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Intervertebral disk (IVD) degeneration is a multifactor process that results in the physical destruction of the nucleus pulposus (NP) and annulus fibrosus (AF). This compromises IVD function and causes significant disability and economic burden. Strategies to replace the entire composite structure of the IVD are limited and most approaches do not recapitulate the heterogenous biochemical composition, microarchitecture or mechanical properties of the native tissue. Our central hypothesis was that donor IVDs which resemble the size and biochemistry of human lumbar IVDs could be successfully decellularized while retaining the tissue's structure and function with the long-term goal of creating a composite scaffold for tissue engineering the human IVD. Accordingly, we optimized a procedure to decellularize bovine tail IVDs using a combination of detergents, ultrasonication, freeze-thaw cycles, and nucleases. The resultant decellularized whole IVD xenografts retained distinct AF and NP regions which contained no visible intact cell nuclei and minimal residual bovine deoxyribose nucleic acid (DNA; 65.98 ± 4.07 and 47.12 ± 13.22 ng/mg, respectively). Moreover, the NP region of decellularized IVDs contained 313.40 ± 50.67 µg/mg glycosaminoglycan. The presence of collagen type II was confirmed via immunohistochemistry. Additionally, histological analysis of the AF region of decellularized IVDs demonstrated retention of the native angle-ply collagen microarchitecture. Unconfined compression testing demonstrated no significant differences in swelling pressure and toe-region modulus between fresh and decellularized IVDs. However, linear region moduli, peak stress and equilibrium moduli were all significantly reduced. Together, this research demonstrates a successful initial step in developing a biomimetic acellular whole IVD xenograft scaffold for use in IVD tissue engineering. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2412-2423, 2018.

Hydrogels are promising materials for biomedical applications, where timely degradation is often preferred. In the conventional design, however, the cleavage of polymer networks essentially causes considerable morphological changes (i.e., degradation-induced swelling), triggering various medical complications. Herein, we report a rational strategy to suppress the degradation-induced swelling based on the synthetic control of the polymer-solvent interaction parameter (χ) of constituent polymer networks. The resultant hydrogels with an optimal χ parameter (χ37 °C ≈0.53; non-osmostic hydrogels) displayed the capability to retain their original shape and degrade without generating significant swelling pressure under physiological conditions (Π37 °C

Soils in the Kansas Cherokee Prairies have formed in various parent materials and exhibit differences in the degree of expression of vertic properties. Despite large clay contents, few soils meet the criteria for a Vertisol. In an effort to investigate the cause of these differences, pedogenic processes, primarily clay illuviation and shrink–swell processes, were evaluated in eight pedons. Relatively high coefficient of linear extensibility (COLE) values were found in all soils. The clay mineralogy of four sites was dominated by smectite, but only two of those sites classified as Vertisols. In the other four sites, smectite was the most common clay mineral, yet there were several other clay minerals present in significant quantities. Disruption of illuvial clay features by shrink–swell movement was evident in the thin sections of all soils. Striated b-fabrics dominated except in surface soils that exhibited a small COLE value and occurred above an argillic horizon. Linear planes lined with stress-oriented clay and representing zones of shear failure were observed, along with argillans that had been distorted and embedded within the matrix by swelling pressure and soil movement. In conclusion, when present, a nonexpansive silty surface layer acts as a buffer and may limit shrink–swell by allowing expansive subsoils to dry more slowly.

The evaluation of several case histories of tunnels in swelling rock with sulfate bearing minerals shows that brittle fracture plays an important role in the development of swelling processes. Brittle failure by spalling has been directly observed in several tunnels, as early as the 19th century and more recently. Numerical analyses applied to different case histories with observed heave and development of strong swelling pressure, considering different construction processes; agree with the observed swelling zones. The effect of construction procedures on swelling in particular the development of pressures and swelling zones becomes evident from these analyses. For a better understanding of swelling processes brittle failure processes have to be considered in the analyses. Die Auswertungen von Beobachtungen aus ausgefuhrten Tunneln im Sulfat fuhrenden Gebirge zeigen, dass Sprodbruchvorgange eine entscheidende Rolle spielen im Aufbau von Quelldrucken und Quellhebungen. Einerseits wurden in verschiedenen Tunneln, teilweise im 19. Jahrhundert, Sprodbruchvorgange direkt beobachtet, wenn Abschalungen auftraten. Andererseits konnte mit numerischen Analysen gezeigt werden, dass je nach Bauvorgang unterschiedlich grose, zerbrochene Zonen auftreten, die mit beobachteten Quellzonen und Hebungen an ausgefuhrten Bauwerken gut ubereinstimmen. Die Auswirkung unterschiedlicher Bauvorgange auf Grose der Quelldrucke und der quellenden Bereiche kann zumindest qualitativ nachgewiesen werden. Bei Tunnelbauten in quellendem Gebirge ist die Ausbildung von Sprodbruchen zu berucksichtigen.

“Swelling” is generally taken to mean the expansion of a rock due to water absorption. The main intention of this paper is to point out the significant difference between the swelling of clay and claystone (Tonstein) on one hand and the swelling of claystone and marl containing anhydrite on the other. In the opinion of the author, these differences are so large that they should be described as different phenomena. Leopold Muller has already proposed the introduction of different German terms: “Quellen” for clay and “Schwellen” for anhydrite. Unfortunately, this terminology has not caught on, probably because the word swelling is used in English for both processes. The resulting merging has hindered research into anhydrite swelling for decades, and the development of calculation methods and technical solutions for tunnelling in anhydrite-bearing ground is still at an early stage. In contrast, the problem of clay swelling can be regarded as largely solved. Unter “Quellen” wird ganz allgemein die Ausdehnung eines Gesteins infolge von Wasseraufnahme verstanden. Hauptanliegen des vorliegenden Beitrags ist es, auf die betrachtlichen Unterschiede zwischen Quellvorgangen in Ton und Tonstein einerseits und in anhydrithaltigem Ton- und Mergelstein andererseits hinzuweisen. Nach der Uberzeugung des Autors sind die Unterschiede so gros, dass man eigentlich von zwei verschiedenen Phanomenen sprechen muss. Schon Leopold Muller hat deshalb getrennte Begriffe einzufuhren versucht: “Quellen” fur Ton und “Schwellen” fur Anhydrit. Bedauerlicherweise hat sich diese Terminologie nicht durchsetzen konnen, vermutlich auch wegen der Verwendung des Worts “swelling” in der englischen Sprache fur beide Vorgange. Die damit verbundene Gleichsetzung hat jahrzehntelang die Erforschung des Anhydritschwellens behindert. Die Entwicklung von Rechenansatzen und von technischen Losungen fur Tunnel in Anhydritgestein befindet sich letztlich immer noch in einer Fruhphase. Dagegen kann das Problem des Tonquellens als weitestgehend gelost angesehen werden.

Underground construction in rock prone to swelling behaviour may result in long-term problems, especially in the invert, if the structure cannot resist swelling pressures. Swelling phenomena are not only a consequence of ground conditions but are strongly influenced by excavation and construction procedures. Evidence of brittle failure observed in the field will be presented and analyzed to prove that brittle failure is the trigger effect of swelling phenomena in shale and clay-anhydrite rocks. Brittle fractures have also been observed in laboratory swelling tests. Brittle failure can create cracks that form pathways for water, leading to changes in the stress-state, and as a consequence trigger swelling phenomena. In clay-anhydrite rock, the swelling pressure is caused by the crystallization pressure of gypsum. The excavation and construction procedures used for the tunnel are a decisive factor for controlling swelling behaviour. Quellvorgange in Tongesteinen und Ton-Anhydritgesteinen fuhren oft zu langfristigen Problemen in Untertagebauten, insbesondere wenn der Ausbauwiderstand der Tragkonstruktion langfristig zu gering ist. Die Quellvorgange, die besonders im Sohlbereich auftreten, sind nicht blos eine Folge der Gesteinseigenschaften, sondern werden auch von den gewahlten Bauvorgangen und der Tragkonstruktion beeinflusst. Sprodbruchvorgange wurden in vielen Untertagbauten in Felsgesteinen mit geringer Festigkeit beobachtet. Deren Ursachen werden mit numerischen Modellen analysiert. Sprodbruche wurden aber auch in Laborquellversuchen in Ton-Anhydritgesteinen, wo sich Gips bildete, beobachtet. Die unterschiedlichen Beobachtungen werden in einen gemeinsamen Rahmen zusammengefugt. Sprodbruche fuhren zur Bildung von Rissen und damit von Wasserwegen. Weiter ergeben sich wesentlichen Anderungen des Spannungszustands um die unterirdische Offnung, und als Folge dieser Vorgange werden Quellerscheinungen ausgelost. In Ton-Anhydritgesteinen wird der hohere Quelldruck durch den Kristallisationsdruck von Gips verursacht. Der gewahlte Bauvorgang muss Sprodbruchvorgange moglichst vermeiden und ist ein wesentlicher Faktor des aufzunehmenden Quelldrucks und der Quellerscheinungen.

The influence of endothelial cell pumping and of cell barrier functions on cultivated corneas has been studied by comparing the rate of weight increase in freeze-treated, ouabain-treated and fresh corneas. Inhibition of the endothelial cell pump activity increased the swelling rate from 0.5% of start weight per h (fresh corneas) to about 2% per h (ouabain-treated corneas), as measured after 24 h in culture medium. The cell barrier effect was estimated by comparing the swelling rate of ouabain-treated corneas after 24 h, and the swelling rate of freeze-treated corneas with the same swelling pressure. The values are 2 and 9.5% per h, respectively. The swelling rate of freeze-treated corneas with different button diameters was found to increase with decreasing corneal button diameter.

This paper reports on microcapsules obtained by layer-by-layer deposition of bio-polyelectrolyte multilayers at the surface of biodegradable dextran microgels. The behavior of the layer-by-layer coating upon degradation of the microgel core strongly depends on the bio-polyelectrolytes used. Two types of microcapsules, “self-rupturing” microcapsules and “hollow” microcapsules, are presented. Self-rupturing microcapsules are obtained when the swelling pressure of the degrading microgel core is strong enough to rupture the surrounding bio-polyelectrolyte membrane. Self-rupturing microcapsules could be of interest as a pulsed drug delivery system. Hollow microcapsules are obtained after applying multiple layers of bio-polyelectrolyte that can withstand the swelling pressure of the degrading microgel core. Biomacromolecules (such as albumin and dextran) spontaneously accumulate in the hollow microcapsules prepared from dex-HEMA microgels, which could be of interest for drug-encapsulation purposes.

We have viewed cooking meat from the perspective of soft condensed physics and posed that the moisture transport during cooking can be described by Flory-Rehner theory of swelling/shrinking polymer gels. This theory contains the essential physics to describe the transport of liquid moisture due to the denaturation and shrinkage of the heated protein matrix. The validity of our hypothesis is shown by a numerical model, which comprises a linearization of the Flory-Rehner theory augmented with Darcy's law for porous media flow, applied to the simulation of cooking experiments performed on a rectangular piece of beef. Reasonably, comparable results are obtained from simulations and experiments. Further analysis of simulations resolves yet another unexplained phenomena observed during heating of meat. Literature review suggests that Flory-Rehner is applicable to cooking of other gel-like foods. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Fluid balance in the intervertebral disc under applied load is determined primarily by its swelling pressure, that is, the external pressure at which it neither loses nor gains water. This depends on the composition of the tissue, in particular on its proteoglycan concentration. Proteoglycans develop a high osmotic pressure due to their fixed negatively charged groups. Because of their size, proteoglycans are excluded from the collagen's intrafibrillar volume; hence their osmotic activity is determined only by the extrafibrillar water. Here, we show that in order to evaluate correctly the swelling pressure in the annuli fibrosi of human intervertebral disc, it is essential to evaluate its proportion of intrafibrillar water. We used low-angle X-ray scattering and osmotic stress techniques to determine the lateral packing of the collagen molecules in the fibrils of the annuli fibrosi (ages: 25-77). It was found that the lateral packing and, hence, the intrafibrillar water content depends on age, external osmotic pressure, and location in the tissue. Subtracting intrafibrillar water from total hydration yields the amount of extrafibrillar water, from which the true fixed charge density of the tissue could be estimated. From a force balance, it would appear that collagen tension plays only a minor role in the equilibrium of the human intervertebral disc under load, in contrast to articular cartilage, where collagen tension is important for load bearing.

Degrading hydroxyethylmethacrylate-grafted dextran (dex-HEMA) hydro- gels generate a relatively sudden increase in osmotic pressure upon degradation into dextran solutions. This phenomenon is currently being examined as a possible means of developing a pulsatile drug-delivery system. Here a mathematical model based on scaling concepts is presented to describe this sudden increase in swelling pressure and to provide a framework for the rational design of pulsatile delivery systems based on this phenomena. The model provides a good fit to the swelling pressures measured for dex-HEMA gel/free dextran mixtures that simulate degrading dex-HEMA gels. © 2004

Agarose hydrogels deswell reversibly over a wide range of concentration. Two types of deswelling measurements are considered here, isotropic and uniaxial. We describe some of the properties of the gels observed in the deswollen state. In both the isotropic and uniaxial geometry, the swelling pressure varies approximately as the square of the concentration.

Differential equations for swelling pressure and swelling equilibria in two-phase systems consisting of many components have been derived. The result includes simple equilibria of gaseous or liquid solvent and a gel which are known from the literature.

Small angle neutron scattering measurements were performed on polydimethylsiloxane-toluene solutions and gels at different degrees of swelling. The scattering signal of the gel was decomposed into a solution-like part and a static part. The thermodynamic information obtained from the solution-like part of the signal is compared with macroscopic swelling pressure observations.

A new method for the determination of the swelling pressure πs of gels is presented. The gel remains in the isotropic state when the isothermal mechanical equilibrium is established. The temperature dependence of πs can be measured at constant composition. The applicability of the method is demonstrated for chemically crosslinked gelatine swollen in water. Es wird eine neue Methode zur Bestimmung des Quellungsdruckes πs von Gelen beschrieben. Das Gel bleibt wahrend der Einstellung des isothermen, mechanischen Gleichgewichts isotrop. Die Temperaturabhangigkeit von πs kann bei konstanter Zusammensetzung gemessen werden. Die Anwendbarkeit der Methode work am Beispiel von chemisch vernetzter, in Wasser gequollener Gelatine Gezeigt.

Durch Emulsionspolymerisation von Styrol mit Divinylbenzol werden kugelige Polystyrolteilchen ziemlich einheitlicher Grose mit Molekulargewichten von M = 5·105 bis 3·107, verschieden starker Vernetzung und vielen Endgruppen hergestellt. Die Charakterisierung mittels Lichtstreuung, Viskosimetrie, Gelpermeation, Diffusion und Rheologie zeigt erhebliche und z. T. nicht bekannte Wirkungen der innermolekularen Vernetzung: Fur Teilchen bestimmten Quellungsgrades ist das Produkt aus dem zweiten Virialkoeffizienten und M, A2·M, im Gegensatz zu der fur ungequollene Kugeln entwickelten Theorie proportional M. Die Durchspulungskonstante ϕ steigt mit wachsender innermolekularer Vernetzung auf den fur Kugeln berechneten Wert, der groser ist als der von Knaueln linearer Molekule. Die Gelchromatographie tastet die Grose von Molekulen ahnlich ab wie die Hydrodynamik, nicht aber so wie die Lichtstreuung. Bei niedrigen Konzentrationen verhalten sich Gellosungen viskosimetrisch wie Kugelsuspensionen, bei hoheren Konzentrationen wegen einer Entquellung der Teilchen jedoch mehr wie Losungen von Fadenmolekulen. Die Viskositat, die Strukturviskositat und die Schubspannung τw im Wendepunkt der log η gegen log τ-Kurven sind aber wesentlich kleiner als bei linearen Molekulen. Der osmotische Druck konzentrierter Losungen ist ein Quellungsdruck und hangt von der Vernetzungsdichte der Gelteilchen ab. Die Schmelzviskositat wird durch innermolekulare Vernetzung zunachst stark reduziert, bei Molekulargewichten der Kettenstucke zwischen den Verzweigungsstellen Mc < 15 000 aber erhoht. Modul und Dichte der Glaser solcher Gele sind nahezu normal, die Bruchfestigkeit nimmt mit wachsender innermolekularer Vernetzung ab. In Gegenwart von Toluol polymerisierte Gele haben hohere Quellungsgrade und damit hohere Viskositatszahlen sowie kleinere Durchspulungskonstanten als losungsmittelfrei polymerisierte Gele. Gele lassen sich nicht oder nicht vollstandig durch Sedimentation abtrennen oder aus der Winkelabhangigkeit der Lichtstreuung ermitteln. Mist man aber an Gemischen der Gele mit linearen Molekulen auser Molekulargewicht und Viskositatszahl eine weitere unabhangige Grose, z. B. die Schmelzviskositat, die Strukturviskositat oder die Konzentrationsabhangigkeit der Viskositat, so kann man die Menge und die charakteristischen Merkmale des Gels bestimmen, wenn die Eigenschaften des linearen Polymeren bekannt sind. Emulsionpolymerisation of styrene with divinylbenzene gives spherical particles of nearly uniform diameter, with molecular weights M between 5.105 and 3.107, with various degrees of crosslinking density and with many endgroups. Light scattering, viscosimetry, gelpermeation, diffusion and rheological measurements show, that intramolecular crosslirrking has significant and partly unknown effects: particles of a definite swelling degree have second virial coefficients A2, which are nearly independent of M. This is contrary to the theory for unsolvated spheres. The FOX-FLORY-constant ϕ increases with intramolecular crosslinking to the value calculated for spheres, which is larger than that for coils of linear molecules. Gel permeation measures the diameter of the particles in a similar way as hydrodynamics but different from light scattering. At low concentrations the solutions of such gels behave viscosimetrically like dispersions of spheres. At higher concentrations the gel particles deswell and show a concentration dependence of viscosity between that of hard spheres and linear molecules. The viscosity of the solution and its shear dependence are smaller than that of linear molecules, the shear stress τw in the turning point of the curves log η vs. log τ being also much smaller. The osmotic pressure at high concentrations is a swelling pressure and depends on the degree of crosslinking. Intramolecular crosslinks reduce the melt viscosity, if the molecular weight of the chain segments between branching points is Me > 15000. At very high crosslinking densities the melt viscosity is increased. Modulus and density of glassy gel polymers are nearly normal, but the stress at breaking is decreased with increasing intramolecular crosslinking. Particles have higher swelling degrees and intrinsic viscosities as well as lower FOX-FLORY-constants, if they are polymerised in the presence of toluene. Gels cannot be separated quantitatively from linear molecules by sedimentation or by evaluating an abnormal angular dependence of scattered light. But one may calculate the amount of gel and its degree of crosslinking, if one knows the behaviour of linear molecules and measures Mw [η] and a third independent quantity, e.g. melt viscosity, non-NEWTONian behaviour or the concentration dependence of the viscosity of solutions.

The effects of variety, harvest date and plant population on breakdown are considered in the light of two current theories relating chemical composition to the texture of cooked potato tubers. Differences between cell surface area could not account for the differences in breakdown found. The results also show the inadequacy of the theory ascribing a primary role in texture control to the “swelling pressure” generated by starch on gelatinisation. It seems likely that breakdown of cooked potato tubers is due to excessive hydration of cell wall material. On this theory high levels of polyuronides and phytate and low levels of polyvalent metals in the cell wall material favour breakdown. Correlation analysis indicates that other chemical factors which have yet to be identified may also play a role in the control of cooked potato texture.

The fracture behavior of human hair has been investigated with a view toward delineating fracture mechanisms that lead to different types of fracture under tensile loading. Principally, three types of fracture are encountered—smooth fractures, step fractures, and fractures involving undefined fibrillated ends. The moisture content of the fiber plays an important role in determining the type of fracture that occurs. Fiber conditioned at either low (∼0%) or high (90%) relative humidity give predominantly smooth fractures, whereas those conditioned at intermediate relative humidities given predominantly step fractures. Surface treatments with polymers or surfactants do not seem to have any effect on the strength or the fracture behavior of fibers. At low moisture contents, fracture initiation occurs more often in the cortex, whereas, at high moisture contents, fracture almost always initiates at the surface of the fiber, suggesting that the swelling pressure of the cortex plays a significant role in fracture initiation. Fibers with larger cross-sectional areas tend to split along the axis because of the higher probability of encountering flaws or medullary cells which direct cracks along the fiber axis. Unlike synthetic polymeric fibers, hair fibers seem to follow the Griffith criterion of brittle fracture. This may be coincidental since electron microscopic evidence suggests that fracture propagation occurs by secondary cracks generated as a result of stress concentrations building up at the periphery of the primary crack. The rate of stress transfer to adjacent cortical cells via intercellular cement probably plays an important role in the fracture mechanism.

A suite of 10 synthetic sodium silica and sodium calcium silica gels was prepared to explore the basic mechanism of expansion of concrete by alkali-silica reaction. Methods were developed for measuring the free swelling capacity and the maximum swelling pressure generated by these gels when they are allowed access to free water. Free swelling ranged from as little as 0.5 to as much as 80%, maximum swelling pressures recorded varied from as little as 0.1 to almost 11 MPa, the latter well in excess of the tensile strength of most concretes. The relations observed between alkali:silica ratio of the gel and its free swelling and swelling-pressure characteristics were suggestive but not straightforward. The presence of calcium in the synthetic gels did not noticeably reduce their activity with respect to either test.

Wasser und organische Mono- und Polyhydroxylverbindungen bilden insbesondere mit 5- bis 7gliedrigen Lactamen bei Raumtemperatur auffallend dunnviskose Assoziate. Eigenschaften und Nutzanwendungen der e-Caprolactam-Assoziate in der Isocyanat-Chemie werden in der vorliegeden Arbeit schwerpunktsmasig behandelt. ϵ-Caprolactam-Wasser-Assoziate sind interessante Losungsmittel fur schwerlosliche Stoffe, enthalten Wasser bzw. Polyole in gegenuber Isocyanaten aktivierter Form gebunden und weisen bei Verschaumungsprozessen interessante Eigenschaften als Kettenverlangerungsmittel und Treibmittel auf. Auf Grund auffallender Eigenschaften der Assoziate werden diesen niedermolekulare, cyclische Strukturen unter Ausbildung von Wasserstoffbruckenbindungen zugeordnet. Auch Mono- und Polyhydroxylverbindungen sowie Oxime werden durch Assoziat-Bildung mit ϵ-Caprolactam stark aktiviert und lassen sich als flussige, vollig losungsmittelfreie Systeme in umweltfreundlichen Verfahren in vielfaltiger Weise als Baukomponenten in der Isocyanatchemie verwenden. ϵ-Caprolactam-Assoziate konnen zur Linearisierung von uber Biuret- und Allophanat-Gruppen vernetzten Polyurethanen und Polyurethanpolyharnstoffen herangezogen werden. Die partielle oder quantitative Linearisierung unter Eliminierung von Biuret- und Allophanatvernetzungsstellen in Schaumstoffen fuhrt zu neuartigen, textilartigen Matrizen mit extrem verminderter Stauchharte. Die starken Quellungsvorgange an linearisierten cellularen Polyurethanmatrizen werden zur Durchfuhrung von Matrizen-Reaktionen ausgenutzt, wobei die zellformige Stoffanordnung in den durch den Quellungsduruck neu erzeugten Raumen und die irreversible Fixierung des Quellungszustandes durch rasch verlaufende Feststoffbildung der verwendeten Reaktionspartner zu interessanten Kombinationsschaumstoffen fuhrt. At room temperature water and organic mono- and polyhydroxyl compounds form – particularly with 5- to 7-membered lactams – associates of strikingly low viscosity. The present paper is concerned with significant aspects of the properties and practical applica-tions of these c-caprolactam associates. 6-caprolactam/water associates are of interest as solvents for materials which are difficult to dissolve, contain water or polyols rcsp. bound in activated form for reaction with isocyanates and exhibit interesting propertics as chain-lengthening and blowing agents in foaming processes. Because of their remarkable properties the associates may be considered as low-molecular weight cyclic structures with hydrogen bonding. Mono- and polyhydroxyl compounds and oximes are also highly activated by forming associates with 6-caprolactam and, being liquid systems completely free of solvent, they can be used in a wide variety of ways as structural elements in isocyanate chemistry which allow non-polluting techniques. 8:-Caprolactam associates can be employed for linearization of polyurethanes and polyurethane polyureas crosslinked by biuret and allophanate groups. Partial or quantitative linearization with elimination of biuret and allophanate crosslinking sites in foams yields new types of matrices similar to textiles with extremely reduced deflection hardness. The heavy swelling which takes place in linearized cellular polyurethane matrices is utilized for inducing matrix reactions and the cellular structure in the spaces newly created by the swelling pressure and the irreversible fixation of the swelling caused by rapid solids formation of the coreactants results in interesting foam combinations.

Es wird ein Uberblick gegeben uber die thermodynamischen Eigenschaften von Polymergelen, den gegenwartigen Stand der experimentellen Untersuchungen und die Anwendbarkeit der statistischen Theorien. Polymergele sind hochmolekulare Mischphasen mit elastischen Eigenschaften. Die Elastizitat beruht auf einer chemischen oder physikalischen Vernetzung der Makromolekule. Die thermodynamischen Eigenschaften von chemisch vernetzten Gelen konnen durch Kombination von Quellungsgleichgewichtsmessungen mit Messungen der Entquellung oder des Quellungsdrucks ermittelt werden. Die in den statistischen Theorien auftretenden Strukturparameter; Netzwerkdichte v, Funktionalitat f, memory-Term η Strukturfaktor A und Volumenfaktor B, werden diskutiert, und es wird gezeigt, welche physikalischen Methoden zu ihrer Bestimmung angewendet werden mussen. Auf die grose Bedeutung der Herstellung von Modellnetzwerken wird hingewiesen. Einige Mesergebnisse an Polystyrol-Gelen werden mitgeteilt. A survey on the thermodynamic properties of polymer gels, the actual state of the experimental investigations and the applicability of the statistical theories will be given. Polymer gels are elastic liquids. The elasticity is caused by a chemical or physical crosslinking of the macro-molecules. The thermodynamic properties of chemically crosslinked gels can be determined by combining swelling equilibrium measurements with measurements of deswelling or swelling pressure. The following structural parameters which appear in the statistical theories are discussed: crosslinking density v, functionality f, memory-term η, structure factor A and volume factor B. The physical methods for their determination will be stated. The importance of the formation of model networks will be pointed out. Some experimental results on gels of crosslinked polystyrene are reported.

1. The swelling characteristics of demembranated bovine corneal stroma were studied as a function of time and of the pH and ionic strength of the bathing solution. 2. Compared with other pH values, the stroma swelled least near pH 4. 3. In the pH range 6--10, increasing the pH resulted in an increase both in the rate of swelling and in the hydration reached in a given time. 4. At pH 2 and 4, a final constant value of hydration was attained. At higher pH values no such equilibrium was attained when the hydration of the tissue was followed for at least 100 hr. 5. The swelling at high pH values was consistent with the hypothesis that the Donnan-osmotic contribution is the major component of the swelling pressure. 6. The ionic strength dependence was complex. There was a general decrease of swelling with increase in the ionic strength (mu) until around mu = 0.1. The swelling at mu = 0.15 was greater than at mu = 0.1 and mu = 0.25. 7. The results were interpreted on the assumption that the Donnan-osmotic effect is the major component of the swelling pressure.

Summary Hydroxy Fe and A1 interlayers reduce the swelling of Na-montmorillonite in NaCl solutions. A deposit of sesquioxide round an aggregate or orientated flake of clay restricts swelling until the sesquioxide coating is broken by the swelling pressure of the clay. A1 is more effective than Fe. The effect of sesquioxides on the permeability to NaCl solutions of an alkali soil depends on the control of clay swelling in a manner expected from the above results. A sesquioxide coating round a soil aggregate stabilizes the structure until the coating is broken by the swelling pressure of the clay in the aggregate.

Summary Pressures exerted against a confining restraint by Na-montmorillonite in equilibrium with NaCl solutions were measured. The swelling pressures decreased with increasing NaCl concentration as predicted theoretically, but the rate of decrease was lower than calculated so that the ratio of observed to calculated pressure increased with increasing salt concentration. These larger swelling pressures could result from a higher activity of the ions between interacting clay particles compared with the ions in the neutral salt of the dialysis solution. It is then not necessary to postulate a non-osmotic force of repulsion.

Summary Acrylic polymers with hydrophilic groups (i.e., ethyl hydroxyl) may be prepared that convert to a soft elastic gel by absorbing water. Such a polymer has been applied to dentistry for use as an elastic lining material for dentures. A commercial product, Hydron, was used in this study. The linear expansion of this material after 520 hr of water immersion was found to be 20.4%. Hardness was found to decrease from 15.7 KHN for the dry polymer to 1.5 KHN at 19% absorbed water content. The swelling pressure was measured and found to reach a maximum value of 157 psi after 204 hr of water immersion. The Young’s modulus was found to decrease from a value of 295,300 psi to 290 psi with 19% absorbed water content. Values were determined on intermediate water contents for the properties studied.

Die Vorgange wahrend der Spannungsriskorrossion sind bei Metallen und bei Kunststoffen aus langen Kettenmolekulen wesentlich verschieden. Die innere Beweglichkeit der Kettenmolekule erlaubt es, vor allem in Gegenwart von Quellmitteln oder bei erhohter Temperatur innere Spannungen abzubauen und unter geeigneten Bedingungen Schwachstellen auszuheilen und damit die Neigung zur Risbildung erheblich zu vermindern. Es werden Modellvorstellungen besprochen, welche die drei Hauptwirkungen eines Netzmittels erklaren, namlich die Erhohung der Kerbspannung durch den von der Oberflachendiffusion in Mikrospalten herruhrenden momentanen Quelldruck, die Zeit erfordernde Schwachstellendiffusion, verbunden mit Mikrofliesen bzw. Mikroorientierung und die noch langsamere Diffusion zwischen die einzelnen Molekulketten. Anschliesend wird eine Reihe von unter ganz verschiedenen Bedingungen durchgefuhrten Versuchen geschildert und an Hand der obigen Modellvorstellungen diskutiert. Model conceptions and tests concerning stress corrosion cracking in high-polymer substances The Phenomena during stress corrosion cracking differ greatly as between metals and plastics consisting of long-chain molevor allem in Gegenwart von Quellmitteln the chain molecues, especially in the presence of swelling agents or at high temperatures, internal stresses can be reduced and weak points can, under suitable conditions, heal so that the crack formation tendency is considerably reduced. Certain model conceptions are discussed which explain the three principal effects of a wetting agent, viz. the increase in the notch stress due to the momentary swelling pressure caused by surface diffusion in microfissures; the long-time diffusion through weak zones connected with micro-flows or micro-orientation, and the even slower diffusion between the individual molecule chains. Finally, a number of tests carried out under entirely different conditions are described and discussed with the aid of the model conceptions referred to above.