Copyright

Preparation & Purification of Lyophilic Colloids

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

Lyophilic colloids are colloids where the particles have a strong affinity with the liquid. In this lesson we will learn about lyophilic colloids and how they are prepared and purified.

Lyophilic Colloids Properties

After you wake up in the morning, you decide to have toast and jelly for breakfast. You pack your lunch, adding a pudding cup into your lunch bag. As you are rushing out the door, you grab a piece of gum to freshen your breath. You have already used several lyophilic colloids - jelly, pudding, and gum.

A colloid is a mixture where large molecules (1 - 1000 nm) are suspended in another compound. In colloids the suspended material is held well enough that it can't be separated using typical filtering (making it different from a suspension).

We call the suspended molecules large, but they are still too small for us to see with our eyes; they are just larger in comparison to other molecules.

Pudding is a lyophilic colloid
Pudding

A lyophilic colloid refers to the nature of the suspended molecules, in that they are liquid loving. Often the liquid used is water, so they may also be referred to as hydrophilic (water-loving).

The colloidal particles and the liquid have such a strong attraction to each other that we end up with a very stable mixture. This stability makes it difficult to coagulate lyophilic colloids. They can be coagulated by adding a large quantity of electrolytes that will disrupt the charge holding the lyophilic colloids in the liquid.

Colloids often look fairly solid, as though they aren't really moving. But particles are always moving, particularly when they are in the liquid state. Since lyophilic colloids are in a liquid dispersion medium, the liquid molecules are moving quite a bit.

The colloidal particles are getting bumped on every side as the liquid molecules bump into them. This causes the colloidal particles to move in a zig-zag direction, a movement referred to as Brownian movement.

Lyophilic Colloid Preparation

Since lyophilic colloidal particles have such a strong affinity with the liquid, lyophilic colloids are fairly simple to prepare. In most instances we can simply mix the particles with the solvent to form the colloid. Sometimes the particles will form a colloid better in the presence of cold or heat.

Let's look at some common colloids, such as the pudding cup that you put into your lunch. The starch used is probably a modified corn or potato starch, and this is the lyophilic colloidal particle. For traditional pudding, the starch will swell and absorb water as it is heated. As it increases in size it is held in suspension by the surrounding water (or milk), thus a colloid is formed.

But when you make pudding from a box you don't need to heat it up - so how does the colloid form? In other words, how does the little starch, sugar, and other particles in the box stay suspended in the milk? Why don't they simply fall out of solution after you stop stirring?

These puddings use a pre-gelatinized starch. These starches are prepared by pre-cooking the starches and then drying them. Thus once they are rehydrated (mixed with water) they go back to the cooked state and can be held in the milk as a colloid.

Lyophilic Colloid Purifications

There are several methods to purifying colloids including:

  • Ultra-filtration
  • Dialysis
  • Ultracentrifugation

Ultra-Filtration

Colloidal particles are larger than many other particles. Ultra-filtration uses the force of gravity (or sometimes shaking) so that particles that aren't held in suspension filter out of tiny holes. These holes are too small for the colloidal particles to fit through, so they remain behind.

Dialysis

Instead of using gravity, dialysis uses osmosis to pull out particles. Osmosis is when solutes will move from high concentration to low concentration.

To unlock this lesson you must be a Study.com Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account
Support