Nanostructured Thin Films of Moderately Functionalized PMMA-b-PS.

A library of poly(methyl methacrylate)-block-polystyrene (PMMA-b-PS) block copolymers (BCPs) bearing small amounts (<10 mol%) of functional comonomer in either one or both blocks is investigated for their phase separation behavior in bulk and in thin films. Particularly, functionalities typically involved in modern postpolymerization modifications are considered, e.g., azide, pentafluorophenyl, furfuryl. Small-angle X-ray scattering and atomic force microscopy are employed to determine the characteristic dimensional features of lamellae-forming BCPs, which differ essentially in the functional groups. It is shown that the presence of the reactive moieties does not perturb the ability to phase separate in bulk, yet has an impact on the dimensions of the domains. Using a classic two-step procedure involving surface neutralization with a statistical PMMA-co-PS copolymer, it is observed that some functional copolymers are not able to form homogeneous thin films. Solvent stability and crosslinking ability of the films are then briefly assessed as a first step to establishing the functional films as nanoresolved molecular immobilization platform with feature sizes of 20 nm and below.

Design Strategies for Structurally Controlled Polymer Surfaces via Cyclophane-Based CVD Polymerization and Post-CVD Fabrication.

Molecular structuring of soft matter with precise arrangements over multiple hierarchical levels, especially on polymer surfaces, and enabling their post-synthetic modulation has tremendous potential for application in molecular engineering and interfacial science. Here, recent research and developments in design strategies for structurally controlled polymer surfaces via cyclophane-based chemical vapor deposition (CVD) polymerization with precise control over chemical functionalities and post-CVD fabrication via orthogonal surface functionalization that facilitates the formation of designable biointerfaces are summarized. Particular discussion about innovative approaches for the templated synthesis of shape-controlled CVD polymers, ranging from 1D to 3D architecture, including inside confined nanochannels, nanofibers/nanowires synthesis into an anisotropic media such as liquid crystals, and CVD polymer nanohelices via hierarchical chirality transfer across multiple length scales is provided. Aiming at multifunctional polymer surfaces via CVD copolymerization of multiple precursors, the structural and functional design of the fundamental [2.2]paracyclophane (PCP) precursor molecules, that is, functional CVD monomer chemistry is also described. Technologically advanced and innovative surface deposition techniques toward topological micro- and nanostructuring, including microcontact printing, photopatterning, photomask, and lithographic techniques such as dip-pen nanolithography, showcasing research from the authors' laboratories as well as other's relevant important findings in this evolving field are highlighted that have introduced new programmable CVD polymerization capabilities. Perspectives, current limitations, and future considerations are provided.

Surfaces Decorated with Enantiomorphically Pure Polymer Nanohelices via Hierarchical Chirality Transfer across Multiple Length Scales.

Mesoscale chiral materials are prepared by lithographic methods, assembly of chiral building blocks, and through syntheses in the presence of polarized light. Typically, these processes result in micrometer-sized structures, require complex top-down manipulation, or rely on tedious asymmetric separation. Chemical vapor deposition (CVD) polymerization of chiral precursors into supported films of liquid crystals (LCs) are discovered to result in superhierarchical arrangements of enantiomorphically pure nanofibers. Depending on the molecular chirality of the 1-hydroxyethyl [2.2]paracyclophane precursor, extended arrays of enantiomorphic nanohelices are formed from achiral nematic templates. Arrays of chiral nanohelices extend over hundreds of micrometers and consistently display enantiomorphic micropatterns. The pitch of individual nanohelices depends on the enantiomeric excess and the purity of the chiral precursor, consistent with the theoretical model of a doubly twisted LC director configuration. During CVD of chiral precursors into cholesteric LC films, aspects of molecular and mesoscale asymmetry combine constructively to form regularly twisted nanohelices. Enantiomorphic surfaces permit the tailoring of a wide range of functional properties, such as the asymmetric induction of weak chiral systems.