Stimuli-Responsive Control over Self-Assembled Nanostructures in Sequence-Specific Functional Block Copolymers.

The precise sequence of a protein's primary structure is essential in determining its folding pathways. To emulate the complexity of these biomolecules, functional block copolymers consisting of segmented triblocks with distinct functionalities positioned in a sequence-specific manner are designed to control the polymer chain compaction. Triblock polymers P- b -C- b -F and P- b -F- b -C and random diblock copolymer P- b -C- r -F consist of a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic block with coumarin (C) and ferrocene (F) moieties that are grafted in a sequence-specific or random manner onto the hydrophilic block. External stimuli such as UVB light, redox, and chemical cues influence the functional hydrophobic block to alter the packing parameters that are monitored with spectroscopic and scattering techniques. Interestingly, the positioning of the stimuli-responsive moiety within the hydrophobic block of P- b -C- b -F, P- b -F- b -C, and P- b -C- r -F affects the extent of the hydrophobic-hydrophilic balance in block copolymers that renders orthogonal control in stimuli-responsive transformation of self-assembled vesicles to micelles.

Orthogonal chain collapse in stimuli-responsive di-block polymers leading to self-sorted nanostructures.

We design amphiphilic di-block copolymers (P-b-F and P-b-C) tethered with stimuli-responsive ferrocene and coumarin hydrophobic pendants that exhibit chain collapse behaviour in response to light, redox and chemical cues, with subsequent transformation of the vesicles into micelles. Interestingly, the co-assembled vesicles of the polymer blend under orthogonal stimuli furnish self-sorted micelles and vesicles.

Twist viscoelastic coefficient of novel thiol terminated alkoxy-cyanobiphenyl nematic liquid crystals.

We report our studies on the refractive indices and twist viscoelastic coefficient of novel thiol terminated alkoxy-cyanobiphenyl nematic liquid crystals. Dynamic light scattering (DLS) was employed to measure the twist viscoelastic coefficient as a function of temperature and the length of alkoxy chain. Our studies show that the twist viscoelastic coefficient is about three times smaller than that of the ordinary alkoxy-cyanobiphenyl nematic liquid crystals. DLS experiments carried out on this system with applied electric field show that the director relaxation frequency increases. These measurements yield the ratio of dielectric anisotropy to twist viscosity. We have also estimated the activation energy corresponding to twist viscosity.