Chemistry @ IU :: Chemistry M501

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Chemistry M501

M501 - Fall 2009

Intermolecular and interfacial forces in molecular materials

The range of forces that drive the organization of molecules and supramolecular complexes into well-defined structures expands beyond those responsible for conventional ionic, covalent, metallic, hydrogen and coordination bonds. The properties of many molecular systare determined by weaker, cooperative interactions e.g. van der Waals and Casimir, hydrophobic, capillary, convective and shear, electrical and optical. At nanoscale, in particular, energies associated with these interactions may have similar magnitudes, which makes for interesting phenomena from the transformations associated with dough kneating, to Brownian ratchets, to the super-hydrophobicity of the lotus leaf, virus assembly and disassembly, self-repairing materials, maskless lithography, flexible electronics, artificial opals, and optical tweezing.

The course intends to provide a grounding in theories and concepts of such intermolecular and interfacial interactions with the goal of allowing students to recognize which forces may be important in the organization and function of any particular system.

INTRODUCTION

What are molecular materials and why are they interesting?
A few (neat) examples.
Recurring themes:
Length scales: properties are born at intermediate scales between atomic and macroscopic
Fluctuations and Brownian motion are important
Propensity towards dynamic and static self-assembly.
Motivation: inspired by biology, driven by progress in chemistry and physics.
Forces between interfaces are key.

PART I

Review of statistical thermodynamics concepts
Equilibria
Phase equilibria
Surface tension
Solutions and mixtures
A lattice model describing mixtures
What is interfacial tension?
Solvation and transfer of molecules between phases
The chemical potential
Solvation
Activity and activity coefficient
Dimerization in solution
Physical kinetics
Linear laws relating forces to flows
The diffusion equation
Sources and sinks: examples from population biology
The Einstein-Smoluchowski equation
Brownian ratchets
The fluctuation-dissipation theorem
Coupled flows: Onsager reciprocal relations
The electrostatic potential
The Poisson equation
The frequency-dependent dielectric constant
Electrochemical equilibria: salt ions shield charged objects
Intermolecular interactions
Short-ranged repulsions and long-ranged attractions
Short-ranged attractions are electrostatic
The lattice model contact energy
Phase transitions
Phase separations are driven to lower the free energy
The spinodal curve and the critical point
Transitions and critical points are universal
Cooperativity: the Landau model
Helix-Coil transitions
The kinetics of phase transitions and nucleation.
Adsorption and binding
The Langmuir model
Multi-site cooperative binding
Water is an unusual liquid
Hydrogen bond structure and anomalous properties
The hydrophobic effect
Signature of hydrophobicity: its temperature dependence
Water is structured near cavities and planar surfaces
Ions can make or break water structure

PART II

Forces between particles and surfaces
Unifying concepts
van der Waals forces between surfaces
The Hamaker constant
The Lifshitz theory
Repulsive van der Waals forces
Retardation effects
Surface and adhesion energies
Electrostatic forces between surfaces in liquids
The electric double layer
van der Waals and double-layer forces acting together: the DLVO theory
Experimental measurements
Solvation, structural and hydration forces
Steric and fluctuation forces
Adhesion
The JKR and Hertz theories

PART III

Thermodynamic principles of self-assembly
Fundamental thermodynamic equations
Conditions necessary for the formation of aggregates
The critical micelle concentration
Infinite aggregates (phase separation) vs. finite-size aggregates (micellization)
Size-distributions of self-assembled structures
Mesophases and multi-layers
Micelles, bilayers, and vesicles
Amphiphilic structures - equilibrium considerations
Optimal headgroup area
Geometric packing considerations
Spherical micelles
Non-spherical micelles
Bilayers
Vesicles
Factors affecting changes from one structure to another.
Biological membranes

Recommended bibliography:

Books:

Molecular driving forces: statistical thermodynamics in chemistry and biology
Ken A. Dill, Sarina Bromberg, Dirk Stigter

Intermolecular and surface forces
J. Israelachvili

Capillarity and Wetting Phenomena: Drops, Bubbles, Pearls
P-G de Gennes et al.

On Food and Cooking: the science and lore of the kitchen
Harold McGee

Articles:

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