Did you ever ponder how paints get their color? Yes, the aesthetic paint you apply to your walls! Or how they stick to the surfaces of walls, fences, furniture, etc? And want kind of solution is the ballpoint pen ink that you use? If not, then it is time to explore! Paint is any colored liquid applied to a surface. There are many types of paints like pictorial, water paint, etc. Another question you may have is why am I talking about paint on my chemistry blog? Well, this is because some paints (or some pigments used in these paints) are colloidal suspensions. So, is paint a colloid? Yes, paint identifies as a colloid. Once water pours into it, it becomes more like a solution and acts like one. They fall under the mixture of solution and gel. There are no definite boundaries between the substance and the surrounding media. As a consequence, these substances are called paints or dyes. When the paint stirs slowly, tiny pigment particles become suspended and spread evenly all over the liquid. This uniform dispersion of pigments is called a colloid. These pigment particles are responsible for the effects like opacity, color, and optical illusions. Let us dive more into the colloidal properties of paints.
Colloids. What are they?
A colloid is an autonomous material that is capable of being dispersed or entrapped via chemical processes. For example, stains, varnishes, grease, ink, and dirt/dirt deposits, etc. In simpler terms, colloids are materials that contain two or more atoms glued to each other in different ways. When solidified, their properties change dramatically and provide new capabilities for materials science and engineering. This phenomenon is so spellbinding that it is given credit for. It even imparts the blue color to the seawater and the magnificent skies.
Discovery
During the early 19th century, Robert Brown, a British botanist unearthed the discovery of random motion of solution particles with the help of a microscope, later named the Brownian motion. Other chemists like Richard Zsigmondy and H.E. Svedberg followed the path and researched sub microscopic particles in their colloidal state and won Nobel Prize for their efforts. In addition, the name ‘colloid’ is derived from two Greek words, ‘kolla’ and ‘eidos’ meaning, ‘glue’ and ‘like’. It was coined by Thomas Graham in 1861 during his experiments of classifying mixtures of starch in water and gelatin.
Types of Colloid
There are two types of colloids: lyophilic and lyophobic. The Greek word ‘Lyo’ means liquid.
- Lyophilic (‘philic’ stands for attraction): These colloids attract the solvent and swiftly transform into the dispersed state. In this state, particles form a strong bond with their dispersion medium. Examples are Starch, gelatin, gum, etc.
- Lyophobic (“phobic’ stands for fear): These colloids are solvent repelling and are tough to disperse into the dispersion medium. They dissolve with the help of special techniques that often leave them unstable. Examples are Gold, Silver, Sulphur in water, etc. The blend of these two types results in the generation of association colloids. Moreover, they can be classified as multimolecular and macromolecular colloids; depending upon the set of molecules in their lyophobic state.
Features of Colloid
Colloids can have electrical, chemical, or miscellaneous properties (e.g., asbestos). In some applications, colloids have proven beneficial due to their ability to transport or hold water (e.g., sand). It is an inorganic substance that acts as an emulsifier and allows certain chemicals (such as water) to pass through it. Some colloids become less unstable as they dry, becoming ideal ingredients for textiles and pharmaceuticals, while others remain highly volatile and react with other surrounding constituents.
- They are not well defined as they do not fall under the category of either liquids or solids in chemistry. In general, a colloid consists of microscopic particles suspended in a liquid(solvent).
- They are heterogeneous mixtures that contain particles of size from 1- 1000 nm(nanometre).
- These mixtures contain large molecules or inert granular materials (aggregates such as sand, cement, concrete, etc.)
- The size of the colloidal molecules holds a middle ground between the size of molecules of a true solution and suspension.
- They can also produce Tyndall Effect; the dissolved particles being larger can scatter penetrating light beams. For instance, during fog or smoke, these beams are evident to the naked eye. It is due to the suspension of these particles in the air. Even the searchlight beams that you see at many concerts.
- Every colloid consists of two phases: dispersed(particles)and dispersion medium (solution in which the particles dissolve)
- There are multiple classes of colloids: Sol and gel, liquid and solid emulsion, liquid and solid aerosol, foam. All these solutions have contrasting combinations of solvent and solute.
- Colloids possess filterability with the aid of ultrafilters. No residue is left behind.
What makes a substance a colloid and separates it from other kinds of mixtures?
The characteristic that separates colloids from other kinds of mixtures is the size of the molecules in those mixtures (either 20 nm or 100 nm). They have a minute structure and can only visible with the aid of a microscope. They exhibit the remarkable property that yields their appearance as homogeneous solutions. For instance, paint made with asphalt would be a suspension, while a mixture of titanium dioxide, carbon black, and linseed oil would be a dispersion. In another example, the pigment particles in some oil paints are so small that they remain scattered in the binder owing to the Brownian motion, creating an emulsion. While other substances exhibit both dispersing and suspending actions when added to paint, the wet paint mixture refuses to mix and does not settle over time. In dry paint, the dispersed particles also indefinitely spread throughout the binder. Therefore, making both of these liquids, a colloid.
Fascinating facts
- Colloids are materials which when mixed with another material, create a more solid mass. Usually, these materials are present in addition to paint. Therefore, while determining if the paint is a colloid, focus on the usage and its applications.
- Paints are of different kinds involving conventional paint, latex, or acrylic, and even paint with a primer built-in. All contain base colors mixed with various additives to increase durability, gloss, and other properties.
- Another distinguishing fact is that paint as a Colloid is the opposite of it as a Fluid. In the fluid state, the amount of solid matter can be transformed into Solid State, Liquid State, etc., But colloidal disposition leaves no chance to change the number of particles present in it.
Application of Colloids and Paints
Paints as colloidal emulsions are used to coat the surface of motor cars, wooden furniture, and other crafts to highlight the glossy look and the colors. This also enhances surface protection. Furthermore, colloids have a wide range of applications in the industrial sector. The manufacturing of paints and inks gels, lubricants, eye lotions (Argyrol), and even toothpaste utilize colloids as the thickening agents. They are also used in the mass production of medicines (ex. Albumin, etc.) to increase the agility of the body.
Conclusion
Out of true solution, suspensions and colloids, paints are purely colloids. The pigment present in paints does not fully immerse in the solvent. These minute solid particles remain intact upon standing and do not segregate like suspension particles. During manufacturing, producers grind the pigments to a size that is small enough to be suspended in the binder.
