Controlled crystallization of CaCO(3) on hyperbranched polyglycerol adsorbed to self-assembled monolayers

The formation of biominerals by living organisms is governed by the cooperation of soluble and insoluble macromolecules with peculiar interfacial properties. To date, most of the studies on mineralization processes involve model systems that only account for the existence of one organic matrix and thus disregard the interaction between the soluble and insoluble organic components that is crucial for a better understanding of the processes taking place at the inorganic-organic interface. We have set up a model system composed of a matrix surface, namely, a self-assembled monolayer (SAM), and a soluble component, hyperbranched polyglycerol. The model mineral calcium carbonate displays diverse polymorphism. It could be demonstrated that the phase selection of calcium carbonate is controlled by the cooperative interaction of the SAM and hyperbranched polyglycerol of different molecular weights (M(n) = 500-6000 g/mol) adsorbed to the SAM. Our studies showed that hyperbranched polyglycerol is adsorbed to polar as well as to nonpolar SAMs. This effect can be related to its highly flexible structure and its amphiphilic character. The adsorption of hyperbranched polyglycerol to the SAMs with different surface polarities resulted in the formation of aragonite for alkyl-terminated SAMs and no phase selection for carboxylate-terminated SAMs.     

Structural development of mercaptophenol self-assembled monolayers and the overlying mineral phase during templated CaCO3 crystallization from a transient amorphous film

Formation of biomineral structures is increasingly attributed to directed growth of a mineral phase from an amorphous precursor on an organic matrix. While many in vitro studies have used calcite formation on organothiol self-assembled monolayers (SAMs) as a model system to investigate this process, they have generally focused on the stability of amorphous calcium carbonate (ACC) or maximizing control over the order of the final mineral phase. Little is known about the early stages of mineral formation, particularly the structural evolution of the SAM and mineral. Here we use near-edge X-ray absorption spectroscopy (NEXAFS), photoemission spectroscopy (PES), X-ray diffraction (XRD), and scanning electron microscopy (SEM) to address this gap in knowledge by examining the changes in order and bonding of mercaptophenol (MP) SAMs on Au(111) during the initial stages of mineral formation as well as the mechanism of ACC to calcite transformation during template-directed crystallization. We demonstrate that formation of ACC on the MP SAMs brings about a profound change in the morphology of the monolayers: although the as-prepared MP SAMs are composed of monomers with well-defined orientations, precipitation of the amorphous mineral phase results in substantial structural disorder within the monolayers. Significantly, a preferential face of nucleation is observed for crystallization of calcite from ACC on the SAM surfaces despite this static disorder.     

Synthesis of Poly(N-ethylaniline) Nanoparticles Synthesis and Characterization of Organically Soluble Conducting Poly(N-ethylaniline) Nanoparticles using Acrylic Acid as a Soft Template

In this paper, we report the synthesis of poly(N-ethylaniline) (PNETA) by using tartaric acid (TA) as an organic acid dopant by aqueous polymerization method of N-ethylaniline using ammonium per sulphate (APS) as an oxidant and acrylic acid (AA) as a soft template. This is a new polymerization method for the direct synthesis of the emeraldine salt form of poly(N-ethylaniline) in bulk quantity, which is soluble in organic solvents such as m-cresol and N-methyl pyrrolidinone. The prepared polymers were characterized by UV, FTIR, XRD, TGA, SEM and conductivity measurement studies. The results are discussed with reference to HCl doped poly(N-ethylaniline). It is observed that PNETA/TA/AA polymer is comparatively more soluble in m-cresol than that doped with HCl in its salt form. The formation of emeraldine salt phase and dopping process was confirmed by FTIR and UV-Vis spectroscropy. We demonstrate the effect of organic dopant on the morphology and conductivity of the PNETA. It was found that, PNETA doped with TA synthesized using acrylic acid (AA) as a soft template display higher doping level, crystallinity and solubility in common organic solvent. On the contrary, HCl doped polymer was lowered at doping level and amorphous in nature which reflects the role of organic dopant and soft template. X-ray diffraction studies indicate that the PNETA/TA/AA doped samples exhibit higher crystallinity, which indicates enhanced polymer sub-chain alignment as compared to HCl doped polymer. This is also manifested by the FTIR studies. SEM result also revealed the continuous morphology and sub-micrometer size, evenly distributed particles of the PNETA/TA/AA doped polymer.     

Haloaldehyde polymers,VII. Polymerization of chlorodifluoroacetaldehyde

Chlorodifluoroacetaldehyde has been prepared by lithium aluminum hydride reduction of methyl chlorodifluoroacetate. Purified chlorodifluoroacetaldehyde was polymerized to crystalline, insoluble polychlorodifluoroacetaldehyde or to a mixture of amorphous polymer soluble in organic solvents and insoluble polymer, depending on polymerization conditions and type and amount of initiators. The polymer, particularly the soluble fraction, could be end-capped by acetylation to improve the thermal stability of the initially unstable polymer. The thermal degradation of polymer prepared by various techniques has been studied before and after acetylation and the stability was compared to that of other polyhaloacetaldehydes. Chlorodifluoroacetaldehyde was copolymerized with other haloacetaldehydes and with phenyl isocyanate.     

Synthesis and characterization of monodispersed core-shell spherical colloids with movable cores

Gold nanoparticles have been conformally coated with amorphous silica (using a sol-gel method) and then an organic polymer (via surface-grafted, atom transfer radical polymerization) to form spherical colloids with a core-double-shell structure. The thickness of silica and polymer shells could be conveniently controlled in the range of tens to several hundred nanometers by changing the concentration of the reagent and/or the reaction time. Selective removal of the silica layer (through etching in aqueous HF) led to the formation of hollow polymer beads containing movable gold cores. This new form of core-shell particles provides a unique system for measuring the feature size and transport property associated with hollow particles. In one demonstration, we showed that the thickness of a closed polymer shell could be obtained by mapping the electrons backscattered from the core and shell. In another demonstration, the plasmon resonance band of the gold cores was used as an optical probe to follow the diffusion kinetics of chemical reagents across the polymer shells.     

Imine polymers containing chiral nanohoops in the backbone obtained through [2 + 2] cyclocondensation

A simple method for synthesis of polymers containing shape persistent imine macrocycles as nanohoops in the main chain is studied. It is based on the cyclocondensation reaction carried out in solution and room temperature of triphenylamine-based tetraaldehyde compounds with (R,R)-trans-1,2-diaminocyclohexane. The pristine polymer P1 bearing long alkyl groups is soluble during the synthesis but becomes insoluble after precipitation due to the strong and multiple C H/π and π-π stacking intermolecular interactions from arene–arene species and entanglement and interpenetrating of flexible alkyl groups inside of rigid macrocycle hollow. Polymer without any solubilizing groups ( P2 ) separates during the polymerization as an insoluble material. Both polymers are amorphous and have good thermal and environmental stability. They have a low surface area because discrete nanovoids introduced by macrocycles are disconnected in the amorphous polymers and non-accessible for gas adsorption. Polymers have inherent luminescent properties due to triphenylamine groups and chirality derived from (R,R)-conformation of the cyclohexane skeleton. In presence of picric acid (PA), the polymer fluorescence in solid state or suspension is strongly quenched, thus the polymers can work as efficient fluorescent probes toward nitrophenolic compounds. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2565–2573     

Structural morphology developments in the interfacial phase of heterocoagulated composite particles: dynamic mechanical measurements

The dynamic mechanical properties of polymeric composites composed of poly (methyl methacrylate) continuous-phase and various inclusion types of heterocoagulated composite particles were investigated in order to relate them to the morphology of shell region of composite particles. Using the heterocoagulation process, large particles were encapsulated with various types of small particles: (1) conventional linear-type polymer particles; (2) crosslinked polymer particles; and (3) reactive polymer particles capable of forming crosslinked structure, whereby the interfacial properties of the composite become modified. These composite particles were subsequently annealed to form continuous shell regions and then mixed with matrix particles. It is shown that chain diffusion movement of the small particles having different chain characteristics influences the network formation at the interfacial shell region. The ability of maintaining interfacial domain structure depends on the degree of network formation.     

Phase ordering in blend films of semi‐crystalline and amorphous polymers

A combination of optical and atomic force microscopy (AFM) is used for probing changes in the morphology of polymer blend films that accompany phase ordering processes (phase separation and crystallization). The phase separation morphology of a “model” semi‐crystalline (polyethyleneoxide or PEO) and amorphous (polymethylmethacrylate or PMMA) polymer blend film is compared to previous observations on binary amorphous polymer blend films of polystyrene (PS) and polyvinylmethylether (PVME). The phase separation patterns are found to be similar except that crystallization of the film at high PEO concentrations obscures the observation of phase separation. The influence of film defects (e.g., scratches) and clay filler particles on the structure of the semi‐crystalline and amorphous polymer films is also investigated.     

Molecularly Mixed Composite Membranes for Advanced Separation Processes

Porous organic cages (POCs) are individual soluble, porous molecules. When fabricated into mixed‐matrix membranes (MMMs), the soluble POC molecules have the potential to exhibit intimate molecular‐level mixing with the polymer matrix. POCs have only recently been incorporated into mixed matrix membrane materials, but this process has not yet resulted in significant improvements of membrane performance. Now, vertex‐functionalized amorphous scrambled porous organic cages (ASPOCs) have been utilized as membrane performance enhancers and the amorphous ASPOC mixtures are observed to distribute throughout the matrix without any indication of particle formation or agglomeration, creating unique, molecularly mixed composite membranes. Overall, the molecularly mixed composite membrane provide significant increases in both membrane permeability and selectivity, offering new avenues for creation of membranes with unique properties in industrially relevant separations.     

Calcium phosphate colloids with hierarchical structure controlled by polyaspartates

 Precipitation of calcium phosphate in a double-jet experiment in the presence of sodium polyaspartic acid results in a structural evolution of stable colloidal objects with a variety of unconventional morphologies. This structural evolution is characterized by a combination of techniques, namely static and dynamic light scattering, small-angle and wide-angle X-ray scattering, and transmission electron microscopy. It is shown that after immediate formation of amorphous precursor nanoparticles with a “parachute architecture”, the system transfers into a hollow sphere morphology in the 500-nm region and is composed of plateletlike nanocrystals, and again is transferred into a final, “snowball-like” morphology of high structural definition and monodispersity. The kinetics depends on the amount and the molecular weight of the polymer, but similar structural elements are found in all the cases examined. When repeated in a triple-jet experiment, which also ensures a constant polymer concentration, it was possible to intercept a postulated intermediate structure in practically complete yield, namely crystalline hydroxyapatite nanofibres with extremely high axial ratios which form an interwoven gel. Received: 11 May 2001 Accepted: 14 September 2001     

Metallic Particles from Complexing Microcapsules Dispersed in a Silica Gel

A new process to control the distribution of metal nanoparticles is proposed. It involves the use of complexing microcapsules obtained by interfacial polycondensation. The latter are hollow spheres constituted of a polymer membrane, containing an insoluble active ingredient, such as a polyacrylic acid, which can complex Co²⁺ ions. These capsules are dispersed in a silica sol followed by thermal treatments and reduction under H₂ which results in metallic Co nanoparticles confined in the capsules domains. The particles do not diffuse in the matrix.     

Production of complex cerium-aluminum oxides using an atmospheric pressure plasma torch

Ceria-alumina particles of a wide variety of structures, from micrometer-sized hollow spheres to nanoparticles, were produced from aerosols of different natures, but all derived from nitrate salts passed through a low power (<1000 W) atmospheric pressure plasma torch. The amount of water present with the nitrate salts was found to significantly affect the morphology of the resulting material. A model was proposed that explains the mechanism in which water acts as a blowing agent to create hollow metal oxide spheres that then shatter to form metal oxide nanoparticles. Further examination of the nanoparticles revealed that they display a core/shell morphology in which the core material is crystalline CeO2 and the shell material is amorphous Al2O3. These unique core/shell materials are interesting candidates for catalyst support materials with high thermal durability. In addition, experiments have shown that the nanoparticles can be readily converted into CeAlO3 perovskite.     

Polymeric micro‐sequential concentric transcrystalline morphology self‐assembly,with intermittent self‐shear‐oriented amorphous layers

The investigation and understanding of polymer crystallization processes, the resulting crystalline morphologies, and the mechanism of their formation is crucial in creating materials with desired properties for specific applications. The present research introduces and investigates a new polymeric crystalline morphology, observed for the first time in this research. This newly observed morphology, is a sequentially micro‐multi‐layered concentric morphology that self‐assembles throughout the bulk polymer matrix, with intermittent self‐shear‐oriented amorphous layers. The research analyses the structure and mechanism of its formation. Polarized light microscopy studies have shown a drastic and sudden morphology change that occurred during crystalline growth. Crystalline‐growth kinetics studies performed, showed a distinct pulsatile repeating growth pattern of approximately two growth pulses per second. Thermal analysis indicated the presence of two different populations of crystalline strength. Crystalline structure was analyzed by XRD pattern measurements. It was demonstrated here, that the sequential concentric transcrystalline morphology is nucleated on a shear‐oriented amorphous molecular layer in the adjacent melt formed during and as a consequence of crystalline growth, which occurs in a micro‐periodic sequences, with intermittent self‐sheared amorphous layers. The structure was confirmed by both scanning electron microscope and reflectance microscopy. Small angle X‐ray scattering measurements of the same materials reported in literature are consistent with the melt shear‐orientation theory described earlier. The discovery of this new crystalline morphology in this research, potentially opens a new door in the vast field of material properties and applications. Copyright © 2017 John Wiley & Sons, Ltd.     

Multidentate-protected colloidal gold nanocrystals: pH control of cooperative precipitation and surface layer shedding

Colloidal gold nanocrystals (AuNCs) with broad size tunability and unusual pH-sensitive properties have been synthesized using multidentate polymer ligands. Because they contain both carboxylic functional groups and sterically hindered aliphatic chains, the multidentate ligands can not only reduce gold precursors but also stabilize gold nanoclusters during nucleation and growth. The "as-synthesized" AuNCs are protected by an inner coordinating layer and an outer polymer layer and are soluble in water and polar solvents. When the solution pH is lowered by just 0.6 units (from 4.85 to 4.25), the particles undergo a dramatic cooperative transition from being soluble to insoluble, allowing rapid isolation, purification, and redispersion of the multidentate-protected AuNCs. A surprising finding is that when a portion of the surface carboxylate groups are neutralized by protonation, the particles irreversibly shed their outer polymer layer and become soluble in nonpolar organic solvents. Furthermore, the multidentate polymer coatings are permeable to small organic molecules, in contrast to the tightly packed self-assembled monolayers of alkanethiols on gold. These insights are important in regard to the design of "smart" imaging and therapeutic nanoparticles that are activated by small pH changes in the tumor interstitial space or endocytic organelles.     

Multiparticle sintering dynamics: from fractal-like aggregates to compact structures

Multiparticle sintering is encountered in almost all high temperature processes for material synthesis (titania, silica, and nickel) and energy generation (e.g., fly ash formation) resulting in aggregates of primary particles (hard- or sinter-bonded agglomerates). This mechanism of particle growth is investigated quantitatively by mass and energy balances during viscous sintering of amorphous aerosol materials (e.g., SiO(2) and polymers) that typically have a distribution of sizes and complex morphology. This model is validated at limited cases of sintering between two (equally or unequally sized) particles, and chains of particles. The evolution of morphology, surface area and radii of gyration of multiparticle aggregates are elucidated for various sizes and initial fractal dimension. For each of these structures that had been generated by diffusion limited (DLA), cluster-cluster (DLCA), and ballistic particle-cluster agglomeration (BPCA) the surface area evolution is monitored and found to scale differently than that of the radius of gyration (moment of inertia). Expressions are proposed for the evolution of fractal dimension and the surface area of aggregates undergoing viscous sintering. These expressions are important in design of aerosol processes with population balance equations (PBE) and/or fluid dynamic simulations for material synthesis or minimization and even suppression of particle formation.     

Silicone nanocapsules templated inside the membranes of catanionic vesicles

A simple and effective way to synthesize hollow silicone resin particles of controlled diameter is presented. The synthesis utilizes catanionic vesicles as templates for the polycondensation/polymerization processes of 1,3,5,7-tetramethylcyclotetrasiloxane (D4H) within their membranes. Two different surfactant systems were used to form the vesicular templates: mixtures of dodecyltrimethylammonium bromide (DTAB) and sodium dodecylbenzenesulfonate (SDBS) in the cationic (the DTAB/SDBS system) or anionic (the SDBS/DTAB system) rich region of the phase diagram. The templates obtained from these surfactant mixtures form spontaneously unilamellar vesicles in aqueous solution. The vesicular templates swell upon addition of D4H, thus increasing their size. The silicone resin was obtained in acid- or base-catalyzed polycondensation and ring-opening polymerization processes of D4H. In the case of the DTAB/SDBS system the formation of a densely cross-linked silicone material with SiO3/2 units allowed the nanocapsules to retain the vesicular shape after removal of the template, whereas in the SDBS/DTAB system, the polymer produces capsules which are too smooth to support surfactant lysis. The morphology of the silicone nanocapsules was analyzed using transmission electron microscopy (TEM) and, in some cases, atomic force microscopy (AFM). TEM and AFM reveal discrete hollow particles with a small amount of linked or aggregated hollow silica shells.     

The influence of polymer morphology on polymer film electrochemistry

The electrochemical behavior of functionalized polystyrene-coated electrodes shows a marked dependence on the nature of the electrolyte ions. Scanning electron microscope and surface profile measurements are presented which show that changes in polymer film volume and morphology accompany electrochemical oxidation. Changing polymer morphology by doping the films with soluble monomers during preparation is shown to produce large changes in electrochemical response. Diffusion coefficients were determined for a neutral organic dye dopant in each of the polymer films investigated, and these correlate very well with the oxidation overpotentials observed electrochemically. The nature of polymer film/solvent interactions and the mechanism by which counter ions penetrate the polymer phase is discussed and is related to other physical properties of amorphous polymers in terms of free volume concepts.     

Control of Polymer Morphology for Biomedical Applications. I. Hydrophilic Polycarbonate Membranes for Dialysis

The control of polymer morphology for biomedical applications is discussed by a detailed reference to the tailormaking of polycarbonates for hemodialysis membranes, a case in which control was necessary on molecular, microcrystalline, and colloidal levels.

On the molecular level, the hydrophilicity of the parent polymer, bisphenol-A polycarbonate, was increased with the introduction of aliphatic ether groups by the copolymerization of bisphenol-A and the polyethylene glycols. On the microcrystalline level it was found that the bisphenol-A polycarbonate blocks formed crystallites within the amorphous matrix composed of the polyethylene oxide blocks. Because of this the modified polymer retained most of the strength of the parent bisphenold polycarbonate. Another striking property exhibited by the copolymer is that the tensile strength of the wet material was in excess of that of the dry. This has been attributed to plasticization and realignment of the polyethylene oxide blocks by water molecules. Finally, morphology on the colloidal level was controlled by the preparation of asymmetric membranes possessing a skin layer and a substructure whose void volume, and hence resistance to material transport, could be varied at will.     

Recent advances in liquid-phase combinatorial chemistry

In combination with high throughput screening, combinatorial organic synthesis of large numbers of pharmaceutically interesting compounds may revolutionize the drug discovery process. Although combinatorial organic synthesis on solid supports is a useful approach, several groups are focusing their research efforts on liquid-phase combinatorial synthesis by the use of soluble polymer supports to generate libraries. This macromolecular carrier, in contrast to an insoluble matrix, is soluble in most organic solvents and has a strong tendency for precipitation in particular solvents. Liquid-phase combinatorial synthesis is a unique approach since homogeneous reaction conditions can be applied, but product purification similar to the solid-phase method can be carried out by simple filtration and washing. This method combines the positive aspects of classical solution-phase chemistry and solid-phase synthesis. This review examines the recent applications (1995-1999) of soluble polymer supports in the synthesis of combinatorial libraries.     

Hydrogels coupled with self-assembled monolayers: an in vitro matrix to study calcite biomineralization

This paper describes the control of the nucleation and growth of calcite crystals by a matrix composed of an agarose hydrogel on top of a carboxylate-terminated self-assembled monolayer (SAM). The design of this matrix is based upon examples from biomineralization in which hydrogels are coupled with functionalized, organic surfaces to control, simultaneously, crystal morphology and orientation. In the synthetic system, calcite crystals nucleate from the (012) plane (the same plane that is observed in solution growth). The aspect ratio (length/width) of the crystals decreases from 2.1 +/- 0.22 in solution to 1.2 +/- 0.04 in a 3 w/v % agarose gel. One possible explanation for the change in morphology is the incorporation of gel fibers inside of the crystals during the growth process. Etching of the gel-grown crystals with deionized water reveals an interpenetrating network of gel fibers and crystalline material. This work begins to provide insight into why organisms use hydrogels to control the growth of crystals.