Influence of relative humidity on the properties of examined materials by means of inverse gas chromatography

Inverse gas chromatography (IGC) at infinite dilution was applied to evaluate the surface properties of sorbents and the effect of different carrier gas humidity. They were stored in different environmental humidity – 29%, 40%, and 80%. The dispersive components of the surface free energy of the zeolites and perlite were determined by Schulz-Lavielle method, whereas their tendency to undergo specific interactions was estimated basing on the electron donor–acceptor approach presented by Flour and Papirer. Surface parameters were used to monitor the changes of the properties caused by the humidity of the storage environment as well as of RH of carrier gas. The increase of humidity of storage environment caused a decrease of sorbents surface activity and increase the ability to specific interaction.     

Influence of relative humidity on electrical properties of alpha-Al2O3 powders: resistivity and electrochemical impedance spectroscopy

The influence of humidity on the electrical properties of alpha-Al2O3 powders has been investigated using adsorption isotherms, DC resistivity, and electrochemical impedance spectroscopy. Samples of two alpha-Al2O3 particle sizes were examined, both individually and mixed together. The results show that the grain-bed resistivity decreases with humidity, whereas the grain capacitance is almost constant. The resistivity difference between the two particle sizes is of several orders of magnitude, while the capacitance values are not very different. These results are interpreted in terms of the layer-by-layer growth of water adsorbed on the grain surfaces. The first, more tightly bound adsorbed layer does not provoke the same effects as those layers adsorbed at higher relative humidity.     

Effect of relative humidity on mechanical properties of a woven thermoplastic composite for automotive application

The purpose of this work is to characterise the influence of moisture content in a woven glass fibre reinforced polyamide 6,6 composite. Two different stacking sequences are studied: [(0/90)₃] and [(±45)₃] as well as the neat PA6,6 matrix. Samples have been conditioned through three ways: either water immersed, left at ambient temperature and humidity or dried in 35 °C oven. A one dimensional Fick's law has been used to model the water uptake in immersed samples. The glass transition temperature is highly affected by the presence of water and has been measured using modulated DSC technique. Finally, the effects of water on these composite materials have been investigated through tensile tests instrumented with acoustic emission monitoring (AE). Mechanical properties are highly affected by the presence of water in the composite. This result is even more visible on [(±45)₃] sample because of the preferential loading of the matrix.     

Influence of UV irradiation and subsequent chemical grafting on the surface properties of cellulose

Cellulose - This work is devoted to the study of surface properties of cellulose before and after a surface modification. Surface modification of polymeric materials was carried out in two steps:...     

Influence of the molecular weight of polystyrene on its thermodynamic properties

The thermodynamic properties of a series of polystyrene samples with different molecular weights (M _w was varied from 2.5·10³ to 6.57·10⁴) were studied by precision adiabatic vacuum, high-accuracy dynamic, and combustion calorimetry: temperature dependences of the heat capacity in a wide temperature range, thermodynamic characteristics of glass transition and glassy state under standard pressure, and energy of combustion. The thermodynamic functions C ^○ _p (T), H ^○(T) - H ^○(0), S ^○(T) - S ^○(0), and G ^○(T) - H ^○(0) of polystyrene with different molecular weights, enthalpies of combustion Δ_c H ^○, thermodynamic parameters of formation from simple substances Δ_f H ^○, Δ_f S ^○, and Δ_f G ^○ at T = 298.15 K, and parameters of their synthesis from monomers were calculated from the experimental data. The temperature dependences of the heat capacity for a region of 0–380 K, glass transition temperatures, and thermodynamic characteristics of formation and synthesis of polystyrene depending on its molecular weight were examined.     

Influence of relative humidity in sensing halogenated hydrocarbons with Reflectometric Interference Spectroscopy (RIfS)

For stand-alone sensor systems apart from defined laboratory circumstances sensors are required, which show a high stability against perturbing environmental influences like the relative humidity (r.h.). We present a portable sensor system, which is capable to quantify tetrachloroethene (TCE) in humid air. The system works highly reproducible and shows only negligible cross-sensitivity towards relative humidity. This allows a single calibration valid from 0 to 80% r.h.. Therefore, referencing with an extra sensor for humidity is not necessary. Binary mixtures of TCE and freone R113 were quantified for 0 and 40% r.h. with a root mean square error of prediction of approximately 3% with respect to the maximum concentration of TCE and R113. The sensitive elements used in the experiments consisted of thin polymer films on glass substrates. The measurements were performed with the optical measurement technique RIfS (Reflectometric Interference Spectroscopy).     

Influence of relative humidity in sensing halogenated hydrocarbons with Reflectometric Interference Spectroscopy (RIfS)

For stand-alone sensor systems apart from defined laboratory circumstances sensors are required, which show a high stability against perturbing environmental influences like the relative humidity (r.h.). We present a portable sensor system, which is capable to quantify tetrachloroethene (TCE) in humid air. The system works highly reproducible and shows only negligible cross-sensitivity towards relative humidity. This allows a single calibration valid from 0 to 80% r.h.. Therefore, referencing with an extra sensor for humidity is not necessary. Binary mixtures of TCE and freone R113 were quantified for 0 and 40% r.h. with a root mean square error of prediction of approximately 3% with respect to the maximum concentration of TCE and R113. The sensitive elements used in the experiments consisted of thin polymer films on glass substrates. The measurements were performed with the optical measurement technique RIfS (Reflectometric Interference Spectroscopy). Received: 29 May 1998 / Revised: 4 August 1998 / Accepted: 8 August 1998     

Influence of temperature and humidity on the mechanical properties of Nafion® 117 polymer electrolyte membrane

The dynamic mechanical properties of Nafion® 117 have been measured in‐plane parallel and perpendicular to the lamination direction in a specially designed humidity cell, which allows measurement of the stiffness and mechanic loss under fuel cell relevant temperature and humidity conditions (50–100% relative humidity, 30–120 °C). The results obtained at different temperature–humidity conditions are compared with the mechanical behavior of the dry as well as the membrane saturated with liquid water. Different regimes of change in mechanical properties were found, although in general water acts as a plasticizer in Nafion®. At elevated temperatures it stiffens the membrane by stabilizing the network of hydrophilic clusters. An intermediate increase of mechanical strength at very low humidity levels is attributed to an enforcement by formation of hydrates and hydrogen bridge bonds between vicinal sulfonic acid groups. This increase is significant for the protonated state of the membrane and disappears after ion exchange. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 786–795, 2005     

Engineering the interface energetics of solar cells by grafting molecular properties onto semiconductors

The electronic properties of semiconductor surfaces can be controlled by binding tailor-made ligands to them. Here we demonstrate that deposition of a conducting phase on the treated surface enables control of the performance of the resulting device. We describe the characteristics of the free surface of single crystals and of polycrystalline thin films of semiconductors that serve as absorbers in thin film polycrystalline, heterojunction solar cells, and report first data for actual cell structures obtained by chemical bath deposition of CdS as the window semiconductor. The trend of the characteristics observed by systematically varying the ligands suggests changes in work function rather than in band bending at the free surface, and implies that changes in band line-up, which appear to cause changes in band bending, rather than direct, ligand-induced band bending changes, dominate.     

Influence of relative humidity and loading frequency on the PA6.6 thermomechanical cyclic behavior: Part II. Energy aspects

In this study, we investigated the influence of relative humidity (RH) and loading rate on the energy response of PA6.6 matrix specimens. The latter were subjected to oligocyclic tensile-tensile tests at 3 different RH and 2 loading rates. Infrared thermography was used to obtain a direct estimate of heat sources using the heat diffusion equation. Using the mechanical and thermal responses discussed in the first part of this work, complete energy rate balances were drawn up. In particular, the time courses of deformation, and dissipated and stored energy rates are discussed. The strong influence of the loading frequency and RH on the energy storage mechanisms is also highlighted.     

Three properties of relative shape envelopes of molecular electron density contours

Summary The relative shapes of molecular electron density contour surfaces (MIDCO's), and various molecular shape constraints in solvent-solute interactions, in external electromagnetic fields and within enzyme cavities, are representable by electron densityT-hulls, introduced earlier. Three general properties ofT-hulls are proven, serving as the justification of a recently proposed computational scheme of molecular similarity measures.     

Effects of the relative humidity and water droplet on adhesion of a bio-inspired nano-film

Inspired by geckos' adhesion, the effect of water membrane forming due to the environmental humidity, on the adhesion between a bio-inspired nano-film and a substrate is investigated first. The disjoining pressure is considered, which results in an enhancing adhesion between the nano-film and substrate. When the thickness of water membrane increases, water droplets will form and a repulsive capillary force between the nano-film and substrate is produced. The total adhesion force decreases with an increasing volume of water droplets. The two opposite results in the two different models are consistent well with two seemingly inconsistent experimental observations by Huber et al. (2005) [4] and Sun et al. (2005) [5], respectively, and may be significant for the development of artificial biomimetic attachment systems.     

Theoretical investigation of substrate effect on deliquescence relative humidity of NaCl particles

A theoretical investigation is conducted for the first time to explore the deliquescence of particles deposited on a substrate. The formulation incorporates the Kelvin effect with the assumption that the dry and wet particles are both spherical caps in shape. Unlike the deposited particles larger than 500 nm, the deliquescence relative humidity (DRH) of smaller particles can substantially depend on the particle size, the contact angles, and the surface tension between the particle and the atmosphere. At certain contact angles, small particles depositing on a substrate could deliquesce at a much lower RH, posing a potential corrosion problem for metallic substrates.     

Effect of relative humidity on OH uptake by surfaces of atmospheric importance

An experimental study of the dependence of the OH uptake coefficient gamma OH over a relative humidity of 0-48% was carried out at 100 Torr and room temperature, using a differential bead-filled flow tube coupled to a high-pressure chemical ionization mass spectrometer. Various organic (paraffin wax, pyrene, glutaric acid, and soot) and inorganic (NaCl, KCl, MgCl2, CaCl2, Na2SO4, and sea salt) surfaces served as proxies for tropospheric aerosols. A virtual cylindrical flow tube approximation and a surface coating dilution technique were successfully employed in the study, which included measurements of high radical uptake with an initial probability of near unity. For inorganic salts, the effect of water vapor, enhancement or inhibition of gamma OH, was found to be dependent on the blocking of anions and changes in surface pH. Although OH uptake by NaCl, the major component of sea-salt aerosols, is weakly dependent on water vapor, it is enhanced by a factor of approximately 2 for MgCl2 and determines the net relative humidity dependence of the radical uptake on sea salt, which is enhanced by a factor of approximately 4. For the organic surfaces studied, the enhancement effect of a factor 4 was also observed only for a hydrophilic organic surface, namely, glutaric acid. Results of the uptake studies suggest that the effect of relative humidity is important and should be accounted for in atmospheric modeling of tropospheric aerosol chemistry.     

Influence of prepolymers molecular weight on the viscoelastic properties of aqueous HEUR solutions

A series of hydrophobically modified ethoxylated urethanes (HEURs) were synthesized by a step growth polymerization of polyethylene glycol with dicyclohexylmethane diisocyanate (H12MDI). The thickeners were produced with different sizes of the hydrophilic section by changing the molar ratios of reactants. The size of the hydrophobic ends was constant for all prepared samples. The changes in hydrophilic lengths were correlated with the rheological properties of HEURs aqueous solutions. The intrinsic viscosity measurements showed that associates are present even at very low concentration. The response of these HEUR systems in aqueous solution to both steady shear and oscillatory shear was determined as a function of hydrophilic chain length and polymer concentration. Dramatic increases in viscosity are observed with decreasing molecular weight of the prepolymer (with a decrease of the hydrophilic components' size and at the same time an increased ratio between hydrophobic and hydrophilic sections of HEURs). Also, a steep increase in viscosity with increasing thickener concentration is obtained. The rheological properties of aqueous solutions of HEUR polymers can be described using a simple Maxwell model with a single relaxation. The dynamic measurements verified the results obtained from the steady state measurements about the hydrophilic section size and its effect on the association phenomenon.     

Influence of isotacticity and molecular weight on the properties of metallocenic isotactic polypropylene

The relationships between structure and properties have been established for isotactic polypropylene, iPP, homopolymers synthesized by metallocene catalyst systems. These iPPs exhibit different isotacticity degrees and molecular weights, and several thermal treatments during their processing have been applied. The most important factor affecting the structure and properties of these polymers is the isotacticity content. The thermal treatment, i.e., the rate of cooling from the melt, is also important and a clear molecular weight effect has been also found for the sample with lowest M_w. These factors affect the thermal properties, the degree of crystallinity and, therefore, the structural parameters and the viscoelastic behavior. A slow cooling from melt favors the formation of the γ phase instead of the α modification. The storage modulus, Young modulus and microhardness values increase as crystallinity does, independently of the origin of this increase: higher isotacticity or application of a slow crystallization from the melt.     

Influence of molecular weight on some properties of liquid crystalline polyurethanes

This investigation extends our previous investigations of liquid crystalline polyurethanes prepared from 4,4′-bis(2-hydroxyethoxy)biphenyl (BHBP), 2,4-tolylene diisocyanate, and poly(oxytetramethylene)diols as the flexible spacers. The influence of molecular weight of investigated polyurethanes on their properties is discussed for two series with the same content of BHBP and different lengths of flexible spacers. The polyurethanes were investigated by means of DSC, polarizing microscopy, x-ray diffractometry, and IR spectroscopy. The molecular weight distribution was determined by GPC. Morphology was studied by the SALS method. The molecular weight of polyurethanes and the length of flexible spacer influence the phase transition temperature and the range of mesophase occurrence. © 1993 John Wiley & Sons, Inc.     

Influence of acidification on the optical properties and molecular composition of dissolved organic matter

Acidification is a common method for preserving dissolved organic matter (DOM) in natural water samples until sophisticated laboratory analyses can be performed. However, little is known about the effects of this practice on the composition and optical properties of DOM. In this study, the effects of acidification on DOM in porewater samples collected from the RL IV bog system of the Glacial Lake Agassiz Peatlands in northern Minnesota were characterized. Molecular composition was determined by ultrahigh resolution mass spectrometry and optical properties by UV absorption and three-dimensional fluorescence spectroscopy. Excitation–emission matrix fluorescence spectroscopy results indicate that the fluorescence properties of the peatland porewater DOM were sensitive to pH and that the observed changes were fluorophore dependent. Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry revealed the appearance of newly formed, oxygen-rich compounds upon acidification. The extent to which these oxygen-rich compounds were formed was also dependent on the composition of the DOM.