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Controlled flocculation (caused by additives): additive molecules cause the pigment particles to form a network; no direct pigment-pigment contact. Such “controlled” flocculates can be destroyed by low shear forces.
How do you achieve controlled flocculation in suspension?
Limited flocculation results in looser sediments because the settled-out flocs incorporate large amounts of the liquid suspending medium. Controlled flocculation of bismuth subnitrate suspensions was achieved by the addition of small amounts of bentonite.
What is flocculation in paint?
Flocculation is a result of pigment particles being attracted to each other to form loose aggregates that can be redispersed under mild shear. Flocculation can be reversed by the application of low shear to the paint. Flocculation can have an adverse effect on color development, gloss and hiding.
How do you disperse and stabilize pigments?
Steps 1 (wetting) and 3 (stabilizing) can be optimized by additives. Wetting additives accelerate the wetting of the pigment agglomerates using the binder. Dispersion additives improve the stabilization of the pigment dispersion.
Why structured vehicle is used in suspension?
The structured vehicle is the vehicle in which viscosity of the preparation under the static condition ofvery low shear on storage approaches infinity. The vehicle behaves like a ‘false body’, which is able to maintain the particles suspended which is more or less stable.
What is settling of paint mention the causes and cures for it?
Humidity condenses on the wet paint due to the cooling effect of solvent evaporation when the substrate temperature is below the dew point. Causes: Unsuitable reducers. Poor air circulation in drying oven. Film thickness too high or low.
Are pigments hydrophobic?
Remember, chlorophylls and carotenoids are hydrophobic or nonpolar and will dissolve in less polar solvents, whereas anthocyanins are extractable and soluble in more polar solvents like water.
Why suspension is formulated?
Suspension can improve chemical stability of certain drug. For example Procaine penicillin G. Drug in suspension exhibits higher rate of bioavailability than other dosage forms.
Which test is used to compare different suspensions?
Bookfield Viscometer is a valuable rheological equipment for measuring the settling behavior and structure of pharmaceutical suspensions. The instrument consists of a slowly rotating T-bar spindle, which while descending slowly into suspensions encounters new, essentially undisturbed material as it rotates.
What does suspension mean in drugs?
A suspension is a liquid with small pieces of drug. The drug is not complete dissolved in the solution. Whenever you take a suspension, you should always shake (or stir) it so that you receive the right amount of drug every time you take it.
What are ingredients used in suspension?
The possible types of excipients commonly used in the formulation of pharmaceutical suspensions include:
- 1 1. Solvents/ Vehicle.
- 2 2. Co-solvent.
- 3 3. Buffering agents.
- 4 4. Preservatives.
- 5 5. Antioxidants.
- 6 6. Wetting agents/ surfactants.
- 7 7. Anti-foaming agents.
What are suspending agents?
: a substance (such as carrageenan, xanthan gum, or cellulose ether) that is added to fluids to promote particle suspension or dispersion and reduce sedimentation All these drinks can contain preservatives, and drinks other than juices can contain additives to colour, flavour and sweeten.
How does particle size affect drug stability?
A product with a smaller, more uniform particle size is more stable and less likely to separate out. This translates to a longer shelf life and less waste.
How does a suspension appear?
An suspension is when you mix a liquid and a solid, where the solid does not dissolve in the liquid. If this appears then you have an suspension. The suspension will appear as small “grain” looking object floating in the solution.
Why are some drugs suspended?
Substances can be chemically unstable, insoluble in water, distasteful etc. Suspensions are often used as a dosage form when the drug is insoluble in water and when use of solubilizing agents is not possible.
What is the size of the suspended drug having the range of?
Pharmaceutical suspension may be defined as coarse dispersions in which insoluble solids are suspended in a liquid medium. Insoluble solids may have a size range from 10 to 1000 µm.
What is flooding in paint?
Flooding, Floating, Surface Tension, Bernard Cells, Flocculation and Agglomeration. Floating describes a mottled, splotchy appearance on the surface of a paint film. It is most apparent in coatings colored with two or more pigments and is a result of the horizontal separation of different pigments.
Which one of properties is applicable to suspension?
The properties of suspension are listed below. A suspension is a heterogeneous solution in which, while standing, several particles move out of the mixture. In a suspension, the volume of the solvent particles is quite high. It has a length of more than 100 mm.
What causes flocculation in paint?
Flocculation is a result of pigment particles being attracted to each other to form loose aggregates that can be redispersed under mild shear. Flocculation can be reversed by the application of low shear to the paint. Flocculation can have an adverse effect on color development, gloss and hiding.
How does a suspending agents increases the viscosity of the liquid?
By reducing particle size, by increasing the viscosity, and by increasing the density of the external phase, we may retard settling. Suspending agents are physiologically inert substances which increase viscosity when added to suspensions.
Where might some of the pigment particles settle?
The particles can settle to the bottom of the container. Occasionally, the particles will rise to the surface, in which case that effect is called creaming. Surfactants even when used for dispersion stabilization can have a dramatic effect on other properties such as surface tension.
What are the ideal properties of a pharmaceutical suspension?
1 It should settle slowly and should be readily re-dispersed on gentle shaking of the container. 2 The particle size of the suspension remains fairly constant throughout its long period of undisturbed standing . 3 The suspension should pour readily and evenly from its container.
Which type of colloidal material is commonly used in preparation of structured vehicle?
For successful flocculation in the structured vehicle, we need an appropriately charged flocculating agent or flocculent and a hydrocolloid as a protective colloid. To formulate a stable suspension containing positively charged drug particles, first of all, flocks are produced by negatively charged flocculants.
What are the advantages of suspension?
Advantages of suspensions dosage form
- Suspensions are a useful drug delivery system for therapeutic agents that have a low solubility.
- Pharmaceutical suspensions may be formulated to mask the unpleasant/ bitter taste of drug.
Why is particle size important for suspension?
Particle size reduction is a fast and cost-effective answer to increasing the exposure of poorly soluble oral drugs by increasing surface area and thereby improving dissolution rate.
