A Light and X‐Ray Scattering Study of Aqueous Micellar Solutions of a Diblock Copolymer of Propylene Oxide and Ethylene Oxide with Solubilized Alkylcyanobiphenyl Liquid Crystals

Abstract

The temperature and concentration dependences of the physicochemical properties of aqueous solutions of the diblock copolymer P₄₃E₃₁₂ (P = oxypropylene, E = oxyethylene) with solubilized liquid crystal (LC) have been studied using static and dynamic light scattering (SLS and DLS), small‐angle x‐ray scattering (SAXS), and ultraviolet (UV) spectroscopy. Relaxation time distributions from DLS obtained from inverse Laplace transformation of intensity correlation functions are multimodal, where the two fastest modes are attributed to diblock copolymer unimers and micelles, respectively. The remaining modes at longer decay times reflect the presence of free LC with hydrodynamic radii (R _h) of hundreds of nm. The R _h of both unimers and micelles were independent of temperature (T), while the hydrodynamic virial coefficient k _D and the second virial coefficient, A ₂, decreased with increasing T. The UV spectroscopy measurements showed that there is a reduction in the amount of solubilized LC per gram of copolymer (c _s) as the copolymer concentration (c _p) is increased. The SAXS results agree well with a model of a homogeneous system of polydisperse interacting hard spheres. In solution, both the effective micellar radius of interaction (R _eff) and the hard‐sphere micellar radius (R¯_s) increase in the presence of LC due to solubilization of the latter in the hydrophobic micellar core. Both SAXS and SLS results show that intermicellar interactions become important at c _p > 1% (w/w) at high temperatures [T > the critical micelle temperature (cmt)].

Keywords:

• Micelles
• SAXS
• Diblock copolymers
• Solubilized liquid crystals

Acknowledgments

The authors thank Miss E. Di Cola in The Department of Physics at the University of Leeds for technical assistance. The United Kingdom Engineering and Physical Sciences Research Council (EPSRC), grant GR/M51994 and The Royal Swedish Academy of Sciences are gratefully acknowledged for financial support.