Hokkaido University Research Profiles

Manufacturing Technology

Observation of the 3D Structure of Soft Matter and the Microrheological Measurement Method

Relationship between structure formation and viscoelasticity in non-equilibrium complex fluids

Since soft matter is literally soft, its structure tends to change depending on the external fields, and at that time its physical properties will also change considerably. We are developing methods to investigate the 3D structure and physical properties of soft matter to apply these to functional materials.

Content of research

It is known that the apparent viscosity of certain blends of two mutually incompatible polymers is reversibly increased by applying an electric field (electrorheological effect). In general, when two polymers are mixed, one of them becomes a droplet and is dispersed in the other. Under shear flow, the droplet structure in Figure 1(a) is observed, but when an electric field is applied to it, it changes to the network structure in (b), and the viscosity increases accordingly. The relationship between this structure and rheology has been clarified for the first time using this newly developed system. This system has made it possible to clearly observe the phase separation caused by shear flow in actin solutions of biological materials. As shown in Fig. 2, when shear is applied, regions with large velocity gradients appear in the upper and lower positions, and these regions widen as the shear rate increases.

  • Fig. 1: (a) Droplet structure (b) Network structure

  • Fig. 2: Flow field under shear application

Potential for social implementation

  • ・Observation of the 3D structure and rheological measurement of soft matter under flow conditions
  • ・The mechanism of the electrorheological effect in emulsions and suspensions
  • ・Flow field measurements and microrheology of biological materials

Appealing points to industry and local governments

The developed system makes it possible to simultaneously observe the structure and measure the rheology of soft matter at a micron scale (flow field measurement) under external fields (shear flow and electric field). This in turn makes it possible to evaluate electrorheological fluids, for example. This system also allows microrheological measurement under flow, and is thus suitable to evaluate non-Newtonian fluids, including those showing shear shedding.