PREDICTION OF THERMODYNAMIC PROPERTIES OF COMPLEX FLUIDS
ABSTRACT The goal of this research has been to generalize Density Functional Theory (DFT) for complex molecules, i.e. molecules whose size, shape, and interaction energies cause them to show significant deviations from mean-field behavior. We considered free energy functionals and minimized them for systems with different geometries and dimensionalities including confined fluids (such as molecular layers on surfaces and molecules in nano-scale pores), systems with directional interactions and order-disorder transitions, amphiphilic dimers, block copolymers, and self-assembled nano-structures. The results of this procedure include equations of equilibrium for these systems and the development of computational tools for predicting phase transitions and self-assembly in complex fluids. DFT was developed for confined fluids. A new phenomenon, surface compression of confined fluids, was predicted theoretically and confirmed by existing experimental data and by simulations. The strong attraction to a surface causes adsorbate molecules to attain much higher densities than that of a normal liquid. Under these conditions, adsorbate molecules are so compressed that they repel each other. This phenomenon is discussed in terms of experimental data, results of Monte Carlo simulations, and theoretical models. Lattice version of DFT was developed for modeling phase transitions in adsorbed phase including wetting, capillary condensation, and ordering. Phase behavior of amphiphilic dimers on surfaces and in solutions was modeled using lattice DFT and Monte Carlo simulations. This study resulted in predictive models for adsorption isotherms and for local density distributions in solutions. We have observed a wide variety of phase behavior for amphiphilic dimers, including formation of lamellae and micelles. Block copolymers were modeled in terms of configurational probabilities and in the approximation of random mixing entropy. Probabilities of different orientations for the segments were considered as order parameters and the free energy was written as a functional of these parameters. Imposing boundary conditions allowed us to apply this approach to confined fluids. Equilibrium self-assembly in fluids was studied in the framework of the lattice density functional theory (DFT). In particular, DFT was used to model the phase behavior of anisotropic monomers. Though anisotropic monomers are a highly idealized model system, the analysis presented here demonstrates a formalism that can be used to describe a wide variety of phase transitions, including processes referred to as self-assembly. In DFT, the free energy is represented as a functional of order parameters. Minimization of this functional allows modeling spontaneous nano-scale phase transitions and self-assembly of supramolecular structures. In particular, this theory predicts micellization, lamellization, fluid – glass phase transitions, crystallization, and more. A classification of phase transitions based on general differences in self-assembled structures is proposed. The roles of dimensionality and intermolecular interactions in different types of phase transitions are analyzed. The concept of “genetic” codes is discussed in terms of structural variety of self-assembled systems.
- Research Organization:
- The Johns Hopkins University
- Sponsoring Organization:
- USDOE - Office of Energy Research (ER)
- DOE Contract Number:
- FG02-87ER13777
- OSTI ID:
- 862351
- Report Number(s):
- DOE/ER/13777-12; TRN: US0702446
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ADSORPTION ISOTHERMS
APPROXIMATIONS
BOUNDARY CONDITIONS
CLASSIFICATION
COMPRESSION
COPOLYMERS
CRYSTALLIZATION
DIMERS
ENTROPY
FORECASTING
FREE ENERGY
FUNCTIONALS
LAMELLAE
MINIMIZATION
MONOMERS
ORDER PARAMETERS
THERMODYNAMIC PROPERTIES
Thermodynamics
complex fluids
adsorption