Mass transportKnowledge of mass transport is important to maintain high product quality in foods and soft biomaterials. For example, water migration leads to staled bread or filled pastry becoming soggy. Fat migration causes chocolate to become grey and loss of texture. Mass transport is also important for liquid up-take in hygiene products, exudate management in wounds and for controlled release properties in pharmaceuticals.
The dominating mass transport mechanisms in foods and soft biomaterials are convective flow, capillary flow and diffusion depending on structural length scale and the detailed microstructure. The microstructure in these types of materials and products are often very heterogeneous making the relationships between mass transport and microstructure complicated. Therefore techniques to determine the microstructure at different length scales must be combined with experimental techniques to determine mass transport and simulations and modelling.
Interfaces are also very important for the mass transport properties. Interfaces are occurring almost everywhere around us, e.g. in our bodies where bone is in contact with soft tissue, in the juice and milk package material, computers components, pharmaceuticals, between different phases in a food matrix etc. The functionality of the materials often depends on the diffusion of molecules/liquids across interfaces. The diffusion across interfaces as well as the microstructure at the interface can be characterized which leads to understanding of the mechanisms behind the diffusion across the interfaces and to develop routes for design of interfaces with controlled diffusion properties.
Microscopy combined with quantitative image analysis provides a powerful tool for the analysis of the microstructure of materials. Statistical tools and models can be used to study the dependence between the geometry and the properties of a material and to construct materials with tailored mass transport properties. Since size distribution of the largest pores, percolation through the material structure, and connectivity of clusters of the largest pores play an important role in mass transport, we are developing tools to model mass transport and to make powerful image analysis. Using such models we will be able to combine experimental characterization of a 3D structure and mass transport properties with systematic computer simulations of 3D structures. This knowledge will be used for structure design of soft materials with optimized properties.
Techniques for determine mass transport
There are several different techniques to be used for the characterization of diffusion across interfaces, ranging from macroscopic characterization with e.g. the diffusion cell method, NMR diffusometry or quartz crystal microbalance (QCM) to microscopic characterization with for instance Fluorescence Recovery After Photobleaching (FRAP), single particle tracking (SPT) and raster image correlation spectroscopy (RICS). We are developing new FRAP and RICS methods that are useful in heterogeneous food and soft biomaterials. With our quantitative microscopy methods, we can determine local mass transport properties at length scales down to a few micrometers. This knowledge can be used to understand mass transport – microstructure relationships and to optimize and develop new food and biomaterial products.