Synthesis of Amphiphilic Naturally-Derived Oligosaccharide-block-Wax Oligomers and Their Self-Assembly.

Self-assembly characteristics of amphiphilic macromolecules into micelles, nanoparticles and vesicles has been of fundamental interest for many applications including designed nanoscale therapeutic delivery systems and enzymatic reactors. In this work, a class of amphiphilic block oligomers was synthesized from naturally occurring oligosaccharides and aliphatic alcohol precursors, which are all currently prominent in the pharmaceutical, food, and supplement industries. These block oligomer materials were synthesized by functionalization of the precursor materials followed by subsequent coupling by azide-alkyne cycloaddition and their bulk self-assembly was investigated after solvent vapor annealing. Self-assembly of the amphiphilic materials into liposomes in aqueous solution was also investigated after preparing solutions using a nanoprecipitation method. Encapsulation of hydrophobic components was demonstrated and verified using dynamic light scattering, transmission electron microscopy, and fluorescence spectroscopy experiments.

Consequences of surface neutralization in diblock copolymer thin films.

Two high-χ block copolymers, lamella-forming poly(styrene-block-[isoprene-random-epoxyisoprene]) (PS-PEI78, with 78 mol % epoxidation) and lamella-forming poly(4-trimethylsilylstyrene-block-d,l-lactide) (PTMSS-PLA), were used to study three combinations of interfacial neutrality involving at least one neutral interface. PS-PEI78 annealed on a nonpreferential polymer mat (SMG) produced perpendicular lamellae independent of film thickness, indicating a neutral substrate and neutral free surface. In contrast, the presence of only one neutral interface results in the formation of surface topography ("islands" and "holes") with 0.5L0 step heights. PS-PEI78 (neutral free surface) annealed on PS brush (PS block preferential) forms "half" islands and holes. The inverse experiment, PTMSS-PLA (with a PTMSS preferential free surface) annealed on a neutral (or near neutral) substrate surface, also generates 0.5L0 topography. These "half" island and hole structures are stable to extended thermal annealing. PS-PEI78 exposes both blocks at the free surface in contrast to PTMSS-PLA, which exposes just one. All three combinations of interfacial neutrality are explained by the precise balancing of the wetting tendencies of the two blocks. Evolution of the 0.5L0 motifs appears to be facilitated by a preference to form half-period thick nuclei in the initial stages of morphological development.

Patterning by Photochemically Directing the Marangoni Effect.

Polystyrene (PS) that has been exposed to ultraviolet light (UV) undergoes partial dehydrogenation of the alkane polymer backbone which increases its surface energy. Exploiting this photochemistry, we exposed polystyrene films to UV light using a photomask to induce a patterned photochemical reaction producing regions in the film with differing surface energy. Upon heating the solid polymer film with the preprogrammed surface energy pattern to a liquid state, the polymer flows from the low surface energy unexposed regions to high surface energy exposed regions. This flow creates three-dimensional topography by the Marangoni Effect, which describes convective mass transfer due to surface energy gradients. The topographical features can be permanently preserved by quenching the film below its glass to liquid transition temperature. Their shape and organization are only limited by the pattern on the photomask.

Polarity-switching top coats enable orientation of sub-10-nm block copolymer domains.

Block copolymers (BCPs) must necessarily have high interaction parameters (χ), a fundamental measure of block incompatibility, to self-assemble into sub-10-nanometer features. Unfortunately, a high χ often results from blocks that have disparate interfacial energies, which makes the formation of useful thin-film domain orientations challenging. To mitigate interfacial forces, polymers composed of maleic anhydride and two other components have been designed as top coats that can be spin-coated from basic aqueous solution in the ring-opened, acid salt form. When baked, the anhydride reforms and switches polarity to create a neutral layer enabling BCP feature alignment not possible by thermal annealing alone. Top coats were applied to the lamella-forming block copolymers poly(styrene-block-trimethylsilylstyrene-block-styrene) and poly(trimethylsilylstyrene-block-lactide), which were thermally annealed to produce perpendicular features with linewidths of 15 and 9 nanometers, respectively.

Oligosaccharide/silicon-containing block copolymers with 5 nm features for lithographic applications.

Block copolymers demonstrate potential for use in next-generation lithography due to their ability to self-assemble into well-ordered periodic arrays on the 3-100 nm length scale. The successful lithographic application of block copolymers relies on three critical conditions being met: high Flory-Huggins interaction parameters (χ), which enable formation of <10 nm features, etch selectivity between blocks for facile pattern transfer, and thin film self-assembly control. The present paper describes the synthesis and self-assembly of block copolymers composed of naturally derived oligosaccharides coupled to a silicon-containing polystyrene derivative synthesized by activators regenerated by electron transfer atom transfer radical polymerization. The block copolymers have a large χ and a low degree of polymerization (N) enabling formation of 5 nm feature diameters, incorporate silicon in one block for oxygen reactive ion etch contrast, and exhibit bulk and thin film self-assembly of hexagonally packed cylinders facilitated by a combination of spin coating and solvent annealing techniques. As observed by small angle X-ray scattering and atomic force microscopy, these materials exhibit some of the smallest block copolymer features in the bulk and in thin films reported to date.