Growth In Pores Research Articles

Macromolecular shape and interactions in layer-by-layer assemblies within cylindrical nanopores

Layer-by-layer (LbL) deposition of polyelectrolytes and proteins within the cylindrical nanopores of anodic aluminum oxide (AAO) membranes was studied by optical waveguide spectroscopy (OWS). AAO has aligned cylindrical, nonintersecting pores with a defined pore diameter d0 and functions as a planar optical waveguide so as to monitor, in situ, the LbL process by OWS. The LbL deposition of globular proteins, i.e., avidin and biotinylated bovine serum albumin was compared with that of linear polyelectrolytes (linear-PEs), both species being of similar molecular weight. LbL deposition within the cylindrical AAO geometry for different pore diameters (d0 = 25–80 nm) for the various macromolecular species, showed that the multilayer film growth was inhibited at different maximum numbers of LbL steps (nmax). The value of nmax was greatest for linear-PEs, while proteins had a lower value. The cylindrical pore geometry imposes a physical limit to LbL growth such that nmax is strongly dependent on the overall internal structure of the LbL film. For all macromolecular species, deposition was inhibited in native AAO, having pores of d0 = 25–30 nm. Both, OWS and scanning electron microscopy showed that LbL growth in larger AAO pores (d0 > 25–30 nm) became inhibited when approaching a pore diameter of deff,n_max = 25–35 nm, a similar size to that of native AAO pores, with d0 = 25–30 nm. For a reasonable estimation of deff,n_max, the actual volume occupied by a macromolecular assembly must be taken into consideration. The results clearly show that electrostatic LbL allowed for compact macromolecular layers, whereas proteins formed loosely packed multilayers.

Hydrate formation and growth in pores

Gas hydrates consist of guest gas molecules encaged in water cages. Methane hydrate forms in marine and permafrost sediments. In this study, we use optical, mechanical and electrical measurements to monitor hydrate formation and growth in small pores to better understand the hydrate pore habit in hydrate-bearing sediments. Hydrate formation in capillary tubes exposes the complex and dynamic interactions between nucleation, gas diffusion and gas solubility. The observation of hydrate growth in a droplet between transparent plates shows that the hydrate shell does not grow homogeneously but advances in the form of lobes that invade the water phase; in fact, the hydrate shell must be discontinuous and possibly cracked to justify the relatively fast growth rates observed in these experiments. Volume expansion during hydrate formation causes water to flow out of menisci; expelled water either spreads on the surface of water-wet substrates and forms a thin hydrate sheet, or remains next to menisci when substrates are oil-wet. Hydrate formation is accompanied by ion exclusion, yet, there is an overall increase in electrical resistance during hydrate formation. Hydrate growth may become salt-limited in trapped water conditions; in this case, aqueous brine and gas CH4 may be separated by hydrate and the three-phase system remains stable within the pore space of sediments.

Modeling Microbial Dynamics in Heterogeneous Environments: Growth on Soil Carbon Sources

We have developed a new kinetic model to study how microbial dynamics are affected by the heterogeneity in the physical structure of the environment and by different strategies for hydrolysis of polymeric carbon. The hybrid model represented the dynamics of substrates and enzymes using a continuum representation and the dynamics of the cells were modeled individually. Individual-based biological model allowed us to explicitly simulate microbial diversity, and to model cell physiology as regulated via optimal allocation of cellular resources to enzyme synthesis, control of growth rate by protein synthesis capacity, and shifts to dormancy. This model was developed to study how microbial community functioning is influenced by local environmental conditions in heterogeneous media such as soil and by the functional attributes of individual microbes. Microbial community dynamics were simulated at two spatial scales: micro-pores that resemble 6-20-μm size portions of the soil physical structure and in 111-μm size soil aggregates with a random pore structure. Different strategies for acquisition of carbon from polymeric cellulose were investigated. Bacteria that express membrane-associated hydrolase had different growth and survival dynamics in soil pores than bacteria that release extracellular hydrolases. The kinetic differences suggested different functional niches for these two microbe types in cellulose utilization. Our model predicted an emergent behavior in which co-existence of membrane-associated hydrolase and extracellular hydrolases releasing organisms led to higher cellulose utilization efficiency and reduced stochasticity. Our analysis indicated that their co-existence mutually benefits these organisms, where basal cellulose degradation activity by membrane-associated hydrolase-expressing cells shortened the soluble hydrolase buildup time and, when enzyme buildup allowed for cellulose degradation to be fast enough to sustain exponential growth, all the organisms in the community shared the soluble carbon product and grew together. Although pore geometry affected the kinetics of cellulose degradation, the patterns observed for the bacterial community dynamics in the 6-20 μm-sized micro-pores were relevant to the dynamics in the more complex 111-μm-sized porous soil aggregates, implying that micro-scale studies can be useful approximations to aggregate scale studies when local effects on microbial dynamics are studied. As shown with examples in this study, various functional niches of the bacterial communities can be investigated using complex predictive mathematical models where the role of key environmental aspects such as the heterogeneous three-dimensional structure, functional niches of the community members, and environmental biochemical processes are directly connected to microbial metabolism and maintenance in an integrated model.

Porosity evolution and crystallization-driven fragmentation during weathering of andesite

[1] A 10 m thick andesitic sill intrusion from the Neuquen Basin, Argentina, shows spectacular examples of spheroidal weathering and Liesegang banding. The Liesegang patterns demonstrate how andesite blocks, initially cut out by a preweathering joint set, are subdivided by fractures formed during the spheroidal weathering process. The stresses that cause fracturing originate from the growth of ferrihydrite and calcite in the pore space of the andesite, partly at the expense of original ilmenite, amphibole, and plagioclase. The porosity evolution and fracture formation during progressive weathering was characterized by scanning electron microscopy studies, X-ray computed tomography, and He- and Hg-porosimetry. Fresh andesite has a porosity of approximately 8%, and a major fraction (>80%) of the pore volume is composed of pores less than 10 μm in diameter. The extent of pore filling during weathering increases with pore size. Pores more than 100 μm are almost completely filled by an intimate intergrowth of calcite and ferrihydrite, whereas pores less than 10 μm are filled less than 50%. The fracturing associated with spheroidal weathering is caused by mineral growth in the largest pores, which account for 10%–20% of the total porosity. The periodic precipitation of the weathering product to form Liesegang bands indicates a significant supersaturation threshold before nucleation commences. The increase in the weathering product growth rate with increasing size is therefore most likely due to higher nucleation probabilities in larger pores.

メタンハイドレートを胚胎する砂質堆積物の特徴とメタンハイドレート胚胎メカニズムへの影響

Methane hydrate-bearing sediments taken by a Pressure Temperature Core Sampler (PTCS), were recovered from the NE-Nankai Trough to clarify the accumulating mechanisms whereby methane hydrate accumulates in pore spaces. The sediments were of the sand and mud alternation layer, which were turbidities and hemi-pelagic mud, respectively. Their sediment features such as grain size, porosity, and methane hydrate saturation of pore spaces were analyzed systematically. Relationships among grain size distribution, Bouma's sequence and hydrocarbon gas volume produced by methane hydrate dissociation were confirmed, thus we understood the correspondence of the features of turbidities features and methane hydrate saturation; i.e., we understood that the part of high methane hydrate saturation had a porosity of 50-55%, median of 1.9-3.3φ, and grain sorting of from -1.4 to -0.4. These features indicate the lower section of turbidite called as Ta and/or Tb. Other sections of turbidite had small amounts of methane hydrate. From these results, we estimated that only permeable sections could maintain the accumulation of methane hydrate from first to last stage. If their pores had been filled with gas-saturated water and the pressure/temperature condition was sufficient for methane hydrate, the methane hydrate would precipitate homogeneously in sediments from its initial accumulation. However, methane hydrate precipitation reduces permeability because methane hydrate growth in pores causes a reduction of pore volume. During accumulation, it is inevitable that gas-rich fluid could not reach into low permeable layers, although it could still be supplied into high permeable layers. This mechanism does not need any cap rock or some trap system in sediments, and it is quite a different mechanism from conventional oil and gas accumulation.

Biomimetic polymer/apatite composite scaffolds for mineralized tissue engineering.

The material surface must be considered in the design of scaffolds for bone tissue engineering so that it supports bone cells adhesion, proliferation and differentiation. A biomimetic approach has been developed as a 3D surface modification technique to grow partially carbonated hydroxyapatite (the bonelike mineral) in prefabricated, porous, polymer scaffolds using a simulated body fluid in our lab. For the rational design of scaffolding materials and optimization of the biomimetic process, this work focused on various materials and processing parameters in relation to apatite formation on 3D polymer scaffolds. The apatite nucleation and growth in the internal pores of poly(L-lactide) and poly(D,L-lactide) scaffolds were significantly faster than in those of poly(lactide-co-glycolide) scaffolds in simulated body fluids. The apatite distribution was significantly more uniform in the poly(L-lactide) scaffolds than in the poly(lactide-co-glycolide) scaffolds. After incubation in a simulated body fluid for 30 d, the mass of poly(L-lactide) scaffolds increased approximately 40%, whereas the mass of the poly(lactide-co-glycolide) scaffolds increased by about 15% (see Figure). A higher ionic concentration and higher pH value of the simulated body fluid enhanced apatite formation. The effects of surface functional groups on apatite nucleation and growth were found to be more complex in 3D scaffolds than on 2D films. Surprisingly enough, it was found that carboxyl groups significantly reduced the apatite formation, especially on the internal pore surfaces of 3D scaffolds. These findings are critically important in the rational selection of materials and surface design of 3D scaffolds for mineralized tissue engineering and may contribute to the understanding of biomineralization as well.SEM micrograph of a poly(L-lactide) scaffold.

Fabrication of Y-type zeolite films by electrophoretic deposition

In the present work, electrophoretic deposition (EPD) has been applied to formation of precursor films consisting of Y-type zeolite particles for fabrication of desired films. The fragile precursor films electrophoretically formed were transformed into continuous dense bodies by hydrothermally treating in reaction mixtures controlled with molar ratio of Na 2O:Al 2O 3:SiO 2:H 2O=8:1:12:360. There were no changes in crystalline phase of Y-type zeolite before and after the hydrothermal treatments. From scanning electron microscopy (SEM) observations, the microstructural changes, i.e., densification of the precursor films, were considered to proceed in two reaction routes: one is secondary growth of the seed Y-type zeolite particles and the other is nucleation from reaction mixture followed by crystal growth in interparticle pores.

Salt damage in porous materials: how high supersaturations are generated

The current theory of crystal growth in pores has been further developed to include thermodynamics of real solutions for sodium sulfate and sodium chloride. This allows better quantification of the stresses developed by crystallization of these salts inside porous materials such as stone, brick or concrete. Results for sodium sulfate show that dissolution of its anhydrate produces supersaturations with respect to its decahydrate capable of generating tensile hoop stresses on the order of 10–20 MPa, largely in excess of the tensile strength of almost all stones. It also explains why, in the accelerated testing that involves cycles of impregnation and drying, all damage occurs during the impregnation and not the drying step. The situation in which crystallization is driven by evaporation is also discussed in light of understanding why sodium sulfate also induces more damage than sodium chloride during continuous capillary rise experiments. Results suggest that the classification of stone resistance to salt damage can change depending on the mode of supersaturation generation.

Relationships of soil microarthropod biomass with organic matter and pore size distribution in soils under different land use

Soil microarthropods were sampled every 3 months for 1 y at 10 sites in the northern Netherlands, varying in soil type and land use. Microarthropods were divided into seven functional groups and biomass-C ha −1 was calculated for the top 10 cm soil layer. The four quantitatively principal functional groups were: cryptostigmatic mites; non-crytostigmatic mites; predatory mites; and omnivorous collembola. Possible relationships between the mean annual biomass of these groups and soil type, land use or soil organic matter were studied. Microarthropod biomass was larger in sandy soil than in loamy and generally larger in meadows than in wheat fields; the mineral layer of forest soils being intermediate. Non-cryptostigmatic mite, omnivorous collembola and predatory mite biomass showed strong positive correlations. Cryptostigmatic mite biomass correlated with lower organic matter input quality, while omnivorous collembola and non-cryptostigmatic mites showed a positive correlation with the amount of input. Omnivorous collembola were negatively affected by a discontinuous input of organic matter to the soil. We found relationships between functional group biomass and either soil organic matter density fractions or soil pore size distribution only when the grassland sites were analyzed separately. Both analyses showed correlation patterns for cryptostigmatic mites to deviate from those of the other three main functional groups. Cryptostigmatic mites showed a positive correlation with the lightest organic matter density fraction, while the non-cryptostigmatic mites and omnivorous collembola were correlated to the heavier fractions. The cryptostigmatic mites correlated with the 6–90 μm pore size class, while the other three groups showed strong correlation to the 1.2–6 μm, as well as the largest (> 90 μm) pore size class. Both observations lead to the conclusion that omnivorous collembola and non-cryptostigmatic mites are related to fungal growth (in the largest pores and on the heavy organic matter fraction), while the cryptostigmatic mites show a more saprovorous feeding mode.

Porous Alginate-Poly(ethylene glycol) Entrapment System for the Cultivation of Mammalian Cells

A novel gel entrapment method has been developed where macropores are created within alginate beads to provide an environment for high-density growth of mammalian cells. The method takes advantage of an interaction between poly(ethylene glycol) (PEG) and alginate to provide a network of pores within the bead for growth while the surrounding alginate matrix retains the integrity of the bead and minimizes cell leakage. Hybridomas were grown to a density approaching 10(8) cells/mL of beads in this system, while conventional alginate restricted growth to a maximum of 2 x 10(7) cells/mL of beads. In addition, cell leakage was minimal even at high cell densities, which was not the case with the conventional alginate system. Study of the conventional system determined that cell growth was limited by the alginate matrix; increasing the alginate concentrations resulted in lower final cell densities. In contrast, the PEG-alginate system permits growth in pores so the alginate matrix serves only as a structural matrix for cells. The pore size can be varied as a function of PEG concentration (10-20 wt % PEG) to provide radially defined areas for cell growth and radial diffusion pathways for nutrients/products in the adjacent alginate matrix. Because the PEG-alginate entrapment process does not require additional chemical reactions or temperature changes, the system offers a simple alternative to attain high cell densities in an immobilized bead system. As an illustration of the concept, cells entrapped in this system were grown to high density in both batch and perfusion modes for the production of monoclonal antibodies. Using the suspension batch culture as the base case, the specific monoclonal antibody production rate increased 1.6-fold for the slower growing batch-immobilized culture and 3-fold for the immobilized perfusion culture.

Simulation of cluster growth in pores with diffusion interaction

We consider local effects of cluster growth in pores which are connected by diffusion interaction. Nucleation is mainly governed by the conditions (supersaturation) inside the cavity, whereas the growth of clusters results from the diffusion of free particles between the pores. A multivariate master equation of the problem is formulated, deterministic equations (reaction-diffusion equations) for the space- and time dependent cluster distribution are derived and solved by means of computer simulations.

Rules of Sandstone Diagenesis Related to Reservoir Quality: ABSTRACT

The reservoir quality of sandstone is almost entirely controlled by diagenetic events. The chemical and physical processes responsible for diagenesis are complex and they influence sand during all stages of burial and, in some basins, during subsequent uplift. Petrographic studies by many workers in the past 10 years provide the basis for formulating rules of sandstone diagenesis that help in predicting reservoir quality in different End_Page 1215------------------------------ formations. Most of the rules listed below are empirical, and causative factors are still poorly understood. The list is also not complete. 1. The detrital mineral composition of a sand predetermines 50-80% of its diagenetic history. 2. Porosity lost by compaction cannot be regenerated during subsequent diagenetic events. Sands with abundant ductile grains (clay clasts, fecal pellets, shale clasts, micaceous rock fragments) can lose much primary porosity from the mashing of these grains during compaction. 3. The loss of primary porosity through compactional deformation of clays and ductile grains takes place during burial of 8,000-10,000 ft (2,450-3,050 m); loss of porosity by compaction at greater depths is by pressure solution of detrital grains. 4. Pressure solution of quartz grains is enhanced by the presence of grain coatings of illite and to a lesser degree by chlorite. 5. Quartz cement has an affinity for the coarser, more permeable sands in a formation. However, it rarely fills all pores in a sandstone except in some coarser grained laminae or in quartzarenites. 6. Carbonate cement may have a patchy distribution in a bed, but it fills all pores to produce a nonporous rock where it is present. 7. Carbonate cement is the dominant or only cement in sands with abundant carbonate fossil fragments or carbonate rock fragments; the carbonate cement is derived from the sand. 8. Poikilotopic calcite cement is the result of cementation that progressed from widely spaced nucleation sites. 9. Kaolinite forms by the replacement of feldspar and to a lesser degree of muscovite and also by free-standing growth in both primary and secondary pores. 10. Kaolinite should be expected as a diagenetic mineral in feldspar-rich sands (arkose and subarkose) that are poor in volcanic rock fragments. 11. Chlorite and/or mixed-layer clay should be expected as a diagenetic mineral in sandstone with more than 10% volcanic rock fragments. 12. Chlorite and mixed-layer clay, because of their tendency to bridge pores and produce baffles in pores, can seriously reduce permeability. 13. Early formed illite, typically present as grain coatings, does not seriously reduce permeability; late-formed illite tends to bridge pores and produce baffles and seriously reduce permeability. 14. Micrite cement is formed in continental sands above the water table. 15. Opal cement is formed in continental sands above the water table in stratigraphic sections where volcanic ash beds are intercalated with sands. 16. Some degree of secondary porosity is to be expected in a sandstone. However, there are few clues at present to predict the degree of secondary porosity or the cleanliness of secondary pores produced. Many secondary pores are micropores within incompletely dissolved feldspar or rock fragments. The best secondary pores are produced by dissolution of carbonate cement and evaporite cement. 17. Secondary porosity develops chiefly at depths greater than 6,000 ft (1,830 m) in the Gulf Coast, but can persist to depths of 20,000 ft (6,100 m). After their generation, secondary pores undergo some destruction during subsequent deeper burial by infilling with late-diagenetic ferroan carbonate and/or kaolinite. 18. Sands that had the greatest permeability at the time of deposition will develop the best secondary porosity. The best permeability will be in the coarsest, well-sorted sandstones (except in quartzarenites, where the coarsest beds selectively may undergo complete cementation by quartz). End_of_Article - Last_Page 1216------------