13 Questions
What is the HLB value of the required emulsifying agents for the basic formula?
10.5
What does the HLB Griffin's Scale measure?
The ratio of the polar to the non-polar portion of the molecule
What is the HLB value range for Spans?
1.8 to 8.6
What type of emulsion is formed with a surfactant having an HLB value of 12?
O/W emulsion
Why is the required HLB value for O/W emulsion higher than for W/O emulsion?
Because O/W emulsions require a more balanced ratio of polar to non-polar portions
What is the purpose of determining the required HLB value for an oil?
To blend surfactants for a stable emulsion
What happens when the surfactant HLB value increases?
It becomes more hydrophilic
What is the HLB value of a mixture consisting of 40% span60 (HLB 4.7) and 60% Tween 60 (HLB 14.9)?
10.82
What is the HLB value of a surfactant blend consisting of 20% tween20 (HLB 16.7), 30% span20 (HLB 8.6) and 50% span80 (HLB 4.3)?
8.07
What is the HLB value of an emulsifier blend consisting of 25% span20 (HLB 8.6) and 75% tween20 (HLB 16.7)?
14.67
What is the purpose of calculating the HLB value of a surfactant blend?
To formulate an oil with a particular required HLB value
What is the advantage of using blends of high and low HLB surfactants?
To obtain the required HLB of an oil
What is the formula used to calculate the HLB value of a mixture?
HLB mixture = x HLBA + (1-x) HLBB
Study Notes
HLB Griffin's Scale
- HLB scale is an arbitrary scale between 0 and 20, expressing the size and strength of the polar portion relative to the non-polar portion of the molecule.
- Originally applied to non-ionic surfactants, now extended to ionic surfactants (HLB up to 50, based on ionization properties).
- The scale allows comparison between different chemical types of surfactants and provides a systematic method of selecting mixtures of emulsifying agents to produce physically stable emulsions.
HLB Value and Hydrophilicity
- The higher the surfactant HLB value, the more hydrophilic it is.
- The lower the surfactant HLB value, the more lipophilic it is.
Examples of Surface-Active Agents
- Spans (sorbitan fatty acid esters) have low HLB values ranging from 1.8 to 8.6, suitable for w/o emulsions.
- Tweens (polyoxyethylene derivatives of spans) have higher HLB values ranging from 9.6 to 16.7, suitable for o/w emulsions.
Determination of Required HLB Values
- Oils used in emulsion formulations require a certain HLB value to be formulated as w/o or o/w emulsions.
- The required HLB value for o/w emulsion is higher than that for w/o emulsion.
Calculating HLB Mixtures
- HLB mixture = fraction of A × HLBA + fraction of B × HLBB
- The HLB of the mixture of surfactants is the algebraic mean of the two HLB numbers.
Worked Examples
- To formulate an o/w emulsion of liquid paraffin, the required HLB value is 10.5, which can be achieved by mixing Tween 80 (HLB 15) and Span 80 (HLB 4.3) in the right proportions.
- The HLB value of a mixture consisting of 40% span60 (HLB 4.7) and 60% Tween 60 (HLB 14.9) is 10.82.
- The HLB value of a surfactant blend consisting of 20% tween20 (HLB 16.7), 30% span20 (HLB 8.6), and 50% span80 (HLB 4.3) is 8.07.
- The HLB value of an emulsifier blend consisting of 25% span20 (HLB 8.6) and 75% tween20 (HLB 16.7) is 14.67.
- The HLB value of a mixture consisting of 45 g of span80 (HLB 4.3) and 55 g of polysorbate (tween 80) (HLB 15) can be calculated using the formula.
This quiz tests your understanding of calculating the required HLB value of an emulsifier blend, including the additive property of HLB values and the algebraic mean of HLB numbers. Calculate the HLB of a mixture of surfactants to obtain the required HLB of an oil.
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