Term
| What is the Hydrophilic Lipophilic Balance (HLB) For Surfactants? |
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Definition
| It's an arbitrary scale of values that can be used as the measure of the hydrophilic-lipophilic balance of surfactants |
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Term
| HLB values help determine ... |
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Definition
| optimum efficiency for surfactants of each class. |
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Term
| HLB system presupposes a scale of HLB numbers and is based on the following facts... |
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Definition
– Every surfactant or emulsifier molecule is in part hydrophilic and in part lipophilic
– A certain balance between these two parts is necessary for various types of surfactant functions. |
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Term
| The lower values are assigned to substances that are predominantly ... |
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Definition
| lipophilic (oil¬loving) and have a tendency to form water-in-oil (w/o) emulsions. |
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Term
| The higher values are given to those materials that show ... |
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Definition
| hydrophilic (water-loving) characteristics and favor the formation of oil-in-water (o/w) emulsions |
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Term
| Define Solubilizing agents and give its HLB range |
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Definition
– These surfactants form large aggregates or micelles in solution when their concentrations exceed certain values. Help increase drug solubility
(HLB: 15 - 18) |
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Term
| Define Detergents agents and give its HLB range |
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Definition
– These agents reduce the surface tension and aid in wetting the surface and the dirt. The soil will be emulsified, and foaming generally occurs.
(HLB: 13-15) |
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Term
| Define Emulsifying agents and give its HLB range |
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Definition
Reduce interfacial tension between oil and water
(HLB: 3 - 6 for W/O) or 8-18 for O/W emulsions). |
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Term
| Define Wetting agents and give its HLB range |
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Definition
Facilitate contact between solid particles and liquids
(HLB: 7 – 9) |
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Term
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Definition
| Forces of attraction between molecules of different phases |
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Term
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Definition
| Forces of attraction between molecules of same phase |
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Term
| Phase affinity increases when adhesional forces become _____ than cohesional forces |
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Definition
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Term
| Define Spreading Coefficient |
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Definition
| • When a small quantity of an immiscible liquid is placed on a clean surface of a second liquid, it may cover the surface with a film or remain as a drop or lens |
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Term
| Miscibility of pharmaceutical additives with water depends on the ________of the substance. |
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Definition
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Term
| As the ratio of polar-nonpolar character of a molecule decreases, the spreading coefficient in water _________. |
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Definition
decreases
For example, propionic acid and ethyl alcohol have high spreading coefficient but as the carbon chain eg. oleic acid, increases, spreading coefficient also decreases. |
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Term
| For a lotion with a mineral base to spread freely and evenly on the skin, its spreading coefficient needs to be ... |
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Definition
| increased by addition of surfactants. |
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Term
| Ability to spread depends on the _______ used in making the dosage form |
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Definition
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Term
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Definition
| Wetting is the contact between a fluid and a surface, when the two are brought into contact. |
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Term
| When a liquid has a high surface tension (strong internal bonds), it will form... |
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Definition
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Term
| A liquid with low surface tension will spread out over a_______ area (bonding to the surface). |
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Definition
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Term
| If a surface has a high surface energy (or surface tension)... |
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Definition
| a drop will spread, or wet, the surface |
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Term
| The primary measurement to determine wettability is .... |
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Definition
| a contact angle measurement |
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Term
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Definition
| is a surfactant that lowers the contact angle when dissolved in water. |
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Term
| How do wetting agents work? |
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Definition
| It displaces air phase at the surface and replaces it with a liquid. |
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Term
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Definition
| is the angle between a liquid droplet and the surface over which it spread. |
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Term
| When the contact angle between a liquid and solid is zero (0)... |
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Definition
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Term
| As the contact angle approaches 180... |
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Definition
| little or no wetting occurs |
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Term
| There are many methods to measure surface tension. For this class, we will discuss only the principles of two methods, which are? |
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Definition
• Capillary rise method
• The DuNouy Ring method |
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Term
| Define Capillary rise method: |
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Definition
| Used to determine the surface tension of the liquid, but this method cannot be used to measure interfacial tension |
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Term
| Define The DuNouy Ring method |
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Definition
| Used to measure surface and interfacial tension |
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Term
| How does Capillary Rise Method work? |
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Definition
| The force of adhesion between the liquid molecule and the capillary wall is greater than force of cohesion between the liquid molecules, which makes a liquid a rise up inside tubes of small diameter or porous material. |
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Term
| Liquids which wet the walls make... |
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Definition
| concave surfaces (eg: water/glass) |
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Term
| Liquids that do not wet them make... |
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Definition
| convex surfaces (eg: mercury/glass) |
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Term
| The principle of DuNouy Ring method is that the force required to separate a platinum-iridium ring immersed from the surface or interface is ________ to the surface or interfacial tension. |
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Definition
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Term
| In the DuNouy Ring method what is measured? |
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Definition
| In this method, weight of the liquid removed by the ring from the interface is measured |
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Term
| Define Electrical Double Layer |
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Definition
| An uneven charge distribution at interface resulting in one type of charge on one side and the opposite charge on the other. |
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Term
| What is the charge of the Electrical Double Layer |
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Definition
| Net charge is zero and neutrality maintained |
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Term
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Definition
| a suspension with positive charge in the solid layer at the interface, there will be strong layer of negative charge in the liquid layer that is strongly attached to solid layer. |
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Term
| What is the Diffuse / Gouy Chapman Layer? |
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Definition
| The layer that surrounds the Stern layer made up of negative ions which are repelled by the stern layer as they approach the interface |
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Term
| What makes up the double layer? |
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Definition
| Stern layer and Diffuse layer make up the Double layer |
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Term
| Electrical potential drops ______ in the stern layer and ______ in the Gouy Chapman layer |
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Definition
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Term
| When 2 particles, each with its own double layer approach each other... |
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Definition
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Term
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Definition
| Magnitude of repulsive forces between particles. It is affected by concentration and valence of electrolyte in solution. |
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