Self-assembly of amphiphilic liquid crystal block copolymers containing a cholesteryl mesogen: Effects of block ratio and solvent

We report on the self-assembly, in water and in bulk, of amphiphilic liquid crystal block copolymers consisting of a cholesterol-based smectic LC polymer block (PAChol) and poly(ethylene glycol) (PEG) block. Two series of block copolymers, PEG₄₅-b-PAChol and PEG₁₁₄-b-PAChol (45 and 114 are the degree of polymerization of PEG blocks) with different hydrophilic/hydrophobic weight ratios were synthesized and characterized in detail. Depending on the diblock composition, smectic polymer vesicles and/or nanofibers were formed by adding water into a dilute solution of copolymers in dioxane. If THF is used instead of dioxane as solvent, solid spherical aggregates were obtained upon water addition for PEG₄₅-b-PAChol series, while macroscopic precipitation occurred for PEG₁₁₄-b-PAChol series. The mesomorphic and microphase segregation structures of the block copolymers in bulk were studied by X-ray scattering, DSC and POM. The interdigital smectic A (SmA_d) phase with a lamellar period of 4.25 nm was detected in all block copolymers. For PEG₁₁₄-b-PAChol₅ (PEG/PAChol weight ratio = 66/34) and PEG₁₁₄-b-PAChol₁₂ (45/55), lamellar type of microphase segregation was observed.