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PHRM 513 > Semisolid dosage forms and rheology part II > Flashcards

Semisolid dosage forms and rheology part II Flashcards

1
Q

rheology

A

The study of flow and deformation of matter

-Addresses the viscosity characteristics of a material

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2
Q

The study of flow and deformation of matter

-Addresses the viscosity characteristics of a materia

A

An expression of the resistance to flow; the higher the viscosity, the
greater the resistance

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3
Q

The unit of viscosity is

A

the poise (p)

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4
Q

Viscosity is involved in

A

the mixing and flow of materials, their packaging into containers
and their removal prior to use, and can affect patient acceptability, physical
stability and even biological availability

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5
Q

Rheology

• Materials divided into two general categories:

A
  1. Newtonian flow

2. Non-Newtonian flow

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6
Q
  1. Newtonian flow
A

•Characterized by constant viscosity, independent of the shear rates applied
• Material can be defined by a single viscosity at a specific temperature
• Direct proportionality between shearing stress and rate of shear
➢ Examples: Water and mineral oil

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7
Q
  1. Non-Newtonian flow
A

Characterized by a change in viscosity with increasing shear rate
• Materials cannot be defined by a single viscosity at a specific temperature
• May be time dependent
• The majority of fluid pharmaceutical products are non-Newtonian systems
➢ Examples: Liquid and solid heterogeneous dispersions such as colloidal solutions,
emulsions, liquid suspensions and ointments

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8
Q

Rate of shear* (G) is the

A

difference of velocity (dv) between two planes of liquid separated by an infinitesimal distance (dr)
➢ G = dv/dr

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9
Q

Shearing stress (F) is the

A

force (F’) per unit area (A) required to bring about flow

➢ F = F’/A

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10
Q

*Shear

A

To cause to move along the plane of contact

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11
Q

Higher the viscosity of a Newtonian liquid, the

A

greater is the shearing stress required to produce a certain rate of shear

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12
Q

F′/A = n(dv/dr), where n =

A

viscosity coefficient or viscosity

➢ More simply, n = F/G

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13
Q

Poise (p)

A

The shearing force required to produce a velocity of 1 cm/s between two parallel planes of liquid each 1 cm2
in area and separated by a distance of 1 cm
➢ g/cms

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14
Q

Capillary viscometer

A

-Time of flow of liquid under test is compared with the time
required for a liquid of known viscosity to pass between two
marks
- Can be used to determine the viscosity of a Newtonian
material, with the following relationship: n = ktp

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15
Q

Kinematic viscosity =

A

n/p, where n is the absolute viscosity and p is the density of a liquid at a specific temperature, and its units are the stoke (s)
‒ Used in the USP and NF

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16
Q

Viscosity of a liquid

increases or decreases when temp is raised?

A

decreases as temperature is raised

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17
Q

What equation shows dependence of viscosity of liquids on temperatre

A

Modified Arrhenius equation
n = AeEv/
RT, where A is a constant depending on the molecular weight and molar
volume of the material, Ev
is an activation energy required to initiate flow, R is the
gas constant and T is temperature

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18
Q

Non-Newtonian materials

A

Plastic
Floc
Pseudoplastic
DIlatant

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19
Q

Plastic

A

Flow does not begin until a shearing stress corresponding to a certain
yield value is exceeded
-The flow curve intersects the shearing stress axis and does not pass
through the origin
• Material is elastic below the yield value
• Associated with the presence of flocculated* particles in concentrated
suspensions
• A yield value exists because of the contacts between adjacent particles
(brought about by van der Waals forces), which must be broken before flow
can occur

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20
Q

In plastic, Once the yield stress is exceeded,

A

, it flows like a Newtonian material

21
Q

Materials that exhibit this type of behavior : Plastic non-newtonian materials

A

are called Bingham bodies

22
Q

*Floc

A

A loose aggregation of particles held together by weak bonds

23
Q

Loose structure of particlaes permits them to

A

break up easily and distribute readily with a

small amount of agitation

24
Q

*Floc prevents

A

the rigid cohesion of small particles of a suspension, which leads to formation of a solid cake

25
Q

Pseudoplastic

A

There is no yield value as there is in a plastic system
– “Shear-thinning”
– Viscosity decreases with increasing shear rat
-

26
Q

Increased shear rate deforms or rearranges particles, resulting in

A

lower flow resistance

27
Q

Example of pseudoplastic

A

Polymeric solutions exhibit this type of flow

28
Q

For pseudoplastic, As shearing stress in increased

A

normally disarranged molecules begin

to align their long axis in the direction of the flow

29
Q

Dilatant

A

Type of flow is the inverse of that possessed by pseudoplastic systems
– “Shear-thickening”
– Viscosity increases with increasing shear rate

30
Q

dilatant is characterized

A

by having a high percentage of deflocculated particles in

the formulation

31
Q

Deflocculated system of titanium dioxide in water exhibits

A

dilatant flow

32
Q

In Newtonian systems, when the rate of shear is reduced

A

the down curve is

super imposable on the up curve

33
Q

In non-Newtonian systems, the down curve can be

A

displaced relative to the

up curve

34
Q

Thixotropy

A

An isothermal and comparatively slow recovery, on standing of a material, of a consistency lost through shearing
-can be applied only to shear-thinning systems

35
Q

Thixotropy are desirable in

A

pharmaceutical systems – Pour and spread easily, but have a high consistency in its container

36
Q

Thixotropy consistency?

A

Material has a lower consistency at any one rate of shear on the down curve than it had on the up curve

37
Q

Antithixotropy

A

Increase rather than a decrease in consistency on the down

curve

38
Q

Antithixotropy -Example in a pharmaceutical system

A

Milk of magnesia at shear rates greater

than 30 sec-1 ; below a shear rate of 30 sec-1 , the magma shows normal thixotropy

39
Q 
Which of the following ointment bases provides the greatest degree of
occlusion?
A. Oleaginous
B. Absorption
C. Water-removable
D. Water-soluble
A

A. Oleaginous

40
Q 
Which of the following ointment bases contains no oleaginous
components?
A. Oleaginous
B. Absorption
C. Water-removable
D. Water-soluble
A

D. Water-soluble

41
Q

A water-in-oil emulsion that permits incorporation of additional
quantities of aqueous solutions is considered what type of base?
A. Oleaginous
B. Absorption
C. Water-removable
D. Water-soluble

A

✓B. Absorption

42
Q

Which of the following is a factor in the selection of an appropriate
ointment base?
A. Desired release rate of the drug substance from the ointment base
B. Stability of the drug in the ointment base
C. Characteristics of the surface to which it is applied
D. All of the above

A

D. All of the above

43
Q

Which of the following statements about the preparation of ointments
via the incorporation method is NOT true?

A

C. The components are melted together

44
Q

Which of the following statements is NOT true of Newtonian systems?
A. They are characterized by a constant viscosity, independent of the
shear rates applied
B. There is direct proportionality between shearing stress and rate of
shear
C. The majority of fluid pharmaceutical products are this type of
material
D. They can be defined by a single viscosity at a specific temperature

A

C. The majority of fluid pharmaceutical products are this type of
material

45
Q 
As the temperature is raised, the viscosity of a Newtonian liquid does
what?A. Increases
B. Decreases
C. Remains the same
D. It is dependent on its yield value
A

✓B. Decreases

46
Q 
In which of the following systems does viscosity increase with
increasing shear?
A. Plastic
B. Pseudoplastic
C. Dilatant
D. None of the above
A

C. Dilatant

47
Q

Which of the following statements is true of thixotropy?
A. It refers to the recovery of viscosity in time when flow is discontinued
B. It is applied only to shear-thinning systems
C. It is desirable in pharmaceutical systems
D. All of the above

A

✓D. All of the above

48
Q

Plastic flow is associated with the presence of flocculated particles in
concentrated suspensions. What is a floc?
A. A solid cake of particles
B. A loose aggregation of particles
C. Component of a two-phase gel system
D. Both B and C

A

D. Both B and C

PHRM 513 (13 decks)

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