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Viscosity and rheology: Thixotropy, determination of viscosity, application...
Thixotropy: Thixotropy is defined as the progressive decrease in viscosity with time for a constant applied shear stress followed by a gradual recovery when the stress is removed. Thixotropy is a...
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Viscosity and rheology: Newtonian system, Law of flow, Kinematic viscosity,...
The term ‘rheology’ was derived from the Greek words rheo (flow) and logos (science) and is used to describe the flow of liquids and the deformation of solids. Viscosity is an expression of the...
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Suspensions: Significance of Electrical Properties in Dispersions,...
Electric double layer: Particles dispersed in a liquid medium may become charged in one of two main ways. Ionic species present in a solution may be adsorbed at the surface or, alternatively, charges...
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Suspensions: Sedimentation of flocculated particles, sedimentation parameters...
SEDIMENTATION OF FLOCCULATED PARTICLES: When sedimentation is studied in flocculated systems, it is observed that the flocs tend to fall together, producing a distinct boundary between the sediment and...
View ArticleSuspensions: Interfacial Properties of Suspended Particles and MCQs for GPAT,...
A Pharmaceutical suspension is a coarse dispersion in which internal phase (therapeutically active ingredient)is dispersed uniformly throughout the external phase. The internal phase consisting of...
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Micromeretics and powder rheology: Derived properties of powders – Densities,...
Density (Ƿ): Density is defined as weight per unit volume. Based on the types of volume defined, the corresponding ‘density’ may be proposed. Table 1 – Types of densities Density Dełnition Formula...
View ArticleMicromeretics and powder rheology: Derived properties of Powders – Packing...
DERIVED PROPERTIES OF POWDERS: There are numerous derived properties that are based on fundamental properties. Those with particular relevance to pharmacy are discussed here. Packing geometry Porosity...
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Micromeretics and powder rheology: Determining surface areas – Permeability...
Specific surface: The specific surface of a powder is defined as the surface area per unit volume (Sv) or per unit weight (Sw). SURFACE AREA DETERMINATION METHODS: The surface area can be determined...
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Micromeretics and Powder Rheology: Methods of determining particle size and...
Optical Microscopy: Equivalent diameter: It is used to determine projected area diameter, Feret’s diameter and Martin’s diameter. Range of analysis: 1 μm to about 100 μm. Methodology: Firstly, the...
View ArticleMicromeretics and powder rheology: Average particle size number and weight...
Average particle size: Suppose that the particle size of a powder is analysed and the number of particles in each size range is determined, from the data, the average particle size of the powder may be...
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Micromeretics and powder rheology: Particle size and distribution and MCQs...
Micromeritics is the science and technology of small particles and includes the study of the fundamental and derived properties of individual as well as a collection of particles. The micromeritic...
View ArticleMicromeretics and powder rheology: Derived properties of powders – Flow...
Flow Property: (1) The flow properties of solids have great impact on the tableting processes since their manufacturing require the flow of powder from a storage container to tablet dies. (2) Weight...
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Surface and interfacial phenomenon: Solubilization and detergency and MCQs...
SOLUBILIZATION: It can be defined as the preparation of a thermodynamically stable isotropic solution of a substance normally insoluble or very slightly soluble in a given solvent by the addition of...
View ArticleSurface and interfacial phenomenon: Complex films and MCQs for GPAT, NIPER,...
SURFACE FILMS: Surface-active agents tend to concentrate at interfaces and are adsorbed at oil–water interfaces as monomolecular films. These monomolecular films formed at the interface depend on the...
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Surface and interfacial phenomenon: Electrical properties of interfaces and...
ELECTRICAL PROPERTIES OF INTERFACES: The existence of difference in electrical potential across a solid–liquid interface is demonstrated by the following phenomena: Electrophoresis: Movement of...
View ArticleSurface and Interfacial Phenomenon: Spreading coefficient and MCQs for GPAT,...
Spreading Coefficient (S): In general, spreading of a liquid occurs when the work of adhesion between two liquids exceeds the work of cohesion between the molecules of each liquid. Work of adhesion...
View ArticlePhysical and chemical adsorption, Adsorption Isotherm, Adsorption...
ADSORPTION PHENOMENA: Adsorption is the process in which materials of one phase (adsorbate) accumulate or concentrate at the interfacial surface of the other phase (adsorbent). It is a spontaneous...
View ArticleBET isotherm, Factors Affecting Adsorption, Adsorption Phenomenon(Part 3) and...
BET isotherm: Langmuir and Freundlich isotherms are based on the formation of a saturated monolayer of the adsorbate on the surface of the adsorbent. The BET isotherm assumes that a multimolecular...
View ArticleLangmuir isotherm and Freundlich isotherm, Adsorption Phenomenon (Part2) and...
Many attempts have been made to develop a mathematical expression that relates the amount of the adsorbate per unit weight of adsorbent to a function of the solute concentration remaining in the...
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Surfactants, Surface active agents and Question Answer for GPAT, NIPER,...
SURFACE-ACTIVE AGENTS (SURFACTANTS): Substances having both hydrophilic and hydrophobic regions in their molecular structures are called surfactants or surface-active agents. When surfactants are added...
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