9/25 Chapter 14

Question 1

Define rhenology

Answer 1

The study of viscosity of a substance. Divided into Newtonian and non-Newtonian Measured in poise(p)

Question 2

Packaging into containers and removal prior to use can affect what 3 factors?

Answer 2

Patient acceptability Physical stability Biological stability

Question 3

Newtonian flow vs non-Newtonian flow

Answer 3

Newtonian

• constant velocity
• defined by a single viscosity at a T.
• proportional to shearing stress and rate of shear. EX: water and mineral oil

non-Newtonian

• change in viscosity
• CANNOT be defined by a single viscosity at a T -time dependent
• **MAJORITY of pharm. products are made under this category**

EX: emulsions, suspensions, ointments

Question 4

KNOW FLOW CURVES

Answer 4

pg. 3

Question 5

Know equations for the viscosity of the Newtonian System.

Answer 5

G = dv/dt F = F’/A n = F/G

Question 6

Name the 4 non-Newtonian materials

Answer 6

1. Plastic 2. Pseudoplastic 3. Dilatant 4. Floc

Question 7

Define Plastic

Answer 7

-Does not flow until yield is exceeded! -Below flow point = elastic -Van der Waals bonds plastic together -Exceeding yield brings out Newtonian properties AKA Bingham bodies

Question 8

Define Pseudoplastic

Answer 8

-No yield value due to involvement in the plastic system. -Shear-thinning - “n” decreases as shear rate increases EX: Polymetric solutions

Question 9

Define Dilatant

Answer 9

-Inverse of Pseudoplastic properties -Shear-thickening -“n” increases as shear rate increases -Characterized by having a high percentage of deflocculated particles in the formulation. EX: Titanium dioxide in water

Question 10

Floc

Answer 10

-“Fl”oc = “Fl”ow -Flowing aggregation of molecules using WEAK bonds.

Question 11

Define Thixotropy

Answer 11

Thixotropy – Refers to the **decrease** in viscosity with time when flow is applied to a material previously at rest and the recovery of viscosity in time when flow is discontinued. -Applies to SHEAR-THINNING -Desirable in pharmaceutical systems • High consistency in container, but pour and spread easily

Question 12

Define Antithixotropy

Answer 12

Antithixotropy – When flow causes a reversible, time-dependent **increase** in viscosity.

Question 13

Define Rheopexy

Answer 13

Rheopexy – Refers to the phenomenon that the gel formation of a system may be facilitated by low shear, compared to keeping it at rest; the reversibility is not defined.

Question 14

What is a Viscometer?

Answer 14

– Instrument used to measure viscosity – Types: Capillary, falling-sphere, cup-and-bob and cone-and-plate – All can be used to determine viscosity of Newtonian systems – Only those with **variable-shear rate controls** can be used for non-Newtonian systems