Nanoporous PS Research Articles

Diamond-structured nanonetwork gold as mechanical metamaterials from bottom-up approach

Herein, this work aims to develop a facile method for the fabrication of metallic mechanical metamaterial with a well-ordered diamond structure from a bottom-up approach using a self-assembled block copolymer for templated electrochemical deposition. By controlling the effective volume fraction of PDMS in PS-b-PDMS via solvent annealing followed by HF etching of PDMS, it is feasible to obtain nanoporous PS with diamond-structured nanochannels and used it as a template for templated electrochemical deposition. Subsequently, well-ordered nanonetwork gold (Au) can be fabricated. As evidenced by nanoindentation and micro-compression tests, the mechanical properties of the diamond-structured Au after removal of PS give the combination of lightweight and mechanically robust characteristics with an exceptionally high reduced elastic modulus of 11.9 ± 0.6 GPa and yield strength of 193 ± 11 MPa above the Hashin-Shtrikman upper bound of 72 MPa with a bending-dominated structure at equivalent density. The corresponding deformation mechanism can be elucidated by morphological observations experimentally and finite element analysis (FEA) numerically. This work demonstrates the bottom-up approach to fabricating metallic monolith with diamond structure in the nanoscale, giving a superior performance as mechanical metamaterials.

Gyroid-structured nanoporous chitosan from block copolymer template for UVC reflection

Bioinspired from structural coloration of butterfly wing structure, this work aims to fabricate nanoporous chitosan for UVC reflection. By taking advantage of self-assembled polystyrene-b-polydimethylsiloxane (PS-b-PDMS) with double gyroid texture followed by hydrofluoric acid etching of PDMS block, nanoporous PS with well-defined nanochannels can be fabricated, and used as a template for templated crosslinking reaction of chitosan through a multiple pore-filling process. Well-ordered nanoporous chitosan with shifting networks in nanoscale can be successfully fabricated after removal of the PS template. With the low absorption of chitosan in the ultraviolet region and the shifting networks for opening the bandgap, it is appealing to exploit the nanonetwork chitosan as high reflective materials for UVC optical devices, as evidenced by finite-difference time-domain (FDTD) simulation and optical measurements experimentally.

Tailoring uniform gold nanoparticle arrays and nanoporous films for next-generation optoelectronic devices

High-density arrays of gold nanodots and nanoholes on indium tin oxide (ITO)-coated glass surfaces are fabricated using a nanoporous template fabricated by the self-assembly of diblock copolymers of poly (styrene-block-methyl methacrylate) (PS-b-PMMA) structures. By balancing the interfacial interactions between the polymer blocks and the substrate using random copolymer, cylindrical block copolymer microdomains oriented perpendicular to the plane of the substrate have been obtained. Nanoporous PS films are created by selectively etching PMMA cylinders, a straightforward route to form highly ordered nanoscale porous films. Deposition of gold on the template followed by lift off and sonication leaves a highly dense array of gold nanodots. These materials can serve as templates for the vapor-liquid-solid (VLS) growth of semiconductor nanorod arrays for next generation hybrid optoelectronic applications.

Gyroid-structured nanoporous polymer monolith from PDMS-containing block copolymers for templated synthesis

Herein, we aim to develop a simple method for the fabrication of well-ordered nanoporous materials from polystyrene-block-poly(dimethylsiloxane) (PS-PDMS) diblock copolymer. By taking advantage of the intrinsic strong segregation strength between PS and PDMS, gyroid-structured PS-PDMS can be simply acquired from initially lamellae-forming PS-PDMS (i.e., PS-PDMS with almost equal volume fractions for the two blocks) by using solution casting with PS selective solvent. With the high etching selectivity of the constituted blocks, nanoporous PS materials with gyroid-structured nanochannels can be obtained from self-assembled PS-PDMS by selectively etching the PDMS block using hydrofluoric acid. The fabricated nanoporous PS can be used as a template for controlled synthesis followed by removal of the PS to obtain various types of nanoporous materials including organics (such as epoxy) and inorganics (such as SiO2 and Ni) with well-defined gyroid textures.

Silicon crystallization in nanodot arrays organized by block copolymer lithography

Asymmetric polystyrene-b-polymethylmethacrylate (PS-b-PMMA) block copolymers are used to fabricate nanoporous PS templates with different pore diameter depending on the specific substrate neutralization protocol. The resulting polymeric templates are used as masks for the subsequent deposition of a thin (h = 5 nm) amorphous Si layer by electron beam evaporation. After removal of the polymeric film and of the silicon excess, well-defined hexagonally packed amorphous Si nanodots are formed on the substrate. Their average diameter (d < 20 nm), density (1.2 × 1011 cm−2), and lateral distribution closely mimic the original nanoporous template. Upon capping with SiO2 and high temperature annealing (1050 °C, N2), each amorphous Si nanodot rearranges in agglomerates of Si nanocrystals (d < 4 nm). The average diameter and shape of these Si nanocrystals strongly depend on the size of the initial Si nanodot.

Transfer of pre-assembled block copolymer thin film to nanopattern unconventional substrates.

In this work, we demonstrate that a preassembled block copolymer (BCP) thin film can be floated, transferred, and utilized to effectively nanopattern unconventional substrates. As target substrates, we chose Cu foil and graphene/Cu foil since they cannot be nanopatterned via conventional processes due to the high surface roughness and susceptibility to harsh processing chemicals and etchants. Perpendicular hexagonal PMMA cylinder arrays in diblock copolymer poly(styrene-block-methyl methacrylate) [P(S-b-MMA)] thin films were preassembled on sacrificial SiO2/Si substrates. The BCP thin film was floated at the air/water interface off of a SiO2/Si substrate and then collected with the target substrate, leading to well-defined nanoporous PS templates on these uneven surfaces. We further show that the nanoporous template can be used for a subtractive process to fabricate nanoperforated graphene on Cu foil in sub-20 nm dimension, and for an additive process to create aluminum oxide nanodot arrays without any polymeric residues or use of harsh chemicals and etchants.

Controlled Ordering of Block Copolymer Gyroid Thin Films by Solvent Annealing

This work presents an approach to achieve controlled ordering of polystyrene-block-poly(l-lactide) (PS–PLLA) gyroid thin films on a neutral substrate using solvent annealing. Interesting morphological evolution from gyroid to cylinder can be found while using a partially selective solvent for the PS block to anneal the PS–PLLA thin film. To acquire a thin-film sample with thermodynamically stable gyroid morphology, a nonpreferential solvent should be used for solvent annealing to enable controlled ordering of gyroid thin film with the (211)G plane parallel to the air surface and also the functionalized substrate. By taking advantage of degradable character of the PLLA block, nanoporous PS with well-defined texture can be fabricated by hydrolysis and used as a template for synthesis of various nanohybrids and nanoporous materials.

Double and Single Network Phases in Polystyrene-block-poly(l-lactide) Diblock Copolymers

Here, the phase behaviors of polystyrene-block-poly(l-lactide) (PS–PLLA) diblock copolymers are studied, and network phases can be found. In addition to conventional double gyroid phase with double networks, a single network phase (an Fddd phase with orthorhombic network) can be found, as evidenced by small-angle X-ray scattering and transmission electron microscopy (TEM). The single network texture with trivalent connectors of the Fddd can be directly visualized by using 3D TEM (i.e., electron tomography), and the observation under polarized light microscopy shows its birefringence character. The formation of stable Fddd is attributed to intrinsic inhomogeneity in the chain conformations of the chiral block (i.e., PLLA). Subsequently, nanoporous PS with continuous nanochannel networks can be obtained by hydrolysis of the PLLA block in the PS–PLLA and then used as a template for sol–gel reaction of tetraethyl orthosilicate. Consequently, nanoporous SiO2 with free-standing, well-defined network texture can be fabricated after removal of the PS template to give an open-cell porous ceramic material with high specific surface area (as high as 1170 m2/g) due to its nanostructured texture and high porosity.

Tailoring the photocatalytic reaction rate of a nanostructured TiO2 matrix using additional gas phase oxygen

Nanostructured TiO2 was synthesized by the sol–gel method. The titania was supported on nanoporous poly (styrene-co-divinylbenzene) (PS). The samples were characterized by several techniques (scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and ultraviolet–visible spectroscopy). Three types of TiO2 samples were prepared using various temperatures and were studied for the photocatalytic degradation of methylene blue. The photocatalytic efficiency of TiO2 was observed to increase by activating the TiO2 surface using nanoporous PS. The photocatalytic performance of the synthesized samples showed a higher performance using molecular O2, which was purged through the reactor.

Nanostructured thin films of degradable block copolymers and their applications

Nanopatterning using self-assembled thin films of degradable block copolymers (BCPs) has attracted considerable attention and inspired a variety of appealing applications in different research areas. To create useful nanopatterns for practical uses, controlling the orientation of the BCP microdomains is essential. The generation of oriented microdomains in BCP thin films will be discussed in this article. This discussion is followed by a review of methods that use polylactide-containing BCP (that is, polystyrene-b-poly(L-lactide) (PS-PLLA)) thin films to generate nanoporous PS after hydrolysis, which can be used for templated synthesis to create functional nanohybrids. The nanoporous PS thin films with well-oriented cylinder nanochannels can be used for pore-filling various ingredients to create specific drug delivery systems and optoelectronic devices. Moreover, by utilizing templated synthesis, nanoporous ceramics with a high-specific surface area and high porosity can be fabricated for optical applications using hydrolyzed gyroid-forming PS-PLLA as a template for the sol–gel reaction. In addition, the nanolithography applications using silicon-containing BCP (that is, polystyrene-b-polydimethylsiloxane) thin films, which can form inorganic nanoporous templates after oxygen plasma treatment, will be discussed in this review. Polymers that consist of two or more different components organized in distinct blocks give rise to intriguing and useful processes. By virtue of their similar properties, blocks of the same kind tend to aggregate. This ‘microphase separation’ phenomenon in turn organizes the bulk material in regular patterns. Subsequently removing one of the blocks selectively, by wet or dry etching, produces materials featuring well-organized, regular pores — sought after for a variety of applications ranging from drug delivery systems to optoelectronic devices. Rong-Ming Ho and co-workers from the National Tsing Hua University in Taiwan review how the blocks’ orientation can be controlled, focusing on materials made of polystyrene and either organic poly(L-lactide) (PS–PLLA) or inorganic, silicon-containing poly(dimethyl-siloxane) (PS–PDMS). For example, removing PLLA segments from the former by hydrolysis produces a nanoporous thin film that serves as a template for sol–gel reactions, whereas removing PS blocks from the latter gives a robust matrix that can be exploited as a mask in nanolithography. In this review, nanoporous thin-film template was obtained from the self-assembly of block copolymer PS-PLLA, at which the PLLA block can be hydrolyzed to form the nanopatterns. Nanoporous PS thin films with well-oriented cylinder nanochannels can be used for pore-filling with various ingredients to create specific drug delivery systems and optoelectronic devices. Moreover, nanoporous ceramics with high-specific surface area and high porosity can be fabricated for optical applications using hydrolyzed gyroid-forming PS-PLLA for templated sol–gel reaction. In addition, the formation of inorganic nanoporous templates from self-assembled PS-PDMS after oxygen plasma treatment and its corresponding applications in nanolithography will be discussed.

Influence of etching parameters on optoelectronic properties of c-Si/porous silicon heterojunction – application to solar cells

Thin layers of nanoporous silicon PS were synthesized by anodic etching, in order to develop photovoltaic cells. We proposed a diluted concentration of hydrofluoric acid with different etching current densities (1, 3, 5 mA/cm 2 ) on a fairly short time anodization. Observations by scanning electron microscope, electrical measurements and optical measurements revealed that the structural properties of PS layers depended on strong conditions of prints. The reverse and forward component of the I-V characteristics showed an appropriate method to explore and extract the parameters of the diode ideality factor n . The optimum conditions of formation of PS were: HF concentration of 1% and an etching current density of mA/cm 2 . Unlike silicon, which has a low absorption of short visible wavelengths, it was shown that the PS had wide energy gap of ≈ 2 eV, and a marked improvement in the absorption between 400 and 600 nm. This property has been used to optimize the response of the solar cell Ni/PS/c-Si. Efficiency performance close to 4.2% was obtained with a V oc of 400 mV, and fill factor of 46%. The solar cell exhibited better response than the reference cell Ni/c-Si. These results show that PS/c-Si heterojunction has a potential for photovoltaic applications.

ABAC Tetrablock Terpolymers for Tough Nanoporous Filtration Membranes

Nanoporous poly(styrene)-b-poly(isoprene)-b-poly(styrene) (PS–PI–PS) was prepared from PS–PI–PS–PLA (PLA = poly(d,l-lactide)) tetrablock terpolymer precursors. Hydroxy end-functionalized PS–PI–PS was synthesized by sequential anionic polymerizations and used to initiate the ring-opening polymerization of d,l-lactide. A combination of small-angle X-ray scattering, transmission electron microscopy and scanning electron microscopy data supports a core–shell cylinder morphology with PLA as the core component. The inherently robust mechanical properties associated with PS–PI–PS block copolymers provide the materials with enhanced flexibility and toughness compared to analogous nanoporous polystyrene samples prepared by etching of PS–PLA diblocks. Composite membranes containing nanoporous PS–PI–PS on top of microporous poly(ether sulfone) (PES) were prepared by direct spin-coating and also by a salt-plate coating/film-transfer strategy. Nanopores (dpore ≈ 15 nm) were created by a combination of reactive ion etc...

Functionalized Nanoporous Thin Films From Blends of Block Copolymers and Homopolymers Interacting via Hydrogen Bonding

AbstractBlends of poly(acrylic acid)‐block‐polystyrene (PAA‐b‐PS) copolymers and poly(ethylene oxide) (PEO) homopolymers in which PAA and PEO interact via hydrogen bonds were used as precursors of nanoporous PS thin films with cavities decorated by PAA blocks. The presence of free carboxylic acid groups inside the pores was evidenced by fluorescence spectroscopy after reacting them with a diazomethane functionalized fluorescent dye. These nanoporous thin films were then used as templates for the preparation of dense arrays of silica nanodots.

Formation of conductive polyaniline nanoarrays from block copolymer template via electroplating

Nanostructured thin films have drawn extensive attention because of their unique properties resulting from nanoscale features. One of the convenient ways to generate nanostructured thin films is to use pattern with nanoscale texture as a template for the reactions carrying out within the template. In this study, nanoporous thin film template was obtained from the self-assembly of degradable block copolymer, polystyrene-b-poly(l-lactide) (PS-PLLA) with PLLA cylinder nanostructure, at which the PLLA block can be hydrolyzed to form the nanopatterns with cylinder nanopores on conductive substrate (i.e., ITO substrate). The nanoporous PS thin film template was stabilized by modification of substrate using hydroxyl terminated PS so as to enhance the adhesion with substrate for following electroplating process. Combining a pulse electroplating method with the control of micro current, polyanilines can be successfully synthesized within the template to fabricate well-defined of conductive polymer nanoarrays.

Amine-functionalized nanoporous thin films from a poly(ethylene oxide)-block-polystyrene diblock copolymer bearing a photocleavable o-nitrobenzyl carbamate junction

The synthesis of a poly(ethylene oxide)-block-polystyrene (PEO-b-PS) diblock copolymer bearing an o-nitrobenzyl carbamate junction is reported via a one-pot atom transfer radical polymerization (ATRP)–copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC). The accordingly obtained block copolymer was self-assembled into thin films showing, after solvent annealing, ordered PEO cylinders oriented normal to the film surface and embedded in a PS matrix. In the next step, the easy photocleavage of the o-nitrobenzyl carbamate junction and the subsequent removal of the PEO nanophase were demonstrated. This led to amine-functionalized nanoporous PS thin films as evidenced by the successful coupling of a fluorescent dye bearing a carboxylic acid group. The possibility to obtain fluorescent nanopores was then further exploited to pattern the films using a photolithographic mask.

Highly Ordered Nanoporous Thin Films from Photocleavable Block Copolymers

Poly(styrene-block-ethylene oxide) with an o-nitrobenzyl ester photocleavable junction (PS-hν-PEO) was synthesized by a combined RAFT polymerization and “click chemistry“ approach and represents the first report utilizing this method for the synthesis of photocleavable block copolymers. After solvent annealing, highly ordered thin films were prepared from PS-hν-PEO. Following a very mild UV exposure and successive washing with water, PS-hν-PEO thin films were transformed into highly ordered nanoporous thin PS films with pore diameters of 15–20 nm and long range ordering (over 2 μm × 2 μm). Afterwards the pores were filled with PDMS by spin-coating in combination with capillary forces. After treatment with oxygen plasma to remove the PS templates, highly ordered arrays of silica nanodots were obtained. This represents the first template application example from highly ordered nanoporous thin films derived from block copolymers featuring a photocleavable junction.

The effect of random copolymer on the characteristic dimensions of cylinder-forming PS-b-PMMA thin films

The block copolymer self-assembly approach has received great attention in recent years as apossible way to overcome the limits of conventional lithography and to fabricate sub-22 nmstructures. At this level, precise nanometric control is crucial for technological applications andthe search for a flexible and reproducible protocol is a great challenge. The polystyrene-b-poly(methylmethacrylate)(PS-b-PMMA) system, with a styrene fraction of 0.71, spontaneously separates into a periodicarray of hexagonally packed PMMA cylinders embedded in a matrix of PS and, undersuitable processing conditions, this is perpendicularly oriented with respect to theunderlying substrate. The selective removal of the PMMA allows us to obtain ananoporous PS matrix with well-defined pore dimensions. Perpendicular orientation ofthe PMMA cylinders requires surface neutralization by means of a suitable PS-r-PMMA random copolymer. The choice of the random copolymer is not trivial, because different PS-r-PMMA copolymers strongly affect the characteristics of the PS-b-PMMA film deposited on it. In this paper the effects of the selected PS-r-PMMA on the arrangement as well as on the peculiar dimensions (pore diameter, pore topore distance) of the final nanoporous PS thin film are studied. Reliable protocols for thefabrication of a disposable polymeric mask are proposed in view of its application inadvanced lithographic processes.

Helical assemblies from chiral block copolymers

Helical assemblies from chiral block copolymers (BCPs*) have been intensively studied due to their unique hierarchical architectures arising from the interplay of various secondary interactions. Helical architectures from BCP* self-assembly in solution have been found in peptide-based and lactide-based BCPs*. Inspired by the concept of chiral information transfer from the molecular level to macroscopic features, polystyrene-block-poly(L-lactide) (PS-PLLA) BCPs* composed of an achiral PS block and a chiral PLLA block has been designed for fabrication of helical assemblies. In contrast to a variety of helical assemblies resulting from solution, a helical phase (H*) having hexagonally packed helical PLLA microdomains in a PS matrix can be obtained in bulk by introducing chirality starting from the molecular level for BCP self-assembly. Phase behavior was examined and phase transitions from the H* phase to both cylinder and gyroid phases were found after long-time annealing, suggesting that the H* phase is a long-lived metastable phase. The morphologies of the H* phase can be manipulated into stretched helices (eventually leading to straight cylinders) by applying the stimulation (i.e., crystallization) so as to result in spring-like behavior. Also, by taking advantage of the degradable character of polylactides, a nanoporous PS polymer can be obtained after PLLA hydrolysis to be used as a template for fabrication of helical nanohybrids.

Inorganic Gyroid with Exceptionally Low Refractive Index from Block Copolymer Templating

Nanoporous polymers with gyroid nanochannels can be fabricated from the self-assembly of degradable block copolymer, polystyrene-b-poly(l-lactide) (PS-PLLA), followed by the hydrolysis of PLLA blocks. A well-defined nanohybrid material with SiO2 gyroid nanostructure in a PS matrix can be obtained using the nanoporous PS as a template for sol-gel reaction. After subsequent UV degradation of the PS matrix, a highly porous inorganic gyroid network remains, yielding a single-component material with an exceptionally low refractive index (as low as 1.1).

Novel Nanostructures from Self‐Assembly of Chiral Block Copolymers

A diblock copolymer system constituting both achiral and chiral blocks, polystyrene-block-poly(L-lactide) (PS-PLLA), was designed for the examination of chiral effects on the self-assembly of block copolymers (BCPs). A unique phase with three-dimensional hexagonally packed PLLA helices in PS matrix, a helical phase (H*), can be obtained from the self-assembly of PS-rich PS-PLLA with volume fraction of PLLA f PLLAv = 0.34, whereas no such phase was found in racemic polystyrene-block-poly(D.L-lactide) (PS-PLA) BCPs. Moreover, various interesting crystalline PS-PLLA nanostructures can be obtained by controlling the crystallization temperature of PLLA (T(c,PLLA) ), leading to the formation of crystalline helices (PLLA crystallization directed by helical confined microdomain) and crystalline cylinders (phase transformation of helical nanostructure dictated by crystallization) when T(c,PLLA) < T(g,PS) (the glass transition temperature of PS) and T(c,PLLA) ≧ T(g,PS) , respectively. As a result, a spring-like behavior of the helical nanostructure can be driven by crystallization so as to dictate the transformation (i.e., stretching) of helices and to result in crystalline cylinders. For PS-PLLA with PLLA-rich fraction (f PLLAv = 0.65), another unique phase, a hexagonally packed core-shell cylinder phase with helical sense (CS*), in which the PS microdomains appear as shells and PLLA microdomains appear as matrix and cores, can be found in the self-assembly of PLLA-rich PS-PLLA BCPs. The formation of those novel phases: helix and core-shell cylinder is attributed to the chiral effect on the self-assembly of BCPs, so we named this PS-PLLA BCP as chiral BCP (BCP*). For potential applications of those materials, the spring-like behavior with thermal reversibility might provide a method for the design of switchable nanodevices, such as nanoscale actuators. In addition, the PLLA blocks can be hydrolyzed. After hydrolysis, helical nanoporous PS bulk and PS tubular texture can be obtained and used as templates for the formation of nanocomposites.