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REVIEW PAPER: IMPORTANCE OF RHEOLOGY IN

SURFACE COATINGS AND ITS MEASUREMENT Sachin Kumar Kashyap

*1

*1Final B.Tech. Chemical Technology (Paint Technology) Department of Paint Technology,

Harcourt Butler Technical University, Kanpur UP, India

ABSTRACT In the paint and several other allied industries many methods and techniques have been developed to relate a flow

quantity to particular coating performance characteristics. Off the various physico-chemical properties studied in

coating technology, rheology, a physical property plays an important role in paint manufacturing. The knowledge of

the rheology of materials and how to manipulate it through formulation is a vital tool in the optimization process. In

addition to that, knowing about the various types of rheometer/viscometer, their conversion units, various factors on

which it actually depends and its effect on different coating properties would be an added advantage. This review

article discusses the concept of rheology, measurement and its application in surface coating.

KEYWORDS: Viscosity, Rheology, Surface Coatings, Flow Behavior, Viscosity Measurement

I. INTRODUCTION One of the most important property of the surface coating is the way in which material flows. The science which

describes how materials change their shape is called Rheology. For liquids and semi-solids, this is typically called

flow behavior. In surface coating rheology is not a simple flow property, after application it must hold up, possibly

on a vertical surface. Most of the coatings are formulated in such a way that the rheology fulfill both requirements

i,e. holds up and flow out. Viscosity is one part of the science of Rheology which quantifies the resistance materials

give to changing shape. It is a measure of the resistance of a fluid to deform under shear stress. It is commonly

perceived as flow behavior or resistance to pouring. Molecule size, molecule shape, molecule nature, molecule

arrangement, force between molecules causes viscosity.

Shear Flow:This is the easiest type of flow to define and control. When a force is applied to the top surface area of

a cube of material produces a deformation in that surface which diminishes in the remaining layers of the material.

This force, F per unit area, A, is termed the shear stress (σ) and a deformation is characterized by the angle ϒ

known as shear.

Shear Rate:If shear stress is maintained with time on the surface of a fluid then angle ϒ would change with time.

This is known as shear rate or we can say that shear rate is a measure of how rapidly a material is deformed and its

unit is per second (Fig1). During shear orientation, extension, deformation, breaking of aggregates takes place in the

sample (Fig.2).

When a force F is applied at the liquid surface of area A, it undergoes deformation or shearing. Tendency of the

liquid to resist this deformation is called Viscosity and is expressed as the ratio of shear stress τ vs shear rate D

according to

ή (viscosity)=τ/D

where τ=F/A (dynes/cm2) and D=v/x(sec

-1)

here v represents the velocity of the liquid and x the liquid thickness. when shear stress is expressed in dynes/cm2

and shear rate in sec-1, viscosity is expressed in poise (Absolute Viscosity)

poise=gm cm-1sec-1

when liquids are sheared under influence of gravitational forces, the viscosities are expressed in terms of kinematic

viscosities and are obtained by dividing the absolute viscosity ή by the density ρ of liquids This is expressed in

stokes units.

Kinematic viscosity (stokes)(ν)=ή/ρ(cm2sec-1)

Here ρ is the mass density of the fluid.



Fig1: Shear Rate

During shear the following changes takes place in the sample

Orientation Extension Deformation Breaking of Aggregates

Fig 2: Changes taking place during shear in the sample

Dimensions and Units of Viscosity

The dimensions of dynamic viscosity are M L-1 T-1 and the basic SI unit is the Pascal second (Pa·s), where 1 Pa·s =

1 N s m-2. The c.g.s. unit of dynes cm-2 is the poise (P). The dimensions of kinematic viscosity are L2T-1 and the SI

unit is m2s-1. For most practical situations, this is usually too large and so the c.g.s. unit of cmor thestoke (St), is

preferred. Table 1 lists some common fluids and their shear dynamic viscosities at atmospheric pressure and 20°C.

η =Viscosity= Shear Stress/Shear Rate=(dynes-cm-2

/sec-1

)^-1

Table 1: Shear Dynamic Viscosity of Some Common Fluids at 20°C and 1 atm

Fluid Shear dynamic viscosity (Pa·s)

Air 1.8 × 10-4

Water 1.0 × 10-3

Mercury 1.6 × 10-3

Automotive engine oil 1.3 × 10-1

Dish soap 4.0 × 10-1

Corn syrup 6.0

According to Newton’s law, the viscosity of a fluid is constant. As shear rate changes, shear stress changes in

proportion such that viscosity is constant. Unfortunately, most fluids do not follow Newton’s law. For this reason,

fluids are classified into two categories: Newtonian and non-Newtonian fluids.

Newtonian fluids:It is most easily understood by thinking of a liquid that has a constant viscosity over a wide range

of shear rates at a given temperature. The viscosity is independent of the shear rate at which it is measured. It plays

a key role in the processing stage. For certain liquids viscosity is a material constant that only depends on

temperature and pressure. This group of materials is termed Newtonian liquids. Oils, some resin solutions, solvents,

some additives are Newtonian fluids (Fig3). on the other hand, the Newtonian fluid follow the law(eq-1) shear

stress proportional to shear rate.



Non-Newtonian fluids: For a non-Newtonian fluid, viscosity is dependent upon the shearing action (shear rate or

shear stress) at which it is measured (Fig3). Non-Newtonian flow may be classified into two categories: non-

Newtonian time independent flow and non-Newtonian time dependent flow. The most common behavior is shear

thinning where with an increasing shear rate the material a decreasing viscosity has. Surface coatings will generally

show this type of behavior and they usually contain both polymers and pigment particles. The converse of shear

thinning is shear thickening, whereby the viscosity is increased by increasing the shear rate. The surface coating

industry often exploits this behavior in paint manufacture by using mill bases. They are highly pigmented mixtures,

exhibiting shear thickening, and hence when caused to flow rapidly show very high viscosity. Thus the non-

Newtonian fluid can be broadly be classified as: -

Types of Non-Newtonian Fluid (most of the paints fall under this category)

1. Time Dependent

Thixotropic

Rheopectic

2. Time Independent

Pseudo plastic

Bingham Plastic

Dilatant

Flow Curves or Rheograms

The nature of flowing materials can be characterized in a graph of shear stress versus shear rate. When we plot the

relationship between shear stress and shear strain for any liquid is displayed graphically shear stress(τ) at y-axis and

shear strain (γ) at x axis. This graph is known as flow curve orrheogram. Flow curves can give us information about

the type of flow (yield stress), effect of shear rate, changing effect of shearing history and recovery after the shear

force is removed.

Fig 3: Flow curve showing Newtonian Non-Newtonian fluids behavior

Rhegrams for Newtonian fluid

Viscosity of Newtonian fluids for increase and decrease in shear rate remains constant.



Rheograms for Non Newtonian

Time independent

Pseudo plastic fluids become thinner when the shear rate increases, until the viscosity reaches a stage of limit

viscosity. Ex:- Nail polish,latex paint,some silicon coatings etc.

Bingham plastic fluid will have a solid or semisolid character under static conditions. A certain amount of

shear force must be applied to the fluid Before any flow is induced this force is called the yield stress Once the

yield value is exceeded and flow begins plastic fluids may display Newtonian, pseudo plastic or dilatant flow

characteristics. Ex :- thooth paste ,some oils etc.

Dilatant fluids become thicker when agitated. The viscosity increases proportionally with the increase of the

shear rate. Ex:- quicksand etc



Thixotropy and Rheopecty: It is found that at a constant shear rate the viscosity of a material continually changes

for a period of time prior to settling to a steady rate value. The liquids whose viscosity decreases with time, like

nondrip paints, which behave like solids until the stress applied by the paint brush for a sufficiently long time

causes them to flow freely, are called thixotropic fluids. Conversely, an increase in the viscosity during shear which

is lost during a period of rest is termed anti-thixotropy. Thixotropy is far more commonly found than anti

thixotropy. Emulsion paint (latex paint or acrylic paint) exhibiting thixotropy where an increase in relative flow

velocity will cause a reduction in viscosity, for example, by stirring. Some other non-Newtonian materials show the

opposite behavior, rheopecty: viscosity going up with relative deformation, and are called shear thickening

or dilatant materials. Since Sir Isaac Newton originated the concept of viscosity, the study of liquids with strain rate

dependent viscosity is also often callednon-Newtonian fluids mechanics. Ex: - clays etc.

Factors Affecting Viscosity

Flow Condition-Laminar or Turbulent

Temperature

Pressure

concentration

attractive force

particle size

Flow condition

In laminar flow, the substance moves in imaginary thin layers in which molecules do not change from one layer to

another layer. The fluid has an uniform structure. While in the turbulent flow, non-uniform structure or layers can

be observed. Molecules moves freely or in random nature.

If testing a fluid under turbulent flow condition, it will give a higher viscosity.

Temperature

A fluid's viscosity depends on its temperature. Temperature has a dominating influence. Viscosity of a fluid

decreases with increase in temperature and decreasing temperature causes an increase in viscosity. The relationship

between temperature and viscosity is inversely proportional for all substances. A change in temperature always

affects the viscosity. It depends on the substance just how much it is influenced by a temperature change. For some

fluids a decrease of 1°C already causes a 10 % increase in viscosity.

http://www.viscopedia.com/basics/factors-affecting-viscometry/#c82http://www.viscopedia.com/basics/factors-affecting-viscometry/#c85http://www.viscopedia.com/basics/factors-affecting-viscometry/#c86



Pressure

viscosity increases with increasing pressure because the amount of free volume in the internal structure decreases

due to compression. Consequently, the molecules can move less freely and the internal friction forces increase. This

results in an increased flow resistance.

In most cases a fluid's viscosity increases with increasing in pressure. Compared to the temperature, liquids are

influenced very little by the applied pressure because liquids (other than gases) are almost non-compressible at low

or medium pressures. a considerable change in pressure from 0.1 to 30 MPa causes about the same change in

viscosity as a temperature change of about 1 K (1°C).

Concentration

Concentration is the amount of substance that is dissolved in a specific volume. An increase in concentration will us

ually result in an increase in viscosity.

Attractive Force

Particles of the same substance have an attractive force on one another. Some substances

have a strong attraction while some substances have a weaker attraction.

The stronger the attraction of particles, the higher the viscosity.

Particle Size

The size of the particles of a substance will greatly affect its viscosity. Small particles can

move more easily past each other and can therefore flow faster, meaning they have a lower viscosity.

Large particles would mean a higher viscosity.

Rheological Measurement in Surface Coating: In the surface coating industry a number of measurement

methods, flow cup to computer-controlled rotation viscometers have been established for the determination of

viscosity. Rheological properties can be measured from bulk sample deformation using a mechanical rheometer, or

on a micro-scale by using a microcapillary viscometer or an optical technique such as Micro rheology. A large

number of commercial instruments are available for the determination of the absolute properties, within well-

defined flow processes. They are generally rotational devices in which the geometry of the device holding the

sample is defined so that one part of the geometry is in rotation, whilst the other part is static, and this creates a



well-defined and constant shear rate throughout the sample. The instrument sets the shear stress and measures the

rotation rate or vice versa. Shear rate and shear stress are known irrespective of which of the two quantities is set

and which is measured.

The basic principle of all viscometers is to provide as simple flow kinematics as possible, preferably 1D (isometric)

flow, in order to determine the shear strain rate accurately, easily, and independent of fluid type. The resistance to

such flow is measured, and thereby the shearing stress is determined. The shear viscosity is then easily found as the

ratio between the shearing stress and the corresponding shear strain rate.

The instruments for viscosity measurements are designed to determine ―a fluid’s resistance to flow,‖ a fluid property

defined above as viscosity. The fluid flow in a given instrument geometry defines the strain rates, and the

corresponding stresses are the measure of resistance to flow. If strain rate or stress is set and controlled, then the

other one will, everything else being the same, depend on the fluid viscosity. If the flow is simple (one dimensional,

if possible) such that the strain rate and stress can be determined accurately from the measured quantities, the

absolute dynamic viscosity can be determined; otherwise, the relative viscosity will be established. For example, the

fluid flow can be set by dragging fluid with a sliding or rotating surface, falling body through the fluid, or by forcing

the fluid (by external pressure or gravity) to flow through a fixed geometry, such as a capillary tube, annulus, a slit

(between two parallel plates), or orifice. The corresponding resistance to flow is measured as the boundary force or

torque, or pressure drop. The flow rate or efflux time represents the fluid flow for a set flow resistance, like pressure

drop or gravity force. The viscometers are classified, depending on how the flow is initiated or maintained.

Types of Viscometer

A viscometer is an instrument used to measure the viscosity of a fluid. For liquids with viscosities, which vary with

flow conditions, an instrument called a rheometer is used. Viscometers only measure under one flow condition. The

instruments for viscosity measurements are designed to determine ―a fluid’s resistance to flow,‖ a fluid property

defined as viscosity. Depending on how the flow is initiated or maintained, the viscometers are mainly classified

into following types:

• Capillary

• Flow Cup

• Rotational

• Falling Sphere

• Gardeners Tube Viscometer

Capillary

Glass capillary viscometer

viscometers are based on the relation between viscosity and time. It uses gravity as the driving force. Therefore

Capillary the results are kinematic viscosity. The main advantage of this method is that gravity is a very reliable

driving force. Because gravity is available everywhere on earth. This principle is widely established in many

standards practices. The disadvantage of this principle is that the driving force cannot be varied. It is too small for

highly viscous samples. Further, many different capillaries are required to cover a wide viscosity range with one

constant driving force. Many types of capillary viscometers are available in market according to capillary size see

fig given below.

Fig 4: Glass capillary viscometer



Flow Cups

For many applications it is not necessary to know the absolute viscosity of a paint system. A parameter permitting a

relative classification and estimation is often sufficient. The efflux time, measured in seconds, has proven to be a

practical measure. It is determined using flow cups of various designs following the appropriate international /

national standards (Fig5). These cups hold a defined volume of liquid which flows through an orifice. The

reproducibility of such measurements depends on

The accuracy of the size of the cup

A constant temperature during measurement

The Newtonian flow behavior of the liquid

To take a reading, the orifice is sealed with a finger and the cup is filled with material with the excess caught in an

overflow trough. The finger is removed and the time for the material to stream out measured. This is a measure of

the viscosity having the units of seconds.

Fig 5 : Flow Cups

The table given below lists the major flow cup types together with a conversion chart of Efflux Time (in seconds) to

Viscosity in Centistokes (cSt). It has been constructed from the various International Standard Calculators. Each

cup design is unique care must be taken when comparing viscosity values between different cup types. These values

are the absolute values and do not include the allowed tolerances, as these differ considerably between each of the

Standards.



Rotational

The main advantage of the rotational as compared to many other viscometers is its ability to operate

continuously at a given shear rate, so that other steady-state measurements can be conveniently performed. That

way, time dependency, if any, can be detected and determined. Also, subsequent measurements can be made with

the same instrument and sampled at different shear rates, temperature,

etc. For these and other reasons, rotational viscometer share among the most widely used class of instruments for

rheological measurements.

The stormer viscometer

The Stormer viscometer is a specialized viscometer type that is designed to test the viscosity of paints and can be

used in other applications as well. It is widely used in the paint industries to test paint quality based on its viscosity.

The viscometer works by using a specialized paddle shaped rotor that rotates with an internal motor. The paddle is

submerged in the cylinder of liquid to be tested then rotates. Viscometer measures the viscosity of a fluid by

measuring the time taken for an inner cylinder in the mechanism to perform a fixed number of revolutions in

response to an actuating weight. The viscometer is calibrated by measuring the time taken with varying weights

while the mechanism is suspended in fluids of accurately known viscosity. The data comes from such a calibration,

and theoretical considerations suggest a nonlinear relationship between time, weight and viscosity, of the form Time

= (B1*Viscosity)/(Weight - B2) where B1 and B2 are unknown parameters to be estimated,

The viscosity value is provided in Krebs units. Some Paints which are not designed to be spread with a paintbrush

or paint roller will not provide sufficient data with this type of viscometer.

Brookfield viscometer

Brookfield Viscometers can measure viscosity through the varying flow conditions of the sample material being

tested. They consist a spindle on a shaft that is designed to be dipped or immersed into a liquid that is then rotated.



The rotation causes the fluid to produce a drag, which is then measured with the applied torque on the liquid’s

viscosity. And the reading in Krebs unit can be seen in the meter given in it. To measure the sample’s viscosity in

the Brookfield viscometer, the material needs to be stationary inside a container while the spindle moves while

immersed in the fluid. The material must be able to produce a laminar flow over the spindle while moving. This is

only possible with a low Reynolds Number.

Parallel plate viscometer

An instrument consisting of two circular parallel plates, the lower one stationary, the upper one rotatable, the disk-

shaped specimen being placed between the plates. The material being tested is placed in the gap and the lower plate

applies a lateral shear force to the test material.

Concentric cylinder-type viscometer

They are usually employed when absolute viscosity needs to be determined, which in turn, requires a knowledge of

well-defined shear rate and shear stress data.(Fig 6)

Such instruments are available in different configurations and can be used for almost any fluid.

Fig 6: Concentric cylinders viscometer geometry.

Cone and Plate Viscometer

The simple cone-and-plate viscometer geometry provides a uniform rate of shear and direct measurements of the

first normal stress difference. It was designed with an acknowledgment that coatings are generally shear thinning



and that brushing spraying or roller coating of paints takes place at high shear rates, around 10,000s-1. The device

uses a small diameter wide angle cone rotated at a constant speed, in contact with a plate. It is the most popular

instrument for measurement of non-Newtonian fluid properties. The working shear stress and shear strain rate

equations can be easily derived in spherical coordinates, as indicated by the geometry. The simple cone-and-plate

viscometer geometry provides a uniform rate of shear and direct measurements of the first normal stress difference.

It is the most popular instrument for measurement of non-Newtonian fluid properties.

.

Fig 7: Cone and Plate Viscometer

Falling Sphere

The falling sphere viscometer is one of the earliest and least involved methods to determine the absolute shear

viscosity of a Newtonian fluid. In this method, a sphere is allowed to fall freely a measured distance through a

viscous liquid medium and its velocity is determined.

It is a schematic diagram (Fig 8) of the falling sphere method and demonstrates the attraction of this method — its

simplicity of design. The simplest and most cost-effective approach in applying this method to transparent liquids

would be to use a sufficiently large graduated cylinder filled with the liquid. With a distance marked on the cylinder

near the axial and radial center (the region least influenced by the container walls and ends), a sphere (such as a ball

bearing or a material that is nonreactive with the liquid) with a known density and sized to within the bounds of the

container correction, free falls the length of the cylinder. As the sphere passes through the marked region of length d

at its terminal velocity, a measure of the time taken to traverse this distance allows the velocity of the sphere to be

calculated. This method is useful for liquids with viscosities between 10-3 and 105 Pa·s. Due to the simplicity the

falling sphere method is particularly well suited to high pressure–high temperature viscosity.

The viscous drag of the falling sphere results in the creation of a restraining force, F, described by Stokes’ law:

F=6πηrv, where r is the radius of the sphere and v is the terminal velocity of the falling bod

Fig 8: Schematic diagram of the falling sphere viscometer. Visual observations of the time taken for the sphere to

traverse the distance d are used to determine a velocity of the sphere

The falling-ball viscometer VISCO BALL is based on the Hopper measurement system. It measures the time taken

by a solid sphere to travel the reference distance through an inclined tube filled with the sample. A return constant

may be established by turning the tube upside-down. The test results are given as dynamic viscosity in the

internationally standardised absolute units of mill Pascal seconds. Temperature is controlled in Falling ball

viscometers is done by maintaining a bath of constant temperature which allow an accurate study of viscosity.



Selection of ball is made on basis of the assumed viscosity of studied liquid and the specification which is given in

table

BALL.NO. Material Density

ρ(gr/cm3 )

Ball weight (gr) Ball constant (mPa.

cm3 /gr)

Measuring

range

(mPa.s)

1. Glass 2.228 4.599 0.00891 0.6-10

2. Glass 2.228 4.816 0.0715 7-130

3. Glass 2.411 4.454 0.07755 30-700

4. Alloy 8.144 16.055 0.1239 200-4800

5. Alloy 7.909 14.536 0.6543 800-10000

Garderner tube viscometer

Gardner bubble viscometers are used to quickly determine kinematic viscosity of known liquids such as resins and

varnishes. This instrument is based on the principle that the viscosity is directly proportional to the bubble speed.

The viscosity of a sample of varnish or other transparent liquid is therefore determined by reference to the standard

tubes in which an air bubble rises with the same speed as it does in a tube of the sample being tested. For this

purpose, two carefully calibrated empty tubes are furnished with each set. The tube has three amber ring marks at

27, 100 and 108 mm from the bottom. Fill the tube up to the 100 mm line, insert the cork down to the 108 mm line

and turn the tube bottom up. Turn the tube around, start the stop watch when the air bubble crosses the 27 mm line

and stop when the bubble crosses the 100 mm line. Gardner tube viscometer mainly use for measuring viscosity of

medium and high viscous clear (transparent) liquid.



The basic principle of all viscometers is to provide as simple flow kinematics as possible, preferably one-

dimensional (isometric) flow, in order to determine the shear strain rate accurately, easily, and independent of fluid

type. The resistance to such flow is measured, and thereby the shearing stress is determined. The shear viscosity is

then easily found as the ratio between the shearing stress and the corresponding shear strain rate.

Because of different types of viscometer , interchange of technical information makes it necessary to provide table

for converting viscosities from one type to another. Table 2 shows comparison of viscosity measured from different

viscometer.

Table 2: Viscosity comparison chart at 250C

Application

Paints are most frequently either highly shear thinning or thixotropic, they tend to aid the application process. High

shear rates generated in these application methods destroy the inherent structure within paint, for the duration of the

application, which considerably increases the ease with which they flow in such processes. Cone and plate

viscometer would be the best suited for this measurement. Another consideration that has to be taken into account



when adapting the rheology for an application process is that in order to apply a sufficiently thick coating to the

substrate the high shear rate viscosities also need to be relatively high.

The paint properties like Gloss, Smoothness, Abrasion resistance, Water resistance Application (brush, spray, roller,

dipping etc.), Sagging, etc. depend on their rheology. Viscometric data can be used for material characterization or

―finger-printing‖,standard testing methods to check for differences between batches, indirect way of measuring

quality, product formulation,quality control, process control, design, optimization and operation of process

equipment.

The processes designed for the application of coatings are based on other criteria than simple flow. The common

methods of application, brush, spray, roller and electro deposition, for instance were developed with consideration

of criteria such as speed of application, mechanical simplicity, transfer efficiency and ease of equipment cleaning

amongst a host of others. In surface coating, viscosity measurement can be used in the following:

It help in formulation e.g.-charging of ball mill, etc.

consistent product quality is ensured e.g.-linseed stand oil

stability of product e.g.-paint packed at 120 s, cough syrup

Quality control & Production e.g. alkyd resin discharged at appropriate viscosity

It helps in material characterization e.g. NC lacquer (1/2s, 3/4s, 4s, 10s, etc)

Design, optimization and operation of process equipment

II. CONCLUSION The science of rheology and the characterization of viscoelastic properties in the production and use

of polymeric materials have been critical for the production of many paint products for use in the industrial sectors.

The deformation and flow properties (rheology) of coatings exhibit many and varied forms of behavior under well

controlled, laminar flow conditions. Adapting these properties to give good performance under the constraints

imposed in all aspects of the coating’s life, from manufacture through storage and application to post application, is

one of the naturally difficult problems for a paint formulator to consider. Rheology can be vital tool in the

optimization process of paints. Flow properties are used as important quality control tools to maintain the

superiority of the product and reduce batch to batch variations.

III. REFERENCES [1] www.kostic.niu.edu/K12208_C046-viscosity-PR.pdf

[2] J. Ferguson and Z. Kemblowski, Applied Fluid Rheology, New York: Elsevier, 1991.

[3] R. W. Whorlow, Rheological Techniques, 2nd edn., New York: Ellis Horwood, 1992.

[4] C. W. Macosko, Rheology: Principles, Measurements, and Applications, New York: VCH, 1994.

[5] F. Gui and T. F. Irvine, Jr., Theoretical and experimental study of the falling cylinder viscometer, Int. J. Heat

Mass Transfer, 37(1), 41–50, 1994.

[6] J. A. Himenez and M. Kostic, A novel computerized viscometer/rheometer, Rev. Sci. Instrum., 65(1), 229–

241, 1994.

[7] Y. Bottinga and P. Richet, Silicate melts: The ―anomalous‖ pressure dependence of the viscosity,Geochim.

Cosmochim. Acta, 59, 2725–2731, 1995.

[8] Cannon-Fenske Viscometer Instrument Manual.

[9] N. A. Park and T. F. Irvine, Jr., Falling cylinder viscometer end correction factor, Rev. Sci. Instrum., 66(7),

3982–3984, 1995.

[10] G. E. LeBlanc and R. A. Secco, High pressure stokes’ viscometry: A new in-situ technique for sphere velocity

determination, Rev. Sci. Instrum., 66(10), 5015–5018, 1995.

[11] 11.A. Marrion, The Chemistry and Physics of Coatings, Second Edition

[12] C. J. Schaschke, High pressure viscosity measurement with falling body type viscometers, Int. Rev. Chem.

Eng., 2, 564–576, 2010.

[13] L. Kulisiewicz and A. Delgado, High pressure rheological measurement methods: A review, Appl. Rheol., 20,

13018, 2010.
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