The nano-revolution is in full swing across a broad range of industries, and the personal care industry is benefiting from the immense amount of progress in this area. Some recent hairstyling innovation using nanotechnology and microtechnology are reviewed in this article. These developments range from the lotus effect for frizz control and the development of liquid silk hair fixatives, to micro-segregating tough copolymers and supramolecular structures built from a scaffolding of soluble polymers that are joined together by tiny particles. The personal care industry has revolutionized sunscreens with nanoparticles, and the industry sector is moving apace with developments in this exciting emerging field.
Hydrophobicity for Hair Frizz
A major trend in hairstyling is the control of frizzy hair.1 Hair becomes frizzy when it is exposed to high humidity, and previous technologies for controlling frizz were based upon coating the hair with silicones. Recent products aim to control frizz for an extended period of time without adversely affecting other properties such as appearance, feel, volume, shine and softness.
Avon has approached this challenge by hydrophobically coating the hair with a composite that includes a hydrophobically surface-modified aluminum oxide (ranging from nanometer to micron size), a silicone acrylate film-former and a silicone fluid. In this producta the Avon researchers invoke the “lotus effect,”2 coined from the observation that water droplets ball up on the leaf surface of the lotus flower (Nelumbo). The small particles in the coating impart a surface roughness to the coating , and this enhances its hydrophobicity. The droplets roll off the leaves, taking with them any dirt that may have been deposited and conferring the property of self-cleaning on the leaf surfaces. Water droplets in air are round due to the high cohesion of the water molecules, which is manifested in a high surface tension. When placed on a surface, the forces of cohesion within the water compete with the forces of adhesion to the surface. If the adhesional forces are stronger than the liquid’s cohesion, then the liquid will spontaneously wet the surface and spread. However, if cohesion prevails, droplets will be formed on the surface, and if the contact angle of a water drop is greater than 90 degrees, the surface is characterized as being hydrophobic. Roughening of a hydrophobic surface will enhance the contact angle and the surface will appear to be more hydrophobic than its smooth analogue. Superhydrophobicity results when the surface possesses arrays of nanosize protrusions, as shown in Figure 1.3–5