Energetics of Phase Change

To understand the thermodynamics of nucleation, let us first consider homogeneous nucleation, also called sporadic nucleation, from an isothermal, quiescent melt whose temperature T is kept below the melting point T . Here, homogeneous refers to the appearance of the new solid phase in the middle 

If we set the derivative of AG with respect to r equal to zero, then using Eq. (11.2.1) we find that r, the value of r corresponding to AG, is 

Because the magnitude of AG increases as the temperature is lowered, both r and AG decrease with decreasing temperature. This variation can be made expUcit by noting that, at the melting point, 

Example 11.1 For a polyolefin it is found that AH = —3 x 10 ergs/cm and y = 90 ergs/cm. If the equilibriiun melting point is 145°C, how do the radius r of a critical-sized nucleus and the associated energy change AG depend on the extent of subcooling, AT  

Although the treatment of the previous section can be extended to nonspherical nuclei, we find that this is not needed in practice because the contribution of 

---