pharmaceutics ii college of (pht 312) pharmacy ??lyophilic colloids ... •stability of colloid...

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  • COLLEGE OF

    PHARMACY

    Dr. Mohammad Javed Ansari, PhD.

    Contact info: javedpharma@gmail.com

    PHARMACEUTICS II (PHT 312)

    mailto:javedpharma@gmail.com

  • 27 N

    ove

    mb

    er 2

    016

  • OBJECTIVES OF THE LECTURE

    At the end of this lecture, you will be aware of:

    What are disperse systems?

    What are various types of colloidal dispersion?

    What are features of colloidal dispersion?

    What are various colloidal formulations?

    How colloids are prepared?

    How colloids are purified?

    What are different properties of colloids?

    What are stability problems of colloids?

    How colloids are stabilized?

    What are pharmaceutical applications of colloids?

  • LECTURE OUTLINES

    Definition of Colloidal dispersion.

    Colloids in nature

    TYPES OF COLLOIDAL SYSTEMS

    Lyophilic colloids

    Lyophobic colloids

    Amphiphilic or Association Colloids

    METHOD OF PREPARATION

    Dispersion method (mill, Ultrasonic treatment)

    Condensation method: (super-saturation, chemical reaction)

    Purification / Separation of colloids.

    Ultra filtration and Dialysis, Electro-dialysis

    Properties of Colloids (Optical, Kinetic, Electrical, Electro-

    kinetic).

    Stability of Colloid Systems

    Application of Colloids

  • Dispersed systems consist of particulate matter known as dispersed phase, dispersed throughout a continuous or dispersion medium.

    Classified based on size of dispersed phase

    Coarse dispersion > 1 m suspension & emulsion

    Colloidal dispersion 1 nm- 1 m colloids

    Colloidal System is defined as the heterogeneous biphasic system in which dispersed phase is subdivided into nano size range (1-1000 nanometer).

    Nanoparticles are small colloidal particles, but not all small colloidal particles are nanoparticles.

    If all particles in a colloidal system are of (nearly) the same size the system is called monodisperse; in the opposite cases the systems are heterodisperse /polydisperse.

    Pharmaceutical Colloidal: Definition & Features

  • It is not necessary for the units of a colloidal system to be discrete (separate particles)

    Therefore continuous network structures, the basic units of which are of colloidal dimensions also fall in this class (e.g. porous solids, gels and foams).

    Nor it is necessary for all three dimensions to be in the colloidal range.

    Films (only one dimension) and fibers (only two dimensions) are in nano range, may also be classified as colloidal.

    Eg. Hydrophillic colloids like alginates, agar gelatin, pectin, cellulose derivatives and polymers.

    Pharmaceutical Colloidal: Definition & Features

  • Colloidal Systems in Nature

  • Classified based upon the interaction / affinity between

    dispersed colloids and dispersion medium

    1. Lyophilic colloids = Solvent loving colloids.

    2. Lyophobic colloids = Solvent hating colloids

    3. Amphiphilic colloids = both loving colloids

    These colloids have affinity with both water as well as

    Lipids therefore these are both hydrophilic and

    Lipophilic.

    Based upon nature of dispersed colloids in liquids

    Liquid: colloidal emulsion

    Solid: colloidal suspension

    TYPES OF COLLOIDAL DISPERSIONS

  • LYOPHILIC COLLOIDS: FEATURES & PREPARATION

    Have affinity with dispersion medium.

    Called as hydrophilic colloids when media is water

    Spontaneous: these colloids are spontaneously formed

    by dispersing the material in the solvent.

    Organic substance like gelatin, gum, starch, egg, albumin

    etc. pass readily into water to give colloidal solution.

    Stable: these colloids are very stable (dont need any

    stabilizing agents) and do not precipitate/coagulate easily.

    However addition of very large quantities of electrolytes

    can cause particles to precipitate.

    Reversible : If solvent is evaporated, the sol can be made

    again by simply re-mixing with solvent.

  • The colloidal particles have very little affinity, if any, for the

    dispersion medium. Eg. In organic materiasl like Metals, their

    hydroxides and sulphides.

    Dont form spontaneously (need special techniques)

    Unstable: require stabilizing agents.

    Irreversible: once precipitated, dont return.

    A- Dispersion method: Coarse particles are reduced in size by

    the use of colloidal mill or ultrasonics.

    Colloidal mill: coarse material is sheared

    in a narrow gap between a static cone and

    a rapid rotating cone.

    Ultrasonic treatment: the passage of

    ultrasonic waves through a dispersion

    medium.

    LYOPHOBIC COLLOIDS: FEATURES & PREPARATION

  • B- Condensation method:

    Sub-colloidal particles are caused to aggregate into

    colloidal ones.

    - condensation by super-saturation: high degree of initial

    super-saturation followed by growth of nuclei (by change

    of solvent or reduction of temperature).

    e.g. addition of water to saturated alcoholic solution of

    sulfur

    - condensation by chemical reaction: Reduction, oxidation

    or hydrolysis

    e.g. oxidation of hydrogen sulfide leads to formation of

    colloidal sulfur.

    LYOPHOBIC COLLOIDS: FEATURES & PREPARATION

  • Amphiphiles or surfactants (surface active

    agents) are molecules characterized by having a

    hydrophilic head and a lipophilic tail.

    When dispersed in a liquid at low concentration

    the amphiphiles exist separately and are in a sub-

    colloidal size range.

    When the concentration exceeds a certain level

    (CMC) the molecules aggregate to form micelles

    (contain 50 or more monomers).

    Micelles lie within the colloidal size range.

    AMPHIPHILIC OR ASSOCIATION COLLOIDS

    FEATURES & PREPARATION

  • Ultra filtration: Filtration using ultra filters (filters with

    very small pores). Colloids can cross normal filter papers.

    Dialysis / Electro-dialysis: Removal of sub colloidal

    species (electrolytes / impurities) by putting the colloidal

    mixture in a dialysis bag.

    An electrical potential may be used to increase the rate of

    movement of ionic impurities through a dialysis membrane.

    Pharmaceutical application of dialysis

    Haemodialysis:

    Small molecular weight impurities from

    the body (blood) are removed by passage

    through a membrane.

    Purification / Separation of colloids

  • Due to their small size they do not settle out of solution.

    Particles lying in the colloidal size range possess an

    enormous surface area compared with the surface area of an

    equal volume of larger particles.

    Large specific surface area results in many unique

    properties of colloidal dispersions.

    Optical properties of colloids. eg. Tyndall (Faraday) Effect

    Kinetic properties of colloids eg. Brownian motion,

    diffusion, osmosis, viscosity etc.

    Electrical Properties of Colloids eg. Zeta potential

    Electro-kinetic Properties of Colloids eg. Electrophoresis

    Properties of Colloids

  • Tyndall Effect (Light scattering Effect )

    John Tyndall, a physicist observed this

    phenomenon in 1869.

    He observed that when a beam of light is

    allowed to pass through a colloidal solution, the

    path of light gets illuminated. (which was due to

    scattering of light by colloidal particles).

    To scatter the Light, size of the colloidal

    particles must be in range within the wavelength

    range of visible light i.e. 200-700 nm.

    High wavelength light (Blue) is scattered more

    than short wavelength light (orange & red).

  • Tyndall Effect (Light scattering Effect )

  • Tyndall Effect (Light scattering Effect )

  • Tyndall Effect (Light scattering Effect )

    The intensity of the scattered light depends on

    the difference between the refractive indices of the

    colloidal particles and the dispersion medium.

    Lyophilic colloidal particles are highly solvated,

    which results into lower difference in refractive

    index of two phases therefore Tyndall effect is less

    pronounced in lyophilic colloids.

    In case of lyophobic colloidal solution, the

    difference in refractive index is quite large and

    therefore it shows pronounced Tyndall effect.

  • Tyndall Effect (Light scattering Effect ) Light scattering measurements are of great value for

    estimating particle size and shape and number of particles

    per unit weight or volume.

    EVALUATION OF COLLOIDS

    Ultra-microscope: Allows the examination of the light

    spots responsible for the Tyndall cone.

    The light spots corresponding to the particles are

    counted and average particle size may be calculated.

    Electron Microscope: It is capable of taking pictures of

    the actual particles even those approaching molecular

    dimensions.

    It is used to observe size, shape and structure of

    colloidal particles.

  • Properties which are related to the motion of particles

    with respect to the dispersion medium

    1. Brownian motion

    Zig zag movement of the colloidal particles.

    Random collision (accident) of the colloidal particles with

    the molecules of the dispersion medium

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