When water beads up on a leaf or detergent works to remove a stain we are witnessing macroscopic phenomena that depend on the hydrophobic effect. The basic principle of this effect is the strong hydrogen bonding of water. When a solute is introduced into water that does not provide an opportunity for hydrogen bonding, the water molecules tend to rotate so as to maximize hydrogen bonding with other waters. That is to say, the water molecules rotate away from the solute. The collective tendency of water to rotate in one direction (away from the solute) creates an unfavorable entropy surrounding that solute molecule. The entropy can be minimized by decreasing the surface area of the solute. This means that the solute molecules tend to aggregate, to form a droplet or if they are longer they may form a structure; a micelle, a bilayer or a complex shape that minimizes the surface area.
