Free Volume Space Research Articles

Dynamics of Water Sorption to Nanopores of Polymer Biomaterials

ABSTRACT Gravimetric studies of the kinetics of water sorption from air of various water activities by chitosan of different deacetylation degrees (and molecular weights) and chitosan/hydroxypropyl cellulose blends were conducted. Analysis of the presented results has shown a clear effect of the deacetylation degree of chitosan and the presence of hydroxypropyl cellulose in chitosan blends on the process rate. The character of sorption curves and calculated values of diffusion coefficients of water have shown that the higher chitosan deacetylation (and higher Mw) the worse are its sorptive properties. The observed effect is explained by a rising ordering of molecular chains leading to an increase of structural packing. Modification of the chitosan structure in blends has been reflected in their sorptive properties which depend on the weight fraction of hydroxypropyl cellulose and water activity. Good compatibility of the components, due to the presence of hydrogen bonds between specific groups (hydroxyl, amide) of chitosan and hydroxypropyl cellulose chains, causes an increase of molecular packing and observed decrease of water diffusivity. Assuming a capillary structure of free volume space of nano size, the total volume of the pores was calculated as a function of deacetylation degree of chitosan and weight fraction of HPC in chitosan blends. Curves of sorption isotherms show sigmoid shape which was discussed on the basis of GAB multilayer absorption theory.

Molecular-level free volume as a crucial complementary factor affecting miscibility and nanoscopic homogeneity of polyarylate/poly(vinyl chloride) blends

Molecular-level miscibility and scale of mixing were characterized and evaluated for three model blends of polyarylates having structural variants with PVC through cross polarization/magic-angle spinning (CP/MAS) 13C nuclear magnetic resonance (NMR) spectroscopy. From this study, we found that the polyarylate with sulfonyl central connector and tetramethyl substitutions on bisphenol rings (shortly, TMBPS-PAr) was nanoscopically miscible with PVC as homogeneously mixed down to a scale of ∼2.3 nm. In contrast, the structurally similar polyarylate, just in absence of tetramethyl substitutions from TMBPS-PAr, (BPS-PAr) was partially mixed with PVC at a homogenization scale of at least ∼27–32 nm, regardless of almost identical specific intermolecular interaction relative to TMBPS-PAr. In the case of polyarylate with isopropyl central connector other than the sulfonyl (TMBPA-PAr) was found to be completely immiscible with PVC, despite the presence of tetramethyl substitutions, due to the lack of polar sulfonyl groups that is known to promote mixing. These observations, in conjunction with the structural combinations of polyarylates, suggest the need to seek another complementary key parameter to promote miscibility and nanoscopic homogeneity in addition to the specific interaction. From the results of the positron annihilation analysis (PALS) on the intermolecular free volume through the entire composition ratio, the TMBPS-PAr/PVC blend resulted in a larger negative deviation of the ortho-positronium ( o-Ps) pick-off lifetimes ( τ 3) and the free cavity sizes ( R) from linear additivity of those parameters of component polymers compared to the BPS-PAr/PVC blend. The larger negative deviation was interpreted to be a higher/greater contraction of free space and more tightly packing of molecular chains in TMBPS-PAr/PVC upon mixing irrespective of similar specific intermolecular interaction between two blend systems, which shows good agreement with the results of densities with blend compositions. Recognizing that the only structural variation between TMBPS-PAr and BPS-PAr was tetramethyl substitutions and that TMBPA-PAr/PVC was completely immiscible despite the tetramethyl substitutions, the combined results obtained from NMR and PALS lead to rationalize additional effects of the molecular free volume space created by the tetramethyl groups on the good miscibility of the blends under the circumstance when enough specific intermolecular interaction existed upon mixing.

Effect of dendritic architecture on localized free volume of poly(ether ketone)s as probed by positron annihilation spectroscopy

Model poly(ether ketone)s (PEKs) with architectural variations were studied by positron annihilation lifetime spectroscopy (PALS) to estimate the average void sizes on a sub-nanometer scale, in conjunction with the hyperbranched (H-), the linear (L-), and their 50:50 block combination (HLH-) structures. The PALS distribution confirmed the unique molecular architecture of the hyperbranched polymer, consisting of an interior cavity space formed by loosely linked core and chain ends of relatively tighter free volume space.

The relationship between gas transport properties and the histology of apple

AbstractThe relation between skin resistance to gas diffusion, diffusivity and several histological characteristics of apple cvs Braeburn and Jonica was investigated. Large discrepancies were found between the skin resistance values measured by the efflux method and a diffusion method. It is believed that these discrepancies are due to the invalidity of Graham's law in tightly packed tissue, the existence of internal gas gradients and the types of tissue measured in the two methods. The differences between cultivars in diffusivity of O2 and CO2 in the same tissue were related to differences in intercellular space volume and cell size. The spatial pattern of the diffusivity of oxygen and carbon dioxide could be linked to the number of cells, the cell area, the cell perimeter and the internal free space volume. The considerably lower diffusivity in the skin was believed to be caused by both the skin and the very dense tissue of the outer cortex. Changes in diffusivity during storage coincided with changes in the amount of intercellular space and in the shape of the cells. Copyright © 2004 Society of Chemical Industry

Spatial Openness as a Practical Metric for Evaluating Built-up Environments

This paper reports on a primary metric tool developed in a collaboration between an architecture researcher and a computer science researcher. The development of this tool emerged from the concept that the spatial openness (SO)—the volume of free space measured from all possible observation points—is an important quality indicator of alternative spatial configurations within given constraints; this concept is based on the idea that the geometry and morphology of the built-up environment influence perception. Previous work showed that comparative SO measurements in alternative spatial configurations are correlated with the comparative perceived density, and in particular that a higher value of SO indicates a lower perceived density. We present a feasible 3D computational method for measuring SO and demonstrate its potential use in the design process. The SO metric is a step towards the development of quantitative comparative evaluation of building shapes and spatial configurations related to the 3D observation of open space.

Factors affecting skin resistance measurements in pipfruit

The accuracy and applicability of different methods for estimating resistance to gas diffusion through the analysis of the efflux of preloaded inert gas out of a fruit were critically assessed. The inert gas neon was introduced as a good replacement for the non-inert gas ethane. A sensitivity analysis was carried out to determine the importance of the different parameters and indicated the importance of the internal free space volume and of the fruit surface area. Experiments with fruit of two apple and two pear cultivars confirmed that the results obtained with non-linear regression were more accurate. The largest resistance to gas diffusion was found in ‘Doyenné du Comice’ pears, followed by ‘Conference’ pears and ‘Braeburn’ apples, and the lowest value was found for ‘Jonica’ apples. Storage duration did not influence the resistance to gas diffusion except for ‘Doyenné du Comice’ pears where a significant increase in resistance to gas diffusion during storage was found. Harvest date had no influence on resistance to gas diffusion.

The overlap volume in hard spheres under shear

The Widom test particle method was used to estimate the overlap volume for hard disks under shear flow. The volume of free space which can house an additional particle without overlap with other particles will differ from its equilibrium value because of the distortion of the solvation shell of every particle under the impact of shearing motion. In this way the overlap volume unambiguously characterizes the structure of nonequilibrium systems. The probability of finding voids with necessary sizes decreases with the shear rate as one might expect. Owing to the technical limitation inherent in the method the economically attainable shear rates and densities produced only small effects. Under certain reasonable assumptions the calculated nonequilibrium overlap volumes can be related to a nonequilibrium generalization of the chemical potential. We discuss this possibility.

Free-space optical mesh-connected bus networks using wavelength-division multiple access

A novel optical free-space mesh-connected bus interconnect network architecture is proposed. A mesh-connected bus [IEEE Trans. Comput. C-30, 264-273 (1981)] is known to have the capability of interconnecting, with a three-stage switching, N nodes with a power distribution loss proportional to √N and is therefore advantageous for networking a large number, say over 1000, of communicating ports. Based on conventional space-invariant optical components in a compact and efficient geometry, the proposed optical mesh-connected bus system concept can be used to build either free-space optical interconnect links for parallel processing applications or central switching systems for local or global lightwave communication networks. The proposed architecture lends itself to networking under both the wavelength-division multiple access and other multiple-access environments. In this paper, based on the wavelength-division multiple-access environment, various optical system implementation and performance issues are discused and parameters are analyzed. It was found that by use of a reasonably compact three-dimensional free-space volume, more than 100,000 dispersion-limited communication nodes at a uniform channel spacing of 0.75 nm can be linked with a moderate power distribution loss of 28 dB. Some preliminary optical wavelength-division multiple-access mesh-connected bus experiments based on a 27 × 27 panchromatic optical source array were performed to confirm the operational principle of the proposed concept.

Internal Pressures, Hard Core and Free Space Volumes and Boltzmann's Rule

Abstract Two fundamental relationships describing natural phenomena are posited to be functions of the free space in which atoms and molecules are confined and interact. These relationships are the Boltzmann energy distribution principle and the equation of state. In both cases the free space is that space available to the centers of mass of the atoms and molecules as they move randomly in translational motion. The hard core volume of atoms and molecules is not available for translational motion of their centers of mass and is excluded from the volume function in both Boltzmann's principle and the equation of state. Only in this way is it possible: 1) to apply Boltzmann's principle to the distribution of atoms or molecules between the two energy states of two phases in equilibrium; solid-gas, liquid-gas or solid-liquid and 2) to apply the equation of state to the gas, liquid or solid phase in order to determine the internal pressure exerted by the translational motion of atoms or molecules and to deduce the internal tension in the cohesion between atoms or molecules. These relationships are applied to water for the determination of the molar free space and molar hard core volumes of pure water.

Increasing Salt Tolerance of Plants Through Cell Culture Requires Greater Understanding of Tolerance Mechanisms

Despite numerous attempts, increasing the salt tolerance of cultured cells has rarely led to increased salt tolerance in regenerated plants. Clearly the role of cultured cells in selecting for salt tolerance needs reappraisal. Although the relationship between salt tolerance of cultured cells and whole plants is crucial to the use of cultured cells in selecting for increased salt tolerance, it is not understood, and neither are the mechanisms of salt tolerance in cultured cells understood. Our understanding of salt tolerance in cultured cells has been limited mainly by poor methodology, particularly failure to consider the large free space volume and the effect of high NaCl on the various phases of culture growth. Further, there has been a reluctance to search for mechanisms and test hypotheses. The relationship of salt tolerance in cultured cells and whole plants needs to be studied since much of the tolerance of whole plants is associated with their integrated functioning. Furthermore, cultured cells grow slowly and have different hormonal, osmotic and nutritional environments from cells in whole plants. Selection of cultured cells may be more productive if focused on specific cell-based physiological traits (such as Na+ accumulation, turgor regulation or tolerance to high Na+ : Ca2+) rather than on tolerance to high NaCl only. Expression in whole plants of traits in cultured cells also needs to be studied.

Migration of Cesium, Strontium and Cobalt in Water-Saturated Concretes

ABSTRACTDiffusivities of Cs, Sr and Co were measured in several kinds of water-saturated concretes. The measured penetration profile of every tracer was composed of two parts. Those were a steep slope near the surface and a gradual slope in the deeper part. This profile was successfully explained by considering two diffusion paths in concrete. One diffusion path was possibly fissure with a width of a few microns and another was network of submicron pores. The volume of submicron pores was approximately 90% of the total free space volume in every concrete. The orders of magnitude of apparent diffusivities for all tracers were 10−12–10−11 m2/s through the fissure and l0−16–10−15 m2/s through the network of pores. The difference between the diffusivities of the two paths is thought to be caused by small geometrical factor of the network of submicron pores.

High-resolution low-voltage electron optical system for very large specimens

This article introduces an unconventional electron optical probe forming system which is particularly suitable for low beam voltages and very large specimens, such as semiconductor wafers which also require a large angle tilting. The system can produce an electron probe of less than 20 Å for a nontilting specimen at 1-kV beam voltage with a working distance of 2.5 mm. The particular design allows a large volume of free space below the specimen which may be used to accommodate a complicated transporting mechanism.

Cation exchange in isolated xylem cell walls of tomato. I. Cd2+ and Rb+ exchange in adsorption experiments.

Purified xylem cell walls were prepared from isolated xylem bundles of tomato (an inbred line of Lycopersicon esculentum Mill, cv. Tiny Tim). Adsorption and exchange experiments were carried out with 115 Cd2+ , 82 Rb+ and 82 Br- . The application of γ-ray spectroscopy permitted the simultaneous measurement of several ions applied together. The cell-wall water volume was shown to be independent of the external pH and solution ionic strength, possibly due to the presence of lignin. The Donnan Free Space (DFS) volume could be determined as a constant 0.15 dm3 per kg cell-wall dry weight. Consequently, the total cell-wall cation exchange capacity (CEC) could be estimated based on the DFS volume, and amounted to approximately 1000 mol m-3 negative charges. The results of Cd2+ -Rb+ exchange experiments indicated an apparent CEC value of about 350-450 mol m-3 DFS, at external pH ∼ 4. These data are in agreement with earlier reports on xylem wall CEC, and indicate the weak acid characteristics of the charge groups. The rational selectivity coefficient RCdRb , of the cell wall was shown to depend on external ion fractions and ionic strength, with a maximum RCdRb of 450 at ionic Cd2+ fraction near 0.3, based at the smallest experimental ionic strength of the external solution. The adsorption of Cd2+ , applied at relatively high concentrations, was shown to be stimulated by simultaneous application of high Rb+ concentrations.

Apparent free space and cell volume estimation: A non-destructive method for assessing the growth and membrane integrity/viability of immobilised plant cells

Pre-existing methods for measuring cell or organelle volume based on the selective permeability of biological membranes have been modified to make them suitable for determining the intracellular volume of immoblised cells. When a freely permeable substance (e.g. tritiated water) and an impermeable substance ((14)C labelled mannitol is often suitable) are mixed with an immobilised cell culture, the two substances are diluted to different degrees. The extent of the difference allows the total intracellular volume of intact cells to be calculated. This volume is shown to be a useful parameter for assessing cell growth. The application of the method to follow membrane integrity and cell viability is also discussed.

The Pathway of Radial Transfer of Photosynthate in Decapitated Stems of Phaseolus vulgaris L.

C)Sucrose was found to be the predominant component of the 14C-photosynthates that accumulated in the free space of decapitated stems of P. vulgaris plants. The 14C-photosynthates appeared to occupy the entire free-space volume of the stems at total sugar concentrations in the range of 3-12 mM. The free-space sugar levels were found to rapidly decline once photosynthate transfer to the stems was halted. Moreover, it was found that estimates of the rate of in vitro sucrose uptake by the stems could account fully for the decline in free-space sugar levels. Overall, the evidence indicated that at least part of the radial pathway of photosynthate transfer in bean stems involved the stem apoplast. It is tentatively proposed that, based on cell and tissue distribution of 14C-photosynthates, the apoplastic pathway extends from the membrane boundary of the sieve element/companion-cell complex to all other cells of the stem.

Mercury pressure over HgTe and HgCdTe in a closed isothermal system

The solid-vapor equilibrium kinetics over HgTe and the mercury-vapor pressure evolution over HgTe in the presence of CdTe are studied by means of mass-loss measurements. For the first case, a theory is given relating the mercury pressure in an isothermal closed system to the mercury vacancy and interstitial concentrations in solid HgTe, the sample-volume–to–free-volume ratio as well as the equivalent pressure of mercury added in excess. In the simplest case—no mercury in excess, no interstitials—it is found that the mercury pressure first increases as the square root of time, before reaching an equilibrium value. At all times the pressure is proportional to the square root of the sample–to–free-space volume ratio. Experiments, conducted at 550 °C, confirm this behavior as well as the relation with the ’’excess mercury pressure’’. The diffusion coefficient of mercury vacancies in HgTe is estimated to be 8×104 μ2/h. For HgTe in the presence of CdTe, equilibrium cannot be reached because of material transport from HgTe to CdTe. The mercury pressure is determined by two main phenomena: outdiffusion from HgTe, as studied above, and diffusion into CdTe and the solid solutions formed on it by the material transport. For a given time, the experimental variations of the mercury pressure with the different parameters are formally similar to the preceding one (HgTe case). The analysis of the pressure evolution with time shows that the mercury pressure passes through a maximum which is experimentally verified.

Water Pathways in Higher Plants

The technique for studying the pathways of water movement described, in the first paper of this series has been applied to the transpiration stream in the roots of higher plants. Free space is confined to the cell walls except in flooded tissue where intercellular spaces are also included. Errors involved in free-space estimates are discussed and free-space volumes of 5.4 per cent have been obtained for wheat root cortex and 4.1 per cent for carrot xylem parenchyma. The main water-absorbing regions of roots begin immediately behind the elongating zone, where the first xylem elements are fully differentiated, and end when the endodermis undergoes secondary wall development. In the cortex the transpiration stream is located mainly in the cell wall. Calculations indicate that the symplastic pathway is of only minor importance in transpiring plants. At the endodermis the free-space pathway is blocked by the Casparian strip and all water and solute entering the stele must pass through the lumen of the endodermal cells. The permeability of individual endodermal cells varies considerably both between cells of the same species and between those of different species. Once inside the endodermis, the transpiration stream returns to the cell-wall pathway until it reaches the xylem vessels where it enters the lumen of the mature xylem elements.

Softener absorption by regenerated cellulose. Uptake from 10% aqueous glycerol

AbstractThe softener content of regenerated cellulose film (gel film) in equilibrium with aqueous glycerol solution was found to be determined primarily by only two factors: the softener concentration of the solution and the volume of free space within the gel film. Volume changes of film in contact with 10% glycerol solutions are negligible. Preferential uptake of glycerol as the solution passes into the film is, at most, slight, amounting to no more than 0.04% at the concentration used. No evidence was found for a large enrichment within the gel film, as has been postulated, or for adsorption of glycerol on cellulose chains. The system, cellulose‐glycerol‐water, appears to be a polymer‐liquid mixture brought to equilibrium principally by diffusion. It appears that at 10% concentration, glycerol and probably other organic compounds are taken in by gel film by a diffusion process in which the free water in the film is replaced by solution without appreciable enrichment or change in volume. Water contained in the interchain spaces of cellulose is simply exchanged for softener solution. The free volume of the film as determined by the cellulose structure and the degree of crystallinity remains essentially unchanged on softener uptake at the softener concentration studied.

Aphis Migration and the Efficiency of the Trapping Method

Reproducible results were obtained when adhesive traps for aphides were placed at the same height in different parts of a potato field. The total catches in different localities in different seasons can therefore justifiably be compared. During the summer dispersal flights, different species flew at different heights, so traps at one height only are not suitable for comparing the relative abundance of different species. There was less variation in numbers caught on traps at 3–4 ft. above the ground than on traps at 5–6 ft. or at ground‐level.During the first fortnight of July an average of 200 aphides, 1.6% of which were Myzus persicae, was caught on traps in the position of potato plants. Most of these were not potato aphides, but it is suggested that some of them might act as vectors of potato viruses. The number of aphides caught was roughly proportional to the volume of free air space around the traps, and as the foliage increased in density the numbers caught on lower traps decreased in proportion.Wind‐speed records within and above the crop are discussed and it is shown that conditions are often suitable for voluntary aphis flight in and near the crop on relatively windy days. Records of catches on the half‐traps facing the wind and on the other halves showed that voluntary flight decreased with increasing height.Brilliant yellow traps, coated with adhesive grease, caught more aphides than white traps, which in turn caught more than black.