Direct experimental evidence of growing dynamic length scales in confined colloidal liquids

The modification of the glass transition in confined domains, particularly the length scales associated with cooperative motion, remains a mystery. Hard-sphere suspensions are confined between two surfaces to progressively smaller dimensions to probe the confinement effect on the growth of dynamic heterogeneities via confocal microscopy. The confinement length scale is defined as the critical spacing where deviations from bulk behaviors begin and is observed to occur at progressively larger gap spacings as the volume fraction is increased. However, dynamic length scales extracted from the four-point correlation function are on average smaller than the confinement length scale.