An emulsification experiment is an experiment in which water and oil, which normally do not mix easily, are dispersed by using a surfactant or stirring to form an emulsion.
Because water and oil have very different properties, they separate within a short period if nothing is done.
However, when a surfactant is added, the oil-water interface is stabilized, allowing oil droplets or water droplets to remain dispersed as small particles and making the emulsified state easier to maintain.
In a discussion of an emulsification experiment, it is not sufficient simply to write that “it became cloudy white” or “it separated.”
It is necessary to explain why water and oil are difficult to mix, how surfactants lower interfacial tension, why surfactants with different HLB values differ in suitability for O/W-type and W/O-type emulsification, and what factors change emulsion stability.
In addition, distinguishing phenomena such as creaming, flocculation, coalescence, and phase inversion makes the discussion more detailed.
This article clearly explains, as examples of discussions that can be used in laboratory reports on emulsification experiments, types of emulsions, surfactant structure, HLB, O/W-type and W/O-type emulsions, emulsion stability, stirring conditions, oil-water ratio, temperature, viscosity, emulsion breakdown, causes of error, and points for improvement.
Note:
This article is a reference intended to assist with discussions of emulsification experimental results obtained in basic chemistry experiments, physical chemistry experiments, colloid chemistry experiments, and food chemistry experiments at universities and similar institutions.
For the actual oil, water, surfactant, HLB value, amount added, stirring conditions, temperature, and safety precautions, always follow the instructions in your university’s laboratory manual and those given by your instructor or TA.
- What Is an Emulsification Experiment?
- Main Items to Include in the Results
- Why Water and Oil Do Not Mix Easily
- Role of Surfactants
- Interfacial Tension and Emulsification
- What Is an O/W-Type Emulsion?
- What Is a W/O-Type Emulsion?
- What Is HLB?
- HLB and Emulsion Stability
- Effect of the Amount of Surfactant Added
- Effect of Stirring Conditions
- Effect of the Oil-Water Ratio
- What Is Emulsion Stability?
- Discussion of Creaming
- Difference Between Flocculation and Coalescence
- Discussion of Phase Inversion
- Effect of Viscosity
- Effect of Temperature
- Effects of pH and Electrolytes
- Methods for Determining the Emulsion Type
- Causes of Error in Emulsification Experiments
- When the Results Can Be Considered Good
- Example Discussions When the Experiment Did Not Go Well
- How to Write Points for Improvement
- Difference Between a Superficial Discussion and a Good Discussion
- Examples of Expressions That Can Be Used in Reports
- Points to Check When Discussing Emulsification Experiments
- Summary
What Is an Emulsification Experiment?
An emulsification experiment is an experiment in which liquids that do not readily mix with each other, such as water and oil, are placed in a state where one liquid is dispersed as small droplets in the other liquid.
Such a dispersed system is called an emulsion.
Milk, mayonnaise, dressings, cosmetic creams, and milky lotions are familiar examples of emulsions.
In an emulsified state, the droplets are finely dispersed, so light may be scattered and the mixture may appear cloudy white.
However, emulsification is thermodynamically unstable, and over time the droplets may approach one another, causing flocculation, coalescence, and separation.
Therefore, in an emulsification experiment, not only whether emulsification occurred but also how stably the emulsified state is maintained is evaluated.
Example Discussion:
In an emulsification experiment, liquids that are difficult to mix, such as water and oil, are stirred so that one is dispersed as small droplets in the other.
The cloudy white appearance after emulsification was considered to result from light scattering by the fine droplets.
However, because an emulsified state tends to separate over time, it is necessary to discuss not only whether emulsification occurred but also droplet stability and resistance to separation.
Main Items to Include in the Results
In the results of an emulsification experiment, organize the types of oil phase and water phase, oil-water ratio, type of surfactant, HLB value, amount added, stirring time, stirring speed, temperature, appearance immediately after emulsification, separation state after a certain period, height of the emulsion layer, presence or absence of creaming, and other information.
Because emulsion stability depends on time, it is important to keep the observation time consistent.
Main Items to Include in the Results
- Type of oil phase
- Type of water phase
- Oil-water ratio
- Type of surfactant
- HLB value of the surfactant
- Amount of surfactant added
- Stirring time
- Stirring speed
- Temperature during emulsification
- Color and turbidity immediately after emulsification
- Fineness of the droplets
- Separation state after a certain period
- Height of the emulsion layer
- Presence or absence of separation into oil and water layers
- Presence or absence of creaming
- Presence or absence of coalescence or flocculation
- Determination of O/W type or W/O type
- Causes of error and points for improvement
Example of How to Write the Results:
When oil and water were stirred in the presence of a surfactant, a milky-white emulsion was obtained.
Under conditions without a surfactant, the sample separated into an oil layer and a water layer within a short period, whereas separation was delayed under conditions with a surfactant.
In addition, comparison of surfactants with different HLB values showed differences in ease of emulsification and stability.
Why Water and Oil Do Not Mix Easily
Water is highly polar and water molecules form hydrogen bonds with one another.
In contrast, oil is a nonpolar substance mainly composed of hydrocarbon chains and interacts poorly with water.
Therefore, even when water and oil are mixed, they do not mix uniformly at the molecular level and tend to separate into two layers with an interface between them.
Energy is required to increase the area of the water-oil interface.
Stirring temporarily disperses oil droplets or water droplets into small droplets, but the system is unstable because the interfacial area becomes large.
Therefore, when nothing is added, droplets coalesce with one another and separate again into an oil layer and a water layer.
Example Discussion:
Water and oil do not mix easily because water is a polar liquid, whereas oil is nonpolar and the interaction between the two is weak.
Even if droplets are temporarily dispersed by stirring, the oil-water interfacial area increases and the system becomes unstable.
Therefore, in the absence of a substance that stabilizes the interface, the droplets were considered to have coalesced and separated into a water layer and an oil layer.
Role of Surfactants
Surfactants are substances that contain both hydrophilic and hydrophobic groups within the same molecule.
Because the hydrophilic group has an affinity for water and the hydrophobic group has an affinity for oil, surfactants tend to gather at the interface between water and oil.
As a result, they lower the interfacial tension at the oil-water interface and make it easier to disperse the droplets finely.
Surfactants also adsorb onto the droplet surface and prevent droplets from directly contacting one another and coalescing.
Electrostatic repulsion, steric hindrance, hydration layers, and other factors are involved in this stabilization.
This is why the type and amount of surfactant greatly affect emulsion stability.
Example Discussion:
Emulsification was more stable under conditions with a surfactant because the surfactant adsorbed at the oil-water interface and lowered the interfacial tension.
When the interfacial tension decreases, it becomes easier to form small droplets through stirring.
Furthermore, the surfactant covered the droplet surfaces and suppressed coalescence between droplets, so the emulsified state was considered to have been maintained.
Interfacial Tension and Emulsification
Interfacial tension is the tendency of the interface between two poorly miscible liquids to become as small as possible.
When the interfacial tension between water and oil is large, a large amount of energy is required to disperse the droplets finely.
Therefore, even after stirring, droplets readily coalesce again and separation occurs easily.
Surfactants adsorb at the oil-water interface and lower the interfacial tension.
This makes the droplets more likely to become smaller under the same stirring conditions and makes it easier to form an emulsion.
Reduction of interfacial tension is one of the most fundamental factors when considering ease of emulsification.
Example Discussion:
Adding a surfactant lowers the interfacial tension at the oil-water interface and reduces the energy required to disperse oil droplets or water droplets finely.
Therefore, the sample containing the surfactant became easier to emulsify even under the same stirring conditions.
Reduction of interfacial tension is an important factor that assists the formation of an emulsion.
What Is an O/W-Type Emulsion?
An O/W-type emulsion is an emulsified system in which oil is dispersed as small oil droplets in water.
O/W is an abbreviation for Oil in Water, with water as the outer continuous phase and oil as the inner dispersed phase.
Milk, some types of mayonnaise, and milky cosmetic products may be treated as O/W-type emulsions.
In an O/W-type emulsion, the outer phase is water, so it is easy to dilute with water and often has a relatively light feel.
Highly hydrophilic surfactants, that is, surfactants with relatively high HLB values, are suitable for forming O/W-type emulsions.
If the emulsion readily disperses in water during an experiment, it may be an O/W-type emulsion.
Example Discussion:
If the obtained emulsion could be easily diluted with water, it can be considered an O/W-type emulsion in which water is the continuous phase.
In an O/W-type emulsion, oil droplets are dispersed in water and their surfaces are stabilized by a highly hydrophilic surfactant.
Therefore, O/W-type emulsification was considered more likely to occur under conditions using a surfactant with a high HLB value.
What Is a W/O-Type Emulsion?
A W/O-type emulsion is an emulsified system in which water is dispersed as small water droplets in oil.
W/O is an abbreviation for Water in Oil, with oil as the outer continuous phase and water as the inner dispersed phase.
Butter, margarine, and some creams may be treated as W/O-type emulsions.
In a W/O-type emulsion, the outer phase is oil, so it has an affinity for oil and tends to be difficult to dilute with water.
Highly hydrophobic surfactants, that is, surfactants with relatively low HLB values, are suitable for forming W/O-type emulsions.
If the emulsion disperses readily in the oil phase but poorly in water during an experiment, it may be a W/O-type emulsion.
Example Discussion:
If the obtained emulsion had little affinity for water and readily mixed with the oil phase, it can be considered a W/O-type emulsion in which oil is the continuous phase.
In a W/O-type emulsion, water droplets are dispersed in oil and their surfaces are stabilized by a highly hydrophobic surfactant.
Therefore, W/O-type emulsification was considered more likely to occur under conditions using a surfactant with a low HLB value.
What Is HLB?
HLB is an abbreviation for Hydrophile-Lipophile Balance and is an index representing the balance between hydrophilicity and lipophilicity of a surfactant.
Surfactants with low HLB values are strongly lipophilic and readily mix with oil.
Surfactants with high HLB values are strongly hydrophilic and readily mix with water.
In general, surfactants with low HLB values are considered suitable for W/O-type emulsions, while surfactants with high HLB values are considered suitable for O/W-type emulsions.
However, actual emulsion stability is also affected by the type of oil, temperature, amount added, stirring conditions, and combination of surfactants.
HLB is an index used as a guideline for selecting an emulsifier.
| HLB Value Trend | Property | Emulsion Type for Which It Is More Suitable |
|---|---|---|
| Low | Strongly lipophilic | W/O type |
| High | Strongly hydrophilic | O/W type |
Example Discussion:
The HLB value is an index representing the balance between the hydrophilicity and lipophilicity of a surfactant.
A surfactant with a high HLB value has a greater affinity for the aqueous phase and is suitable for O/W-type emulsification, in which oil droplets are dispersed in water.
On the other hand, a surfactant with a low HLB value has a greater affinity for the oil phase and is considered suitable for W/O-type emulsification, in which water droplets are dispersed in oil.
HLB and Emulsion Stability
Emulsion stability is greatly affected by whether a surfactant with an HLB value suitable for the oil being used is selected.
The HLB value required to prepare a stable O/W-type emulsion differs depending on the type of oil.
Therefore, there is no simple relationship in which a high HLB value always means stable and a low value always means unstable.
If the HLB value deviates from the appropriate value, the surfactant may not orient properly at the oil-water interface and may fail to sufficiently stabilize the droplet surface.
As a result, droplets become more likely to coalesce and the emulsion separates within a short period.
By comparing surfactants with different HLB values in an experiment, conditions suitable for emulsifying a particular oil can be discussed.
Example Discussion:
Emulsion stability changed among surfactants with different HLB values because their affinity for the oil-water interface differed.
With a surfactant having an HLB value appropriate for the oil used, the droplet surfaces were effectively covered and coalescence was suppressed.
On the other hand, when the HLB value was inappropriate, stabilization of the interface was insufficient and the emulsion became more likely to separate.
Effect of the Amount of Surfactant Added
If too little surfactant is added, it cannot sufficiently cover all droplet surfaces and the droplets become more likely to coalesce.
Therefore, even if the emulsion appears cloudy white immediately after emulsification, it may separate into an oil layer and a water layer over time.
To stabilize an emulsion, a sufficient amount of surfactant is required relative to the total interfacial area of the droplets formed.
On the other hand, adding more surfactant does not necessarily always increase stability.
Excess surfactant may cause micelle formation, viscosity changes, foaming, phase-behavior changes, and other effects.
Optimization of the amount added is an important point of discussion in emulsification experiments.
Example Discussion:
The emulsion separated within a short period under conditions with a small amount of surfactant because there was not enough surfactant to sufficiently cover the surfaces of the droplets formed.
If the droplet surfaces are not sufficiently protected, droplets readily coalesce when they come into contact with one another.
Therefore, to improve emulsion stability, an appropriate amount of surfactant must be added relative to the total interfacial area of the droplets.
Effect of Stirring Conditions
In emulsification, stirring disperses the oil phase or water phase into fine droplets.
If stirring is weak, the droplets tend to become large, making separation due to gravity and coalescence more likely.
Stronger stirring may make the droplets finer and may increase emulsion stability.
However, stronger stirring does not necessarily always produce greater stability.
Excessively strong stirring may increase foaming, generate heat, or damage the surfactant film.
In addition, if stirring time or stirring speed differs among samples, comparison of emulsion stability becomes inaccurate.
Example Discussion:
Emulsification was more stable under conditions with longer stirring time or higher stirring speed because the droplets were more finely dispersed.
Smaller droplets are less likely to settle or rise and are more easily stabilized at the surface by surfactants.
However, because differences in stirring conditions among samples cause errors in comparison of emulsion stability, the stirring time and intensity must be kept constant.
Effect of the Oil-Water Ratio
The proportions of oil and water affect the emulsion type and stability.
Conditions with a larger amount of water tend to produce O/W-type emulsions, while conditions with a larger amount of oil tend to produce W/O-type emulsions.
However, the final emulsion type is also affected by the HLB of the surfactant and stirring conditions.
As the proportion of the dispersed phase increases, droplets become more likely to contact one another and coalescence or flocculation may become more likely.
In addition, changing the oil-water ratio also changes the amount of surfactant required.
Even with the same amount added, the surfactant may become insufficient under conditions where the interfacial area becomes larger.
Example Discussion:
Changing the oil-water ratio changes the proportions of the dispersed and continuous phases and therefore affects the emulsion type and stability.
Under conditions with a large proportion of the dispersed phase, droplets are more likely to contact one another and separation due to coalescence is more likely to occur.
In addition, because the total interfacial area of the droplets increases, the same amount of surfactant may be insufficient to cover the surface completely, making the emulsion unstable.
What Is Emulsion Stability?
Emulsion stability is a property indicating how well an emulsion can maintain a dispersed droplet state without separating over time.
When emulsion stability is high, the droplets remain finely dispersed and coalescence or separation is less likely to occur.
When emulsion stability is low, the emulsion may separate into an oil layer and a water layer within a short period or form a cream layer at the top.
Emulsion stability is related to droplet size, type and amount of surfactant, HLB, oil-water ratio, viscosity, temperature, pH, electrolyte concentration, storage time, and other factors.
In experiments, stability can be evaluated by observing the separation state not only immediately after emulsification but also after allowing the sample to stand for a fixed period.
Example Discussion:
Emulsion stability indicates whether an emulsion can maintain a dispersed droplet state without separating over time.
In this experiment, separation was slower in samples containing surfactant because the droplet surfaces were covered with surfactant and coalescence was suppressed.
Emulsion stability is affected by droplet size, HLB, amount added, viscosity, and storage conditions.
Discussion of Creaming
Creaming is a phenomenon in which dispersed droplets move upward or downward without coalescing and form a concentrated layer.
When oil droplets are lighter than water, they may rise in an O/W-type emulsion and form a cream layer at the top.
This does not mean that the droplets have completely fused together; rather, they have moved because of the density difference.
Creaming occurs more readily when the droplet size is larger and when the viscosity of the continuous phase is lower.
Even if creaming occurs, the droplets may redisperse when the sample is gently shaken.
It is important to distinguish creaming from coalescence and complete separation.
Example Discussion:
If a white layer formed at the top of the emulsion, creaming may have occurred as the oil droplets rose because of the density difference.
Creaming is not a state in which the droplets have completely coalesced, but rather a state in which the droplets are concentrated at the top.
Larger droplets rise more readily, and creaming is considered to progress more easily when the viscosity of the continuous phase is low.
Difference Between Flocculation and Coalescence
Flocculation is a state in which droplets gather together to form clusters while the interface of each droplet remains.
In contrast, coalescence is the phenomenon in which droplets fuse together to form one larger droplet.
As coalescence progresses, the droplet size becomes larger and final separation into oil and water layers becomes more likely.
Surfactants cover the droplet surfaces and prevent droplets from directly contacting one another and coalescing.
However, if the amount of surfactant is insufficient or the interfacial film is weak, flocculated droplets may readily coalesce.
When discussing emulsion breakdown, it is useful to distinguish flocculation from coalescence.
| Phenomenon | State | Effect on Separation |
|---|---|---|
| Flocculation | Droplets gather together but interfaces remain | Redispersion may be possible |
| Coalescence | Droplets fuse and become larger | Separation tends to progress |
Example Discussion:
If droplets appeared to gather together in the emulsion, flocculation may first have occurred.
In flocculation, droplets approach one another, but the interface of each individual droplet remains.
If the interfacial film subsequently breaks and the droplets fuse, coalescence occurs, increasing droplet size and promoting oil-water separation.
Discussion of Phase Inversion
Phase inversion is the phenomenon in which an O/W-type emulsion changes into a W/O-type emulsion or a W/O-type emulsion changes into an O/W-type emulsion.
Changes in the oil-water ratio, surfactant HLB, temperature, salt concentration, stirring conditions, and other factors may cause the continuous and dispersed phases to exchange.
When phase inversion occurs, viscosity, appearance, dilutability, conductivity, and other properties may change greatly.
Because the continuous phase is water in an O/W-type emulsion, it may conduct electricity relatively easily, whereas conductivity is low in a W/O-type emulsion because the continuous phase is oil.
If conductivity or dilutability changes suddenly during an experiment, phase inversion can be considered.
Phase inversion may indicate that the emulsification conditions have moved outside the stable region.
Example Discussion:
If dilutability with water or conductivity changed greatly when the emulsification conditions were changed, phase inversion between O/W and W/O types may have occurred.
When the oil-water ratio or surfactant HLB changes, which phase is more stable as the continuous phase may also change.
Therefore, phase inversion is an important phenomenon showing that emulsion type can change depending on the conditions.
Effect of Viscosity
The higher the viscosity of the continuous phase, the slower the droplets move, making creaming and sedimentation less likely to occur.
Therefore, adding a thickener or polymer may increase emulsion stability.
In foods and cosmetics, viscosity adjustment plays an important role in stabilizing emulsions.
However, if the viscosity is too high, uniform mixing during stirring may become difficult and the droplet size may become nonuniform.
Viscosity suppresses separation while also affecting ease of emulsification.
If a highly viscous sample was more stable in an experiment, suppression of droplet movement can be discussed.
Example Discussion:
Separation of the emulsion was slower under high-viscosity conditions because the droplets became more difficult to move through the continuous phase.
Suppression of droplet flotation or sedimentation makes creaming and separation less likely to progress.
However, if the viscosity is too high, the droplets may not become uniformly fine during stirring, so there is an appropriate range of viscosity.
Effect of Temperature
Temperature affects the viscosity of oil and water, the solubility of surfactants, the effective HLB balance, and droplet movement.
As temperature increases, viscosity decreases and droplets move more easily, which may promote separation.
On the other hand, surfactants may dissolve more readily and emulsification may become easier.
In nonionic surfactants, hydrophilicity may change with temperature, causing changes in emulsion type and stability.
If emulsion stability is compared under different temperature conditions, it becomes difficult to distinguish the effects of HLB and amount added.
Therefore, it is important to keep the temperature constant in emulsification experiments.
Example Discussion:
Changes in temperature affect the viscosity of the oil and water phases, surfactant solubility, and droplet movement, thereby influencing emulsion stability.
Under high-temperature conditions, viscosity decreases and droplets move more easily, so separation may progress more readily.
Therefore, the temperature must be kept constant when comparing emulsion stability.
Effects of pH and Electrolytes
pH and electrolyte concentration affect the charges of surfactants and droplet surfaces.
When ionic surfactants are used, the charge state and solubility may change depending on pH and salt concentration, causing changes in emulsion stability.
At high electrolyte concentrations, electrostatic repulsion between droplet surfaces may weaken, making flocculation more likely.
When natural emulsifiers such as proteins or polysaccharides are used, molecular charge and structure change with pH.
Near the isoelectric point, repulsion due to charge weakens and flocculation or separation may become more likely.
The effect of pH is particularly important in food-related emulsification experiments.
Example Discussion:
Changes in pH and electrolyte concentration alter the charge state of surfactants and droplet surfaces and therefore affect emulsion stability.
When electrostatic repulsion between droplets is weakened by electrolytes, the droplets become more likely to flocculate.
In addition, with protein-based emulsifiers, the charge becomes small near the isoelectric point, making the emulsion more likely to become unstable.
Methods for Determining the Emulsion Type
Methods for determining whether an emulsion is O/W type or W/O type include the dilution method, dye method, and conductivity measurement.
In the dilution method, an emulsion that readily disperses in water is judged to be O/W type, while one that readily disperses in oil is judged to be W/O type.
In the dye method, the distribution of a water-soluble dye or oil-soluble dye between the phases is observed.
In conductivity measurement, O/W-type emulsions with water as the continuous phase tend to show relatively high conductivity, whereas W/O-type emulsions with oil as the continuous phase tend to show low conductivity.
However, because conductivity changes depending on the presence of electrolytes and composition of the water phase, combining multiple methods rather than relying on only one method provides a more reliable determination.
Example Discussion:
If the emulsion could be easily diluted with water and conductivity was also observed, it can be judged to be an O/W-type emulsion with water as the continuous phase.
On the other hand, if it dispersed in oil but was difficult to disperse in water and showed low conductivity, it is highly likely to be W/O type.
It is important to determine the emulsion type by considering dilutability, dye behavior, and conductivity together.
Causes of Error in Emulsification Experiments
Causes of error in emulsification experiments include deviations in the oil-water ratio, errors in the amount of surfactant added, inappropriate selection of the HLB value, differences in stirring time or stirring speed, temperature differences, order of sample addition, container shape, differences in observation time, and subjectivity in judgment.
Because emulsification is sensitive to operating conditions, even slight differences may change droplet size and stability.
When the degree of separation is judged visually, differences among observers are likely to occur.
More objective evaluation can be achieved by measuring the height of the emulsion layer, thickness of the separated layer, turbidity, conductivity, or by microscopic observation.
Causes of error are easier to discuss when organized into preparation conditions, emulsification operation, and observation method.
Example Discussion:
Possible causes of error in the emulsification experiment include differences in stirring time or stirring speed, errors in the amount of surfactant added, deviations in the oil-water ratio, and temperature changes.
Because emulsion stability is strongly affected by droplet size, differences in stirring conditions cause variation in the results.
In addition, when the presence or absence of separation is judged visually, subjective error may be included in the judgment.
When the Results Can Be Considered Good
An emulsification experiment can be considered to have produced good results when an emulsion forms under conditions with a surfactant and separation occurs more slowly than under conditions without a surfactant.
In addition, if differences in emulsion type or stability are observed when the HLB value or oil-water ratio is changed and those differences can be explained in relation to the hydrophilicity and lipophilicity of the surfactant, the results can be considered reasonable.
If the emulsion layer is maintained not only immediately after emulsification but also after a certain period, emulsion stability can be judged to be high.
However, if creaming occurs but redispersion is possible, it should be distinguished from complete separation or coalescence.
It is important that the observations correspond to emulsion theory.
Example Discussion:
In this experiment, a milky-white emulsion formed under conditions with a surfactant, and oil-water separation was slower than under conditions without a surfactant.
This was considered to result from the surfactant adsorbing at the oil-water interface, lowering the interfacial tension, and suppressing droplet coalescence.
In addition, because differences in stability were observed among surfactants with different HLB values, an HLB value appropriate for the oil used was judged to be important for emulsion stability.
Example Discussions When the Experiment Did Not Go Well
When an emulsification experiment does not go well, possible causes should be considered from results such as failure to emulsify, immediate separation, coarse droplets, excessive foaming, disagreement with the HLB-based prediction, or poor reproducibility.
Organizing the causes according to surfactant, stirring conditions, oil-water ratio, temperature, order of addition, and observation method makes the discussion easier.
Example Discussion:
In this experiment, the sample was cloudy white immediately after emulsification but separated into an oil layer and a water layer within a short period.
One possible cause is that the amount of surfactant was too small to sufficiently cover the surfaces of the droplets formed.
In addition, if stirring was insufficient and the droplet size was large, the droplets may have risen and coalesced more easily, causing separation to proceed rapidly.
Another Example Discussion:
One possible reason why the emulsion type predicted from the HLB value did not agree with the actual result is that the required HLB differed depending on the type of oil.
Emulsion type and stability also change depending on temperature, oil-water ratio, surfactant concentration, and stirring conditions.
Therefore, the emulsification result should not be judged from the HLB value alone, and the overall experimental conditions must be considered.
How to Write Points for Improvement
In a discussion of an emulsification experiment, writing not only the causes of error but also points for improvement makes the report easier to organize.
Points for improvement can be organized according to surfactant selection, preparation conditions, stirring conditions, and stability evaluation.
Improvements to Surfactant Selection
- Select a surfactant with an HLB value appropriate for the oil
- Measure the amount of surfactant added accurately
- Adjust the HLB by combining multiple surfactants
- Dissolve the surfactant uniformly
- Confirm the balance between hydrophilicity and lipophilicity
- Select an emulsifier appropriate for the emulsion type
Improvements to the Emulsification Operation
- Accurately standardize the oil-water ratio
- Keep the order of addition consistent
- Keep the stirring time constant
- Keep the stirring speed constant
- Keep the temperature constant
- Suppress foaming
- Use the same container
Improvements to the Evaluation Method
- Fix the observation time
- Measure the heights of the emulsion layer and separated layers
- Record the samples with photographs
- Confirm the emulsion type using the dilution method or dye method
- Determine O/W type or W/O type from conductivity
- Observe droplet size under a microscope
- Perform multiple measurements to confirm reproducibility
Example of How to Write Points for Improvement:
To improve the reproducibility of an emulsification experiment, it is necessary to keep the oil-water ratio, amount of surfactant added, stirring time, stirring speed, and temperature constant.
It is also important to select a surfactant with an HLB value appropriate for the oil being used and add an amount sufficient to stabilize the droplet surfaces.
When evaluating emulsion stability, using not only visual observation but also the height of the separated layer, conductivity, and microscopic observation allows a more objective comparison.
Difference Between a Superficial Discussion and a Good Discussion
In a discussion of an emulsification experiment, simply writing that “it became white” or “it separated” results in a superficial discussion.
A good discussion relates interfacial tension, surfactants, HLB, emulsion type, droplet size, coalescence, and emulsion stability.
| Superficial Discussion | Good Discussion |
|---|---|
| It became cloudy white. | Oil droplets or water droplets were finely dispersed by stirring, and the emulsion was considered to appear cloudy white because the droplets scattered light. |
| It became stable because of the surfactant. | The surfactant adsorbed at the oil-water interface, lowered the interfacial tension, and covered the droplet surfaces, thereby suppressing coalescence between droplets and improving emulsion stability. |
| HLB was related. | The HLB value indicates the balance between the hydrophilicity and lipophilicity of a surfactant, and surfactants with high HLB values tend to be suitable for O/W-type emulsification, while those with low HLB values tend to be suitable for W/O-type emulsification. |
| It separated quickly. | The amount of surfactant may have been insufficient to adequately protect the droplet surfaces, or insufficient stirring may have resulted in large droplets, causing creaming or coalescence to progress and leading to separation. |
Examples of Expressions That Can Be Used in Reports
The following expressions can be used when writing the results and discussion of emulsification experiments.
Adjust the necessary parts according to your own experimental results.
- Emulsification is the phenomenon in which one liquid is dispersed as fine droplets in another liquid.
- Water and oil do not mix easily because of differences in polarity.
- Surfactants have hydrophilic and hydrophobic groups and adsorb at oil-water interfaces.
- Surfactants lower interfacial tension and make it easier to disperse droplets finely.
- When droplet surfaces are covered with surfactant, coalescence is suppressed.
- The HLB value represents the balance between the hydrophilicity and lipophilicity of a surfactant.
- Surfactants with high HLB values tend to be suitable for O/W-type emulsification.
- Surfactants with low HLB values tend to be suitable for W/O-type emulsification.
- Emulsion stability is affected by droplet size, surfactant amount, oil-water ratio, viscosity, and temperature.
- Causes of separation include creaming, flocculation, coalescence, and phase inversion.
Points to Check When Discussing Emulsification Experiments
Checking the following points before writing the report makes the discussion easier to write.
- Is the definition of emulsification explained?
- Is the reason why water and oil do not mix easily described?
- Are the hydrophilic and hydrophobic groups of surfactants explained?
- Is the reduction of interfacial tension related to emulsification?
- Are O/W-type and W/O-type emulsions distinguished?
- Is the HLB value related to emulsion type?
- Is the effect of the amount of surfactant added considered?
- Are stirring conditions related to droplet size?
- Is emulsion stability evaluated over time?
- Are creaming, flocculation, and coalescence distinguished?
- Are the effects of temperature, pH, and electrolytes considered?
- Do the points for improvement correspond to the causes of error?
Summary
An emulsification experiment is an experiment in which liquids that do not readily mix, such as water and oil, are dispersed using surfactants or stirring to form an emulsion.
Water and oil readily separate because of differences in polarity, but when a surfactant adsorbs at the oil-water interface, the interfacial tension decreases and the droplets become easier to disperse finely.
In addition, the surfactant covers the droplet surfaces and suppresses coalescence between droplets.
The HLB value is an important index representing the balance between the hydrophilicity and lipophilicity of a surfactant.
In general, surfactants with high HLB values tend to be suitable for O/W-type emulsification, while surfactants with low HLB values tend to be suitable for W/O-type emulsification.
However, actual emulsion stability is also affected by the type of oil, oil-water ratio, amount added, stirring conditions, temperature, viscosity, and other factors.
In a report, rather than simply writing that “it became cloudy white” or “it separated,” organize and discuss interfacial tension, the role of surfactants, HLB, O/W type and W/O type, droplet size, creaming, flocculation, coalescence, phase inversion, emulsion stability, causes of error, and points for improvement.
Emulsification experiments are important experiments for understanding the fundamentals of interfacial chemistry and colloidal dispersion.
