health and medicine for pharmacy field field

Film Formation of
Waterborne Coatings
Joe Keddie
University of Surrey
Guildford,
iS
Emulsion Polymerization Procassss Course
16 September zuub, Donostia-t›an t›ebastian
J.L.Keddie -Copyright reserved at›05
UHmmlnl•a dMPas Vâeoo
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Idealised View of Latex Film Formation
Polymer-in-water dispersion
O O O 0 O
OO
O
O O O O
O O O O
0
O
O Water loss
O
Homogenous Film
Close-packing of particles
T > MFFT
lnterdiffusion
and coalescence
Deformation
of particles
Optical Clarity
T » T Dodecahedral structure
(honey-comb)
g
Emulsion Polymerization Processes Course
16 September Euct›, Donostia-can Sebastian
J.L. Keddie - Copyright reserved 2005

Sta es of Latex Film Formation
Dark field optical
microscopy
Atomic force microscopy
TEM on C replica

Overview
• Factors affecting Minimum Film Formation
Temperature MFFT
• Lateral and vertical drying
• Particle packing
• Fundamental driving forces for particle
deformation
• Diñusion and particle coalescence
• Factors influencing surfactant distribution
Em on Po er at o P ocesse Cou e
16 September 2005, Donostia-San Sebastián

ical Mor holooies
Randomly-packed array of
deformable particles in dry film
Source: A. Tzitzinou e 000)2695
H O L Y
Particles are flattened at their
boundaries in dry film
|JITl X
A
F
M Images
1
•
ym x1.5 ym
E ..:.ion y e z
a
o
o ”uce se33ou2
uniyer sJond del Pais /asea

ical Mor holooies
J.L. Keddie Copyright reserved 2005
Voids in randomly-packedarray of particles:
Yetfilm is optically transparent

Percolating Phase within Deformed Particles
From: R. Mezzenga ef a/., “Templating Organic Semiconductors via Self-
Assembly of Polymer Colloids,” Science 299 (2003) p. 1872.
ay EmuIs PoI P Cou
16 September 2005, Donostia-San 5ebasti8n

Measurin
MFFT
Picture courtesy of Dr P. Sperry, Rohm and Haas

Hot
+10°C
-10°C
Clear
Formation Temperature
(MFFT)
C l o u d y
Picture courtesy of Dr P. Sperry
Emulsion Pol merization Processes Course
16 September 2005, Donostia-San Sebastiàn

Factors Affecting FFT
•MFFThasanimprecise definition - subjectto
h
u
ma
nperception
• Usually is within a few degrees of the glass
transition temperature of the polymer
•Optical claritycanincrease over time w
i
t
hfurther
coalescence ofparticles
• For the same polymer, MFFT decreases with
particle size. Driving force for coalescence is
higher for smaller particles. Also, there is an optical
eñect: less light scattering from smaller voids!
-—
Euax

Effect of Particle Size on FT
ae-
0 1OO 500 800
ZOO 300 400
Particle Size (rim)
" Th Ot the latex is
37 - 40 O
¢
Source: D.P. Jensen & L.W. Morgan, 1. Appl. Pol. Sci., 42 (1991) 2845.
Euax

EffectofParticle Sizeo
n FT
1.0
0.0 0.2 0.4 0.8 0.8
Fraction of 458 nm Particles
m
B
l
endof6
3n
mand4
5
8
n
mparticles w
i
t
ha
n
averageTtof3
8°C.
Source: D.P. Jensen & L.W. Morgan, 1. Appl. Pol. Sci., 42 (1991) 2845.
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i Latex il
16 September auut›, Donostia-t›an t›ebastian
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Experimentai evidence for
Cryogenic
SEM
E. Sutanto e/ a/., in Film Formation in Coatings, ACS Symposium
Series 790 (2001) Ch. 10

Films dr first in the thinnest re ions
Hard particles
Film
• = SI min
Relevant when coating large surface areas:
lateral transport of water is observed
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a = particle radius
cop
Préssure of
Darcy flow
Capillary pressure:
Reducedcapillary
a p
ressure:
Darcy

Theory: Reduced capillary pressure
controls /afera/ ryi
• Reduced capillary pressure, p„ can pin the
water at the film edge.
20
* 75
• a = particle size
• H = film thickness
• E —
—
evaporation rate
A.F. Routh and W.B. Russel, A.I.Ch.E.J., 44 (1998) 2088.
* " * ' H Surface tension;
viscosity;
solids fraction

Wet,
colloidal
dispersion
imagi lateral
22 mm
J.M. Salamanca et at., Langmuir, 17 (2001) 3202.
2.6 mm
Packed
particle
bed filled
with water
MR Image
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109
160
W
a
t
e
ris n
n
e
da
tt
h
efilme
d
g
e
PC 1.0
w
h
e
nthereisa P
c
PC 420
22 mm
2.4mm
time (hr)
22 mm
H = 1.2 mm and a = 25 nm H 0.32 mm and a 4.4 ym

O
.
5
0
.
4
0
.
3
_ 02
0.1
Experime
10-2
10’
theory
Lower t
h
i
c
k
n
e
s
s
,
larger par
t
i
cl
e
size, a
n
dslower
evaporation r
a
t
e
e
n
c
o
u
r
a
g
e
uniform lateral
drying

Experimentai Evidence for
Verticai Non-Uniformity
Cryogenic
SEM
Densely-packed
particle layer
E. Sutanto et a/., in
Film Formation in
Coatings, ACS
Symposium Series 790
(2001) Ch. 10

Theory: Peclet number for
vertical dryi uniformity
• Competition between Browcian diffusion that
re-distributes pai1icles and evaporation that
causes particles to accumulate at the surface
16 September 2v05. Donostia-can Sebastian
The Univer siry of the Bcsrr a Com ry

Experimental Observation of
Brownian Movement
16September zuub, Donostia-t›an t›ebastian
Euax
Phenomenon was
first reported by a
Scottish botanist
named Brown (19
cent.)
Brown observed the
motion of pollen
grains but realised
that they were not
living.
Brownian motion

Peclet number for vertical drvin
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uniformit
Pe<< 1
Pe=
Pe>> 1
Dilute limit
kT
6›ryR

Scaling Relation for
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dg 1
2
d› - Pe
A.F. Routh and W.B. Zimmerman, Chem. Eng. Sci., 59 (2004) 2961-68.

muiations of the Vertical
Distribution of Pai1icles
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Close- *m“ ,
packed
0.5
0.45
0
Pe= 0.2 ,,
02 0.4 0.6
Top
Vertical Position " z

Close-.
packed
Emulsion Polymanzation Procassss Course
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mulations of the Vertical
istribution of Particles
0.5
n 0.2 0.4 0.6
Vertical Position
1

mulations of the Vertical
istribution of Particles
0
.
O
0
.
2 0.1 0
.
8
Pe 10
Vertical Position
D.8
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t-0.1
1
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GARField depth profiling magnet
for planar samples
Characteristics :
• 0.7 T permanent magnet
(Bo)
• 17.5 T.m-1 gradient in the
vertical direction (Gb)
P. M. Glover, et al., J.
Magn. Reson. (1999)
139, 90.
Gravity
B,
Abilities :
• accommodates samples of 2
c
mby 2c
marea
• achieves better than 10 ym
pixel resolution!
B,
RF Coil
Signal inJensity

" " " " " “ E y e f ? B P ? 8 f
with simulations
0.45
0.3
* 0.I fi
0
—
50 U
• Slow evaporation rate, small particle size, low film
thickness and low serum viscosity favor uniform
vertical drying.
High humidity Pe = 0.2
H 255 ym, E = 0.2 x 10-8 ms-1, D = 3.23 x 10-12 m2s-1
0.75
W 10hours
—
a
—14 hours
8o
.
J.-P
. G
o
r
c
e et
al., Eur Phys J
E, 8 (2002) 421
Height (qm)
Emulsion Pol
September 2005, Donoctia-San 5ebasti8n
J.L.Kaddie- Copyright racarvad2XIS

with simulations
• High evaporation rate, large particle size, high film
thickness and high serum viscosity favor non-uniform
vertical drying.
Flowing Air Pe 16
D = 3.23 x 10 1* m2
s—1
H = 340 y‹m, E = 15 x 10—8 ms—1
.2 0.7
05
:c 0.1
ttiinute.s
There is no
$ =0.15 discontinuity
inthew
a
t
e
r
oncentration.

ixed modes of ryi
Flowing air: High E and Static air: Low E and non-
vertical uniformity of water uniformit of water vertically
Time

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Particle Packin
Defects
Requires monodisperse
particle sizes
Slow drying favours
ordering
FcC
Packing defects are often-
associated with particles of,.
differing size!
Particles of “wrong” size
Emulsion Pol me
BCC

Solids Fraction of Packed Particles
•Ifmonosized particles packinto aface-
centered array, thevolume fraction of solids, g
,
is0.74 - thedensest possible for hard spheres.
• If the particles are randomly-packed, g= 0.6
• If smaller particles fit into the void space
between larger particles, then g will be higher.
• Also, if an electric double-layer prevents
particle-particle contact, then g will be lower at
“close packing".

Effect of Double-Layers
Confinement of particles but without
particle/particle contact
Emulsion PolymarizationProcassss Course
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Solids Fractions of Hard Particles
Solids fraction is
74 voIO
›t for FCC
packing of both sma
and large particles
If small particles fit into the
voids between large
particles1the packing
fraction can be increased!

Cubic
stal Structure
# Nearest
Nei hbors
Large/Small
Ratio
CsCI(Simple) 8 1.37:1
NaCI (Face-centred) 6 2.41:1
ZnS(Diamond) 4 4.45:1
Formation of loidal Crystals
These size ratios are required to create various types of
colloidal crystal:
This strategy requires tight control of particle sizes and
controlled drying conditions.
An alternative approach is to disperse large particles in
a continuous phase of small particles.

Ordered Arrays of Particle Blands
MRS Bulletin,
Feb 2004, p. 86

Critical Volume of Particle to Achieve
a Continuous Phase
Enough small particles
to percolate around
larger particles
Large/Small Ratio

Example of Morphologyfrom the
Packing of BimodalParticles
Euax
Atomic force microscopy images of a latex film made by
blending 80 wtO
›300 nm particles with 20 wto
A 50 nm particles
1.5 km x 1.5 ym
Source: A. Tzitzinou et al., Macromolecules, 33 (2000) 2695.

In Latex with Bimodal Size Distribution:
Number Fraction x Weight Fraction
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Example: 10:1 ratio of Large:Small Particles
Weight/Vol. Fraction Large, Number Fraction Large
0.01 0.00001
0.10 0.00011
0.50 0.00100
0.95 0.01865
0.97 0.03132
0.99 0.90082
Actual sizes are irrelevant. Calculations assume large and
small particles have the same density.

Effects of Shear Stress
on Colloidal Dispersions
Emulsion PolymerizationProcassss Course
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With no shear under a shear stress
RS Bulletin, Feb ‘04, p. 88 Confocal Microscope Images

ec i
i I eformati
esce ce
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Typical Morphologies
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Face-centered cubic
array of pai1icles:
12 neighbours
for each particle

Typical Morphologies
Particles are
deformed tofill all
available space:
dodecahedra
Y. Wang et al., Lanpmu/r 8
(1992) 1435.

ParticieCoaiescence
Same polymer volume before and after coalescence:
Surface area of N particles:
4/Vx/*
Sur1ace area of particle made
from coalesced particles:
4x/Y
Change in area, bA - 4xz*(/V-V 3)
In1Lofl
a
t
e
x(50%solids), w
i
t
haparticle diameter o
f
200nm, N is -1.3 x104m2
101
7
particles. Then bA

ríxi Force for Coal
Reductionin Free
nce:
nergy
Decrease in Gibbs Free Energy, óG, with particle
coalescence:
bG ybA
y = interfacial energy (J m 2)
bA change in inteJacial area
Coalescence is favorable when G is reduced (óG < 0).
For coalescence of N 10’7 particles with a 200 nm
diameter, with y = 3 x 10-2 J m-2, óG = 390 J.
Emulsion Polymarization Procassss Course
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Concept of EnergyBaiance
Energy “gained” by the reduction in surface
area with particle deformation is “spent” on the
deformation of pai1icles:
D
e
f
o
r
m
a
t
i
o
n iseitherelastic. v
i
s
c
o
u
s(i.e. f
l
o
w
)
o
rviscoe
l
as
t
i
c (i.e.bot
h)

TypicaiVal
i rfaciai nergy
y(10* J m2)
Interface
Water/Air
Polymer/Water
Polymer/Air
1

Particle Deformation Mechanisms
Water recedes before particles
are deformed. Reduction of
the polymer/air interfacial
energy is the driving force.
Dry Sintering: yha
Particles are deformed before
water has evaporated.
Reduction of the
polymeriwater interfacial
energy is the driving force.
Wet Sintering: ypw

16 September Euet›, Donostia-van Sebastian
&OLY
gp 12.9y„
r
For ywa 3 x 10-2 Jm-
2 and r= 150 nm,
óP is MPa!
Capillary Action: Y
w
a

In those cases in which the water distribution is
non-uniform A ND
in which wet sintering is favoured,
skin formation is predicted to occur.
Skin Formation

Scaling Prediction for Particle
De?érmation Mechanism
A single parameter has been proposed to predict
which mechanism of deformation is operative.
It represents the ratio of time for viscous deformation
(Rio/ wa)over the evaporation time (H/Ej:
where yo is the zero-shear viscosity of the polymer.
-—
Euax

Theory: Deformation mechanism is a function of
the dimensionless arameters, £ and Pe
y *
*
^ Low T: Near T
h
, H Dry Sintering: yp
10000
Receding Water Front
100
Capilla Deformation: -
Wet Sintering: ypW
T- Ty > 15 ”C
0
på
Partial Skinnin
' Skinning
1 6x: RHE
A.F. Routh & W.B. Russel, Langmuir, 15 (1999) 7762-73.
kT

At later stages, water les
de end on article deformation
50
45
3S
2S
20
15
* 4?
40
10
Time
Dry älntedng.
Water recedes from the
film surface
-
4
0 0 40 80 0 1ù0 200 240
Capillary deformation:
Water is always near the
film surface
autsion Povmekaation Processes Course
Séptember 20 Donostia-San Sebastiàn

Water
durin
ncentratio
iatex film formation
Acrylic Latex near T :
Uniform water recession
from surface
* fJ.2
Time
0
-TO
Consistent with dry sintering
50 100 150 200 2fi0
Height
(» ) ‹
with some particle deformation

Relative
intensity
Evidence for Camilla
Deformation
• Ty -45 O
C
t
)
.
2
—25 () 25 ?
(
) 75 1UU 12?
Height (Atm)
Water is “pinned” at the air surface of the film
throughout the drying process!
J. Mallégol et al., Langmuir, 18 (2002) 4478

I I terdi i

Example of Good Coalescence
Hydrated film
Immediate film formation
upon drying!

Coaiescence and inte iffusi n
• Particles can be deformed without being coalesced.
(Coalescencemeans that the boundary between particles
no longer exists!)
• Molecules must diffuse across the boundary between
particles to achieve coalescence: analogy to crack
healing.
• If the molecules entangle over a distance on the order of
the radius of gyration of the polymer, then the film is
stronger. Otherwise, the boundaries will be weak.

ntangl
mer/
at
mer interface
Time
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Factorsthat infiuence Diffusivit
, D
• Molecular weight, M:
•Te^ e••tu•e•T: = D exp(
-E p T )
• Particle membranes: e.g. hydrophilic acrylica
c
i
d
c
o
p
o
l
y
m
e
r o
rs
e
r
u
mp
h
a
s
ea
tpapicle b
o
u
n
d
a
r
i
e
s
• Crosslinking:C
a
nentirely p
r
e
v
e
n
t diflusion!
• Molecular branching: Slows downdiñusion
Emulsion PolymerizationProcassss Course
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Coalesci Aids Increase Diffusivity
• Volatile solvents can decrease the T
h ¿tnd MFFT of the
polymer, enhance the rate of polymer interdiffusion and
then evaporate to create a hard (high Th) fiIm•
• A c
o
m
m
o
n e
x
a
m
p
l
e o
f a c
o
a
l
esc
i
ng aid is 2,2,4-
trimethyI-1,3-pentanediolmonoisobutyrate(
T
e
x
a
n
o
l TM).
• A negative aspect is that the use of coalescing aids
increases the VOC concentration of a waterborne
system!

Factors in Selecting a Coalescing Aid
• Evaporation rate: D
e
t
e
r
m
i
n
e
s h
o
wlongt
h
e
plasticizer r
e
m
a
i
n
si
nt
h
efilm.
• Solvent Ty: Determines theextent of
plasticization; T
hztpproximately 2T /3.
• Solubility: Determines the amount of solvent
in thepolymer and aqueous phases and
hencethe extentof plasticization.
• Ab
a
l
a
n
c
eo
ft
h
è
s
ef
a
c
t
o
r
sisrequired t
o
achieve thebestfilm formation andahard
finalcoating.

Exam ie Plasticizer Data
Solvent K = C„/CR *PBMA T
Texanol (TPM) 0.01 10 °C
Diethylene glycol monobutyl ether (DGB) 3 13
Hexylene glycol (HG) 13 16
Benzyl alcohol (BA) 0.22 24
Diacetone alcohol (DA) 8 26
”Th When PBMA contains 10 wt.% solvent
Source: Juhué and Lang, Macromolecules, 27 (1994) 695.

Comparison of the Evaporation Rates
of Coalescing Aids
300
29
29.0
26.5
26
0 5 10
anne aling time (hours)
Texanol is retained in a film for an extended
period of time: a “remnant plasticiser”
1 = TPM
2 = HG
3 DGB
4 BA
5 = DA
6 Neat PBMA
Juhué and
Lang, (1994)

Surfactants and latex serum
= -45 D
C
Mallégol et al., Langmuir (2001) 17, 7022.

Serum hase can revent coalescence
Particles are not
coalesced in this
acrylic Iatex with a
bimodal panicle
size
Goodcoalescence
is achieved when
the sameIatex has
been “cleaned" via
dialysis

Surfactant sometimes forms
re ates

Membranes m break-
enabieinterdiffusion

Phase separation
J.L. Keddie - Copyright ‹ese‹ved atXt5
Euax

Measurin
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diffusion and mixin
Phe
Phe
Phe
Phe Phe
Phe
Phe
Phe =
Phenanthrene
r
An —
Anthracene
Phe
r'he
Phe
Phe
Phe
Phe
Phe
For Phe and An, energy transfer is instantaneous when
r is < 12 A and very slow when r > 50 â.

nergy Transfer Tech
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Fluorescence
Intensity
Time (ns)
Fraction mixing
1.0
0
.
8
‹
Time
0
.
0
2
O
0 400 600 8
0
O
Tizoe (min.)
Source: M.A. Winnik et a/.,1. Coatings Techn., 64, No. 811, (1992), 51-61.

Exam Ie Diffusion Coefficients from NRET
Pol mer
PBMA
Tern
70
Diff. Coeñ. (10-16 cm2s-1)
-1
PBMA 90 10
PBMA 120 100 —
1000
PMMA 130 6
PMMA 170 800
See J.L. Keddie, Mat. Sci. Eng. Rep. (1997) R23, 101.

Effect of Texanol on PBMA Diffusion Coefficients
Texanol Content wt.% *DiV. Coeff. (cm2s-1)
0 1 x 10 ’8
3 2 x 10 '7
6 1 x 10-16
8 8 x 10—16
10 2 x 10-1
12 1 x 10—14
* D measured when fraction of mixing is 0.5
See J.L. Keddie, Mat. Sci. Eng. Rep. (1997) R23, 101.

rfacta ist i i

Surfactant Trans ort Mechanisms
• During the drying stage, surfactant must be
either:
• Adsorbed on particle surfaces, where it moves
along with the particles OR....
• Diñusing in the latex serum OR....
• Adsorbing on particles, described by adsorption
isotherm OR...
• Desorbing from particles, as particles compact
together.

Changi me ncentration
of Adsorbed Surfactant, F
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3’surfi!*pol
Micelles
po|increases as water
evaporates and particles
pack together

Changi me ncentration
of Adsorbed Surfactant, F
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‘surf
//surf
6surf iS given by a Langmuir isotherm as a
function of surfactant concentration/sur. which
increases over time.

Surfactant desor tion
Desorption might be caused by the repulsion from
anionic head groups forced into close proximity.
• It might be opposed by particle rigidity.

Wide variety of surfactant distributions
HTAB SDS
sodium dodecyl sulfate
Height
hexadecyl trimethyl
ammonium bromide
Height
sur
HPCI
hexadecyl pyridinium
chloride
Sli1'
NP10
polyethoxylated
nonyl phenol
Height Height
C.L. Zhao, et al., Coll. Polym. Sci., 265 (1987) 823

Further Reading
• Books on Latex Film Formation and Wb Coatings:
Film Formation in Waterborne Coati”ngs, T. Provder, M.A. Winnik, and M.W.
Urban, ed., ACS Symposium Series, Vol. 648, 1996.
Film Formatlo I in Coatings. Mechanisms, Properties and Morphology, T.
Provder and M.W. Urban, ed., ACS Symposium Series. Vol. 790, Oxford
University Press, 2001.
• Review Articles on Latex Film Formation:
J.L. Keddie, Mater. Sci. Eng. Reports, 21 (1997) 101.
J. Hearn, P.A. Steward, M.C. Wilkinson, Adv. Co//o/d /n/er/., 86 (2000) 195.
M.A. Winnik, Curr. Opinion Coll. Interf. Sci., 2 (1997) 192.
• Process model of film formation:
A.F. Routh and W.B. Russel, Langmuir, 15 (1999) 7762.
• Review of experimental work on film formation:
A.F. Routh and W.B. Russel, Ind. Eng. Chem. Res., 40 (2001) 4302.

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