Using DLS Spectroscopy and Optical Probe Diffusion to Examine Structure of Brij Micelles

Document Type

Conference Proceeding

Publication Date


Publication Title

APS March Meeting


We studied properties of Brij-35 surfactant micelles in solution using Dynamic Light Scattering (DLS) Spectroscopy and Optical Probe Diffusion method. Aqueous solutions of Brij-35 with concentrations ranging from 2 to 100g/L were prepared, both with and without polystyrene latex probes of diameters 24, 50, 186, 282 and 792nm. Solutions were studied at four temperatures of 10, 25, 40 and 70oC with DLS to obtain micelle and probe diffusion coefficients (Dm, Dp). Using both diffusion coefficients we deduced micelle radius (am), micelle water content (δ), and number of surfactant molecules per micelle (N) using two different models. First, hard sphere model of micelles/probe interaction was used to analyze the data by two methods, after am was obtained from intercept of Dm(c). The first method uses the slope of Dm(c) and size of probes to determine N and δ. The second method uses the linear least-squares fit of Dp(c) for different probe sizes to determine N and δ. Both methods reveal that with increase in solution temperature am increases by 10{\%}, N increases and δ decreases by a factor of 2. The second model treats micelles as core-shell particles with corona radius (ac). This model used two different approaches based on linear least-squares fits of Dm(c) and Dp(c). We found amto be 4-4.5nm and ac-am to be 1nm without relying on Stokes-Einstein equation. Results for N and δg were also consistent.