AGGREGATION NUMBER ACID HYDRODYNAMIC HYDRATION LEVELS OF BRIJ-35 MICELLES FROM OPTICAL PROBE STUDIES

Light-scattering methods were used to study the physical properties of micelles of Brij-35 (poly(oxyethylene(23)) lauryl ether; C12H25(OCH2CH2)(23)OH). A minimal model of Brij-35 micelles describes them as hydrodynamic hard spheres enclosing an anhydrous core and a hydrated outer shell. An adequate model of spherical Brij-35 micelles embodies an inner hydrodynamic core (radius a(m)), containing anhydrous and hydrated zones that block solvent flow, and an outer coronal zone (radius a(c)), permitting solvent flow but obstructing the closer approach of two micelles. By combining quasi-elastic light-scattering spectroscopy and multiple-size mesoscopic optical probes, we determined simultaneously the aggregation number (N), micelle hydrodynamic radius (a(m)), micellar radius of closest approach (a(c)), and degree of hydration (delta). The simple hard-sphere model finds a(m) similar to 44 Angstrom and N approximate to 40 and (at T less than or equal to 25 degrees C) overestimates delta approximate to 4 g of H2O/g of Brij-35. With increasing T, N increases and 6 falls, reaching N approximate to 63 and delta approximate to 1.4 at T = 70 degrees C. The better micelle model. finds a coronal thickness a(c)-a(m) approximate to 13 Angstrom at 10 degrees C, falling progressively to approximate to 7 Angstrom at 70 degrees C. With this model, delta is approximate to 3 at 10 degrees C, falling to approximate to 1.5 at 70 degrees C.