Nanoporous Poly Research Articles

Preparation of nanoporous poly (L-lactic acid) microspheres with controllable morphology via thermally-induced phase separation

This article describes a facile method to prepare nanoporous poly (l-lactic acid) microspheres via a thermally-induced phase separation method with controllable diameters. It was found that the morphology and diameter of PLLA microspheres were easily controlled by adjusting solvent ratio, quenching temperature, and PLLA concentrations. The results revealed that by using a ternary solvent system consisting of 1,3-dioxolane as a good solvent, 2-butanone as mid-solvent, and water as a poor solvent, the diameter of PLLA microspheres can be easily controlled by changing the ratio of 1,3-dioxolane and water. The diameter of PLLA microspheres prepared ranged from 28.8 ± 5.9 μm to 63.8 ± 12.5 μm. Moreover, the evolution of PLLA spherulitic structures grown from polymer solution was confirmed as well through varying solvent ratios and PLLA concentrations. The presence of water as a non-solvent governed the phase separation mechanism of the phase separation process. At the same time, the diameter of the spherulites is affected by the ratio of 1,3-dioxolane controlling the polymer crystallization process in the polymer-rich region. Interestingly, the surface of these spherulites contains nanopores due to the stacking of lamellar crystals of PLLA during polymer crystallization which contributed to its superhydrophobicity and superoleophilicity. Hence, the prepared PLLA spherulites were utilized as PLLA microspheres with nanoporous surfaces for the adsorption and removal of oil in oil/water and oil-in-water emulsion. This facile method provides a novel pathway to prepare nanoporous PLLA microspheres with controllable diameters for eco-friendly oil/water and oil-in-water separation applications.

Porous poly(bismaleimide-co-divinylbenzene) microspheres as dispersive solid-phase extraction adsorbent coupled to high-performance liquid chromatography for the determination of triazine herbicide residues in vegetable samples.

In this work, monodisperse and nano-porous poly(bismaleimide-co-divinylbenzene) microspheres with large specific surface area (427.6 m2 /g) and rich pore structure were prepared by one-pot self-stable precipitation polymerization of 2,2'-bis[4-(4-maleimidophenoxy) phenyl] propane and divinylbenzene. The prepared poly(bismaleimide-co-divinylbenzene) microspheres were employed as dispersive solid-phase extraction (DSPE) adsorbent for the extraction of triazine herbicides. Under optimized conditions, good linearities were obtained between the peak area and the concentration of triazine herbicides in the range of 1-400µg/L (R2 ≥ 0.9987) with the limits of detection of 0.12-0.31µg/L. Triazine herbicides were detected using the described approach in vegetable samples (i.e., cucumber, tomato, and maize) with recoveries of 93.6%-117.3% and relative standard deviations of 0.4%-3.5%. In addition, the recoveries of triazine herbicides remained above 80.7% after being used for nine DSPE cycles, showing excellent reusability of poly(bismaleimide-co-divinylbenzene) microspheres. The adsorption of poly(bismaleimide-co-divinylbenzene) microspheres toward triazine herbicides was a monolayer and chemical adsorption. The adsorption mechanism between triazine herbicides and adsorbents might be a combination of hydrogen bonding, electrostatic interaction, and π-π conjugation. The results confirmed the potential use of the poly(bismaleimide-co-divinylbenzene) microspheres-based DSPE coupled to the high-performance liquid chromatography method for the detection of triazine herbicide residues in vegetable samples.

Potential removal of benzene-toluene-xylene toxic vapors by nanoporous poly(styrene-r-methylmethacrylate) copolymer composites

In this study, we report the potential capability of nanoporous poly(styrene-r-methylmethacrylate) (PS-PMMA) copolymer composites in removing toxic benzene-toluene-xylene (BTX) vapors. PS-PMMA copolymer composites have been prepared with the nanofillers of commercial graphene (CG), hexagonal boron nitride nanosheets (h-BN), reduced graphene oxide (rGO), and Fullerene C60. The nanocomposites have been prepared by in-situ bulk polymerization method and the nanoporous structures were obtained solvent nano-crystallization induced phase separation method. The BET results showed the specific surface areas of the composites are ranging from 225 to 280 m2/g with an average pore size of 12 to 40 nm. The PS-PMMA copolymer nanocomposites can be able to adsorb as high as 300 mg/g of BTX vapors from bulk liquids. The demonstrated high adsorption capacity for the toxic BTX vapor by the copolymer nanocomposites and their highly reusable nature (up to 10 consecutive cycles) demonstrate the potential of these materials to be successfully applied for toxic gas removal in relevant industries.

Improved NO2 gas sensing performance of nanoporous conjugated polymer (CP) thin films by incorporating preformed CP nanowires

Conjugated polymer (CP)-based organic field-effect transistor (OFET) gas sensors can detect gas molecules at room temperature with high sensitivity and selectivity. However, their performance, particularly when detecting oxidizing gases, has fallen behind that of their metal oxide counterparts. Hence, improving their sensing performance as well as understanding the correlation between it and the structural and electrical properties of the sensing materials is necessary. Herein, we demonstrate that gas sensing performance of an OFET sensor based on nanoporous poly(3-hexylthiophene) (P3HT) films can be improved simply by incorporating preformed P3HT nanowires (NWs), which act as an efficient charge transport pathway. It detects nitrogen dioxide (NO2) molecules with high sensitivity due to the efficient charge transport pathway as well as ultrathin nanoporous structure of the P3HT films. Upon exposure to 10 ppm NO2 at room temperature, the OFET gas sensor based on the P3HT-NW embedded nanoporous P3HT film exhibits excellent responsivity (34%), fast response and recovery times (∼69 and ∼133 s, respectively), and a low limit of detection of under 0.1 ppm, which are comparable to those of conventional metal oxide-based gas sensors. Based on the correlation study between the morphology, charge transport ability, and sensing performance of the P3HT-NWs embedded nanoporous P3HT films, it is revealed that the efficient charge transport ability is an important factor for realizing high-performance CP-based OFET gas sensors, along with excellent morphological features such as thinness and high pore density.

Preparation of nano-porous poly(ether ether ketone) hollow fiber membrane and its performance for desalination in vacuum membrane distillation

Nano-porous poly(ether ether ketone) (PEEK) hollow fiber membranes were successfully fabricated from PEEK/polyetherimide (PEI) blends via thermally-induced phase separation (TIPS) followed by chemical extraction of PEI method. The gas permeation rates, morphologies and mechanical properties of membranes were systematically investigated under different spinning conditions. The content of PEEK in blends substantially determined the gas permeation rates following the order: PEEK30/PEI70 (~9000 GPU) > PEEK40/PEI60 (~5100 GPU) > PEEK50/PEI50 (~1700 GPU) > PEEK60/PEI40 (~300 GPU) > PEEK70/PEI30 (below 1.0 GPU). Faster winding rates and bigger N2 bore fluid flow rates would result in bigger pores, higher porosity and larger gas permeation rates, while would cause lower mechanical strength. Furthermore, the silane-grafted hydrophobic PEEK hollow fiber membranes were successfully prepared via one-step reduction followed by silane modification. The performance of virgin and modified membranes was evaluated by treating saline feed containing 3.5 wt% sodium chloride in vacuum membrane distillation (VMD) process. Compared with virgin PEEK membrane, the modified membranes exhibited a more stable flux and higher salt rejection over 99.9 % for 33 h, indicating the significant improvement in the anti-wetting property caused by silane modification. The application attempt expands the research direction of PEEK membranes and promotes its further application potential in VMD process.

Immunized Microspheres Engineered Hydrogel Membrane for Reprogramming Macrophage and Mucosal Repair.

The "double-edged sword" effect of macrophages under the influence of different microenvironments determines the outcome and prognosis of tissue injury. Accurate and stable reprogramming macrophages (Mφ) are the key to rapid wound healing. In this study, an immunized microsphere-engineered GelMA hydrogel membrane is constructed for oral mucosa treatment. The nanoporous poly(lactide-co-glycolide) (PLGA) microsphere drug delivery system combined with the photo-cross-linkable hydrogel is used to release the soybean lecithin (SL)and IL-4 complexes (SL/IL-4) sustainedly. In this way, it is realized effective wound fit, improvement of drug encapsulation, and stable triphasic release of interleukin-4 (IL-4). In both in vivo and in vitro experiments, it is demonstrated that the hydrogel membrane can reprogram macrophages in the microenvironment into M2Mφ anti-inflammatory types, thereby inhibiting the local excessive inflammatory response. Meanwhile, high levels of platelet-derived growth factor (PDGF) secreted by M2Mφ macrophages enhanced neovascular maturation by 5.7-fold, which assisted in achieving rapid healing of oral mucosa. These findings suggest that the immuno-engineered hydrogel membrane system can re-modulating the biological effects of Mφ, and potentiating the maturation of neovascularization, ultimately achieving the rapid repair of mucosal tissue. This new strategy is expected to be a safe and promising immunomodulatory biomimetic material for clinical translation.

Maximizing the ionic liquid content and specific surface area in hierarchically nanoporous hypercrosslinked poly(ionic liquid)s towards the efficient conversion of CO2 into cyclic carbonates

Nanoporous poly(ionic liquid)s with both great porosities and high IL contents are prepared through a two-step synthetic strategy, serving as efficient heterogeneous catalysts for CO2 cycloaddition with epoxides under mild conditions.

Tuning the pore structure of templated mesoporous poly(melamine-co-formaldehyde) particles toward diclofenac removal

The increasing demand and implementation of pharmaceutics poses severe risk to different aquatic species as detectable contaminant in almost every surface water worldwide. Diclofenac (DCF) as one of the most common used analgesics was investigated as contaminant to be removed by adsorption onto nanoporous poly(melamine-co-formaldehyde) (PMF) particles featuring a very high amount of nitrogen functionalities. To achieve a high specific surface area (up to 416 m2/g) and a tunable pore system by hard templating, four different SiO2 nanoparticles were used as template. Differences in the pore formation and achieved pore structure were elucidated. For the first time, the adsorption of DCF onto PMF was tested. In batch adsorption experiments, impactful adsorption capacities as high as 76 μmol/g were achieved and complete removal at initial concentrations of 2 mg/L DCF. Differences in the connectivity and the micropore structure were decisive for uptake in low concentrations and the achieved adsorption capacity, respectively. As the presented PMF particles can be easily synthesized with the monomers formaldehyde and melamine combined with colloidal silica as sacrificial template and water as green solvent, this material presents a viable adsorbent for the removal of DCF at a larger scale. Our study further indicates a high potential for the removal of other pharmaceuticals.

Zinc detection in oil-polluted marine environment by stripping voltammetry with mercury-free nanoporous gold electrode

Detection of Zn(II) in oil-polluted seawater via square-wave anodic stripping voltammetry (SW-ASV) utilizing thin gold electrodes sputtered onto nanoporous poly(acrylic acid)-grafted-poly(vinylidene difluoride) (PAA-g-PVDF) membrane is herein reported. Prior to SW-ASV, PAA grafted nanopores demonstrated to efficiently trap Zn(II) ions at open circuit. This passive adsorption followed a Langmuir law. An affinity constant of 1.41 L upmu mol^{-1} and a maximum Zn(II) adsorbed mass q_{max} of 1.21 upmu mol g^{-1} were found. Applied SW-ASV protocol implied an accumulation step (− 1.2 V for 120 s) followed by a stripping step (− 1.2 to 1 V; 25 Hz; step: 4 mV; amplitude: 25 mV; acetate buffer (pH 5.5)). It revealed a Zn redox potential at − 0.8 V (Ag/AgCl pseudo-reference). Multiple measurements in synthetic waters close to the composition of production waters exhibited a decreasing precision with the number of readings R (1.65% (R = 2) and 6.56% (R = 3)). These membrane-electrodes should be used as disposable. The intra-batch mean precision was 14% (n = 3) while inter-batches precision was 20% (n = 15). Linear and linear-log calibrations allow exploitation of Zn(II) concentrations ranging from 10 to 500 upmu g L^{-1} and 100 to 1000 upmu g L^{-1} respectively. The LOD was 4.2 upmu g L^{-1} (3S/N). Thanks to obtained calibration, a detected Zn(II) content of 1 ppm in a raw production water from North Sea oil platform was determined.

Novel Bismaleimide Porous Polymer Microsphere by Self-Stabilized Precipitation Polymerization and Its Application for Catalytic Microreactors

Herein, monodisperse and nanoporous poly(bismaleimide-co-divinylbenzene) microspheres (PBMs) are fabricated via one-pot self-stabilized precipitation polymerization of 2,2′-bis[4-(4-maleimidophenoxy)phenyl]propane and divinylbenzene in the absence of any dispersants and templates. The particle size, specific surface area, and pore structure of the PBMs could be effectively tailored by tuning the monomer feed ratio and solvent composition. Under optimum reaction conditions, uniform PBMs with a particle size of 1.37 μm were obtained, which exhibit a maximum Brunauer–Emmett–Teller (BET) surface area (556.25 m2/g) and pore volume (0.48 cm3/g). This novel fabrication method for PBMs has significant merits including a simple process free of additives and high efficiency. Furthermore, PBMs loaded with Pd nanoparticles (PBMs@Pd) were easily synthesized via in situ chemical reduction and used as a catalytic microreactor due to their abundant pore structure. As an efficient heterogeneous catalyst for the reduction of 4-nitrophenol (4-NP) by sodium borohydride (NaBH4), the as-prepared PBMs@Pd exhibited excellent catalytic activity with a high turnover frequency value (967.92 h–1) and excellent recyclability. This facile strategy opens up new horizons for the synthesis of porous microspheres with a well-controlled morphology and tunable pore structure, which have great application prospects in the fields of catalysis, adsorption, and energy storage.

Au Nanoparticle-decorated Nanoporous PEDOT Modified Glassy Carbon Electrode: A New Electrochemical Sensing Platform for the Detection of Glutathione

Glutathione (GSH) is an important bio-thiol which is playing vital role in the human system, such as treating glaucoma, preventing asthma, cancer, etc. Therefore, electrochemical sensing of GSH is becoming very vital to know the level of the biomolecule in living systems. Hence, the present work aims to develop a sensor matrix for electrochemical biosensing of GSH at Au nanoparticle decorated Nanoporous poly(3,4)ethylene dioxythiophene (PEDOT) modified glassy carbon electrode (AuNPPEDOT/ GCE). The electrode is modified with a nanoporous fibrillar network of PEDOT containing Au nanoparticles and characterized using UV-Visible spectroscopy and Field Emission Scanning Electron Microscopy (FESEM). The platform is capable of producing enhanced signal against the bio-analyte at the applied overpotential of 0.6 V. Whereas bare glassy carbon electrode is unable to produce the signal. Conversely, Nanoporous PEDOT modified glassy carbon electrode can sense GSH of very low sensitivity at an applied overpotential of 0.7 V. From single step chronoamperometric measurements, kinetic parameters such as diffusion coefficient and apparent rate constant of the reaction were found as 5.01 × 10-5 cm2·s-1 and 1.106 × 103 M-1·s-1 respectively. From the amperometric response, the sensitivity and limit of detection (LOD) of the electrode were to be 10.7μA cm-2/μM and 0.173 μM respectively with the linear range of 0.5 to 10 μM. The matrix can detect GSH in the presence of other possible interfering molecules present in blood samples.

An Efficient Electrochromic Supercapacitor Based on Solution-Processable Nanoporous Poly{tris[4-(3,4-ethylenedioxythiophene)phenyl]amine}.

A new green synthetic route to tris[4-(3,4-ethylenedioxythiophene)phenyl]amine (TEPA) monomer has been developed and the molecular structure of TEPA has been determined by using single-crystal XRD. Solution-processable nanoporous poly{tris[4-(3,4-ethylenedioxythiophene)phenyl]amine} (PTEPA) is prepared by a chemical oxidative polymerization in a microemulsion. Based on the distorted structure of TEPA in the solid state, it is proposed that dendritic PTEPA has a distorted 3 D conformation with multiple twisted channels and pores that are narrowed and blocked by bifurcation and distortion of PTEPA, which is consistent with the observed hierarchical pore structure. As a cathode material, PTEPA exhibits a discharge capacity of 89.5 mAh g-1 in the initial cycle with a highly sloping two-stage discharge curve and relatively stable cycling performance. Beyond its excellent energy storage properties, PTEPA also shows relatively good electrochromic performance. Furthermore, an efficient all-solid-state electrochromic supercapacitor (ECSC) with good electrochromic performance and high energy storage capacity (13.3 mF cm-2 ) is assembled from PTEPA and nanoporous graphene films. During charge-discharge processes, the color of the ECSC changes between yellow-green and steel blue. Thus, the energy storage level of the ECSC can be monitored by the corresponding color changes. The fabricated ECSC may have practical applications, for example, in self-powered electrochromic smart windows.

Prevascularized, multiple-layered cell sheets of direct cardiac reprogrammed cells for cardiac repair.

We previously demonstrated that the efficiency of direct cardiac reprogramming from fibroblasts could be enhanced via mimicking of the in vivo cardiac microenvironment through coculture with cardiomyocytes and by providing electric cues. In the present study, we developed cell sheets using the direct cardiac reprogrammed cells and a nanothin, nanoporous poly(lactic-co-glycolic acid) membrane. Cell sheets were laid layer-by-layer and prevacularized with endothelial cells between the layers. These prevascularized, multilayered cell sheets were implanted on the epicardium of infarcted rat hearts, which led to an improvement in cardiac function and reduction in adverse cardiac remodeling post-myocardial infarction (MI). Thus, the in vivo mimicking direct cardiac reprogramming and prevascularization technique can enhance the efficiency of cell sheets in clinical applications and provide new opportunities to prevent heart failure following MI.

The influence of different rewetting procedures on the thrombogenicity of nanoporous poly(ether imide) microparticles.

Nanoporous microparticles prepared from poly(ether imide) (PEI) are discussed as candidate adsorber materials for the removal of uremic toxins during apheresis. Polymers exhibiting such porosity can induce the formation of micro-gas/air pockets when exposed to fluids. Such air presenting material surfaces are reported to induce platelet activation and thrombus formation. Physical or chemical treatments prior to implantation are discussed to reduce the formation of such gas nuclei. Here, we report about the influence of different rewetting procedures - as chemical treatments with solvents - on the thrombogenicity of hydrophobic PEI microparticles and PEI microparticles hydrophilized by covalent attachment of poly(vinyl pyrrolidone) (PVP) of two different chain lengths.Autoclaved dry PEI particles of all types with a diameter range of 200 - 250 μm and a porosity of about 84% ±2% were either rewetted directly with phosphate buffered saline (24 h) or after immersion in an ethanol-series. Thrombogenicity of the particles was studied in vitro upon contact with human sodium citrated whole blood for 60 min at 5 rpm vertical rotation. Numbers of non-adherent platelets were quantified, and adhesion of blood cells was qualitatively analyzed by bright field microscopy. Platelet activation (percentage of CD62P positive platelets and amounts of soluble P-Selectin) and platelet function (PFA100 closure times) were analysed.Retention of blood platelets on the particles was similar for all particle types and both rewetting procedures. Non-adherent platelets were less activated after contact with ethanol-treated particles of all types compared to those rewetted with phosphate buffered saline as assessed by a reduced number of CD62P-positive platelets and reduced amounts of secreted P-Selectin (P < 0.05 each). Interestingly, the hydrophilic surfaces significantly increased the number of activated platelets compared to hydrophobic PEI regardless of the rewetting agent. This suggests that, apart from wettability, other material properties might be more important to regulate platelet activation. PFA100 closure times were reduced and within the reference ranges in the ethanol group, however, significantly increased in the saline group. No substantial difference was detected between the tested surface modifications. In summary, rewetting with ethanol resulted in a reduced thrombogenicity of all studied microparticles regardless of their wettability, most likely resulting from the evacuation of air from the nanoporous particles.

Enabling sustainable green close-loop membrane lithium extraction by acid and solvent resistant poly (ether ether ketone) membrane

Membrane extraction (ME) for separating lithium ions from salt-lake brine is a green process comparing to conventional liquid-liquid extraction. Previous research has identified suitable organic extractant and membrane materials for extracting lithium from salt-lake brine. However, stripping solution, a concentrated hydrochloride acid (HCl), dissolves current solvent resistant membrane. We presents here a novel application of acid and solvent resistant poly (ether ether ketone) (PEEK) membrane for membrane stripping. PEEK membranes were prepared via immersion precipitation using a mixture solvent consisting of methanesulphonic acid (MSA) and sulfuric acid (SA). A linear cloud point curve of PEEK/MSA/SA/H2O quaternary system was determined and the phase separation kinetics was analyzed. Competition of solid-liquid and liquid-liquid demixing was proposed as the mechanism for the morphology change varying with PEEK concentration. Increase of PEEK concentration lead to high crystallinity in membrane, but comparably high mass transfer resistance; this lead to similar trend in the water permeability, lithium ion diffusion and stripping fluxes as well. Successful stripping of lithium ions from lithium-loaded extractant using 7 mol/L HCl solution was demonstrated. The resistance of PEEK membrane in HCl solution and organic extractant (tributyl phosphate (TBP)/kerosene) was demonstrated by monitoring the weight change and mechanical strength of PEEK membrane. Long-term stable stripping performance for 504 h further confirmed the stability of PEEK membrane. An extraction-stripping close-loop is thus available by combining with the solvent resistant nanoporous poly (ethylene vinyl alcohol, EVAL) in extraction and PEEK membrane in the stripping steps. Besides lithium extraction, the membrane based extraction/stripping process is suitable for a wider ion separation and purification.

Bioinspired Microfluidic Device by Integrating a Porous Membrane and Heterostructured Nanoporous Particles for Biomolecule Cleaning.

Mimicking the structures and functions of biological systems is considered as a promising approach to construct artificial materials, which have great potential in energy, the environment, and health. Here, we demonstrate a conceptually distinct design by synergistically combining a kidney-inspired porous membrane and natural sponge-inspired heterostructured nanoporous particles to fabricate a bioinspired biomolecule cleaning device, achieving highly efficient biomolecule cleaning spanning from small molecules to macromolecules. The bioinspired biomolecule cleaning device is a two-layer microfluidic device that integrates a polyamide porous membrane and heterostructured nanoporous poly(acrylic acid)-poly(styrene divinylbenzene) particles. The former as a filtration membrane isolates the upper sample liquid and the latter fixed onto the bottom of the underlying channel acts as an active sorbent, particularly enhancing the clearance of macromolecules. As a proof-of-concept, we demonstrate that typical molecules, including urea, creatinine, lysozyme, and β2-microglobulin, can be efficiently cleaned from simulant liquid and even whole blood. This study provides a method to fabricate a bioinspired biomolecule cleaning device for highly efficient biomolecule cleaning. We believe that our bioinspired synergistic design may expand to other fields for the fabrication of integrated functional devices, creating opportunities in a wide variety of applications.

Solid-phase combinatorial synthesis using microarrays of microcompartments with light-induced on-chip cell screening.

The process of drug discovery includes individual synthesis and characterization of drug candidates, followed by a biological screening, which is separated from synthesis in space and time. This approach suffers from low throughput and associated high costs, which in turn lead to inefficiency in the field of drug discovery. Here, we present a miniaturized platform combining combinatorial solid-phase synthesis with high-throughput cell screenings. The method is based on the formation of nanoporous poly(2-hydroxyethyl methacrylate-co-ethylene dimethacrylate) layers patterned with hydrophilic spots separated from each other by superhydrophobic liquid-impermeable barriers. The porous polymer inside the hydrophilic spots is used as a support to conduct solid-phase synthesis. The hydrophilic spots can be then filled with droplets containing either reagents for synthesis or live cells. Upon irradiation with UV light, products of solid-phase synthesis are released from the porous polymer because of the photo-cleavable linkers used and diffuse into separate droplets. The light-induced release of the products allows the control of the release spatially, temporally, and quantitatively. To demonstrate the versatility and usability of the platform for various cell lines, we have successfully implemented peptide synthesis to create an exemplary chemical library and demonstrated high cell viability after the UV-triggered small-molecule release.

Confining Photoacidity

Confining Photoacidity

Polyhedral oligomeric silsesquioxane-capped poly(N-vinyl pyrrolidone) amphiphiles: synthesis, self-assembly, and use as porogen of nanoporous poly(vinylidene fluoride)

In this contribution, we reported the synthesis of polyhedral oligomeric silsesquioxane (POSS)-capped poly(N-vinyl pyrrolidone) (PVPy) via reversible addition-fragmentation chain transfer/macromolecular design via interchange of xanthate (RAFT/MADIX) polymerization. First, a POSS macromer bearing xanthate moiety was synthesized and was then used as the chain transfer agent to mediate the radical polymerization of N-vinylpyrrolidone (NVP). By controlling the mass ratios of the POSS-CTA to NVP, a series of the POSS-capped PVPy amphiphiles were successfully synthesized with various molecular weights. It was found that in bulks, the POSS-capped PVPy was microphase-separated and the POSS end groups were self-organized into the spherical microdomains with the size of 10~100 nm in diameter. In the solvent selective for PVPy (e.g., water), the POSS-capped PVPy was capable of self-assembling into the spherical micelles with an average diameter of 20~50 nm as evidenced by dynamic laser scattering (DLS) and transmission electron microscopy (TEM). Owing to the amphiphilicity, POSS-capped PVPy also displayed the self-assembly behavior in poly(vinylidene fluoride) (PVDF), in which the POSS cages were aggregated into 10~30 nm microdomains. In the nanocomposites of PVDF with POSS-capped PVPy, the spherical POSS microdomains were readily etched by using hydrofluoric acid, leaving the nanopores in the materials.

Ultralow-dielectric, nanoporous poly(methyl silsesquioxanes) films templated by a self-assembled block copolymer upon solvent annealing

A homogenous, nanoporous poly(methyl silsesquixoxane) (PMSSQ) with a uniform pore size distribution was prepared by templating with a poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) block copolymer. The self-assembly of the PS-b-P4VP and PMSSQ precursor (PMSSQ-P) blends thin films was achieved by solvent annealing firstly; then the self-assembled thin films were thermally cured to prepare nanoporous PMSSQ films after removal of the PS-b-P4VP porogen. The influence of annealing solvent and PS-b-P4VP loading on the self-assembly behavior of the PS-b-P4VP/PMSSQ-P blends films were studied. By exposing to CHCl3 vapor, fingerprint-type microphase-separated structures were achieved for the PS-b-P4VP/PMSSQ-P blends films with PS-b-P4VP loading ranging from 30% to 60%. The formation of the microphase-separated structures is attributed to the substantial mobility of the PS blocks and the P4VP/PMSSQ-P complexes, and segregated repulsion between them under the CHCl3 vapor. Atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) results demonstrated the prepared nanoporous PMSSQ films had a homogenous spherical pore morphology, with closed nanopores and a uniform size distribution over large areas. The porosity and dielectric properties of the homogenous, nanoporous PMSSQ could be adjusted by the content of PS-b-P4VP in the PS-b-P4VP/PMSSQ-P blends. As the PS-b-P4VP loading increased to 60 wt%, an ultralow dielectric constant of 1.41 was obtained, making the nanoporous PMSSQ films have potential applications in microelectronic devices.