Sequential Infiltration Synthesis Research Articles

Integrated learning framework for multistep pick-place-arrange of arbitrarily shaped objects in a narrow crate

To maximize the space occupied by unknown objects in a narrow crate and handle uncertain situations, we propose a novel human-like system-level learning framework: sequential infiltration synthesis of combined learning (SISCL). This framework leverages the synergies between picking by grasping, three-dimensional modeling, preferable placement, and seamless arranging by pushing in a systematic perspective. Within SISCL, a closed-loop system organizes different designing methods including reinforcement learning, knowledge induction, and analytic methods. This integration trains the system to autonomously package unknown objects and accommodate for uncertainties in measurements or executions, combining efficiency and flexibility. Initially trained in simulations, the SISCL framework underwent comprehensive evaluation in the laboratory. Furthermore, an initial validation was conducted on an extraterrestrial test ground. The results demonstrate the adaptability of the proposed framework to different shapes, materials, and stiffness of objects, as well as the capacity for uncertainties, thereby considerably reducing the need for precision in each sub-procedure in a human-like manner, facilitating seamless operations and efficient utilization of limited space.

Sequential Infiltration Synthesis of Silicon Dioxide in Polymers with Ester Groups-Insight from In Situ Infrared Spectroscopy.

New strategies to synthesize nanometer-scale silicon dioxide (SiO2) patterns have drawn much attention in applications such as microelectronic and optoelectronic devices, membranes, and sensors, as we are approaching device dimensions shrinking below 10 nm. In this regard, sequential infiltration synthesis (SIS), a two-step gas-phase molecular assembly process that enables localized inorganic material growth in the targeted reactive domains of polymers, is an attractive process. In this work, we performed in situ Fourier transform infrared spectroscopy (FTIR) measurements during SiO2 SIS to investigate the reaction mechanism of trimethylaluminum (TMA) and tri(tert-pentoxy) silanol (TPS) precursors with polymers having ester functional groups (poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), polycaprolactone (PCL), and poly(t-butyl methacrylate) (PBMA)), for the purpose of growing patterned nanomaterials. The FTIR results show that for PMMA and PEMA, a lower percentage of functional groups participated in the reactions and formed weak and unstable complexes. In contrast, almost all functional groups in PCL and PBMA participated in the reactions and showed stable and irreversible interactions with TMA. We discovered that the amount of SiO2 formed is not directly correlated with the number of interacting functional groups. These insights into the SiO2 SIS mechanism will enable nanopatterning of SiO2 for low-dimensional applications.

Self-Cleaning Highly Porous TiO2 Coating Designed by Swelling-Assisted Sequential Infiltration Synthesis (SIS) of a Block Copolymer Template.

Photocatalytic self-cleaning coatings with a high surface area are important for a wide range of applications, including optical coatings, solar panels, mirrors, etc. Here, we designed a highly porous TiO2 coating with photoinduced self-cleaning characteristics and very high hydrophilicity. This was achieved using the swelling-assisted sequential infiltration synthesis (SIS) of a block copolymer (BCP) template, which was followed by polymer removal via oxidative thermal annealing. The quartz crystal microbalance (QCM) was employed to optimize the infiltration process by estimating the mass of material infiltrated into the polymer template as a function of the number of SIS cycles. This adopted swelling-assisted SIS approach resulted in a smooth uniform TiO2 film with an interconnected network of pores. The synthesized film exhibited good crystallinity in the anatase phase. The resulting nanoporous TiO2 coatings were tested for their functional characteristics. Exposure to UV irradiation for 1 h induced an improvement in the hydrophilicity of coatings with wetting angle reducing to unmeasurable values upon contact with water droplets. Furthermore, their self-cleaning characteristics were tested by measuring the photocatalytic degradation of methylene blue (MB). The synthesized porous TiO2 nanostructures displayed promising photocatalytic activity, demonstrating the degradation of approximately 92% of MB after 180 min under ultraviolet (UV) light irradiation. Thus, the level of performance was comparable to the photoactivity of commercial anatase TiO2 nanoparticles of the same quantity. Our results highlight a new robust approach for designing hydrophilic self-cleaning coatings with controlled porosity and composition.

Al2O3 growth in PMMA thin films by sequential infiltration synthesis: in situ thickness evolution and mass uptake investigation

Nucleation of Al2O3 seeds (I) followed by the formation of an Al2O3 network (II) during the initial stages of sequential infiltration synthesis into a polymer matrix.

Sequential infiltration of two-photon polymerized 3D photonic crystals for mid-IR spectroscopic applications

Photonic crystals (PhCs) are spatially organized structures with lattice parameters equivalent to the operational wavelength of light. PhCs have been subject to extensive research efforts in the last two decades and are known for controlling light propagation with applications in sensing and time-delayed communication due to the slow-light phenomenon. Despite their exceptional properties, PhCs are difficult to fabricate using planar micromachining techniques due to their periodic structures. Techniques like two-photon stereolithography have been discussed for PhC fabrication in the literature, but the inherent disadvantage of poor refractive index (RI) contrast results in limited application. In this work, we present sequential infiltration synthesis performed on two-photon stereolithographically printed 3D PhCs for infiltration with zinc oxide to increase the RI of 3D PhCs. Finite element analysis was performed over a range of RI contrast values to study the change in photonic bandgap (PBG) with RI contrast. The transmission spectra were recorded on 3D PhCs before and after infiltration to demonstrate the change experimentally. An increase in the PBG width and absorbance is seen postinfiltration due to enhanced RI. This work presents the first, to our knowledge, sequentially infiltrated enhanced 3D PhC fabricated with two-photon stereolithography.

Atomic Layer Depostion within Polymers Templates for Spatially Controlled Growth and Doped Materials

Today’s nanofabrication techniques require multistep and costly processes in order to fabricate complex, multi-materials nanostructures. Performing atomic layer deposition (ALD) within polymeric templates can offer a simple solution for nanostructure fabrication. In this process, named sequential infiltration synthesis (SIS), high partial pressures and long exposures times lead to inorganic materials growth within polymers. Sequential polymer removal results in polymer-templated inorganic nanostructure. While SIS shows great potential in fabricating large variety of structures, it is currently limited to a single material growth process.In our research, we utilized SIS properties to achieve two different objectives: selective spatial growth and homogenous growth for doped materials. We demonstrated, for the first time, multi-material SIS process with control over the spatial location of each material and fabricate heterostructure nanorods and nanowires. Doping materials were fabricated using simultaneously growth of two precursors.We studied SIS within self-assembled block copolymer (BCP) films and electrospun polymer fibers and developed multi-material SIS, where two metal oxides are grown together in a single process, with precise control over their location within the polymer template. We used cylinder forming poly (styrene-block-methyl methacrylate) (PS-b-PMMA) films and electrospun PMMA as the polymeric template and DEZ (diethyl zinc), TMA (trimethyl aluminum) as the organometallic precursors. We achieved control over the growth location of each metal oxide by tuning the organometallic precursors diffusion time, forming heterostructures after polymer removal. A short exposure of the first precursor resulted in a limited growth only at the outer part of the polymer, while a long exposure of the second precursor enabled it to reach the full depth of the polymer besides the section which was already occupied by the first precursor. An exposure to water completed the cycle. We demonstrated this process on BCP films to achieve AlOx-ZnO nanorods arrays (Figure 1A-B) and on polymer fibers to achieve AlOx-ZnO fibers (Figure 1C-D). We performed structural characterization using scanning and transmission electron microscopy (SEM and TEM, respectively) to characterize the nanowires and nanorods as well as three-dimensional characterization scanning TEM (STEM) tomography and energy-dispersive X-ray spectroscopy (EDS) STEM tomography in order to probe the structure and the chemical composition in 3D. To fabricate doped materials, we applied SIS process with TMA and DEZ in the same exposure within homopolymer film. We preformed SEM-EDS to quantify each element and evaluate the doping percentage. This research opens new pathways for multi-materials nano scale structure fabrication through ALD-based growth within polymers.Figure 1 caption: AlOx-ZnO nanorods array: cross-sectional views using A) EsB detector and B) secondary electron in-lens detector. AlOx-ZnO fibers C) EDS map D) HAADF image [1] R. Azoulay et al., Small, 15, 1904657 (2019).[2] R. Azoulay et al., ACS Appl. Nano Mater., 5, 7228 (2022). Figure 1

Nanoscale Periodic Modulation of Doping over Large Areas with Block Copolymer Lithography and Ion Implantation

Whenever periodic patterning at the nanoscale over a large surface is required, block-copolymers (BCPs) represent an extremely attractive alternative for lithography1 and nano-templating,2 because of the low cost, if compared to conventional photolithography,3 and the high throughput, if compared to serial lithographic processes, such as electron beam lithography (EBL).4 Despite the relatively simple structure of BCPs, two different linear homopolymers linked to each other at one end by a covalent bond, when annealed above the glass transition temperature, they spontaneously microphase separate generating a variety of periodic nanostructures. The periodicity (L0 ) of the microdomains can be varied in the 10 – 100 nm range by properly adjusting the molecular weight and the interaction parameter of the two blocks.5 In this work, the combination of BCP lithography and ultra-low energy implantation of phosphorus ions at high fluences is investigated to promote a periodic modulation at the nanoscale of the concentration of dopant impurities over the near-surface layer of a silicon substrate.For the fabrication of the masks, two different poly(styrene-b-methyl methacrylate) (PS-b-PMMA) BCPs were used, to obtain two different geometries: the first with out of plane hexagonally packed PMMA cylinders, with an average diameter of 22 nm and center-to-center distance of 35 nm (Figure 1A) , and the second with out of plane lamellae having a periodicity of 28 nm (Figure 1B). The thickness of the BCP films was 35 nm thick. In addition, a graphoepitaxy protocol was implemented to obtain different sets of perfectly aligned 20 μm long parallel lamellae. A mesoporous soft mask can be readily obtianed by selective removal of PMMA cylinders with UV light and acetic acid. Conversely, a different process is required to avoid the collapse of the PS lamellae. Using Sequential Infiltration Synthesis (SIS),6 Al2O3 is incorporate into the PMMA phase of the BCP film. Upon the removal of the organic material by a mild O2 plasma cleaning, a nanostructured Al2O3 layer, that perfectly matches the PMMA pattern, remains on the substrate (Figure 1B).Phosphorus ions were implanted through the soft masks into the Si substrate operating at ultra-low energy (3 keV) to prevent the degradation of the polymeric film and reduce P penetration (10 nm) into the Si substrate. Additionally, high implantation doses are considered, to induce local amorphization of the silicon substrate. In this way Solid Phase Epitaxial Regrowth (SPER) can be exploited to recover the crystallinity of the substrate by thermal treatments at relatively low temperatures.7 During the SPER process the phosphorus atoms are substitutionally incorporated into the silicon lattice preserving their spatial confinement.AFM morphological analysis and ToF-SIMS depth profiling of the mask confirm the capability of the PS and alumina matrix to properly shield the low energy phosphorus ions in the dose range under investigation. AFM and ToF-SIMS characterization of the samples upon removal of the mesoporous template demonstrated that the P ions were effectively implanted into the Si substrate through the mask, leading to localized implantation (Figure 1C - 1E). Raman spectra suggested the presence of a thin layer of amorphous Si in the implanted samples and subsequent recrystallization after the annealing. By specific SPM measurements, it was possible to compare the morphology, the map of surface potential and the map of conductivity of the samples. The analysis of the Si surface after implantation through the mask with cylindrical pores and activation of the P is reported (Figure 1F, 1G). Small variations of the surface potential that perfectly match the implanted regions were obtained, suggesting a local modification of the electrical properties of Si. This result is also supported by conductivity measurements and finite element method (FEM) simulations. Further results will be presented, to investigate the electrical properties of the samples as a function of the implanted P dose and of the geometry of the mask.(1) Feng, H. et al., Nat. Mater. 21, 1426–1433 (2022).(2) Chai, J. & Buriak, J. M., ACS Nano 2, 489–501 (2008).(3) Levinson, H. J., Jpn. J. Appl. Phys. 61, (2022).(4) Yang, X. M. et al., ACS Nano 3, 1844–1858 (2009).(5) Seguini, G. et al. Soft Matter 16, 5525–5533 (2020).(6) Tseng, Y. C. et al. J. Phys. Chem. C 115, 17725–17729 (2011).(7) Luce, F. P. et al., Nucl. Instruments Methods Phys. Res. Sect. B Beam Interact. with Mater. Atoms 370, 14–18 (2016). Figure 1

Chemical Vapor Functionalization of Polymer Membranes for Water Treatment

Polymer membranes are used extensively in water purification to filter and remove particulate and molecular contaminants. Ideally, these membranes should exhibit high permeance, selectivity, and fouling resistance, but these attributes are rarely achieved simultaneously. One approach to improve membrane performance is to modify the polymer using reactive chemical vapors to impart the desired physiochemical properties. In this presentation, I will describe recent work at Argonne using atomic layer deposition (ALD), sequential infiltration synthesis (SIS), and vapor-phase grafting to modify polymer membranes used for ultra- and nano-filtration in water treatment. These techniques rely on self-limiting chemical reactions between gaseous precursors and a solid surface to grow material in an atomically controlled fashion. We have used ALD to produce ultrathin and conformal inorganic layers allowing the membrane pore size and pore wall composition to be precisely tuned, SIS for the bulk modification of polymers by creating an organic-inorganic hybrid material, and vapor-phase grafting of small molecules to achieve additional control over the membrane surface properties. Our studies employ a suite of in-situ and in-operando measurements to elucidate the surface chemistry for these processes and extensive ex-situ characterization and testing to understand the effects of chemical vapor treatment on polymers and how they impact membrane performance.

Accessibility and Mechanical Stability of Nanoporous Zinc Oxide and Aluminum Oxide Coatings Synthesized via Infiltration of Polymer Templates.

The conformal nanoporous inorganic coatings with accessible pores that are stable under applied thermal and mechanical stresses represent an important class of materials used in the design of sensors, optical coatings, and biomedical systems. Here, we synthesize porous AlOx and ZnO coatings by the sequential infiltration synthesis (SIS) of two types of polymers that enable the design of porous conformal coatings-polymers of intrinsic microporosity (PIM) and block co-polymer (BCP) templates. Using quartz crystal microbalance (QCM), we show that alumina precursors infiltrate both polymer templates four times more efficiently than zinc oxide precursors. Using the quartz crystal microbalance (QCM) technique, we provide a comprehensive study on the room temperature accessibility to water and ethanol of pores in block copolymers (BCPs) and porous polymer templates using polystyrene-block-poly-4-vinyl pyridine (PS75-b-P4VP25) and polymers of intrinsic microporosity (PIM-1), polymer templates modified by swelling, and porous inorganic coatings such as AlOx and ZnO synthesized by SIS using such templates. Importantly, we demonstrate that no structural damage occurs in inorganic nanoporous AlOx and ZnO coatings synthesized via infiltration of the polymer templates during the water freezing/melting cycling tests, suggesting excellent mechanical stability of the coatings, even though the hardness of the inorganic nanoporous coating is affected by the polymer and precursor selections. We show that the hardness of the coatings is further improved by their annealing at 900 °C for 1 h, though for all the cases except ZnO obtained using the BCP template, this annealing has a negligible effect on the porosity of the material, as is confirmed by the consistency in the optical characteristics. These findings unravel new potential for the materials being used across various environment and temperature conditions.

Mechanical Behavior of Hybrid Thin Films Fabricated by Sequential Infiltration Synthesis in Water-Rich Environment.

Sequential infiltration synthesis (SIS) is an emerging technique for fabricating hybrid organic-inorganic materials with nanoscale precision and controlled properties. Central to SIS implementation in applications such as membranes, sensors, and functional coatings is the mechanical properties of hybrid materials in water-rich environments. This work studies the nanocomposite morphology and its effect on the mechanical behavior of SIS-based hybrid thin films of AlOx-PMMA under aqueous environments. Water-supported tensile measurements reveal an unfamiliar behavior dependent on the AlOx content, where the modulus decreases after a single SIS cycle and increases with additional cycles. In contrast, the yield stress constantly decreases as the AlOx content increases. A comparison between water uptake measurements indicates that AlOx induces water uptake from the aqueous environment, implying a "nanoeffect" stemming from AlOx-water interactions. We discuss the two mechanisms that govern the modulus of the hybrid films: softening due to increased water absorption and stiffening as the AlOx volume fraction increases. The decrease in the yield stress with SIS cycles is associated with the limited mobility and extensibility of polymer chains caused by the growth of AlOx clusters. Our study highlights the significance of developing hybrid materials to withstand aqueous or humid conditions which are crucial to their performance and durability.

Controlling Nanoscale Pore Size and Wall Composition in Polycarbonate Membranes via Atomic Layer Deposition and Sequential Infiltration Synthesis: Implications for High Water Permeance

Controlling Nanoscale Pore Size and Wall Composition in Polycarbonate Membranes via Atomic Layer Deposition and Sequential Infiltration Synthesis: Implications for High Water Permeance

(Invited) Extended Thin Film Platinum Group Metal Electrocatalysts with Different Mesoscale Morphologies

The lack of sufficiently active oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) electrocatalysts is a bottleneck to the proliferation of PEM fuel cells and water electrolyzers. Commercially available PGM electrocatalysts fail to attain DOE technical targets due to instabilities and activity losses incurred at low loadings. Morphology control of PGM nanostructures is an enticing route towards activity and stability enhancements of electrocatalysts, but not much is known about the structure-property relationships between PGM mesoscale geometry (5 to 100 nm) and their activity and stability.This talk presents our work on model Pt extended surface electrocatalysts of tunable feature sizes and morphologies prepared from self-assembled block copolymer templates. The morphology, either perpendicular lamellae, cylinders, or perforated cylinders, of the extended surface electrocatalyst was controlled by the block copolymer volume fraction. The periodic lateral feature sizes (10 to 40 nm in this work) were controlled by the block copolymer degree of polymerization. The self-assembled block copolymers were transformed into extended surfaces using sequential infiltration synthesis to prepare aluminum oxide followed by reactive ion etching to remove the block copolymer template. Pt was sputtered onto the aluminum oxide supports. ORR data in a RDE with the new extended nanostructured thin films of Pt showed mass activity values of 0.35 A mgPt-1 to 0.46 A mgPt -1 at 0.9 V vs. RHE. The measured electro-chemically active surface area (ECSA) values obtained from hydrogen underpotential deposition were 64 to 70 m2 gPt -1. The lower values hailed from lamellae morphology while the larger values corresponded to a cylindrical morphology. The measured mass activity values, which have no cobalt or nickel additives and are unoptimized and display competitive mass activity values for ORR. We envision that the block copolymer templated extended surfaces could be an alternative to 3M’s state-of-the-art nanostructured thin film technology.

Key Factors in Enhancing Pseudocapacitive Properties of PANI-InOx Hybrid Thin Films Prepared by Sequential Infiltration Synthesis.

Sequential infiltration synthesis (SIS) is an emerging vapor-phase synthetic route for the preparation of organic-inorganic composites. Previously, we investigated the potential of polyaniline (PANI)-InOx composite thin films prepared using SIS for application in electrochemical energy storage. In this study, we investigated the effects of the number of InOx SIS cycles on the chemical and electrochemical properties of PANI-InOx thin films via combined characterization using X-ray photoelectron spectroscopy, ultraviolet-visible spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and cyclic voltammetry. The area-specific capacitance values of PANI-InOx samples prepared with 10, 20, 50, and 100 SIS cycles were 1.1, 0.8, 1.4, and 0.96 mF/cm², respectively. Our result shows that the formation of an enlarged PANI-InOx mixed region directly exposed to the electrolyte is key to enhancing the pseudocapacitive properties of the composite films.

Understanding the unique optical and vibrational signatures of sequential infiltration synthesis derived indium oxyhydroxide clusters for CO2 absorption

Sequential infiltration synthesis (SIS) is a vapor phase synthesis technique with potential to exert precise control over metal oxyhydroxide incorporation into polymer scaffolds. We observe strong size-dependent properties of InOx(OH)y few-atom clusters deposited with variable SIS cycle numbers within a polymethylmethacrylate (PMMA) matrix. Infrared spectroscopy and ultraviolet-visible absorption spectroscopy reveal that the metal atom coordination and optical properties of the clusters depend on the number of SIS cycles performed as well as the choice of processing parameters. The incorporation of indium oxyhydroxide in PMMA via SIS presents an opportunity to improve the CO2 absorption capacity and gas selectivity of inexpensive polymers.

Developing Quantitative Nondestructive Characterization of Nanomaterials: A Case Study on Sequential Infiltration Synthesis of Block Copolymers.

The sequential infiltration synthesis (SIS) of inorganic materials in nanostructured block copolymer templates has rapidly progressed in the last few years to develop functional nanomaterials with controllable properties. To assist this rapid evolution, expanding the capabilities of nondestructive methods for quantitative characterization of the materials properties is required. In this paper, we characterize the SIS process on three model polymers with different infiltration profiles through ex situ quantification by reference-free grazing incidence X-ray fluorescence. More qualitative depth distribution results were validated by means of X-ray photoelectron spectroscopy and scanning transmission electron microscopy combined with energy-dispersive X-ray spectroscopy.

Conductive Polyaniline-Indium Oxide Composite Films Prepared by Sequential Infiltration Synthesis for Electrochemical Energy Storage.

Composites of conductive polymers (CP) and metal oxides (MO) have attracted continued interest in the past decade for diverse application fields because the synergistic effects of CP and MO enable the realization of unusual electronic, electrochemical, catalytic, and mechanical properties of the composites. Herein, we present a novel method for the sequential infiltration synthesis of composite films of polyaniline (PANI) and indium oxide (InO x ) with high electrical conductivities (4-9 S/cm). The synthesized composite films were composed of two phases of graded concentration: InO x with oxygen vacancies and PANI with partially protonated molecular units. The PANI-InO x composite films displayed enhanced electrochemical activity with a pair of well-defined redox peaks. The open interfacial regions between the InO x and PANI phases may provide efficient pathways for ion diffusion and active sites for improved charge transfer.

Sequential Infiltration Synthesis with Organic Co-reactants for Extensively Swollen Organic–Inorganic Hybrid Thin Films

Sequential Infiltration Synthesis with Organic Co-reactants for Extensively Swollen Organic–Inorganic Hybrid Thin Films

Spatially Templated Nanolines of Ru and RuO2 by Sequential Infiltration Synthesis

Nanoscale patterning of inorganics is crucial for the fabrication of advanced electronic, photonic, and energy devices. The emerging sequential infiltration synthesis (SIS) method fabricates nanofeatures by block-selective vapor-phase growth in block copolymer templates with tunable patterns. Yet, SIS has been demonstrated mainly for Al2O3 and a few other metal oxides, while deriving metal nanostructures from a single SIS process is a challenge. Here, we present SIS of the Ru metal in polystyrene-block-polymethyl methacrylate (PS-b-PMMA) templates without any pretreatment, using alternating infiltration of RuO4 and H2. RuO4 interacts selectively and strongly with the aromatic C═C and C–H groups in PS, leaving the PMMA domains inert. Density functional theory calculations corroborate that the PS–RuO4 interaction is energetically favorable, with a calculated interaction energy of −1.65 eV, whereas for PMMA–RuO4, the calculated energy of −0.05 eV indicates an unfavorable interaction. Morphological analysis on the di-BCP after the RuO4-H2 process indicates an increase in contrast as a function of SIS cycles and templated Ru incorporation. The crystalline nature of the Ru deposits is confirmed using grazing incidence wide-angle X-ray scattering. Plasma-aided removal of the organic components yields Ru nanolines with lateral dimensions of ca 20 nm. We further highlight the broad potential of RuO4 as a reactant for SIS by generating RuO2 nanopatterns via alternating RuO4 and methanol infiltration.

(Invited) ALD-Based Infiltration and Growth of Inorganic Materials in Polymers

Sequential infiltration synthesis (SIS) has emerged in the past decade as a powerful technique for growth of inorganic materials within polymers through atomic layer deposition (ALD) chemistry. In SIS, ALD precursors diffuse into the polymer and interact with it, leading to inorganic materials growth within the polymer’s free volume. If desired, the polymer can later be removed, yielding polymer-templated inorganic structures. Combining SIS with self-assembled block copolymer (BCP) patterns results in selective growth of inorganic materials within the polar domains of the BCP, making it an attractive method for directed templating of inorganic nanostructures. Thus, SIS opens a pathway for exploiting ALD precision and rich materials library in new 3D morphologies, defined by the polymer.To build SIS design rules and expand SIS’ possibilities, we probed SIS growth and evolution at the atomic scale and explored the role of reversible polymer-precursor interactions in SIS growth through a plethora of methods: in-situ growth analysis (microgravimetry and FTIR), ex-situ high-resolution electron microscopy and extended X-ray absorption fine structure (EXAFS), and density functional theory (DFT) calculations. This knowledge was then applied in fabrication by design of metal oxide fibers, porous particles, and membranes.We fabricated Al2O3 and ZnO nanofibers, nanobelts, and core-shell fibers using designed growth profiles within electrospun polymer fibers. By controlling the organometallic precursors’ diffusion time, simultaneous but spatially controlled growth of Al2O3 and ZnO within the fibers was achieved, leading to the formation of metal oxide core-shell fibers. Self-assembled BCP particles were used to template porous metal oxide particles by selective growth of Al2O3 in the major block of the self-assembled structure. The uniform BCP assembly led to uniporous pores in the metal oxide particles. Finally, we utilized SIS and ALD within and onto BCP membranes for exceptional pore size control and pores’ surface engineering, yielding highly selective filtration membranes.

Precise Pore Size Tailoring and Surface Chemistry Modification of Polycarbonate Membranes Using Atomic Layer Deposition

Physical and chemical surface modifications are commonly used in many applications such as energy generation and storage, microelectronics, water purification, gas separation, and medical/plant biology. In recent several years, sequential infiltration synthesis (SIS), a variant of atomic layer deposition (ALD), has emerged as a promising technology that uses self-limiting reactions to create hybrid organic/inorganic materials within the polymer-free volume. Herein, we employed ALD/SIS of Al2O3, SnO2, Ga2O3, TiO2, and In2O3 to precisely tune the pore size and surface characteristics of track-etched polycarbonate membranes. We used in situ Fourier transform infrared spectroscopy to elucidate the chemistry for Al2O3 SIS in polycarbonate and in situ quartz crystal microbalance measurements to probe the extent of Al2O3 infiltration during SIS in polycarbonate thin films. Next, we used scanning electron microscopy, thermogravimetric analysis, and water permeance measurements to probe the pore size reduction and conformality of SIS Al2O3 in the track-etched polycarbonate membranes. We then used water permeance measurements to compare the water flux for a series of membranes with similar pore size but different pore wall chemistry and compared these results with water contact angle measurements. Interestingly, the hydrophilic metal oxide coatings yielded higher water flux values compared to hydrophobic coatings. Finally, we examined ion-selective transport in the modified track-etched polycarbonate membranes and rationalized the results using zeta potential measurements of the ALD metal oxides. Keywords: atomic layer deposition; sequential infiltration synthesis; metal oxides; hydrophilicity/hydrophobicity; permeability; surface charge; ion conductivity/selectivity.