Hydrogels are three-dimensional networked materials that are similar to soft biological tissues and have highly variable mechanical properties, making them increasingly important in a variety of biomedical and industrial applications. Herein we report the preparation of extremely high water content hydrogels (up to 99.7% water by weight) driven by strong host-guest complexation with cucurbituril (CB). Cellulosic derivatives and commodity polymers such as poly(vinyl alcohol) were modified with strongly binding guests for CB ternary complex formation (K-eq = 10(12) M-2). When these polymers were mixed in the presence of CB, whereby the overall solid content was 90% cellulosic, a lightly colored, transparent hydrogel was formed instantaneously. The supramolecular nature of these hydrogels affords them with highly tunable mechanical properties, and the dynamics of the CB ternary complex cross-links allows for rapid self-healing of the materials after damage caused by deformation. Moreover, these hydrogels display responsivity to a multitude of external stimuli, including temperature, chemical potential, and competing guests. These materials are easily processed, and the simplicity of their preparation, their availability from inexpensive renewable resources, and the tunability of their properties are distinguishing features for many important water-based applications.
The composition and physical properties of aged atmospheric aerosol were characterized at a remote sampling site on the northern coast of Crete, Greece during the Finokalia Aerosol Measurement Experiment in May 2008 (FAME-2008). A reduced Dry-Ambient Aerosol Size Spectrometer (DAASS) was deployed to measure the aerosol water content and volumetric growth factor of fine particulate matter. The particles remained wet even at relative humidity (RH) as low as 20%. The aerosol was acidic during most of the measurement campaign, which likely contributed to the water uptake at low RH. The water content observations were compared to the thermodynamic model E-AIM, neglecting any contribution of the organics to aerosol water content. There was good agreement between the water measurements and the model predictions. Adding the small amount of water associated with the organic aerosol based on monoterpene water absorption did not change the quality of the agreement. These results strongly suggest that the water uptake by aged organic aerosol is relatively small (a few percent of the total water for the conditions during FAME-08) and generally consistent with what has been observed in laboratory experiments. The water concentration measured by a Q-AMS was well correlated with the DAASS measurements and in good agreement with the predicted values for the RH of the Q-AMS inlet. This suggests that, at least for the conditions of the study, the Q-AMS can provide valuable information about the aerosol water concentrations if the sample is not dried.
With the world's focus on reducing our dependency on fossil-fuel energy, the scientific community can investigate new plastic materials that are much less dependent on petroleum than are conventional plastics. Given increasing environmental issues, the idea of replacing plastics with water-based gels, so-called hydrogels, seems reasonable. Here we report that water and clay (2-3 per cent by mass), when mixed with a very small proportion (<0.4 per cent by mass) of organic components, quickly form a transparent hydrogel. This material can be moulded into shape-persistent, free-standing objects owing to its exceptionally great mechanical strength, and rapidly and completely self-heals when damaged. Furthermore, it preserves biologically active proteins for catalysis. So far no other hydrogels, including conventional ones formed by mixing polymeric cations and anions or polysaccharides and borax, have been reported to possess all these features. Notably, this material is formed only by non-covalent forces resulting from the specific design of a telechelic dendritic macromolecule with multiple adhesive termini for binding to clay.
In this tutorial review, we describe the current state of the art in water sensors and provide an overview of the major advances made in this field post 2000. The field is currently still in its early development stages and subject to continuous improvements, and the current work provides a structured approach describing different sensing mechanisms and potential future applications associated with each of these. With these developments and their potential implications for the diverse scientific fields requiring tight control over the water content, we strongly believe the discipline is potentially at the threshold of translation into more widespread application and we hope the current review might allow for an expedited process thereof. Recent advances in the field of fluorescent and colorimetric sensors for water content/humidity are described.
Water flow from soil to plants depends on the properties of the soil next to roots, the rhizosphere. Although several studies showed that the rhizosphere has different properties than the bulk soil, effects of the rhizosphere on root water uptake are commonly neglected. To investigate the rhizosphere's properties we used neutron radiography to image water content distributions in soil samples planted with lupins during drying and subsequent rewetting. During drying, the water content in the rhizosphere was 0.05 larger than in the bulk soil. Immediately after rewetting, the picture reversed and the rhizosphere remained markedly dry. During the following days the water content of the rhizosphere increased and after 60 h it exceeded that of the bulk soil. The rhizosphere's thickness was approximately 1.5 mm. Based on the observed dynamics, we derived the distinct, hysteretic and time-dependent water retention curve of the rhizosphere. Our hypothesis is that the rhizosphere's water retention curve was determined by mucilage exuded by roots. The rhizosphere properties reduce water depletion around roots and weaken the drop of water potential towards roots, therefore favoring water uptake under dry conditions, as demonstrated by means of analytical calculation of water flow to a single root.
Water contents of the Martian mantle have previously been investigated using Martian meteorites, with several comprehensive studies estimating the water content in the parental melts and mantle source regions of the shergottites and Chassigny. However, no detailed studies have been performed on the Nakhla meteorite. One possible way to determine the water content of a crystallizing melt is to use the water content in nominally anhydrous minerals (NAMs) such as clinopyroxene and olivine. During or after eruption on the surface of a planetary body and during residence in a degassing magma, these minerals may dehydrate. By reversing this process experimentally, original (pre-dehydration) water concentrations can be quantified. In this study, hydrothermal rehydration experiments were performed at 2 kbar and 700 degrees C on potentially dehydrated Nakhla clinopyroxene crystals. Rehydrated clinopyroxene crystals exhibit water contents of 130 +/- 26 (2 sigma) ppm and are thus similar to values observed in similar phenocrysts from terrestrial basalts. Utilizing clinopyroxene/melt partition coefficients, both the water content of the Nakhla parent melt and mantle source region were estimated. Despite previous assumptions of a relatively dry melt, the basaltic magma crystallizing Nakhla may have had up to 1.42 +/- 0.28 (2 sigma) wt.% H2O. Based on an assumed low degree of partial melting, this estimate can be used to calculate a minimum estimate of the water content for Nakhlas mantle source region of 72 +/- 16 ppm. Combining this value with values determined for other SNC mantle sources, by alternative methods, gives an average mantle value of 102 +/- 9 (2 sigma) ppm H2O for the Martian upper mantle throughout geologic time. This value is lower than the bulk water content of Earths upper mantle (similar to 250 ppm H2O) but similar to Earths MORB source (54330 ppm, average similar to 130 ppm H2O).
The recognition of temporally stable locations with respect to soil water content is of importance for soil water management decisions, especially in sloping land of watersheds. Neutron probe soil water content (0 to 0.8 m), evaluated at 20 dates during a year in the Loess Plateau of China, in a 20 ha watershed dominated by Ust-Sandiic Entisols and Aeolian sandy soils, were used to define their temporal stability through two indices: the standard deviation of relative difference ( ) and the mean absolute bias error ( ). Specific concerns were (a) the relationship of temporal stability with soil depth, (b) the effects of soil texture and land use on temporal stability, and (c) the spatial pattern of the temporal stability. Results showed that temporal stability of soil water content at 0.2 m was significantly weaker than those at the soil depths of 0.6 and 0.8 m. Soil texture can significantly ( < 0.05) affect the stability of soil water content except for the existence of an insignificant difference between sandy loam and silt loam textures, while temporal stability of areas covered by bunge needlegrass land was not significantly different from those covered by korshinsk peashrub. Geostatistical analysis showed that the temporal stability was spatially variable in an organized way as inferred by the degree of spatial dependence index. With increasing soil depth, the range of both temporal stability indices showed an increasing trend, being 65.8–120.5 m for and 148.8–214.1 m for , respectively. This study provides a valuable support for soil water content measurements for soil water management and hydrological applications on sloping land areas.
The gravimetric water content (GWC, %), a commonly used measure of leaf water content, describes the ratio of water to dry matter for each individual leaf. To date, the relationship between spectral reflectance and GWC in leaves is poorly understood due to the confounding effects of unpredictably varying water and dry matter ratios on spectral response. Few studies have attempted to estimate GWC from leaf reflectance spectra, particularly for a variety of species. This paper investigates the spectroscopic estimation of leaf GWC using continuous wavelet analysis applied to the reflectance spectra (350–2500 nm) of 265 leaf samples from 47 species observed in tropical forests of Panama. A continuous wavelet transform was performed on each of the reflectance spectra to generate a wavelet power scalogram compiled as a function of wavelength and scale. Linear relationships were built between wavelet power and GWC expressed as a function of dry mass (LWC ) and fresh mass (LWC ) in order to identify wavelet features (coefficients) that are most sensitive to changes in GWC. The derived wavelet features were then compared to three established spectral indices used to estimate GWC across a wide range of species. Eight wavelet features observed between 1300 and 2500 nm provided strong correlations with LWC , though correlations between spectral indices and leaf GWC were poor. In particular, two features captured amplitude variations in the broad shape of the reflectance spectra and three features captured variations in the shape and depth of dry matter (e.g., protein, lignin, cellulose) absorptions centered near 1730 and 2100 nm. The eight wavelet features used to predict LWC and LWC were not significantly different; however, predictive models used to determine LWC and LWC differed. The most accurate estimates of LWC and LWC obtained from a single wavelet feature showed root mean square errors (RMSEs) of 28.34% ( = 0.62) and 4.86% ( = 0.69), respectively. Models using a combination of features resulted in a noticeable improvement predicting LWC and LWC with RMSEs of 26.04% ( = 0.71) and 4.34% ( = 0.75), respectively. These results provide new insights into the role of dry matter absorption features in the shortwave infrared (SWIR) spectral region for the accurate spectral estimation of LWC and LWC . This emerging spectral analytical approach can be applied to other complex datasets including a broad range of species, and may be adapted to estimate basic leaf biochemical elements such as nitrogen, chlorophyll, cellulose, and lignin. ►First attempt to estimate leaf water content using continuous wavelets. ►Demonstrates water estimation for 47 leaf species. ►Improves the estimation of leaf water content with the derived wavelet features. ►Wavelet features capture water-induced spectral variations at a variety of scales. ►Leaf dry matter absorption shows sensitivity to changes in leaf water content.
Summary The expectation behind seismoelectric field measurements is to achieve a combination of the sensitivity of electrical properties to water content and permeability and the high spatial resolution of seismic surveys. A better understanding of the physical processes and a reliable quantification of the conversion between seismic energy and electric energy are necessary, and need to take into account the effect of water content, especially for shallow subsurface investigations. We performed a field survey to quantify the seismoelectric signals as the water content changed. We measured seismoelectric signals induced by seismic wave propagation, by repeating the observations on the same two profiles during several months. The electrical resistivity was monitored to take into account the water content variations. We show that the horizontal component of the seismoelectric field, normalized with respect to the horizontal component of the seismic acceleration is inversely proportional to the electrical resistivity ρ0.42 ± 0.25. Assuming that the observed resistivity changes depend only on the water content, this result implies that the electrokinetic coefficient should increase with increasing water saturation. Taking into account the water saturation and combining our results with the Archie law for the resistivity in non-saturated conditions, the normalized seismoelectric field is a power-law of the effective saturation with the exponent (0.42 ± 0.25)n where n is Archie′s saturation exponent.
Poly(N-isopropylacrylamide) (PNIPAM)-based ionic microgels with different diameters were first prepared and then used as particulate stabilizer or seed in dispersion polymerization of styrene. The role of PNIPAM-based ionic microgels could be transformed from particulate stabilizer to seed by controlling the water content in methanol-water mixture. Generally, PNIPAM-based ionic microgels served as particulate stabilizer in methanol in the absence of water, leading to the formation of spherical polystyrene nanoparticles. However, they turned into seeds when water was added into the methanol solution, with the formation of octopus-like nanoparticles. Further study demonstrated that the mechanism for this role transition was related to the special thermosensitivity of PNIPAM microgels in methanol-water mixture. They lost their thermosensitivity in pure methanol solution but restored their thermosensitivity when increasing the water content in methanol-water mixture.