Tuning the Optical and Electrical Properties of Few‐Layer Black Phosphorus via Physisorption of Small Solvent Molecules

Black phosphorus (BP) is recently becoming more and more popular among semiconducting 2D materials for (opto)electronic applications. The controlled physisorption of molecules on the BP surface is a viable approach to modulate its optical and electronic properties. Solvents consisting of small molecules are often used for washing 2D materials or as liquid media for their chemical functionalization with larger molecules, disregarding their ability to change the opto‐electronic properties of BP. Herein, it is shown that the opto‐electronic properties of mechanically exfoliated few‐layer BP are altered when physically interacting with common solvents. Significantly, charge transport analysis in field‐effect transistors reveals that physisorbed solvent molecules induce a modulation of the charge carrier density which can be as high as 10¹² cm^?2 in BP, i.e., comparable to common dopants such as F₄‐TCNQ and MoO₃. By combining experimental evidences with density functional theory calculations, it is confirmed that BP doping by solvent molecules not only depends on charge transfer, but is also influenced by molecular dipole. The results clearly demonstrate how an exquisite tuning of the opto‐electronic properties of few‐layer BP can be achieved through physisorption of small solvent molecules. Such findings are of interest both for fundamental studies and more technological applications in opto‐electronics.     

Dipole-directed assembly of lines of 1,5-dichloropentane on silicon substrates by displacement of surface charge

One-dimensional nanostructures at silicon surfaces have potential applications in nanoscale devices. Here we propose a mechanism of dipole-directed assembly for the growth of lines of physisorbed dipolar molecules. The adsorbate chosen was a halide, in preparation for the patterned imprinting of halogen atoms. Using scanning tunnelling microscopy, physisorbed 1,5-dichloropentane on Si(100)-2x1 was shown to self-assemble at room temperature into molecular lines that grew predominantly perpendicular to the Si-dimer rows. Line formation was triggered by the displacement of surface charge by the dipolar adsorbate. Experimental and simulated scanning tunnelling microscopy images were in agreement for a range of positive and negative bias voltages. The geometry of the physisorbed molecules and nature of their binding were evident from the scanning tunnelling microscopy images, as interpreted by scanning tunnelling microscopy simulation.     

Probing the conformation of physisorbed molecules at the atomic scale using STM manipulation

We use scanning tunneling microscope (STM) manipulation and density functional theory calculation to investigate the structural properties of individual sexiphenyl molecules physisorbed on a Ag(111) surface at 6 K. The molecule-surface atomic registry is precisely determined by using atomic markers and a sexiphenyl functionalized tip. The calculations confirm the alternating twist of the sexiphenyl pi-rings on Ag(111). The pi-ring torsional angle, 11.4 degrees, is directly determined from the geometry of STM manipulation. This innovative experiment opens up a novel application of STM manipulation to probe the properties of "physisorbed" species on surfaces at the atomic level.     

Studies of liquid-phase complexes in acetonitrile/water solutions by attenuated total reflection infrared spectroscopy with acetaldehyde as a model solute

Chemometric methods combined with infrared (IR) spectroscopy, using attenuated total reflectance (ATR) sampling, are employed here to characterize the stoichiometry of complexes of solvent molecules in the liquid phase. The spectral information provides insight into the liquid microstructure present in liquid chromatographic mobile phases. This information should make it easier to understand and predict the effects of changes in mobile phase composition on the results of chromatographic separations. In this paper, mobile phases consisting of 0 mol % to 100 mol % acetonitrile in water were studied, with the addition of acetaldehyde as a model solute at concentrations ranging from 3 to 8 mol %. Using three-way multivariate curve resolution by the alternating least squares method (MCR-ALS) it was possible to resolve eight unique spectra: four mobile phase components, and four unique spectra of acetaldehyde solvated in different environments. The directions of the shifts of the important acetaldehyde infrared bands show good correlation with those predicted by gas-phase ab initio calculations of small solvated clusters.     

Lattice Model for Thermodiffusion in Polymer Solutions

When a temperature gradient is applied to a polymer solution, the polymer typically migrates to the colder regions of the fluid as a result of thermal diffusion (Soret effect). However, in recent thermodiffusion experiments on poly(ethylene-oxide) (PEO) in a mixed ethanol/water solvent it is observed that for some solvent compositions the polymer migrates to the cold side, while for other compositions it migrates to the warm side. In order to understand this behavior, a two-chamber lattice model for thermodiffusion in liquid mixtures and dilute polymer solutions has been developed. For mixtures of PEO, ethanol, and water, the compressibility and hydrogen bonding between PEO and water molecules are taken into account and Soret coefficients are calculated for a given temperature, pressure, and solvent composition. The sign of the Soret coefficient of PEO is found to change from negative (polymer enriched in warmer region) to positive (polymer enriched in cooler region) as the water content of the solution is increased, in agreement with experimental data. A close relationship between the solvent quality and the partitioning of the polymer between the two chambers is noted, which may explain why negative Soret coefficients for polymers are so rarely observed. The Soret effect in ethanol/water mixtures is also investigated and a change in sign of the Soret coefficient of water is found at high water concentrations, in qualitative agreement with experimental data. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Study of lithium intercalation into tungsten oxide films prepared by different methods

The interaction of lithium atoms into amorphous tungsten oxide films deposited by thermal evaporation, sputtering and sol-gel synthesis is studied spectroscopically. The mechanism of insertion of lithium into the film depends on the amount and the bonding state of water to the tungsten oxide network. Thermally evaporated tungsten oxide film contains water bonded chemically in the form of a hydrogen tungsten bronze which facilitates the accommodation of a high number of lithium atoms. In the sputtered film, water is physisorbed and the lithiation is incomplete. Tungsten oxide films prepared by sol-gel synthesis have structural water molecules directly involved in the lithiation process. The formation of lithium tungstate independent of the preparation method is demonstrated.     

The phase diagram of the system PBZT/ polyphosphoric acid/water

The phase diagram of the system PBZT/polyphosphoric acid/water has been investigated using differential scanning calorimetry, optical microscopy and ³¹P nuclear magnetic resonance spectroscopy. A peritectic line at higher temperatures and a eutectic line at lower temperatures have been found independent from the polycondensation degree of the polyphosphoric acid (PPA). The phase transitions between the different regions in the phase diagram are strongly dependent on the condensation degree of the solvent. All phase transitions are completely reversible. The formation of crystal solvate phases is connected with the water content of the system and therefore with the polycondensation reaction of the PPA. The solvent molecules are strongly associated with the macromolecules. The nematic phase is formed by interaction of six solvent molecules per monomeric unit of the polymer and proton transfer from the solvent towards the polymer in the nematic phase.     

Measuring diffusion of molecules into individual polymer particles by confocal Raman microscopy

Raman microscopy is a powerful method for providing spatially resolved, chemically selective information about the composition of materials. With confocal collection optics, the method is well suited to the analysis of small particles in contact with liquid solutions. In this work, the transport of an organic solvent component into small polystyrene particles is investigated. An inverted confocal Raman microscope is used to acquire spectra from individual 75-microm polystyrene particles in contact with acetonitrile/water mixtures. Monitoring the Raman scattering from the C[triple bond]N stretching mode of acetonitrile provides a measure of solvent uptake into the polymer material. The small collection volume defined by the confocal optics provides the micrometer spatial resolution needed to track solvent concentration at different locations within the particle with 30-s time resolution. The volume fraction of acetonitrile in water in the surrounding solution was varied in order to determine the concentration dependence of the diffusion kinetics. Modeling the transport of molecules into a particle was addressed by using finite element methods for the evaluation of the coupled space- and time-dependent differential equations that govern the molecular transport. The results indicate that the diffusion coefficient changes with the local solvent concentration in the polymer. At longer times, with the highest acetonitrile concentrations, an evolution of the solvent transport mechanism was observed, from a diffusive rate that depends on local concentration to a linear increase in concentration with time accompanied by measurable swelling of the particle volume.     

聚酰胺复合膜的改性及其选择渗透性

非对称性的反渗透(RO)聚酰胺(PA)复合膜可以通过溶剂处理方法改性成为渗透汽化(PV)分离有机物水溶液的均相膜．实验选用了PA良溶剂(甲酸、乙酸、磷酸、盐酸、苯酚)作为PA膜的改性剂．溶剂改性条件(改性剂类型、浓度和处理时问)对改性膜的吸着性有明显影响．用质量分数8％的乙酸处理1h的PA膜，较之未改性膜，优先吸水性增强，对水的溶胀率SW增大，对异丙醇的溶胀率SIPA减小．乙酸处理的PA膜的SW与SIPA差值在所有溶剂处理的膜中最大，相应地PV分离IPA水溶液时，膜的分离因子和渗透通量也最大，处理过程溶剂分子与PA高分子链的接触和PA膜中微囊内高分子链段向外运行，是PA膜结构改变的主要因素．溶剂处理改变了膜的结构的机理能很好地解释非对称性RO膜的改性．     

Influence of adsorption behaviour of a silane coupling agent on interlaminar fracture in glass fibre fabric-reinforced unsaturated polyester laminates

The relationship between the interphase consisting of physisorbed and chemisorbed silane on glass fibres and the resultant composite Mode I delamination fracture toughness in glass fibre fabric laminate, was studied. The Mode I interlaminar fracture toughness of the laminate specimen was obtained by using a double cantilever beam (DCB) specimen. The delamination resistance of the laminate specimen finished with two silane concentrations and washed in methanol solvent, is discussed on the basis of the interlaminar fracture toughness. In order to determine the amount of physisorbed and chemisorbed silane on the glass fibre, the amount of total carbon was determined using an analysis instrument. The physisorbed silane migrated into the resin matrix and influenced the mechanical properties and interlaminar fracture of the laminate specimen. The amount of unsaturated polyester resin blended with a silane coupling agent was measured using dynamic mechanical spectroscopy, and a DCB specimen for mechanical properties and fracture toughness.     

In situ evaluation of density, viscosity, and thickness of adsorbed soft layers by combined surface acoustic wave and surface plasmon resonance

We show the theoretical and experimental combination of acoustic and optical methods for the in situ quantitative evaluation of the density, the viscosity, and the thickness of soft layers adsorbed on chemically tailored metal surfaces. For the highest sensitivity and an operation in liquids, a Love mode surface acoustic wave (SAW) sensor with a hydrophobized gold-coated sensing area is the acoustic method, while surface plasmon resonance (SPR) on the same gold surface as the optical method is monitored simultaneously in a single setup for the real-time and label-free measurement of the parameters of adsorbed soft layers, which means for layers with a predominant viscous behavior. A general mathematical modeling in equivalent viscoelastic transmission lines is presented to determine the correlation between experimental SAW signal shifts and the waveguide structure including the presence of the adsorbed layer and the supporting liquid from which it segregates. A methodology is presented to identify from SAW and SPR simulations the parameters representatives of the soft layer. During the absorption of a soft layer, thickness or viscosity changes are observed in the experimental ratio of the SAW signal attenuation to the SAW signal phase and are correlated with the theoretical model. As application example, the simulation method is applied to study the thermal behavior of physisorbed PNIPAAm, a polymer whose conformation is sensitive to temperature, under a cycling variation of temperature between 20 and 40 degrees C. Under the assumption of the bulk density and the bulk refractive index of PNIPAAm, thickness and viscosity of the film are obtained from simulations; the viscosity is correlated to the solvent content of the physisorbed layer.     

Solvent assisted inlet ionization: an ultrasensitive new liquid introduction ionization method for mass spectrometry

A new inlet ionization method requiring no voltage or laser, and using water, methanol, or water/organic solvent mixtures, is shown to produce mass spectra similar to those obtained with electrospray ionization (ESI) for small molecules, peptides, and proteins, at least as large as carbonic anhydrase, with sensitivity that surpasses ESI. With the use of wide mass range acquisitions at 100,000 mass resolution on an Orbitrap Exactive, detection limits below parts per trillion are obtained for small molecules such as arginine, ciprofloxacin, and acetaminophen. Low attomoles of bovine insulin consumed produced a multiply charged mass spectrum. Ions are generated, even using pure water as solvent, within the heated inlet tube linking atmospheric pressure with the first vacuum stage of the Orbitrap Exactive. The extremely high sensitivity observed at this early stage of solvent assisted inlet ionization (SAII) development suggests that inlet ionization may surpass nanoelectrospray in sensitivity but without the need for extremely low solvent flows.     

Bonding and tribological properties of perfluorinated lubricantsand hydrogenated amorphous carbon films

Molecular properties of perfluorinated lubricants and amorphous carbon films relevant to the tribological performance of hard disk drives have been measured. The bonding of water and model perfluorinated lubricants to amorphous carbon surfaces has been studied by thermal desorption spectroscopy. Binding energies consistent with a physisorbed state are found for each of these small molecules. Binding energies are found to increase with increasing molecular weight and polarity of the adsorbate as well as increasing surface free energy of the carbon film. Adhesion forces and coefficients of friction have been measured with atomic force microscopy at hydrogenated amorphous carbon surfaces as a function of hydrogen content. An increase in both adhesion and friction forces is observed with increasing hydrogen contents and is attributed to changes in the surface free energy of the carbon films     

A Stability Study of Clindamycin Hydrochloride and Phosphate Salts in Topical Formulations

The stability of clindamycin hydrochloride and clindamycin phosphate was studied in topical liquid formulations prepared with the following solvents: solvent A (70% isopropanol, 10% propylene plycol and 20% water), solvent B (48% isopropanol, polyoxyethelene ethers, acetone, salicylic acid and allantoin), solvent C (40% alcohol, acetone, polysorbate 20, fragrance and water) and “standard” (50% isopropyl alcohol, propylene glycol and water) in glass and plastic containers at 25°, 40°, and 50°C.

It was found that, in general, better stability was obtained in glass containers than in plastic containers. At 25°C both the clindamycin hydrochloride and phosphate formulations in solvent B showed poorer stability than in the other solvents irrespective of the type of container, while formulations in solvent C showed the best stability. In addition, the effect of the pH on the stability of the formulations was determined, and it was clear that at pH values below 4 the stability of all formulations decreased.     

A Stability Study of Clindamycin Hydrochloride and Phosphate Salts in Topical Formulations

Abstract

The stability of clindamycin hydrochloride and clindamycin phosphate was studied in topical liquid formulations prepared with the following solvents: solvent A (70% isopropanol, 10% propylene plycol and 20% water), solvent B (48% isopropanol, polyoxyethelene ethers, acetone, salicylic acid and allantoin), solvent C (40% alcohol, acetone, polysorbate 20, fragrance and water) and “standard” (50% isopropyl alcohol, propylene glycol and water) in glass and plastic containers at 25°, 40°, and 50°C.

It was found that, in general, better stability was obtained in glass containers than in plastic containers. At 25°C both the clindamycin hydrochloride and phosphate formulations in solvent B showed poorer stability than in the other solvents irrespective of the type of container, while formulations in solvent C showed the best stability. In addition, the effect of the pH on the stability of the formulations was determined, and it was clear that at pH values below 4 the stability of all formulations decreased.     

Application of dispersion–solidification liquid–liquid microextraction for the determination of triazole fungicides in environmental water samples by high-performance liquid chromatography

A simple, rapid and environmentally friendly method has been developed for the determination of four triazole fungicides (myclobutanil, tebuconazole, triadimenol, hexaconazole) in water samples by dispersion–solidification liquid–liquid microextraction coupled with high performance liquid chromatography-diode array detection. Several variables that affect the extraction efficiencies, including the type and volume of the extraction solvent and dispersive solvent, extraction time, effect of pH and salt addition, were investigated and optimized. Under the optimum conditions, the proposed method is sensitive and shows a good linearity within a range of 0.5–200 ng mL⁻¹, with the correlation coefficients (r) varying from 0.9992 to 0.9998. High enrichment factors were achieved ranging from 190 to 450. The recoveries of the target analytes from water samples at spiking levels of 1.0, 5.0 and 50.0 ng mL⁻¹ were between 84.8% and 110.2%. The limits of detection (LODs) for the analytes were ranged in 0.06–0.1 ng mL⁻¹, and the relative standard deviations (RSD) varied from 3.9% to 5.7%. The proposed method has been successfully applied for the determination of the triazole fungicides in real water samples.     

油墨溶剂在食品软包装中的残留及迁移规律

目的研究油墨溶剂在食品软包装材料中的残留及迁移行为,为食品包装生产企业提供安全风险控制方面的参考。方法采用顶空气相色谱-质谱联用(HS-GC-MS)技术,对印刷油墨的挥发性溶剂在食品软包装中的残留进行定性定量分析,以检出率较高的苯类溶剂甲苯、酯类溶剂乙酸丁酯和酮类溶剂丁酮为迁移研究对象,分别以PE,PP,PET/CPP,PET/PE,OPP/CPP,PET/PA/CPP为包装材料,研究油墨溶剂在水性食品模拟液(蒸馏水)、酸性食品模拟液(体积分数为3%的乙酸)、醇性食品模拟液(体积分数为10%的乙醇)和脂肪性模拟液(正己烷)中的迁移残留行为。结果研究表明,印刷后的食品软包装材料中大部分都有苯类、酯类和酮类等有机挥发物的残留,残留溶剂在食品模拟液中迁移量的大小依次为正己烷乙醇(体积分数为10%)乙酸(体积分数为3%)蒸馏水,而且对于不同的包装材料迁移量的大小也不同。结论油墨溶剂在食品软包装材料上的残留和迁移行为,主要与环境温度、食品性质以及包装材料的性能有关。     

Evaluation of some water-miscible organic solvents for spray-drying enzymes and carbohydrates

The spray-drying behaviour of 16 water-miscible organic solvents on a bench-scale machine (Büchi B290 with inert loop) was determined under mild-to-moderate process conditions, namely inlet gas temperature of 130?°C and liquid feed flow rate of ≤3?mL/min. The solvents with boiling points below the inlet gas temperature could be fully dried (Group 1 solvents). The two exceptions were DMSO and DMF which despite their higher boiling points could be fully dried. The remaining solvents with boiling points above the inlet gas temperature were not fully dried during passage through the spray-dryer (Group 2 solvents). Trypsin and lysozyme when spray-dried from Group 1 solvent binary mixtures with water showed similar inactivation and residual water content, independent of solvent. The level of residual solvent was, however, strongly dependent on solvent. Trehalose (20%) and mannitol (10%) could be spray-dried from DMSO/water binary mixtures, but the amorphous disaccharide required higher inlet gas temperature. Trehalose/trypsin and mannitol/trypsin formulations showed differing degrees of protection against enzyme inactivation when spray-dried from Group 1 solvent binary mixtures with water. In all solvents the mannitol protected as well, if not better, than the trehalose. This study identifies some suitable organic solvents for spray-drying protein formulations, but also shows the difficulties of remaining organic solvent under the moderate inlet gas temperature used.     

Hydrophobic Hydrogels with Fruit‐Like Structure and Functions

Normally, a polymer network swells in a good solvent to form a gel but the gel shrinks in a poor solvent. Here, an abnormal phenomenon is reported: some hydrophobic gels significantly swell in water, reaching water content as high as 99.6 wt%. Such abnormal swelling behaviors in the nonsolvent water are observed universally for various hydrophobic organogels containing omniphilic organic solvents that have a higher affinity to water than to the hydrophobic polymers. The formation of a semipermeable skin layer due to rapid phase separation, and the asymmetric diffusion of water molecules into the gel driven by the high osmotic pressure of the organic solvent–water mixing, are found to be the reasons. As a result, the hydrophobic hydrogels have a fruit‐like structure, consisting of hydrophobic skin and water‐trapped micropores, to display various unique properties, such as significantly enhanced strength, surface hydrophobicity, and antidrying, despite their extremely high water content. Furthermore, the hydrophobic hydrogels exhibit selective water absorption from concentrated saline solutions and rapid water release at a small pressure like squeezing juices from fruits. These novel functions of hydrophobic hydrogels will find promising applications, e.g., as materials that can automatically take the fresh water from seawater.     

Inlet ionization: a new highly sensitive approach for liquid chromatography/mass spectrometry of small and large molecules

Inlet ionization is a new approach for ionizing both small and large molecules in solids or liquid solvents with high sensitivity. The utility of solvent based inlet ionization mass spectrometry (MS) as a method for analysis of volatile and nonvolatile compounds eluting from a liquid chromatography (LC) column is demonstrated. This new LC/MS approach uses reverse phase solvent systems common to electrospray ionization MS. The first LC/MS analyses using this novel approach produced sharp chromatographic peaks and good quality full mass range mass spectra for over 25 peptides from injection of only 1 pmol of a tryptic digest of bovine serum albumin using an eluent flow rate of 55 μL min(-1). Similarly, full acquisition LC/MS/MS of the MH(+) ion of the drug clozapine, using the same solvent flow rate, produced a signal-to-noise ratio of 54 for the major fragment ion with injection of only 1 μL of a 2 ppb solution. LC/MS results were acquired on two different manufacturer's mass spectrometers using a Waters Corporation NanoAcquity liquid chromatograph.