Analysis of aggregation and dispersion states of small particles in concentrated suspension by using diffused photon density wave spectroscopy.

Recently, inspection of chemical components like melamine plays an important role in food industry for the food safety. However, conventional analyzing methods require a lot of preparations and much of time. We propose a real-time method for investing the mean particle size and number density of concentrated suspensions without any preparations. There are several techniques of analyzing concentrated suspensions. Laser light scattering (LLS) and dynamic light scattering (DLS) are used to measure the particle size. Fourier transform infrared spectroscopy (FT-IR) is used to measure the number density. They have been successfully describing the physical and dynamics characteristics near single light scattering regions. On the other hand, they require samples to be highly diluted. This is a major disadvantage in studying real concentrated suspensions, or phenomena such as gelation. Our proposed method diffused photon density wave spectroscopy (DPDWS) is based on the multiple light scattering theory. Thus, DPDWS measures the particle size and number density of the concentrated suspensions without dilution in real time. Diffused photon density wave (DPDW) is a spherical energy wave generated from the intensity-modulated point light source in the concentrated suspensions. The absorption and scattering coefficients can be simultaneously obtained from the amplitude and phase of DPDW propagated through the concentrated suspensions. Furthermore, the particle size and number density of nanoparticles can be estimated from the obtained optical properties using the absorption and the scattering theory. In this study, we qualitatively estimated the gelation of milk from the measured particle size and number density by use of DPDWS.