Structure and protein binding capacity of a planar PAA brush

We performed neutron reflectometry (NR) and total internal reflection fluorescence (TIRF) spectroscopy to characterize the structure and the protein binding capacity of a planar poly(acrylic acid) (PAA) brush at different temperatures. A PAA brush was prepared by spin-coating planar quartz or silicon wafers with a thin film of poly(styrene). Then, the diblock copolymer poly(styrene)-poly(acrylic acid) was deposited on these modified wafers using the Langmuir-Sch?fer or Langmuir-Blodgett technique. PAA grafting densities of about 0.1 chains per nm2 were obtained. The NR experiments indicate a remarkable swelling of the PAA brush in contact with a buffer solution, when it is heated to 40 degrees C for several hours. The swollen brush structure remains upon cooling back to 20 degrees C suggesting a disentanglement of the initially formed PAA brush by the temporary heating. At pD = 6.7, the protein bovine serum albumin (BSA) with a negative net charge is strongly adsorbed to the swollen PAA brush. From the scattering length density profiles obtained from the NR curves, an almost homogeneous filling of the whole PAA brush space with BSA molecules can be deduced corresponding to an average BSA volume fraction of about 7-10% and an adsorbed protein mass of about 1.4 mg m-2. By analyzing the TIRF experiments, it is found that BSA adsorption is enhanced when increasing the temperature which represents an evidence for an entropic driving force for protein adsorption. However, the mechanism of BSA adsorption at a PAA brush appears to be different at 20 and 40 degrees C.     

Fabrication of polyelectrolyte multilayer films comprising nanoblended layers

Polyelectrolyte multilayer thin films were prepared via the alternate deposition of poly(allylamine hydrochloride) (PAH) and a blend of poly(acrylic acid) (PAA) and poly(styrenesulfonate) (PSS). When the pH of the blend solution was 3.5, the presence of PAA in this solution significantly increased the total film thickness. With only 10 wt % PAA in the blend adsorption solution, a large increase in film thickness was observed (92 nm cf. 18 nm). It was also demonstrated that the total amount of PSS adsorbed was enhanced by the presence of PAA in the blend solution, showing that the blend solution composition influenced that of the multilayer films. Thin films prepared with nanoblended layers also showed improved pH stability, because they exhibited reduced film rearrangement upon exposure to acidic conditions (pH = 2.5).     

Anisotropic thermal expansion behavior of thin films of polymethylsilsesquioxane, a spin-on-glass dielectric for high-performance integrated circuits

Thin films of poly(methylsilsesquioxane) (PMSSQ) are candidates for use as interdielectric layers in advanced semiconductor devices with multilayer structures. We prepared thin films of PMSSQ with thicknesses in the range 25.0-1151.0 nm by spin-casting its soluble precursor onto Si and GaAs substrates with native oxide layers and then drying and curing the films under a nitrogen atmosphere at temperatures in the range 250-400 degrees C. The out-of-plane thermal expansion coefficient alpha(perpendicular) of each film was measured over the temperature range 25-200 degrees C using spectroscopic ellipsometry and synchrotron X-ray reflectivity, while the in-plane thermal expansion coefficient alpha(parallel) of each film was determined over the temperature range 25-400 degrees C by residual stress analysis. PMSSQ films cured at higher temperatures exhibited reduced thermal expansion, which is attributed to the denser molecular packing and higher degree of cross-linking that arises at higher temperatures. Surprisingly however, all the PMSSQ films were found to exhibit very strong anisotropic thermal expansion; alpha(perpendicular) and alpha(parallel) of the films were in the ranges 140-329 ppm/ degrees C and 12-29 ppm/ degrees C respectively, depending on the curing temperature. This is the first time that cured PMSSQ thin films have been shown to exhibit anisotropic thermal expansion behavior. This anisotropic thermal expansion of the PMSSQ thin films might be due to the anisotropy of cross-link density in the films, which arises because of a combination of factors: the preferential orientation of methyl groups toward the upper film surface and the preferential network formation in the film plane that occurs during curing of the confined film. In addition, the film electron densities were determined using synchrotron X-ray reflectivity measurements and the film biaxial moduli were obtained using residual stress analysis.     

Polyelectrolyte blend multilayer films: surface morphology, wettability, and protein adsorption characteristics

We report the influence of polyelectrolyte (PE) multilayer films prepared from poly(styrene sulfonate)-poly(acrylic acid) (PSS-PAA) blends, deposited in alternation with poly(allylamine hydrochloride) (PAH), on film wettability and the adsorption behavior of the protein immunoglobulin G (IgG). Variations in the chemical composition of the PAH/(PSS-PAA) multilayer films, controlled by the PSS/PAA blend ratio in the dipping solutions, were used to systematically control film thickness, surface morphology, surface wettability, and IgG adsorption. Spectroscopic ellipsometry measurements indicate that increasing the PSS content in the blend solutions results in a systematic decrease in film thickness. Increasing the PSS content in the blend solutions also leads to a reduction in film surface roughness (as measured by atomic force microscopy), with a corresponding increase in surface hydrophobicity. Advancing contact angles (theta) range from 7 degrees for PAH/PAA films through to 53 degrees for PAH/PSS films. X-ray photoelectron spectroscopy measurements indicate that the increase in film hydrophobicity is due to an increase in PSS concentration at the film surface. In addition, the influence of added electrolyte in the PE solutions was investigated. Adsorption from PE solutions containing added salt favors PSS adsorption and results in more hydrophobic films. The amount of IgG adsorbed on the multilayer films systematically increased on films assembled from blends with increasing PSS content, suggesting strong interactions between PSS in the multilayer films and IgG. Hence, multilayer films prepared from blended PE solutions can be used to tune film thickness and composition, as well as wetting and protein adsorption characteristics.     

Temperature responsive complex coacervate core micelles with a PEO and PNIPAAm corona

In aqueous solutions at room temperature, poly( N-methyl-2-vinyl pyridinium iodide)- block-poly(ethylene oxide), P2MVP 38- b-PEO 211 and poly(acrylic acid)- block-poly(isopropyl acrylamide), PAA 55- b-PNIPAAm 88 spontaneously coassemble into micelles, consisting of a mixed P2MVP/PAA polyelectrolyte core and a PEO/PNIPAAm corona. These so-called complex coacervate core micelles (C3Ms), also known as polyion complex (PIC) micelles, block ionomer complexes (BIC), and interpolyelectrolyte complexes (IPEC), respond to changes in solution pH and ionic strength as their micellization is electrostatically driven. Furthermore, the PNIPAAm segments ensure temperature responsiveness as they exhibit lower critical solution temperature (LCST) behavior. Light scattering, two-dimensional 1H NMR nuclear Overhauser effect spectrometry, and cryogenic transmission electron microscopy experiments were carried out to investigate micellar structure and solution behavior at 1 mM NaNO 3, T = 25, and 60 degrees C, that is, below and above the LCST of approximately 32 degrees C. At T = 25 degrees C, C3Ms were observed for 7 < pH < 12 and NaNO 3 concentrations below approximately 105 mM. The PEO and PNIPAAm chains appear to be (randomly) mixed within the micellar corona. At T = 60 degrees C, onion-like complexes are formed, consisting of a PNIPAAm inner core, a mixed P2MVP/PAA complex coacervate shell, and a PEO corona.     

Dewetting Behavior of Hydrogen Bonded Polymer Complex Film under Hydrothermal Condition

Hydrogen-bonded polymer complex films with the thickness ranging from 50 nm to 2400 nm were prepared by layer-by-layer (LbL) assembly of poly(2-ethyl-2-oxazoline) (PEOX) and poly(acrylic acid) (PAA). The dewetting behavior of PEOX/PAA films under hydrothermal condition was investigated. It was found that the dewetting occurred at solid-liquid interface, and the typical morphologies such as holes, irregular cellular structure, and droplets were observed. Atomic force microscopy (AFM) revealed the initial rupture of the film. Microscopic Raman and infrared (IR) imaging demonstrated that the PEOX and PAA chains remained association during the dewetting process.     

Selective hydrogenation of monosubstituted alkenes by Pd nanoparticles embedded in polyelectrolyte films

Pd nanoparticles embedded in multilayer polyelectrolyte films can be easily prepared through layer-by-layer adsorption of poly(acrylic acid) (PAA) and poly(ethyleneimine)-Pd2+ (PEI-Pd(II)) complexes followed by reduction of Pd(II) with NaBH4. Transmission electron microscopy confirms the formation of Pd particles with diameters of 1-3 nm. Remarkably, [PAA/PEI-Pd(0)]3PAA films catalyze the hydrogenation of monosubstituted alkenes with turnover frequencies that are as much as 100-fold higher than turnover frequencies for hydrogenation of multiply substituted double bonds. Selectivities in the hydrogenation of monosubstituted over multisubstituted double bonds are higher than those of Wilkinson's catalyst. Moreover, the turnover frequency for the hydrogenation of allyl alcohol did not change when the catalyst was recycled three times. Intramolecular selectivity for the hydrogenation of monosubstituted alkenes also occurs when substrate molecules contain both mono and multiply substituted double bonds. The combination of the encapsulating polyelectrolyte film and small nanoparticles apparently results in hindered access of multiply substituted double bonds to catalytic sites.     

Characterization of stimuli-sensitive polymers for biomedical applications

Stimuli-sensitive polymers were synthesized by copolymerizing varying ratios of N-isopropyl acrylamide(NIPAAm) and acrylic acid(AAc). The influence of polyelectrolytes on the lower critical solution temperatures(LCSTs) of these temperature/pH sensitive polymers was investigated in the pH range of 2-12. Polyelectrolyte complexes were prepared by mixing poly(NIPAAm-co-AAc) as anionic polyelectrolyte with poly(allyl amine)(PAA) or poly(L-lysine)(PLL) as cationic polyelectrolytes, respectively. Back titration was performed to determine the pK_a values of PAAc in poly(NIPAAm-co-AAc) and to study the effect of comonomer ionization on the cloud point temperature. The effect of polyelectrolyte complex formation on the conformation of PLL was studied as a function of temperature by means of circular dichroism(CD). The swelling ratio of poly(NIPAAm-co-AAc) hydrogels as a function of pH at various temperature was obtained by measuring the weight of the hydrogels in buffer solutions. The LCSTs of the poly(NIPAAm-co-AAc) were strongly affected by pH, polyelectrolyte solutes, AAc content, and charge density. The influence of more hydrophobic PLL as a polyelectrolyte on the cloud point of PNIPAAm/water in the copolymer was stronger than that of poly(allyl amine)(PAA). Indomethacin was loaded into these hydrogels, and controlled release of this molecule from the hydrogel was determined under various temperature and pH conditions using UV/Vis spectrophotometry.     

Synthesis, multilayer film assembly, and capsule formation of macromolecularly engineered acrylic acid and styrene sulfonate block copolymers

We report the use of copolymers synthesized with specific block ratios of weakly and strongly charged groups for the preparation of stable, pH-responsive multilayers. In this study, we utilized reversible addition-fragmentation chain transfer (RAFT) polymerization in the synthesis of novel pH-sensitive copolymers comprising block domains of acrylic acid (AA) and styrene sulfonate (SS) groups. The PAA x- b-SS y copolymers, containing 37%, 55%, and 73% of AA groups by mass (denoted as PAA 37- b-SS 63, PAA 55- b-SS 45, and PAA 73- b-SS 27, respectively), were utilized to perform stepwise multilayer assembly in alternation with poly(allylamine hydrochloride), PAH. The ratio of AA to SS groups, and the effect of the pH of both anionic and cationic adsorption solutions, on multilayer properties, were investigated using ellipsometry and atomic force microscopy. The presence of SS moieties in the PAA x- b-SS y copolymers, regardless of the precise composition, lead to films with a relatively consistent thickness. Exposure of these multilayers to acidic conditions postassembly revealed that these multilayers do not exhibit the characteristic large swelling that occurs with PAA/PAH films. The film stability was attributed to the presence of strongly charged SS groups. PAA x- b-SS y/PAH films were also formed on particle substrates under various adsorption conditions. Microelectrophoresis measurements revealed that the surface charge and isoelectric point of these core-shell particles are dependent on assembly pH and the proportion of AA groups in PAA x- b-SS y. These core-shell particles can be used as precursors to hollow capsules that incorporate weak polyelectrolyte functionality. The role of AA groups in determining the growth profile of these capsules was also examined. The multilayer films prepared may find applications in areas where pH-responsive films are required but large film swelling is unfavorable.     

High-capacity binding of proteins by poly(acrylic acid) brushes and their derivatives

Polymeric coatings with high protein-binding capacities are important for increasing the output of affinity-based protein purification and decreasing the detection limits of antibody microarrays. This report describes the use of thick poly(acrylic acid) (PAA) brushes to immobilize as much as 80 monolayers of protein. The brushes were prepared using a recently developed procedure that allows polymerization of 100-nm-thick poly(tert-butyl acrylate) films from a surface in just 5 min along with hydrolysis of these films to PAA in 15 min. Covalent binding of bovine serum albumin (BSA) to PAA brushes that were activated using standard coupling agents, however, resulted in immobilization of less than two monolayers of BSA because of competitive hydrolysis of the esters in the activated film. In contrast, derivatization of PAA with nitrilotriacetate (NTA)-Cu2+ complexes yielded films capable of binding many monolayers of protein via metal-ion affinity interactions. For example, derivatization of 55-nm-thick PAA films with NTA-Cu2+ allowed immobilization of about 15 monolayers (5.8 microg/cm2 or 58 nm) of BSA. The binding capacity was even higher for myoglobin (7.7 microg/cm2) and anti-IgG (9.6 microg/cm2). Remarkably, electrostatic adsorption of lysozyme in 55-nm-thick, underivatized PAA resulted in as much as 80 monolayers (16.2 microg/cm2 or 162 nm) of adsorbed protein. Polymer synthesis, derivatization, and swelling, as well as BSA immobilization kinetics and thermodynamics were characterized using reflectance FT-IR spectroscopy, ellipsometry, and protein assays.     

Robust, functionalizable, nanometer-thick poly(acrylic acid) films spontaneously assembled on oxidized aluminum substrates: structures and chemical properties

Immersion of oxidized aluminum substrates in ethanol solutions of poly(acrylic acid) (PAA), followed by extensive solvent immersion, results in tenaciously chemisorbed, nanometer scale, controllable thickness films for a wide range of solution concentrations and molecular weights. Atomic force microscope images reveal isolated polymer globules from adsorption in low-concentration solutions with crossover to conformal, highly uniform, nanometer-thickness films at higher concentrations, an indication that the chemisorbing chains start to overlap and trap underlying segments to form planar chemisorbed films only two or three chains in thickness. Quantitative IR reflection spectroscopy in combination with chemical derivitization on a standard set of 1.0(±0.2) nm thick films reveals a film structure with 5.5(±1) chemisorbed -CO(-)(2) groups/nm(2) and 6.3 unattached -CO(2)H groups/nm(2), with up to ～3.6/nm(2) available for chemical derivitization, a comparable number to typical self-assembled monolayer coverages of ～4-5 molecules/nm(2). Thermal treatment of the ～1 nm chemisorbed films, at even extreme temperatures of ～150 °C, results in almost no anhydride formation via adjacent -CO(2)H condensation, in strong contrast to bulk PAA, a clear indication that the films have a frozen glass structure with effectively no segment and side group mobility. Overall, these results demonstrate that these limiting thickness nanometer films provide a model surface for understanding the behavior of strongly bound polymer chains at substrates and show potential as a path to creating highly stable, chemically functionalized inorganic substrates with highly variable surface properties.     

Gradient immobilization of a cell adhesion RGD peptide on thermal responsive surface for regulating cell adhesion and detachment

Using surface initiated atomic transfer radical polymerization (ATRP) and an injection method, a poly(N-isopropylacrylamide)-b-poly(acrylic acid)-g-RGD (PNIPAAm-b-PAA-g-RGD) gradient surface was prepared. First, a thermoresponsive surface with a constant thickness of PNIPAAm was fabricated, onto which the AA monomers were block copolymerized using the PNIPAAm macromolecules as initiators. During this process, a continuous injection method was employed to yield a molecular weight gradient of PAA on the underlying uniform PNIPAAm layer. RGD peptide was finally covalently immobilized onto the PAA gradient by carbodiimide chemistry. In vitro culture of HepG2 cells showed that immobilization of the RGD peptide could accelerate cell attachment, while the thermoresponsive layer beneath could effectively release the cells by simply lowering temperature. Thus, the PNIPAAm-b-PAA-g-RGD gradient surface, combining the thermal response with cell affinity properties, can well regulate the cell adhesion and detachment, which may thus be useful for investigation of cell-substrate interactions with a smaller number of samples.     

Temperature-controlled flow switching in nanocapillary array membranes mediated by poly(N-isopropylacrylamide) polymer brushes grafted by atom transfer radical polymerization

We report actively controlled transport that is thermally switchable and size-selective in a nanocapillary array membrane (NCAM) prepared by grafting poly(N-isopropylacrylamide) (PNIPAAm) brushes onto the exterior surface of a Au-coated polycarbonate track-etched membrane. A smooth Au layer on the membrane surface, which is key to obtaining a uniform polymer film, was prepared by thermal evaporation of approximately 50 nm Au on both exterior surfaces. After evaporation, the inner diameter of the pore is reduced slightly, but the NCAM retains a narrow pore size distribution. PNIPPAm brushes with 10-30 nm (dry film) thickness were grafted onto the Au surface through surface-initiated atom transfer radical polymerization (ATRP) using a disulfide initiator, (BrC(CH3)2COO(CH2)11S)2. Molecular transport through the PNIPAAm polymer brush-modified NCAMs was investigated by real-time fluorescence measurements using fluorescein isothiocyanate (FITC)-labeled dextrans ranging from 4.4 to 282 kDa in membranes with variable initial pore diameters (80, 100, and 200 nm) and different PNIPAAm thicknesses. Manipulating the temperature of the NCAM through the PNIPAAm lower critical solution temperature (LCST) causes large, size-dependent changes in the transport rates. Over specific ranges of probe size, transport is completely blocked below the LCST but strongly allowed above the LCST. The combination of the highly uniform PNIPAAm brush and the monodisperse pore size distribution is critical in producing highly reproducible switching behavior. Furthermore, the reversible nature of the switching raises the possibility of using them as actively controlled filtration devices.     

Effect of thickness on the thermal properties of hydrogen-bonded LbL assemblies

Layer-by-layer (LbL) assemblies have attracted much attention for their functional versatility and ease of fabrication. However, characterizing their thermal properties in relation to the film thickness has remained a challenging topic. We have investigated the role of film thickness on the glass transition temperature (T(g)) and coeffecient of thermal expansion for poly(ethylene oxide)/poly(acrylic acid) (PEO/PAA) and PEO/poly(methacrylic acid) (PEO/PMAA) hydrogen-bonded LbL assemblies in both bulk and ultrathin films using modulated differential scanning calorimetry (modulated DSC) and temperature-controlled ellipsometry. In PEO/PAA LbL films, a single, well-defined T(g) was observed regardless of film thickness. The T(g) increased by 9 °C relative to the bulk T(g) as film thickness decreased to 30 nm because of interactions between the film and its substrate. In contrast, PEO/PMAA LbL films show a single glass transition only after a thermal cross-linking step, which results in anhydride bonds between PMAA groups. The T(g), within error, was unaffected by film thickness, but PEO/PMAA LbL films of thicknesses below ~2.7 μm exhibited a small amount of PEO crystallization and phase separation for the thermally cross-linked films. The coefficients of thermal expansion of both types of film increased with decreasing film thickness.     

Controlling the internal structure of giant unilamellar vesicles by means of reversible temperature dependent sol-gel transition of internalized poly(N-isopropyl acrylamide)

In this work, we present preparation and basic applications of lipid-bilayer-enclosed picoliter volumes (microcontainers) of solutions of poly(N-isopropylacrylamide) (PNIPAAm). Giant unilamellar vesicles (GUVs) were prepared from phospholipids using a standard swelling procedure and subsequently surface immobilized. Clear, slightly viscous solutions of PNIPAAm of varying concentration in aqueous buffer were directly pressure-microinjected into the GUVs, using a submicrometer-sized, pointed capillary. The GUV was subjected to changing temperature over a 21-40 degrees C range. The typical phase transition of the polymeric material upon heating and cooling across the lower critical solution temperature was followed using optical microscopy and shown to be reversible over multiple sequential heating/cooling cycles without compromising the integrity of the GUV membrane. Fluorescent, carboxylic acid modified 200 nm latex beads, co-injected with the PNIPAAm solution, were temperature-reversibly immobilized during the phase transition, practically freezing the Brownian motion of the entrapped particles in the volume. Furthermore, a co-injected water soluble fluorescent polysaccharide-dye conjugate was shown not to migrate from the aqueous phase into the hydrophobic polymer part upon heating, whereas the fluorescent beads were completely but reversibly immobilized in the hydrophobic domains of dense polymer agglomerates. The system reported here provides a feasible method for the reversible stabilization and solidification of GUV interior volumes, e.g., as a micrometer-sized model system for controlled drug release.     

接枝聚合物PAA—g—PIPA微球的制备及其温控释药研究

采用自由基溶液聚合法合成出Ｎ－异丙基丙烯酰胺齐聚物（Ｐｏｌｙ—Ｎ—Ｉｓｏｐｒｏｐｙｌａｍｉｄｅ，ＰＩＰＡ）．通过缩合将ＰＩＰＡ接枝在聚烯丙胺盐酸盐（Ｐｏｌｙａ－ｌｌｙａｍｉｎｅｈｙｄｒｏｃｈｌｏｒｉｄｅ，ＰＡＡ）上得到接枝聚合物ＰＡＡ—ｇ—ＰＩＰＡ．用化学交联法将ＰＡＡ－ｇ－ＰＩＰＡ制备成１０μｍ左右的微球．所得微球通过物理法吸附阿霉素（Ａｄｒｉａｍｙｃｉｎ，ＡＤ）后，采用动力学透析法测定其体外释药性能．实验数据拟合数学模型得到表征药物微球的释药特性的药物扩散系数Ｋｍ．Ｋｍ在３０℃—４５℃范围内随温度的升高而增大，反映了载药ＰＡＡ—ｇ—ＰＩＰＡ微球具有温控释药性．     

Structure and dynamics of alpha-lactalbumin adsorbed at a charged brush interface

We have studied the adsorption of alpha-lactalbumin at a planar poly(acrylic acid) (PAA) brush using neutron reflectometry (NR) and total internal reflection fluorescence (TIRF) spectroscopy. The PAA brush has been prepared by spin-coating silicon or quartz plates with a hydrophobic poly(styrene) film and by transferring the copolymer poly(styrene)-poly(acrylic acid) onto the modified surface. In the case of NR, the poly(styrene) film and the poly(styrene) chain ends of the copolymer were perdeuterated in order to generate a high contrast to the non-deuterated PAA brush. alpha-Lactalbumin was chosen as the model protein because it is a relatively small globular protein with a negative net charge at neutral pH-values, as chosen in the experiments. Thus, it is interacting with the PAA brush on the 'wrong' side of its isoelectric point. In addition, the effects of temperature on the volume fraction profile and the reorientational mobility of the protein within the PAA brush were determined. From the analysis of the NR data, it has been found that despite of its negative net charge, alpha-lactalbumin is penetrating into the PAA brush. Its volume fraction profile parallels that of the PAA brush, indicating an exclusive interaction between the protein and the PAA. No protein accumulation is found at the inner poly(styrene) or the outer solution interface of the PAA brush. When increasing the temperature from 20 to 40 degrees C, less protein is adsorbed, suggesting the presence of enthalpic interaction contributions. From the analysis of the TIRF data, a high degree of reorientational mobility of alpha-lactalbumin within a PAA brush can be inferred. The reorientational correlation time of alpha-lactalbumin labeled with the Alexa Fluor 488 dye was found to increase from 5.5 to 32 ns upon adsorption, which can well be explained by the higher viscosity inside the PAA brush. Overall, the results of this study quantify for the first time the molecular details of the unique interaction of a protein on the 'wrong' side of its isoelectric point with a planar charged brush interface. It is concluded that the high mobility of alpha-lactalbumin within a PAA brush can partially be understood by the presence of repulsive electrostatic interactions. There is no 'freezing' of the protein dynamics, which is a precondition for biological activity.     

Cross‐linked Multilayer Polymer‐Clay Nanocomposites and Permeability Properties

Abstract

Electrostatically layered aluminosilicate nanocomposites have been prepared by the sequential deposition of poly(allylamine hydrochloride)/poly(acrylic acid)/poly(allylamine hydrochloride)/saponite (PAH/PAA/PAH/saponite)₁₀ on poly(ethylene terephtalate) (PET) film. Exfoliated saponite nanoplatelets were obtained by extensive shaking, sonication, and centrifugation of a water suspension. To minimize permeability and improve the mechanical integrity, cross‐linking of composite films was carried out at different temperatures. The formation of amide linkage induced through heating was observed by Fourier Transform Infrared (FT‐IR) and x‐ray photoelectron spectroscopy (XPS). The cross‐linking of nanocomposites (PAH/PAA/PAH/saponite)₁₀ showed 60% decrease in permeability of oxygen when compared with the pristine PET substrate film. In contrast, water permeability of the nanocomposite membrane was not affected by heating temperature and deposition cycles.     

Fabrication of Fe3O4/SiO2 core/shell nanoparticles attached to graphene oxide and its use as an adsorbent

Thermoresponsive gelling behavior of concentrated alumina suspensions with poly(acrylic acid) (PAA) and triblock copolymer (PEO(101)-PPO(56)-PEO(101), Pluronic F127) was investigated as a function of PAA concentration (0.4-1.2 mass%) for ceramic solid free forming. The copolymer species assemble into micelles at temperatures above 15°C, yielding aqueous physical gel. In this study, the concentrated alumina aqueous suspensions (φ=35 vol%) were first prepared using the anionic dispersant of PAA, and then the copolymer species (10 mass%) were dissolved at a cooled temperature at 10°C. The addition of the copolymer species had a negligible influence on the adsorption state of PAA onto the alumina surfaces. The PAA concentration needed for the saturation adsorption on the alumina surfaces was ~0.6 mass%. When the PAA concentration was this value or slightly less, the suspension became gel state at 30°C from low viscous state at 10°C. The thermally induced alumina gel had excellent viscoelastic properties, and thereby the three dimensional periodic ceramic structures were successfully fabricated by a direct colloidal printing method that using the gels as "solid" inks at the room temperature. On the other hand, when it exceeded the saturation adsorption limit, the gelling behavior was not observed, indicating that the non-adsorbing PAA species may partly suppress the micellization of the copolymer on the heating.     

Partial poly(glutamic acid) <--> poly(aspartic acid) exchange in layer-by-layer polyelectrolyte films. Structural alterations in the three-component architectures

Layer-by-layer (LBL) polyelectrolyte films were constructed from poly(L-glutamic acid) (PGA) and poly(L-aspartic acid) (PAA) as polyanions, and from poly(L-lysine) (PLL) as the polycation. The terminating layer of the films was always PLL. According to attenuated total reflection Fourier transform infrared measurements, the PGA/PLL and PAA/PLL films, despite their chemical similarity, had largely different secondary structures. Extended beta-sheets dominated the PGA/PLL films, while alpha-helices and intramolecular beta-sheets dominated the PAA/PLL films. The secondary structure of the polyelectrolyte film affected the adsorption of human serum albumin (HSA) as well. HSA preserved its native secondary structure on the PGA/PLL film, but it became largely deformed on PAA/PLL films. Both PGA and PAA were able to extrude to a certain extent the other polyanion from the films, but the structural consequences were different. Adding PAA to a (PGA/PLL)5-PGA film resulted in a simple exchange and incorporation: PGA/PLL and PAA/PLL complexes coexisted with their unaltered secondary structures in the mixed film. The incorporation of PGA into a (PAA/PLL)5-PAA film was up to 50% and caused additional beta-structure increase in the secondary structure of the film. The proportions of the two polyanions were roughly the same on the surfaces and in the interiors of the films, indicating practically free diffusion for both polyanions. The abundance of PAA/PLL and PGA/PLL domains on the film surfaces was monitored by the analysis of the amide I region of the infrared spectrum of a reporter molecule, HSA, adsorbed onto the three-component polyelectrolyte films.