Chemical potential and Gibbs free energy
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Covalent linkage
10–2
s
m
Controlled phase separation
Block-copolymer
C6H13
Change in Absorption
variety of scientific fields; contemporary research is commonly exposed in sessions segregated by discipline. Physical chemists can also publish more perspective or tutorial articles on applying spectroscopy to materials systems. Developing new functional materials is becoming increasingly important. The fusion of materials synthesis, fabrication, and characterization with time-resolved optical spectroscopy would be a huge step toward advancing the technologies of our everyday world.
s
10–3 10–4
s N
C8H17 C8H17
s
10–5
N
s m
C8H17 C8H17
10–9
s N
s
N
n
Extensive phase separation
Lower charge density 10–12
Nanoscopic polymer domains
n
Polymer mixture
C6H13
Charge recombination
s
10–6
Large polymer domains
Time (s) +
h
–
e
References
1. C. Grieco, M.P. Aplan, A. Rimshaw, Y. Lee, T.P. Le, W. Zhang, Q. Wang, S.T. Milner, E.D. Gomez, J.B. Asbury, J. Phys. Chem. C 120 (13), 6978 (2016). 2. M.K. Petti, J.P. Lomont, M. Maj, M.T. Zanni, J. Phys. Chem. B 122 (6), 1771 (2018).
Figure 2. Transient absorption kinetic decays of charge carriers that form in polymer films upon light absorption. Charge recombination is tracked over time, revealing a lower charge density for the polymer mixture at later times. The cartoons illustrate phase separation of the polymer domains that occurs in the films.
Chemical potential and Gibbs free energy By Long-Qing Chen
C
hemical potential is a thermodynamics concept familiar to many, not only in materials science but also in physics, chemistry, chemical engineering, and biology. It is a central concept in thermodynamics of materials because all of the thermodynamic properties of a material at a given temperature and pressure can be obtained from knowledge of its chemical potential. Under the most common thermodynamic condition of constant temperature and pressure, chemical potential determines the stability of substances, such as chemical species, compounds, and solutions, and their tendency to chemically react to form new substances, to transform to new physical states, or to migrate from one spatial location to another. Chemical potential is considered by many to be one of the most confusing and difficult concepts to grasp, although there appears to be no confusion about temperature, pressure, and electric potential. Chemical potential has been
underappreciated and underutilized in applications of thermodynamics to materials science and engineering. One of the reasons for this is the widespread use of molar Gibbs free energy, partial molar Gibbs free energy, or simply Gibbs energy or Gibbs free energy but with the unit of J/mol. Adding to the confusion is the occasional use of Gibbs potential in place of Gibbs energy or Gibbs free energy, even when it refers to the Gibbs free energy of an entire system rather than on a per mole basis. Another reason why chemical potential is underappreciated is the surprising lack of a unique unit associated with such a qu
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