Optical force measurements in concentrated colloidal suspensions

摘要: This work concerns the construction and testing of an optical tweezers-based force transducer, its application to a hard-sphere colloidal system. A particle in trap forward-scatters fraction trapping light, which is collected order give high-resolution information on trapped particle’s position relative centre. The system then calibrated convert displacements forces. colloid used this study densityand refractive index-matched suspension PMMA particles, radius 860 ± 70nm, with volume fractions range φ = 40 → 62%. Passive microrheological measurements have yielded about rearrangements tracer’s cage nearest neighbours, as well highly localised high-frequency viscosity, where presence host causes around tenfold increase compared bare solvent case. Measurements also demonstrated effect sample history local short-time self-diffusion coefficient, perturbations caused by translating within taking up hour relax 58% sample. high resolution tracking offered technique has allowed for first measurement structure at shorter lengthscale than ‘dynamic size’ observed using other experimental techniques. In addition, active shown emergence yield stress 5Pa approaches glass transition ≈ 58%.