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LUND UNIVERSITY
Particle characterization
Chapter 6
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LUND UNIVERSITY
Why determinate particle size
•
List three things that you know will be affected by
particle size
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LUND UNIVERSITY
My three things
•
•
•
Delivery of particles to the lungs
Solubility of active pharmaceutical compounds
Bulk density
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LUND UNIVERSITY
What do you want to characterize
Particle
• Size
• Morphology
• Material properties
– Porosity
– Density
– Hardness/elasticity(later)
• Surface properties
– Chemical composition
– Surface energy
– Roughness
Powder
• Particle distribution
• Flowability/cohesion
• Specific surface
• Density
• Porosity
• Air content
• Water content (later)
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LUND UNIVERSITY
Size and Morphology
Describe these two particle collections
QuickTime™ and a
decompressor
are needed to see this picture.
QuickTime™ and a
decompressor
are needed to see this picture.
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LUND UNIVERSITY
Size and Morphology
Different descriptive terms for particles
Particle form
spherical, ellipsoid, granular, blocky, flaky,
platy,prismodal, rodlike, acicular, needle shaped, fibrous
irregular,dendrites, irregular, agglomerates
But also particle surface
Smooth, spotty, rough, porous, with cracks, hairy
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LUND UNIVERSITY
Size and Morphology
Measurement of particle size
•
Reduce to known geometry
– Volume
•
•
•
–
Area
•
•
•
A= Projected a rea
P=Perimeter
d=equivalent diameter•
S=surface area
V=volume
–
Cubes
Spheres
Ellipsoids
Circles
Squares
Ellipses
Lengths
•
•
Characteristic lengths
Feret and Martin diameters
Relate to the geometry
– Fit into the geometry
– Have equal Volume or Area
– Have equal properties
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LUND UNIVERSITY
Size and Morphology
Descriptors based on diameters of circles
dcirc=Diameter of
circumscribed minimum circle
dinsc=Diameter of inscribes
maximum circle
deq=Diameter of the circle
having same area as
projection area of particle
Shape descriptor:Circularity
deq/dcirc
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LUND UNIVERSITY
Size and Morphology
More descriptors according to the same principles
Namn
Definition
Formula
Volume
diameter
Diameter of a sphere having the same
volume as the particle
3

d
V
6
Surface
diameter
Diameter of a sphere having the same
surface as the particle
S  d 2
Surface
volume
diameter
Diameter of a sphere having the same

surface to volume ratio as the particle
Projected
area diameter
Diameter of the circle having the same
area as the projection area of particle
Perimeter
diameter
Diameter of the circle having the same
perimeter as the projection peramiter of
particle
dsv  dv3 /6d 2s


2

d
A
4
P  d

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LUND UNIVERSITY
Size and Morphology
Feret and Martin diameter
Df0
Dm0
•
•
•
The Feret diameter the distance
between two tangents to the
contour of the particle in a well
defined orientation.
The Martin diameter, is the length
of a line that divide the area of the
particle into two equal halves.
Normally measured
– Mean= the mean over several
orientations
– Y=largest
– X=smallest
– Elongation= Y/X
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LUND UNIVERSITY
Size and Morphology
Unrolled diameter
•
The mean chord length through the center of gravity of
the particle
E(dg) 
1

2
 d d
g
g
0
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LUND UNIVERSITY
Size and Morphology
Diameter Defined from equal properties
Drag diameter
•
Diameter of a sphere having the same resistance to motion as the
particle in a fluid of the same viscosity and the same speed
Free-falling diameter
•
Diameter of a sphere having the same density and the same freefalling speed as the particle in a fluid of the same density and
viscosity
Stoke diameter
•
The free falling diameter of a particle in the laminar flow region
Aerodynamic diameter
•
the diameter of a sphere of unit density (1g/cc) that has the same
gravitational settling velocity as the particle in question.
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LUND UNIVERSITY
Size and Morphology
Stoke diameter
•
Brownian motion
D
msolvent*g
•
kT
6a
For small particles <0.5m Brownian
motions counteract gravitational forces
and the system will be stable
For larger particles
2d 2 g
v
18
a
2a 2 g
v
9
mpart*g
•
Density matching will hinder
sedimentation

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LUND UNIVERSITY
Size and Morphology
Diameter Defined from equal properties contin..
Equivalent light-scattering diameter
•
Diameter of the sphere giving the same intensity of light
scattering as that of a particle, obtained by the lightscattering method
Sieve diameter
•
The diameter of the smallest grid in a sieve that the
particle will passe through
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LUND UNIVERSITY
Size and Morphology
From descriptors
•
•
•
Elongation: L/B or dferet(max)/dferet (min)
Circularity: for example dins/dcirc
Sphericity (Wandells):
2
2
dv 

  
S p ds 
dv

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LUND UNIVERSITY
Size and Morphology
Form descriptors
•
Form factors: f/k will describe the form
S p  f * da2
Vp  k * d
•
3
a
Space Filling Factor: The ratio between the
area of a circumscribed rectangle or
circumscribed circle of the image and that of the
particle eg A/LB eller 4A/πr2
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LUND UNIVERSITY
Material properties
Density
•
•
•
True particle density: The density of the material
Apparent particle density: Density of the particle
when inner porosity is included
Effective or aerodynamic particle density: Density
if outer porosity is included. Related to the
density that a air or gas stream will measure.
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LUND UNIVERSITY
Surface properties
Particle surface
•
•
Properties
– Roughness of the surface
– Composition
– Surface energy
Influences
– Stability
– Total area
– Particle size reduction
– Adsorption of other substances
to the surface
– Aggregation
– Release of adsorbed material
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LUND UNIVERSITY
Surface properties
To evaluate surfaces properties
•
•
•
•
•
ESCA, XPS - Composition
FTIR - Composition
AFM- Surface morphology
and surface energy
Raman microscopycomposition
Electron microscopy Surface morphology
Evaluation of Ascorbyl Palmitate-loaded NLC Gel using Atomic Force Microsco
V.Teeranachaideekul.1,2, S. Petchsirivej3,4 , R.H. Müller1, V.B. Junyaprasert2
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LUND UNIVERSITY
Surface properties
To evaluate surface energy - Contact angles
L/V
S/V
S/V
•
•
•
Gives information on how easily a
liquid wets a surface.
Low contact angle with water for
hydrophilic surfaces.
Contact angle hysteresis:
– Chemically heterogeneous
surface.
– Surface roughness.
– Surface porosity
– Surface changes when
wetted.
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LUND UNIVERSITY
Assignments particles
Task
•
•
•
Test and compare two different techniques for
size determinations (half a day)
– Microscopy
– Light scattering
Answer the questions in the assignment
description on a seminar (Tue 28 Apr 13.15)
As usuell hand in a short technical note
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LUND UNIVERSITY
Assignments particles
Practical issues
•
•
•
Do the assignment in groups of three
Use our sample or your own
Microscopy use the microscope to take picture
but do the major part of the analyses afterwards
Image J is a free program
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LUND UNIVERSITY
Size distribution
Particle size distribution
•
•
Why is the mean value not enough to describe particle size
distributions
How can we describe the distribution
– Based on what properties
– Based on what type of statistic distribution
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LUND UNIVERSITY
Size distribution
Type of distributions
•
•
Different type of diameters
Different type of
distribution
– Number (0)
– Length (1)
– Area (2)
– Volume (3)
– Weight (w) =V*
•
•
•
How will these differ from
one another?
How do you calculate the
mean particle size
Can you transfer mean
particle size between the
different distributions?
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LUND UNIVERSITY
Size distribution
Average particle size
Number mean length diameter d(1,0)
 dL  dN
d   dS  dN
d   dV  dN
d   dL  dw
d
Number mean surface diameter d(2,0)
2
2,16
3
Number mean volume diameter d(3,0) 
Weighted mean length diameter d(3,0) 
Length surface mean diameter
d(2,1)

Length volume mean diameter d(3,1) 

Surface Volume mean diameter d(3,2)

weight moment mean diameter d(4,3)
d   dS
d
dL
 dV  dL
d   dV
d   dM
2,29
2,33
2,45
dS
2,57
dW
2,72


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LUND UNIVERSITY
Size distribution
Different distributions
0,8
0,7
distribution
0,6
N
L
S
V
0,5
0,4
0,3
0,2
0,1
0
1
2
3
size
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LUND UNIVERSITY
Size distribution
Type of statistic distribution
QuickTime™ and a
decompressor
are needed to see this picture.
Normal distribution
QuickTime™ and a
decompressor
are needed to see this picture.
Log Normal

Rosin–Rammler (Weibull)
Distribution
QuickTime och en
-dekomprimerare
krävs för att kunna se bilden.
d n
q  exp 
d 
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LUND UNIVERSITY
Size distribution
Special properties of log distributions
•
•
•
If the number is log distributed so is the length,
surface, and volume
With the same geometric mean deviation
Hatch-Choate relationships will transfer one type
of mean diameter into another
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LUND UNIVERSITY
Size distribution
Description of particle size distribution
•
Mean diameter
– Standard mean,
– Geometric mean ln dg   dN *ln x
•
variability
•
Standard deviation
– Geometric
standard
deviation ln  g   dN(ln x  ln x )2 /  N 
Skewness
N
–
IQCS 
(D75%  Dg )  (Dg  D25% )

(D
75%  Dg )  (Dg  D25% )
0
5
10
15
20
25
30
35
1
(x i - x) 3

n
3/2
1

2
  (x i - x) 
n

29
40
LUND UNIVERSITY
Powder
Specific surface
•
•
•
Surface per weight
Factors that increase surface
area
– Decrease in particle size
– Increase in surface
roughness
– Inner porosity (if available)
Method dependent parameter
– Permeatry
– Gas adsorption
– Gas diffusion
– Porosimetery
•
Importance
– Dissolution
– Chemical reactions
– Adsorption of other
molecules
– Flow though particle
beds
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LUND UNIVERSITY
Powder
Density, air content and porosity
•
•
•
Density (b)= weight of
powder/Volume of powder
Air content= air in
pores(entrapped air) and air in
between particles (void air)
Porosity
•
•
In particle
Between particles
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
LUND UNIVERSITY
Powder
Flow properties and powder density
•
•
Angle of repose
Bulk density
– Tapping density
Flow
character
Angle
Very good
<20
Good
20-30
Ok
Carrs indextapped  poured density
Carr sin xdes 
tapped density
–
poured density
tapped density
Hausner
Hausner
ratioration

–
Poor
30-34
Very poor
Extremely
poor
>40
Carrs
index
5-15
12-16
18-21
25-35
33-38
>40
32