Micelle formation of Tyr-Phe dipeptide and Val-Tyr-Val tripeptide in aqueous solution and their influence on the aggregation of SDS and PEO-PPO-PEO copolymer micelles

The aggregation properties of Tyr-Phe dipeptide and Val-Tyr-Val tripeptide were studied in aqueous solution and in the presence of SDS and SDS-polymer environments using UV-visible, surface tension, fluorescence and circular dichroism (CD) techniques. Both the peptides formed micelles. The cmc values obtained for dipeptide and tripeptide are 2×10(-5) and 4×10(-5) M, respectively in aqueous solution at 25°C. The presence of additives (SDS and polymer) hindered the micelle formation of peptides. The cmc values obtained by various methods are in good agreement with each other. Effect of peptides on the aggregation properties of SDS also was investigated. The cmc of SDS was decreased in presence of peptides and were reduced with increase in temperature. Using monophasic micellization concept, the association constant (K(A)) for the SDS-peptide mixed micellar systems was determined. Using biphasic model, the thermodynamic parameters viz; ΔG°(m), ΔH°(m) and ΔS°(m) for SDS-water and SDS-peptide-water mixed micellar systems, the standard free energy for transfer of SDS from aqueous to peptide additive environments were estimated at various temperatures. These results suggest that the SDS is more stable in micellized form in the SDS-water-peptide ternary systems compared to the situation in the corresponding SDS-water binary systems.     

The aggregation of Tyr-Phe dipeptide and Val-Tyr-Val tripeptide in aqueous solution and in the presence of SDS and PEO-PPO-PEO triblock copolymer: fluorescence spectroscopic studies

The micelle formation of Tyr-Phe dipeptide and Val-Tyr-Val tripeptide has been studied for the first time. The aggregation numbers were determined for both the peptides in aqueous solution and in the presence of SDS and PEO-PPO-PEO triblock copolymer additive environments. The results obtained by steady state and time-resolved fluorescence spectroscopic techniques are in good agreement with each other. The higher value of aggregation number confirms the formation of mixed micelles. The fluorescence lifetime of tyrosine in various micellar and mixed micellar systems were also determined. The decreased lifetime values with the quencher suggested the dynamic nature of the quenching process. However, the possibility of static quenching cannot be ruled out. The accessibility of DPC quencher was found to be more in dipeptide than tripeptide.     

Binding of sodium dodecyl sulfate and hexaethylene glycol mono-n-dodecyl ether to the block copolymer L64: electromotive force, microcalorimetry, surface tension, and small angle neutron scattering investigations of mixed micelles and polymer/micellar surfactant complexes

The interactions of sodium dodecyl sulfate (SDS) with the triblock copolymer L64 (EO13-PO30-EO13) and hexaethylene glycol mono-n-dodecyl ether (C12EO6) were studied using electromotive force, isothermal titration microcalorimetry, differential scanning microcalorimetry, and surface tension measurements. In certain regions of binding, mixed micelles are formed, and here we could evaluate an interaction parameter using regular solution theory. The mixed micelles of L64 with both SDS and C12EO6 exhibit synergy. When L64 is present in its nonassociated state, it forms polymer/micellar SDS complexes at SDS concentrations above the critical aggregation concentration (cac). The cac is well below the critical micellar concentration (cmc) of pure SDS, and a model suggesting how bound micelles are formed at the cac in the presence of a polymer is described. The interaction of nonassociated L64 with C12EO6 is a very rare example of strong binding between a nonionic surfactant and a nonionic polymer, and C12EO6/L64 mixed micelles are formed. We also carried out small angle neutron scattering measurement to determine the structure of the monomeric polymer/micellar SDS complex, as well as the mixed L64/C12EO6 aggregates. In these experiments, contrast matching was achieved by using the h and d forms of SDS, as well as C12EO6. During the early stages of the formation of polymer-bound SDS micelles, SDS aggregates with aggregation numbers of approximately 20 were found and such complexes contain 4-6 bound L64 monomers. The L64/C12EO6 data confirmed the existence of mixed micelles, and structural information involving the composition of the mixed micelle and the aggregation numbers were evaluated.     

Interactions between hen egg-white lysozyme, PEG2,000, and PLA50 at the air-water interface

In this paper, we compared the efficiency of polymer films, made of a poly(ethylene glycol) (PEG2,000)/poly(d,l-lactide) (PLA50) mixture, or a PEG2,000-PLA50 copolymer, to prevent adsorption of a model protein, the hen egg-white lysozyme (HEWL), at the air-water interface. This was achieved by analyzing the surface pressure/surface area curves, and the X-ray reflectivity data of the polymer films spread on a Langmuir trough, obtained in absence or in presence of the protein. For both the mixture and the copolymer, the amount of protein adsorbed at the air-water interface decreases when the density of the polymer surface coverage increases. It was shown that even in a condensed state, the polymer film made by the mixture can not totally prevent HEWL molecules to adsorb and penetrate the polymer mixed film, but however, protein molecules would not be directly exposed to the more hydrophobic phase, i.e. the air phase. It was also shown that the configuration adopted by the copolymer at the interface in its condensed state would prevent adsorption of HEWL molecules for several hours; this would be due in particular to the presence of PEG segments in the interfacial film.     

Interactions of Ionic Surfactants With PEO-PBO-PEO Triblock Copolymers in Aqueous Solutions

The interactions of triblock copolymers (TBP) with ionic surfactants were studied employing surface tensiometry, electrical conductivity, steady-state fluorescence (SSF), and dynamic light scattering (DLS) techniques. An increasing trend in the critical micelle concentration (CMC) of SDS/CTAB in the presence of triblock copolymers was observed especially at higher polymer to surfactant ratio. The delay in the CMC of surfactants was more pronounced in the presence of E₄₈B₁₀E₄₈ possibly due to its less hydrophobic nature. The negative values of free energy of micellization (ΔG_m) both in case of SDS and CTAB confirmed the spontaneity of the processes. The aggregation number (N_agg) and hydrodynamic radius (R_h) of polymer/surfactant mixed systems were determined by SSF and DLS. The suppression of the surfactant micelle size in the presence of TBP was confirmed by SSF and DLS studies.     

Preparation of end-grafted polymer brushes by nitroxide-mediated free radical polymerization of vaporized vinyl monomers

In this work, we report a gas-phase polymerization approach to create end-grafted vinyl based polymer films on silicon oxide based substrates. The "surface-initiated vapor deposition polymerization" (SI-VDP) of vaporized vinyl monomers, via the nitroxide-mediated free radical polymerization mechanism, was developed to fabricate various homo- and block copolymer brushes from surface-bound initiators, 1-(4'-oxa-2'-phenyl-12'-trimethoxysilyldodecyloxy)-2,2,6,6-tetra-methylpiperidine ("TEMPO"). The resulting polymer thin films were characterized by the Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, ellipsometry, and contact angle goniometry, respectively, to identify the surface composition, film thickness, surface coverage, and water contact angles. Through the SI-VDP, end-grafted polymer films of polystyrene (PSt), poly(acrylic acid) (PAAc), poly(N-(2-hydroxypropyl) methacrylamide) (PHPMA), and poly(N-isopropylacrylamide) (PNIPAAm) with 10-200 nm thicknesses were fabricated. Furthermore, the block copolymer films of PAAc (1st block)-b-PSt (2nd block), PSt (1st block)-b-PAAc (2nd block), and a triblock copolymer film of PAAc (1st)-b-PSt (2nd)-b-PHPMA (3rd), were also fabricated, suggesting the "renewability" of the TEMPO-initiated polymerization in the SI-VDP scheme. It is also noticed that the SI-VDP is more efficient than the conventional solution phase polymerization in producing functional polymer brushes such as PNIPAAm, PAAc, or PAAc-b-PSt end-grafted films. In summary, our studies have shown clear advantages of the SI-VDP setup for the nitroxide-mediated polymerization scheme in controlling synthesis of end-grafted homo- and copolymer thin films.     

Surface properties and abhesion of undecyl oxazoline block and homopolymers

The surface properties of three undecyl oxazoline homopolymers and two phenyl/undecyl oxazoline block copolymers (as comparison) were studied. After coating on glass slides and annealing, all films had a low critical surface energy of 21 dynes/cm. Water contact angles were higher than 107° for the most hydrophobic films. The deduction that the polymer surfaces contained close-packed methyl groups was further confirmed by electron spectroscopy chemical analysis (ESCA) angle profiling on an annealed undecyl oxazoline homopolymer film. A model was developed for the variation of elemental ratios as a function of photoelectron take-off angle. This verified that the polymer films had the polymer backbones parallel to the surface with the undecyl tails oriented toward the surface. When these block and homopolymers were coated on copy paper and glass slides, the peel strengths of pressure-sensitive adhesives with these surfaces were very low for short dwell times at room temperature. At long dwell times or at elevated temperatures, the peel strengths remained low for the homopolymers but increased greatly for the block copolymers to values higher than those in the tape on glass. After 24 h at 70°C, ESCA analysis showed that the adhesive diffused into the phenyl block domains of the diblock copolymer, generating high peel strength and cohesive failure. However, under the same annealing conditions, the triblock copolymer showed adhesive failure while peel strength increased. ESCA analysis showed very litle diffusion of the adhesive into the triblock copolymer. The homopolymers were stable toward vinyl acetate type adhesives even at elevated temperature; they were abhesive up to 100°C with no interdiffusion.     

Substrate surface energy dependent morphology and dewetting in an ABC triblock copolymer film

A gradient combinatorial approach was used to examine the effect of substrate surface energy on the morphology and stability of films of a poly(isoprene-b-styrene-b-ethylene oxide) triblock copolymer that exhibits an alternating gyroid morphology in the bulk. Atomic force microscopy data across our surface energy (water contact angle) library suggest a transformation to predominantly surface parallel lamellae with an antisymmetric ordering. For substrate water contact angles below 70 degrees the film exhibited autophobic dewetting from an adsorbed half-period triblock copolymer monolayer at longer annealing times. X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure analysis along gradient specimens indicated that the substrate surface energy governed the composition profile of the monolayer, and this variation in chemical expression was key to whether the film was stable or autophobically dewet. These observations demonstrate that enthalpic interactions, in addition to entropic considerations, can play a major role in autophobic dewetting of block copolymer films.     

Rapid Fabrication of Mesoporous Titania Films with Controlled Macroporosity to Improve Photocatalytic Property

Hierarchically porous titania films were fabricated by dual templating using a triblock copolymer such as Pluronic F127 and polystyrene (PS) beads, affording mesoporous films with controlled macroporosity. The presence of the triblock copolymer in the precursor solutions suppressed a regular accumulation of spherical PS beads, and PS‐derived macropores could be dispersed over the whole mesoporous titania film through rapid fabrication by spin‐coating. Some of the macropores were clustered, but the presence of the large spaces was important for keeping the mesostructure after calcination. Photodegradation of methylene blue (MB) was investigated by using the photoactive anatase films. The photodegradation of MB over the porous anatase films was accelerated by effective diffusion of MB molecules in the PS‐derived macropores, but it was important for improving photocatalytic performance to regulate the balance between the effectiveness of the diffusion in the macropores and the decrease of the surface area from the embedded macropores, as well as the reduction in the transparency of the porous films.     

The surface morphology evolution of an ultrathin film of poly[styrene-b-(ethylene-co-butylene)-b-styrene] during its dewetting process

The dewetting process of an ultrathin film of a triblock copolymer, poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) was studied with an atomic force microscope. The surface morphology of the dewetting process exhibited two distinct dewetting processes of the 5.6 nm thick films: a slower dewetting for the polymer layer at the very vicinity of the substrate's surface, and a faster one for the polymer on top of this layer. The surface-induced difference in the kinetics of these two-step dewetting processes resulted in a special morphology evolution, including the absence of the dewetting rim, and a final unique network-like morphology.     

Gas permeability in polymer- and surfactant-stabilized bubble films

The gas permeabilities of thin liquid films stabilized by poly(N-isopropylacrylamide) (PNIPAM) and PNIPAM-SDS (sodium dodecyl sulfate) mixtures are studied using the "diminishing bubble" method. The method consists of forming a microbubble on the surface of the polymer solution and measuring the shrinking rates of the bubble and the bubble film as the gas diffuses from the interior to the exterior of the bubble. PNIPAM-stabilized films exhibit variable thicknesses and homogeneities. Interestingly, despite these variable features, the gas permeability of the film is determined principally by the structure of the adsorbed polymer layer that provides an efficient gas barrier with a value of gas permeability coefficient that is comparable to that of an SDS Newton black film. In the presence of SDS, both the film homogeneity and the gas permeability coefficient increase. These changes are related to interactions of PNIPAM with SDS in the solution and at the interface, where coadsorption of the two species forms mixed layers that are stable but that are more porous to gas transfer. The mixed PNIPAM-SDS layers, studied previously for a single water-air interface by neutron reflectivity, are further characterized here in a vertical free-draining film using X-ray reflectivity.     

Novel Dual Two‐Dimensional Liquid Chromatography Online Coupled to Ultraviolet Detector,Fluorescence Detector,Ion‐Trap Mass Spectrometer for Short Peptide Amino Acid Sequence Determination with Bottom‐Up Strategy

A novel dual two‐dimensional (2D) high‐performance liquid chromatography (LC) setup coupled online to an ultraviolet (UV) detector, fluorescence (FL) detector, and ion‐trap mass spectrometer (MS) has been developed for determining the amino acid sequence of short peptides using a novel bottom‐up strategy. Short peptides were electrothermally hydrolyzed to shorter peptides and amino acid enantiomers. The first 2D LC‐UV and FL system was used to separate and identify the produced parent and daughter short peptides and amino acid isomers and enantiomers in the hydrolysate; the second 2D LC‐MS was used to identify the presence of cysteine and obtain the molecular mass signals and N‐terminal peptide fragment ion signals for parent and daughter short peptides. The identified amino acid enantiomers are used to form any possible short peptides by permutation and combination in an order from dipeptide to a tripeptide, to a tetrapeptide, and to even higher short peptides. The correct short peptides are confirmed by comparing the molecular weights of the constituent amino acid enantiomers and the molecular weights of identified short peptides together, with the characteristic N‐terminal peptide fragment ion signals. The amino acid sequence of the dipeptide ester aspartame and the tripeptide glutathione was successfully determined by this method.     

SELF ASSEMBLY OF ABC TRIBLOCK COPOLYMER THIN FILMS ON A BRUSH-COATED SUBSTRATE

Self assemblies of ABC triblock copolymer thin films on a densely brush-coated substrate were investigated by using the self-consistent field theory.The middle block B and the coated polymer form one phase and the alternating phase A and phase C occur when the film is very thin either for the neutral or selective hard surface(which is opposite to the brushcoated substrate).The lamellar phase is stable on the hard surface when it is neutral and interestingly,the short block tends to stay on this hard surf...     

Synthesis of ordered mesoporous zirconium phosphate films by spin coating and vapor treatments

Ordered mesoporous zirconium phosphate films were prepared on a silicon substrate by spin coating using a mixture of zirconium isopropoxide, triethyl phosphate, Pluronic P123 triblock copolymer, nitric acid, ethanol, and water. The spin-on film was consecutively treated with vapors of phosphoric acid and ammonia. The post-vapor treatments effectively enhanced the thermal stability of an ordered mesostructure when heated to 500 degrees C. XRD and TEM analyses show that the calcined zirconium phosphate film has a hexagonal structure with straight channels parallel to the film surface. The zirconium phosphate film exhibited high proton conductivity of 0.02 S/cm parallel to the film surface at 80% RH and 25 degrees C.     

Disruption of viscoelastic beta-lactoglobulin surface layers at the air-water interface by nonionic polymeric surfactants

Nonequilibrium interfacial layers formed by competitive adsorption of beta-lactoglobulin and the nonionic triblock copolymer PEO99-PPO65-PEO99 (F127) to the air-water interface were investigated in order to explain the influence of polymeric surfactants on protein film surface rheology and foam stability. Surface dilatational and shear rheological methods, surface tension measurements, dynamic thin-film measurements, diffusion measurements (from fluorescence recovery after photo bleaching), and determinations of foam stability were used as methods. The high surface viscoelasticity, both the shear and dilatational, of the protein films was significantly reduced by coadsorption of polymeric surfactant. The drainage rate of single thin films, in the presence of beta-lactoglobulin, increased with the amount of added F127, but equilibrium F127 films were found to be thicker than beta-lactoglobulin films, even at low concentration of the polymeric surfactant. It is concluded that the effect of the nonionic triblock copolymer on the interfacial rheology of beta-lactoglobulin layers is similar to that of low molecular weight surfactants. They differ however in that F127 increases the thickness of thin liquid films. In addition, the significant destabilizing effect of low molecular weight surfactants on protein foams is not found in the investigated system. This is explained as due to long-range steric forces starting to stabilize the foam films at low concentrations of F127.     

Phase behavior in thin films of cylinder-forming ABA block copolymers: experiments

We experimentally establish a phase diagram of thin films of concentrated solutions of a cylinder forming polystyrene-block-polybutadiene-block-polystyrene triblock copolymer in chloroform. During annealing the film forms islands and holes with energetically favored values of film thickness. The thin film structure depends on the local thickness of the film and the polymer concentration. Typically, at a thickness close to a favored film thickness parallel orientation of cylinders is observed, while perpendicular orientation is formed at an intermediate film thickness. At high polymer concentration the cylindrical microdomains reconstruct to a perforated lamella structure. Deviations from the bulk structure, such as the perforated lamella and a wetting layer are stabilized in films thinner than approximately 1.5 domain spacings.     

Chemical synthesis and characterization of aniline and o-anthranilic acid copolymer

The chemical co-polymerization of aniline with o-anthranilic acid (AA) to form copolymer films has been made in aqueous hydrochloric acid medium. The copolymer films were monitored by using the quartz crystal microbalance (QCM) technique. The effect of AA and its concentrations on the film formation was investigated. The results were justified by measuring the UV-Vis absorption spectra for the in situ copolymer films grown onto glass slides immersed into the polymerization media and the in situ UV-Vis absorption spectra for the copolymer in the bulk during the co-polymerization. The conductivity for the copolymer films and powder pellets at different molar ratios of aniline/AA were measured. Also, the IR spectra, X-ray diffraction and the thermal gravimetric analysis for the copolymer powder formed in the bulk in the absence and presence of AA were measured and discussed. It is found that the presence of AA affects the yield, induction period, depletion time and growth rate of the film formation. It also affects the crystallinity, and conductivity as well as the solubility of the polymer. Finally, the dopant weight fraction (w) associated with the copolymer was determined. It is almost half the value determined for the polymer in absence of AA.     

Measuring the enthalpies of interaction between glycine,L-cysteine,glycylglycine, and sodium dodecyl sulfate in aqueous solutions

Calorimetric measurements of enthalpies of solution Δ_sol H ^m for glycine, L-cysteine, and glycylglycine in aqueous solutions of sodium dodecyl sulfate (SDS) with concentrations of up to 0.05 mol kg^–1 are made. Standard enthalpy of solution Δ_sol H ⁰ and enthalpy of transfer Δ_tr H ⁰ of the dipeptide from water into mixed solvent are calculated. The calculated enthalpy coefficients of paired interactions of amino acids and dipeptide with SDS prove to be positive. Hydrophobic interactions between the biomolecules and SDS are found to have a major impact on the enthalpies of interaction in the three-component systems under study, within the indicated range of concentrations.     

Preparation and characterization of electrically conducting Langmuir-Blodgett films of poly(N-octadecylaniline)

A stable monolayer of N-octadecylaniline containing stearic acid at the air-water interface has been obtained. However, the Langmuir monolayer of pure poly(N-octadecylaniline) was not stable, but mixed Langmuir-Blodgett films of this polymer with stearic acid in different ratios as a spreading aid were stable. The electrical conductivity of these films increased by five orders of magnitude after doping with iodine as compared to that before iodine doping (5.8x10(-7) S cm(-1)). Temperature-dependent electrical conductivity suggested that these films were semiconducting in nature with low thermal activation energy. Impedance analyses of these films revealed that the equivalent circuit for poly(N-octadecylaniline) was (RQ) whereas that for mixed poly(N-octadecylaniline) with stearic acid was (RQ)(RQ).     

淬火和退火对称三嵌段共聚物薄膜形貌和结构的Monte Carlo模拟

嵌段共聚物薄膜淬火形貌与初始化时嵌段共聚物熔体的状态相关,淬火得到的有序形貌有时存在缺陷,而退火则可以消除这些缺陷形成更规整的层状结构,且退火得到的嵌段共聚物分子的均方回转半径等都小于淬火得到的.与淬火比较,退火使高分子链充分松弛,增加了薄膜中有利于提高材料物理力学性能的桥键含量.不同于受限自由表面间的对称二嵌段共聚物首先在表面区域形成有序结构,三嵌段共聚物则在薄膜内部先形成有序的层状结构.