Orientation of Lamellar Nanostructures in the Patterned Thin Films of a Diblock Copolymer

Methods for Silk Property Analyses across Structural Hierarchies and Scales

Silk from silkworms and spiders is an exceptionally important natural material, inspiring a range of new products and applications due to its high strength, elasticity, and toughness at low density, as well as its unique conductive and optical properties. Transgenic and recombinant technologies offer great promise for the scaled-up production of new silkworm- and spider-silk-inspired fibres. However, despite considerable effort, producing an artificial silk that recaptures the physico-chemical properties of naturally spun silk has thus far proven elusive. The mechanical, biochemical, and other properties of pre-and post-development fibres accordingly should be determined across scales and structural hierarchies whenever feasible. We have herein reviewed and made recommendations on some of those practices for measuring the bulk fibre properties; skin-core structures; and the primary, secondary, and tertiary structures of silk proteins and the properties of dopes and their proteins. We thereupon examine emerging methodologies and make assessments on how they might be utilized to realize the goal of developing high quality bio-inspired fibres.

Enhanced crystallization by the virtue of the complete confinement of a ultrathin poly(3-hexylthiophene) film during the patterning process

The enhanced crystallization of the patterned poly(3-hexylthiophene) film based on the nanoimprinting lithography technique due to complete confinement.

Multiscale mechanisms of nutritionally induced property variation in spider silks

Variability in spider major ampullate (MA) silk properties at different scales has proven difficult to determine and remains an obstacle to the development of synthetic fibers mimicking MA silk performance. A multitude of techniques may be used to measure multiscale aspects of silk properties. Here we fed five species of Araneoid spider solutions that either contained protein or were protein deprived and performed silk tensile tests, small and wide-angle X-ray scattering (SAXS/WAXS), amino acid composition analyses, and silk gene expression analyses, to resolve persistent questions about how nutrient deprivation induces variations in MA silk mechanical properties across scales. Our analyses found that the properties of each spider's silk varied differently in response to variations in their protein intake. We found changes in the crystalline and non-crystalline nanostructures to play specific roles in inducing the property variations we found. Across treatment MaSp expression patterns differed in each of the five species. We found that in most species MaSp expression and amino acid composition variations did not conform with our predictions based on a traditional MaSp expression model. In general, changes to the silk's alanine and proline compositions influenced the alignment of the proteins within the silk's amorphous region, which influenced silk extensibility and toughness. Variations in structural alignment in the crystalline and non-crystalline regions influenced ultimate strength independent of genetic expression. Our study provides the deepest insights thus far into the mechanisms of how MA silk properties vary from gene expression to nanostructure formations to fiber mechanics. Such knowledge is imperative for promoting the production of synthetic silk fibers.

Nanoimprinting-induced molecular orientation in poly(3-hexylthiophene) nanogratings and its extraordinary retention after thermal annealing

Face-on orientation of poly(3-hexylthiophene) nanogratings induced by nanoimprinting and its remarkable retention after thermal annealing.

Maintaining nanoimprinting-induced face-on alignment in poly(3-hexylthiophene) nanopillars after thermal annealing

The nanoimprinting-induced face-on alignment in poly(3-hexylthiophene) nanopillars is surprisingly maintained after thermal annealing.

Self-Assembly of PS-b-PDMS on a Tunable PDMS Template with Nanoscale Channels and Enhanced Anisotropic Wetting

In this article, we systematically studied the self-assembly of poly(styrene-block-dimethylsiloxane) (PS-b-PDMS) on a poly(dimethylsiloxane) (PDMS) substrate with nanoscale channels. The channeled PDMS substrate was achieved by a simple replica molding method. To decrease the effect that the subsequent solvent treatments had in distorting the soft PDMS substrate, a simple UV/O3 treatment was provided before the self-assembly, resulting in a relatively stable, harder and hydrophilic silicon oxide (SiO2) layer on the channeled PDMS surface. Ultimately, the isotropic SiO2 nanopatterns with spherical and long cylindrical morphologies were successfully fabricated by the self-assembly of two kinds of PS-b-PDMS on the PDMS substrate with nanoscale channels, respectively. In particular, we demonstrated that the introduction of isotropic SiO2 patterns is an effective approach to greatly enhance anisotropic wetting rather than that of the anisotropic structure with channels.

Tailoring nanostructures using copolymer nanoimprint lithography

The generation of defect-free polymer nanostructures by nanoimprinting methods is described. Long-range nanorheology and shorter-range surface energy effects can be efficiently combined to provide alignment of copolymer lamellae over several micrometers. As an example, a perpendicular organization with respect to circular tracks is shown, demonstrating the possibility of writing ordered radial nanostructures over large distances.

Phase segregation of a symmetric diblock copolymer in constrained space with a square-pillar array

In this study, we apply a self-consistent field theory of polymers to study the structures of a symmetric diblock copolymer in parallel substrates filled with square-pillar arrays in which the substrates and pillars exhibit a weak preference for one block of the copolymer. Three classes of structures, i.e., lamellae, perpendicular cylinders, and bicontinuous structures, are achieved by varying the polymer film thickness, the pillar pitch (the distance between two centers of the nearest neighboring pillars), the gap and rotation of the pillars. Because of the confinement along horizontal directions imposed by the pillar array, eight novel types of perpendicular lamellar structures and eight novel types of cylindrical structures with various shapes and distributions occur. In the hybridization states of the parallel and perpendicular lamellar structures, several novel bicontinuous structures such as the double-cylinder network, pseudo-lamellae, and perforated lamellar structure are also found. By comparing the free energies of the various possible structures, the antisymmetric parallel lamellae are observed to be stable with the larger pillar gap at a certain film thickness. The structural transformations between the alternating cylindrical structures (alternating cross-shaped, square-shaped, and octagonal perpendicular cylinders) and parallel lamellae with increasing film thickness or pillar gap are well explained by the modified strong separation theory. Our results indicate that array confinement can be an effective method to prepare novel polymeric nanopattern structures.

Sub-10 nm nanofabrication via nanoimprint directed self-assembly of block copolymers

Directed self-assembly (DSA) of block copolymers (BCPs), either by selective wetting of surface chemical prepatterns or by graphoepitaxial alignment with surface topography, has ushered in a new era for high-resolution nanopatterning. These pioneering approaches, while effective, require expensive and time-consuming lithographic patterning of each substrate to direct the assembly. To overcome this shortcoming, nanoimprint molds--attainable via low-cost optical lithography--were investigated for their potential to be reusable and efficiently template the assembly of block copolymers (BCPs) while under complete confinement. Nanoimprint directed self-assembly conveniently avoids repetitive and expensive chemical or topographical prepatterning of substrates. To demonstrate this technique for high-resolution nanofabrication, we aligned sub-10 nm resolution nanopatterns using a cylinder-forming, organic-inorganic hybrid block copolymer, polystyrene-block-polydimethylsiloxane (PS-b-PDMS). Nanopatterns derived from oxidized PDMS microdomains were successfully transferred into the underlying substrate using plasma etching. In the development phase of this procedure, we investigated the role of mold treatments and pattern geometries as DSA of BCPs are driven by interfacial chemistry and physics. In the optimized route, silicon molds treated with PDMS surface brushes promoted rapid BCP alignment and reliable mold release while appropriate mold geometries provided a single layer of cylinders and negligible residual layers as required for pattern transfer. Molds thus produced were reusable to the same efficacy between nanoimprints. We also demonstrated that shear flow during the nanoimprint process enhanced the alignment of the BCP near open edges, which may be engineered in future schemes to control the BCP microdomain alignment kinetics during DSA.

Domain patterns in a diblock copolymer-diblock copolymer mixture with oscillatory particles

We investigate the orientational order transition of striped patterns in microphase structures of diblock copolymer-diblock copolymer mixtures in the presence of periodic oscillatory particles. Under certain conditions, although the macrophase separation of a system is almost isotropic, microphase separation of one diblock copolymer takes place and becomes anisotropic gradually. By changing the oscillatory frequency and amplitude, the orientational order transition of a striped microphase structure from the state parallel to the oscillatory direction to the state perpendicular to the oscillatory direction is observed. We also find that the order transition occurs when we change the initial composition ratio. Furthermore, we examine the domain size and the orientational order parameter of microstructure in the process of orientational order transition. The results may provide guidance for experimentalists. This model system can also give a simple way to realize orientational order transition of soft materials by changing the oscillatory field.

Self-assembly of AB diblock copolymers under confinement into topographically patterned surfaces

Motivated by recent experiments of copolymer patterning by nanoimprinting, we investigate microphase separation and morphology for symmetric AB diblock copolymers with lamellar structure in bulk, confined between a flat bottom surface and a square-wave top surface by using the self-consistent field theory (SCFT). The efficient and high-order accurate pseudospectral method is adopted to numerically solve the SCFT equations in irregularly shaped domains with the help of the "masking" technique by embedding the confined domains of arbitrary shape within a larger rectangular computational cell. Our simulations reveal that the inverted T-style and trapezoid structures occurring in the relatively strong and weak surface fields, respectively, are following our topographically patterned surface. For neutral walls, when the thickness of the lower section is commensurate with the lamellae period of bulk block copolymers, the topographically patterned surface in this work leads to parallel lamellae, and completely parallel lamellae are favored when both the width and height of the upper section are equal to the lamellae bulk period. Furthermore, the prevalent structures are the parallel lamellae in the upper section combined with the perpendicular lamellae in the lower section. When the walls repel one of the block species, parallel lamellae occur in a wide range of film thicknesses compared to the case of neutral walls. To our knowledge, some new structures, however, such as square and partial square structures and reversed-T and trapezoid structures, have not been reported before under parallel surface confinement. In general, the required structures can be obtained by choosing the proper degree of spatial confinement, characterized by variations of the ratio of film thicknesses to bulk repeat period, and the block-substrate interactions. Moreover, we show that the confinement width of the lower section (or the period of the square wave) plays a critical role in microstructure formation. These findings provide a guide to designing novel microstructures involving symmetric diblock copolymers via topographically patterned surfaces and surface fields, relevant to nanoimprinting.