Confined Active Matter Aggregation and Segregation of Confined Active Particles

When a gas of particles is placed in a confined environment such as a room or box, the particles can bounce off the wall creating a pressure. In fact, the system can readily be very well described by the ideal gas law PV = nRT, where P is the pressure, V is the volume, and T is the temperature. This means that if one increases the temperature while holding the volume fixed, the pressure will increase due to the increased energy the particles have when they strike the walls and the increased rate at which the particles strike the walls. Additionally, if the volume is fixed, the shape of the container has no effect on the pressure. One picture of an ideal gas is randomly walking particles that explore all space in the container with equal probability. As the temperature increases, the particles diffuse faster. Since the diffusion constant obeys the Einstein relation D = kbT, the faster the particles can diffuse, the higher the pressure. Additionally, if one places all particles in one corner of the container as an initial state, the particles rapidly diffuse throughout the whole system, filling it evenly. If a second species of gas particles is added to the system then the pressure again should increase and the two gas species will become evenly mixed.