Disperse System

download Disperse System

of 35

  • date post

    02-Jun-2018
  • Category

    Documents

  • view

    222
  • download

    0

Embed Size (px)

Transcript of Disperse System

  • 8/11/2019 Disperse System

    1/35

    PR 1102 Physical Pharmacy

    Kang Lifenglkang@nus.edu.sg

    Disperse System

  • 8/11/2019 Disperse System

    2/35

    Disperse System

    Dispersed phase

    Continuous phase

    Interface

  • 8/11/2019 Disperse System

    3/35

    Disperse System

    Disperse systems consist of particulate matter(dispersed phase) distributed throughout acontinuous medium

    Dispersed material ranges in size, from moleculardimensions to particles of millimeters

    Many biological drugs that have been discovered aremacromolecules that exist in colloidal systems (e.g.

    proteins and DNA). Nanoparticulate systems are also emerging for

    improved drug delivery.

  • 8/11/2019 Disperse System

    4/35

    Classification by State

    a Continuous phase

    Gas Liquid Solid

    D i s p e r s e

    d p

    h a s e

    Gas Nil Foam Solid foam

    Liquid Liquid aerosol Emulsion Gel

    Solid Sold aerosol Suspension Solid sol

    http://www.naturalhealthlibrarian.com/images/asprin.gifhttp://nickobeano.files.wordpress.com/2008/01/cheese_oh_cheese.jpghttp://www.universalws.com/images/topcare%20calamine%20lotion%20(Small).JPGhttp://www.medgadget.com/archives/img/Exubera.jpghttp://www.dollychar.com/blog/wp-content/uploads/2009/01/dettol-173x300.jpghttp://www.firstpr.com.au/show-and-tell/green-ants/DSC00286-beach-foam-rainbow-colours-trippier.jpg
  • 8/11/2019 Disperse System

    5/35

  • 8/11/2019 Disperse System

    6/35

    Dispersion Stability

  • 8/11/2019 Disperse System

    7/35

  • 8/11/2019 Disperse System

    8/35

    Brownian Motion

    Spontaneous, irregular zig-zag movement ofparticles because of random collisions withmolecules .

    t -time D-diffusion coefficient; r-averagedisplacement

  • 8/11/2019 Disperse System

    9/35

    Reynolds Number

    Re vr r is the radius of a sphere v is the velocity of the sphere is the density of the liquid is the viscosity of the liquid Reynolds number measures the relative

    importance of inertia and viscosity For particles on a colloidal scale, Re is small

    http://en.wikipedia.org/wiki/File:Stokes_sphere.svg
  • 8/11/2019 Disperse System

    10/35

    Stokess Law

    6d F rv r is the radius of a sphere v is the velocity of the sphere is the viscosity of the liquid F d is the drag force Stokes law is derived from the Navier Stokes

    equations for small Reynolds numbers.

    http://en.wikipedia.org/wiki/File:Stokes_sphere.svg
  • 8/11/2019 Disperse System

    11/35

    Einsteins Relation

    k B is the Boltzmanns constant D is the diffusion coefficient T is the temperature k drag is the drag coefficient

    B

    drag

    k T D k

  • 8/11/2019 Disperse System

    12/35

    Stokes-Einstein Equation

    If we know the diffusion coefficient D, thenthe size of the particle can be estimated bythe Stokes-Einstein equation .

    B

    drag

    k T D

    k

    6d drag F rv k v

    6 Bk T D

    r

  • 8/11/2019 Disperse System

    13/35

    Rate of Sedimentation

    To calculate v when the gravitational anddrag forces are balanced

    Smaller particles and higher viscosities give

    smaller sedimentation rate

    3 3 34 4 4

    3 3 3 g solid Liquid F r g r g r g

    3463

    rv r g

    6d F rv

    22

    9

    r g v

    http://en.wikipedia.org/wiki/File:Stokes_sphere.svg
  • 8/11/2019 Disperse System

    14/35

    One Example: Suppositories

    Suppository bases include cocoa butter,glycerinated gelatin, hydrogenated vegetableoils, polyethylene glycols

    Cocoa butter melt to incorporate fine particlesand then cool in molds. It is a colloid-coarsedisperse system and particles may sediment

    Copper sulphate suppository preparationprocess: Grind coarse powders, melt base andincorporate the find powders

    http://www.detronizator.org/wp-content/uploads/2007/09/buttercocoadeo.jpg
  • 8/11/2019 Disperse System

    15/35

    Interactions Between Particles

    Inter-particle forces DLVO theory Zeta potential

    Dispersed phase interactions

  • 8/11/2019 Disperse System

    16/35

    DLVO Theory Deryagin-Landau and Verwey-Overbeck The stability of a particle in solution depends on

    its total potential energy function

  • 8/11/2019 Disperse System

    17/35

  • 8/11/2019 Disperse System

    18/35

    Van der Waals Attractive Forces

    212 A A

    V d A is a constant and d is the particle separation

    distance. If a repulsion mechanism does not

    exist then flocculation will eventually takeplace.

  • 8/11/2019 Disperse System

    19/35

    Electrostatic Repulsive Forces V R2

    2 kd

    RV r e

    r is the particle radius, k is a function of theionic composition and is the zeta potential

  • 8/11/2019 Disperse System

    20/35

    Colloid Stability Mechanism

  • 8/11/2019 Disperse System

    21/35

    To Increase Repulsive Forces V R Steric repulsion - this involves polymers added

    to the system adsorbing onto the particlesurface and preventing the particle surfaces

    coming into close contact and at thoseseparations the van der Waals forces are tooweak to cause the particles to adhere

    Electrostatic or charge stabilization - this is theeffect on particle interaction due to thedistribution of charged species in the system

  • 8/11/2019 Disperse System

    22/35

    Charged Particle and Zeta Potential

    Stern layer

    Negatively charged particle

  • 8/11/2019 Disperse System

    23/35

    Diffuse Layer

    Diffuse layer

  • 8/11/2019 Disperse System

    24/35

    Slipping Plane

    Hydrodynamic planeof shear (slippingplane)

  • 8/11/2019 Disperse System

    25/35

  • 8/11/2019 Disperse System

    26/35

    Zeta Potential

    The zeta potential is the electrical potential atthe hydrodynamic plane of shear

    It depends not only on the particle surface but

    also on the dispersant It can be affected by small changes in the pH

    or ionic strength of the medium Particles interact according the magnitude of

    the zeta potential, not their surface charge Therefore, it can be used to predict stability

  • 8/11/2019 Disperse System

    27/35

    Significance of Zeta Potential

    If all the particles have a large negative orpositive zeta potential they will repel eachother and there is dispersion stability

    If the particles have low zeta potential valuesthen there is no force to prevent particlescoming together and there is dispersion

    instability The dividing line of stable and instable zeta

    potential is +30 mV or -30mV

  • 8/11/2019 Disperse System

    28/35

    Factors Affecting Zeta Potential

    Changes in the pH of the sample The conductivity of the medium

    (concentration and type of salt)

  • 8/11/2019 Disperse System

    29/35

    pH Effects on Bovine Serum Albumin(BSA) Zeta Potential

    Stable

    Stable

    Unstable

    Z e t a P o t e n t i a

    l ( m

    V )

    pH

    The rule of thumb of stability +/- 30 mV.

  • 8/11/2019 Disperse System

    30/35

    Conductivity Effects on BSA Zeta Potential

    Z e t a P o t e n t i a

    l ( m V

    )

    Concentration (Log(mol/l)

  • 8/11/2019 Disperse System

    31/35

    An Example of Liposome

    Plasmids Cationic liposome

    Plasmid - cationic liposome complex

  • 8/11/2019 Disperse System

    32/35

    Liposome Complex Zeta-potential

    Molar ratio of Plasmid and liposome

    Z e t a P o t e n t i a

    l ( m V

    )

    P a r t i c

    l e d i a m

    e t e r ( n m

    )

  • 8/11/2019 Disperse System

    33/35

    PEG-coated Liposome

    PEG Liposome complex

    Liposome Polyethylene glycol (PEG)

  • 8/11/2019 Disperse System

    34/35

    Z e t a P o t e n t i a

    l ( m V

    )

    Ratio of PEG2000

    PEG-coated Liposome Zeta-potential

  • 8/11/2019 Disperse System

    35/35

    If an electric field is applied across a sample,charged particles suspended in the mdeiumare attracted towards the electrode ofopposite charge

    The particles move with a velocity dependson: (i)Field strength, (ii) dielectric constant ofmedium and (iii) viscosity of the medium and(iv) zeta potential.

    Parameters (i)-(iii) are know, so zeta potentialcan be determined

    Measure Zeta-potential