Anisotropic Dye Adsorption and Anhydrous Proton Conductivity in Smectic Liquid Crystal Networks: The Role of Cross-Link Density, Order, and Orientation.

In this work, the decisive role of rigidity, orientation, and order in the smectic liquid crystalline network on the anisotropic proton and adsorbent properties is reported. The rigidity in the hydrogen-bonded polymer network has been altered by changing the cross-link density, the order by using different mesophases (smectic, nematic, and isotropic phases), whereas the orientation of the mesogens was controlled by alignment layers. Adding more cross-linkers improved the integrity of the polymer films. For the proton conduction, an optimum was found in the amount of cross-linker and the smectic organization results in the highest anhydrous proton conduction. The polymer films show anisotropic proton conductivity with a 54 times higher conductivity in the direction perpendicular to the molecular director. After a base treatment of the smectic liquid crystalline network, a nanoporous polymer film is obtained that also shows anisotropic adsorption of dye molecules and again straight smectic pores are favored over disordered pores in nematic and isotropic networks. The highly cross-linked films show size-selective adsorption of dyes. Low cross-linked materials do not show this difference due to swelling, which decreases the order and creates openings in the two-dimensional polymer layers. The latter is, however, beneficial for fast adsorption kinetics.

On the Dimensional Control of 2 D Hybrid Nanomaterials.

Thermotropic smectic liquid crystalline polymers were used as a scaffold to create organic/inorganic hybrid layered nanomaterials. Different polymers were prepared by photopolymerizing blends of a hydrogen bonded carboxylic acid derivative and a 10 % cross-linker of variable length in their liquid crystalline phase. Nanopores with dimensions close to 1 nm were generated by breaking the hydrogen bonded dimers in a high pH solution. The pores were filled with positively charged silver (Ag) ions, resulting in a layered silver(I)-polymeric hybrid material. Subsequent exposure to a NaBH4 reducing solution allowed for the formation of supported hybrid metal/organic films. In the bulk of the film the dimension of the Ag nanoparticles (NPs) was regulated with subnanometer precision by the cross-linker length. Ag nanoparticles with an average size of 0.9, 1.3, and 1.8 nm were produced inside the nanopores thanks to the combined effect of spatially confined reduction and stabilization of the nanoparticles by the polymer carboxylic groups. At the same time, strong Ag migration occurred in the surface region, resulting in the formation of a nanostructured metallic top layer composed of large (10-20 nm) NPs.

Patterned silver nanoparticles embedded in a nanoporous smectic liquid crystalline polymer network.

A nanoporous smectic liquid crystalline polymer network has been exploited to fabricate photo patternable organic-inorganic hybrid materials, wherein, the nanoporous channels control the diameter and orientational order of the silver nanoparticles.

Partial hydrolysis of poly(2-ethyl-2-oxazoline) and potential implications for biomedical applications?

The hydrolysis of PEtOx is studied to evaluate the potential toxicity of partially hydrolyzed polymers that might interfere with its increasing popularity for biomedical applications. The hydrolysis of PEtOx is studied in the presence of digestive enzymes (gastric and intestinal) and at 5.8 M hydrochloric acid as a function of temperature (57, 73, 90, and 100 °C). It is found that PEtOx undergoes negligible hydrolysis at 37 °C and that thermal and solution properties are not altered when up to 10% of the polymer backbone is hydrolyzed. Mucosal irritation and cytotoxicity is also absent up to 10% hydrolysis levels. In conclusion, PEtOx will not decompose at physiological conditions, and partial hydrolysis will not limit its biomedical applications.

Enhanced selectivity for the hydrolysis of block copoly(2-oxazoline)s in ethanol-water resulting in linear poly(ethylene imine) copolymers.

The ability of merging the properties of poly(2-oxazoline)s and poly(ethylene imine) is of high interest for various biomedical applications, including gene delivery, biosensors, and switchable surfaces and nanoparticles. In the present research, a methodology for the controlled and selective hydrolysis of (co)poly(2-oxazoline)s is developed in an ethanol-water solvent mixture, opening the path toward a wide range of block poly(2-oxazoline-co-ethylene imine) (POx-PEI) copolymers with tunable properties. The unexpected influence of the selected ethanol-water binary solvent mixture on the hydrolysis kinetics and selectivity is highlighted in the pursue of well-defined POx-PEI block copolymers.

Thermoresponsive poly(2-oxazine)s.

The monomers 2-methyl-2-oxazine (MeOZI), 2-ethyl-2-oxazine (EtOZI), and 2-n-propyl-2-oxazine (nPropOZI) were synthesized and polymerized via the living cationic ring-opening polymerization (CROP) under microwave-assisted conditions. pEtOZI and pnPropOZI were found to be thermoresponsive, exhibiting LCST behavior in water and their cloud point temperatures (T(CP)) are lower than for poly(2-oxazoline)s with similar side chains. However, comparison of poly(2-oxazine) and poly(2-oxazoline)s isomers reveals that poly(2-oxazine)s are more water soluble, indicating that the side chain has a stronger impact on polymer solubility than the main chain. In conclusion, variations of both the side chains and the main chains of the poly(cyclic imino ether)s resulted in a series of distinct homopolymers with tunable T(CP).