A novel resistive‐type humidity sensor based on poly(p‐diethynylbenzene)

Poly(p‐diethynylbenzene) (PDEB) synthesized with nickel catalyst Ni(CC ○ CCH)₂(PPh₃)₂ (Ni C) in dioxane–toluene mixed‐solvent system at 25°C shows a rich trans structure with pendant‐group ( ○ CCH) content of about 35% having higher molecular weight and good solubility. A novel resistive‐type humidity sensor based on PDEB is presented. Its humi‐sensing characteristics are described and discussed. The impedance of the sensor changed from ∼ 10³–10⁷ Ω in almost the whole humidity range [∼ 15–92% relative humidity (RH)], which is low compared with sensors based on other humi‐sensitive conjugate polymers, and hysteresis of no more than 3% RH was observed. The sensor prepared by Langmuir–Blodgett (LB) deposition method shows the best humidity response. An explanation of humi‐sensing behavior of PDEB is attempted by taking into account the interaction between hydrogen protons and super π‐conjugate orbits in PDEB. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2010–2015, 1999     

The mechano-sorptive behavior of flexible water-blown polyurethane foams

Samples of flexible water-blown slabstock polyurethane foams were compressed under constant load to study the effects of cycling moisture content on creep behavior and compare this behavior with the creep response where either a constant high or low moisture environment existed at the same temperature. Three sets of foams were tested: (1) 4 pph water content slabstock foam; (2) 5 pph water content slabstock foam; and (3) 2 pph water content molded foam. As the moisture conditions were cycled from low to high humidity while maintaining constant temperature in an environmental chamber, the compressive strain increased in subsequent steps with larger increases observed during the desorption portion of the humidity cycling. All three sets of foams showed similar behavior at a given temperature. At a temperature of 40°C, the strain levels under cyclic moisture conditions surpassed those levels observed at the highest constant relative humidity. During the first absorption step, the creep level increased. During any subsequent absorption step, the creep level either increased very little or none at all. Finally, during any desorption step, the creep level increased. This overall phenomenon of enhanced creep under cyclic moisture levels is attributed to water interacting with the hydrogen bonded structure within the foam. These hydrophillic interactions, principally promoted within the hard segment regions due to high hydrogen bonding, are disrupted causing slippage and increased in strain. As the foam is rapidly dired, regions of free volume are induced by the loss of water thus causing further increases in strain Prior to the reestablishment of well ordered hydrogen bonding. Further support to this proposition was given by the results obtained at a temperature of 90° C where it is well known that hydrogen bonds are much more mobile. Here, the strain levels under cyclic moisture conditions were nearly the same as those under constant high relative humidity. Weakening of the hydrogen bonds by means such as increased temperature resulted in similar strain levels to those under cyclic moisture levels. © 1993 John Wiley & Sons, Inc.     

Sorption and transport of water vapor in nylon 6,6 film

The sorption and transport of water in nylon 6,6 films as functions of the relative humidity (RH) and temperature were studied. Moisture‐sorption isotherms determined gravimetrically at 25, 35, and 45°C were described accurately by the GAB equation. Water‐vapor transmission rates were enhanced above ≈ 60–70% RH, primarily due to the transition of the polymer from glassy to rubbery states. The glass transition temperatures (T_g's) of nylon 6,6 were measured at various moisture contents using differential scanning calorimetry. The results showed that the sorbed water acted as an effective plasticizer in depressing the T_g of the polyamide. Fourier transform infrared spectroscopy (FTIR) was utilized to characterize the interaction of water and the nylon. Evidence from FTIR suggested that the interaction of water with nylon 6,6 took place at the amide groups. Based on the frequency shift of the peak maxima, moisture sorption appeared to reduce the average hydrogen‐bond strength of the N H groups. However, an increase was seen for the CO groups. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 197–206, 1999     

Synthesis and humidity sensitivity of conducting polyaniline in SBA‐15

Conducting polyaniline (PANI) was synthesized in mesoporous silica SBA‐15. The investigations of XRD, N₂ adsorption–desorption, and IR spectra confirm the existence of polyaniline in the channels of SBA‐15 hosts. The impedance of PANI/SBA‐15 composites was studied at different relative humidity (RH) levels, ranging from 11 to 95% RH. The loadings of PANI as well as the concentration of HCl solution have substantial influence on the impedance values. The variation in impedance value of all PANI/SBA‐15 composites is more obvious than that of bulk PANI samples at the same RH. All these results imply that PANI/SBA‐15 composites may have better humidity‐sensitive properties than those of bulk PANI samples. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1597–1601, 2004     

Synthesis,characterization, and preliminary antimicrobial evaluation of bisphenol‐A formaldehyde resin coordinated with transition metal complexes of ethylenediamine

Coordination polymers containing bisphenol‐A, formaldehyde, and transition metal complexes of ethylenediamine [M(en)₂] were synthesized by the reaction of bisphenol‐A, formaldehyde, and M(en)₂ complex in alkaline medium, using M for Fe⁺³, Co⁺², Ni⁺², Cu⁺², and Zn⁺². The materials were characterized by elemental analysis, FTIR, UV–Vis, ¹H‐NMR spectra, TGA, and magnetic susceptibility measurement. The geometry of the central metal ions was determined by electronic spectral studies and magnetic moment measurement. The M N and C N bonds were confirmed by the IR spectra of the polychelates. The ¹H‐NMR spectra of the chelating resins confirmed polycondensation with well‐defined peaks for bridging methylene functions. Complexation studies with transition metal ions revealed effective coordination of the bisphenol‐A formaldehyde resin. The antimicrobial activities of these chelated resins were screened against E. coli, S. dysantrea (bacteria), and C. albicans, A. niger (fungi) by using agar well diffusion method. All the polymeric chelates show promising antimicrobial activities. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Drying characteristics and modeling of yam slices under different relative humidity conditions

The drying characteristics of yam slices under different constant relative humidity (RH) and step-down RH levels were studied. A mass transfer model was developed based on Bi-Di correlations containing a drying coefficient and a lag factor to describe the drying process. It was validated using experimental data. Results showed that the drying air with constant RH levels of 20, 30, and 40%, temperature of 60°C, and air velocity of 1.5 m/s had an insignificant effect on drying time. This phenomenon was likely attributed to the fact that higher RH led to a rapid increase in sample’s temperature. The higher sample temperature could provide an additional driving force to water diffusion and thereby promote the moisture movement, which could minimize the negative effect of lower the drying rate in the initial drying stage. Applying air with 40% RH for 15 min in the initial stage achieved the desired color and reduced the drying time by 25% compared to the drying time under continuous dehumidification from an initial RH of 40%. Using the developed Bi-Di correlation, the estimated Biot number, effective moisture diffusivity, and mass transfer coefficient ranged from 0.1024 to 0.1182, 1.1133 × 10^?10 to 8.8144 × 10^?9 m²/s, and 1.8992 × 10^?9 to 1.7364 × 10^?7 m/s, respectively. A rather high correlation coefficient of determination (R² between 0.9871 and 0.9971) was determined between the experimental and predicted moisture contents. The present findings contribute to a better understanding of the effect of relative humidity on drying characteristics. The developed Bi-Di correlation provided a new method to determine the effective diffusivity of moisture in drying.     

Experimental Investigation of Air Relative Humidity (RH) Cycling Tests on MEA/Cell Aging in PEMFC Part I: Study of High RH Cycling Test With air RH at 62%/100%

The effect of high air relative humidity (RH) cycling (RH_C 62%/100%) on the degradation mechanisms of a single (5 × 5 cm²) proton exchange membrane fuel cells was investigated. The cell performance was compared to a cell operated at constant humidification (RH_C = 62%). Runs were conducted over approximately 1,500 h at 0.3 A cm^–2. The overall loss in cell performance for the high RH cycling test was 12 μV h^–1 whereas it was at 3 μV h^–1 under constant humidification. Impedance spectroscopy reveals that the ohmic and charge transfer resistances were little modified in both runs. H₂ crossover measurement indicated that both high RH cycling and constant RH test did not promote serious effect on gas permeability. The electroactive surface loss for anode and cathode during high air RH cycling was more significant than at constant RH operation. The water uptake determined by ¹H nuclear magnetic resonance within the membrane electrode assembly (MEA) after high RH cycling was reduced by 12% in comparison with a fresh MEA. Transmission electron microscopy showed bubbles and pinholes formation in the membrane, catalyst particles agglomeration (also observed by X‐ray diffraction), catalyst particles migration in the membrane and thickness reduction of the catalytic layers. Scanning electron microscopy was conducted to observe the changes in morphology of gas diffusion layers after the runs.     

Humidity-switch chromism of aniline-pentamer in Nafion

Aniline-pentamer (AP) in Nafion triggered with humidity content displays an interesting chromism from blue to pink, which is much wider of color shift than general polyaniline. Thermogravimetric analysis confirms the reversal color change related to the moisture content in the sample. IR absorption spectra make known AP having high degree of protonation at lower water content. UV-Vis absorption expose the chromism process having something more than just protonation. The change of electronic energy levels and PL spectra reveal that there must be a complex interaction in NaAP. Raman scattering mapping confirms that drying causes the -SO₃ ^? hydrophilic channels transforming to isolated domains dispersed in matrix, which induces heavy protonation and complexation of AP with -SO₃ ^?groups. We can infer that the interesting humidity-switch chromism is due to the reversible protonation/deprotonation as well as complexation of AP with -SO₃ ^? groups through the reversible change of Nafion’s morphology.     

Predicting Creep Behavior of Wood Adhesives by Torsional Braid Analysis

Rheological changes in four cured wood adhesives exposed to temperature and humidity conditions were determined using torsional braid analysis. The adhesives ranged from thermosetting to thermoplastic types. Creep extension in shear also was measured for wood laminates bonded with these adhesives and exposed to conditions of 27°C/90% RH and 60°C/60% RH. A positive trend was found between creep extension and both the maximum rigidity change and the damping loss occurring during humidity and temperature exposure. These findings suggested TBA can be a useful method for predicting wood adhesive creep and failure behavior in the presence of heat and moisture.     

Preparation and properties of a novel green solid polymer electrolyte for all-solid-state lithium battery

Solid polymer electrolyte (SPE)-based lithium batteries have easy processing and safety for energy vehicles and storage. However, the preparation process of SPEs mostly used a lot of organic solvents, which will threaten human living space and body health. Herein, a novel green solid polymer electrolyte (ionic liquid type waterborne polyurethane, IWPUS) without no organic solvents was prepared from hybrids of ionic liquid-based waterborne polyurethane (IWPU) and LiClO₄. The structure and properties of IWPUS were investigated by IR, SEM, XRD, TGA, ion conductivity test. The results showed that Li⁺ of LiClO₄ could coordinate with  CO and  C O C in the polyurethane matrix. LiClO₄ had been well dispersed in IWPU. The conductivity of IWPUS increased with the increase of LiClO₄ content. The higher conductivity of IWPUS with 20% LiClO₄ at 80°C was 1.8 × 10⁻⁴ s•cm⁻¹. IWPUS based on ionic liquid-based waterborne polyurethane would be promised to become an environmentally friendly candidate for all solid-state lithium ion batteries.     

Modified atmosphere packaging bags of peanuts with effect of inhibition of aflatoxin growth

In this article, packaging bags composited with selective barrier film and moisture absorbent nonwoven fabrics were prepared to design a kind of functional bags, which can inhibit the growth of aflatoxin of peanuts. The influences of the super‐absorbent fiber (SAF) and jute fiber on the internal relative humidity (RH) were investigated. It is found that jute nonwoven/selective barrier film composite bag can prevent the growth of aflatoxin B₁ of peanuts under the environment studied in this article because peanuts with higher moisture content can reduce O₂ content inside the bag by the aerobic respiration, achieving the modified atmosphere packaging (MAP) effect. In addition, a low RH micro‐environment can be achieved by using SAF as moisture absorbent. It is promising to design a packaging bag with the effect of inhibition of the growth of aflatoxin of peanuts, by selecting proper moisture absorbent and selective barrier film of the composite bag. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40190.     

Moisture sensor device of plasma-films doped with methylbromide

Summary Films plasma-polymerized from the tetramethylsilane/ammonia gas mixture were sensitive in electrical resistance to moisture. A linear relationship between the logarithm of the electrical resistance and the relative humidity was observed. This susceptibility in the electrical resistance to moisture was improved by doping of methylbromide. This improvements by the doping treatment may be as results of quaternization of amino groups and of hydrolysis of methylbromide. The improved device could detect relative humidity from 20 to 90 % where the electrical resistance varied from 10⁷ to 10⁴ . The response time was less than twenty-five seconds, and the hysteresis in cyclic changing of the relative humidity was negligible.     

Study on superabsorbent composite XXV. Synthesis,characterization, and swelling behaviors of poly(acrylic acid‐co‐N‐acryloylmorpholine)/attapulgite superabsorbent composites

In this work, a novel poly(acrylic acid‐co‐N‐acryloylmorpholine)/attapulgite superabsorbent composite was prepared by graft copolymerization among acrylic acid, N‐acryloylmorpholine and attapulgite in aqueous solution, using N,N′‐methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator. The result from FTIR spectra showed that  OH of attapulgite participated in graft copolymerization with acrylic acid and N‐acryloylmorpholine. Proper monomer ratio and atapulgite content could form a loose surface, and improve reswelling ability and initial swelling rate. The buffer action of the  COOH and  COO⁻ groups in the superabsorbent composite keeps the water absorbency a rough constant in the pH range of 4.4–9.6. Both polarity and structure of an organic solvent are responsible for the phase transition point of the superabsorbent composite. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Linking micro‐scale predictions of capillary forces to macro‐scale fluidization experiments in humid environments

The effects of increasing relative humidity (RH) on fluidization/defluidization are investigated experimentally and understood via particle‐level predictions for the resulting capillary force. Experimentally, defluidization is found to be more sensitive to small changes in RH than fluidization. This sensitivity is captured by a new defluidization velocity U_df, which characterizes the curvature of the defluidization plot (pressure drop vs. velocity) observed between the fully‐fluidized (constant pressure drop) and packed‐bed (linear pressure drop dependence on velocity) states; this curvature is indicative of a partially‐fluidized state arising from humidity induced cohesion. Plots of U_df vs. RH reveal two key behaviors, namely U_df gradually increases with a relatively constant slope, followed by an abrupt increase at RH ～55%. Furthermore, the bed transitions from Group A to Group C behavior between RH of approximately 60–65%. From a physical standpoint, these macro‐scale trends are explained via a theory for capillary forces that, for the first time, incorporates measured values of particle surface roughness. Specifically, a model for the cohesive energy of rough surfaces in humid environments shows the same qualitative behavior as U_df vs. RH for RH <55%, unlike predictions of the cohesive force. Furthermore, the abrupt transition at RH ～60–65% is explained via the previously observed onset of liquid‐like water adsorption, rather than crystal/ice‐like adsorption, onto glass surfaces. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3585–3597, 2016     

Effect of CeO2 on the Glass Structure of Sodium Germanate Glasses

Germanate glasses have potential applications as optical fibers. Materials doped with rare earth ions are good candidates for optical, lasing, and magnetic applications. Based on the ternary system, CeO₂–Na₂O–GeO₂ a series of six glasses were fabricated using powder fusion, and varying the Na₂O content from 0 to 45 mol%, and a CeO₂ content constant at 3 mol%. The glasses were analyzed by FT‐IR, Raman and X‐ray photoelectron (XPS) spectroscopies to obtain information about the glass structure, cerium oxidation's state and how it is introduced in the glass network. FT‐IR and Raman spectra revealed the presence of GeO₆ and GeO₄ groups as well as Q² and Q³ units in the glasses with alkali low content. XPS spectra analysis revealed that the cerium ions were reduced from Ce⁴⁺ to Ce³⁺. The nonbonding to total oxygen ratio was estimated from the curve fitting of the O 1s core level spectra. Density and elastic parameters showed a nonlineal tendency in the change of the physical properties as a function of Na₂O content. Finally, photoluminescence spectroscopy confirmed the presence of Ce³⁺ ions. The characteristic 4f → 5d electronic transitions at 360 nm were detected, when a 280 nm excitation line of pulsed laser was used as excitation source.     

Structurally modified poly(vinyl alcohol) ionic composites as efficient humidity indicators

Synthesis of structurally modified poly(vinyl alcohol) (PVA) ionic composites is presented. Low‐molecular‐weight PVA (M_n = 18,000 g mol⁻¹) is prepared and blended together with either copper or borate ions under ambient conditions to yield PVA–Cu and PVA–B ionic composites, respectively. The borate ions coalesce together with different polymeric chains of PVA, forming a 3D network structure, which is identified by the weakening of  OH absorption in the infrared spectrum. On the other hand, copper ions yield a weakly crosslinked polyelectrolyte by forming a coordinated complex with the hydroxyl groups of PVA, which leads to an increase in the λ_max value in the ultraviolet–visible spectrum. The surface morphology of these PVA‐based ionic composites is studied via atomic force microscopy. Furthermore, the quantitative estimation of copper in PVA–Cu composites is performed by atomic absorption spectroscopy. Among these PVA ionic composites, the PVA–Cu exhibits excellent moisture absorption capability and dramatic changes in the color of thin composite film, when exposed to 75% humidity atmosphere. The absolute recovery, recyclability, and stability of the PVA–Cu ionic composites not only enable them to be good humidity indicators but the results show that these composites can be employed as efficient humidity‐sensitive material on suitable transducers for environmental and industrial applications. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Humidity switching properties of sensors based on multiwalled carbon nanotubes/polyvinyl alcohol composite films

Multiwalled carbon nanotubes (CNTs) were used as the conductive filler of composites for switching type humidity sensor. The CNTs were oxidized by mixed acids (H₂SO₄ : HNO₃) at a mild temperature to modify carboxylic acid (COOH) groups on the surface of the nanotubes. The dispersibility of acid treated CNTs (CNTs‐COOH) in water is much improved, which is beneficial for dispersing CNTs in the polyvinyl alcohol (PVA) matrix without external additives. The obtained CNTs‐COOH/PVA sensors show nonlinear response to relative humidity (RH), that is, switching properties. The resistances of the sensors remain constant before 80% relative humidity (RH) and then increase sharply with RH, indicating excellent switching characteristic of the sensors. The 10 wt % CNTs‐COOH/PVA sensor shows a sensitivity (ΔR/Ro) of 32.3 at 100% RH. The humidity switching properties of CNTs‐COOH/PVA are much better than that of pristine CNTs/PVA. The improvements are attributed to the improved balance between the dispersibility of CNTs‐COOH and electrical conductivity of the composite films. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39726.     

MgAl2O4 spinel powders from oxide one pot synthesis (OOPS) process for ceramic humidity sensors

MgAl₂O₄ spinel powders can be prepared via the oxide one pot synthesis (OOPS) process. Porous ceramic oxide bodies can be produced with these powders and used as humidity-sensing materials. Pellets were characterized by SEM and their electrical properties were measured using impedance spectroscopy in the frequency range from 10⁻² to 10⁵ Hz at different relative humidity (RH) levels in the range 4–90%. The spinel pellets made of powder from the OOPS process exhibited good humidity sensitivity with a linear response of the logarithm of resistance with RH in the whole RH range tested.     

Chelation of chitosan derivatives with zinc ions. II. Association complexes of Zn2+ onto O,N‐carboxymethyl chitosan

The chelation of zinc ions onto O,N‐carboxymethyl chitosan (ONCMCh) was characterized using a Fourier transform infrared (FTIR) spectrophotometer and a scanning electron microscope (SEM). From the FTIR spectra, little change in the absorption intensities and frequencies at 3300–3600 cm⁻¹ of Zn²⁺ ONCMCh chelated specimens suggested that  OH and  NH₂ groups were not participating in the chelation reaction. The absence of absorption bands at 1755–1700 cm⁻¹ suggested that the carboxyl group CO was not ionized, and the ionized CO bands were observed at 1400–1600 cm⁻¹ for chelated specimens. Thus, the chelation sites took place at the carboxyl group rather than at the  OH and NH₂ groups. It also confirmed that water‐insoluble chelates, which were formed through the Zn O and Zn N bonds, presented a tetrahedral structure. The water‐soluble complexes where zinc ions connected with oxygen of CO and water molecules were only due to electron attraction. Formation of different microstructures on the surfaces, as revealed by SEM, provided evidence to distinguish different chelating mechanisms between water‐soluble and water‐insoluble complexes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1476–1485, 2001     

Ag‐Loaded WO3 Ceramic Nanomaterials: Characterization and Moisture Sensing Studies

Pellet samples of 0–4% weight Ag‐loaded WO₃ prepared through soft chemical route were sintered at 700°C and exposed to humidity. Resistance of the pellets decreased with increase in relative humidity. Sensitivity increased with increase in the % loading of Ag. Four percent Ag‐loaded WO₃ showed maximum sensitivity of 2.38 MΩ/% RH in 20–90% relative humidity range. This sensing element manifests highest crystallinity as well as maximum void concentration. Hysteresis and repeatability for this sensing element after 6 months are within ±2%. A polynomial fit of the humidification data revealed a strong correlation between resistance and relative humidity.