Molecular thermodynamics of soft self-assembling structures for engineering applications

Abstract

Controlling self‐assembly is a key issue in many applications such as encapsulation of drugs, micelle separation, and fabrication of nanoporous materials. For providing guidance to control self‐assembly, a reliable prognosis of aggregation behavior is indispensable. Molecular thermodynamic models have been developed for different types of soft mesoscale structures formed by aggregating chainlike amphiphilic molecules. Examples include nonionic and ionic copolymer gels swelling in selective solvents, surfactant micellar solutions and amphiphilic membranes. Though rather different in chemical nature and applications, these systems are all characterized by self‐assembly into soft mesoscale structures that are sensitive to external conditions or applied stimuli. The models predict a number of thermodynamic and structural characteristics (equilibrium size and stability of different morphologies, equilibrium swelling, elastic properties, solute partitioning, etc.) in terms of several adjustable parameters and molecular characteristics of components. Consideration of nanoscale morphology gives rise to interesting structure–property relations reflected by relatively simple models. New findings help estimate how variations of controllable factors such as pH, salinity and additives affect self‐assembly patterns and aggregate properties. Recent advances in the development of molecular thermodynamic aggregation models, factors restricting implementation of these models and trends in the field are discussed. © 2015 Society of Chemical Industry

Driving Force for Spontaneous Perforation of Bilayers Formed by Ionic Amphiphiles in Aqueous Salt

“…Perforated bilayers are found in a variety of systems containing classical surfactants and block copolymers . Numerous cryo-transmission electron microscopy (TEM) images of such systems show the sequence of aggregate’s shape transitions where perforated structures appear between the nonperforated bilayers and the spatial networks of branched wormlike micelles. , Description of these structural transformations is very important per se and in view of many engineering applications. , …”

“…9,10 Description of these structural transformations is very important per se and in view of many engineering applications. 11,12 The classical aggregation models 13−16 are widely used to describe aggregates of regular shapes, e.g., spheres, cylinders, or lamellae. More difficult is to model aggregates of complex geometry, e.g., a perforated bilayer or a spatial network of branched micelles.…”

Molecular Thermodynamic Modeling of Self-Assembly into Branches and Spatial Networks in Solution

“…Understanding the equilibrium balance between branches and end-caps depends on our ability to model the aggregation free energies of these two parts of a self-assembled structure. 3 Molecular thermodynamic models make it possible to estimate the free energies for a number of systems 3 that contain branching chains, including fluids of sticky spheres, 4 surfactant solutions of wormlike micelles, 5 and mixtures of associative polymers. 6,7 An individual microscopic "portrait" of the system is reflected in specific models of these free energies.…”

“…It also controls the phase transitions for systems with 3-fold (Y-shaped) junctions because the existence of such junctions induces an effective attraction between the chains even if there were no interchain attraction forces on the microscopic level. Understanding the equilibrium balance between branches and end-caps depends on our ability to model the aggregation free energies of these two parts of a self-assembled structure …”

“…Molecular thermodynamic models make it possible to estimate the free energies for a number of systems that contain branching chains, including fluids of sticky spheres, surfactant solutions of wormlike micelles, and mixtures of associative polymers. , An individual microscopic “portrait” of the system is reflected in specific models of these free energies. , In this work we discuss recent advances of molecular thermodynamic models in describing self-assembly in systems with branching chains and give several illustrative examples for these systems. We model transformation of an amphiphilic membrane into a spatial micellar network via the appearance of perforations in a bilayer.…”