Lecture
This lecture focuses on the concept of diffusion coefficients and their significance in understanding molecular movement in fluids. The instructor begins by discussing the estimation of diffusion coefficients based on models and comparing them to real-world measurements. The lecture explains self-diffusion, where a labeled molecule diffuses in a sea of identical molecules, and how to estimate the diffusion coefficient using molecular velocity and jump size. The Stokes-Einstein relation is introduced, relating diffusion to the viscosity of the fluid and the radius of suspended particles. The instructor emphasizes the importance of viscosity in determining how quickly particles can diffuse through different fluids. The lecture transitions to a continuum approach to derive the diffusion equation, highlighting the historical context of diffusion knowledge prior to the understanding of molecular theory. The instructor concludes by introducing Fick's law, which formalizes the observation that diffusion occurs from regions of high concentration to low concentration, setting the stage for further exploration of mass conservation and the diffusion equation in subsequent lectures.