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The chemical vapor deposition of polycrystalline diamond (PCD) films is typically done on substrates seeded with diamond nanoparticles. Specular laser reflectance and a continuous film model have been used to monitor the thickness of these films during their deposition. However, most seeds are isolated during the early stages of the deposition, which questions the utility of applying such a continuous film model for monitoring deposition before film formation. In this work, we present a model based on the Rayleigh theory of scattering for laser reflectance at substrates with growing nanodiamonds to capture the early stages of PCD deposition. The reflectance behavior predicted by our model differs from that of a continuous film, which is well-described by the continuous film model. This difference enlarges as the seed density used in our model decreases. We verify this trend experimentally by depositing diamond under identical conditions on substrates with various seed densities. A relation derived from our model is used to fit reflectance data from which seed densities are obtained that are proportional to those found with electron microscopy. We also show that relying on the continuous film model for describing the early stages of deposition can result in falsely deducing the existence of incubation, and that the continuous film model can be used safely beyond the early stages of deposition. Based on these findings, we delineate a robust method for obtaining growth rates and incubation periods from reflectance measurements. This work may also advance the general understanding of nanoparticle growth and formation., 32 pages, 9 figures, 1 table

Polymer-nanodiamond composites are excellent candidates for the fabrication of multifunctional hybrid materials. They integrate polymer flexibility and exceptional properties of nanodiamonds (NDs), such as biocompatibility, mechanical strength, color centers, and chemically-tailored surfaces. However, their development is hindered by the challenge of ensuring that NDs are homogeneously distributed in the composites. Here, we exploit colloidal coassembly between poly(isoprene-b-styrene-b-2-vinyl pyridine) (ISV) block copolymers (BCPs) and NDs to avoid ND self-agglomeration and direct ND spatial distribution. NDs were first air oxidized at 450 degrees C to obtain stable dispersions in dimethylacetamide (DMAc). By adding ISV into the dispersions, patchy hybrid micelles were formed due to H-bonds between NDs and ISV. The ISV-ND coassembly in DMAc was then used to fabricate nanocomposite films with a uniform sub-50 nm ND distribution, which has never been previously reported for an ND loading [Formula: see text] of more than 50 wt%. The films exhibit good transparency due to their well-defined nanostructures and smoothness and also exhibit an improved UV-absorption and hydrophilicity compared to neat ISV. More intriguingly, at a [Formula: see text] of 22 wt%, ISV and NDs coassemble into a network-like superstructure with well-aligned ND strings via a dialysis method. Transmission electron microscopy and dynamic light scattering measurements suggest a complex interplay between polymer-polymer, polymer-solvent, polymer-ND, ND-solvent, and ND-ND interactions during the formation of structures. Our work may provide an important foundation for the development of hierarchically ordered nanocomposites based on BCP-ND coassembly, which is beneficial for a wide spectrum of applications from biotechnology to quantum devices.

A prevalent strategy for synthesizing patchy nanoparticles is through the self-assembly of triblock terpolymers in selective solvents. Since the thermodynamic and kinetic factors that govern the morphology of the particles produced in this way are not fully understood, this strategy usually demands trial-and-error methodologies. We investigate the fundamental mechanisms that produce multiple types of patchy nanoparticles and identify the conditions needed to program the shapes of the nanoparticles and predict their assembly. Our findings demonstrate that particle morphology can be described in a generic fashion by accounting for the energetic balance between the conformation of the polymer coils and the formation of interfaces. This allows us to forecast the synthesis of patchy nanoparticles for systems with different triblock terpolymers and solvents. Since the shape, size, and distribution of the patches influence the growth of larger microscale structures, we construct a library of elemental nanoparticles, or building blocks, suitable for the study of hierarchically larger self-assembled aggregates and useful for streamlining the design of functional materials. Our results provide new insights into the intriguing mechanisms that determine the morphology of soft nanoscale objects, whether synthetic or naturally occurring.

We developed composite membranes by stacking functionalized nanospheres (20 nm size) with a high density of H-bonds. The functionalized nanospheres were formed by a click-reaction in toluene between the polybutadiene segment of poly(styrene-b-butadiene-b-styrene) (PS-b-PB-b-PS) triblock copolymer and an azodicarbonyl (PTAD) compound. The strong hydrogen-bond interaction promoted by the pendant urazole groups of the PTAD-modified copolymer is an important parameter for obtaining stable and defect-free membranes, acting in analogy to self-healing systems. The hydrodynamic transport is facilitated by the high porosity of the membranes and the unique hourglass-shaped pores. The composite membrane has water permeation as high as 60 L m−2 h−1 bar−1 and can exclude more than 95% of proteins with a molecular weight as small as 12 kg mol−1. This novel class of nanoparticle-stacked membranes has therefore excellent separation properties for biomolecular separation.

Two-dimensional (2D) lamellar membranes are highly advantageous in molecular separations. However, the permeance-rejection trade-off is always a major challenge, since the permeant transport mostly occurs in single-spacing channels with undesired microenvironments. Inspired by the structure of aquaporins, we design alternating dual-spacing channel graphene oxide (GO) membranes, with locally tailored chemical microenvironments, that give high permeance, high rejection and high stability in organic solvent nanofiltration. This unique structure is easily constructed by in situ intercalating and cross-linking scattered sub-5 nm silica nanoparticles in the GO interlayers. The hydrophilic nanoparticles locally widen the interlayer channels to enhance the solvent permeance. In the alternating nanoparticle-free areas, the GO layers simultaneously bend and the π–π interactions retain the narrow and hydrophobic channels, promoting high solute rejection. With a 10-fold increase in water permeance and unaffected rejection, the dual-spacing channel membranes exhibit one of the best performances for organic solvent nanofiltration. The methanol permeance reaches 290 L m−2 h−1 bar−1, with more than 90% rejection of dyes larger than 1.5 nm. This new approach of designing hierarchical channels in 2D materials can be used for a wide spectrum of applications.

In this letter, we demonstrate a relation between the boundary curvature $\kappa$ and the wrinkle wavelength $\lambda$ of a thin suspended film under boundary confinement. Experiments are done with nanocrystalline diamond films of thickness $t \approx 184$~nm grown on glass substrates. By removing portions of the substrate after growth, suspended films with circular boundaries of radius $R$ ranging from approximately 30 to 811 $\mu$m are made. Due to residual stresses, the portions of film attached to the substrate are of compressive prestrain $\epsilon_0 \approx 11 \times 10^{-4}$ and the suspended portions of film are azimuthally wrinkled at their boundary. We find that $\lambda$ monotonically decreases with $\kappa$ and present a model predicting that $\lambda \propto t^{1/2}(\epsilon_0 + \Delta R \kappa)^{-1/4}$, where $\Delta R$ denotes a penetration depth over which strain relaxes at a boundary. This relation is in agreement with our experiments and may be adapted to other systems such as plant leaves. Also, we establish a novel method for measuring residual compressive strain in thin films.

Biological systems are the ultimate model for an effective selective permeation device. Biomimetic artificial channels based on the assembly of peptides have been previously integrated in vesicles and lipid layers with the expectation of leading in the future to a more efficient water purification and biological separation. We demonstrate here the design of scalable membranes constituted by synthesized copolymers with α-helical polypeptide blocks. They have unique featherlike and lamellar structures and were obtained from poly(styrene-b-γ-benzyl-l-glutamate) copolymers via phase inversion or spin-coating. The membranes were then hydrolyzed using acid vapor annealing, which preserved the helical morphology after hydrolysis. Water permeation up to 3.5 L m–2 h–1 bar–1 was obtained. Dialysis experiments with membranes prepared via phase inversion had high retention of cytochrome c. High rejection of cytochrome c and the negatively charged dye Brilliant Blue was demonstrated for the spin-coated membranes. The ...

A unique method for the preparation of cellulose-polyethyleneimine (PEI) blend membranes for nanofiltration is presented. Trimethylsilyl cellulose was used as a precursor for the blend membrane fabrication followed by a simple hydrolysis to regenerate the cellulose structure. The resulting homogeneous blend membranes exhibited high neutral solute rejection in water, which was surprisingly better than the performance of the individual membranes due to the strong interactions between the blended polymers. More interestingly, the same membrane demonstrated over five times higher flux of methanol after solvent activation with water as compared to the fluxes of the pure membranes, attributed to formation of nanocracks. High rejection of negatively charged dyes in this solvent with around 450 Da molecular weight cut-off was obtained at an exceptionally high flux of 160 Lm−2 h−1 at a pressure of 4.5 bar. The membranes will be beneficial in nanofiltration of polar solvents containing neutral and charged molecules.

Polystyrene-b-poly(2-vinylpyridine)-b-poly(ethylene oxide) (PS-b-P2VP-b-PEO) terpolymer is a versatile polymer to form isoporous films and membranes, due to the possibility of self-assembly control and the properties of the different blocks, such as the P2VP ability of complexation, and H-bond formation, and the PEO biocompatibility. Copolymers with different block ratios and sizes were synthesized. The correlation between their equilibrium bulk morphology, the self-assembly in dilute and semi-dilute solutions and the non-equilibrium porous structures of membranes, obtained by non-solvent induced phase separation, was investigated and discussed in detail. The characterization was performed by small-angle X-ray scattering (SAXS), scanning (SEM) and transmission electron microscopy (TEM). Hexagonal, cubic and lamellar arrangements were observed. The preparation conditions were optimized and a regular, isoporous morphology, suitable for membrane application, was successfully obtained with PS80.5k-b-P2VP64.4k-b-PEO16.1k.

We combine self-assembly in solution, complexation with metallic salts and phase separation induced by solvent–non-solvent exchange to prepare nanostructured membranes for separation in the nanofiltration range. This method was applied to prepare membranes from newly synthesized poly(acrylic acid)-b-polysulfone-b-poly(acrylic acid) copolymers dissolved in a selective solvent mixture and immersed in aqueous Cu2+ or Ag+ solutions.

A poly(styrene-b-tert-butoxystyrene-b-styrene) copolymer was synthesized by anionic polymerization and hydrolyzed to poly(styrene-b-4-hydroxystyrene-b-styrene). Lamellar morphology was confirmed in the bulk after annealing. Membranes were fabricated by self-assembly of the hydrolyzed copolymer in solution, followed by water induced phase separation. A high density of pores of 4 to 5 nm diameter led to a water permeance of 40 L m−2 h−1 bar−1 and molecular weight cut-off around 8 kg mol−1. The morphology was controlled by tuning the polymer concentration, evaporation time, and the addition of imidazole and pyridine to stabilize the terpolymer micelles in the casting solution via hydrogen bond complexes. Transmission electron microscopy of the membrane cross-sections confirmed the formation of channels with hydroxyl groups beneficial for hydrogen-bond forming sites. The morphology evolution was investigated by time-resolved grazing incidence small angle X-ray scattering experiments. The membrane channels reject polyethylene glycol with a molecular size of 10 kg mol−1, but are permeable to proteins, such as lysozyme (14.3 kg mol−1) and cytochrome c (12.4 kg mol−1), due to the right balance of hydrogen bond interactions along the channels, electrostatic attraction, as well as the right pore sizes. Our results demonstrate that artificial channels can be designed for protein transport via block copolymer self-assembly using classical methods of membrane preparation.

Block copolymer self-assembly and non-solvent induced phase separation are now being combined to fabricate membranes with narrow pore size distribution and high porosity. The method has the potential to be used with a broad range of tailor-made block copolymers to control functionality and selectivity for specific separations. However, the extension of this process to any new copolymer is challenging and time consuming, due to the complex interplay of influencing parameters, such as solvent composition, polymer molecular weights, casting solution concentration, and evaporation time. We propose here an effective method for designing new block copolymer membranes. The method consists of predetermining a trend line for the preparation of isoporous membranes, obtained by computing solvent properties, interactions and copolymer block sizes for a set of successful systems and using it as a guide to select the preparation conditions for new membranes. We applied the method to membranes based on poly(styrene-b-ethylene oxide) diblocks and extended it to newly synthesized poly(styrene-b-2-vinyl pyridine-b-ethylene oxide) (PS-b-P2VP-b-PEO) terpolymers. The trend line method can be generally applied to other new systems and is expected to dramatically shorten the path of isoporous membrane manufacture. The PS-b-P2VP-b-PEO membrane formation was investigated by in situ Grazing Incident Small Angle X-ray Scattering (GISAXS), which revealed a hexagonal micelle order with domain spacing clearly correlated to the membrane interpore distances.

The perspective of adding stimuli-response to isoporous membranes stimulates the development of separation devices with pores, which would open or close under control of environment chemical composition, temperature or exposure to light. Changes in pH and temperature have been previously investigated. In this work, we demonstrate for the first time the preparation of photoresponsive isoporous membranes, applying self-assembly non-solvent induced phase separation to a new light responsive block copolymer. First, we optimized the membrane formation by using poly(styrene-b-anthracene methyl methacrylate-b-methylmethacrylate) (PS-b-PAnMMA-b-PMMA) copolymer, identifying the most suitable solvent, copolymer block length, and other parameters. The obtained final triblock copolymer membrane morphologies were characterized using atomic force and electron microscopy. The microscopic analysis reveals that the PS-b-PAnMMA-b-PMMA copolymer can form both lamellar and ordered hexagonal nanoporous structures on the membrane top layer in appropriate solvent compositions. The nanostructured membrane emits fluorescence due to the presence of the anthracene mid-block. On irradiation of light the PS-b-PAnMMA-b-PMMA copolymer membranes has an additional stimuli response. The anthracene group undergoes conformational changes by forming [4 + 4] cycloadducts and this alters the membrane's water flux and solute retention.

Membranes are prepared by self-assembly and casting of 5 and 13 wt% poly(styrene-b-butadiene-b-styrene) (PS-b-PB-b-PS) copolymers solutions in different solvents, followed by immersion in water or ethanol. By controlling the solution-casting gap, porous films of 50 and 1 µm thickness are obtained. A gradient of increasing pore size is generated as the distance from the surface increased. An ordered porous surface layer with continuous nanochannels can be observed. Its formation is investigated, by using time-resolved grazing incident small angle X-ray scattering, electron microscopy, and rheology, suggesting a strong effect of the air-solution interface on the morphology formation. The thin PS-b-PB-b-PS ordered films are modified, by promoting the photolytic addition of thioglycolic acid to the polybutadiene groups, adding chemical functionality and specific transport characteristics on the preformed nanochannels, without sacrificing the membrane morphology. Photomodification increases fivefold the water permeance to around 2 L m-2 h-1 bar-1 , compared to that of the unmodified one. A rejection of 74% is measured for methyl orange in water. The membranes fabrication with tailored nanochannels and chemical functionalities can be demonstrated using relatively lower cost block copolymers. Casting on porous polyacrylonitrile supports makes the membranes even more scalable and competitive in large scale.