Dynamical Arrest in Attractive Colloids: The Effect of Long-Range Repulsion

We study gelation in suspensions of model colloidal particles with short-ranged attractive and long-ranged repulsive interactions by means of three-dimensional fluorescence confocal microscopy. At low packing fractions, particles form stable equilibrium clusters. Upon increasing the packing fraction the clusters grow in size and become increasingly anisotropic until finally associating into a fully connected network at gelation. We find a surprising order in the gel structure. Analysis of spatial and orientational correlations reveals that the gel is composed of dense chains of particles constructed from face-sharing tetrahedral clusters. Our findings imply that dynamical arrest occurs via cluster growth and association.Comment: Final version: Phys. Rev. Lett. 94, 208301 (2005

Enantiomeric Discrimination by Surface- Enhanced Raman Scattering- Chiral Anisotropy of Chiral Nanostructured Gold Films

A surface- enhanced Raman scattering- chiral anisotropy (SERS- ChA) effect is reported that combines chiral discrimination and surface Raman scattering enhancement on chiral nanostructured Au films (CNAFs) equipped in the normal Raman scattering Spectrometer. The CNAFs provided remarkably higher enhancement factors of Raman scattering (EFs) for particular enantiomers, and the SERS intensity was proportional to the enantiomeric excesses (ee) values. Except for molecules with mesomeric species, all of the tested enantiomers exhibited high SERS- ChA asymmetry factors (g), ranging between 1.34 and 1.99 regardless of polarities, sizes, chromophores, concentrations and ee. The effect might be attributed to selective resonance coupling between the induced electric and magnetic dipoles associated with enantiomers and chiral plasmonic modes of CNAFs.Absolution by SERS: A surface- enhanced Raman scattering chiral anisotropy effect is presented that combines chiral discrimination and surface Raman scattering enhancement on chiral nanostructured Au films. It is applied in the normal Raman scattering system to identify the absolute configuration and composition of enantiomers, overcoming disadvantages of polarimeter systems and chromatography.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156470/3/ange202006486_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156470/2/ange202006486.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156470/1/ange202006486-sup-0001-misc_information.pd