Colloids and surfaces

Colloids and surfaces are both types of dispersed systems. Colloids are systems that typically don’t mix well with each other because they have particles suspended in a medium, where two different immiscible liquids form a suspension. Surfaces are systems that usually contain adsorbed molecules, which are molecules that have an attractive force to the surface of the system in question.

Colloids:

Colloids are mixtures of liquids that don’t dissolve in each other. Colloids are solutions with a continuous liquid phase and solid or liquid particles dispersed within.

Suspension:

Suspension is a colloid that has two different phases, usually water and oil (in our everyday life we usually encounter food such as chocolate pudding, salad dressing, coffee creamers, mayonnaise etc.).

Sedimentation:

Sedimentation is when a colloidal system that is not moving or being stirred, disperses along a line into two separate layers due to gravity (sedimentation is different from sedimentation equilibrium). The top layer will be the stuff that was lighter and the bottom layer will be heavier. This process is done in filtration/separation processes.

Colloidal solution:

A colloidal solution is when solid (usually tiny) particles are dispersed in the liquid of which they are dissolved. The particles do not dissolve into the solvent in which they dissolve. The particles must be big enough to be visible to the human eye.

Examples of Colloids:

Examples of Colloids include chocolate pudding, salad dressing, coffee creamer and mayonnaise. These are all immiscible liquids (not miscible).

Surface:

A surface is a system that has adsorbed molecules on its surface. They are usually weakly bonded to the surface of the system in question. A gas phase and a solid phase may have a surface between them (e.g. the boundary layer on water). There are two main types of surfaces, hydrophobic (oil-hating) and hydrophilic (water-loving). Hydrophobic surfaces work by using van der Waals forces to repel water while hydrophilic surfaces use hydrogen bonding to attract water. Examples include Teflon, building windows and paper.

Difference between Colloids and Surface:

One of the most widely known differences between colloid and surface is that a surface is usually in contact with a solid, while a colloid is not. Another difference is that colloids are liquids while surfaces are solids. A third major difference is that particles of colloids usually have no fixed shape whereas the particles of surfaces always have fixed shapes.

Applications of both Colloids and Surface are:

1) Sediments in water filters

2) Foam for shaving

3) Chocolate Pudding

4) Colourful Dye for Dye-Sensitised Solar Cells

5) Artificial blood and artificial organs

6) Keeping food fresh, because the food is coated with a layer of fat (mostly used to keep butter fresh)

7) Keep paint wet and flowing. This is used to create glossy or dry finishes on cars, walls, and floors.     

8) Soft contact lenses

9) Some pharmaceutical drugs that are taken orally or injected may exist in colloidal form.

Significance of Colloids and Surface:

The significance of Colloids and Surface is that it helps in various processes such as filtration, suspension stabilisation, emulsions, protection from corrosion and drug delivery.

In general: the smaller the particles that make up a colloid or surface (called the “diameter” in physics), the more stable they are. Other factors include gravity and density. Normally gravity is negligible for colloids and surfaces, but for systems like foams (suspensions of air bubbles in a liquid), gravity is a major factor. The density of colloids and surfaces is usually low, because most molecules are not touching other molecules (this also depends on what molecules are involved). Gravity and diffusion of particles in a colloid or surface often makes the particles settle, or spread/mix after some period of time (depending on the system’s velocity). A small interaction can even cause particles to disappear completely from a system. This process is called self-gravity (colloids and surfaces use this to move from one region of the container to another). As a result, colloids and surfaces look very different from each other. Colloid systems are typically non-Newtonian, meaning that their properties change viscosity as concentration changes, but their density does not change after some period of time.

Advantages of Colloids and Surface:

1) Both colloids and surfaces provide protection from corrosion and staining.

2) Colloids and surfaces are used to keep paint wet and flowing.

3) Colloids can also be used as an artificial blood, an artificial heart valve, a replacement for red blood cells, clots that block arteries, artificial joints and cartilage, lumbar support, skin burn treatments and cosmetics. Surfaces are used to pack electronic equipment with liquid cooling systems that don’t include moving parts like fans or pumps. Surfaces can also be used in solar energy (Dye-Sensitised Solar Cells), air conditioning and dehumidifier equipment.

4) Food is often coated with a layer of fat (mostly used to keep butter fresh).

5) A foam is an emulsion of fine bubbles that are used to make shaving easier, reduce skin irritation and give the surface a protective coating.

6) Colloids are often the constituents of cosmetics 

7) Colloids in cosmetics are used as foaming agents that help make creams, lotions and foundations remain in place longer. The colloids also help keep the complexion looking fresh after application.

8 ) Surfaces can be used in some pharmaceutical drugs that are taken orally or injected may exist in colloidal form.

Conclusion:

After reading the article above, you may conclude that the difference between surface and colloids is that surface is a system that has adsorbed molecules on its surface and colloids do not have fixed shape as well as particles of colloids do not have fixed shape.

A surface has no interactions. They are usually weakly bonded to the surfaces of the system in question. A gas phase and a solid phase may have a surface between them (e.g., the boundary layer on water). The particles of a surface are the constituent elements of a surface and they have fixed shape whereas particles of colloids do not have fixed shape.