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CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 1
ppt00 1 1
Coating Rheology Coating Rheology -- OutlineOutline
Rheological Properties of CoatingsRheological Properties of Coatings–– Viscosity, ShearViscosity, Shear--thinning, thinning, ThixotropyThixotropy, , ViscoelasticityViscoelasticity, ,
Surface & Interfacial Tension, etc.Surface & Interfacial Tension, etc.
Impact of Rheology on Coating ProcessImpact of Rheology on Coating Process–– Paint Mixing, Application, Sag & Leveling, etc.Paint Mixing, Application, Sag & Leveling, etc.
Effect of Coating Formulation Aspects on Effect of Coating Formulation Aspects on RheologyRheology–– Solids Level, Binders, Pigments, Additives, Solids Level, Binders, Pigments, Additives,
InteractionsInteractions
ppt00 2 2
Rheological Properties of CoatingsRheological Properties of Coatings
Rheology & Viscosity Definitions
Effect of Shear Rate on Viscosity
Newtonian Vs Non-Newtonian Behavior
Shear-Thinning, Pseudoplasticity, Thixotropy, etc.
Shear Vs Extensional Viscosity
Viscoelasticity
Measurement of Rheological Properties
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 2
ppt00 3 3
Coating Process OverviewCoating Process Overview
Raw Materials
Mixing / Blending
Storage (Shelf / Pot)
Delivery to Applicator
Application
Flow & Leveling
Drying / Curing
What are the Requirementsin Each Step?
ppt00 4 4
RheologyRheology
Science concerned with the Science concerned with the flow and deformation of flow and deformation of
materialsmaterials
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 3
ppt00 5 5
Which is more viscous?Which is more viscous?
Water or cooking oil?
Cooking oil or honey?
Honey or mayonnaise?
ppt00 6 6
Viscosities of Common MaterialsViscosities of Common Materials
100 centipoise (cps) = 1 poise 10 poise = 1 Pa s
1 cps = 1 mPa s
5000Honey
1000Glycerine
100Olive Oil
1Water
Viscosity (cps)
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 4
ppt00 7 7
ViscosityViscosity
Viscosity is resistance of a material to flow
ppt00 8 8
ViscosityViscosity
Velocity = 0
Velocity = V
ViscosityViscosityMeasure of the resistance of a fluid to an Measure of the resistance of a fluid to an
imposed flowimposed flow
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 5
ppt00 9 9
Viscosity Viscosity –– Quantitative DefinitionQuantitative Definition
Shear Rate = (V1-V2)/d [ s-1]Shear Stress = F/A [N cm-2]
Velocity = V2
dVelocity = V1
A - Area
F - Force
Viscosity = Shear Stress / Shear Rate [Pa s]
ppt00 10 10
If Viscosity is Independent of Shear If Viscosity is Independent of Shear Rate Coating is NewtonianRate Coating is Newtonian
Shea
r Stre
ss, P
a
Visc
osity
, Pa s
Shear Rate, s-1 Shear Rate, s-1
Stress Rate
Viscosity
γητ &=
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 6
ppt00 11 11
Bubble ViscometersBubble ViscometersSimilar in Concept to Falling Ball. However, Bubble is Deformable -Theoretical Analysis is Difficult.– e.g. Gardner Bubble Viscometer
(ASTM D1545)
Falling Body Type has Very Limited Control Over Measurement Parameters (Shear Rates, Shear Stress)
Not Recommended for non-Newtonian Fluids
ppt00 12 12
Orifice Viscometers (Viscosity Cups)Orifice Viscometers (Viscosity Cups)η (poise)ν (stoke) = ρ (g/cm3)
For low viscosity (<10cps)Kinetic Energy Correctioncan be as high as 90%
Not Suitable for non-Newtonian Fluids
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 7
ppt00 13 13
Rotational Viscometers
ppt00 14 14
NonNon--Newtonian Viscosity BehaviorNewtonian Viscosity Behavior
RPM Viscosity (cps) Spindle #0.5 8000 41 5000 "
2.5 2560 "5 1520 "10 1000 "20 550 250 316 "100 227 "
Brookfield Viscosities @ Different RPMsWaterborne Coating
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 8
ppt00 15 15
ShearShear--Thinning BehaviorThinning Behavior
As viscometer RPM increases Shear Rate increasesCoating is Shear-Thinning
4""""2""
Viscosity Measured withBrookfield
100
1000
10000
0.1 1 10 100
RPM
Visc
osity
(cps
)
ppt00 16 16
Shear Thinning BehaviorShear Thinning Behavior
Viscosity Measured with ARES
10
100
1000
10000
100000
0.01 0.10 1.00 10.00 100.00 1000.00
Shear Rate (s-1)
Visc
osity
(cps
)
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 9
ppt00 17 17
Shear Thinning & Thickening BehaviorShear Thinning & Thickening Behavior
Shea
r Stre
ss, P
a
Shear Rate, s-1
γητ &=
)( 1<= nnKγτ &
)( 1>= nnKγτ &
ppt00 18 18
Continuous Phase Continuous Phase CompositionComposition–– Thickener, OtherThickener, Other
Hydrodynamic VolumeHydrodynamic VolumeChain EntanglementsChain Entanglements
Volume Fraction and Volume Fraction and Nature of Dispersed Nature of Dispersed ComponentsComponents–– Binder, Pigment, FillerBinder, Pigment, Filler
What makes a coating nonWhat makes a coating non--Newtonian?Newtonian?
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 10
ppt00 19 19
Polymer Conformation Hydrodynamic Polymer Conformation Hydrodynamic Volume Volume RheologyRheology
Intrinsic Viscosity, [η] = K Mva
Mv - Viscosity average molecular weightK - Huggins Constanta - Mark-Houwink Constant
a = 0.5 at theta(θ) conditions(e.g., polyisobutylene in benzeneat 24oC)a > 0.5 in a good solvent
ppt00 20 20
Polymer Concentration Polymer Concentration RheologyRheology
Viscosity dependence on shear-rate increases
Viscosity dependence on time increases
Dilute Critical(Overlapping)
Concentrated(Entanglements)
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 11
ppt00 21 21
Polymer Molecular Weight Effect on Polymer Molecular Weight Effect on ViscosityViscosity
Log
Vis
cosi
ty
Log Mc
1.0
3.4
24,000Polydimethyl siloxane
23,000Polyvinyl acetate
5,0001,4 polybutadiene
15,000Polyisobutylene
10,000Cis-polyisoprene
13,000Polycarbonate
28,000Polymethyl methacrylate
30,000Polystyrene
4,000Polyethylene
Critical MWPolymer
Chain entanglements above a critical polymer chain length
Ferry, Viscoelastic Properties of Polymers, 3rd ed, Wiley, New York, 1980
ppt00 22 22
High shear can break up High shear can break up entanglementsentanglements
Vis
cosi
ty
Shear Rate
Visc
osity
Molecular Weight
LSV
HSV
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 12
ppt00 23 23
Polymer MWD impacts shear Polymer MWD impacts shear --thinningthinning
Vis
cosi
ty
Shear Rate
Narrow
Broad
ppt00 24 24
Effect of Molecular Weight on Effect of Molecular Weight on ThickeningThickening
HMW Shear-thinning
LMW Newtonian
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 13
ppt00 25 25
Effect of HEC Concentration on Viscosity
Glass, J. Oil Colour Chem. Assoc., 58, 169 (1975)
ppt00 26 26
ThixotropyThixotropy
Vis
cosi
ty
Shear Rate
Vis
cosi
ty
Time
Shea
r Stre
ss
Shear Rate
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 14
ppt00 27 27
UltraUltra--Fine Clay ThickenersFine Clay ThickenersHighly Shear thinning
High Yield Stress
Low Thixotropy
++
_ _ _ _
Positive Edges & NegativeFaces – Weak Structure
e.g., Laponite
ppt00 28 28
Effect of Dispersed Phase on Viscosity
Visc
osity
% Volume Solids 64
Cubic PackingCritical Volume
Fraction - 0.5236
Hexagonal PackingCritical Volume
Fraction - 0.7405
For Random Packing, Critical For Random Packing, Critical Volume Fraction Volume Fraction -- 0.640.64
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 15
ppt00 29 29Krieger, Trans. Soc. Rheol., 7, 101 (1963)
ppt00 30 30
Effect of Particle Size Distribution Effect of Particle Size Distribution on Viscosityon Viscosity
Polydispersed
Monodispersed
“Vis
cosi
ty”
% Volume Solids 64
Monodispersed Polydispersed
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 16
ppt00 31 31
Effect of Particle Shape on Effect of Particle Shape on ViscosityViscosity
“Vis
cosi
ty”
% Volume Solids 64
Spheres
PlateletsNeedles
ppt00 32 32
Flocculation & Aggregation of Flocculation & Aggregation of Particles in CoatingsParticles in Coatings
DLVO Theory(Two Particles)
S
a - Van der Waals, Long-range (Attractive)b - Electrostatic, Long-range (Attractive orRepulsive)c - Steric, Short-range (Repulsive)d - Solvation, Short-range (Attractive orRepulsive)e - Born, Atomic-range (Repulsive)
Inter-Particle Forces
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 17
ppt00 33 33
Flocculation & Aggregation of Flocculation & Aggregation of Particles in CoatingsParticles in Coatings
Pot
entia
l Ene
rgy
S
Repulsive
Attractive
Pot
entia
l Ene
rgy
S
Repulsive
Attractive
a
bc
de
AggregationFlocculation/Agglomeration
ppt00 34 34
Effect of Particle Flocculation / Effect of Particle Flocculation / Aggregation on ViscosityAggregation on Viscosity
“Vis
cosi
ty”
% Volume Solids 64
Non-aggregated
Aggregated
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 18
ppt00 35 35
Effect of Solids Level on Viscosities Effect of Solids Level on Viscosities at Various Shear Ratesat Various Shear Rates
log
(Vis
cosi
ty)
log (Shear Rate)
SolidsSolidsIncreasesIncreases
LowLow--ShearShear MediumMedium--ShearShear HighHigh--ShearShear
ppt00 36 36
Effect of Solids Level on Viscosities Effect of Solids Level on Viscosities at Various Shear Ratesat Various Shear Rates
Vis
cosi
ty
%Volume Solids
LowLow--ShearShear MediumMedium--ShearShear HighHigh--ShearShear
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 19
ppt00 37 37
Types of Viscosity BehaviorTypes of Viscosity Behavior
Newtonian
Dilatant (Shear-thickening)Yield Stress
Rate
Stre
ss
Plastic
Shear-thinning (Pseudo-plastic)
2/12/12/10
2/1 γηττ &∞+= Casson
Approx.
ppt00 38 38
SummarySummaryViscosity– Hydrodynamic Volume
Shear Thinning– Chain Entanglements– Flocculation / Aggregation
Thixotropy– Chain Entanglements– Flocculation / Aggregation
Yield Stress– Weak Structure (gel)
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 20
ppt00 39 39
10-2 10-1 100 10+1 10+2 10+3 10+4 10+5 10+6
log (V
iscos
ity)
log (Shear Rate (s-1))
What is the Ideal Viscosity Profile?What is the Ideal Viscosity Profile?
Shear-Thinning
Newtonian
ppt00 40 40
Shear Rates for Coating SagShear Rates for Coating Sag
t - film thicknessρ - densityμ - viscosity
μρ2
gt=Shear Rate
For a 1.1g cm-3 density, 3 mil (0.0076cm) thick, 1Pa s (10 poise)
coating,sag shear rate is 0.4 s-1
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 21
ppt00 41 41
Shear Rates for ReverseShear Rates for Reverse--Roll ApplicationRoll Application
Reverse Roll Coater Nip Region
v
vd/2
V = 100 F/mind = 2 mil
Shear Rate = ___________200x12x103
60x2
Shear Rate = 2.0x104 s-1
ppt00 42 42
Shear Rates for Various SubShear Rates for Various Sub--ProcessesProcesses
10-2 10-1 100 10+1 10+2 10+3 10+4 10+5 10+6
log
(Vis
cosi
ty)
log (Shear Rate (s-1))
Settling
WickingMixing
(Slurries) RollCoating
SprayCoating
Sag & Leveling
Brush/RollPick Up
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 22
ppt00 43 43
Shear Thinning BehaviorShear Thinning Behavior
V isco s ity M easu red w ith AR E S
10
10 0
10 0 0
10 0 0 0
10 0 0 0 0
0 .0 1 0 .10 1.0 0 10 .0 0 10 0 .0 0 10 0 0 .0 0
S h ear R ate (s -1 )
Visc
osity
(cps
)
ppt00 44 44
Shear Thinning BehaviorShear Thinning Behavior
V isco s ity M easu red w ith AR E S
0
2 0 0 0
4 0 0 0
6 0 0 0
8 0 0 0
10 0 0 0
12 0 0 0
14 0 0 0
16 0 0 0
18 0 0 0
0 .0 0 50 .0 0 10 0 .0 0 150 .0 0 2 0 0 .0 0 2 50 .0 0
S h ear R ate (s -1 )
Visc
osity
(cps
)
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 23
ppt00 45 45
Other NonOther Non--Newtonian Phenomena Newtonian Phenomena ((ViscoelasticityViscoelasticity))
ppt00 46 46
Surface Tension? Other Forces?Surface Tension? Other Forces?
Externally applied force
Gravitational force
Inertial force
Surface (interfacial) tension forceOther forcesViscous resistance force
What are all the forces impacting flow?
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 24
ppt00 47 47
Surface TensionSurface Tension
Soap Film
Surface tension = Energy required to expand soap bubble (creating surface)
Soap Film
l
w
l
w
dl Force = σ w x 2Energy = σ w dl x 2
σ is surface tension (dynes/cm) or freesurface energy (ergs/cm2)
ppt00 48 48
Surface TensionSurface Tension
Liquid Surface Tension (dyne/cm)
Water 72 Ethyl Alcohol 22.8
Molecules at the surface aresubject to a net attractive forcetowards bulk liquid.
This is the origin ofSurface Tension
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 25
ppt00 49 49
Why does water haveWhy does water havesuch a high surface tension ?such a high surface tension ?
H
H OH O
H
CH HCH H
HH
O
H
H O
Small positive chargeon H atom
Small negative chargeon O atom
Hydrogen bonding attractions
ppt00 50 50
Surface (Interfacial) Tension Surface (Interfacial) Tension Causes FlowCauses Flow
Waxed Surface – 32 dynes/cmWater - 72 dynes/cm
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 26
ppt00 51 51
Surfactants are used to lower Surfactants are used to lower surface tension of watersurface tension of water
Surfactant concentrationCMC
Sur
face
Ten
sion
hydrophilic lipophilic
C12H25SO4-Na+
C2H5OH
ppt00 52 52
Solvent Surface Tension ValuesSolvent Surface Tension Values
24.6N-Butanol
24.0MEK
18.0Hexane
27.7Dowanol PM®
28.4Toluene
30.0O-Xylene
36.0Propylene Glycol
48.4Ethylene glycol
72.3Water
Surface Tension
(dynes/cm)Solvent
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 27
ppt00 53 53
Surface Tension of Common Surface Tension of Common SubstratesSubstrates
16PTFE
29-31PP, PE
41PMMA
35-50Most Organic Coatings
>55Steel
Surface Tension (dynes/cm)
Substrate
ppt00 54 54
Contact Angle Contact Angle –– Wetting Wetting
Interfacial tension between
Liquid / Air
Solid / Air
Solid / Liquid
Must be considered
θ
θ - Contact Angle
Zero Contact Angle
Spontaneous Wetting& Spreading
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 28
ppt00 55 55
ppt00 56 56
Equilibrium Equilibrium vsvs Dynamic Dynamic Surface TensionSurface Tension
•What is the surface tension of just mixed surfactantl/water ?
•What is it sometime later ?•What is it in between ?
SurfaceTension
TimeThis is important when creating new surfaces/interfaces
e.g., creation of spray dropletscreation of coating films
CHEM 550 – Formulation of Modern Coatings Spring 2006
Polymers and Coatings ProgramCalifornia Polytechnic State University 29
ppt00 57 57
MarangoniMarangoni Effect Effect –– Flow Driven by Flow Driven by Surface Tension ForceSurface Tension Force
Evaporation of alcohol raises surface tension near the rim of glass
Alcohol-rich wine flows upwards due to surface tension force
Drops cascade down as gravity takes over
ppt00 58 58
Surface Tension flows
Crawling: When γimpurities < γfilm, the coating naturally begins to
minimize free surface energy by flowing from low γ to high γ, leaving a crater with the impurity in the center
Substrate
Low Surface Tension
Fluid Flow Fluid Flow
Low Surface TensionContaminant