Controlling Domain Spacing and Grain Size in Cylindrical Block Copolymer Thin Films by Means of Thermal and Solvent Vapor Annealing

Real-time grazing-incidence small-angle X-ray scattering (GISAXS) experiments were used to study the self-assembly of cylinder-forming block copolymers (BCPs) in thin films during thermal annealing and solvent vapor annealing. BCP thin films were annealed in near-neutral solvent vapor for solvent vapor annealing and on a hot plate under an inert gas atmosphere for thermal annealing. The initially ordered films were heated or swollen to induce an order–disorder transition (ODT) and then cooled or the solvent was removed, respectively. The domain spacings of BCPs as determined from <i>in situ</i> GISAXS measurements during solvent removal and cooling were analyzed with respect to the polymer concentration and the reciprocal temperature. Close to the ODT the domain spacing was found to be nearly identical for thermal and solvent vapor annealing. At lower solvent concentrations ϕ and lower temperatures <i>T</i>, the domain spacing was found to increase for both thermal and solvent vapor annealing until structural reorganization in the film was limited by the slow kinetics at solvent concentrations and temperatures close to the glass transition. In this regime, the domain spacing in solvent annealed films was found to be higher than that in thermally annealed films, which is likely due to a significantly smaller diffusion coefficient in the case of thermal annealing. On the basis of an <i>ex situ</i> scanning electron microscopy characterization of annealed block copolymer thin films, we show that the grain size of the cylindrical microdomains can be strongly increased by annealing films close to the ODT. Well below ϕ_ODT and <i>T</i>_ODT the formation of large grains is kinetically limited. In thermally annealed films the grain size was found to be smaller than that for the solvent annealed films, which was attributed to a smaller diffusion coefficient in the absence of solvent

Circular Nanopatterns over Large Areas from the Self-Assembly of Block Copolymers Guided by Shallow Trenches

We report the fabrication of ultradense circular nanolines of block copolymer (BCP) microdomains over macroscopic areas. These lines were generated by the directed self-assembly (DSA) of BCPs on the topographically patterned substrates, where the trenches with circular shape are patterned on a flat substrate. The width of the trench and the distance between trenches are varied for commensurability issues, and difference BCPs are used to demonstrate the generality of this strategy. When a commensurability condition is satisfied, BCPs on the topographically patterned substrates undergo a DSA with solvent annealing, resulting in a flat film with an areal density amplification of the circular patterns over large areas. The methodology described here may provide an easy approach to high densities of circularly shaped nanopatterns for data storage device manufacturing

Carbohydrate-Containing Conjugated Polymers: Solvent-Resistant Materials for Greener Organic Electronics

Organic semiconducting polymers are exciting materials for electronic applications because of their good mechanical and optoelectronic properties. A major advantage of organic semiconductors is their solution processability. This allows access to a variety of simple and cost-effective device fabrication methods compared to the expensive, high-temperature processing methods required for silicon-based electronics. However, these materials often have low solubility, which limits their processing to toxic halogenated solvents. Also, their limited solubility often leads to interfacial mixing during device fabrication. This work explores the incorporation of environmentally friendly carbohydrate side chains in conjugated polymers to enhance processability in eco-friendly solvents. Moreover, a mild postprocessing treatment was designed to enable solvent resistance. Isoindigo-based polymers with varied ratios of acetyl-protected galactose side chains were synthesized to improve solubility in o-anisole in the protected state, while inducing solvent resistance through intramolecular hydrogen bonding in the deprotected state. Solvent resistance was confirmed both visually upon submersion in various solvents and using UV–visible spectroscopy. Importantly, the mild basic treatment to achieve solvent resistance has no negative impact on the electronic performance of these materials in organic field-effect transistors, even after subsequent submersion in various solvents, making them a valuable platform for the production of green processable multilayer electronics

Ptychography of Organic Thin Films at Soft X‑ray Energies

Organic photovoltaics (OPV) are a sustainable and inexpensive source of energy comprised of a mixture of an electron-donating and an electron-accepting material (often a polymer and fullerene derivative, respectively) to create a bulk heterojunction (BHJ). However, these devices are held back by low efficiencies. Improving the efficiency in a systematic way requires a comprehensive understanding of the device function and microstructure, but directly imaging the subsurface active layer structure is challenging. Here we demonstrate that ptychography may be used to image the OPV active layer with good film stability and materials contrast in both polymer:fullerene and all-polymer BHJ films. This is possible using soft X-ray ptychography available at the Advanced Light Source beamline 5.3.2.1. We achieve a resolution of 30–50 nm with no discernible radiation damage and discuss the potential for further improvements. This characterization technique could complement widely used electron microscopy and soft X-ray scattering

Side Chain Effects on the Conductivity of Phenothiazine-Derived Polyaniline

Side chain alkyl groups have become the standard for incorporating solubilizing groups into conjugated polymers. However, the variety of alkyl groups available and their location on the polymer’s backbone can contribute to the packing of the polymer chains in many different ways, resulting in many different morphologies in the polymer that can affect its properties and performances. In this paper, we investigate the effects on the conductivity of nine phenothiazine-containing polyaniline derivatives (P1–P9) with alkyl or aryl side chains on the phenothiazine core while also varying the number of methyl groups on the p-phenylenediamine unit. 1H nuclear magnetic resonance spectroscopy, ultraviolet–visible spectroscopy, differential scanning calorimetry, scanning electron microscopy, atomic force microscopy, and wide-angle X-ray scattering (WAXS) were all used to study the polymers’ structures, physical and thermal properties, and morphologies. The t-butylphenyl substituent on the phenothiazine core seems to provide more rigidity in the polymer’s backbone resulting in higher Tg for series 3, while series 2 containing the 2-hexyldecyl-substituted polymers had the lowest Tg, which is attributed to the large volume of the side chain, that limits interchain interactions. Consequently, series 2 had the lowest conductivity. However, the strongest effect on the conductivity was seen from the tetramethyl groups on the PPDA unit, which resulted in the lowest conductivity in each series due to torsional strain (twisting) in the polymer’s backbone. The WAXS data suggest mostly amorphous films; thus, the conductivity in these materials seems to be dominated by a multiscale charge transport phenomenon that occurs in amorphous conjugated materials. Our results will aid in the understanding of side chain engineering of PANI derivatives for their optimum performances

Elucidating the Role of Hydrogen Bonds for Improved Mechanical Properties in a High-Performance Semiconducting Polymer

Incorporation of hydrogen bond moieties into the backbone or side chain of conjugated polymers is an effective strategy to enhance mechanical performance, facilitate morphological organization, and promote self-healing ability. However, the understanding of hydrogen bonds, particularly the effect of bond strength and directionality, on thermomechanical and optoelectronic performance is still in its infancy due to the competing influence of morphology, glass transition phenomena, and the measurement process itself. Here, we compare the influence of statistically incorporated amide and urea moieties on the mechanical properties of DPP-TVT parent polymers. We observed a profound difference in ductility; amide functionalization increases the strain at failure by over 100% relative to the pure DPP-TVT polymer, while urea functionalization results in a loss of strain at failure by 50%. This is attributed to the crystalline behavior of functionalized conjugated polymers that is promoted by intermolecular interactions of urea groups, which we elucidated via an in-depth investigation of the swelling, crystalline packing, thermal behavior, and strain-dependent charge transport. Furthermore, we employed a novel free-standing tensile test to validate our mechanical measurements supported on a water surface. Our results demonstrated that hydrogen bond moieties must be carefully chosen to achieve a delicate balance of morphological control and mechanical performance, as simply increasing the hydrogen bond strength can result in detrimental mechanical and electrical performance

Roll-to-Roll Scalable Production of Ordered Microdomains through Nonvolatile Additive Solvent Annealing of Block Copolymers

A new method, “nonvolatile solvent vapor annealing” (NVASA), has been developed to anneal block copolymers during film deposition by controlling the solvent drying process. Precise amounts of high boiling point additive added to the polymer solution briefly remain in the polymer film after casting, leaving the film in a swollen state, increasing its chain mobility, and ultimately improving domain order. We demonstrated the effectiveness of NVASA on several block copolymer systems and used in situ grazing incidence small-angle X-ray scattering (GISAXS) to validate the ordering process during the self-assembly. The simplicity and reproducibility of the method is attractive for implementation in large-scale manufacturing processes such as roll-to-roll printing as swell ratio is easily controlled by the amount of additive used and separate annealing steps are not needed. This work potentially introduces a new way to quickly and cost effectively anneal block copolymers

Elucidating the Role of Hydrogen Bonds for Improved Mechanical Properties in a High-Performance Semiconducting Polymer

Incorporation of hydrogen bond moieties into the backbone or side chain of conjugated polymers is an effective strategy to enhance mechanical performance, facilitate morphological organization, and promote self-healing ability. However, the understanding of hydrogen bonds, particularly the effect of bond strength and directionality, on thermomechanical and optoelectronic performance is still in its infancy due to the competing influence of morphology, glass transition phenomena, and the measurement process itself. Here, we compare the influence of statistically incorporated amide and urea moieties on the mechanical properties of DPP-TVT parent polymers. We observed a profound difference in ductility; amide functionalization increases the strain at failure by over 100% relative to the pure DPP-TVT polymer, while urea functionalization results in a loss of strain at failure by 50%. This is attributed to the crystalline behavior of functionalized conjugated polymers that is promoted by intermolecular interactions of urea groups, which we elucidated via an in-depth investigation of the swelling, crystalline packing, thermal behavior, and strain-dependent charge transport. Furthermore, we employed a novel free-standing tensile test to validate our mechanical measurements supported on a water surface. Our results demonstrated that hydrogen bond moieties must be carefully chosen to achieve a delicate balance of morphological control and mechanical performance, as simply increasing the hydrogen bond strength can result in detrimental mechanical and electrical performance

Roll-to-Roll Scalable Production of Ordered Microdomains through Nonvolatile Additive Solvent Annealing of Block Copolymers

A new method, “nonvolatile solvent vapor annealing” (NVASA), has been developed to anneal block copolymers during film deposition by controlling the solvent drying process. Precise amounts of high boiling point additive added to the polymer solution briefly remain in the polymer film after casting, leaving the film in a swollen state, increasing its chain mobility, and ultimately improving domain order. We demonstrated the effectiveness of NVASA on several block copolymer systems and used in situ grazing incidence small-angle X-ray scattering (GISAXS) to validate the ordering process during the self-assembly. The simplicity and reproducibility of the method is attractive for implementation in large-scale manufacturing processes such as roll-to-roll printing as swell ratio is easily controlled by the amount of additive used and separate annealing steps are not needed. This work potentially introduces a new way to quickly and cost effectively anneal block copolymers

Elucidating the Role of Hydrogen Bonds for Improved Mechanical Properties in a High-Performance Semiconducting Polymer

Incorporation of hydrogen bond moieties into the backbone or side chain of conjugated polymers is an effective strategy to enhance mechanical performance, facilitate morphological organization, and promote self-healing ability. However, the understanding of hydrogen bonds, particularly the effect of bond strength and directionality, on thermomechanical and optoelectronic performance is still in its infancy due to the competing influence of morphology, glass transition phenomena, and the measurement process itself. Here, we compare the influence of statistically incorporated amide and urea moieties on the mechanical properties of DPP-TVT parent polymers. We observed a profound difference in ductility; amide functionalization increases the strain at failure by over 100% relative to the pure DPP-TVT polymer, while urea functionalization results in a loss of strain at failure by 50%. This is attributed to the crystalline behavior of functionalized conjugated polymers that is promoted by intermolecular interactions of urea groups, which we elucidated via an in-depth investigation of the swelling, crystalline packing, thermal behavior, and strain-dependent charge transport. Furthermore, we employed a novel free-standing tensile test to validate our mechanical measurements supported on a water surface. Our results demonstrated that hydrogen bond moieties must be carefully chosen to achieve a delicate balance of morphological control and mechanical performance, as simply increasing the hydrogen bond strength can result in detrimental mechanical and electrical performance