Microrheology: Structural evolution under static and dynamic conditions by simultaneous analysis of confocal microscopy and diffusing wave spectroscopy

Abstract

An oscillatory shear configuration was developed to improve understanding of structural evolution during deformation. It combines an inverted confocal scanning laser microscope ͑CSLM͒ and a special sample holder that can apply to the sample specific deformation: oscillatory shear or steady strain. In this configuration, a zero-velocity plane is created in the sample by moving two plates in opposite directions, thereby providing stable observation conditions of the structural behavior under deformation. The configuration also includes diffusion wave spectroscopy ͑DWS͒ to monitor the network properties via particle mobility under static and dynamic conditions. CSLM and DWS can be performed simultaneously and three-dimensional images can be obtained under static conditions. This configuration is mainly used to study mechanistic phenomena like particle interaction, aggregation, gelation and network disintegration, interactions at interfaces under static and dynamic conditions in semisolid food materials ͑desserts, dressings, sauces, dairy products͒ and in nonfood materials ͑mineral emulsions, etc.͒. Preliminary data obtained with this new oscillatory shear configuration are described that demonstrate their capabilities and the potential contribution to other areas of application also.

A new parallel plate shear cell for in situ real-space measurements of complex fluids under shear flow

“…Thus, shear cells have been combined with optical microscopy in recent years. 22,[28][29][30][31][32][33][34][35][36][37][38][39][40][41] As not every type of shear cell is amenable to microscopic inspection, these cells are usually of the cone-plate or parallel plate type.…”

“…The study of sheared complex fluids at submicrometer resolution places extreme demands on the stability of the shear cell as well as on the uniformity of the flow created by it. Recently, a parallel plate shear cell with a ZVP was described 32 that is accessible with CSLM, but it lacks the mechanical stability needed to stably image colloidal objects. A cone plate shear cell with a ZVP was constructed that does achieve the required stability.…”

Scaling Behavior of Delayed Demixing, Rheology, and Microstructure of Emulsions Flocculated by Depletion and Bridging

“…26,27 Moreover, the DWS-echo technique can be used to investigate structural changes caused by controlled oscillatory shear, as has been shown for, for example, densely packed emulsions 28 and colloidal glasses. 29 The combination of DWS echo with CSLM imaging 30,31 was shown to be applicable to flocculated emulsions. 32 The focus of the present paper is twofold.…”

Dynamic Light Scattering Techniques and Their Applications in Food Science

“…They presented data showing that DWS can detect differences, not only in the rate of aggregation/flocculation, but also in the type of destabilization, flocculation or creaming that the system is undergoing [70] In an original configuration combining DWS with inverted confocal scanning laser microscopy (CSLM) and with the sample material under shear and/or compression, they were able to monitor particle mobility and directly compare this to the amount of strain applied, while at the same time monitoring the conditions of the structural behavior with the CSLM [71,72]. The authors also carried out some theoretical modeling of short-and long-range interactions and applied them to the DWS data they had obtained [73].…”