Makeup is no longer just for girly girls and rockstars. In the near future, it may also become a requirement for the men and women who protect our country.
Synthetic polymers have long been a part of cosmetic formulations. Traditionally, they are added into formulas to increase the stability of emulsions, preventing heavy creams and lotions from separating into distinctive oil and water phases. Polymers are also added to enhance desirable tactile properties. For example, silicones are often added to increase silkiness; polymeric acrylates are added to increase thickness. However, more recently, synthetic polymers are being added to certain formulations to protect the skin from extreme temperatures... such as those created by explosions.
Building Blocks
Chemically, polymers are defined as large molecules of repeating structural units. Each of the structural subunits is covalently bonded to a single backbone. Along these lines, an individual polymer may be constructed of a single repeating unit or a combination of several. These are known as homopolymers and copolymers, respectively. A set of Christmas lights can be used as an analogy: A set of all white lights can be descriptive of a homopolymer and a set of multicolored lights representative of a copolymer. The physical properties of the macromolecule are largely dependant upon the structure of the repeating unit, though, generally, the melting and boiling points increase with the length of polymerization.
The synthesis of polymers occurs in three steps: chain initiation, propagation, and, finally, termination. The initiation step generally makes use of a catalyst, typically a peroxide. During propagation, the length of the polymer grows to the desired length. In this step, the monomeric subunits bind to one another either via free radical addition or by electron transfer. This step-wise growth can be visualized as the beading of a necklace, one pearl at a time. The termination step occurs when the supply of subunits is exhausted, or when the reactive ends of two chains combine.
War Paint
Soldiers are not unfamiliar with wearing makeup. It is common for soldiers to coat their faces with paints in varying shades of green and brown to camouflage themselves during battle. Usually these paints are basic oil-in-water emulsions, non-toxic, and hypoallergenic. However, these formulations do not fare well with heat. With high temperature, the oily layer that is deposited on the skin may melt away or ignite, burning the skin.
Polymer scientists at the University of Southern Mississippi may have created a solution to this problem. At this year's American Chemical Society (ACS) conference, researchers from Robert Lochhead's group presented a silicone polymer that can potentially protect the skin from extreme temperatures for up to 30 seconds after a thermal blast.
To many, 30 seconds of heat protection may sound trivial. However, a typical blast lasts mere seconds. In the seconds following the blast, the skin can be exposed to temperatures greater than 600C. The third-degree burns that result are often life-threatening; any means to mitigate this possibility is welcomed. Moreover, scientists reported that their formula prevents the skin from reaching 60C, the temperature at which skin burns.
Formulae such as these likely take advantage of the fact that silicones do not absorb heat as rapidly as oils. For example, dimethicone, a basic silicone polymer that is used in most cosmetic preparations, has a flashpoint of greater than 200C, as opposed to that of mineral oil, which is 168C. Remember, the melting point of polymers often increases as the size of the macromolecule increases. This means that depending upon the degree of polymerization, Lochhead's polymer likely has a flashpoint that far exceeds that of dimethicone. Mineral oil is not a polymer, and, therefore, its physical properties cannot be altered.
Like other camouflage paints, Lochhead's silicone-based formula comes in a variety of colors. In addition, according to military mandate, it also contains a hydrogel-encapsulated DEET preparation to repel insects.