Larger Molecular Area Research Articles

Ionic strength and anion‐specificity effects on the interfacial behavior of double hydrophilic block copolymer PNIPAM‐b‐POEGA

AbstractIn our prior paper, surface micelles with the core‐shell‐petal structure of the double hydrophilic block copolymer poly(N‐isopropylacrylamide)‐block‐poly[oligo(ethylene glycol) acrylate] (PNIPAM‐b‐POEGA) were successfully evaluated. In this work, ionic strength (under acidic conditions) and anion‐specificity effects (under neutral conditions) on the aggregation behavior of PNIPAM‐b‐POEGA at the air/water interface and the morphologies of its Langmuir–Blodgett (LB) films were systematically studied. Under acidic conditions, the salting‐out effect prevails over the electrostatic shielding effect, and the amide group shells with a slight protonation degree are covered up by the large POEGA petals. Under neutral conditions, the stretching degrees of POEGA blocks at low/moderate salt concentrations are close. At high salt concentrations, the isotherms gradually shift to large molecular areas in the order of the NaCl, Na2SO4, NaNO3, and NaSCN cases. The hysteresis degrees of the monolayers increase with the increase of salt concentrations due to the gradually increased interfacial stretching degree and compression‐induced underwater solubility of POEGA blocks. All the initial LB films of PNIPAM‐b‐POEGA exhibit isolated circular micelles with small cores. Upon compression, the LB films exhibit slightly large micelles because of the possible coalescence of some neighboring cores.

Multifaceted Sulfone-Carbazole-Based D-A-D Materials: A Blue Fluorescent Emitter as a Host for Phosphorescent OLEDs and Triplet-Triplet Annihilation Up-Conversion Electroluminescence.

Electroluminescence (EL) from the singlet-excited (S1) state is the ideal choice for stable, high-performing deep-blue organic light-emitting diodes (OLEDs) owing to the advantages of an adequately short radiative lifetime, improved device durability, and low cost, which are the most important criteria for their commercialization. Herein, we present the design and synthesis of three donor-acceptor-donor (D-A-D)-configured deep-blue fluorescent materials (denoted as TC-1, TC-2, and TC-3) composed of a thioxanthone or diphenyl sulfonyl acceptor and phenyl carbazolyl donor. These systems exhibit strong deep-blue photoluminescence (422-432 nm) in solutions and redshifted emission (472-486 nm) in thin films. The solid-state photoluminescence quantum yield (PLQY) was estimated to be 78 and 94% for TC-2 and TC-3, respectively. TC-2 and TC-3 possess good molecular packing and large molecular cross-sectional areas, which not only improves the PLQY but enhances the triplet-triplet annihilation up-conversion (TTAUC) efficiency of fluorescent emitters. Furthermore, both compounds were applied as an acceptor for confirming their TTAUC property using bis(2-methyldibenzo[f,h]quinoxaline)(acetylacetonate)iridium(III) (Ir(MDQ)2acac) as the sensitizer. Non-doped OLEDs based on TC-2 and TC-3 exhibit blue EL in the 461-476 nm range. In particular, TC-3 exhibits a maximum external quantum efficiency (EQEmax) of 5.1%, and its EL maximum is 476 nm. In addition, the three emitters were employed as hosts in red OLEDs using bis(1-phenylisoquinoline)(acetylacetonate)iridium(III) (Ir(piq)2acac) as the phosphorescent dopant. The red phosphorescent OLEDs based on TC-1, TC-2, and TC-3 achieve excellent EQEmax values of 21.6, 22.9, and 21.9%, respectively, and peak luminance efficiencies of 12.0, 14.0, and 12.3 cd A-1. These results highlight these fluorophores' versatility and promising prospects in practical OLED applications.

Studies on the interactions of tiny amounts of common ionic surfactants with unsaturated phosphocholine lipid model membranes

In order to provide the fundamental information about the interactions of common anionic surfactants with the basic unsaturated phospholipids the influence of three cationic (dodecyltrimethylammonium bromide, DTAB; tetradecyltrimethylammonium bromide, TTAB and hexadecyltrimethylamonium bromide, CTAB) and one anionic (sodium dodecylsulfate, SDS) surfactants on the properties of the 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) layers was investigated. The studies proved that a tiny amount of the ionic surfactant added to the already synthesized liposome suspension is sufficient to change the zeta potential of the POPC and DOPC liposomes significantly. This impact increases with the surfactant concentration, the alkyl chain length of the surfactant and the degree of lipid saturation. Moreover, this effect is greater for the anionic surfactant than for the cationic one of the same alkyl chain length. The observed findings were confirmed in the course of the research carried out with the use of the corresponding Langmuir monolayers where the surface pressure – mean area isotherms, the compressibility modulus – surface pressure dependences, the monolayer penetration tests, the surface potential – mean molecular area isotherms and Brewster angle microscopy were discussed. It was found that the presence of the surfactants shifts the isotherms towards larger molecular area, to the higher extent for the SDS than DTAB. This effect increases with the increasing surfactant concentration in the subphase. Moreover, the investigated surfactants remain in the monolayer even at high surface pressure. Nevertheless, no effect on the morphology of the POPC and DOPC monolayers was detected from the BAM images. The surface potential and surface charge of the liposomes calculated on the basis of the zeta potential results reflected the interactions between the surfactant and the lipid layers.

Correlation among copolyether spacers, molecular geometry and interfacial properties of extended surfactants

Extended surfactants (e-surfactants) generally occupy larger surface adsorption areas and display better properties than conventional surfactants, which is attributed to propoxy-containing polyether spacers coiled more and collapsed more on various interfaces but lack of firm evidences. In this work, the target products of sodium dodecyl poly(propoxy-ethoxy) sulfates are synthesized on the basis of designing copolyether spacers by both diblock and random copolymerization mechanisms. A unique insoluble monolayer experiment is proposed to estimate surface spreading areas of the copolyether intermediates. Moreover, the correlation between copolyether spacers and molecular geometry and interfacial properties of the e-surfactants is investigated. We find that surface spreading areas of the copolyether intermediates are much larger than that of the dodecanol precursor and slightly larger than and positively correlated with surface adsorption areas of the corresponding target e-surfactants, which provides a direct evidence for biphasic affinity of the copolyether spacers to drive the spacers three-dimensionally extended on various interfaces and make e-surfactants becoming rugby ball shapes. Furthermore, it is shown that the more random copolyether spacer, the larger molecular area on the surface the e-surfactant occupies, being responsible for many unique interfacial properties of e-surfactants.

Effects of Ionic Strength and Ion Specificity on the Interface Behavior of Poly(dimethylaminoethyl methacrylate)-Poly(lauryl methacrylate).

The ion specificity effect on the water solubility of poly(N-isopropylacrylamide)-containing copolymers complies with the Hofmeister series, which is applicable to other copolymers or not need to be explored. In this work, effects of ionic strength under acidic conditions and ion specificity under alkaline conditions on the air/water interface behavior of two amphiphilic diblock copolymers poly(dimethylaminoethyl methacrylate)-poly(lauryl methacrylate) (PDMAEMA-PLMA) were systematically studied. Under acidic conditions, the surface pressure-area isotherms of a predominantly hydrophilic copolymer are insensitive to ionic strength. In contrast, the isotherms of a predominantly hydrophobic copolymer successively shift to the large, small, and large molecular area with the increase of ionic strength. Under alkaline conditions, the interfacial stretch degrees of PDMAEMA chains of two copolymers change with salt species and concentrations, which do not comply with the Hofmeister series. All of the Langmuir-Blodgett films of the former copolymer exhibit separate circular micelles. Nevertheless, those of the latter copolymer obtained under alkaline conditions exhibit various distinctive morphologies such as separate circular micelles, large separate PLMA cores within large PDMAEMA domains, and large PLMA domains/aggregates surrounded by short PDMAEMA shells. It can be attributed to the high deformability of PLMA chains, the ion specificity effect on the stretch degree of PDMAEMA blocks, and their underwater solubility upon compression.

Interfacial Behavior of Oligo(Ethylene Glycol) Dendrons Spread Alone and in Combination with a Phospholipid as Langmuir Monolayers at the Air/Water Interface.

Dendrons consisting of two phosphonate functions and three oligo(ethylene glycol) (OEG) chains grafted on a central phenoxyethylcarbamoylphenoxy group were synthesized and investigated as Langmuir monolayers at the surface of water. The OEG chain in the para position was grafted with a t-Bu end-group, a hydrocarbon chain, or a partially fluorinated chain. These dendrons are models of structurally related OEG dendrons that were found to significantly improve the stability of aqueous dispersions of iron oxide nanoparticles when grafted on their surface. Compression isotherms showed that all OEG dendrons formed liquid-expanded Langmuir monolayers at large molecular areas. Further compression led to a transition ascribed to the solubilization of the OEG chains in the aqueous phase. Brewster angle microscopy (BAM) provided evidence that the dendrons fitted with hydrocarbon chains formed liquid-expanded monolayers throughout compression, whilst those fitted with fluorinated end-groups formed crystalline-like domains, even at large molecular areas. Dimyristoylphosphatidylcholine and dendron molecules were partially miscible in monolayers. The deviations to ideality were larger for the dendrons fitted with a fluorocarbon end-group chain than for those fitted with a hydrocarbon chain. Brewster angle microscopy and atomic force microscopy supported the view that the dendrons were ejected from the phospholipid monolayer during the OEG conformational transition and formed crystalline domains on the surface of the monolayer.

Effects of spreading and subphase conditions on the interfacial behavior of an amphiphilic copolymer poly(n-butylacrylate)-b-poly(acrylic acid)

Aggregation behavior of an amphiphilic diblock polyelectrolyte poly(n-butylacrylate)-b-poly(acrylic acid) (PnBA-b-PAA) at the air/water interface and its Langmuir−Blodgett (LB) films were respectively characterized by the Langmuir film balance technique and atomic force microscopy. Effects of spreading solution concentration and volume, and subphase temperature and ionic strength on the interfacial aggregation behavior of PnBA-b-PAA under alkaline condition were systematically studied. With the increase of spreading concentration, surface pressure−molecular area isotherms shift to small molecular areas at the corresponding spreading volumes. With the rise in subphase temperature, the isotherms shift to small molecular areas due to the decreased pKa value and increased solubility of PAA blocks. With the increase of subphase ionic strength, the isotherms shift to large molecular areas because of the predominant salting out effect. The LB films transferred from alkaline subphase with different ionic strengths are more likely to exhibit isolated circular micelles. With the increase of spreading concentration, diameters of micelle cores first decrease and then increase, a behavior which is attributed to the gradually increased chain entanglements and surface polymer concentration, respectively. For small spreading volume, core diameters in the LB films first decrease and then increase with the rise in subphase temperature. For large spreading volume, however, core diameters increase with temperature due to the higher mobility and weaker entanglements of PAA blocks underwater. With the increase of subphase ionic strength, furthermore, core diameters first increase and then decrease, which is attributed to the predominant electrostatic shielding and salting out effects, respectively.

Establishing the impact of model surfactants on cloud condensation nuclei activity of sea spray aerosol mimics

Abstract. Surface-active compounds present in aerosols can increase their cloud condensation nuclei (CCN) activation efficiency by reducing the surface tension (σ) in the growing droplets. However, the importance of this effect is poorly constrained by measurements. Here we present estimates of droplet surface tension near the point of activation derived from direct measurement of droplet diameters using a continuous flow streamwise thermal gradient chamber (CFSTGC). The experiments used sea spray aerosol (SSA) mimics composed of NaCl coated by varying amounts of (i) oleic acid, palmitic acid or myristic acid, (ii) mixtures of palmitic acid and oleic acid, and (iii) oxidized oleic acid. Significant reductions in σ relative to that for pure water were observed for these mimics at relative humidity (RH) near activation (∼ 99.9 %) when the coating was sufficiently thick. The calculated surface pressure (π = σH2O − σobserved) values for a given organic compound or mixture collapse onto one curve when plotted as a function of molecular area for different NaCl seed sizes and measured RH. The observed critical molecular area (A0) for oleic acid determined from droplet growth was similar to that from experiments conducted using macroscopic solutions in a Langmuir trough. However, the observations presented here suggest that oleic acid in microscopic droplets may exhibit larger π values during monolayer compression. For myristic acid, the observed A0 compared well to macroscopic experiments on a fresh subphase, for which dissolution has an important impact. A significant kinetic limitation to water uptake was observed for NaCl particles coated with pure palmitic acid, likely as a result of palmitic acid (with coating thicknesses ranging from 67 to 132 nm) being able to form a solid film. However, for binary palmitic-acid–oleic-acid mixtures there was no evidence of a kinetic limitation to water uptake. Oxidation of oleic acid had a minor impact on the magnitude of the surface tension reductions observed, potentially leading to a slight reduction in the effect compared to pure oleic acid. A CCN counter was also used to assess the impact on critical supersaturations of the substantial σ reductions observed at very high RH. For the fatty-acid-coated NaCl particles, when the organic fraction (εorg) was > 0.90 small depressions in critical supersaturation were observed. However, when εorg < 0.90 the impact on critical supersaturation was negligible. Thus, for the fatty acids considered here, the substantial σ reductions observed at high RH values just below activation have limited impact on the ultimate critical supersaturation. A surface film model is used to establish the properties that surface-active organic molecules must have if they are to ultimately have a substantial impact on the activation efficiency of SSA. To influence activation, the average properties of surface-active marine-derived organic molecules must differ substantially from the long-chain fatty acids examined, having either smaller molecular volumes or larger molecular areas. The model results also indicate that organic-compound-driven surface tension depression can serve to buffer the critical supersaturation against changes to the organic-to-salt ratio in particles in which the organic fraction is sufficiently large.

Analyte and matrix evaporability - key players of low-temperature plasma ionization for ambient mass spectrometry.

The introduction of ambient ionization at atmospheric pressure for mass spectrometry (AI-MS) attracted the interest of many researchers in the field and various ionization techniques have been described in recent years that allow a quick and easy-to-handle analysis of samples under ambient conditions without or with only minor sample preparation. Among those, plasma-based techniques including the low-temperature plasma probe require very little resources thereby providing great potential for implementation in mobile analytical devices. However, systematic studies on signal responsiveness with this technique, such as the influence of the analyte and matrix characteristics on relative signal intensity, are still rare. Therefore, we used a low-temperature plasma source based on dielectric barrier discharge with helium as process gas to assess influencing factors on signal intensity in mass spectrometry. Among 12 tested molecular descriptors, in particular a low vaporization enthalpy and a large molecular nonpolar surface area improve the relative signal intensity. In addition, we show that the impact of compound characteristics strongly outperforms the influence of simple sample matrices such as different organic solvents and water, with a weak trend that volatile solvents tend to decrease the signal responsiveness of the analytes. However, several specific solvent-analyte interactions occurred, which have to be considered in targeted applications of this method. Our results will help further in improving the implementation and standardization of low-temperature plasma ionization for ambient mass spectrometry and understanding the requirements and selectivity of this technique. Graphical abstract Influencing factors (analyte and matrix characteristics) on signal intensity in dielectric-barrier discharge plasma for ionization in mass spectrometry.

Experimental Measurement of the Gibb's Free Energy of Mixing for Hydroxycholesterol-Phospholipid Monolayers

Hydroxycholesterols are implicated in the management cell membrane cholesterol levels as well as various pathologies. These oxidized versions of cholesterol include a second hydroxyl functional group. We have previously used fluorescence microscopy and traditional Langmuir trough techniques to measure the unique phase behavior of multicomponent hydroxycholesterol-phospholipid monolayers (7ß-OH, 20-OH, 22(R)-OH, 22(S)-OH, 25-OH and 27-OH ). Here we have extended that analysis to utilize pressure-area isotherms to measure area-condensation and expansion as well as the Gibbs free energy of mixing. The unique area expansion exhibited by these model monolayer systems at low compressions (large molecular area) and novel miscibility phase behavior provide a potential insights into more commonly studied systems of phospholipids and cholesterol.

Simultaneous determination of bifenox, dichlobenil and diclofop methyl by hollow carbon nanospheres enhanced magnetic carboxylic multi-walled carbon nanotubes

A novel analytical method based on magnetic solid-phase extraction (MSPE) coupled with high performance liquid chromatography-diode array detection (HPLC-DAD) was established for three herbicides simultaneous determination. The key of the method was the explored extractant, which was a composite of hollow carbon nanospheres (HCSs) enhanced magnetic carboxylic MWCNTs (HCSs@Fe3O4-MWCNTs-COOH). MWCNTs-COOH was inserted in the pores of HCSs by oscillation and sonication with the capillary forces, making the carboxylic groups and structure intervals of the composite increase as compared to MWCNTs-COOH, therefore the extractant exhibited enhanced hydrophilicity, dispersibility, adsorptivity and selectivity. The extractant was sensitive to analytes with the structure of multi-aromatic ring, more hydrogen bond acceptor and large molecular polar surface area, which can be attributed to hydrogen bonding and π-π electron-donor-acceptor (EDA) interactions. The morphology, structure and magnetic property of the extractant were characterized. Then the explored extractant based MSPE-HPLC-DAD method was applied for bifenox (BFO), dichlobenil (DCB) and diclofop methyl (DCM) determination from wheat flour samples. Prior to real sample analysis, critical extraction parameters such as solution pH, extraction time, salt addition and temperature were investigated and optimized, and the analytical method was evaluated. It was indicated that the method had satisfactory linearities with the linear coefficients above 0.99, good precision with the RSD less than 3.5%, desirable recoveries ranged from 88.8% to 96.6%, and low limits of detection (LOD) that were 0.39, 0.24, and 0.68 ng/g for DCB, BFO and DCM, respectively. The established MSPE-HPLC-DAD method has great potentials for trace polar herbicides selective determination from complex matrix samples.

An example of green copper corrosion inhibitors derived from flavor and medicine: Vanillin and isoniazid

The use of some industrial materials such as medicine and flavor in the anti-corrosion field is an attractive topic. A Schiff base (N-isonicotinamido-3-methoxy-4-hydroxybenzalaldimine, IM) based on flavor (vanillin) and medicine (isoniazid) has been synthesized and utilized as a green corrosion inhibitor for copper in NaCl media. Electrochemical techniques are employed to analyze its inhibition property. The copper surface is characterized by scanning electron microscopy, infrared spectroscopy, and energy-dispersive X-ray spectroscopy. IM acts as an anodic inhibitor and its inhibition efficiency is up to 93% at 120mg/L and more remarkable than its corresponding reactants. With a large molecular surface area and better electron donation ability, IM has a better corrosion inhibition performance and may be adsorbed on the copper surface through NH and CN groups, according to theoretical studies.

Surface properties of polyene glycol phospholipid monolayers

We studied the surface properties of monolayers composed of polyunsaturated conjugated ethylene glycol phospholipids (carotenoid lipids), compared the data with monolayers of dipalmitoylphosphatidylcholine (DPPC) to which carotenoids were added and evaluated the impact of the unsaturated glycol lipids on monolayers with the glycerolipid DPPC. The carotenoid based glycol lipids formed monolayers at the air/water interface. Using the Langmuir method we obtained series of pressure-area (π-A) isotherms and determined the limiting area A per molecule of three glycol lipids, C30:9-C0A=42.6±1.4Å2, C30:9-C2A=76.1±2.5Ǻ2 and C30:9-C12A=354.0±12.0Å2 and their mixtures with DPPC at various mole fraction X. C30:9-C0 and C30:9-C2 did not affect significantly the shape of the isotherm, but caused their slight shift toward a lower and larger molecular area, respectively. C30:9-C12 at mole fractions X>0.02 affected the shape of isotherm. The compressibility modulus Cs−1 of monolayers depended on the surface pressure. Cs−1 value was substantially higher for DPPC monolayers in comparison with those of pure glycol lipids. At low surface pressure π=5–10mN/m and low mole fractions X<0.02 the glycol lipids formed complexes with DPPC; at higher surface pressure the separation of pure components took place. The dipole potential of the monolayers composed of cationic glycol lipids C30:9-C2 and C30:9-C12 was higher in comparison with those of zwitterionic DPPC and C30:9-C0. This may be connected with various contributions of dipole moments of the molecules and their orientation in the monolayer.

Contrasting Topological Effect of PEG-Containing Amphiphiles to Natural Lipids on Stability of Vesicles.

Topology of amphiphiles is important to control physicochemical properties of supramolecular assemblies. Nature demonstrates higher stability of membrane composed of lipids with a macrocyclic aliphatic tail than those with linear tails, which likely results from the restricted molecular structures of the macrocyclic lipids, allowing for closer molecular packing. In contrast, here we report that a PEG-containing macrocyclic amphiphile shows lower stability of vesicles than the corresponding acyclic one. The macrocyclic amphiphile consists of an aromatic hydrophobic part with chirality in which both ends are strapped by octaethylene glycol via phosphoric ester groups, while the acyclic amphiphile bears tetraethylene glycol chains attached to both ends of the hydrophobic part. Because of the thermoresponsive property of PEG to change its conformation, the hydrophobic part of the macrocyclic amphiphile undergoes a larger thermal conformational change than that of the acyclic one. In addition, the cyclic amphiphile has a larger molecular area, which likely reduces the vesicular stability compared with the acyclic one. Such a contrasting topological effect caused by macrocyclization at the aliphatic part seen in the natural system and at the hydrophilic part demonstrated in this study leads to expand the molecular design of amphiphiles for both increasing and decreasing the stability of vesicles by molecular topology.

Alkyl-imidazolium glycosides: non-ionic—cationic hybrid surfactants from renewable resources

A series of surfactants combining carbohydrate and imidazolium head groups were prepared and investigated on their assembly behavior. The presence of the imidazolium group dominated the interactions of the surfactants, leading to high CMCs and large molecular surface areas, reflected in curved rather than lamellar surfactant assemblies. The carbohydrate, on the other hand, stabilized molecular assemblies slightly and reduced the surface tension of surfactant solutions considerably. A comparative emulsion study discourages the use of pure alkyl imidazolium glycosides owing to reduced assembly stabilities compared with APGs. However, the surfactants are believed to have potential as component in carbohydrate based surfactant mixtures.

Surface Behavior of Sphingomyelins with Very Long Chain Polyunsaturated Fatty Acids and Effects of Their Conversion to Ceramides

Molecular species of sphingomyelin (SM) with nonhydroxy (n) and 2-hydroxy (h) very long chain polyunsaturated fatty acids (n- and h-28:4, 30:5, and 32:5) abound in rat spermatogenic cells and spermatozoa. These SMs are located on the sperm head, where they are converted to the corresponding ceramides (Cer) after the completion of the acrosomal reaction, as induced in vitro. The aim of this study was to look into the surface properties of these unique SM species and how these properties change by the SM → Cer conversion. After isolation by HPLC, these SMs were organized in Langmuir films and studied alone, in combination with different proportions of Cer, and during their conversion to Cer by sphingomyelinase. Compression isotherms for all six SMs under study were compatible with a liquid-expanded (LE) state and showed large molecular areas. Only the longest SMs (n-32:5 and h-32:5 SM) underwent a phase transition upon cooling. Interestingly, the abundant h-28:4 Cer exhibited a highly compressible liquid-condensed (LC) phase compatible with a high conformational freedom of Cer molecules but with the characteristic low diffusional properties of the LC phase. In mixed films of h-28:4 SM/h-28:4 Cer, the components showed favorable mixing in the LE phase. The monolayer exhibited h-28:4 Cer-rich domains both in premixed films and when formed by the action of sphingomyelinase on pure h-28:4 SM films. Whereas the SMs from sperm behaved in a way similar to that of shorter acylated SMs, the corresponding Cers showed atypical rheological properties that may be relevant to the membrane structural rearrangements that take place on the sperm head after the completion of the acrosomal reaction.

Phase Behavior and Molecular Packing of Octadecyl Phenols and their Methyl Ethers at the Air/Water Interface

Noncovalent molecular interactions, such as hydrogen bonding and van der Waals forces, play an important role in self-assembling to supramolecular structures. To study these forces, we chose monolayers at the air/water interface to limit the possible arrangements of the interacting molecules. Furthermore, monolayers provide useful tools to understand and study interactions between molecules in a controlled and fundamental way. The phase behavior and molecular packing of the phenols 1-(4-hydroxyphenyl)-octadecane (5a), 1-(3,4-dihydroxyphenyl)-octadecane (6), and 1-(2,3,4-trihydroxyphenyl)-octadecane (3) and their methyl ethers in monolayers at the air/water interface have been examined by π/A isotherms, Brewster angle microscopy (BAM), grazing incidence X-ray diffraction (GIXD) measurements, and density functional theory (DFT) calculations. The phenols are synthesized by Friedel-Crafts acylation of methoxybenzenes, hydrogenation of the resulting aryl ketones, and cleavage of the aryl methyl ethers. In the π/A isotherms and in BAM, the phenols show patches of the solid condensed phase at large molecular areas and the monolayers collapse at high pressures. Furthermore, the dimensions of the unit cell obtained by GIXD measurements are compatible with an arrangement of the phenyl rings that allows one aryl ring to interact with four adjacent phenyl rings in an edge-to-face arrangement, which leads to a significant binding energy. The experimental data are in good agreement with DFT calculations of 2D crystalline benzene and p-cresol arrangements. The enhanced monolayer stability of phenol 5a can be explained by hydrogen bonds of the hydroxyl group with water and van der Waals forces between the alkyl chains and aryl-aryl interactions.

The synthesis and characterization of dinuclear ruthenium sensitizers and their applications in photocatalytic hydrogen production

A dinuclear ruthenium(II) dye sensitizer, ([Ru2(bpy)4BL](ClO4)2) referred as Compound 1, where bpy=2,2′-bipyridine, BL=2,2′-((1E,1′E)-(((E)-diazene-1,2-diyl-bis(2,1-phenylene))-bis(azanylylidene))-bis (methanylylidene)) diphenol (a bidentate bridging ligand), was designed, synthesized and characterized. The dye sensitizer was used on the photocatalytic water splitting for hydrogen (H2) production over TiO2 (P25) under visible light (λ⩾400nm) irradiation using triethanolamine (TEOA) as a sacrificial electron donor. The dye sensitized-TiO2 demonstrated a good stability and sufficient reproducibility for over 6h. The photosensitization ability of the sensitizer was due to its conjugation system, large molecular area, TiO2 linkage mode and the antenna effect.

Self-assembly of PBzMA-b-PDMAEMA diblock copolymer films at the air–water interface and deposition on solid substrates via Langmuir–Blodgett transfer

The aggregation behavior and morphological characteristics of amphiphilic block copolymer polybenzyl methacrylate-block-poly(dimethylamino)ethyl methacrylate (PBzMA-b-PDMAEMA) at the air–water interface were investigated through surface pressure measurements, atomic force microscopy (AFM) imaging, electrochemical measurements and X-ray reflectivity. Ionization of PDMAEMA blocks significantly affects the isotherms of the surface films at the air–water interface and, consequently, originates different morphologies of Langmuir–Blodgett films obtained under different experimental conditions. At low pH the PDMAEMA blocks are fully protonated and therefore dissolved in the aqueous subphase. Under this condition, the effects of the solubility and electrostatic repulsion of submerged PDMAEMA chains prevail over hydrophobic interactions and the Langmuir film exhibits low surface pressure at large molecular area values. Upon compression, the isotherm shows a pseudoplateau corresponding to the “pancake-to-brush” transition followed by an increase in surface pressure at smaller MMA values. These results were correlated with the morphological features of Langmuir–Blodgett films transferred onto silicon substrates, where dispersed dot-like domains that gradually transformed into an island-like structure, followed by further percolation into a continent-like morphology, were observed through AFM imaging. On the other hand, at high pH the isotherm is more expanded and the film exhibits higher surface pressure at relatively high MMA values due to the strong repulsive interactions between interface-confined hydrophobic aggregates constituted of PBzMA cores and neutral PDMAEMA shells. In this case, the AFM results show a structural evolution from circular and quasi-hexagonally packed micelles, followed by a worm-like structure that collapses into a homogeneous film. Furthermore, the study of the copolymer behavior under different subphase ionic strength conditions confirmed the critical role of electrostatic interactions in determining the characteristics of the isotherm. We could also demonstrate that our system follows accurately the scaling relationship for surface pressure of annealed brushes. Complementary studies performed by means of X-ray reflectivity were carried out to probe the buried interfacial structure of the diblock copolymer film, corroborating that the organization of both blocks on the silicon substrates is strongly dependent on the pH conditions of the subphase during the LB transfer.

Distribution of cooperative unit size of amphiphilic molecules in the phase coexistence region in Langmuir monolayers

The dependence of the size of the cooperative unit (C.U.) of amphiphilic molecules on surface pressure (π) in the liquid expanded (LE)–liquid condensed (LC) phase coexistence region of Langmuir monolayers has been formulated and calculated using measured isotherm data. The C.U. size changes largely depending on the surface pressure in the coexistence region: these submicroscopic molecular aggregates are not static objects, but dynamic ones characterized by large fluctuations in size. It has been found that the C.U. size distribution can be a natural consequence of the significant change of monolayer compressibility, which reflects large molecular area density fluctuations, in the coexistence region.