The routine formation of nanometer-sized structures remains a challenge that limits advances in many fields of nanotechnology. Increasingly ªbottom±upº self-assembly approaches for the nanometer-scale patterning of surfaces are competing with traditional ªtop±downº lithographic processes such as scanned-probe lithography or high-resolution electron-beam (e-beam) lithography. Block copolymer thin films (< 100 nm) are among the more promising materials being examined as they offer ease of processing combined with phase separation induced structure formation on the nanometer scale.Recent work in block copolymer thin film pattern formation has included the use of poly(styrene-block-isoprene) to form periodic structures combined with ozonolysis to remove the isoprene phase, thereby creating arrays of holes in the polymer thin film.[1] In another case, poly(styrene-blockmethyl methacrylate) has been processed in electric fields to align a cylinder phase perpendicular to the film surface, and subsequently exposed to UV light to both mildly crosslink the styrene phase and degrade the methyl methacrylate domains.[2] Similar strategies have been employed to process other block copolymer systems that contain a variety of chemical structures and architectures.[3] Examples of desirable target applications of such porous thin films include photonic bandgap materials, structures to serve as molecular sieves, or templates for magnetic structures.[4]A typical means for improving the processing of bulk polymers is through the use of small-molecule additives.[5] While such additives in bulk polymer structures are ubiquitous, their application in block copolymer thin film processing has not been substantially explored to date. Given the enormous numbers of property variations possible this is surprising. Here we will show several strategies for the use of additivedriven chemistries that take place in only one type of the nanosized domains of block copolymer thin films. We then use such an approach to examine the convergence of ªtop± downº with ªbottom±upº fabrication through light-driven processes.In Figure 1, the structures of the three polymer systems and their respective phase selective additives are introduced. They are: (system 1) poly(a-methyl styrene-b-4-hydroxystyrene) (P(aMS-b-HOST)) and tetramethoxymethyl glycuril (TMMU) with photoacid generator; (system 2) poly(a-methyl styrene-b-isoprene) (P(aMS-b-I)) and 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO); and (system 3) poly(isoprene-b-ethylene oxide), (P(I-b-EO)) and 3-glycidoxypropyltrimethoxysilane/aluminum sec-butoxide (GLYMO)/ Al(O s Bu) 3 . While the first two systems are all-organic, in the case of P(I-b-EO) inorganic additives were used. All polymers were produced using living anionic polymerization, because of its excellent control of architecture and molecular weight (Fig. 1). Films of various controlled thicknesses down to monolayer (see below) were obtained by spin-coating from dilute solution onto silicon wafers.Selection of the appropriate chemistry makes...

In this report, we show that the microstructures of hydrogen‐bonded side‐chain liquid‐crystalline block copolymers can be rapidly aligned in an alternating current (AC) electric field at temperatures below the order–disorder transition but above the glass transition. The structures and their orientation were measured in real time with synchrotron X‐ray scattering. Incorporation of mesogenic groups with marked dipolar properties is a key element in this process. A mechanism related to the dissociation of hydrogen bonds is proposed to account for the fast orientation switching of the hydrogen‐bonded blends.

No abstract

No abstract

No abstract