The structure of electrical double layer of silica in the presence of polyvinyl alcohol (PVA) at different temperatures

The effect of polyvinyl alcohol (PVA) adsorption on the structure of the electrical double layer of silica (SiO₂) in the temperature range 15-35 °C was studied. The potentiometric titrations were applied in the experiments, which enable determination of the surface charge density of silica systems without and with adsorbed polymer. The preferential adsorption of acetate groups of not fully hydrolysed PVA chains (degree of hydrolysis 97.5%) through hydrogen bridges is mainly responsible for bonding process of polymer with adsorbent surface. The obtained results indicate that temperature increase causes more stretched conformation of adsorbed macromolecules and the greater number of acetate groups can be adsorbed on the solid surface. It leads to changes in structure of polymer adsorption layer on the solid surface and the increase of the SiO₂ surface charge with the rising temperature was observed.     

Adsorption of phenylalanine on layered double hydroxides: effect of temperature and ionic strength

In this work we report the adsorption of phenylalanine (Phe) on Magnesium Aluminum Layered Double Hydroxides (Mg–Al–CO₃-LDH) at two different temperatures (298 and 310 K) and under two distinct ionic strength conditions (with and without the addition 0.1 M of NaCl). The adsorption isotherms exhibit the same profile in all conditions, and they only differ in the amount of removed Phe. At lower ionic strength, the isotherms are almost identical at both temperatures, except for the last points, where the increase in temperature causes a decrease in the amount of adsorbed Phe. An increase in ionic strength results in a decrease in Phe adsorption. The electrokinetic potential decreases as the amount of adsorbed Phe increases, and only positive values are observed. This indicates that the surface of the adsorbent is not totally neutralized and suggests that more Phe could be removed by adsorption. The presence of Phe on the solid is confirmed by FTIR spectra, which present the specific bands assigned to Phe. The hydrophobicity of the amino acid probably contributes to its extraction, thus enabling the removal of a great amount of Phe. In conclusion, LDH is potentially applicable in the removal of Phe from wastewater.     

Influence of poly(ethylene glycol) block length on the adsorption of thermoresponsive copolymers onto gold surfaces

The adsorption of a series of four poly(N-isopropylacrylamide)-based copolymers composed of a hydrophilic block of methoxy poly(ethylene glycol) (MPEG) with a variable length and a PNIPAAM block of fixed size (MPEG _n -b-PNIPAAM₇₁) onto flat and spherical citrate-coated gold surfaces has been investigated. The adsorption onto planar surfaces was studied by means of the quartz crystal microbalance with dissipation monitoring, whereas polymer adsorption onto gold nanoparticles was examined using dynamic light scattering and visible spectroscopy. Experiments were performed with two different concentrations of polymer in bulk solution, namely 0.05 and 0.0005 wt%. The influence of the MPEG length on the thickness of the adsorbed layer on the nanoparticles, and the adsorbed mass onto the planar surfaces were recorded at different temperatures.     

Resistance to nonspecific protein adsorption by poly(vinyl alcohol) thin films adsorbed to a poly(styrene) support matrix studied using surface plasmon resonance.

Thin films of poly(vinyl alcohol) (PVA) polymer were prepared on a flat, nonporous, poly(styrene) support matrix by adsorption from aqueous solution and were characterized in order to investigate the nonspecific adsorption of proteins to a chromatographically relevant surface. The integrity and surface coverage of the PVA thin films were established by surface analysis and atomic force microscopy imaging. The adsorption of the PVA polymers to the poly(styrene) substrate and the nonspecific adsorption of proteins to the PVA-coated surface were monitored using surface plasmon resonance. PVA was strongly bound to the poly(styrene) surface, but the surface density of the adsorbed PVA polymers was affected substantially by the concentration, molecular weight, and degree of hydrolysis of PVA polymers used. There was evidence of increasing degrees of unfolding of the PVA polymer onto the poly(styrene) surface as the concentration of the the PVA coating solution increased. Complete PVA coverage of the poly(styrene) surface was observed at PVA concentrations of 0.1 mg/mL or greater but with significant influence of both molecular weight and degree of hydrolysis of the PVA polymers. Resistance of the PVA-coated poly(styrene) surface to the nonspecific adsorption of human serum albumin (HSA) correlated with the degree of surface coverage of the PVA. The use of anti-HSA as a probe for adsorbed HSA suggested that HSA was displacing PVA from the poly(styrene) surface at the lower PVA surface coverage. A complete barrier to nonspecific protein adsorption was observed with a PVA coating solution concentration of greater than 0.1 mg/ mL with a degree of hydrolysis of <88%.     

Temperature-swing adsorption of proteins in water using N-isopropylacrylamide copolymer gel particles

The adsorption and desorption behaviors of bovine serum albumin (BSA) in water for temperature-responsive polymer gel particles have been investigated by the temperature-swing operation between 298 and 313 K, where the cationic N-isopropylacrylamide (NIPA) gels copolymerized with vinylbenzyl trimethylammonium chloride (VBTA) or 2-(dimethylamino)ethyl methacrylate (DMAEMA) were used. The NIPA-VBTA and the NIPA-DMAEMA copolymer gels adsorbed BSA while the NIPA homopolymer gel hardly adsorbed BSA, indicating that the copolymer gels adsorb BSA through the electrostatic attraction between the positively charged groups in the gels and the negatively charged BSA. The adsorption amounts for the NIPA-DMAEMA gels were smaller than those for the NIPA-VBTA gels. This may be because almost every VBTA group, which is a quaternary ammonium salt, can be positively charged in water, while only some of the tertiary amine DMAEMA groups are protonated in water. Moreover, it was found that both the copolymer gels with a large mesh size of the polymer network repeatedly adsorbed BSA at 298 K and desorbed some of pre-adsorbed BSA at 313 K by the temperature-swing operation. This BSA desorption may result from the decrease of the number of the positively charged groups accessible to BSA due to the shrinking of the constituent polymer chains.     

Templated growth of superparamagnetic iron oxide nanoparticles by temperature programming in the presence of poly(vinyl alcohol)

Magnetite (Fe₃O₄) nanostructures with different morphologies including uniform nanoparticles, magnetic beads and nanorods were synthesized via a co-precipitation method. The synthesis process was performed at various temperatures in the presence of polyvinyl alcohol (PVA) at different concentrations. It is shown that small amounts of PVA act as a template in hot water (70 °C), leading to the oriented growth of Fe₃O₄ nanorods, which was confirmed by selected area electron diffraction. Individually coated magnetite nanoparticles and magnetic beads were formed at a relatively lower temperature of 30 °C in the folded polymer molecules due to the thermo-physical properties of PVA. When a moderate temperature (i.e. 50 °C) was used, nanorods and nanobeads co-existed. At higher concentrations of PVA (polymer/iron mass ratio of 5), however, the formation of magnetic beads was favored. The nanorods were shown to be unstable upon exposure to electron beams. Freezing/thawing process was applied post synthesis as temperature programming to fabricate stable nanorods with rigid walls.     

Studies on structural,electrical and dielectric properties of nickel ion conducting polyvinyl alcohol based polymer electrolyte films

Polyvinyl alcohol (PVA) complexed with different weight percent ratios of Nickel Bromide (NiBr₂) salt were prepared by using solution cast technique. X-ray diffraction analysis confirmed the complexation of the salt with the polymer. Differential scanning calorimetry was used to determine the glass transition and melting temperatures of pure PVA and PVA:NiBr₂ complexed films. Electrical conductivity was measured using ac impedance analyzer in the frequency and temperature range 1 Hz–1 MHz and 303–373 K respectively. It was observed that the magnitude of electrical conductivity increases with NiBr₂ salt concentration as well as temperature. Frequency dependence electrical conductivity of the complexed polymer electrolyte films follows the Jonscher’s equation. The dielectric behavior was analyzed using dielectric permittivity\(\left( {{\varepsilon ^\prime}} \right)\) and loss tangent \(\left( {\tan \delta } \right)\) of the samples. Relaxation time was determined from the variation of loss tangent with frequency at different temperatures. The modulus spectra indicated the non-Debye nature of the material.     

Thermoresponsive Amphoteric Metal–Organic Frameworks for Efficient and Reversible Adsorption of Multiple Salts from Water

Regenerable, high‐efficiency salt sorption materials are highly desirable for water treatment. Here, a thermoresponsive, amphoteric metal–organic framework (MOF) material is reported that can adsorb multiple salts from saline water at room temperature and effectively release the adsorbed salts into water at elevated temperature (e.g., 80 °C). The amphoteric MOF, integrated with both cation‐binding carboxylic groups and anion‐binding tertiary amine groups, is synthesized by introducing a polymer with tertiary amine groups into the cavities of a water‐stable MOF such as MIL‐121 with carboxylic groups inside its frameworks. The amphoterized MIL‐121 exhibits excellent salt adsorption properties, showing stable adsorption – desorption cycling performances and high LiCl, NaCl, MgCl₂, and CaCl₂ adsorption capacities of 0.56, 0.92, 0.25, and 0.39 mmol g^?1, respectively. This work provides a novel, effective strategy for synthesizing new‐generation, environmental‐friendly, and responsive salt adsorption materials for efficient water desalination and purification.     

Molecular interactions at biointerfaces: a study of lipid adsorption

The study of the behaviour of biointerfaces is of great interest because it enables us to gain a much better understanding of the interactions between different biological compounds. Superficial processes are strongly dependent on such interactions. In the present work, we have focused our attention on the adsorption of a cationic lipid onto different colloidal polymer systems. Subsequently, the coadsorption of this lipid and an immunoprotein (F(ab') ₂) was performed trying to achieve stable latex particles. The aim was to obtain a structured interface similar to that of a simple biological membrane. Mainly, we have placed emphasis on the study of interaction forces that govern lipid adsorption when we change the dielectric constant in the medium. In order to obtain homogeneous aqueous lipid solutions some ethanol was added to samples. The adsorption isotherms were carried out at different experimental conditions, changing the ethanol contents and the pH of the environment. Moreover, the electrokinetic behaviour and the colloidal stability of these biocomplexes were studied, and both yielded highly compatible results. The adsorption of lipid onto polymeric sorbents is an irreversible process that takes place rapidly. The preferential interaction between the lipid and polymeric surfaces is electrostatic. Only in those samples with low alcohol concentration, hydrophobic forces take place weakly. Lipid-surface interactions are influenced by the nature of buffer ions. The colloidal stability of the systems decreases as the amount of the adsorbed lipid is higher. Sequential coadsorption experiments showed that the lipid molecules adhere both to the polymer surface and to the previously adsorbed immunoprotein.     

Polyimide survival in high temperature high pressure dilute aqueous solutions

Measurements of the gross properties of polyimides at high temperature and pressures in dilute aqueous environments are reported. The polyimide polymer solution is spun onto SiO₂ substrates prepared with an aluminum chelate adhesion promoter. The cured films are subjected to temperatures exceeding 150 °C and pressures of more than 1000 lbf in^-2 in dilute aqueous solutions ranging in pH from 3 to 10 for 2–4 h. Film quality, adhesion and water adsorption determined by IR measurements are reported.     

Reversibility of Polyester Adsorption on Glass

The adsorption of poly(ethylene o-phthalate) from chloroform solution on glass powder and aluminum oxide was studied. The adsorption of a number of fractions, varying in number average molecular weight from 970 to 6250 showed a decrease in the moles of polymer adsorbed with increase in molecular weight. The results are interpreted to indicate that this polymer molecule lies in a relatively flattened conformation on the glass surface. More polymer was adsorbed on glass powder at 50 °C than at 0 °C. Adsorption on glass powder that had been outgassed to remove adsorbed water was less than on untreated glass. Initial adsorption at one temperature followed by exposure at the other temperature resulted in complete reversibility of sorption on the untreated glass. Decreasing the temperature from 50 to 0 °C resulted in desorption from the outgassed glass, but increasing the temperature did not result in additional adsorption. These differences are ascribed in part to adsorption across an adsorbed water layer on the untreated glass. An explanation for the “one-direction reversibility” observed for the outgassed glass is presented.     

Low temperature and cost-effective growth of vertically aligned carbon nanofibers using spin-coated polymer-stabilized palladium nanocatalysts

Abstract

We describe a fast and cost-effective process for the growth of carbon nanofibers (CNFs) at a temperature compatible with complementary metal oxide semiconductor technology, using highly stable polymer–Pd nanohybrid colloidal solutions of palladium catalyst nanoparticles (NPs). Two polymer–Pd nanohybrids, namely poly(lauryl methacrylate)-block-poly((2-acetoacetoxy)ethyl methacrylate)/Pd (LauMA_x-b-AEMA_y/Pd) and polyvinylpyrrolidone/Pd were prepared in organic solvents and spin-coated onto silicon substrates. Subsequently, vertically aligned CNFs were grown on these NPs by plasma enhanced chemical vapor deposition at different temperatures. The electrical properties of the grown CNFs were evaluated using an electrochemical method, commonly used for the characterization of supercapacitors. The results show that the polymer–Pd nanohybrid solutions offer the optimum size range of palladium catalyst NPs enabling the growth of CNFs at temperatures as low as 350 °C. Furthermore, the CNFs grown at such a low temperature are vertically aligned similar to the CNFs grown at 550 °C. Finally the capacitive behavior of these CNFs was similar to that of the CNFs grown at high temperature assuring the same electrical properties thus enabling their usage in different applications such as on-chip capacitors, interconnects, thermal heat sink and energy storage solutions.     

Layer-by-layer self-assembly of glucose oxidase and Os(Bpy)2CIPyCH2NH-poly(allylamine) bioelectrode

The uptake of glucose oxidase (GOx) onto a polycationic redox polymer (PAA-Os)-modified surface, by adsorption from dilute aqueous GOx solutions, was followed by the quartz crystal microbalance (QCM) and shows double exponential kinetics. The electrochemistry of the layer-by-layer-deposited redox-active polymer was followed by cyclic voltammetry in glucose-free solutions, and the enzyme catalysis mediated by the redox polymer was studied in beta-D-glucose-containing solutions. AFM studies of the different layers showed the existence of large two dimension enzyme aggregates on the osmium polymer for 1 microM GOx and less aggregation for 50 nM GOx solutions. When the short alkanethiol, 2,2'-diaminoethyldisulfide was preadsorbed onto gold, a monoexponential adsorption law was observed, and single GOx enzyme molecules could be seen on the surface where the enzyme was adsorbed from 50 nM GOx in water.     

Adsorption of Reactive Red 141 from wastewater onto modified chitin

This research involved the adsorption of synthetic reactive dye wastewater (SRDW) by chitin modified by sodium hypochlorite and original chitin in batch experiments. The comparison of maximum adsorption capacity used the Langmuir model to describe SRDW adsorption onto chitin and modified chitin under a system pH of 11.0. Maximum dye adsorption by chitin increased from 133mgg(-1) to 167mgg(-1) at temperatures of 30-60 degrees C, respectively. For modified chitin, the capacity decreased from 124mgg(-1) to 59mgg(-1) when the temperature increased from 30 degrees C to 60 degrees C, respectively. Both Na(2)SO(4) and Na(2)CO(3) increased in dye adsorption. The spectra of attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectrometry confirmed the hydroxyl groups as functional groups of modified chitin, which affected the modification and the SRDW adsorption. The adsorbed dyes were eluted by distilled water and 1M NaOH to confirm the dye adsorption mechanism. Total elution of modified chitin and chitin were 92.76% and 55.29%, respectively. Although modified chitin had a maximum adsorption capacity less than chitin, elution of the dye from modified chitin was easier than chitin. Therefore, modified chitin could be suitable in a column system for dye pre-concentration as well as wastewater minimisation. In addition, the column study showed that modified chitin could be used for more than four cycles of adsorption and elution by distilled water.     

Interactive behavior of caffeine at a platinum electrode surface

Interactive behavior of caffeine at a charged platinum/solution interface was investigated in a wide temperature range, from 295 to 333 K, in a phosphate buffer solution pH 7.0. It was shown that the amount of adsorbed caffeine (surface concentration) is directly proportional to the measured adsorption surface charge density resulting from caffeine oxidation to theophilline. At low temperatures, a monolayer of caffeine molecules laying in a flat orientation on the Pt surface is adsorbed, while at higher temperatures, conformational changes occur, resulting in tilting of the adsorbed molecules to allow for higher surface concentrations to be achieved. A highly negative Gibbs energy of adsorption, ranging from −51.1 kJ mol⁻¹ at 295 K to −60.6 kJ mol⁻¹ at 333 K, demonstrated a high affinity of caffeine for the Pt surface. Although the adsorption process was found to be endothermic (ΔH_ADS = 20 kJ mol⁻¹), it was determined that a large positive change in the adsorption entropy (TΔS_ADS = 75 ± 3 kJ mol⁻¹) represents the driving force for the strong interaction of caffeine with Pt.     

Multi-Peptide Adsorption on Uncharged Solid Surfaces: A Coarse-Grained Simulation Study

On-aim control of protein adsorption onto a solid surface remains challenging due to the complex interactions involved in this process. Through computational simulation, it is possible to gain molecular-level mechanistic insight into the movement of proteins at the water–solid interface, which allows better prediction of protein behaviors in adsorption and fouling systems. In this work, a mesoscale coarse-grained simulation method was used to investigate the aggregation and adsorption processes of multiple 12-alanine (12-Ala) hydrophobic peptides onto a gold surface. It was observed that around half (46.6%) of the 12-Ala peptide chains could form aggregates. 30.0% of the individual peptides were rapidly adsorbed onto the solid surface; after a crawling process on the surface, some of these (51.0%) merged into each other or merged with floating peptides to form adsorbed aggregates. The change in the solid–liquid interface due to peptide deposition has a potential influence on the further adsorption of single peptide chains and aggregates in the bulk water. Overall, the findings from this work help to reveal the mechanism of multi-peptide adsorption, and consequentially build a basis for the understanding of multi-protein adsorption onto a solid surface.     

Adsorption equilibrium and kinetics of polyvinyl alcohol from aqueous solution on powdered activated carbon

In this study, powdered activated carbon (PAC) was used to remove polyvinyl alcohol (PVA) from the aqueous PVA solution. The adsorption kinetics has been studied pertaining to various initial PVA concentration and PAC dosage. The rates of adsorption were found to conform to the second-order kinetics with good correlation. Boyd plot confirmed that external mass transfer was the rate-limiting step in the sorption process. The adsorption isotherm obtained resembled with H-type of isotherm, which indicated a high affinity of the solute for the sorption sites. The Freundlich model appeared to fit the isotherm data better than the Langmuir model. The thermodynamic parameters such as Delta H degrees , Delta S degrees and Delta G degrees were evaluated from the slope and intercept of linear plot of log Kc against (1/T) x 1000. The change in entropy (DeltaS degrees ) and heat of adsorption (Delta H degrees ) of PAC was estimated as 1.45 kJ mol(-1)K(-1) and 365 kJ mol(-1), respectively. The free energy of the adsorption at all temperatures was negative indicating a spontaneous process. The maximum PVA removal of 92% was obtained at a pH of 6.3 and contact time of 30 min for an adsorbent dose of 5 g/L.     

Viscosity of Toluene+Cyclopentane Mixtures: Measurements and Prediction

New measurements of the viscosity of binary mixtures of toluene+cyclopentane are presented. The measurements, performed in a vibrating-wire viscometer, cover the temperature range from 210 to 310 K at pressures up to 25 MPa. The concentrations studied are 60 and 30%, by weight, toluene. The uncertainty of the measurements, confirmed at room temperature and higher temperatures with the measurement of the viscosity of water, is estimated to be ±0.5%, increasing to ±1% at temperatures below 240 K. The present measurements are employed to examine the predictive power of two recent theoretically based schemes proposed for the calculation of the viscosity of mixtures.     

HDPE的紫外辐照官能化研究

通过FT-IR、凝胶分析、水接触角和力学性能测定,研究了空气中不同环境温度下紫外辐照官能化HDPE的结构变化、亲水性和紫外辐照官能化HDPE对HDPE／PVA共混体系的增容作用。在相同的紫外辐照时间下,随环境温度提高,引入HDPE分子链的C=O和C--O含氧基团的含量增加,其HDPE的亲水性变好,但它的凝胶含量也有所增加。与HDPE／PVA体系相比,经过紫外辐照官能化HDPE增容的HDPE／PVA体系的拉伸强度和缺口冲击强度均得到提高。     

Thermodynamic Analysis of Water Interaction with Excipient Films

The interaction of water with excipients that can form moisture-protective coatings was examined earlier by the application of theoretical models. In this study, thermodynamic analysis of water-excipient film systems has been performed to elucidate the mechanistic details of the water-excipient interaction. Partial molal free energies, enthalpies, and entropies were computed for films of lipidic (glyceryl behenate, GB) and polymeric (polyvinyl alcohol, PVA) coating excipients using the temperature dependence of the adsorption process. The analysis of free energy changes showed that excipient films were not inert participants in the water sorption process. The isoteric heats of adsorption confirmed that water formed hydrogen bonds with the excipient films and allowed estimation of number of hydrogen bonds per water molecule. This result also provided the reason for hysteresis during drying. A comparative evaluation of the application of theoretical models and thermodynamic analysis revealed that results obtained from both approaches were not always complementary. An exponential relationship was found to exist between sorption microrate constants and water activity for the PVA films at all temperatures.