PAH Chains Research Articles

Location of Polyelectrolytes in Swollen Lipid Oligobilayers.

Osteoarthritis is caused by degeneration of the cartilage, which covers the bone ends of the joints and is decorated with an oligolamellar phospholipid (PL) bilayer. The gap between the bone ends is filled with synovial fluid mainly containing hyaluronic acid (HA). HA and PLs are supposed to reduce friction and protect the cartilage from wear in joint movement. However, a detailed understanding of the molecular mechanisms of joint lubrication is still missing. Previously, we found that aqueous solutions of HA and poly(allylamine hydrochloride) (PAH), the latter serving as a polymeric analogue to HA, adsorb onto the headgroups of surface-bound 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) oligobilayers and significantly enhance their stability with respect to shear forces, typically occurring in joint movement. We now investigated the precise location of PAH chains across the lipid films in neutron reflectivity measurements, as bridging of the oligobilayers by polyelectrolytes (PEs) might be the cause for their improved mechanical stability. In a first set of experiments, we used hydrogenated PAH and chain-deuterated DMPC (DMPC-d54) to improve the contrast between the lipids and potentially intruding PAH. However, due to difficulties in distinguishing between incorporation of water and PAH, penetration into the lipid chain region could hardly be proven quantitatively. Therefore, we designed a more elaborate experiment based on mixed films of DMPC-d54 and hydrogenated DMPC, which is insensitive to water penetration into the films. Beside facilitating a detailed structural characterization of the oligolamellar system, this elaborate approach showed that PAH adsorbs to the DMPC heads and penetrates the lipid tail strata. No PAH was found in the lipid head strata, which excludes bridging of several lipid bilayers by the PE chains. The data are consistent with the assumption that PAH bridges are formed between the headgroups of two adjacent bilayers and contribute to the enhanced mechanical stability.

Tuning the Self-Assembled Morphology of Ti3C2Tx MXene-Based Hybrids for High-Performance Electromagnetic Interference Shielding.

Hybrid materials based on transition metal carbide and nitride (MXene) nanosheets have great potential for electromagnetic interference (EMI) shielding due to their excellent electrical conductivity. However, the performance of final products depends not only on the properties of constituent components but also on the morphology of the assembly. Here, via the controlled diffusion of positively charged poly(allylamine hydrochloride) (PAH) chains into the negatively charged Ti3C2Tx MXene suspension, MXene/PAH hybrids in the forms of thin films, porous structures, and fibers with distinguished internal morphologies are obtained. Our results confirm that PAH chains could effectively enhance the oxidation stability and integrity of wet and dry MXene structures. The flexibility to tune the structures allows for a thorough discussion of the relations between the morphology, electrical conductivity, and EMI shielding mechanism of the hybrids in a wide range of electrical conductivity (2.5 to 3347 S·cm-1) and thickness (7.7 to 1900 μm) values. The analysis of thin films shows the direct impact of the polymer content on the alignment and compactness of MXene nanosheets regulating the films' electrical conductivity/EMI shielding effectiveness. The colloidal behavior of the initial MXene suspension determines the interconnection of MXene nanosheets in MXene/PAH porous assemblies and the final electrical properties. In addition to the internal morphology, examining the laminated MXene/PAH fibers with geometrically different arrangements demonstrates the role of conductive network configuration on EMI shielding performance. These findings provide insights into tuning the EMI shielding effectiveness via the charge-driven bottom-up assembly of electrically conductive MXene/polyelectrolyte hybrids.

Supramolecular tripeptide self-assembly initiated at the surface of coacervates by polyelectrolyte exchange

Spatial control of supramolecular self-assembly can yield compartmentalized structures, a key feature for the design of artificial cells. Inducing self-assembly from and on compartments is still a challenge. Polyelectrolyte complex coacervates are simple model droplet systems able to reproduce the basic features of membrane-less organelles, appearing in cells. Here, we demonstrate the supramolecular self-assembly of a phosphorylated tripeptide, Fmoc-FFpY (Fmoc: fluorenyl-methoxycarbonyl; F: phenyl alanine, pY: phosphorylated tyrosine), on the surface of poly(l-glutamic acid)/poly(allylamine hydrochloride) (PGA/PAH) complex coacervate microdroplets. The phosphorylated peptides self-assemble, without dephosphorylation, through ion pairing between the phosphate groups of Fmoc-FFpY and the amine groups of PAH. This process provides spontaneous capsules formed by an amorphous polyelectrolyte complex core surrounded by a structured peptide/PAH shell. Similar fibrillar Fmoc-FFpY self-assembled structures are obtained at the interface between the peptide solution and a PGA/PAH polyelectrolyte multilayer, a complex coacervate in the thin film or “multilayer” format. In contact with the peptide solution, PAH chains diffuse out of the coacervate or multilayer film and complex with Fmoc-FFpY at the solution interface, exchanging any PGA with which they were associated. Self-assembly of Fmoc-FFpY, now concentrated by complexation with PAH, follows quickly.

Effects of Non-Electrostatic Intermolecular Interactions on the Phase Behavior of pH-Sensitive Polyelectrolyte Complexes

Polyelectrolyte complexes (PECs) offer enormous material tunability and desirable functionalities, and consequently have found broad utility in biomedical and material industries. While poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH) are a commonly used pairing, various aspects of the phase behavior of PAA–PAH complexes have not been sufficiently quantified. We present a comprehensive experimental study depicting the binodal phase boundaries for the PAA–PAH complexes prepared under acidic, neutral, and basic conditions using thermogravimetric analysis, turbidimetry, and optical microscopy. Under neutral and basic conditions, phase behaviors of the complexes were largely similar to one another and followed general expectations of PEC phase behavior, except for unusually high resistance to disruption of the complex with added salt. Stable complexes are observed up to 4 M NaCl concentrations. Under acidic conditions, strikingly different phase behaviors of the PAA–PAH complexes were observed. The polymer content in the complex phase increased initially, followed by an expected decrease as salt was added to the complexes. This behavior may result from a combination of associative phase separation of PAA and PAH chains, influenced by electrostatic interactions, and segregative phase separation, which can be ascribed to the influence of a combination of the hydrophobic interactions of the aliphatic polymer backbone and the interpolymer hydrogen bonding of un-ionized acrylic monomer units. Our systematic investigations over a range of pH detailing these discrepancies in the PAA–PAH phase behavior are expected to clarify the inconsistencies among the reports in the literature and provide the material design strategies for practical use of the PAA–PAH complexes and multilayer assemblies.

Poly(acryloyl hydrazide)-grafted cellulose nanocrystal adsorbents with an excellent Cr(VI) adsorption capacity

In this study, we prepared poly(acryloyl hydrazide) (PAH)-grafted cellulose nanocrystal (CNC-PAH) particles via the atom transfer radical polymerization method for application to Cr(VI) adsorption. The closely-packed PAH chains grafted on the cellulose nanocrystal (CNC) surface provide a high density of amine groups that can adsorb Cr(VI) through strong electrostatic, hydrogen bonding and chelating interactions. CNC-PAH exhibited the optimum Cr(VI) adsorption capacity at the solution pH = 3, where its electrostatic attraction with Cr(VI) was maximized. Cr(VI) was chemisorbed in CNC-PAH by following the Langmuir isotherm mechanism (homogeneous monolayer adsorption). The Cr(VI) adsorption kinetics of CNC-PAH was controlled predominantly by intra-particle diffusion resistance imparted by the PAH shell layer. Thermodynamic analysis revealed that Cr(VI) adsorption of CNC-PAH is a spontaneous and endothermic process. Importantly, CNC-PAH grafted with the higher Mw (∼50 kg mol−1) PAH exhibited a rapid Cr(VI) adsorption rate and remarkably high Cr(VI) adsorption capacity (∼457.6 mg g-1 at 298.15 K), exceeding those of previously reported adsorbents owing to its numerous Cr(VI)-adsorptive amine groups provided by the closely-packed grafted PAH polymers. Furthermore, CNC-PAH showed excellent reusability to maintain its high adsorption ability during repeated adsorption–desorption cycles owing to the covalently binding nature of the PAH polymers.

Facile preparation of salt-tolerant anion-exchange membrane adsorber using hydrophobic membrane as substrate

In this study, a polyvinylidene fluoride (PVDF) hydrophobic membrane with high mechanical property was used as substrate to prepare salt-tolerant anion-exchange (STAE) membrane adsorber. Effective hydrophilization and functionalization of PVDF membrane was realized via polydopamine (PDA) deposition, thus overcoming the drawbacks of hydrophobic substrates including poor water permeability, inert property as well as severe non-specific adsorption. The following polyallylamine (PAH) coupling was carried out at pH 10.0, where unprotonated amine groups on PAH chains were more prone to couple with PDA. This membrane adsorber could remain 75% of protein binding capacity when NaCl concentration increased from 0 to 150mM, while its protein binding capacity was independent of flow rate from 10 to 100 membrane volume (MV)/min due to its high mechanical strength (tensile strength: 43.58±2.30MPa). With 200mM NaCl addition at pH 7.5, high purity (above 99%) and high recovery (almost 100%) of Immunoglobulin G (IgG) were obtained when using the STAE membrane adsorber to separate IgG/human serum albumin (HSA) mixture, being similar to that without NaCl at pH 6.0 (both under the flow rate of 10–100MV/min). Finally, the reliable reusability was confirmed by five reuse cycles of protein binding and elution operations. In comparison with commercial membrane adsorber, the new membrane adsorber exhibited a better mechanical property, higher IgG polishing efficiency and reusability, while the protein binding capacity was lower due to less NH2 density on the membrane. The outcome of this work not only offers a facile and effective approach to prepare membrane adsorbers based on hydrophobic membranes, but also demonstrates great potential of this new designed STAE membrane adsorbers for efficient monoclonal antibody (mAb) polishing.

Modification of Spherical Polyelectrolyte Brushes by Layer-by-Layer Self-Assembly as Observed by Small Angle X-ray Scattering.

Multilayer modified spherical polyelectrolyte brushes were prepared through alternate deposition of positively charged poly(allylamine hydrochloride) (PAH) and negatively charged poly-l-aspartic acid (PAsp) onto negatively charged spherical poly(acrylic acid) (PAA) brushes (SPBs) on a poly(styrene) core. The charge reversal determined by the zeta potential indicated the success of layer-by-layer (LBL) deposition. The change of the structure during the construction of multilayer modified SPBs was observed by small-angle X-ray scattering (SAXS). SAXS results indicated that some PAH chains were able to penetrate into the PAA brush for the PAA-PAH double-layer modified SPBs whereas part of the PAH moved towards the outer layer when the PAsp layer was loaded to form a PAA-PAH-PAsp triple-layer system. The multilayer modified SPBs were stable upon changing the pH (5 to 9) and ionic strength (1 to 100 mM). The triple-layer modified SPBs were more tolerated to high pH (even at 11) compared to the double-layer ones. SAXS is proved to be a powerful tool for studying the inner structure of multilayer modified SPBs, which can establish guidelines for the a range of potential applications of multilayer modified SPBs.

Role of Hydrogen Bonding and Polyanion Composition in the Formation of Lipid Bilayers on Top of Polyelectrolyte Multilayers.

The self-assembly of mixed vesicles of zwitterionic phosphatidylcholine (PC) and anionic phosphatidylserine (PS) phospholipids on top of polyelectrolyte multilayers (PEMs) of poly(allylamine hydrochloride) (PAH), as a polycation, and polystyrenesulfonate (PSS), as a polyanion, is investigated as a function of the vesicle composition by means of the quartz crystal microbalance with dissipation (QCM-D), cryo-transmission electron microscopy (Cryo-TEM), atomic force microscopy (AFM), and atomic force spectroscopy (AFS). Vesicles with molar percentages of PS between 50% and 70% result in the formation of lipid bilayers on top of the PEMs. Vesicles with over 50% of PC or over 80% of PS do not assembly into bilayers. AFS studies performed with a PAH-modified cantilever approaching and retracting from the lipid assemblies reveal that the main interaction between PAH and the lipids takes place through hydrogen bonding between the amine groups of PAH and the carboxylate and phosphate groups of PS and with the phosphate groups of PC. The interaction of PAH with PS is much stronger than with PC. AFS measurements on assemblies with 50% PC and 50% PS revealed similar adhesion forces to pure PS assemblies, but the PAH chains can reorganize much better on the lipids as a consequence of the presence of PC. QCM-D experiments show that vesicles with a lipid composition of 50% PC and 50% PS do not form bilayers if PSS is replaced by alginate (Alg) or poly(acrylic acid) (PAA).

Delivery of functional polyelectrolytes from complexes induced by salt addition: Impact of the initial binding strength

This paper focuses on polyelectrolyte complexes (PECs) soft nanoparticles and how dissociation occurs upon salt addition. The system is composed of a strong polyanion (polystyrene sulfonate, PSS) and a weak polycation (poly(allylamine) hydrochloride, PAH) in large excess. Soft nanoparticles were obtained by pouring a PSS solution into a PAH one under constant stirring. As the charge density of PAH chain depends on the pH of the polyelectrolyte solution, PEC particles exhibit distinct behaviors under salt addition depending on the pH of the continuous phase. At pH=5.5, PAH chains are fully charged and the addition of salt produces particle aggregation followed by sedimentation. Conversely, at pH=10 where PAH is only partially charged, the addition of salt drives a progressive disentanglement of the two polyelectrolytes, as revealed by both viscosimetric and spectroscopic measurements. At sufficiently high ionic strength, the two electrolytes are fully dissociated. Our results emphasize differences in behavior (binding reversibility) between strongly and weakly bound polyelectrolytes of opposite charge upon addition of salt. We discuss the potential use of these systems as stimulus responsive materials for the delivery of scale nucleation inhibitors in application around petroleum recovery.

One-pot synthesis and gelation by borax of glycopolymers in water

A glycosylated polyamine is synthesized using a straightforward route in aqueous solution. An optimum of grafting is obtained when equimolar amounts of gluconolactone and NaOH are added to an aqueous solution of poly(allylamine hydrochloride), PAH. Under these conditions, up to 60% of gluconolactone is grafted onto the PAH chain, the remaining being transformed into gluconate. The very fast grafting reaction, completed in less than 5 minutes at room temperature, may be applicable to a large range of water-soluble polymers bearing amino groups. Upon addition of borax before any purification process, the reaction mixture can be transformed in situ into a hydrogel. The gelation is attributed to the formation of borate diesters acting as cross-linkers of a number of PAH chains bearing glycosylated grafts. The viscoelastic properties of the gels can be triggered by the amounts of gluconolactone and borax incorporated in the mixture as well as by the final pH. Owing to the remaining ammonium groups along the chains which stabilize the borate complex, gels can be obtained at physiological pH, a performance superior to those obtained with comparable poly(vinyl alcohol)- or guar/borax systems.

Electrochemical sensors based on porous nanocomposite films with weak polyelectrolyte-stabilized gold nanoparticles

Porous hybrid multilayer films composed of cationic poly(allylamine hydrochloride) (PAH)- and anionic poly(acrylic acid) (PAA)-stabilized gold nanoparticles (AuNPs) (i.e., PAH-AuNPs and PAA-AuNPs) were prepared on indium tin oxide (ITO) electrodes using pH-controlled layer-by-layer (LbL) assembly method with subsequent acid treatment. The exponential growth of AuNP deposition layers was caused by the “in-and-out” diffusion of PAH and PAA chains not bound to AuNPs. Immersion of the films in an acidic solution (pH 2.4) converted the nonporous films to porous films via the disruption of ionic bonds and the rearrangement of free PE chains. In this case, the pH-induced porous films showed high electrochemical activity. Nonporous/dense films were found to prevent direct contact between probe molecules in solution and the catalytic components immobilized on an electrode. Electrodes coated with porous films, however, exhibited higher electrocatalytic activity toward nitric oxide oxidation compared with electrodes coated with nonporous films, despite the same levels of AuNP loading. This work demonstrates that structural transformations via a facile pH treatment can significantly improve electrode sensitivity without the aid of porous supports or additional catalytic components.

Direct Surface Force Measurements of Polyelectrolyte Multilayer Films Containing Nanocrystalline Cellulose

Polyelectrolyte multilayer films containing nanocrystalline cellulose (NCC) and poly(allylamine hydrochloride) (PAH) make up a new class of nanostructured composite with applications ranging from coatings to biomedical devices. Moreover, these materials are amenable to surface force studies using colloid-probe atomic force microscopy (CP-AFM). For electrostatically assembled films with either NCC or PAH as the outermost layer, surface morphology was investigated by AFM and wettability was examined by contact angle measurements. By varying the surrounding ionic strength and pH, the relative contributions from electrostatic, van der Waals, steric, and polymer bridging interactions were evaluated. The ionic cross-linking in these films rendered them stable under all solution conditions studied although swelling at low pH and high ionic strength was inferred. The underlying polymer layer in the multilayered film was found to dictate the dominant surface forces when polymer migration and chain extension were facilitated. The precontact normal forces between a silica probe and an NCC-capped multilayer film were monotonically repulsive at pH values where the material surfaces were similarly and fully charged. In contrast, at pH 3.5, the anionic surfaces were weakly charged but the underlying layer of cationic PAH was fully charged and attractive forces dominated due to polymer bridging from extended PAH chains. The interaction with an anionic carboxylic acid probe showed similar behavior to the silica probe; however, for a cationic amine probe with an anionic NCC-capped film, electrostatic double-layer attraction at low pH, and electrostatic double-layer repulsion at high pH, were observed. Finally, the effect of the capping layer was studied with an anionic probe, which indicated that NCC-capped films exhibited purely repulsive forces which were larger in magnitude than the combination of electrostatic double-layer attraction and steric repulsion, measured for PAH-capped films. Wherever possible, DLVO theory was used to fit the measured surface forces and apparent surface potentials and surface charge densities were calculated.

In situ synthesis of Ag nanoparticles in polyelectrolyte multilayers

Self-assembled multilayer thin films, fabricated by the sequential adsorption of appositivelycharged polyelectrolytes, were used as a template for the in situ nucleation and growthof silver (Ag) nanoparticles. Since weak polyelectrolytes have a pH-dependentdegree of dissociation, the multilayer film formed of polyallylamine (PAH) andpolyacryllic acid (PAA) at low pH values contains free carboxylic acid groupsthat do not electrostatically bind to the positive groups of PAH chains duringthe film assembly. These free acid groups in the polyelectrolyte multilayer filmwere used to bind the silver ions, which were subsequently reduced with aNaBH4 solution to form Ag nanoparticles. Electron-microscopy examination of the films andUV–vis spectroscopy showed that the concentration and size of the Ag nanoparticles aredetermined by the processing conditions of the multilayer assembly. Furthermore, due tothe regeneration of the acid groups upon reduction, the synthesis process can be repeatedlycycled to increase the volume fraction of Ag in the polyelectrolyte multilayerfilms. After three reaction cycles, Ag nanoparticles with an average diameter of7 nm at a volume fraction of 65% were obtained in the polyelectrolyte multilayers(PEMs).

Reversible Disulfide Cross-Linking in Layer-by-Layer Films: Preassembly Enhanced Loading and pH/Reductant Dually Controllable Release

This paper describes the fabrication of polyelectrolyte multilayer film which combines preassembly of poly(allylamine hydrochloride) (PAH) and 5,10,15,20-tetraphenyl-21H,23H-porphine-p,p',p' ',p' ''-tetrasulfonic acid tetrasodium hydrate (TPPS) in aqueous solution with the layer-by-layer (LbL) assembly of the PAH-TPPS complex and cross-linkable polyelectrolyte, PAASH60, which is a poly(acrylic acid) with 60% of its carboxylic acid grafted of thiol groups. During preassembly, TPPS was incorporated into PAH chains. After oxidative cross-linking to form disulfide bonds in between the layers, the multilayer with preassembly of the PAH-TPPS complex allowed for release and loading of TPPS in a reproducible way. The release of TPPS from the loaded film was a pH-controlled process. To compare with the conventional multilayer, the reloading capacity was greatly enhanced, which was related to the charge binding sites that formed by release of TPPS from the multilayer. Moreover, the release of TPPS could also be achieved by breaking off the cross-linking through reduction of disulfide bonds, and the release rates could be controlled by the reductive efficiency of the reductants in the media. In this way, the release of TPPS is pH/reductant dually controllable, thereby facilitating a new route to multistimuli controllable materials.

Interactions between Multivalent Ions and Exponentially Growing Multilayers: Dissolution and Exchange Processes

The interactions between multivalent ions (small ions or polyelectrolytes) and two exponentially growing polyelectrolyte multilayers, namely, (HA-PLL)(n)() and (HA-PAH)(n)() films, are investigated (HA = hyaluronic acid, PLL = poly-l-lysine, PAH = poly(allylamine)). Ferrocyanide and ferricyanide ions are used as small ion probes. The most striking finding is that, even though these two ions differ only by one charge unit, the ferrocyanide ions induce a partial dissolution of both multilayers whereas these films remain stable in the presence of ferricyanide ions. The dissolution process of (HA-PLL)(n)() films is more rapid than that of (HA-PAH)(n)() films, indicating a stronger interaction between HA and PAH compared to HA and PLL. This is confirmed by polyelectrolyte exchange experiments: when an (HA-PLL)(n)() multilayer film is put into contact with a PAH solution, PLL is quantitatively exchanged with the PAH chains and transformed into an HA-PAH film, whereas an (HA-PAH)(n)() multilayer remains stable in the presence of a PLL solution.

Effect of Thiocyanate Counterion Condensation on Poly(allylamine hydrochloride) Chains on the Buildup and Permeability of Polystyrenesulfonate/Polyallylamine Polyelectrolyte Multilayers

In this study, we investigate the buildup of PEI-(PSS-PAH)(n) polyelectrolyte multilayers at pH 7.4 in the presence of either NaCl or NaSCN as a supporting electrolyte. It appears that in the presence of increasing thiocyanate concentrations (from 0.1 to 0.5 M), the thickness increment, obtained from optical waveguide lightmode spectroscopy experiments, increases whereas it stays practically constant for increasing sodium chloride concentrations (between 0.1 and 0.5 M). The hydration of the films differs also markedly between both electrolyte solutions. The differences in the construction of the polyelectrolyte multilayers in the presence of both supporting electrolytes are rationalized in terms of strong SCN(-) condensation on the PAH chains. The occurrence of this ion condensation is indirectly demonstrated by means of zeta potential measurements and directly demonstrated by means of attenuated total internal reflection infrared spectroscopy on the multilayer films. Moreover when the films are built up in the presence of SCN(-), these ions are only slowly exchanged by the Cl(-) ions introduced in the bulk. Conversely the thick films obtained from 0.5 M NaSCN solutions do not deswell when the buffer solution is replaced by a 0.5 M NaCl containing buffer. The permeability of the films constructed in the presence of both sodium salts is also studied by means of cyclic voltametry and is found to be markedly different in the case of films made from five bilayers at 0.5 M salt concentration. This difference is due to the different morphology and porosity of the films constructed in the presence of 0.5 M NaCl and 0.5 M NaSCN.

Multivalent Ion/Polyelectrolyte Exchange Processes in Exponentially Growing Multilayers

We show, in this paper that multivalent ferrocyanide anions can penetrate into exponentially growing (PGA/PAH)n multilayer films whatever the nature of the last deposited layer. These ions are not able to diffuse out of the film when it is brought in contact with a pure buffer solution. However, the contact of this film with a poly(allylamine) (PAH) or a poly(L-glutamic acid) (PGA) solution leads to the release of ferrocyanide ions from the multilayer. It is shown that the release of ferrocyanide anions, when the film is in contact with a PGA solution, is due to the diffusion of the PGA chains into the film so that an exchange between ferrocyanide ions and PGA chains takes place inside the film. On the other hand, PAH chains do not diffuse into PGA/PAH multilayers. When the film is then brought in contact with a PAH solution, the PAH chains from the solution are expected to strongly interact with the ferrocyanide ions and thus induce a diffusion mechanism of the multivalent anions out of the film, the film/solution interface playing the role of a sink for these ions. This work thus shows that interactions between multivalent ions and exponentially growing films are much more complex than expected at first sight and that polyelectrolyte multilayers must be seen as dynamic entities in which diffusion and exchange processes can take place.

Photoinduced Phenomena in Layer-by-Layer Films of Poly(Allylamine Hydrochloride) and Brilliant Yellow Azodye

The nanoscale interactions between adjacent layers of layer-by-layer (LBL) films from poly(allylamine hydrochloride) (PAH) and azodye Brilliant Yellow (BY) have been investigated, with the films employed for optical storage and the formation of surface-relief gratings. Using Fourier transform infrared spectroscopy, we identified interactions involving SO3- groups from BY and NH+ groups from PAH. These electrostatic interactions were responsible for the slow kinetics of writing in the optical storage experiments, due to a tendency to hinder photoisomerization and the subsequent reorientation of the azochromophores. The photoinduced birefringence did not saturate after one hour of exposure to the writing laser, whereas in azopolymer films, saturation is normally reached within a few minutes. On the other hand, the presence of such interactions prevented thermal relaxation of the chromophores after the writing laser was switched off, leading to a very stable written pattern. Moreover, the nanoscale interactions promoted mass transport for photoinscription of surface-relief gratings on PAH/BY LBL films, with the azochromophores being able to drag the inert PAH chains when undergoing the trans-cis-trans photoisomerization cycles. A low level of chromophore degradation was involved in the SRG photoinscription, which was confirmed with micro-Raman and fluorescence spectroscopies.

04/01932 Thermal conductivity measurement of geothermal cementing systems: an experimental comparison between the line source and Jaeger methods: García-Gutierrez, A. and Espinosa-Paredes, G. Energy Conversion and Management, 2004, 45, (5), 755–764

In this study, a polyvinylidene fluoride (PVDF) hydrophobic membrane with high mechanical property was used as substrate to prepare salt-tolerant anion-exchange (STAE) membrane adsorber. Effective hydrophilization and functionalization of PVDF membrane was realized via polydopamine (PDA) deposition, thus overcoming the drawbacks of hydrophobic substrates including poor water permeability, inert property as well as severe non-specific adsorption. The following polyallylamine (PAH) coupling was carried out at pH 10.0, where unprotonated amine groups on PAH chains were more prone to couple with PDA. This membrane adsorber could remain 75% of protein binding capacity when NaCl concentration increased from 0 to 150 mM, while its protein binding capacity was independent of flow rate from 10 to 100 membrane volume (MV)/min due to its high mechanical strength (tensile strength: 43.58 ± 2.30 MPa). With 200 mM NaCl addition at pH 7.5, high purity (above 99%) and high recovery (almost 100%) of Immunoglobulin G (IgG) were obtained when using the STAE membrane adsorber to separate IgG/human serum albumin (HSA) mixture, being similar to that without NaCl at pH 6.0 (both under the flow rate of 10–100 MV/min). Finally, the reliable reusability was confirmed by five reuse cycles of protein binding and elution operations. In comparison with commercial membrane adsorber, the new membrane adsorber exhibited a better mechanical property, higher IgG polishing efficiency and reusability, while the protein binding capacity was lower due to less NH2 density on the membrane. The outcome of this work not only offers a facile and effective approach to prepare membrane adsorbers based on hydrophobic membranes, but also demonstrates great potential of this new designed STAE membrane adsorbers for efficient monoclonal antibody (mAb) polishing.