Density Multiplication of Highly Periodic Sub-5 nm Supramolecular Dendrimer Cylinders on Block Copolymer Lamellar-Assisted High-Resolution Patterns.

Density multiplication in nanopatterning is one of the most efficient techniques for increasing the resolution of the inherent patterns. Thus far, most of the density multiplication techniques integrate bottom-up (or top-down) patterning onto guide patterns prepared by the top-down approach. Although the bottom-up approach exhibits several advantages of cost-effectiveness and high resolution, very few studies have reported bottom-up patterning within a bottom-up template. In this study, the density multiplication of supramolecular cylinders into a block copolymer (BCP)-based guide lamellar pattern is demonstrated by the directed self-assembly (DSA) of a dendrimer and BCPs for the first time. Supramolecular cylinders of sub-5 nm scale are confined into trenches based on 50 and 100 nm scales of a lamellar polystyrene (PS)-poly(methyl methacrylate) (PMMA) BCP, which led to 10×-level to 20×-level density multiplication. Moreover, the orientation of the dendrimer is dependent on the dendrimer film thickness, and the corresponding mechanism is revealed. Notably, the strong guiding effect from the high-resolution guide patterns improved the ordering behavior in the highly curved pattern. Graphoepitaxy via the confinement of an ultrahigh-resolution dendrimer into the guide pattern based on BCP demonstrates promise as a density multiplication method for generating highly ordered nanostructures and complex structures.

Facile Synthesis of Self-Adhesion and Ion-Conducting 2-Acrylamido-2-Methylpropane Sulfonic Acid/Tannic Acid Hydrogels Using Electron Beam Irradiation.

Tannic acid (TA) can be used as an additive to improve the properties of hydrogels, but it acts as a radical scavenger, which hinders radical polymerization. In this study, we successfully and easily synthesized a TA-incorporated 2-acrylamido-2-methylpropanesulfonic acid (AMPS) hydrogel using an electron beam (E-beam) in a one-pot process at room temperature. TA successfully grafted onto AMPS polymer chains under E-beam irradiation, but higher TA content reduced grafting efficiency and prevented hydrogel formation. Peel strength of the AMPS hydrogel increased proportionally with TA, but cohesive failure and substrate residue occurred above 1.25 phm (parts per 100 g of AMPS) TA. Tensile strength peaked at 0.25 phm TA but decreased below the control value at 1.25 phm. Tensile elongation exceeded 2000% with TA addition. Peel strength varied significantly with substrate type. The wood substrate had the highest peel strength value of 150 N/m, while pork skin had a low value of 11.5 N/m. However, the addition of TA increased the peel strength by over 300%. The ionic conductivity of the AMPS/TA hydrogel increased from 0.9 S/m to 1.52 S/m with TA content, while the swelling ratio decreased by 50% upon TA addition and increased slightly thereafter.

Correction: Preparation of UV-curable PSAs by grafting isocyanate-terminated photoreactive monomers and the effect of the functionality of grafted monomers on the debonding properties on Si wafers.

[This corrects the article DOI: 10.1039/D3RA00398A.].

Preparation of UV-curable PSAs by grafting isocyanate-terminated photoreactive monomers and the effect of the functionality of grafted monomers on the debonding properties on Si wafers.

Photoreactive pressure-sensitive adhesives (PSAs) were prepared by grafting mono- or difunctional photoreactive monomers onto acrylic PSA, and their adhesion properties were evaluated before and after ultraviolet (UV) curing for application as dicing tape. In this study, the NCO-terminated difunctional photoreactive monomer (NDPM) was newly synthesized and compared with 2-acryloxyloxyethyl isocyanate (AOI), a monofunctional monomer. The 180° peel strengths of pristine and photoreactive PSAs were similar before UV curing (1850-2030 gf/25 mm). After UV curing, the 180° peel strengths of the photoreactive PSAs decreased significantly and converged to nearly zero. When a UV dose of 200 mJ cm-2 was used, the 180° peel strength of 40% NDPM-grafted PSA decreased to 8.40 gf/25 mm, which was much lower than that of 40% AOI-grafted PSA (39.26 gf/25 mm). NDPM-grafted PSA also showed that its storage modulus shifted more to the upper right side of Chang's viscoelastic window than AOI-grafted PSA, and this is because NDPM provided a higher degree of crosslinking than AOI. Furthermore, SEM-EDS analysis showed that UV-cured NDPM-grafted PSA retained almost no residue on the silicon wafer after debonding.

All polymeric conductive strain sensors with excellent skin adhesion, recovery, and long-term stability prepared from an anion-zwitterion based hydrogel.

Developing a high-performing hydrogel with long-lasting skin adhesion, high ionic conductivity, mechanical stability, and fatigue resistance is a crucial issue in the field of wearable electronic devices. Because of their weak mechanical properties, zwitterion-based hydrogels are not suitable for application in wearable strain sensors despite their excellent adhesion to the skin. In this study, a hydrogel of polymer without additive was prepared by using polymerizable monomers consisting of zwitterionic 3-(1-vinyl-3-imidazolio)propanesulfonate (VIPS), anionic 2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt (AMPSs), and acrylamide (AAm); the hydrogel is abbreviated as P(AMPSs/VIPS-co-AAm). The P(AMPSs/VIPS-co-AAm) hydrogel shows exceptional adhesive strength, reaching up to 26.29 kPa (lap shear to porcine skin) and high stretchability (with a fracture strain of 1282% and stress of 40 kPa). The high polarity of the AMPSs/VIPS pair improves the interfacial adhesion to the skin, the internal cohesion and recovery tendency. Unique structural characteristics of the hydrogel impart excellent fatigue resistance, network toughening, and electrical stability after multiple deformations. Thus, the prepared hydrogel has an ionic conductivity (0.51 S m-1), strain sensitivity, and long-term skin adhesion, and it demonstrates potential to be applied for wearable strain sensors.

Synthesis and Assessment of AMPS-Based Copolymers Prepared via Electron-Beam Irradiation for Ionic Conductive Hydrogels.

In this study, ionic conductive hydrogels were prepared with 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS). Acrylic acid (AA), acrylamide (AAm), and 2-hydroxyethyl acrylate (HEA) were used as comonomers to complement the adhesion properties and ion conductivity of AMPS hydrogels. Hydrogels were prepared by irradiating a 20 kGy dose of E-beam to the aqueous monomer solution. With the E-beam irradiation, the polymer chain growth and network formation simultaneously proceeded to form a three-dimensional network. The preferred reaction was determined by the type of comonomer, and the structure of the hydrogel was changed accordingly. When AA or AAm was used as a comonomer, polymer growth and crosslinking proceeded together, so a hydrogel with increased peel strength and tensile strength could be prepared. In particular, in the case of AA, it was possible to prepare a hydrogel with improved adhesion without sacrificing ionic conductivity. When the molar ratio of AA to AMPS was 3.18, the 90° peel strength of AMPS hydrogel increased from 171 to 428 gf/25 mm, and ionic conductivity slightly decreased, from 0.93 to 0.84 S/m. By copolymerisation with HEA, polymer growth was preferred compared with chain crosslinking, and a hydrogel with lower peel strength, swelling ratio, and ionic conductivity than the pristine AMPS hydrogel was obtained.

Wafer-Scale Unidirectional Alignment of Supramolecular Columns on Faceted Surfaces.

The long-range alignment of supramolecular structures must be engineered as a first step toward advanced nanopatterning processes aimed at miniaturizing features to dimensions below 5 nm. This study introduces a facile method of directing the orientation of supramolecular columns over wafer-scale areas using faceted surfaces. Supramolecular columns with features on the sub-5 nm scale were highly aligned in a direction orthogonal to that of the facet patterning on unidirectional and nanoscopic faceted surface patterns. This unidirectional alignment of supramolecular columns is also observed by varying the thickness of the supramolecular film or by altering the dimensions of the facet pattern. The ordering behavior of the supramolecular columns can be attributed to the triangular depth profile of the bottom facet pattern. Furthermore, this directed self-assembly principle allows for the continuous alignment of supramolecular structures across ultralarge distances on flexible patterned substrates.

Comparative Study of the Impact Wedge-Peel Performance of Epoxy Structural Adhesives Modified with Functionalized Silica Nanoparticles.

Epoxy structural adhesives have strong adhesion, minimal shrinkage and high thermal and chemical resistance. However, despite these excellent properties, their high-energy impact resistance should be improved to satisfy the increasing demands of the automotive industry. For this reason, we used four types of silica nanoparticles with different surface groups, such as polydimethylsiloxane (PDMS), hydroxyl, epoxy and amine groups, as toughening agents and examined their effect on the glass transition temperature (Tg), crosslinking density and phase separation of epoxy structural adhesives. High-energy impact resistance, mode I fracture toughness and lap shear strength were also measured to explain the effect of surface functional groups. Silica nanoparticles with reactive functional groups increased the mode I fracture toughness of epoxy structural adhesives without sacrificing the crosslinking density. Although the mode I fracture toughness of epoxy structural adhesives could not clearly show the effect of surface functional groups, the dynamic resistance to cleavage obtained by impact wedge-peel tests showed quite different values. At a 0.3 vol% content, epoxy-functionalized silica nanoparticles induced the highest value (40.2 N/mm) compared to PDMS (34.1 N/m), hydroxyl (34.9 N/mm), and amine (36.1 N/m). All of these values were significantly higher than those of pristine epoxy structural adhesive (27.7 N/mm).

Enhanced Heat Resistance of Acrylic Pressure-Sensitive Adhesive by Incorporating Silicone Blocks Using Silicone-Based Macro-Azo-Initiator.

To improve the heat resistance of acrylic-based pressure-sensitive adhesive (PSA), silicone-block-containing acrylic PSAs (SPSAs) were synthesized using a polydimethylsiloxane (PDMS)-based macro-azo-initiator (MAI). To evaluate the heat resistance of the PSA films, the probe tack and 90° peel strength were measured at different temperatures. The acrylic PSA showed that its tack curves changed from balanced debonding at 25 °C to cohesive debonding at 50 °C and exhibited a sharp decrease. However, in the case of SPSA containing 20 wt% MAI (MAI20), the balanced debonding was maintained at 75 °C, and its tack value hardly changed with temperature. As the MAI content increased, the peel strength at 25 °C decreased due to the microphase separation between PDMS- and acryl-blocks in SPSA, but the shear adhesion failure temperature (SAFT) increased almost linearly from 41.3 to 122.8 °C. Unlike stainless steel substrate, SPSA showed improved peel strength on a polypropylene substrate due to its low surface energy caused by PDMS block. Owing to the addition of 20 wt% silicone-urethane dimethacrylate oligomer and 200 mJ/cm2 UV irradiation dose, MAI20 showed significantly increased 90° peel strength at 25 °C (548.3 vs. 322.4 gf/25 mm for pristine MAI20). Its heat resistance under shear stress assessed by shear adhesion failure test (SAFT) exhibited raising in failure temperature to 177.3 °C when compared to non-irradiated sample.

Large-Area Alignment of Supramolecular Columns by Photothermal Laser Writing.

Controlling the orientation of highly periodic supramolecular structures of small feature size (<5 nm) is the first step for potential applications in optoelectronics, membranes, and template synthesis. A new method, namely, laser photothermal writing, is introduced to direct the orientation of supramolecular columns over a large area. Supramolecular columns consisting of taper-shaped molecules with long aliphatic tail groups are aligned by a thermal gradient, which is induced by exposing a near-infrared laser beam to a graphene photothermal conversion layer. Intriguingly, the orientation of the supramolecular columns can be controlled in a facile manner by varying the laser scanning velocity and power. In contrast to previous methodologies for aligning supramolecular structures, this laser photothermal mechanism allows the directional and continuous alignment of supramolecular structures over an arbitrary large area with the easy control of laser irradiation. Besides, the laser process also enables area-selective orientation of the supramolecular structures for device-oriented nanopatterning.

Ultra-dense (~20 Tdot/in2) nanoparticle array from an ordered supramolecular dendrimer containing a metal precursor.

The fabrication of an ultra-dense, highly periodic nanoparticle array from a soft template is one of the most important issues in the fields of material science and nanotechnology. To date, block copolymer (BCP) structures have been primarily used as templates for fabricating highly periodic nanoparticle arrays with high areal densities. Herein, we demonstrate for the first time the use of a supramolecular dendrimer assembly for the formation of a highly ordered nanoparticle array with a high areal density of ~20 Tdot/in2, four times larger than that of the currently reported BCP-based nanoparticle arrays. By the simple thermal annealing of a dendrimers containing a metal precursor between two flat, solid substrates, a hexagonal array of small gold nanoparticles (with a diameter of ~1.6 nm and center-to-center distance of ~5.3 nm), oriented normal to the bottom, was achieved. Density functional theory calculations demonstrated that the gold cation strongly bound to the head group of the dendrimer. This structure served as a building block for self-assembly into a stable cylindrical structure. We anticipate that this study will lead to the creation of a large family of supramolecular dendrimers that can be utilized as soft templates for creating periodic, ultra-dense nanoparticle arrays.

Long-range single domain array of a 5 nm pattern of supramolecules via solvent annealing in a double-sandwich cell.

In nanotechnology and microelectronics research, the generation of an ultradense, single-grain nanostructure with a long-range lateral order is challenging. In this paper, we report upon a new solvent-annealing method using a double-sandwich confinement to promote the formation of a large-area, single-domain array (>0.3 × 0.3 mm2) of supramolecular cylinders with a small feature size (4.7 nm). The in situ GISAXS experiment result shows the ordering process during solvent evaporation. The diffusion of the solvent molecules led to the disassembly of the supramolecules confined between the top and bottom surfaces and their subsequent mobilization, thereby producing a highly ordered hexagonal array of supramolecular materials under the double-sandwich confinement upon solvent evaporation. In addition, two key factors were found to be crucial in this process for generating highly-ordered supramolecular building blocks: (i) the presence of a top coat during solvent evaporation to provide a geometric confinement template, and (ii) the control of the solvent evaporation rate during the solvent evaporation step to provide the dendrimer sufficient time to self-assemble into the highly ordered state over a large area. Our developed approach, which can be extended to be used for a large family of supramolecules, is of critical importance in providing a new bottom-up lithographic method based on supramolecular self-assembly.

Controlling Smectic Liquid Crystal Defect Patterns by Physical Stamping-Assisted Domain Separation and Their Use as Templates for Quantum Dot Cluster Arrays.

Controlling the organization of self-assembling building blocks over a large area is crucial for lithographic tools based on the bottom-up approach. However, the fabrication of liquid crystal (LC) defect patterns with a particular ordering still remains a challenge because of the limited close-packed morphologies of LC defects. Here, we introduce a multiple-stamping domain separation method for the control of the dimensions and organization of LC defect structures. Prepatterns with various grid shapes on planar polyimide (PI) surfaces were fabricated by pressing a line-shaped stamp into the PI surfaces in two different directions, and then these surfaces were used to prepare LC defect structures confined to these grid domains. The dimensions of the LC defect structures, namely, the equilibrium diameter and the center to center spacing, are controlled by varying the line spacing of the stamps and the film thickness. A variety of arrangements of LC defects, including square, rhombic, hexagonal, and other oblique lattices, can be obtained by simply varying the stamping angle (Ω) between the first and second stamping directions. Furthermore, we demonstrate that the resulting controllable LC defect arrays can be used as templates for generating various patterns of nanoparticle clusters by trapping quantum dots (QDs) within the cores of the LC defects.

Direct Observation of Highly Ordered Dendrimer Soft Building Blocks over a Large Area.

Developing large-area, single domain of organic soft-building blocks such as block copolymers, colloids, and supramolecular materials is one of the most important issues in the materials science and nanotechnology. Owing to their small sizes, complex molecular architectures, and high mobility, supramolecular materials are not well-suited for building large area, single domain structures. In the described study, a single domain of supramolecular columnar dendrimers was created over large area. The columnar structures in these domains have smaller (4.5 nm) diameters, higher area densities (ca. 36 Tera-dots/in(2)) and larger domains (>0.1 × 0.1 mm(2)) than those of all existing BCP and colloidal assemblies. By simply annealing dendrimer thin films between two flat solid surfaces, single domains of hexagonal columnar structures are created over large macroscopic areas. Observations made in this effort should serve as the foundation for the design of new routes for bottom-up lithography based on supramolecular building blocks.