q

greatest fault of carbomers

A

salt sensitivity

44
Q

What is required for anionic polymers?

A

They must be neutralized with equivalent weight

45
Q

What is difficult about carbomers once they have been neutralized?

A

Hard to thin out

46
Q

Neutralizing Carbopol and Pemulen polymers in aqueous and hydroalcoholic solutions has this result

A

Hydroxyl groups associate to form cross links

Too much salt can break down the structure though

47
Q

Describe the process of creating a liquid dispersion polymer

A
  • Disperse polymer in liquid
  • add in HLB emulsifier
  • this thickens the water and inverts the emulsion
48
Q

Croda’s Liquid dispersion polymers

A
  • Polyacrylate polymers dispersed in carrier oil with an inverting surfactant
  • Add to water–> turns into a w/o emulsion
  • Polyacrylate molecules swell by osmosis, thickening the water phase
49
Q

The three forms of Carrageenan depend on

A

levels of sulfation

50
Q

Chitosan is a ________ polymer

A

cationic

51
Q

Chitosan can be used for ________

A

coacervation encapsulation

52
Q

Scleroglucan has ______ rheology

A

pseudoplastic

53
Q

Locust Bean Gum retards ice crystal growth by

A

forming structured gel at solid/liquid interface for freeze/thaw stabilization

54
Q

Gellan comes from

A

bacterium

55
Q

Xanthan gum exhibits ______ rheology

A

shear thinning

56
Q

______ are used in the scale-up process for processing gums

A

Eductors

57
Q

Microcrystalline cellulose is a product of

A

partial cellulose depolymerization by mineral acid

58
Q

Microcrystalline cellulose colloidal dispersion acts as

A

emulsion stabilizer

59
Q

CMC is used as a

A

dispersion agent

60
Q

Polyquaternium-10 consists of

A

cationic group attached to hydroxycellulose

61
Q

Smectite clays can be used in low levels due to

A

synergy with organic thickeners

62
Q

Synthetic polymers are synthesized with

A

free radical initiators

63
Q

Synthetic polymers are ________ likely to be sensitive to salt and pH than natural gums

A

more

64
Q

Thickeners for anhydrous systems

A
  • Aluminum Stearate
  • Trihydroxystearin
  • SiO2
  • Organoclays
  • Polyethylene
65
Q

Quat-18 is derived from

A

tallow

66
Q

fatty quats react with smectite clay to

A

replace monovalent anions between clay platelets

67
Q

Organic solvents have this effect on organoclays

A

interstitial space swelling

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