Science: Colloid and Dispersed Droplets Essay

Submitted By Khalilah2
Words: 871
Pages: 4
Open Document
FST 1800 Fundamentals of Food Science

Week 2 – Food Colloids: Emulsions

Learning objectives
• To study emulsion and type of emulsions • To understand interactions between dispersed droplets
• To classify emulsifiers and mechanism of action for emulsifiers

Lecture outline
• • • • • • Terminology Interactions between dispersed droplets Types of emulsion Emulsifiers Mechanism action HLB values

Terminology
• Colloidal dispersion – dispersion of two or more immiscible materials, containing a dispersed phase in the size range of 1 nm – 1 µm
• Simplest type of colloidal system – a single dispersed phase of particles in a continuous phase (dispersion medium)

Dispersed phase

Continuous phase Interface

Terminology cont.
• A system containing particles > 1 µm that prone to settle under gravity – suspension
• A dispersion or suspension of liquid droplets in a liquid continuous phase – emulsion

• Foam???

Food Colloids
• In food systems, “colloids” includes dispersions containing larger particles (> 1 µm)
• Food dispersions encompass suspensions such as sugar fondant (solid sugar particles in a saturated sugar solution), emulsions such as milk, cream and spread, and foams such as in beer, ice cream & bread

Interactions Between Dispersed Droplets • Two main interacting forces in affecting colloid systems – (1) van der Waals attractive forces and (2) electrostatic • Attractive forces – destabilize colloids
• Repulsive forces – impart stability

Van der Waals Interactive Forces
• Originate interactions from dipole-dipole

• Force between two droplets arising from van der Waals interaction is always attractive for like droplets • The attractive force increases more rapidly as the droplets approach close to each other

Van der Waals Interactive Forces

-

+

-

+

F = -β/r6 β = constant; r = distance in between two droplets

Electrical Double Layer
---- ++++++ --- ++++++ --- ++++++ --- ++++++ --

• Oppositely charged ions – attracted towards surface
• Same charge ions repel away

Electrical Double Layer
• Double layer is important for the stability of colloid • Double layer is sensitive to electrolytes & temperature • The stability of colloid may be manipulated by adding electrolytes or changing temperature

Electrostatic Forces & DLVO Theory
• DLVO theory – named after four scientists: Derjaguin, Landau, Verwey & Overbeek • When two charged surfaces approach so that double-layers overlap, a repulsive force is induced
• DLVO theory suggests that electrical doublelayer repulsion will stabilize emulsion, when the electrolyte concentration phase is less than a certain value

Electrostatic Forces & DLVO Theory cont.

Increasing interdroplet distance

Electrostatic Forces & DLVO Theory cont.
• DLVO theory – the stability of emulsified droplets with two independent potentials that come into action when two droplets approach each other • For small distance, the sum of the two energies is always negative (i.e. net attractive) – aggregation
• When the sum of two energies is +ve – repulsive force

Surface & Interfacial Tension
• Surface tension (N/m) – force acting over the surface of the liquid per unit length on the surface perpendicular to the force

Surface & Interfacial Tension
• Surface tension (γs) – the amount of energy (ΔE) required to increase the surface area between a liquid & gas (e.g. air & water) by an amount ΔA ΔE = γsΔA • Interfacial tension (γi) – the amount of energy required to increase the interfacial area between two immiscible liquids (e.g. oil & water)

Importance of Large Interfacial Area
For a fixed composition: • Decrease size, increase number of particles • Increase area of interfacial contact

Emulsion
• Is thermodynamically unstable • Must be stabilized using emulsifier • Type of emulsion – (1) w/o; (2) o/w
Oil Water

Water

Oil

Identifying Emulsion
• Dilution test – An emulsion can be diluted using same
Show More

Related Documents: Science: Colloid and Dispersed Droplets Essay

Essay Molecules: Colloids

C13 Colloids This topic focuses on a variety of colloidal systems and stresses their importance in everyday life. Hand cream, salad cream and milk are all emulsions. For example, milk is an emulsion of fat droplets in water. Jelly baby sweets are a gel and muddy river water is a sol. Fog or mist is an example of a colloid called an aerosol. |Syllabus Core |Page |Notes…

Words 1822 - Pages 8

Essay on Chemistry of Food Science

1. Introduction Food chemistry is important in food science because it gives a better understanding of food, it allows to create better food through applying science and technology. It also explains food safety, healthfulness, quality, cost, if it is convenient and the diversity of the products. Food chemisrty involves the application of biochemistry, organic, pchem and analytical chemistry to improve the understanding and manipulation of foods and their components. The importance of food chemistry…

Words 1760 - Pages 8

Sexually Transmitted Diseases Essay

Science For Living Notes (Compiled) Table of Contents Unit 1 Measurement 5-10 Unit 2 Matter 11-48 Unit 3 Basic materials for maintaining life Air 49-54 Water 55-68 Food 69-71 Other biomolecules of life 72-76 Unit 4 Energy in the Community Electricity 77-78 Heat 78-81 Light 82-91 Sound 92 Simple Machines 93-99 Unit 5 The Physical Environment Weather and Climate 100-113 Soils 114-128…

Words 35677 - Pages 143