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Home > Senior Science > Core > Lifestyle Chemistry > Lifestyle Chemistry: 2. Colloids and surfactants

9.2 Lifestyle chemistry: 2. Colloids and surfactants  

Syllabus reference (October 2002 version)
2. A wide range of cleaning products are made from colloids and surfactants	Students learn to: state the relationship between the properties of an emulsion and the types of molecules present outline the purpose of the emulsifying agent in a range of consumer cleaning products  identify that soaps and detergents are emulsifying agents and surfactants explain why cleaning agents must be surfactants and emulsifiers define the term biodegradable discuss the biodegradability of soaps and soapless detergents	Students: perform a first-hand investigation to prepare an emulsion and compare its properties to those of a solution and suspension plan, choose equipment or resources for, and perform a first-hand investigation to gather information about the properties of different emulsions and use available evidence to compare those properties

Extract from Senior Science Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW

Prior learning: Stages 4-5 outcomes 4.3 and 5.3; outcome 4.7 (content 4.7.1, 4.7.2, 4.7.5, 4.7.6); outcome 5.7 (content 5.7.1); outcome 5.12 (content 5.12 f, g).

perform a first-hand investigation to prepare an emulsion and compare its properties to those of a solution and suspension

Background: Emulsions are mixtures of two immiscible liquids such as oil and water that are suspended in one another indefinitely. They contain emulsifying agents that stabilise them.

About emulsions Key Centre for Polymer Colloids. University of Sydney, NSW Australia

For this investigation, you need to make an emulsion, such as cold cream. Before you perform the investigation, you should identify safety issues. In the case of cold cream, the use of heating appliances and boiling water present physical hazards. You should write down what safe work practices you intend to use during the first-hand investigation. In performing the procedure, apply the safe work practices you have planned and be able to describe and evaluate them. Complete the activity by comparing the properties of the emulsion you have produced to the properties of a solution, such as salt or sugar solution, and to the properties of a suspension, such as salad dressing or calamine lotion. You may find it useful to use a table like the one following to record your findings.

Mixtures	Properties
	Appearance after vigorous shaking	Appearance after standing (20 minutes)	Can be separated by filtration	Scatters light
mayonnaise  (an emulsion)
salt water  (a solution)	clear, homogenous	clear, homogenous	no	not at all
salad dressing  (a suspension)

(Note: For this activity, you could use emulsions, such as mayonnaise and salad dressing, produced earlier in the module.)

plan, choose equipment or resources for, and perform a first-hand investigation to gather information about the properties of different emulsions and use available evidence to compare those properties

plan, choose equipment or resources for, and perform a first-hand investigation to distinguish between oil-in-water and water-in-oil based emulsions.

The activities described in the two syllabus points presented above could be done together in the one investigation. 

• For the investigation, you need to make some emulsions, such as cold cream, mayonnaise, cream, butter or ice cream (some recipes are provided below). In your planning, you need to design your investigations to ensure that valid and reliable data and information can be collected. To validly compare the properties of a range of emulsions, you need to consider how testing can be consistently applied to show the properties of each emulsion.
• You will also need to identify safety issues as you choose equipment and before you perform any procedures. In some cases, the use of mixing equipment, heating appliances and boiling water present physical hazards. You should write down what safe work practices you intend to use during the first-hand investigation. In performing the procedure, apply the safe work practices you have planned and be able to describe and evaluate them.
• In gathering information, consider the measurements and observations needed in relation to the extent each mixture:
  - conducts electricity
  - diffuses oil soluble or water soluble dyes
  - produces cooling or warming effects on skin (only for non-hazardous mixtures).

Carry out repeat tests if appropriate. Select a form to record results so that comparisons are easily accessible. 

• Use the evidence available in your recorded results to propose generalized properties for different types of emulsions. You must particularly distinguish between oil-in-water and water-in-oil based emulsions, making sure you use correct scientific terminology and ideas.

Recipes for emulsions Cold Cream: 28 g white beeswax 175 mL rosewater 175 mL oil (grapeseed is best as it is non-greasy) 3-4 drops fragrant oil (optional) Melt beeswax in a bowl over a pan of boiling water. Slightly warm the oil and rosewater together (microwave, 30 seconds). If put in cold, it will solidify too quickly. Whisk together with the wax until the mixture is cool and thickened. Add the fragrant oil. Mix well together. Put in jars.  Hand cream  Beat together in a blender, 1 egg yolk and 30 mL lemon juice. Slowly add 100 mL almond or vegetable oil, while still beating. Beat in 6 drops of tincture of benzoin (a preservative available at some pharmacies), and 6 drops lavender, rose or lemon oil, to perfume. Keep refrigerated. Making mayonnaise-an edible emulsion  : activity notes for students investigating and explaining emulsions in comparison to solutions (from the Smile Program, Department of Biological, Chemical and Physical Sciences, Illinois Institute of Technology USA) Finding science in ice cream - an experiment for secondary school classrooms  Professor Doug Goff, Dept. of Food Science, University of Guelph, Ontario

Normal and inverse emulsions Key Centre for Polymer Colloids. University of Sydney NSW Australia

state the relationship between the properties of an emulsion and the types of molecules present 

Water-based (oil-in-water) emulsions, such as hand lotions, face cleansing lotions and conditioners, contain some oil or fat. They are used to moisturise or protect the skin and hair by placing oil onto the surface. They have a lubricating effect and provide sheen. These are miscible with water. This means that if a small amount is placed into water and shaken or stirred it will remain suspended. The types of surfactant molecules present in oil-in-water based emulsions are large molecules with very polar chemical groups at one end. This end becomes attracted to the polar water molecules. The other non-polar end of the surfactant is attracted to the non-polar oil molecules. Many of the surfactant molecules become positioned around the very small droplets of oil, preventing them from merging together.

Oil-based (water-in-oil) emulsions, such as cold creams, night creams and hair creams, contain some water. These are not miscible with water and so if a small amount is placed into water, the emulsion will not be maintained. They are useful to cleanse the skin, moisturise very dry skin and hold hair in place, but are greasy and sticky to the touch. The types of surfactant molecules present in water-in-oil based emulsions are long starch molecules or protein chains. The chains wind among minute water droplets and prevent them from merging together.

Surfactants in emulsions   Key Centre for Polymer Colloids. University of Sydney NSW Australia

outline the purpose of the emulsifying agent in a range of consumer cleaning products

• The molecules in emulsifying agents that are used in dishwashing and laundry detergents (anionic) have a negative end when they dissolve. This allows them to keep oily substances away from any article that has negatively charged surfaces, such as glass and crockery.

• The molecules in emulsifying agents that are used in fabric softeners and hair conditioners have a positive end when they dissolve (cationic). This allows them to keep oily substances away from any article that has positively charged surfaces, as is often the case with plastic.

• The molecules in emulsifying agents that are used in personal cleaning products are amphoteric, which means they can have positive ends in alkaline solutions and negative ends in acidic solutions. This allows them to keep oily substances away from some objects that have positively charged surfaces or negatively charged surfaces. However, they are not strong cleaners.

identify that soaps and detergents are emulsifying agents and surfactants 

• Soaps and detergents are emulsifying agents because they assist two immiscible substances, such as oil and water, to mix. Soaps and detergents allow oil to disperse in water.

• Soaps and detergents are surfactants because they act at the surfaces between two immiscible substances, such as oil and water.

Detergency   Key Centre for Polymer Colloids. University of Sydney, NSW Australia

explain why cleaning agents must be surfactants and emulsifiers 

• Cleaning agents must be surfactants because they interact at the interface between two immiscible substances, creating an emulsion.

• Cleaning agents must be emulsifiers because they maintain the emulsion. They act as emulsifying agents by causing the drops of oil to break up and remain suspended in the water. This means that the grease or oil can be washed or rinsed away with the water that is holding them. The role of the emulsifying agent is to ensure that the oil stays with the water particles.

To be effective as cleaning agents, soap and detergents must be effective both as surfactants and emulsifiers. Not all emulsifiers are good cleaning agents, for example egg yolk provides the emulsifying agent for the oil and vinegar to make mayonnaise.

Introduction to surfactants   Key Centre for Polymer Colloids. University of Sydney, NSW Australia.

define the term biodegradable 

• Biodegradable is a term to describe a substance that can be broken down by living organisms, such as microbes.

discuss the biodegradability of soaps and soapless detergents 

• Soap is commonly the sodium or potassium salt of a natural long chain fatty acid. Soap is broken down by micro-organisms to smaller naturally occurring molecules.

• Soapless or synthetic detergents were originally made from aromatic compounds that produced good cleaning agents. Unfortunately, however, they were not broken down by micro-organisms and remained in water systems creating foam.

• Modern detergents, although still produced synthetically, can be broken down by micro-organisms and so are considered to be biodegradable. They have an added advantage over soap in that they are effective as cleaning agents in hard water and in cold water.

Soaps Vs detergents   Key Centre for Polymer Colloids. University of Sydney NSW Australia

Soaps in hard water   Key Centre for Polymer Colloids. University of Sydney NSW Australia