Interest in soft materials has experienced tremendous growth in the past decade. This stems from the fact that such materials include many important industrial products, such as plastics, foods and lubricants. This chapter provides a brief overview of the subject.
Interest in soft materials has experienced tremendous growth in the past decade. This stems from the fact that these materials include many important industrial products, such as plastics, foods and lubricants. This study is particularly relevant today because of the need to find more green, sustainable and environmentally friendly inputs for manufacturing. The formation of such materials is contingent on the ability of relatively simple molecules to self-assemble into highly complex structures. Many foods are edible soft materials and their study can make use of the myriad of experimental techniques developed over the last century for characterizing such materials. One need not constrain oneself by the requirement to study food only in the “physically relevant” regime. Insight into material structures and dynamics frequently requires information from outside the temperature or pressure ranges of direct applicability, and the study of foods need not be bound by constraints. Current efforts geared towards the improvement in the nutritional quality of food products and security of food systems requires a materials science level approach to food structuring to minimize unhealthy components and deliver nutritionally functional compounds, as well as to decrease cost and increase availability.
The process of creating a supramolecular structure does not simply entail finding a thermodynamic global free energy minimum. Kinetic factors play a key role in determining which local free energy minima are chosen along the formation pathway. Environmental effects become even more important (than molecular effects) beyond the microscopic world, where heat and mass transfer effects will strongly influence the formation of nanostructures, microstructures, and eventually a network (Figure 1.1).
Structural hierarchy in many food soft materials.
Several research groups have now observed that several food soft materials of industrial interest, such as triglyceride (fat) crystal networks, display such structural hierarchy, and that the elasticity of such materials is dependent on the interactions between clusters of nanocrystals (Figure 1.2).1,2
Idealized structure of a nanostructured colloidal network.
Furthermore, the final size and morphology of these nanostructures and microstructures is strongly influenced by heat and mass transfer phenomena. For example, when triglycerides are cooled from the melt to a temperature below their melting point, i.e., when they are supercooled, they undergo a liquid–solid transformation to form crystalline nanoplatelets with characteristic polymorphism and polytypism.3,4 These primary nanocrystals aggregate, or grow into each other, to form clusters, which further interact, resulting in the formation of a continuous three-dimensional network (Figure 1.3).5,6
Duotone polarized light–phase-contrast micrograph (50% overlay) of a crystal network of the high melting fraction of milk fat in triolein.
Duotone polarized light–phase-contrast micrograph (50% overlay) of a crystal network of the high melting fraction of milk fat in triolein.
The macroscopic properties of such systems are somehow affected by all these levels of structure, as well as external fields, which should all be taken into account when predicting and engineering material functionality.
In order to truly understand, and eventually predict, the macroscopic properties of food, it is necessary to characterize and define the different levels of structure present in the material and their respective relationship to a macroscopic property. In our experience, the macroscopic properties of many soft materials cannot always be directly related to molecular structure. Rather than always invoking “molecular interpretations” to explain the macroscopic properties of materials, relationships between the appropriate level of structure and macroscopic properties should be sought instead. Knowledge of the relationships between molecular composition and phase behavior, solid state structure, growth mode, static structure, dynamic structure, and macroscopic properties will eventually allow for the rational design of specific macroscopic properties.
Discovery and knowledge – the unification of data accumulation and understanding, thereby giving rise to a single overarching picture of the world – form one of the basic aspects of the scientific paradigm. But there is also a less-appreciated journey: the journey from the large-scale to the small-scale. Not the “small-scale” of reducing all phenomena to non-interlocking components, but the appreciation of how the small-scale components interlock to give rise to the larger, more complex static and dynamic structures. The latter can go by many names: cooperative phenomena, spontaneous self-assembly and long-range order are only three aspects of the creation of the large-scale from the small-scale. But, and this is the key point, understanding the small-scale units enables one to manipulate the large-scale structures – it enables one to create new large-scale structures.
