SUSPENSIONS

suspension

is a heterogeneous mixture in which some of the mixture in which some of the particles settle out of the mixture upon standing.

> 1000nm

Suspension particle size

sedimentation volume

is a ratio of the ultimate volume of sediment (Vu) to the original volume of sediment (Vo) before settling.

F = Vu/Vo

Vu = final or ultimate volume of sediment

Vo = original volume of suspension before settling

sedimentation volume formula

F= 1

No sedimentation (ideal stability).

F < 1

Some sedimentation occurs.

F>1

Sediment volume is greater than the original volume due to the network of flocs formed in the suspension and so loose and fluffy sediment.

Higher F values

indicate better suspension stability.

F is too low

it means the suspension is unstable, leading to caking.

larger F values

Flocculated suspensions typically have ___ than deflocculated ones, preventing hard sediment formation.

smaller, uniform particles

Particle Size & Shape: ___lead to better stability.

increases and prevents

Flocculation: : Controlled flocculation ____hard settling.

higher viscosity

Viscosity of the Medium: ___ reduces sedimentation.

electrolytes and polymers

Affect particle interactions and floc formation..

redispersibility

is the ability of a suspension to easily reform a uniform mixture after settling, usually by

shaking. This ensures accurate dosing and consistent drug deliver

hard cake (irreversible sediment)

A well-formulated suspension should not form a ___ but instead allow particles to be easily redispersed with gentle shaking.

lower RI value

indicates better redispersibility.

formula for redispersibility

≤ 3 inversions

Easily Redispersible

Moderately Redispersible

4-10 inversions

>10 inversions or sediment remains

Poorly Redispersible

caking

If shaking does not fully redisperse the sediment

particle size distribution

determination of the ____ is based on the effect of attenuation of the light beam intensity proportionally to the projected area.

particle size analysis

is therefore a standard procedure in many quality control and research labs to ensure the highest quality final product.

D10

acceptance criteria: = 83 pm/ 10%

D50

acceptance criteria: = 330 pm/ 50%

D90

acceptance criteria: = 1600 pm / 90%

sieving

is most suitable measuring particle size distribution for powders whose average particle size is greater than 25-50 um.

Laser Diffraction Method

It typically covers a particle size range of 10 nm to 4 mm. A laser beam is targeted towards an ensemble of particles dispersed in either a liquid or an airstream.
The resulting deflection pattern of scattering angles of the laser is characteristic of the particle size of the material and detected by an according sensor.

Nanoparticle Tracking Analysis

It measure nanoparticles in the size range of 30 nm to 1000 nm.

Nanoparticle Tracking Analysis

This technique is based on Brownian Motion, which is measured to calculate the translational diffusion diameter and the hydrodynamic diameter.

laser beam, CD or CMOS

Particles in suspension are illuminated by a ___, and the particles scatter light, which is detected by a camera (C___).

rheology

is a general term referring to the science of studying flow and deformation of materials.

shear rate

is the rate at which a fluid is sheared or "worked" during flow. In more technical terms, it is the rate at which the fluid layers move past each other.

shear stress

is the force per area

rheological testing

evaluates the flow and deformation properties of materials using instruments like rheometers and viscometers

viscometer

measures a fluid's viscosity, which is essential in rheology.

rotational, capillary, or falling ball

Selecting the Viscometer - Choose the appropriate type (___) based on the fluid.

homogeneous

Sample Preparation - Ensure the fluid is ___ and maintain the required temperature.

rotational viscometer

insert the spindle, set speed, and record viscosity.

capillary viscometer

Measure flow time through a thin tube.

falling ball viscometer

Time how long a ball falls through the liquid.

#10%

rheological properties: acceptance criteria must fall within a specified range (e.g., ___of target value) to ensure consistency.

rheological properties formula

temperature

is a measure of the average kinetic energy of the particles in a substance. It determines how hot or cold something is and is commonly measured in Celsius (°C), Kelvin (K), or Fahrenheit (°F).

gravitational stress

refers to the internal forces experienced by an object due to gravity. It occurs when different parts of an object experience varying gravitational forces, which can lead to deformation or strain.

2-8°C

Cold Stress

25°C +- 2°C

Room Temperature

40°C +-2°C

Elevated Temperature:

-20°C to 40°C (cycled over 24-48 hours)

Freeze-Thaw Cycling

1, 7, 14, and 30 days

Check for sedimentation, aggregation, or phase separation after

laser diffraction or microscopy

Measure particle size distribution (using ____)

zeta potential

Evaluate __ (for electrostatic stability).

higher stability index (S)

A ___indicates better stability.

(<‡20 mV)

A drastic drop in zeta potential __suggests particle instability.

temperature and gravitational stress formula

zeta potential

is a measure of the surface charge on particles in suspension and emulsions.

zeta potential

is an indicator of dispersion stability. The magnitude (not the sign of the charge) of the ___ provides information on the electrostatic repulsion between the particles or emulsion droplets in a suspension.

two gold electrodes

Adding a solution procedure contains ___

voltage

Apply ___ to the electrode, the particles will move toward the electrode with the opposite charge.

mV

Electrophoretic mobility is calculated, and from that, zeta potential is determined. Unit is expressed in terms of ___

High Zeta Potential (#30 mV or higher)

indicates that the particles are well dispersed and have strong repulsive forces between them. In colloidal systems, this generally means the system will be stable, as the particles are less likely to aggregate.

Low Zeta Potential (+-5 to +- 10 mV):

suggests weaker repulsive forces, and particles are more likely to aggregate or flocculate. This indicates that the system might be unstable and prone to settling or clumping.

Near Zero Zeta Potential (0 mV

the system is at risk of aggregation, as there is little to no electrostatic repulsion between the particles.

High Zeta Potential with +30 mV or higher

must be obtained to prevent aggregation of particles.

Degree of flocculation (B)

is a measure how much a dispersed system (such as a suspension) has undergone flocculation. It helps determine the stability of the suspension by comparing the sedimentation volume of a flocculated system to that of a deflocculated system.

one with a flocculating agent and another with a deflocculating agent

To determine B, two suspensions are prepared

degree of flocculation formula

• ß = 1

If __, the system is completely deflocculated (no flocculation).

ß > 1

If __, the system is flocculated, meaning particles have aggregated into flocs, leading to higher sedimentation volume.

lower B

A ___ indicates deflocculation, leading to dense sedimentation, whic may be difficult to redisperse.