Alazhr universityAlazhr universityFaculty of pharmacyFaculty of pharmacy

For GirlsFor Girls

Essay of Essay of RheologyRheology

UnderUnderSupervisionSupervision

Dr. Maha AbdelhmeedDr. Maha AbdelhmeedHead masterHead master

Of pharmaceutics departmentOf pharmaceutics department

Prepared byPrepared by

The science of deformation and The science of deformation and flow of matterflow of matter..

  Therefore the term includes the most Therefore the term includes the most complex cases. Pharmaceutical complex cases. Pharmaceutical preparation in particular along with preparation in particular along with many natural foods and food many natural foods and food products are complex and products are complex and rheological materials. Rheology is the rheological materials. Rheology is the branch of physics, which deals with branch of physics, which deals with deformation and flow of matter.deformation and flow of matter.

It is important in many It is important in many fieldsfields

1- To the physiologist, rheology covers or provides  the 1- To the physiologist, rheology covers or provides  the circulation of blood through capillaries and large circulation of blood through capillaries and large vessels.vessels.

2- To the physician, the fluidity (reciprocal of viscosity) of 2- To the physician, the fluidity (reciprocal of viscosity) of solution to be injected with hypodermic syringes, solution to be injected with hypodermic syringes, flexibility of tubing use in catheters as well as strength flexibility of tubing use in catheters as well as strength of sutures and ligatures are in rheological properties.of sutures and ligatures are in rheological properties.

3- To the pharmacist, rheology is important in the flow of 3- To the pharmacist, rheology is important in the flow of emulsion, ointments and the mechanical properties of emulsion, ointments and the mechanical properties of glass or plastic containers and of rubber closures.glass or plastic containers and of rubber closures.

4- To the consumer, quality comes into place when 4- To the consumer, quality comes into place when squeezes to toothpaste from a collapsible tube, spread squeezes to toothpaste from a collapsible tube, spread lotion on skin or spreading the butter on bread or paint lotion on skin or spreading the butter on bread or paint on a surface, sprays liquid or aerosol canes.on a surface, sprays liquid or aerosol canes.

5- From the rheological point of view the systems 5- From the rheological point of view the systems are solid if they preserve shape and volume, are solid if they preserve shape and volume, liquid if they preserve the volume and gases if liquid if they preserve the volume and gases if neither shape and nor volume constant when neither shape and nor volume constant when forces are applied to them.forces are applied to them.

6- In the three systems, the transport properties of 6- In the three systems, the transport properties of gases described by kinetic theory of gases (to gases described by kinetic theory of gases (to study) are best understood but they are of minor study) are best understood but they are of minor importance in pharmacy.importance in pharmacy.

7- Rheology of pharmaceutical formulation is 7- Rheology of pharmaceutical formulation is essential part of the work of the pharmacist, both essential part of the work of the pharmacist, both the quality assurance and drug delivery systems. the quality assurance and drug delivery systems. The associated study known as bio-rheology, The associated study known as bio-rheology, could be assigned for the patient with defected could be assigned for the patient with defected body fluid function as well as circulatory diseases body fluid function as well as circulatory diseases either as a primary cancer or as the additional either as a primary cancer or as the additional effect of another diseases of diabetic is essential effect of another diseases of diabetic is essential for effective pharmacological management.for effective pharmacological management.

8- In addition there are important features to 8- In addition there are important features to study rheological consideration as a part of study rheological consideration as a part of rheology. The pharmaceutical industry has a rheology. The pharmaceutical industry has a direct interest in the area of bio-rheology direct interest in the area of bio-rheology because of the existence of a range of drugs, because of the existence of a range of drugs, which are designed to control the flow which are designed to control the flow properties of various body fluids in diseases. properties of various body fluids in diseases. Medical practitioner and clinical dentist Medical practitioner and clinical dentist might wish to ass rheological properties of might wish to ass rheological properties of human body fluid e.g. saliva, mucous and to human body fluid e.g. saliva, mucous and to their clinical pathological test.their clinical pathological test.

  9- The pharmacist has a mandatory interest in 9- The pharmacist has a mandatory interest in pharmaceutical rheology in as much as pharmaceutical rheology in as much as affects the therapeutic value of medicine affects the therapeutic value of medicine and unit doses. The scope of pharmaceutical and unit doses. The scope of pharmaceutical rheology is concerned not only with the rheology is concerned not only with the handling of liquids and semi-solids but also handling of liquids and semi-solids but also provide its behavior to the preparation of provide its behavior to the preparation of powders in a specialized area of knowledge powders in a specialized area of knowledge and function.and function.

10- Pharmaceutical rheology is important in every 10- Pharmaceutical rheology is important in every stage in lifetime of medicine that is design, stage in lifetime of medicine that is design, manufacture, transport, uses and storage.manufacture, transport, uses and storage.

Liquid and semi-solid products are largely directed Liquid and semi-solid products are largely directed towards the oral and topical routes of administration. towards the oral and topical routes of administration. Certain IM injections may contain suspended Certain IM injections may contain suspended insoluble particles. Further more intensive care insoluble particles. Further more intensive care products may also require delivering by pumps. The products may also require delivering by pumps. The oral medicine must reach the patient in such a oral medicine must reach the patient in such a condition that a unit dose is easily obtain without condition that a unit dose is easily obtain without error. The suspensions or emulsions that is too thick, error. The suspensions or emulsions that is too thick, when it reaches to the consumer. The rheological when it reaches to the consumer. The rheological concentration during manufacture of the medicine concentration during manufacture of the medicine may be complex specially when the scale of may be complex specially when the scale of operation changes. Structure products may be operation changes. Structure products may be destroyed and wasted by using an incorrect destroyed and wasted by using an incorrect temperature-time profile on manufacture, all of temperature-time profile on manufacture, all of which can be avoided by product rheological which can be avoided by product rheological supervision.supervision.

STRESSSTRESS

The deformation takes place The deformation takes place only under the influence of only under the influence of stress, which is a type of stress, which is a type of force.force.

TYPES OF STRESSTYPES OF STRESS 1- Tensile stress.1- Tensile stress.  2- Tangential stress: we can call as tangile 2- Tangential stress: we can call as tangile

stress, which is applied to the surface of stress, which is applied to the surface of body vertically or it may be applied body vertically or it may be applied tangentionally to the surface of the body. tangentionally to the surface of the body. applied perpendicular to the surface or applied perpendicular to the surface or tangentionally to the surface. If applied tangentionally to the surface. If applied tangentionally then it is called as sharing tangentionally then it is called as sharing stress.stress.

3- Strain: At any other angle to the surface, 3- Strain: At any other angle to the surface, the resulting deformation is known as strain.the resulting deformation is known as strain.

Measure of strain is non-dimensional quality, Measure of strain is non-dimensional quality, a fractional increase or decrease in length a fractional increase or decrease in length or volume.or volume.

Deformation that may be results from Deformation that may be results from the application of stress may be the application of stress may be

divided intodivided into::

Spontaneous reversible Spontaneous reversible deformation or elastic deformation or elastic deformationdeformation

It comes to its original form e.g. rubber It comes to its original form e.g. rubber band. When we stretch it, its length band. When we stretch it, its length increases and when we release force, increases and when we release force, it comes into its original shape. The it comes into its original shape. The process is reversible and non-process is reversible and non-permanent.permanent.

Permanent or irreversible deformationPermanent or irreversible deformation

It is referred to as flow and are exhibited by It is referred to as flow and are exhibited by viscous bodies. When we apply force, it viscous bodies. When we apply force, it doesn’t comes to its original shape e.g. doesn’t comes to its original shape e.g. chalk. When we apply force on chalk it will chalk. When we apply force on chalk it will break and on releasing force it will not break and on releasing force it will not come back into its original shape.come back into its original shape.

The work used in producing elastic The work used in producing elastic deformation is reversible. When the body deformation is reversible. When the body returns to its original shape after the returns to its original shape after the removal of the applied force/stress. removal of the applied force/stress. However in case of irreversible deformation, However in case of irreversible deformation, the work don’t recoverable when the stress the work don’t recoverable when the stress is removedis removed

Rheology involves in mixing and flow of Rheology involves in mixing and flow of material and their packaging into material and their packaging into containers and their removal prior to containers and their removal prior to use. Rheology of a particular productuse. Rheology of a particular product

  can range in consistency from fluid to can range in consistency from fluid to semi-solid to the solid can accept its semi-solid to the solid can accept its patient acceptability, physical stability patient acceptability, physical stability and even biologic availability. Thus the and even biologic availability. Thus the viscosity, which is expressed as a viscosity, which is expressed as a resistance of fluid to flow, the higher the resistance of fluid to flow, the higher the viscosity the more the resistance has viscosity the more the resistance has been shown to effect the absorption been shown to effect the absorption rate of drug from GIT.rate of drug from GIT.

Rheology is also important in physiology Rheology is also important in physiology e.g. flow of blood, stressing of muscle, e.g. flow of blood, stressing of muscle, deformation of bony structure.deformation of bony structure.

In man pharmaceutical industries, In man pharmaceutical industries, Rheology is also applied in various Rheology is also applied in various operations such as stirring, mixing and operations such as stirring, mixing and compressing also in the application of compressing also in the application of the pharmaceutical products.the pharmaceutical products.

The mechanical properties of packaging The mechanical properties of packaging material, strength and the toughness material, strength and the toughness of the bottle, deformation of rubber of the bottle, deformation of rubber stopper are also the rheological stopper are also the rheological properties.properties.

PHARMACEUTICAL AREAS IN PHARMACEUTICAL AREAS IN WHICH RHEOLOGY IS SIGNIFICANTWHICH RHEOLOGY IS SIGNIFICANT

FLUIDSFLUIDS  in fluids we have different properties.in fluids we have different properties.  Mixing.Mixing.Particle size reduction of dispersed system.Particle size reduction of dispersed system.Passages from smaller areas and packing in bottles.Passages from smaller areas and packing in bottles.Fluid transfer including pumping and flow through Fluid transfer including pumping and flow through

pipes.pipes.Physical stability of dispersed system.Physical stability of dispersed system.Processing.Processing.Processing efficacy.Processing efficacy.Production capacity of the equipments.Production capacity of the equipments.

RHEOLOGICAL SYSTEMS AND RHEOLOGICAL SYSTEMS AND STRESSSTRESS

Fro the rheological point of view, solids are Fro the rheological point of view, solids are characterized by having a constant characterized by having a constant volume and permanent shape and are volume and permanent shape and are capable of supporting loadscapable of supporting loads

  that is pressure. Liquid has constant volume that is pressure. Liquid has constant volume at constant temperature but at very high at constant temperature but at very high pressure, variable shapes and support no pressure, variable shapes and support no load. Gases have neither constant volume load. Gases have neither constant volume nor a permanent shape.nor a permanent shape.

Load is express as stress, which have a Load is express as stress, which have a dimension of Force (F)/area (A). And unit dimension of Force (F)/area (A). And unit will be will be

F/A = dynes/cm2 = gm. cm/ sec2. cm2 = gm/ F/A = dynes/cm2 = gm. cm/ sec2. cm2 = gm/ cm.sec2cm.sec2

As we know that F/A may be F’/A, required to As we know that F/A may be F’/A, required to bring about the flow which is called as bring about the flow which is called as sharing stress and given by symbol F.sharing stress and given by symbol F.

The higher the viscosity of liquid, the greater The higher the viscosity of liquid, the greater the F/A (sharing stress) required to the F/A (sharing stress) required to produce a certain rate of share.produce a certain rate of share.

Rate of share can be given by a symbol G.Rate of share can be given by a symbol G.The rate of share could be directly The rate of share could be directly

proportional to sharing stress orproportional to sharing stress orF’/A = n du/dx, n dv/drF’/A = n du/dx, n dv/dr                  And n is referred to as viscosity, which is And n is referred to as viscosity, which is

given as, given as, n = F/Gn = F/GF = F/AF = F/AG = dv/dr.G = dv/dr.

UnitUnit of viscosity is called as poise of viscosity is called as poise

  Poise:Poise: the sharing force required to the sharing force required to produce a velocity of 1cm/sec between the produce a velocity of 1cm/sec between the two parallel lines or planes of liquids each two parallel lines or planes of liquids each having cm2 in area and separated by a having cm2 in area and separated by a distance of 1cm. distance of 1cm. 

Unit of poiseUnit of poise

Dynes x sec/cm2Dynes x sec/cm2

This unit is obtained by dimensional analysis This unit is obtained by dimensional analysis of viscosity co-efficient. of viscosity co-efficient.

The value of centi-poise is The value of centi-poise is 1cp = 0.01 poise1cp = 0.01 poise

FLOW OF FLUIDFLOW OF FLUID

  A-   NEWTONIAN FLOW OF FLUIDA-   NEWTONIAN FLOW OF FLUID

B-   NON-NEWTONIAN FLOW OF B-   NON-NEWTONIAN FLOW OF FLUIDFLUID

  TYPES OF VISCOSITYTYPES OF VISCOSITY

A-   DYNAMIC VISCOSITYA-   DYNAMIC VISCOSITY

B-   KINEMATIC VISCOSITYB-   KINEMATIC VISCOSITY

The definition of viscosity was put on the The definition of viscosity was put on the quantitative basis while Newton was 1st to quantitative basis while Newton was 1st to realize the rate of flow which was directly realize the rate of flow which was directly related to the applied stress. The constant related to the applied stress. The constant of proportionality is the co-efficient of of proportionality is the co-efficient of dynamic viscosity symbol as more usually dynamic viscosity symbol as more usually referred to as viscosity sample fluid which referred to as viscosity sample fluid which obey relationship are referred to as obey relationship are referred to as Newtonian fluid where as those which Newtonian fluid where as those which deviate known as Non-Newtonian fluid. The deviate known as Non-Newtonian fluid. The phenomenon of viscosity is explained by the phenomenon of viscosity is explained by the e.g. of the cube of box made up of infinite e.g. of the cube of box made up of infinite thin layers which are able to slide over each thin layers which are able to slide over each other like a packet of a plane cards.other like a packet of a plane cards.

When a logical force is applied to the upper When a logical force is applied to the upper most layers, it is assumed that the layer most layers, it is assumed that the layer will move at a decreasing viscosity and that will move at a decreasing viscosity and that the bottom layer will just show as a the bottom layer will just show as a stationary phase.stationary phase.

A viscosity gradient will therefore exist and it A viscosity gradient will therefore exist and it will be equal to the viscosity of the upper will be equal to the viscosity of the upper layer divided by the height of the cube. The layer divided by the height of the cube. The resultant gradient which is effectively rate resultant gradient which is effectively rate of flow but usually referred as ratio of share of flow but usually referred as ratio of share and denoted by symbol of delta which has and denoted by symbol of delta which has unit of reciprocal to the other value.unit of reciprocal to the other value.

KINETIC VISCOSITYKINETIC VISCOSITY

The USP include explanation of kinetic The USP include explanation of kinetic viscosity which is the absolute viscosity which is the absolute viscosity divided by the density of the viscosity divided by the density of the liquid and at definite temperature.liquid and at definite temperature.

  K.V =  K.V =  rourou                     densitydensityHowever the dynamic viscosity not However the dynamic viscosity not

only co-efficient which can be used only co-efficient which can be used characterize a fluid unit of K.V is characterize a fluid unit of K.V is known as stocks (s), centi stocks (cs).known as stocks (s), centi stocks (cs).

NEWTONIAN AND NON-NEWTONIAN AND NON-NEWTONIAN SYSTEMNEWTONIAN SYSTEM

When classifying materials according to When classifying materials according to the type of flow and deformation it has the type of flow and deformation it has been takes place into 2 categories. The been takes place into 2 categories. The choice of this will depend upon weather choice of this will depend upon weather or not, their flow are in accordance with or not, their flow are in accordance with the Newtonian law of flow fluids which the Newtonian law of flow fluids which doesn’t obey Newton equation of flow doesn’t obey Newton equation of flow are said to be Non-Newtonian fluids or are said to be Non-Newtonian fluids or liquids.liquids.

The characteristic describes above will The characteristic describes above will referred to as Non-Newtonian fluid. referred to as Non-Newtonian fluid. However most pharmaceutical fluid don’t However most pharmaceutical fluid don’t follow this law because the viscosity of follow this law because the viscosity of fluids varies with the rate of share. The fluids varies with the rate of share. The reason for theirreason for their

deviation is that the fluids concerned are not deviation is that the fluids concerned are not simple fluids like water and syrups but simple fluids like water and syrups but including emulsion, suspension and gels. including emulsion, suspension and gels. These materials are known as non-These materials are known as non-Newtonian and with the increasing Newtonian and with the increasing application such system are more to be application such system are more to be found in pharmaceutical preparations.found in pharmaceutical preparations.

PSEUDO PLASTIC FLOWPSEUDO PLASTIC FLOW

Rheogram shown in the figure arises at the origin and Rheogram shown in the figure arises at the origin and since no yield value exist then the ,material will since no yield value exist then the ,material will flow as soon as a share stress is applied and the flow as soon as a share stress is applied and the slop of the curve gradually increases with slop of the curve gradually increases with increasing rate of share. The viscosity is derived increasing rate of share. The viscosity is derived from the reciprocal of the slop and therefore from the reciprocal of the slop and therefore decreases as the share rate increased. Materials decreases as the share rate increased. Materials exhibiting this nature are said to be PSEUDO exhibiting this nature are said to be PSEUDO PLASTIC and no single value of the viscosity can PLASTIC and no single value of the viscosity can only be calculated from the reciprocal of the slop of only be calculated from the reciprocal of the slop of a tangent drawn to the curve at specific point. a tangent drawn to the curve at specific point. Such viscosities are known as apparent viscosities. Such viscosities are known as apparent viscosities. It is frequently noticed that at high share stresses, It is frequently noticed that at high share stresses, the flow curve tends towards linearity indicating the flow curve tends towards linearity indicating that a minimum viscosity has been attained.that a minimum viscosity has been attained.

DILATED FLOWDILATED FLOWThe opposite type of flow to the pseudo The opposite type of flow to the pseudo

plasticity is determined by the curve shown plasticity is determined by the curve shown in figure. In that the viscosity increases with in figure. In that the viscosity increases with the increase in share rate. Such materials the increase in share rate. Such materials increase in the volume during sharing then increase in the volume during sharing then they are referred to as dilated and exhibit they are referred to as dilated and exhibit shear thickening. This type of behavior is shear thickening. This type of behavior is less common then pseudo plastic flow but less common then pseudo plastic flow but they may be exhibited by dispersions they may be exhibited by dispersions containing high concentration (more than containing high concentration (more than 50% of the deflocculated particle). At a low 50% of the deflocculated particle). At a low shear rate, such as those created during shear rate, such as those created during pouring the fluid can lubricate the relative pouring the fluid can lubricate the relative movement of the particles. movement of the particles.

As the shear rate in increased the particles As the shear rate in increased the particles become displaced from their even become displaced from their even distribution and the clumps, which are distribution and the clumps, which are produced, result in a large voids/place into produced, result in a large voids/place into which the vehicle can drain so that the which the vehicle can drain so that the resistance to flow is increased and the resistance to flow is increased and the viscosity rises. The effective is progressive viscosity rises. The effective is progressive with increase in shear rate until the with increase in shear rate until the material may appear as paste like flow material may appear as paste like flow stops. The effect irreversible and the stops. The effect irreversible and the removal of shear rate results in the removal of shear rate results in the establishment of the fluid like substances.establishment of the fluid like substances.

Dilitancy may be a problem during the Dilitancy may be a problem during the processing of the dispersions and processing of the dispersions and granulation of tablet masses when a granulation of tablet masses when a high-speed blender is used. If the high-speed blender is used. If the material being processed becomes material being processed becomes dilated in nature then the resultant dilated in nature then the resultant solidification can be over loaded. solidification can be over loaded. Changing of batches of material used Changing of batches of material used can lead to the problem, which can only can lead to the problem, which can only be avoided by rheological evaluation of be avoided by rheological evaluation of the dispersion before the introduction the dispersion before the introduction to the production processes. to the production processes.

DETERMINATION OF FLOW DETERMINATION OF FLOW PROPERTIESPROPERTIES

A wide range of instruments exists which may A wide range of instruments exists which may be used to determine flow properties of be used to determine flow properties of Newtonian fluids, however only some of Newtonian fluids, however only some of these are capable of providing data, which these are capable of providing data, which can be used to calculate the viscosity in can be used to calculate the viscosity in fundamental units. The design of many of fundamental units. The design of many of instruments provides the application of instruments provides the application of absolute viscosities since they are capable absolute viscosities since they are capable of providing data. There are several of providing data. There are several instruments, which can be used to measure instruments, which can be used to measure the viscosity mentioned in B.P together with the viscosity mentioned in B.P together with others, which are commonly used for simple others, which are commonly used for simple fluids and the dilute colloidal solution.fluids and the dilute colloidal solution.

VISCOMETERSVISCOMETERS

Capillary viscometer.Capillary viscometer.

Ostwald u-type viscometer Suspended Ostwald u-type viscometer Suspended level viscometerlevel viscometer

Falling sphere viscometerFalling sphere viscometer

CAPILLARY VISCOMETERCAPILLARY VISCOMETER

It can be used to determine the It can be used to determine the viscosity provided that the fluid is viscosity provided that the fluid is Newtonian. The rate of flow of the Newtonian. The rate of flow of the fluid through the capillary is fluid through the capillary is measured under the influence of measured under the influence of gravity or an externally applied gravity or an externally applied pressurepressure

OSTWARD U-TYPE OSTWARD U-TYPE VISCOMETERVISCOMETER

Such instruments are described in BP Such instruments are described in BP 1980 and are the specifications for the 1980 and are the specifications for the subject of flow properties of fluids for the subject of flow properties of fluids for the fluids where there is a viscosity fluids where there is a viscosity specification in BP. It states the size of specification in BP. It states the size of instruments, which must be used in the instruments, which must be used in the determination of their viscosity. These determination of their viscosity. These include liquid paraffin, dextran injection include liquid paraffin, dextran injection or R-N sorbitol injectionsor R-N sorbitol injections

The viscometer is clamped vertically in The viscometer is clamped vertically in a constant water bath and allowed to a constant water bath and allowed to attain the required temperature. The attain the required temperature. The level of the liquid is adjusted up to level of the liquid is adjusted up to the required mark and the fall the required mark and the fall between the 2 marks (upper and between the 2 marks (upper and lower marks) is recorded. lower marks) is recorded. Determination should be repeated at Determination should be repeated at least 3 times and care should be least 3 times and care should be taken not to introduce or allow air taken not to introduce or allow air bubbles to enter into the capillaries.bubbles to enter into the capillaries.

SUSPENDED LEVEL SUSPENDED LEVEL VISCOMETERVISCOMETER

It is actually the modified form of u-type It is actually the modified form of u-type viscometer or u-type viscometer, which viscometer or u-type viscometer, which allows the necessary filling of the allows the necessary filling of the instruments with the required volume of instruments with the required volume of fluid. Also the fact that the pressure held in fluid. Also the fact that the pressure held in u-type viscometer is continuously changing. u-type viscometer is continuously changing. Once again it is also described in the BP Once again it is also described in the BP where 1980 where it is used to determine where 1980 where it is used to determine the viscosity of an aqueous solution of the viscosity of an aqueous solution of methyl cellulose-450.methyl cellulose-450.

FALLING SPHRE FALLING SPHRE VISCOMETERVISCOMETER

  It is based on stock’s law. When a It is based on stock’s law. When a body falls through a viscous medium, body falls through a viscous medium, it provides or gives a resistance or it provides or gives a resistance or viscous which opposes the downward viscous which opposes the downward motion of the liquid.motion of the liquid.

The BP gives detail explanation of falling The BP gives detail explanation of falling sphere viscometer and specifies its use sphere viscometer and specifies its use in the determination of viscosity of a in the determination of viscosity of a solution. This type of viscometers are solution. This type of viscometers are only used or applied with Newtonian only used or applied with Newtonian fluids and a validation has involved or fluids and a validation has involved or obtained if the time for a sphere to roll obtained if the time for a sphere to roll up through a fluid contained in an up through a fluid contained in an inclined tube. This instrument can only inclined tube. This instrument can only be used after calibration with the be used after calibration with the standard fluids since the fundamental standard fluids since the fundamental derivation of the viscosity is not derivation of the viscosity is not possible.possible.

DETERMINATION OF THE FLOW DETERMINATION OF THE FLOW PROPERTIES OF NON-NEWTONIAN PROPERTIES OF NON-NEWTONIAN

FLUIDSFLUIDSWith such a wide range of rheological behavior With such a wide range of rheological behavior

it is important to carry out measurements, it is important to carry out measurements, which will produce meaningful results. If it is which will produce meaningful results. If it is not acceptable or usual therefore we should not acceptable or usual therefore we should not determine the viscosity at one shear rate not determine the viscosity at one shear rate and in such type it would acceptable for a and in such type it would acceptable for a Newtonian fluid. There are several types of Newtonian fluid. There are several types of viscometers for producing the rheogram viscometers for producing the rheogram concerning the flow of Non-Newtonian fluids.concerning the flow of Non-Newtonian fluids.

Rotational viscometerRotational viscometerConcentric cylindersConcentric cylindersCone-plate viscometerCone-plate viscometer

ROTATIONAL ROTATIONAL VISCOMETERVISCOMETERThese instruments carried out the flow of These instruments carried out the flow of

viscous bodies when it is rotated in the fluid viscous bodies when it is rotated in the fluid to determine the viscosity. The major to determine the viscosity. The major advantage of such instruments is that, wide advantage of such instruments is that, wide range of shear rate can be achieved and a range of shear rate can be achieved and a program of shear rate can be produced program of shear rate can be produced automatically thus the flow curve of a automatically thus the flow curve of a material may b obtained directly. A number material may b obtained directly. A number of commercial instruments are available but of commercial instruments are available but each shows a common features. In that 2 each shows a common features. In that 2 different measuring geometries are utilized. different measuring geometries are utilized. These are concentric cylinder and cone-plate.These are concentric cylinder and cone-plate.

CONCENTRIC CYLINDERCONCENTRIC CYLINDER

In this geometry there are 2 co-axils cylinder In this geometry there are 2 co-axils cylinder of different diameter. The outer forming the of different diameter. The outer forming the cup containing the fluid in which the inner cup containing the fluid in which the inner cylinder is situated in center. In older type cylinder is situated in center. In older type of instruments, the outer cylinder is rotated of instruments, the outer cylinder is rotated and the viscous matter exerted by the fluid and the viscous matter exerted by the fluid is transmitted to the inner cylinder so that it is transmitted to the inner cylinder so that it rotates against its torsion wire suspension.rotates against its torsion wire suspension.

CONE-PLATE CONE-PLATE VISCOMETERVISCOMETER

This geometry is composed of flat This geometry is composed of flat circular plate with a wide angle con circular plate with a wide angle con placed centrally above the tip of the placed centrally above the tip of the cone just touches the plate and the cone just touches the plate and the sample is loaded into the gap. If the sample is loaded into the gap. If the plate is rotated, then the cone will be plate is rotated, then the cone will be paused, rotate against a torsion wire paused, rotate against a torsion wire in the same way as the inner cylinderin the same way as the inner cylinder

CHOICE OF VISCOMETERCHOICE OF VISCOMETERThe correct and successful determination and The correct and successful determination and

the evaluation of rheological properties of the evaluation of rheological properties of a particular system depend on choosing a particular system depend on choosing the correct viscometer. Since the rate of the correct viscometer. Since the rate of shear in a Newtonian system is directly shear in a Newtonian system is directly proportional to the shearing stress, one can proportional to the shearing stress, one can use this instrument that operates at a use this instrument that operates at a single rate of shear. These ONE POINT single rate of shear. These ONE POINT instruments provide a single point on a instruments provide a single point on a rheogram, extrapolation of the line through rheogram, extrapolation of the line through this point to the origin will result in a this point to the origin will result in a complete rheogram. It is essential that in complete rheogram. It is essential that in Non-Newtonian system, the instruments Non-Newtonian system, the instruments used, must be able to operate a variety of used, must be able to operate a variety of rate of shear. rate of shear.

By the use of multiple point instruments for By the use of multiple point instruments for which it is possible to obtain the complete which it is possible to obtain the complete rheogram for those systems, however the rheogram for those systems, however the use of ONE POINTuse of ONE POINT

  quality control in industry. The use of various quality control in industry. The use of various viscometers can be utilized to determine the viscometers can be utilized to determine the viscosity of Newtonian systems. Only those viscosity of Newtonian systems. Only those with variable shear stress can be used for with variable shear stress can be used for determination of viscosity of Non-Newtonian determination of viscosity of Non-Newtonian systems. Pseudoplastic materials should be systems. Pseudoplastic materials should be studies with instrument that is capable of studies with instrument that is capable of wide range of shearing rates. The result can wide range of shearing rates. The result can then be used to represent the viscosity of then be used to represent the viscosity of suspending agent at rest that is at a suspending agent at rest that is at a negligible rate of shear and while the negligible rate of shear and while the agitated poured from the bottle or even agitated poured from the bottle or even apply to the skin at moderately high rate of apply to the skin at moderately high rate of shear. shear.

Capillary and falling sphere viscometer Capillary and falling sphere viscometer operating at single rate of shear are operating at single rate of shear are unable to describe these changes. unable to describe these changes. However the rotational instrument However the rotational instrument unless possibly design will not unless possibly design will not provide a satisfactory result.provide a satisfactory result.

Weather a cone-plate or concentric cylinder Weather a cone-plate or concentric cylinder geometry is used, instruments particularly geometry is used, instruments particularly the modern e.g. is the modified, common the modern e.g. is the modified, common modification make one part of geometry, modification make one part of geometry, usually the plate or outer cylinder stationary usually the plate or outer cylinder stationary or to rotate the other member at a constant or to rotate the other member at a constant speed. This developed shear stress can be speed. This developed shear stress can be measured. An alteration is to rotate the measured. An alteration is to rotate the upper member under a constant stress then upper member under a constant stress then the developed shear rate is measured. Either the developed shear rate is measured. Either of the method has been the subject of of the method has been the subject of considerable or have one part of geometry considerable or have one part of geometry stationary meaning that it can be circulated stationary meaning that it can be circulated with water or other fluids at a temperature with water or other fluids at a temperature appropriate to the measurement.appropriate to the measurement.

Concentric cylinder viscometer is very Concentric cylinder viscometer is very useful for Newtonian and Non-useful for Newtonian and Non-Newtonian fluids provided later are not Newtonian fluids provided later are not true solid like in nature. Wide ranges true solid like in nature. Wide ranges of shear rate can be achieved by of shear rate can be achieved by varying the diameter of the cylinders. varying the diameter of the cylinders. However this geometry does suffer However this geometry does suffer various disadvantages. The major one various disadvantages. The major one is the shear rate approx the gap is not is the shear rate approx the gap is not constant and this is specially the case constant and this is specially the case when the gap is too large. when the gap is too large.

Those effects can usually be noted for Those effects can usually be noted for the method by calibration of the the method by calibration of the instrument with a fluid of known instrument with a fluid of known viscosity. Frictional heating can also viscosity. Frictional heating can also a problem at a high rate of shear and a problem at a high rate of shear and thus the temperature control is thus the temperature control is essential. With such instruments essential. With such instruments cleaning and filling are often difficult cleaning and filling are often difficult when gap is too small but if it is too when gap is too small but if it is too large then volume of sample large then volume of sample required may be prohibited.required may be prohibited.