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Tham khảo tài liệu 'thermodynamics systems in equilibrium and non equilibrium part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 290 Thermodynamics - Systems in Equilibrium and Non-Equilibrium so that TASdf kT N In N - n In n - N - n In N-n 18 and AGDF n nAHDF - kT N ln N - n ln n - N - n ln N-n 19 where AGDF n represents the free energy cost of forming n defects in the system. This formulism allows a plot of free energy against n N the defect ratio as shown in Figure 3. Three plots Figures 3A-C are shown for three different defect formation energies typical of what might be expected for a BCP system e.g. Hammond Hammond et al. 2008 has measured the defect formation energy in a PS-W2VP system at around 30 kJ mol-1. Although these are simple calculations they illustrate the salient features of equilibrium defect formation. At low defect concentrations defect formation is entropy driven until a critical concentration of defects allows the activation energy term to compensate for entropy. There is usually an equilibrium defect density indicated at the minimum free energy. As might be expected as the activation energy for defect formation increases this equilibrium defect density. At high activation energy values e.g. around 30 kJ mol 1 and low temperature 300 K there is no thermodynamic driving force for defect formation and the data suggests that in BCP systems it should be possible to form highly regular structures. 3.2 Non-equilibrium defects Practically there are few examples of defect free microphase separation of BCP thin film systems even in cases where the number of equilibrium defects is vanishingly small. As these films are normally prepared by non-equilibrium methods such as spin- or dip-coating the microphase separated structure evolves by either thermal or solvent annealing and defects are introduced nucleation of microphase separated regions or removed by growth kinetics. Through the annealing cycle phase separated regions will nucleate in various places grow and increase in order Segalman et al. 2003 . This growth will produce the classical structural motif of a polycrystalline .
