流变学教学课件.ppt

1、 Robyn McMillan October 11,20021 What is Rheology?Rheology:Science of Deformation and Flow-From the Greek Word“Rheos”(River)-Refers to both Liquids and Solids2 Motivation-optimize the process of synthesis,formulation and application?-achieve good appearance(no sag,no orange peel,)?-achieve good defe

2、ct resistance?Would you wish toAll rheology related!3 Edge Coverage and Corrosion4 Cratering5 Types of Responses Viscous deformation Apply force Material flows Irreversible Elastic deformation Apply force Material returns to original shape Reversible Visco-elastic Both responses observed6 Shear Defo

3、rmation A=Area(m2)F=Force(N)=Shear Stress =F/A(N/m2)V=Velocity(m/s)h=Height(m)=Shear Rate =V/h(1/s)7 Definition:Viscosity()=Shear Stress()/Shear Rate()Units:Common Units:Poise(P,cP)SI Units:Pascal.seconds(Pa.s,mPa.s)Conversion:1 P=100cP=100mPas 1cP=1 mPa.sExamples of Viscosity Value:Material Approxi

4、mate Viscosity(cp)Air 10-2 Water 1 Olive Oil 10 Honey 104 Asphalt 1011 Glass 1015(molten);1040(solid)Common Coatings 1-108 Viscosity()-Resistance to Flow 8 Flow Behaviors:Newtonian vs.Shear Thinning vs.Shear Thickening ViscosityShear Rate NewtonianViscosityShear Rate ShearThinningViscosityShear Rate

5、 Shear ThickeningNewtonian Fluids:-Viscosity is independent of load-Examples:water,mineral oils,solventsShear Thinning Fluids(Pseudoplastic):-Viscosity decreases with increasing load-Examples:polymer solutions/melts,shampoo,glue,blood Shear Thickening Fluids:-Viscosity increases with increasing load

6、-Examples:wet sand,high concentration of starch 9Example:Shear Thinning of Automotive Waterborne Basecoat101102103104105106cP 10-310-210-11001011021031041/sShear Rate .Diagram00-051-7E(hexanol)10Significance of Shear Rate in Coatings IndustriesRaw MaterialsPreparation (Sand mill orhigh speed dispens

7、er)Settling(During Storage)PaintShakerCoatingPickupApplication(Brushing,Spraying,RollerCoating)Sagging,Leveling,PenetrationVery Slow FlowDry PaintVery Fast Flow 0.0010.010.11101001,00010,000100,000Shear Rate(1/sec)11Application Shear Rate RangeProcessShear Rate Range(1/s)Spraying10,000-1,000,000Roll

8、 Coating5,000-100,000Brushing5,000-20,000Dip/Flow Coating10-100Dispersing100-50,000Mixing20-100Pumping100-10,000Leveling0.01-100Sagging0.01-0.1Pigment Settling0.00112 Flow Behavior-Plastic(Yield Point)Yield PointStressShear Rate Shear stress must surpass some critical value before flow occurs Exampl

9、e:toothpaste,ketchups,lipstick,butter,dispersion paintToothpaste:the daily overcoming of yield stress13 Example:Yield Stress of Automotive Waterborne Basecoat10-310-210-1100101102Pa 0.00010.0010.010.111010010,0001/sShear Rate .DiagramCopyright(C)1997 Physica Metechnik GmbH00-051-7E(Hexanol)Shear Str

10、essYield Stress14 Flow Behavior-Thixotropy LoadLoadLoadNoLoadNoLoadNoLoad Viscosity is time-dependent -Degrades during loaded phase -Increases during unloaded phases Examples:ketchup15Measurement of Viscosity-Flow(Efflux)Cups Ford,Fisher,DIN,Zahn,Shell,etc.Stress:Gravity Shear Rate:Rate offlow Limit

11、ation Designed for Newtonian FluidTemperature control2.0 in ID1.68 in0.92 in0.40 in0.20 in450.30 in ID16Measurement of Viscosity-Spindle Viscometer Problems Undefined flow field Wide range of shearstresses Value measured is anaverage over a largerange of viscositiesTest LiquidRotating Diskw wxr0.44x

12、Theoretical additionto compensate foredge effects17Measurement of Viscosity-Cone/Plate ViscometerConePlateSpecimenw w Very accurateMost commonly usedCan perform varioustests,including measureviscoelasticity18Viscosity Conversion between Different Measuring Techniques Viscosity Conversion Chart(25 C)

13、Kinematic Viscosity()=Dynamic Viscosity()/Density()KinematicViscosity(Stokes)#4 Ford Cup(sec)Zahn Cups(sec)Gardner-HoldtBubbleBubble TravelTime for 100mm(sec)Stormer(Krebs Units)Saybolt(Saybolt Units)0.15#2 Zahn16A-4600.21018A-21000.31420A-11600.51924A302600.62227B333200.82634C374301.03141D1.6405301

14、.23549E435801.44158F2.1466901.64566G487902.05582H2.85210002.26090I5411002.466#3 Zahn27J5612002.87632K5913803.08134L4.26014753.28636M15303.49139N4.816303.810043O18504.046P5.66419505.057S7.168248010W13.5854600Viscosity(P)(if Density=1.0)0.1 0.2 0.3 19 Significance of Viscosity to Sag ResistanceThe dri

15、ving force for sagging is gravity.Under an ideal condition,the sagging can be quantified by,V:velocity of sag Vat coating surface=gX2/2 :density X:coating thickness :viscosity Example:In 1998,PPG white waterborne spray liner(70w30)experienced unsatisfactory appearance.The low/zero shear viscosity wa

16、s identified as the key parameter to the uniformity problem(due to sagging).10102103cP 0.11101021031041/sShear Rate .Flow Curves of Spray LinersPhysica Messtechnik GmbHPPG 70W30 WhiteViscosityDexter GoldViscosityPPG 76W40 grayViscosityPPG 70W30 White,low shearViscosityBetter SagResistanceFlow Curves

17、 of Spray Liners20Silly Putty21Powder Coatings22Electrocoat Additive Study100010000100000100000010000000100000000051015Time(Minutes)Complex Viscosity(mPa sec or cps)020406080100120140160180200Temperature(C)(0/0/0)(0/1.2/0)(4/0/0)(0/0/.7)(4/1.2/.7)Temperature(C)23Correlation of Edge Corrosion and Min

18、imum ViscosityR2=0.84430500010000150002000025000300003500040000450005000000.20.40.60.811.21.41.6Edge Corrosion(mm)Minimum Complex Viscosity 1Hz/5%strain(mPa sec.)24Microdielectrometry25 Concentration(solids)Molecular weight of resins Resin flexibility(Tg)Latex particle size Quality of dispersion Viscosity of solvent Resin-solvent interactions AdditivesHow Do We Control Rheology?26 SummaryRheology has a significant influence on coatings process,application,appearance/defect resistance etc.It is important tounderstand the fundamentals and apply them to the point of interest.27