Critical concentration for colloidal crystallization determined with microliter centrifuged suspensions

Area of Science:

• Colloidal Science
• Materials Science
• Physical Chemistry

Background:

• Determining the critical particle concentration for colloidal crystallization is essential for understanding phase transitions.
• Traditional methods can be time-consuming and require larger sample volumes.
• Accurate measurement is crucial for controlling crystal formation in colloidal systems.

Purpose of the Study:

• To develop an elegant and efficient method for determining the critical particle concentration for colloidal crystallization.
• To utilize centrifugal sedimentation for creating and analyzing phase boundaries in colloidal suspensions.
• To establish a technique applicable to high concentration regimes without inducing particle aggregation.

Main Methods:

• Employed centrifugal sedimentation on a dilute suspension of monodispersed particles in a flat capillary cell.
• Generated a temporary nonequilibrium particle concentration gradient, including a crystalline-noncrystalline phase boundary.
• Utilized spatially resolved spectrometry during the recovery process post-centrifugation to determine equilibrium concentration.

Main Results:

• The particle concentration at the crystalline phase boundary consistently maintained its equilibrium value during the recovery phase.
• The method successfully determined the critical concentration, even with evolving global concentration distributions.
• The technique requires only microliter-scale sample volumes and is effective near closest packing concentrations.

Conclusions:

• Centrifugal sedimentation provides an elegant and accurate method for determining the critical concentration for colloidal crystallization.
• The developed technique is efficient, requires minimal sample, and avoids particle aggregation issues.
• This method offers a reliable approach for studying colloidal phase behavior in various concentration regimes.