Chemistry, in general, is all about putting substances together and observing the results. It would be surprising for many of you to realize that you can access the most basic real-life chemistry lab, anytime you want, in your own home. Yes, you guessed it right – It’s your kitchen. Mixing is the most common technique for ingredients to join up. Most of the cuisines we enjoy are prepared by mixing ingredients. However, some ingredients are generally immiscible. We are all familiar with the immiscibility of oil and water. Yet within our home are numerous examples of products in which oil and water do mix. To name a few, they are mayonnaise, milk, salad dressings, hand lotion, and hair conditioners. These examples represent a distinctive class of mixture known as an emulsion. Basically, an emulsion is a mixture of two or more liquids that are commonly immiscible. In a more general sense, the particles of one liquid (the dispersed phase) are suspended throughout another liquid (the continuous phase) to make an emulsion. Although, this state does not last more than a few minutes on its own. This problem is addressed by a process called emulsification, in which emulsifiers are added to the mixture. Simple emulsions are either oil suspended in an aqueous phase (o/w) or water suspended in oil (w/o). Let’s understand the chemistry of emulsion with the following examples.
1. Homogenized Milk
For thousands of years, milk has been a part of the human diet. Most of us think of milk as a simple healthy drink, but the chemistry of milk is not as simple as it seems. Milk is an emulsion with fat particles (globules) dispersed in an aqueous (watery) environment. The fat globules do not coalesce and form a separate layer because they are protected by a membrane layer that keeps the fat particles separate from the water phase. It is an example of an o/w emulsion. You might have noticed labels on the dairy cases that milk is homogenized. When milk is left on its own, the naturally occurring milkfat particles rise to the surface to produce a layer of cream. Milk homogenization is a simple process that combines and disperses milkfat by using a high-pressure process. This breaks up fat particles and makes them small enough to disperse through the milk evenly. Milk is homogenized, not for taste, but to give milk its rich, white color and smooth texture that we are used to. This process prevents the cream from rising to the top and saves you the step of mixing the cream back into the milk yourself before drinking it. The homogenization process does not affect how your milk tastes or what’s in it.
A rather common objection people have when it comes to eating a healthy diet is that healthy food does not taste good. Well, it is completely natural as our tongue is generally sensitive to salty, sour, bitter, and sweet substances. When you eat factory-made foods, you’re eating a lot of salt, sugar, artificial flavors, and sweeteners. And therefore, cakes seem tastier than vegetable salad. But even vegetable salad can become tasty if we add few spoons of mayonnaise to it. Many of us take mayonnaise for granted. Typically, the big jar sits on a shelf in the refrigerator door, ready when we need to fix a sandwich or whip up potato salad. But have you ever paused to consider how it is made? Basically, mayonnaise is an emulsion of oil droplets suspended in a base composed of egg yolk, lemon juice, or vinegar, which provides both flavor and stabilizing particles and carbohydrates. Commercial egg-free alternatives are made for vegans and those who avoid chicken eggs or dietary cholesterol, as well as people with egg allergies. It also forms the base for many other sauces, such as tartar sauce, remoulade, salsa golf, and rouille.
For many of us, coffee is essential. It allows us to function in the morning and gives a much-needed boost during the day. The popularity of coffee around the world has provided it with several fancy named variants. One of them is “Espresso coffee.” Many of us might have learned this word because of the specific machine required to make it. But, there is more to it than what meets the eye. Coffee beans contain lots of water-soluble compounds that provide flavor and aroma, but they also contain oils. And since oils and water do not blend, the espresso machine provides the required pressure to mix the oils with the water. Therefore, an espresso is nothing more than an emulsion (a liquid composite made up of laminated oils). Everything from fats, sugars, natural oils, compounds like melanoidin, and caffeine, are extracted and form the makeup of the espresso. Often, these minerals and oils exist in abundance in fresh coffee and help form a layer of cream on an espresso. Simply put, the crema is what we call the soft, dark tan foam layer found on the surface of an espresso shot. The cream itself does not technically affect the flavor of the espresso, but coffee experts usually believe that the cream is a strong indicator of what the quality of the rest of the espresso would be like.
If you are a health-conscious person or maybe trying to be one, you might have heard that salad is the best way to shed some weight. But seldom, the idea of eating raw veggies is enough to drain out all the motivation. Therefore, sometimes, it is necessary to dress the food to make it look enticing. There may be no better way to dress your salad than with a healthy vinaigrette. If you’ve ever tried making salad dressing from scratch, you know that one of the biggest problems is getting the oil and vinegar to blend properly. No matter how hard you try to shake, stir, or whisk oil and vinegar together, they will inevitably split. Homemade vinaigrettes are technically called temporary emulsions because nothing is holding the oil and water droplets together on a chemical level and they eventually separate back out again. Commercial salad dressings are usually made with a lot of additives and emulsifying agents that keep the vinaigrette from separating. Some of them are natural, like lecithin (found in egg yolks).
Butter is one of the many dairy products that we use in our daily life. Have you ever wondered how butter is made? How does that creamy spread come from something as liquid as milk? The science of butter starts with the primary ingredient — milk. Milk is 88 percent water, 3.5 percent fat, 3.25 percent protein, and 4.6 percent lactose (sugar). After a cow is milked, we typically do two important things to refine it and make it safe for drinking. Pasteurization treats milk to destroy any harmful microbes. And milk is homogenized to prevent the fat from rising to the top of the milk. Making butter may sound easy, but it’s not quite as simple as it seems. Changing whole milk to butter is a process of transforming a fat-in-water emulsion (milk) to a water-in-fat emulsion (butter). The cream separated from milk after pasteurization is an emulsion in which fat molecules are dispersed in the main component, water. Whipping up cream, however, shakes the system enough to invert the emulsion. Fat molecules become the continuous phase with particles of water dispersed within. As a result, we get butter and buttermilk that can be separated via physical processes.
Over time, the science on the issue of dietary fat and heart disease has undergone drastic changes. In the mid-19th Century, European demographics were changing as more people moved to cities. Butter became hard to acquire because of industrialization and a recession. Imports were unable to fulfill demand, particularly military need. In the food industry, these issues have given rise to another safe alternative, margarine. It is used as a spread for flavoring, baking, and cooking. Basically, margarine is a food product made usually from vegetable oils churned with ripened skim milk to a smooth emulsion and used like butter. The basic method of making margarine today consists of emulsifying a blend of hydrogenated vegetable oils with skimmed milk, chilling the mixture to solidify it. The resulting blend is then mixed with water, citric acid, carotenoids, vitamins, and milk powder. Emulsifiers such as lecithin help disperse the water phase evenly throughout the oil, and salt and preservatives are also commonly added. This oil and water emulsion is then heated, blended, and cooled.
7. Cold Cream
Many of us have grown up watching our mother and grandmother applying cold cream before going to bed and boasting about the benefits it has on our skin. If you belong to a non-tropical region, you must be familiar with the harsh conditions skin faces during the winters. Cold creams are a must-have during the winter months. Cold cream is an emulsion of water and certain fats, usually including beeswax and various scent agents, designed to smooth skin and remove makeup. The name “cold cream” derives from the cooling feeling that the cream leaves on the skin. Cold cream generally consists of four main ingredients including water, oil, an emulsifier, and a thickening agent, with the amount of water and oil being in approximately equal proportions. This allows the cream to penetrate the outer layer of the skin. However, it cannot be absorbed as deeply into your skin as water-based products. Because of the high concentrations of mineral oils and waxes, such as beeswax or ceresin, the cream tends to sit on your face more like a facemask than a face moisturizer.
8. Emulsion Paints
Color is more than a visual experience. It is also a psychological one that can radically affect mood and emotion. Therefore, people invest a great deal of time while deciding the paint for their room. You might think that paint is just a color chemical dissolved in a liquid to make it spread, but it’s a bit more than that. While paints designed for various purposes will have different formulations, they all have certain main characteristics in common. Most paints have three main components called the pigment, binder, and solvent. The binder and solvent are sometimes collectively called the vehicle. Emulsion paint consists of tiny polymer particles within which the pigments are trapped. They are made of small droplets of liquid polymer binder spread out instead of dissolving in water. The polymer is made by the addition polymerization of alkene monomers such as ethenyl ethanoate, methyl 2-methyl propanoate, and 2-Ethylhexyl acrylate. This emulsion can be spread easily. After an emulsion paint is applied, the water evaporates, and the closely packed polymer particles fuse together to form a continuous film. The use of water rather than an organic liquid means that emulsion paints produce fewer VOC (volatile organic compounds) when they are used.
For more than a century, emulsions have been used as drug carriers. They are used in the pharmaceutical industry to make medications more palatable, to improve potency by regulating the dosage of active ingredients, and to include topical products such as ointments with improved aesthetics. Today, several types of emulsions exist and are used for a variety of applications from solubilizing drugs to controlled release. Emulsions can be delivered by oral, topical, and parenteral routes. O/W emulsions can effectively increase the oral absorption and bioavailability of poorly water-soluble drugs when delivered through the oral route. Nonionic emulsions are most popular due to their low toxicity, ability to be injected directly into the body, and compatibility with many drug ingredients. Cationic emulsions are also used in certain products due to their antimicrobial properties.
Emulsion comes in handy when firefighters are dealing with small scale fires involving medium or low fuel leakage. They use a specially designed high-pressure spray nozzle to achieve emulsion during the process. These nozzles spray an aqueous surfactant solution that can reach the surface of burning oil, penetrating the flame zone. This results in the formation of the noncombustible emulsion layer of oil-water on the surface of the burning oil. This emulsification along with the cooing smothering effects extinguishes the fire. However, emulsifiers are not effective at extinguishing large fires involving bulk/deep liquid fuels, because the amount of emulsifier agent needed for extinguishment is a function of the volume of the fuel.