RHEOLOGY - PowerPoint PPT Presentation

Loading...

PPT – RHEOLOGY PowerPoint presentation | free to download - id: 6d56d8-OWMyM



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

RHEOLOGY

Description:

RHEOLOGY Roselyn Aperocho-Naranjo Faculty, College of Pharmacy USPF Rheology rheo to flow logos science ology the study of is the study of the flow of ... – PowerPoint PPT presentation

Number of Views:7
Avg rating:3.0/5.0
Date added: 2 September 2020
Slides: 21
Provided by: pers532
Learn more at: http://roselynnaranjo.yolasite.com
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: RHEOLOGY


1
RHEOLOGY
  • Roselyn Aperocho-Naranjo
  • Faculty, College of Pharmacy
  • USPF

2
Rheology
  • rheo to flow
  • logos science
  • ology the study of
  • is the study of the flow of materials that behave
    in an interesting or unusual manner.
  • Unusual materials such as mayonnaise, peanut
    butter, chocolate, bread dough, paints, inks,
    road building aterials, cosmetics, dairy
    products, etc.

3
Rheology
  • The study of viscosity is of true liquids,
    solutions, dilute and concentrated colloidal
    systems is of much importance in this study
  • It is involved in the mixing and flow of
    materials, their packaging into containers, the
    pouring from the bottle, extrusion from a tube or
    a passage of the liquid to a syringe needle.

4
Rheology
  • Can affect the patients acceptability of the
    product, physical stability, biologic
    availability, absorption rate of drugs in the
    gastrointestinal tract
  • Influence the choice of processing equipments in
    the pharmaceutical system

5
Two Categories of Flow Deformation
  • Newtonian (Newtonian Law of Flow)
  • the higher the viscosity of a liquid, the
    greater is the force per unit area (shearing
    stress) required to produce a certain rate of
    shear
  • Shear as a stress which is applied parallel or
    tangential to a face of a material, as opposed to
    a normal stress which is applied perpendicularly.
  • Shear stress
  • Measured in (SI unit) pascal
  • Commonly used symbols t
  • Expressed in other quantities t F / A

6
A shear stress, is applied to the top of the
square while the bottom is held in place. This
stress results in a strain, or deformation,
changing the square into a parallelogram.
7
Two Categories of Flow Deformation
  • Newtonian (Newtonian Law of Flow)
  • A Newtonian fluid (named for Isaac Newton) is a
    fluid whose stress versus rate of strain curve is
    linear and passes through the origin. The
    constant of proportionality is known as the
    viscosity.
  • A simple equation to describe Newtonian fluid
    behavior is where
  • t is the shear stress exerted by the fluid
    ("drag") Pa
  • µ is the fluid viscosity - a constant of
    proportionality Pas
  • du is the velocity gradient perpendicular to
    the direction
  • dy of shear s-1

8
Two Categories of Flow Deformation
  • Newtonian (Newtonian Law of Flow)
  • In common terms, this means the fluid continues
    to flow, regardless of the forces acting on it.
    For example, water is Newtonian, because it
    continues to exemplify fluid properties no matter
    how fast it is stirred or mixed.
  • For a Newtonian fluid, the viscosity, by
    definition, depends only on temperature and
    pressure (and also the chemical composition of
    the fluid if the fluid is not a pure substance),
    not on the forces acting upon it.

9
Two Categories of Flow Deformation
  • Newtonian (Newtonian Law of Flow)
  • For a Newtonian fluid, the viscosity, by
    definition, depends only on temperature and
    pressure (and also the chemical composition of
    the fluid if the fluid is not a pure substance),
    not on the forces acting upon it.
  • If the fluid is incompressible and viscosity is
    constant across the fluid, the equation governing
    the shear stress is expressed in the Cartesian
    coordinate system

10
Two Categories of Flow Deformation
  • Newtonian (Newtonian Law of Flow)
  • Cartesian coordinate system
  • where, by the convention of tensor notation,
  • tij is the shear stress on the ith face of a
    fluid element in the jth direction
  • ui is the velocity in the ith direction
  • xj is the jth direction coordinate

11
Two Categories of Flow Deformation
  • Newtonian (Newtonian Law of Flow)
  • Cartesian coordinate system
  • Tensor - are geometrical entities introduced into
    mathematics and physics to extend the notion of
    scalars, (geometric) vectors, and matrices
  • - Components of stress, a second-order tensor,
    in
  • three
    dimensions. The tensor in the image is the
  • row vector, of
    the forces acting on the X, Y, and
  • Z faces of the
    cube. Those forces are represented
  • by column
    vectors. The row and column vectors
  • that make up
    the tensor can be represented
  • together by a
    matrix.

12
Two Categories of Flow Deformation
  • Non-Newtonian
  • A non-Newtonian fluid is a fluid whose flow
    properties are not described by a single constant
    value of viscosity.
  • Many polymer solutions and molten polymers are
    non-Newtonian fluids, as are many commonly found
    substances such as ketchup, starch suspensions,
    paint, blood and shampoo.
  • In a Newtonian fluid, the relation between the
    shear stress and the strain rate is linear (and
    if one were to plot this relationship, it would
    pass through the origin), the constant of
    proportionality being the coefficient of
    viscosity.

13
Two Categories of Flow Deformation
  • Non-Newtonian
  • A In a non-Newtonian fluid, the relation between
    the shear stress and the strain rate is
    nonlinear, and can even be time-dependent.
    Therefore a constant coefficient of viscosity
    cannot be defined.
  • A ratio between shear stress and rate of strain
    (or shear-dependent viscosity) can be defined,
    this concept being more useful for fluids without
    time-dependent behavior.

14
Two Categories of Flow Deformation
  • Non-Newtonian Examples
  • An inexpensive, non-toxic example of a
    non-Newtonian fluid is a suspension of starch
    (e.g. cornflour) in water, sometimes called
    oobleck (uncooked imitation custard, being a
    suspension of primarily cornflour, has the same
    properties).
  • The sudden application of force for example
  • by stabbing the surface with a finger, or rapidly
    inverting the container holding it leads to the
    fluid behaving like a solid rather than a liquid.
  • This is the "shear thickening" property of this
    non-Newtonian fluid. More gentle treatment, such
    as slowly inserting a spoon, will leave it in its
    liquid state.
  • Trying to jerk the spoon back out again, however,
    will trigger the return of the temporary solid
    state.
  • A person moving quickly and applying sufficient
    force with their feet can literally walk across
    such a liquid.

15
Two Categories of Flow Deformation
  • Non-Newtonian Examples
  • There are fluids which have a linear shear
    stress/shear strain relationship which require a
    finite yield stress before they begin to flow.
    That is the shear stress, shear strain curve
    doesn't pass through the origin.
  • These fluids are called
  • 1. Bingham plastics.
  • clay suspensions, drilling mud, toothpaste,
    mayonnaise, chocolate, and mustard. The classic
    case is ketchup which will not come out of the
    bottle until you stress it by shaking.

16
Two Categories of Flow Deformation
  • Non-Newtonian Examples
  • These fluids are called
  • 1. Pseudoplastic Flow
  • Polymers in solutions such as tragacant, sodium
    alginate, methylcellulose
  • Viscosity decreases with an increase in shear
    thinning
  • Caused by the re-alignment of polymer and/or the
    release of solvents associated with the polymers
  • 2. Dilatant Flow
  • Volume increases when sheared
  • Shear thickening
  • Suspension containing high-concentration of small
    deflocculated particles

17
Two Categories of Flow Deformation
  • Non-Newtonian Examples
  • There are also fluids whose strain rate is a
    function of time. Fluids that require a gradually
    increasing shear stress to maintain a constant
    strain rate are referred to as rheopectic.
  • An opposite case of this, is a fluid that thins
    out with time and requires a decreasing stress to
    maintain a constant strain rate (thixotropic).

18
THIXOTROPY
  • is the property of some non-Newtonian
    pseudoplastic fluids to show a time-dependent
    change in viscosity the longer the fluid
    undergoes shear stress, the lower its viscosity.
  • A thixotropic fluid is a fluid which takes a
    finite time to attain equilibrium viscosity when
    introduced to a step change in shear rate.
  • the term is sometimes applied to pseudoplastic
    fluids without a viscosity/time component. Many
    gels and colloids are thixotropic materials,
    exhibiting a stable form at rest but becoming
    fluid when agitated.

19
THIXOTROPY
  • pseudoplastic fluids
  • Shear thinning is an effect where viscosity
    decreases with increasing rate of shear stress.
    Materials that exhibit shear thinning are called
    pseudoplastic.
  • This property is found in certain complex
    solutions, such as lava, ketchup, whipped cream,
    blood, paint, and nail polish.
  • Pseudoplasticity can be demonstrated by the
    manner in which shaking a bottle of ketchup
    causes the contents to undergo an unpredictable
    change in viscosity. The force causes it to go
    from being thick like honey to flowing like
    water.
  • thixotropic fluid viscosity decreases over time
    at a constant shear rate.

20
THIXOTROPY
  • The distinction between a thixotropic fluid and a
    shear thinning fluid
  • A thixotropic fluid displays a decrease in
    viscosity over time at a constant shear rate.
  • A shear thinning fluid displays decreasing
    viscosity with increasing shear rate.
  • Some fluids are anti-thixotropic constant shear
    stress for a time causes an increase in viscosity
    or even solidification. Constant shear stress can
    be applied by shaking or mixing. Fluids which
    exhibit this property are usually called
    rheopectic. They are much less common.
About PowerShow.com