Application Notes DWS

 
 
 

Link directs to the application note "DWS Microrheology of Aqueous Polymer Solutions"

 

The traditional characterization of (bio)-polymer solutions using time-temperature superposition (TTS) require long. total measurement times and tedious data treatment to achieve data over a broad frequency range. Using DWS microrheology, the whole frequency range can be measured by a single measurement within a few minutes.

 
 
 

DWS microrheology is applied to a series of model low fat mayonnaises with different contents of thickener to a commercial low fat mayonnaise

 

Emulsions constitute a base for a vast number of commercially available products ranging from food and cosmetics to pharmaceuticals. With the increasing need for understanding the microrheological properties, fast and simple methods are required for to facilitate the formulation process and quality control. Here, we apply DWS microrheology to a series of model low fat mayonnaises with different contents of thickener and compare it to a commercial low-fat mayonnaise.

 
 
 

gelation, temperature, gelatin, DWS, light scattering, storage, loss, gel point

 

Particle motion in colloidal media, such as gelling systems, can be probed by DWS. A microrheological analysis of the particle motion may further provide the medium’s rheological properties, namely the frequency-dependent storage and loss moduli, G’(ω) and G’’(ω), respectively. Here we apply DWS microrheology to the determination of the gelation temperature of a commercially available, food grade gelatin solution.

 
 
 

aging, emulsion, ostwald ripening, DWS, interfacial tension, hydrodynamic radius, droplet size

 

Ostwald ripening is a common aging process, which typically arises in the early stages of the emulsion life. Due to interfacial tension that makes smaller droplets less stable than bigger droplets, the dispersed phase subsequently diffuses from smaller to larger droplets through the continuous phase. This results in an increase in the mean droplet size with time. Here the time-evolution of the mean hydrodynamic radius of oil droplets dispersed in water was followed in situ by DWS Sizing. After an initial transient period, we observe that diffusion-controlled Ostwald ripening becomes the mechanism that determines the aging rate of the emulsion.

 
 
 

emulsion, characterization, particles, DWS, liquid droplets, mechanical, rheology, external force, sample, conditions

 

Although solid particles dispersed in a solution are the most frequently measured samples by means of light scattering, they are not the only ones. DWS additionally enables analysis of emulsions, i.e. liquid droplets dispersed in a continuous liquid phase. The results of the viscoelastic properties of such systems obtained by DWS microrheology in ~ 1 min are in good agreement with those obtained by traditional mechanical rheology in 30 min - 1 h.

 
 
 

viscosity, DWS, measurements, transparent, mixtures, water, glycerol, turbidity

 

When fluidity of a sample is comparable to that of water, accurate viscosity measurements with conventional rheometers become very tricky, and typically couette geometries, that require several mL of sample, should be used. As shown in this application note, however, DWS microrheology can be used to accurately measure the viscosity of very fluid samples, with volumes as small as a few hundreds of µL.

 
 
 

gelling process, milk, acidifying milk, yoghurt, colloidal stability, autocorrelation function

 

Milk consists of water-dispersed fat droplets and casein micelles. Upon lowering the pH of milk, proteins start to lose their charges, and hence, to aggregate. At some point, milk gels to become yoghurt. DWS can probe the changes in colloidal mobility throughout the entire gelling process of milk, and determine the gel point from which yogurt is formed.