Hydrated Gel Research Articles

Granular Gels as Growth Media for Tomato Seedlings

Abstract The granulated, insoluble acrylamide-based hydrophilic polymers, Terrasorb HB and Alcosorb AB3C, hydrated initially with all the essential nutrients (15 g gel solids/liter of 1-fold Hoagland solution), were effective media for the production of 3-week seedlings of tomato (Lycopersicon esculentum Mil.) in plug (modular) trays. Higher concentrations of the nutrient solution used to hydrate gels or incorporation of resin-encapsulated, slow-release fertilizer (Osmocote, 17N–3.9P–10.8K, 1.5 or 3.0 g·liter–1) in the hydrated gels decreased seedling growth. Daily application of fertilizer solution (100 mg N/liter) or water resulted in similar seedling growth. Seedlings were healthy, with roots permeating the voids between the hydrated granules of the entire gel mass. The gel mass adhering to the root system could be extracted readily and intact from the plug tray cell.

Amphiphilic properties of synthetic glycolipids based on amide linkages, 3. Temperature and concentration dependence of the reduced viscosity of gel‐forming alkyl gluconamides

AbstractIn order to follow the process of aggregation, viscosity measurements in dilute aqueous solution were performed with two carbohydrate amphiphiles: (i) N‐octylgluconamide (C8‐GA) and (ii) N‐decanoyl‐N‐methylglucamide (C10‐MGA). Both compounds ten to form a gel on cooling, the former at 65°C, the latter at 10°C. Electron micrographs have shown that the gels are composed of a loose network of thin, regularly twisted helical ropes. By viscosity measurements over a wide range of temperatures and concentrations, typical changes of the reduced viscosity were observed. Results are discussed with respect to the critical micelle concentration (CMC), the Krafft point, i. e. the critical temperature of crystallization (Tc), and the cloud point (Tcp). It is concluded that micellar aggregation to rod‐shaped particles, quasi‐crystalline aggregation to highly hydrated gels, and crystallization of monomers, the latter mediated by hydrogen bonding, are involved and compete with each other.

Counter-ion intradiffusion in sulphonic ion-exchange systems

The intradiffusion data of the sodium counter-ion in different sulphonic ion-exchange systems in the sodium form (from linear polystyrene to commercial membranes of graft copolymers of styrene) are analysed as a function of q, the number of water molecules per ionic group. These data represent experimental results from a considerable number of workers during the last three decades. A general comprehensive picture is obtained, which shows how individual characteristics (water content, exchange capacity, crosslinking and inert material added) affect in a gradual and congruent way the value of the intradiffusion coefficient. The comparison with simple electrolyte systems such as aqueous sodium chloride and sodium p-ethylbenzene sulphonate shows not only a clear similarity, which shows that the transport mechanism is of the same type in all these systems, but also a clear differentiation owing to the polymeric and polyelectrolytic character of the ion-exchange systems. The complex nature of the obstruction to ion movement (tortuosity) is evidenced. The overall behaviour observed leads to the view that it is realistic to consider ion-exchange systems as homogeneous hydrated gels, since intermolecular interactions between charged sites, counter-ions and water are very important. Consequently, it is more convenient to study the transport properties as functions of the swelling variable q than in terms of the commonly used stoichiometric volume fraction of polymer. For several systems a linear relation between ln D†Na+ and 1/q holds, within the range 2 ⩽q⩽ 70. The effect of cross-linking and of inert material on these relations is discussed. Furthermore, a similar analysis leads to the verification of a previously obtained linear equation between ln D†Na and a0, the thermodynamic activity of water.

The adsorption properties of hydrated zirconia gels: Influence of the preparation conditions and temperature of dehydration on the porous texture

The adsorptive characteristics of several hydrated zirconia gels prepared by different procedures have been investigated by the adsorption of several vapors: nitrogen, argon, oxygen, and carbon dioxide. Although the precipitation procedures included a wide range of different conditions (organic and inorganic “zirconyl” solutions, a range of pH extending from 2.5 to 11, partial dehydration in air and in vacuo) all these materials are microporous. Some of them have a micropore volume of up to 0.2 cm 3/g. On the contrary, the external area never exceeds 31 m 2/g. Lowpressure hysteresis is another interesting property of these materials.

Study of Phase Transformation of Al2O3—SiO2Gel and Kaolinitic Clay

Alumina gel was prepared in presence of colloidal or amorphous hydrated silicic acid gel. The gel gives a first exothermic peak which is exactly similar to that of kaolinitic clay. Thermal characteristics of this gel were studied by qualitative identification of phases and quantitative estimation of mullite formed, by X-ray, and then compared to that of kaolinitic clay. It is found that the thermal change of the gel (of molar ratio SiO2: Al2O3 2:1) is quite analogous to that of kaolinite, and that mullite formation in both the cases follows the same course and same mechanisms.

Glycol methacrylate copolymerized with glutaraldehyde and urea as an embedment retaining lipids

Glycol methacrylate can be copolymerized with glutaraldehyde and urea in the presence of substantial amounts of water to produce an embedment suitable for ultrathin sectioning. This is accomplished at a pH close to neutrality by ultraviolet radiation in the presence of trace quantities of benzoin as a free radical catalyst. The polar nature of this embedment permits the retention of lipids in sectioned material. Thus, thick sections of myelin exhibit a brilliant birefringence. Also, spatial relationships maintained in life by highly hydrated carbohydrate gels appear generally to be faithfully retained. These factors permit the demonstration of a 180–200 A periodicity in myelin, corresponding to X-ray diffraction information of the true value for the fresh, wet state. Protein systems are well differentiated with uranyl acetate—lead citrate staining. Lipids are demonstrated by osmium vapor staining or are seen in negative contrast. The embedments section well with a glass knife, at relatively high speed, providing the fairly hydrophilic block face does not get wet. Disadvantages include an intrinsic fine graininess which unfortunately limits the resolution of high magnification micrographs. Also, the embedment is unstable during electron bombardment so that supporting films are almost essential. Phosphotungstic acid staining at low pH damages the embedment.

A cids as chemical stabilizers of clay soils

1. In the acid stabilization of clay soils the aluminosilicate nucleus of the clay minerals is attacked. This process is accompanied by the escape of primarily the aluminum ion from the crystal lattice and the formation of depolymerized silicic acid. As the acid medium is neutralized to pH>3, the latter is condensed into an acid, highly hydrated silica gel, which cements the soil.

Polymerizable glutaraldehyde—urea mixtures as polar, water-containing embedding media

Glutaraldehyde and urea are polymerizable, even in the presence of substantial amounts of water, to produce an “aminoplastic” that can serve as a tissue embedment for ultrathin sectioning. The highly polar nature of the resin mixture permits the retention of lipid structures in situ. Also, since dehydration is not completed until after polymerization, the use of this embedding medium permits superior preservation of highly hydrated carbohydrated gels which otherwise are apt to collapse. An insoluble glutaraldehyde—urea polymer is produced only by acid catalysis (pH ≊ 4.0), easily achieved with oxalic acid. Two successful protocols are offered. One demands pH monitoring to initiate polymerization, the other involves the blending of two independently stable mixtures. Experiences with other related potential monomers are described. Polymerization is allowed to occur with the specimens in small, individual drops of the resin mixture. The final plastic is hard, and so brittle that rough trimming almost has to be done by grinding. It is quite hydrophilic, necessitating a relatively high cutting speed and a carefully controlled trough meniscus. Glass knives are much to be preferred. Representative tissues, stained in various ways, illustrate some of the potentialities, as well as the limitations, of the method. Sections exposed to osmium tetroxide vapors demonstrate completely stained cytomembranes. This is regarded as indicative of the retention of lipids in the embedment. The contents of lipid droplets are similarly stainable. Phosphotungstic and silicotungstic acids at a pH ≅ 4.5 demonstrate carbohydrate moieties, particularly the glycocalyx, and some of its specializations including the material of synaptic and desmosomal clefts (the stainable material drops out in tight junctions). Mucous droplets and layers are stained as well, as is frequently at least a part of the Golgi complex in secretory cells. Glycogen is preserved and stained. Spaces occupied by membrane lipids are then seen in negative contrast. After uranyl acetate and lead citrate staining, the hydrophobic layers of cytomembranes are not stained either, but are outlined by neighboring structures. These substances do stain proteins generally, but usually without good differentiation or contrast which is a decided limitation. The preservation of presumably normal spatial relations in lipid systems, including cytomembranes, is a special virtue of the technique. Also, normal relationships appear to be preserved in unparalleled fashion in systems dependent in life upon highly hydrated carbohydrate gels. This particularly is the case where specific gaps are maintained in contact relations between cells, in specializations of the extracellular compartment in such diverse places as kidney epithelium, neuropil and the intraperiod “line” of myelin.

Myelin embedded in polymerized glutaraldehyde-urea

Glutaraldehyde-fixed myelin, embedded in polymerized glutaraldehyde-urea, maintains the periodicity seen in X-ray diffraction studies of fresh wet nerve. An aspect of this is the preservation of relatively thick (35–40 Å) layers thought still to be occupied even in sections by the hydrophobic hydrocarbon chains of the phospholipids. The retention of lipids is attributed to the highly polar character of the embedding mixture. That lipids are indeed unextracted is demonstrated by the brilliant birefringence seen in thick sections, by the “staining” of the lipid bilayers of ultrathin sections following exposure to osmium tetroxide vapors, and by the nearly identical X-ray diffraction patterns of embedded myelin when compared with unembedded myelin exposed to no more than a conventional glutaraldehyde fixation. (The latter experiments constitute a joint study with A. K. Akers and D. F. Parsons.) The “intraperiod gap” (the extracellular extension of the mesaxon) is also seen as a relatively thick layer (≅ 25 Å exclusive of the “outer leaflets”). In life this gap is thought probably to be maintained by a highly hydrated carbohydrate gel (the “glycocalyx”). Its maintenance in the present material is attributed to the fact that the glutaraldehyde—urea embedment is polymerized while there is still substantial water in the system. Otherwise, with conventional procedures, collapse is thought usually to occur as dehydration nears completion, thus leading to a very common, but largely unrecognized artifact. After aqueous staining a sharp discontinuity is apparent between the outer leaflets and the underlying hydrophobic zone occupied by the bilayer of hydrocarbon chains. The inner leaflets cannot be as well differentiated, emphasizing the fundamental asymmetry of the membrane. Macromolecular intrusions into the hydrophobic layers (if they occur) are not recognized. Measurements of the thickness of the five fundamentally distinct layers that constitute the repeating structures of myelin have been made, and are correlated with some models that have been derived from a combination of X-ray diffraction and biochemical information.

“ECM”: Its nature, origin and function in cell aggregation

Evidence is presented to show that a viscous material referred to elsewhere as “ECM”, reportedly elaborated in vitro by aggregating embryonic cells and suggested to possess a variety of functions in the processes of cell aggregation and tissue reconstruction, is in reality a highly hydrated deoxyribonucleoprotein gel. The gel appears to be formed by the chromosomes of ruptured cells as a result of the enzymatic removal of a portion of the chromosomal protein by the trypsin employed for tissue dissociation. It originates in greatest part, in the material studied, from the broken cells at the cut surfaces of the tissue fragments, and it appears to form complexes with a variety of macromolecular materials present in cell suspensions or culture media. Cells aggregate normally in its total absence, by processes, it is assumed, involving intimate contact of the cell surfaces themselves. The possible role of cell products in promoting cell aggregation in vitro is discussed.