There is one nanotechnology product that is so pivotal to our lifestyles, to a level that the human civilization as we know it wouldn’t exist without it. Strangely enough, anyone would use it not once, twice but number of times during the day yet many wouldn’t know the mechanism behind it. It is also a great example how nanotechnology products can strongly influence our lifestyles and our civilizations as a whole. Also, it shows the benefits such a product can bring to people and its contribution towards the wellbeing of each of them. So what is this strange product that hides in the plain sight? Well it’s the humble soap or in more general terms, detergents.
Cleaning dirty stuff
We use detergents to clean ourselves, our cloths and the places we live in. From simple bar of soap to the shampoo we use to wash our hair with, there are range of unique detergent products fine-tuned for specific applications. All these products are ultimately converge towards single function; cleaning. Whether it be your dirty carpet or daily share of dirt and grime in your skin and hair, detergents are usually up to the job.
But what about water. Isn’t water a great washing liquid? We know that many things dissolve in water and others like soil, dust and mud are easily dispersed and removed by water. So it should work as a great cleaning liquid. Well, it turns out that some of the dirt and grime we get in our stuff are actually not water soluble at all. These, so called lipophilic substances, binds in to dirt and dust which make it harder for water to wash off the stuff that otherwise readily washable. These lipophilic (likes oil) substances are everywhere, in the air, on the ground and we even secrete some of these oils ourselves. For an example, our body oils are lipophilic. Hence despite how harder we wash our skin with just water, there will always be a tiny layer of oil attached to our skin. This oil layer will eventually attract more oily substances from the environment, dust, dirt and grime over the course of day. Then comes the bacteria, they will feed on the lipophilic substances and rich with nutrients and cause numerous problems like acne. This is the reason why oily skinned people have more acne problems than other skin types. Now this is just the face. Now think about the other places of the body, our cloths, plates we eat on, spoons we use, floors we walk on, cars we drive and for that matter everything we touch. If we just have water to clean all these things, grime will continuously accumulate and trigger a bacterial outbreak. But nothing to worry, we have detergents to make stuff clean.
The soap update
Detergents are a class of special molecules, that contain both nonpolar (lipophilic) and a polar (hydrophilic or likes water) groups in the same molecule. Structurally, a simple detergent molecule would look like a lollipop with a long stick. The head of the lollipop; the candy is much like the polar group while the plastic stick would resemble the nonpolar group which is typically a long chain hydrocarbon. Sodium stearate, most common compound in the normal laundry soap or laundry detergent is about 2.8 nanometers. Some more complex detergents such as polyethylene ethoxylates, used in biomedical applications can go up to 30 nm in length.
However, it’s not on the nanoscale length of these molecules that the cleaning action of the soaps and detergents resides. These polar and nonpolar groups in a detergent solution would self-assemble in such a way that similar species get close to each other. If we take sodium stearate, in an aqueous solution the long fatty chains of the sodium stearate get close to each other and make a hydrophobic core while the polar acid group orient themselves towards the water medium. This special self-assembled structure is called soap micelle. It’s this formation that give rise to amazing cleaning ability of these molecules. The size of these micelles may depend on many factors and can range from few tens of nanometers up to some micrometers.
When used as a cleaning agent, nonpolar, fatty hydrocarbon groups sinks in to any oily particles in the dirty surface leaving hydrophilic polar group out. This gives the fatty grime a surface charge (polarity) that increases the solubility. Due to this increased solubility detergent molecules would break away small pieces of lipophilic bodies from the dirty surface. Once in the solution, more and more fatty hydrocarbon groups of the detergent molecules will sink in to the fatty body leaving more polar charges on the surface. Ultimately, the fatty grime substances on the dirty surface that had no charge at the beginning now carries a surface charge that make it dispersible in water. The hydrophobic core of the self-assembled soap micelle provides a perfect stage for lipophilic oily substances to dissolve. As lipophilic grime get slowly solubilized, its grip on other dirt slowly diminishes. This releases more and more dirt that was previously kept together by the oily substances.
Although, soap and detergents are not classified as nanotech materials, their cleaning function occur at a nanoscale dimensions. The sizes of both detergent molecules and micelles are also at nanoscale. For most of us, nanotechnology is still a futuristic technology that needs to prove its worth in the years to come. But most of us tend to forget nanotech materials that we use almost every day and that has become integral parts of our everyday life.