PAA Domains Research Articles

Li0.5PAA domains filled in porous sodium alginate skeleton: A 3D bicontinuous composite network binder to stabilize micro-silicon anode for high-performance lithium ion battery

An important strategy to improve energy density of Li-ion batteries is to substitute the traditional graphite anode by Si-based anode which is endowed with ultra-high theoretical specific capacity. However, the commercialization of Si anodes is hindered by its huge volume variation that results in electrode pulverization. In the current study, we fill up the pores of sodium alginate (SA) network with lithiated polyacrylic acid (LixPAA) to form a cross-linked bicontinuous composite network binder (b-Li0.5PAA@SA), in which the pores of the SA skeleton are dominated with the Li0.5PAA domains; within such composite the SA and Li0.5PAA interlock tightly each other via extensive interfacial ester bonding. The resulting b-Li0.5PAA@SA network binder can effectively buffer the volume variation of Si microparticles (m-Si) during repeating cycling and prevent pulverization of the electrode, which is evidenced by a cycling capacity of 2762 mAh g−1 in the 1st cycle and a retention of 1584 mAh g−1 after 150 cycles. As a comparison, the m-Si electrode with only SA binder suffers from fatal capacity degradation after merely 20 cycles under the same conditions. Moreover, since the Li0.5PAA domains are ionic conductive and significantly reduce the porosity of the SA network, the b-Li0.5PAA@SA network binder could also enable a stable solid electrolyte interphase (SEI) film and fast electron/ion transfer, leading to an enhanced rate capability of the m-Si anodes.

Enhancing air-dehumidification performance of polyimide membranes by generating hydrophilic Poly(amic acid) domains using partial hydrolysis

Membrane-based air-dehumidification has been considered as one of the most promising technologies for the next-generation heating, ventilation, and air-conditioning (HVAC) systems. Though attractive, polymeric membranes suffer from limitation between their H2O/N2 separation performance (i.e., H2O/N2 separation factor and H2O permeability) and their mechanical stability. Herein, we propose a facile and effective strategy, controlled partial hydrolysis, to improve the H2O/N2 separation performance of polyimide (PI) membranes while maintaining their mechanical stability. Controlled hydrolysis turned the PI membranes partially into poly (amic acid) (PAA)/PI membranes, exhibiting an asymmetric configuration with the inner layers more hydrolyzed. Interestingly, the hydrolysis in a highly concentrated NaOH solution led to formation of localized domains that were hydrolyzed (i.e., PAA domains). The localized hydrolysis of mechanically stable PI membranes led to formation of hydrophilic PAA channels embedded in the PI, thereby enhancing H2O/N2 separation performance (i.e., H2O permeability from ~6400 Barrer to ~11,000 Barrer and H2O/N2 separation factor from ~190 to ~ 320) while preserving the mechanical strength of the membranes.

Janus colloidal copolymers

We propose a new type of nanocomposite that we call Janus colloidal copolymers (JCCPs). JCCPs have two different polymers conjugated on opposite sides of a nanosized colloid. Janus clusters of copolymer PS-b-PAA (where PS is polystyrene and PAA is poly(acrylic acid)) are self-organized within confined mesoporous silica channels onto the surface of iron oxide (Fe3O4) core particles by coordination-induced adsorption. PScPAA diblock JCCPs are fabricated by selective crosslinking of the nanosized PAA domains. In addition, the crosslinked PAA domains are terminated with amine-capped polyethylene glycol (PEG) to form PS-cPAA-PEG triblock JCCPs. The cPAA domain containing functional groups can serve as a nanoreactor to allow in situ preparation of functional materials. The composite JCCPs combine the functionality of nanosized colloids with the amphiphilic performance and self-organization capability of copolymers.

Multifunctional Core‐Shell‐Corona‐Type Polymeric Micelles for Anticancer Drug‐Delivery and Imaging

We have developed core-shell-corona-type polymeric micelles that can integrate multiple functions in one system, including the capability of accommodating hydrophobic dyes into core and hydrophilic drug into the shell, as well as pH-triggered drug-release. The neutral and hydrophilic corona sterically stabilizes the multifunctional polymeric micelles in aqueous solution. The mineralization of calcium phosphate (CaP) on the PAA domain not only enhances the diagnostic efficacy of organic dyes, but also works as a diffusion barrier for the controlled release.

Polyelectrolyte–Surfactant Complex as a Template for the Synthesis of Zeolites with Intracrystalline Mesopores

Mesoporous zeolite silicalite-1 and Al-ZSM-5 with intracrystalline mesopores were synthesized with polyelectrolyte-surfactant complex as the template. Complex colloids were first formed by self-assembly of the anionic polymer poly(acrylic acid) (PAA) and the cationic surfactant cetyltrimethylammonium bromide (CTAB) in basic solution. During the synthesis procedure, upon the addition of the silica source, microporous template (tetrapropylammonium hydroxide), and NaCl, these PAA/CTA complex colloids underwent dissociation and gave rise to the formation of hollow silica spheres with mesoporous shells templated by CTAB micelles and PAA domains as the core. Under hydrothermal treatment, the hollow silica spheres gradually merged together to form larger particles with the PAA domains embedded as the space occupant, which acted as a template for intracrystalline mesopores during the crystallization of the zeolite framework. Amphiphilic organosilane was used to enhance the connection between the PAA domain and the silica phase during the synthesis. After calcination, single crystal-like zeolite particles with intracrystalline mesopores of about 5-20 nm were obtained, as characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and N(2) adsorption measurements. With the addition of an aluminum source in the synthesis, mesoporous zeolite Al-ZSM-5 with intracrystalline mesopores was also synthesized, and enhanced catalytic property was observed with mesoporous Al-ZSM-5 in acetalization of cyclohexanone with methanol.

Surface Chemistry of Protein Adhesion Domains on Diblock Copolymer Films Characterized by Chemical Force Spectroscopy Mapping Technique

Adhesions play an important role in adherent cell structures encouraging a variety of chemical and mechanical signals which, in turn, regulate cell behaviors including differentiation. In Vitro, cell substrates were modified by coating with protein ligands homogeneously, in cellular scale, allowing cell attachment and proliferation. However, extracellular matrices in reality provide heterogeneous adhesive sites. To mimic this, diblock copolymer films (dBCP) of polystyrene-block-polyacrylic acid (PS-b-PAA)and polystyrene-block-polyethylene oxide (PS-b-PEO) were introduced. The combinations by molar of PS-b-PAA and PS-b-PEO, 100:0, 75:25, 50:50, 25:75, and 0:100, were applied to establish the patched-like structure. Consequently, the films were examined the surface chemicals by chemical force spectroscopy mapping (CFSM) based on atomic force microscopy. The probe coated by the protein of poly-l-lysine to enhance the adhesive interaction between the probe and the surface was applied on the surface spatially and revealed the features of adhesive domains down to nanoscale. Area fraction of PAA decreases from 90% to 10% corresponding to the amount of PAA, as well as the PAA domain decreasing from 2 to 0.02 μm2. Because PAA offers protein immobilization, meanwhile PEO prevents protein adsorption, therefore dBCP combinations show differences in concentration of protein lysates. Adherent cells like mesenchymal stem cell, in future work, will be cultured on the films and examined responses, like morphology, proliferation, and differentiation.

Deposition of silver nanoparticles on single wall carbon nanotubes via a self assembled block copolymer micelles

We demonstrate a facile route to decorate the surface of networked single walled carbon nanotubes (SWNTs) with silver nanoparticles (Ag NPs). The method is based on utilization of either spherical poly(styrene- b-4vinylpyridine) (PS- b-P4VP) or cylindrical poly(styrene- b-acrylic acid) (PS- b-PAA) copolymer micelles capable of stabilizing nanotubes in solution and subsequently forming a thin and uniform block copolymer/SWNTs composite film upon spin coating. The selective doping of silver acetate into either P4VP or PAA domains in a thin composite film, followed by thermal treatment, results in the formation of Ag NPs in the cores of micelles. Further heat treatment at 500 °C sufficiently high for degrading both block copolymers allows us to fabricate a thin SWNTs network in which Ag NPs are efficiently deposited on the surface of nanotubes. A sharp surface plasmon absorption band around 400 nm of the networked SWNTs with Ag NPs confirms the presence of Ag NPs with narrow distribution in their size.

Amphiphilic Block Copolymer Films: Phase Transition, Stabilization, and Nanoscale Templates

A morphological transition of asymmetric poly(styrene-b-acrylic acid) (PS-b-PAA) films is observed by in situ scanning probe microscopy (SPM) in aqueous media. Upon initial exposure to buffer solution at pH 7.4, spherical PAA domains swell through a glassy PS surface layer to form negatively charged mushroom caps. With further exposure, the PAA caps coalesce to produce a smooth, highly wettable surface. However, if films are exposed to a buffer solution containing 3-aminopropyltriethoxysilane (APTES) for 1 h, the PAA domain swelling is greatly reduced and the mushroom caps stabilize at a diameter of 33 nm. This stabilization results from a cross-linking reaction between PAA and APTES, which also converts the PAA domains from a net negative to net positive charge. By varying molecular weights of PAA block in PS-b-PAA, the feature size and spacing can be tuned. To demonstrate an application for this template with positively charged domains, a cytoskeletal filament, F-Actin with a net negative charge, is org...

Functional Nanocavity Arrays via Amphiphilic Block Copolymer Thin Films

The amphiphilic block copolymer polystyrene-block-poly(acrylic acid) (PS-b-PAA) forms micelles in toluene that can be cast onto a planar substrate to create quasi-hexagonal arrays of spherical PAA domains in a PS matrix. Treatment of these ultrathin films with an appropriate selective solvent swells the PAA domains and fractures open (cavitates) the PS matrix, thereby exposing the PAA chains to solution. Here we have investigated the conditions required for this cavitation process to occur and the end-state polymer morphology of close-packed films of PS-b-PAA micelles following treatment with a series of short alkyl chain alcohols or aqueous solutions of varying pH and ionic strength. Atomic force microscopy (AFM) and transmission electron microscopy (TEM) were employed to characterize the morphologies of the precursor and solvent-treated films. In addition to the effects of solvent conditions, we show that the cavitation process is influenced by the molecular weight of the PS block and is thermally rever...

Creating Patterned Carbon Nanotube Catalysts through the Microcontact Printing of Block Copolymer Micellar Thin Films

We report a route for synthesizing patterned carbon nanotube (CNT) catalysts through the microcontact printing of iron-loaded poly(styrene-block-acrylic acid) (PS-b-PAA) micellar solutions onto silicon wafers coated with thin aluminum oxide (Al(2)O(3)) layers. The amphiphilic block copolymer, PS-b-PAA, forms spherical micelles in toluene that can form quasi-hexagonal arrays of spherical PAA domains within a PS matrix when deposited onto a substrate. In this report, we dip a poly(dimethylsiloxane) (PDMS) molded stamp into an iron-loaded micellar solution to create a thin film on the PDMS features. The PDMS stamp is then put in contact with a substrate, and uniaxial compressive stress is applied to transfer the micellar thin film from the PDMS stamp onto the substrate in a defined pattern. The polymer is then removed by oxygen plasma etching to leave a patterned iron oxide nanocluster array on the substrate. Using these catalysts, we achieve patterned vertical growth of multiwalled CNTs, where the CNTs maintain the fidelity of the patterned catalyst, forming high-aspect-ratio standing structures.

Ethoxylated Nonionic Surfactants in Hydrophobic Solvent: Interaction with Aqueous and Membrane-Immobilized Poly(acrylic acid)

Interaction between ethoxylated nonionic surfactants and poly(acrylic acid) (PAA) in aqueous solutions is well-documented in the literature. In the present study, pure ethoxylated surfactant solution in a hydrophobic solvent was permeated through a partially cross-linked PAA composite membrane to quantify the surfactant-PAA interaction in the heterogeneous system. Partitioning of the mixture of the surfactants (15-S-5) between the hydrophobic solvent and aqueous solution of PAA was also studied. The role of ethylene oxide group variation in the surfactant-PAA interaction for the heterogeneous system was established by performing experiments with pure surfactants having the same alkyl chain length but varying ethoxylate chain lengths. It was observed that the surfactants with a higher number of ethylene oxide groups per molecule exhibit stronger interaction with PAA. The literature data for adsorption of pure ethoxylated surfactants (C12E(n)) on a hydrophobic solid-water interface was correlated and compared with the data obtained in our study. It was calculated that resistance in terms of transfer of surfactant molecules from a hydrophobic solvent domain to PAA domain lowers the extent of PAA-surfactant interaction by an order of magnitude. Only 40% of available carboxyl groups were accessible for interaction with the ethoxylated nonionic surfactants due to diffusion limitations. Finally the pH sensitivity of the PAA-surfactant complex was verified by successful regeneration of the membrane on permeation of slightly alkaline water. The regeneration and reuse of membrane is especially attractive in terms of process development for nonionic surfactant separation from hydrophobic solvents.

Strategies for Controlling the Planar Arrangement of Block Copolymer Micelles and Inorganic Nanoclusters

We report several strategies for varying the diameter, the center-to-center spacing, and the areal density of block copolymer micelles, or inorganic nanoclusters synthesized in the cores of the micelles, on planar substrates. The amphiphilic block copolymer, poly(styrene-b-acrylic acid) (PS/PAA), forms micelles in toluene solution that can be spin-coated onto a substrate to create quasi-hexagonal arrays of spherical PAA domains within a PS matrix. The carboxylic acid groups within the PAA domains can be utilized in a nanoreactor synthesis scheme to create inorganic nanocluster arrays, or the PAA domains can be cavitated to expose the carboxylic acid groups to the surface for possible covalent coupling reactions. The strategies we use to vary the planar arrangements include variation of the molecular weight of PS/PAA, variation of the amount of metal loaded into the micellar solution, addition of PS homopolymer into the micellar solution, and the mixing of different micellar solutions. Through these routes, we demonstrate varying the diameter of the inorganic nanoclusters from 4.7 to 16 nm and the areal density from 8 × 1010 to 6.5 × 109 nanoclusters cm-2. We are also able to create arrays of nanoclusters containing more than one inorganic species, with each nanocluster containing either one or all of the inorganic species, depending on the sequence of processing conditions employed. We characterize these arrays using energy-dispersive X-ray analysis on a scanning transmission electron microscope.

A pH-sensitive EVAL membrane by blending with PAA

The purpose of this study was to produce pH-sensitive domain in the dense poly(ethylene-co-vinyl-alcohol) (EVAL) membrane for colonic delivery of anti-cancer drug 5-fluorouracil (5-FU) by blending with a small amount of poly(acrylic acid) (PAA). The Fourier transform infrared (FTIR) spectroscopy analysis shows that PAA and EVAL were not very compatible in the PAA/EVAL blended membrane, whereas the intensity of self-association of both polymers was higher than that of inter-association between PAA and EVAL. It was proposed that PAA molecules would aggregate to act as the access for the transport of 5-FU through the blended membranes. The aggregated PAA gel phases were beyond the observable sensitivity of the scanning electron microscopy (SEM) and were low permeable for 5-FU at low pH, but significantly improved the permeability of 5-FU by the increase of pH of the medium, which agreed with the application of colon-specific drug delivery. When the membrane preparation temperature was changed from 60 to 45 °C, PAA domain contained in the blended membrane did not affect the permeation rate of 5-FU at different pH. This is because the membrane prepared at 45 °C was not so dense as that prepared at 60 °C. Therefore, the pH-sensitive characteristic of PAA domains would be applicable only to the membrane with a dense structure. Finally, it was demonstrated that 5-FU separated by the blended membranes still exhibited cytotoxicitiy toward Caco-2 cells at pH 7.4. Thus, the PAA/EVAL blended membrane is a potential material for the specific delivery of 5-FU to the colon for local treatment of colorectal cancer in the future clinical application.

Fabrication of Hybrid Nanocapsules by Calcium Phosphate Mineralization of Shell Cross-Linked Polymer Micelles and Nanocages

Self-assembled shell cross-linked poly(acrylic acid-b-isoprene) (PAA78-b-PI97) micelles or cross-linked PAA nanocages in aqueous solution were used as templates for the preparation of novel polymer-inorganic nanocapsules. The hybrid nanostructures were typically 50-70 nm in diameter and consisted of spherical polymer nanoparticles or nanocages enclosed within a continuous 10-20 nm thick surface layer of amorphous calcium phosphate. Nucleation of calcium phosphate specifically in association with the polymer nanoparticles was facilitated by low supersaturation levels and by sequestration of Ca2+ ions within the carboxylate-rich PAA domains prior to addition of HPO4(2-). Modifications in ionic concentrations were used to control the calcium phosphate surface layer thickness and prepare mineralized cross-linked PAA-b-PI micelles with variable shell permeability. The permeability of beta-carotene into the hydrophobic PI core of mineralized shell cross-linked PAA-b-PI micelles was reduced by approximately 50 or 100% respectively for hybrid nanostructures enclosed within 10 or 20 nm thick calcium phosphate layers. Our results suggest that calcium phosphate-polymer cross-linked nanocapsules could have potential applications as pH-responsive biocompatible hybrid nanostructures for use in applications such as drug delivery, bioimaging, and therapeutics.

Using Block Copolymer Micellar Thin Films as Templates for the Production of Catalysts for Carbon Nanotube Growth

We report a novel approach that uses block copolymer micelles as a means to create large area arrays of iron-containing nanoclusters capable of catalyzing the growth of carbon nanotubes (CNTs). The amphiphilic block copolymer poly(styrene-block-acrylic acid) (PS-b-PAA) forms micelles in solution which are capable of self-organizing into ordered structures on surfaces. By spin-coating these solutions onto a variety of substrates, we can create quasi-hexagonal arrays of PAA spheres within a PS matrix. The carboxylic acids groups in the PAA domains can be utilized in an ion-exchange protocol to selectively sequester iron ions, which results in iron-containing nanoclusters that are nearly monodisperse in size (diameter ∼8 nm) and patterned at a density of approximately 1011 particles per cm2. In principle, this route for synthesizing iron-containing nanoclusters offers the capability of controlling the cluster size and spacing by altering the molecular weight of the block copolymer. In this report, we demonst...

About the compatibility of polymer components in polymer complexes based on poly(acrylamide) and poly(vinyl alcohol)

The issue of applying the usual concepts of polymer compatibility to nonstoichiometric PVA/PAA mixtures of chemically complementary poly(vinyl alcohol) and poly(acrylamide), which form in water solution InterPC (intermolecular polymer complex) stabilyzed by H-bonds, and PAA to PVA graft copolymers (PVA-PAA N ) with different grafted chains number N, that are IntraPC (intramolecular polymer complexes) is discussed. PVA and PAA are compatible on molecular level. At the same time PVA/PAA mixture (50/50 W/W) is characterized by heterogeneous structure consists of InterPC with φ char =9g PVA /g PAA and the excess of unconnected PAA. In the case of IntraPC, yet, only PVA-PAA N , where N=25, is characterized by a single glass transition temperature (Tg). At larger values of N separate PAA domains form giving rise to the corresponding Tg. These results are discussed in view of IntraPC structure peculiarities as a function of N investigated by IR spectroscopy.

Molecular Mechanism of Diltiazem Interaction with L-type Ca2+ Channels

Benzothiazepine Ca2+ antagonists (such as (+)-cis-diltiazem) interact with transmembrane segments IIIS6 and IVS6 in the alpha1 subunit of L-type Ca2+ channels. We investigated the contribution of individual IIIS6 amino acid residues for diltiazem sensitivity by employing alanine scanning mutagenesis in a benzothiazepine-sensitive alpha1 subunit chimera (ALDIL) expressed in Xenopus laevis oocytes. The most dramatic decrease of block by 100 microM diltiazem (ALDIL 45 +/- 4.8% inhibition) during trains of 100-ms pulses (0.1 Hz, -80 mV holding potential) was found after mutation of adjacent IIIS6 residues Phe1164(21 +/- 3%) and Val1165 (8.5 +/- 1.4%). Diltiazem delayed current recovery by promoting a slowly recovering current component. This effect was similar in ALDIL and F1164A but largely prevented in V1165A. Both mutations slowed inactivation kinetics during a pulse. The reduced diltiazem block can therefore be explained by slowing of inactivation kinetics (F1164A and V1165A) and accelerated recovery from drug block (V1165A). The bulkier diltiazem derivative benziazem still efficiently blocked V1165A. From these functional and from additional radioligand binding studies with the dihydropyridine (+)-[3H]isradipine we propose a model in which Val1165 controls dissociation of the bound diltiazem molecule, and where bulky substituents on the basic nitrogen of diltiazem protrude toward the adjacent dihydropyridine binding domain.

Morphological Study of Polymer Blend of Poly (acrylic acid) and Polystyrene by Inverse Gas Chromatography

The surface structure of a polymer blend of poly(acrylic acid) (PAA) and polystyrene (PS) was investigated by means of inverse gas chromatography (IGC) and scanning electron microscopy (SEM). The following morphological changes were found: The PAA and PS domains form the sea and island phases, respectively, regardless of the composition. The size of the PS domain greatly increases in the range from ca. 30 to ca. 50 wt% PS. At ca. 60 wt% PS, the PS domain becomes small in size and is dispersed on the PAA domain, and protrudes from the PAA domain in a ball-like shape. Above ca. 75 wt% PS, the ball-like PS domains are aggregated and spread over the surface of the PAA domain. However, the PS domain does not completely cover the PAA domain and leaves some vacant spaces. The surface structure undergoes no great change by thermal treatment below ca. 50 wt% PS. Above ca. 60wt% PS, the ball-like PS domain is melted by thermal treatment and spreads over the PAA domain. The change in the surface area of a polymer blend by thermal treatment can be estimated from the difference in retention volume of the first and second measurements carried out using the same column.

Porosity of membranes consisting of hydrophilic domains in a hydrophobic matrix

Vapour adsorption curves of water for poly(acrylic acid) (PAA) grafted onto polypropylene (PP) show a larger water uptake for membranes than for moulded samples. Both adsorptions are higher than that calculated for the water dissolved by adsorption in the PAA alone. This shows the existence of porosity, which was confirmed by permeance and ultrafiltration tests. Porosity can be related to microfractures in the PP matrix caused by the swelling of PAA domains. A simplified mechanical model of the system based on the stress analysis of a sphere which swells in a rigid matrix, shows the possibility of microfracture formation.