Exam 1 Spring 17 Flashcards
Consistency can affect what?
flow of materials, mixing, choice of processing equipment, packaging into container, patient acceptability, physical stability, bioavailability, removal from container for use
Define viscosity
- resistance to flow
- internal friction of a system
How do you determine viscosity (via layers)?
strength that a layer exerts on adjacent layers determines the system viscosity
What is the rate of shear and what is the variable that denotes it?
Rate of shear = G = dv/dr
dv = displacement of each layer
dr = thickness of each layer
What is the shearing stress and what is the variable that denotes it?
Shearing stress = F = Force/A
Force applied / surface area of each layer
What is the relationship between rate of shear and shearing stress?
F ∝ G
In variables, what is Newton’s law of flow?
F = ηG
the more shearing stress = the more rate of shear
How does viscosity affect F and G?
The higher the viscosity, the greater is the shearing stress required to produce a certain rate of shear
What are the types of non-Newtonian flow?
- Plastic flow
- Pseudoplastic flow
- Dilatant flow
What is η?
Coefficient of Viscosity (poise)
In a rheogram, when you plot F vs G, you get a straight line/slop (direct relationship). What is the slope (in variable) and what does it represent?
1/η
- Represents fluidity (Φ)
In variables, define kinematic viscosity.
η/ρ
Viscosity/Density
What are the units for kinematic viscosity?
stokes = centipoise / [g/cm^3]
What are the characteristics of a rheogram of a Newtonian system?
Rate of shear (y) and shearing stress (x) are directly related
What are some examples of non-Newtonian systems?
ointments, suspensions, emulsions
What is another name for plastic flow?
Bingham bodies
What is a yield value?
f = the amount of force you have to apply to a non-newtonian fluid in order for it to move
What happens when shear stress doesn’t exceed yield value?
the material will act as an elastic material
How can you determine the yield value?
when shearing stress exceeds yield value, the relationship between F and G are proportion; extend the line of their slop and where it touches the x-axis is the yield value
What is the variable for plastic viscosity and how do you solve for it?
U = (F - f) / G
What are the contributions to yield value?
Vanderwaals forces and interparticle friction
What is an example of plastic fluid?
flocculated suspensions
What effect does flocculated suspensions have on yield values?
more flocculated = larger the yield value
What is another name for pseudoplastic flow?
Shear thinning systems
Define pseudoplastic flow
neither plastic or totally newton; curve starts at origin with linear approach but never reaches a straight line because slope is constantly changing; viscosity is different at every point so F value must be reported when determining viscosity
What is an example of pseudoplastic material?
natural and synthetic gums
What are the reasons for the curved rheogram with respect to pseudoplastic flow?
- shear force aligns polymers along their long axis, reducing the internal resistance to flow
- Uncoiling releases the entrapped solvent resulting in lowering the concentration and size of the dispersed molecules
What are examples of shearing stress and how does that affect viscosity of pseudoplastic materials?
- Examples: shaking suspension, pumping blood, blinking eye
- Applying stress makes the flat/linear which creates a larger surface area so that flow increases and viscosity decreases
What is another name for dilatant flow?
Shear thickening systems
In dilatant flow, describe the relationship between shearing stress and viscosity. What happens when you remove this stress?
as you increase shearing stress, the viscosity increases
when the stress is removed, the system returns to the original state of fluidity
What are characteristics of dilatant materials?
- higher percentage of dispersed solids (more than 50%)
- small, deflocculated particles
What causes a solution to dilate?
increased stress -> increased volume -> dilate
In a Newtonian system, what happens when the shearing stress is removed from the system?
viscosity is restored at the same rate at which it was lost
In a non-Newtonian system, what happens when the shearing stress is removed from the system?
viscosity is not restored at the same rate at which it was lost
Define thixotropy
An isothermal and comparatively slow recovery, on standing of a material, of a consistency lost through shearing
The curves of the rheograms of thixotropic systems are highly dependent on?
- the rate at which stress is applied or removed
- the length of time the material is subjected to stress
How does length of time the material is subjected to stress affect recovery time?
it’s much slower
Under which systems is thixotropy applicable?
shear-thinning systems only; plastic and pseudoplastic flow
What are benefits of thixotropy ?
upon shaking container, formulation is easily spread
What is negative thixotropy?
when a solution increases in consistency on the downcurve
Define rheopexy
A phenomenon in which a solid forms a gel more readily when sheared than when allowed to form a gel while the material is kept at rest
Under which systems is rheopexy applicable?
dilatant flow
What is the name of the property which combines solid and liquid like properties?
Viscoelasticity
What are examples of viscoelastic materials?
creams, lotions, ointments, suppositories, suspensions, suspending agents, blood
What does viscoelasticity measures?
tests rheologic ground state
How is viscoelasticity applied in pharmeutics?
- Modifications and improvement of Non-Newtonian dermatologic and cosmetic vehicles
- Analysis of sputum for the design of mucolytic agents
- Measurement of shear in synovial fluids during the simulated movements of joints
What are the qualities of ideal suspensions?
- high viscosity at negligible shear
- low viscosity at higher shear
What kind of substances achieve the qualities of ideal suspensions?
Pseudoplastic substances with thixotropic properties
What are examples of structured vehicles?
- Carboxymethylcellulose (CMC)
- Polyvinylpyrrolidine (PVP)
- Xanthan gum
- Benotnite
- Tragacanth gum
What are characteristics of structured vehicles?
- Entrap particles in a deflocculated manner to prevent settling
- Pseudoplastic or plastic in nature
- Usually associated with thixotropy
- Some sedimentation occurs anyway, but could be redispersed because of the ‘shear thinning’ property
What is PVR?
Phase volume ratio = how much dispersed phase is present in how much of the dispersion medium
Emulsion properties with change of PVR
- At low PVR (<0.05) the system is Newtonian
- s the PVR increases, the system attains Pseudoplasticity -> Plasticity
- At PVR= 0.74, phase inversion may occur with a sharp change in η
Emulsion properties with change of droplet size
- Reduction in size increases viscosity of emulsion
- Wider the size distribution -> lower the viscosity
Smaller particle size = increased viscosity. Why?
it causes disturbance with flow
Which dosage form falls under 0.01-0.1 µm?
Nanoparticles, nanosuspensions
What are nanoparticles and nanosuspensions size range?
0.01-0.1 µm
Which dosage form falls under 0.1-1.0 µm?
Liposomal formulations
What are liposomal formulations size range?
0.1-1.0 µm
Which dosage form falls under 0.5-10.0 µm?
Suspensions, fine emulsions aerosols (for lung)
What are suspensions and fine emulsions aerosols size range?
0.5-10.0 µm
Which dosage form falls under 10.0- 50.0 µm?
Coarse emulsion particles, flocculated suspension particles, Nasal powders and droplets (Upper limit of subsieve range)
What are coarse emulsion particles, flocculated suspension particles, nasal powders and dropets size range?
10.0- 50.0 µm
Which dosage form falls under 50.0-100.0 µm?
(Range for fine powders) Drug particles for oral dosage forms
(Lower limit of sieve range)
What are drug particles for oral dosage forms size range?
50.0-100.0 µm
Which dosage form falls under 150.0-1000.0 µm?
Coarse powder range, Excipients for oral dosage forms
What are coarse powder and excipients for oral dosage form size range?
150.0-1000.0 µm
Which dosage form falls under 1000.0-3360.0 µm?
Average granule size
What are average granule size range?
1000.0-3360.0 µm
What are the ways in which you can measure particle size?
- Geometric or projected area diameter
- Volume diameter
- Stroke’s diameter
- Equivalent surface diameter
- Aerodynamic diameter
What are examples of measuring with geometric or projected area diameter?
- microscopy
- sieving
What are examples of measuring with volume diameter?
- laser diffraction
- light obscuration
- coulter counter
What are examples of measuring with Stoke’s diameter?
sedimentation
What are examples of measuring with equivalent surface diameter?
gas adsorption
What are examples of measuring with aerintertial imodynamic diameter?
inertial impaction
What are the different types of microscope?
- Transmission Electron Microscope
- Scanning Electron Microscope
- Optical microscope
In microscopy, what are the different types of diameters?
- Projected diameter
- Feret diameter
- Martin diameter
What are advantages of microscopy?
- Direct, simple, convenient
- Provides size distribution by number
- Can assess complete particle formation or dryness
What are disadvantages of microscopy?
- 1 dimension only
- Slow, tedious, requires statistical analysis
What value of standard deviation is a very good powder?
between 1 and 2
What are important things to consider via sieving?
- Amount of powder loaded on top sieve
- Duration of shaking
- Composition of the material (eg. aggregation, attrition)
- Condition of sieves
What determines the terminal velocity of the particle?
- gravitational forces
- drag forces
What are the limitations for determining particle size via sedimentation?
- Assume all particles have the same density
- Assumes all particles are spheres, thus it has low accuracy for irregular particles
- Does not detect powder aggregation
What are the media for determination via volume diameter?
- Conducting liquid
- Media in which particle is not soluble
- Air
What are the sensing mechanisms for determination via volume diameter?
- Voltage
- Laser diffraction
- Light scattering - Brownian motion
Dynamic light scattering is also referred to as what?
- Photon Correlation Spectroscopy
- Quasi-Elastic Light Scattering
- Brownian Motion
What are the advantages of determining particle size via automated methods?
- Quick and “easy” calculation of particle size and distribution
- A wide range of particle sizes (submicron to mm) can be determined with the appropriate instrument/lenses
What are the disadvantages of determining particle size via automated methods?
- Does not discriminate between individual particles and aggregates
- Instrument is expensive and requires maintenance and specialized training
Gas adsorption is based on what?
Brunauer Emmett Teller (BET) Equation
Air permeability method is based on what?
Kozeny-Carman Equation
What are the methods to determine surface area?
- Gas adsorption
- Air permeability method
What is another name for porosity what does it measure?
- aka void fraction
- measure void spaces in a powder
- fraction of the volume of voids in each particle over the total volume of the powder
What are the properties that porosity influences?
Density, Mixing of different powders, Packing arrangements, Flow properties, Compressibility, Dissolution rate of oral solid dosage forms, Aerodynamic properties in inhalable powders
What are the IUPAC classification on pores base on size?
- Macroporous >50 nm
- Mesoporus 2-50 nm
- Microporus < 2 nm
Define true density
For the material itself, without pores or interparticulate spaces.
Define granule density
For the material itself, considers pores >10µm and inter-particular spaces
Define bulk density
Relationship of the volume occupied by a determined mass of powder
Define tapped density
Relationship of the volume occupied by a determined mass of powder
Selection of capsule size is influenced by what?
- bulk density
- porosity (ε)
- Flow-ability and compressibility
Flow properties of powders are influenced by what?
size, distribution, shape, porosity, density, surface texture
What are examples of inter-particulate forces?
- Capillary forces
- Vanderwaal forces
- Electrostatic charge
- Mechanical interlocking
