Aggregation numbers, and bimolecular collision rate constants of guest molecules confined in the micelles (by TRFQ); interfacial hydration index and microviscosity, (by ESR); axial ratio (from solution viscosity); micelle self-diffusion coefficient (by PGSE NMR) and the critical micelle concentrations (from surface tension) were determined for various molar compositions defined by the ratio R [NaDC]/[DMPC] and concentrations ([NaDC]+[DMPC]). Aggregate properties depend on the ratio, R and reveal behavior unlike that in micelles of surfactants with aliphatic non-polar chains. With increase in concentration from [NaDC] = 0.010 M to [NaDC] = 0.200 M, the hydration index and the aggregation number exhibit non-monotonic variations. The data interpretation showed the micelles to be polydisperse rods with a composition and concentration dependent average length to diameter ratio. Formulation of a polar shell model for cylindrical micelles yielded a set of non-linear equations for the structural features of the micelle. The solutions give the microstructural description of the mixed micelle that includes the length, diameter, number of water molecules in the hydration shell, thickness of the headgroup region and an additional property namely the distribution, defined by the fraction f, of the non-polar part between the core and the shell region. The axial ratio depends on molar composition and increases from about 4 to 7 for a bile salt/lipid ratio change from 5 to 1. The bile salt and lipid monomers have a fraction (f) of their non polar parts in the headgroup region overlapping with water. This fraction is about 0.30 at R = [NaDC]/ [DMPC] = 5, increasing to 0.64 for R=1. The number of water molecules per monomer depends on micelle composition and is about 3 to 7 when [NaDC]/ [DMPC] = 2.5 and 5 and 1 to 2 for an equimolar ratio.