Structural changes of poly(N-isopropylacrylamide)-based microgels induced by hydrostatic pressure and temperature studied by small angle neutron scattering.

We study the structural properties of microgels made of poly(N-isopropylacrylamide) and acrylic acid as a function of hydrostatic pressure and temperature using small angle neutron scattering. Hydrostatic pressure induces particle deswelling by changing the mixing of the microgel with the solvent, similar to temperature. We extend this analogy to the structural properties of the particles and show that the form factor at a certain temperature is equal to the form factor at a certain hydrostatic pressure.

Osmotic shrinkage in star/linear polymer mixtures.

Multiarm star polymers were used as model grafted colloidal particles with long hairs, to study their size variation due to osmotic forces arising from added linear homopolymers of smaller size. This is the origin of the depletion phenomenon that has been exploited in the past as a means to melt soft colloidal glasses by adding linear chains and analyzed using dynamic light scattering experiments and an effective interactions analysis yielding the depletion potential. Shrinkage is a generic phenomenon for hairy particles, which affects macroscopic properties and state transitions at high concentrations.

Small-angle neutron scattering study of protein unfolding and refolding.

Small-angle neutron scattering has been used to study protein unfolding and refolding in protein bovine serum albumin (BSA) due to perturbation in its native structure as induced by three different protein denaturating agents: urea, surfactant, and pressure. The BSA protein unfolds for urea concentrations greater than 4 M and is observed to be independent of the protein concentration. The addition of surfactant unfolds the protein by the formation of micellelike aggregates of surfactants along the unfolded polypeptide chains of the protein and depends on the ratio of surfactant to protein concentration.

A new instrument for time-resolved static and dynamic light-scattering experiments in turbid media.

We present a new 3D cross-correlation instrument that not only allows for static and dynamic scattering experiments with turbid samples but measures at four angles simultaneously. It thus extends the application of cross-correlation light scattering to time-resolved studies where we can, for example, efficiently investigate the temporal evolution of aggregating or phase separating turbid dispersions. The combination of multiangle 3D and on-line transmission measurements is an essential prerequisite for such studies.

Small-angle neutron scattering study of structure and kinetics of temperature-induced protein gelation.

The phase diagram, structural evolution, and kinetics of temperature-induced protein gelation of protein Bovine Serum Albumin (BSA) have been studied as a function of solution pH and protein concentration. The protein gelation temperature represents the onset of turbidity in the protein solution, which increases significantly with increasing pH beyond the isoelectric pH of the protein molecule. On the other hand, the gelation temperature decreases with an increase in protein concentration only in the low-protein-concentration regime and shows a small increasing trend at higher protein concentrations.