Super-hydrophobicity fundamentals: implications to biofouling prevention

The theory of wetting on super-hydrophobic surfaces is presented and discussed, within the general framework of equilibrium wetting and contact angles. Emphasis is put on the implications of super-hydrophobicity to the prevention of biofouling. Two main lines of thought are discussed, viz. i) "mirror imaging" of the Lotus effect, namely designing a surface that repels biological entities by being super-hydrophilic, and ii) designing a surface that minimises the water-wetted area when submerged in water (by keeping an air film between the water and the surface), so that the suspended biological entities have a low probability of encountering the solid surface.     

Wetting control through topography and surface hydrophilic/hydrophobic property changes by coarse grained simulation

Abstract

The changes of wetting state of water droplet on the solid surface featuring pillared structures are quantitatively studied by Coarse Grained simulation. Our results demonstrate that wetting state changes with the different topography (surface roughness), and it depends on the intrinsic hydrophilic/hydrophobic property of surface as well. Only if the contact angle of water droplet on the smooth surface is larger than 93.13°, the wetting state translates from the Wenzel state to the Cassie state on the rough surface with certain pillar height and width, and the contact angle climb up to the highest point and then remain almost unchanged with the increasing of pillar height and the same pillar distance. However, the wetting state does not change if the contact angle on the smooth surface is 85.1° or less, no matter what pillar structure the surface has. Additionally, the contact angles will remain almost unchanged if the pillar height is higher than a certain value. Our simulation results provide a quantitative understanding about the wetting state of water droplet on solid rough surfaces, and the results show the wetting state can be controlled by combining rough structure design and hydrophilic/hydrophobic property change of surfaces.     

Two Algorithms for Defining Atoms and Molecules in Condensed Phases

Abstract

Two algorithms for defining single entities in condensed phase based on the calculation of a zero flux surface of the gradient of the electron density are proposed. First the two approaches are applied to a water molecule in a liquid system; the different behaviour of the two algorithms is graphically shown in the planar section of the molecular plane (i.c., HOH plane of the molecule analyzed). Next, using the two algorithms for partitioning electron density, the average molecular dipole moment of the water molecule in liquid phase is calculated averaging over several configurations; analogies and differences with other methods are reported and their physical interpretation is discussed. There exist different approaches for calculating the zero flux surface (or equivalently the volume defined by such a surface); the two described in this work differ from the others because the calculation in both cases is straightforward (i.e., the surface is determined directly from the data corresponding to the electron density) and is characterized by a relatively short computational time.     

Flora of the Isle su Cardulinu (Southern Sardinia)

Abstract

The results of two years of collection in a small isle in the southern Sardinia are reported, consisting in a floristic list of 116 entities distributed in 96 genera and 41 families. The biological spectrum of this flora puts in evidence a typical Mediterranean environment, characterized by a marked summer dryness. The ratio: number of entities/surface of the studied site has been compared with that of other small southern Sardinian islands, resulting the highest value. This floristic aspect, as well as differences in the biological spectrum, is interpreted as the result of the presence in the area under study of a desultory link with the mainland, in form of a sandy isthmus. This seems important in breaking the biological balance of the small island.     

Wetting characterisation of silicon (1,0,0) surface

Water droplets on bare silicon surfaces are studied to examine the wetting behaviour as a function of the surface energy and to parameterise water–silicon interactions in order to recover the hydrophobic behaviour measured by experiments. Two different wetting regimes characterised by a critical interaction strength value are observed. At a threshold value of the water–silicon interaction parameter, water molecules start penetrating into the first layer of silicon surface under thermally vibrating walls, resulting in two distinct wetting behaviours. Fixed (cold) silicon walls do not exhibit the two different wetting characteristics. Size effects are studied for nano-scale droplets, and line tension influence is observed depending on the surface wettability. Decrease in the droplet size increases the contact angle values for the low wetting cases, while contact angles decrease for smaller droplets on the high wetting surfaces. Considering the line tension effects and droplet size, ?_Si–O for water–silicon interactions to recover the hydrophobic behaviour of silicon surfaces is estimated to be 12.5% of the value predicted using the Lorentz–Berthelot mixing rule.     

不同类型生物土壤结皮覆盖下风沙土的入渗特征及模拟

干旱荒漠区广泛分布的生物土壤结皮(BSCs)对土壤水分入渗过程有重要影响。以古尔班通古特沙漠南缘的BSCs为研究对象,基于野外采样与室内模拟实验等方法,探究藓类、地衣和藻等3种类型BSCs覆盖下沙土的入渗特征。结果表明:与无结皮覆盖的风沙土对照,3种类型BSCs均显著降低了沙土初渗速率,藓类结皮、地衣结皮、藻结皮覆盖下初渗速率降低幅度依次为36.10%、46.42%、50.39%;藓类结皮、地衣结皮(P0.05)和藻结皮(P0.05)均明显降低了沙土稳渗速率,降低幅度依次为16.50%、33.98%和35.92%;3种类型BSCs均限制了湿润锋在沙土的推进过程,表现为:藓类结皮、地衣结皮、藻结皮的渗漏时间分别为裸沙对照的2.13、3.04和2.98倍;各类型BSCs均减小了沙土累积入渗量,阻碍了沙土水分入渗,与裸沙对照相比,藓类结皮、地衣结皮、藻结皮的1 h累积入渗量分别降低16.10%、28.56%和26.56%。在实验条件下,Kostiakov模型最适用于模拟不同类型BSCs覆盖下土壤水分入渗过程,Horton模型模拟效果次之。     

Microcalorimetric studies on the lyophilic properties of pectic substances

The exothermic effects observed on wetting pectins with water and aliphatic alcohols were studied using a microcalorimeter.The heat released on wetting 1 g pectin with water was found to be 171 ± 7·5 J g^?1. It was experimentally established that 1 g of dry pectin exothermically bonded up to 0·57 g of water.By using the Gibbs-Helmholtz-Young equation which relates the heat released by wetting to the area of the wetted surface, it was estimated that the surface accessible to water in 1 g of pectin was 1·46 × 10³ m² g^?1. The heat of hydration was independent of the degree of esterification of the pectin. The experimental results revealed that there were about six molecules of energetically bonded water per monomer unit of pectin.A specific interaction between methanol and the methoxyl groups of pectin was observed on wetting pectins with methanol and dependence was established between the released heat and the degree of esterification. No similar dependence was reported for the remaining aliphatic alcohols.     

Interfacial free energies of intact and reconstituted erythrocyte surfaces: Implications for biological adhesion

Model cell surfaces consisting of phospholipids or phospholipids and the erythrocyte membrane glycoprotein glycophorin have been formed at an oil/water interface. Interfacial free energies have been estimated from surface wetting by both hydrophobic and hydrophilic test droplets on both the model surfaces and on intact erythrocytes. The use of a dense fluorocarbon oil to form the oil/water interface facilitates analysis by minimising surface deformation by the test drop. Hydrophobic test droplets (polar hydrocarbon oils) show increasing contact angles (decreasing wetting) with increasing hydrophilicity (decreasing interfacial free energy) of the model interface. Hydrophilic test droplets (phase separated aqueous polymer systems) show the opposite behaviour, spreading more as the interfacial free energy is decreased. Both systems give similar estimates of the interfacial free energy. Glycophorin reproduces the wetting properties of intact cell surfaces by reducing the lipid-water interfacial free energy from 5·10^?3 J·m^?2 to 1·10^?6 J·m^?2. From molecular considerations it is concluded that ‘cell surface free energy’ is an ambiguous term; its magnitude depends on the location of the interface in question. Thus, in a thermodynamic analysis of interactions at biosurfaces (such as cellular adhesion, chemotaxis or membrane fusion), the interfacial free energies may vary by more than three orders of magnitude depending on the location of the particular interface.     

Partial Sequence Analysis of the 5S to 18S rRNA Gene Region of the Maize Mitochondrial Genome

Measurements of the rate of imbibition by isolated cotyledons of soybean (Glycine max (L.) Merr cv Wayne) indicated that water uptake rates were slowed by low temperatures and by low initial moisture contents of the tissue. The role of water viscosity in the temperature effects on imbibition was examined, and a linear relation between imbibition rate and the reciprocal of viscosity was found only for seeds of very high initial moisture content. Adding solutes which lowered the surface tension, or increased the wetting ability of the water, yielded markedly increased rates of imbibition, especially for tissue of low initial moisture content. The data are interpreted as indicating a first component of water entry which is a wetting reaction influenced by the surface tension of the water, and a second component which resembles water flow through a porous matrix and is influenced by the water viscosity. We speculate that damage to soybeans during imbibition, such as in the case of chilling injury, may be particularly related to the initial wetting reaction rather than to the longer-term imbibitional rate.     

Radioiodination of extravesicular surface constituents to study the biocorona,cell trafficking and storage stability of extracellular vesicles

BackgroundExtracellular vesicles (EVs) are produced by all cell types and serve as biological packets delivering a wide variety of molecules for cell-to-cell communication. However, the biology of the EV extravesicular surface domain that we have termed EV ‘biocorona’ remains underexplored. Upon cell secretion, EVs possess an innate biocorona containing membrane integral and peripheral constituents that is modified by acquired constituents post secretion. This distinguishes EVs from synthetic nanoparticulate biomaterials that are limited to an adsorption-based, acquired biocorona.MethodsThe EV biocorona molecular constituents were radiolabeled with ¹²⁵I to study biocorona constituents and its surface dynamics. As example toolset applications, ¹²⁵I-EVs were utilized to study EV cell trafficking and the stability of the EV biocorona during storage.ResultsThe biocorona of EVs consisted of proteins, lipids, DNA and RNA. The cellular uptake of ¹²⁵I-EVs was temperature dependent and internalized ¹²⁵I-EVs were rapidly recycled by cells. When ¹²⁵I-EVs were stored in a purified state, they exhibited time and temperature dependent biocorona shedding and proteolytic degradation that was partially inhibited in the presence of serum.ConclusionThe EV biocorona is complex and dynamic. Radiolabeling of the EV biocorona enables a unique platform methodology to study the biocorona and will facilitate unlocking EV's full clinical translation potential.General significanceThe EV biocorona affects EV mediated biological processes in health and disease. Acquiring knowledge of the EV biocorona composition, dynamics, stability and structure not only informs the diagnostic and therapeutic translation of EVs but also aids in designing biomimetic nanomaterials for drug delivery.     

THE FRACTIONATION OF CLAY SIZED PARTICLES FROM THE WURAS DAM WATER PHASE

SUMMARY

The Coulter Counter has been employed with success to estimate the number and sizes of suspended particles in seawater. In the present study this method was applied to Wuras Dam, a turbid man made lake south of Bloemfontein.

High concentrations of larger clay sized particles occur in the inflow water as well as in the water of the dam proper. Fractionation of particles between ca 1 and 2 pm in diameter have been achieved, and a higher concentration of small sized particles (ca 1 μm) occurred in the dam water while the concentration of the larger particles (1,69 to 2,03 μm) was lower.

Surface area estimations were made for each size fraction. A considerable surface area (ca 163 m² m^?3) was associated with the investigated suspended particles in Wuras Dam. This might be of extreme importance for the physical, chemical and biological characteristics of the dam. The limnological importance of the suspended particles is briefly discussed.     

Rapid Recovery of Cyanobacterial Pigments in Desiccated Biological Soil Crusts following Addition of Water

We examined soil surface colour change to green and hydrotaxis following addition of water to biological soil crusts using pigment extraction, hyperspectral imaging, microsensors and ¹³C labeling experiments coupled to matrix-assisted laser desorption and ionization time of flight-mass spectrometry (MALD-TOF MS). The topsoil colour turned green in less than 5 minutes following water addition. The concentrations of chlorophyll a (Chl a), scytonemin and echinenon rapidly increased in the top <1 mm layer while in the deeper layer, their concentrations remained low. Hyperspectral imaging showed that, in both wet and dehydrated crusts, cyanobacteria formed a layer at a depth of 0.2–0.4 mm and this layer did not move upward after wetting. ¹³C labeling experiments and MALDI TOF analysis showed that Chl a was already present in the desiccated crusts and de novo synthesis of this molecule started only after 2 days of wetting due to growth of cyanobacteria. Microsensor measurements showed that photosynthetic activity increased concomitantly with the increase of Chl a, and reached a maximum net rate of 92 µmol m⁻² h⁻¹ approximately 2 hours after wetting. We conclude that the colour change of soil crusts to green upon water addition was not due to hydrotaxis but rather to the quick recovery and reassembly of pigments. Cyanobacteria in crusts can maintain their photosynthetic apparatus intact even under prolonged periods of desiccation with the ability to resume their photosynthetic activities within minutes after wetting.     

Marginal product pricing in the ecosystem.

Surface membrane biosynthesis and turnover is reviewed focusing mainly on the fate of cell surface constituents after they terminated their sojourn as part of a functional cell structure. The different experimental approaches to study this problem are described and original data are presented on the turnover of surface membrane constituents of chicken embryo cells in culture. It is proposed that as a consequence of surface membrane turnover, certain surface macromolecules are continuously shed from cells. The size and charge of these molecules was found to be identical to molecules released from cells by mild trypsin treatment. The term shedding is proposed for this process which is assumed to occur both in vitro and in vivo. Many systems in which shedding of cell surface constituents is clearly demonstrated or can be tentatively suggested are described. The biological significance of cell surface carbohydrate containing macromolecules and the possible role of these shed cellular entities is discussed.     

LEAF SURFACE WETNESS AND GAS EXCHANGE IN THE POND LILY NUPHAR POLYSEPALUM (NYMPHAEACEAE)

As part of a continuing study of the effects of leaf surface wetness on gas exchange, the occurrence of leaf surface wetting by dewfall and associated effects on photosynthesis were evaluated for floating and aerial leaves of the pond lily Nuphar polysepalum Engelm. Because of nighttime radiation exchange with a cold sky, high humidity, and the presence of adaxial stomata, we predicted that pond lily leaves would be particularly susceptible to wetting events such as dewfall. A substantial reduction in net photosynthesis (up to 20%) occurred for leaves that were experimentally misted to simulate leaf wetting by dewfall. Aerial leaves remained below dewpoint temperatures for long periods on clear nights. However, floating leaves rarely approached dewpoint temperatures at night because minimum nighttime temperatures of leaves were up to 10 C warmer than air temperature. Thus, floating leaves of N. polysepalum did not experience dew formation primarily because of strong thermal coupling to a substrate (water) that was much warmer than air temperature at night. This coupling to a warmer substrate prevented a potentially strong inhibition of photosynthetic CO₂ exchange the following morning.     

Flora Delle Argille e Dei Tufi di Civita di Bagnoregio (Alto Lazio)

Abstract

Flora of the clays and the tuffs of Civita di Bagnoregio (Upper Latium). — This work is the result of floristic research developed from 1968 to 1970 on tuffs and mainly on the clays of Civita di Bagnorcgio. After having summarily described the geo-ecological conditions, the author lists in all 489 entities. The biological spectrum of clays shows a high presence of Therophyta and a low percentage of Phanerophyta; on the contrary on the tuffs are present more Phanerophyta and less Therophyta; on the whole the flora is marked from the Emicryptophyta. Phytogeographical analysis indicates a prevalence of mediterranean elements. The author delineates moreover the most important floristic aspects, refering the frequentest entities and point out the intense anthropization wich has prevented the preservation of the woody formations, today completely away from clayey area.     

Further reading in geomicrobiology

Microbial volatilization of selenium (Se) may be an effective bioremediation technique to remove Se from dewatered sediments. In this laboratory study, soil management parameters (wetting and drying cycles, aeration, mixing, aggregate size, and water quality) were assessed for their influence upon Se volatilization. Selenium volatilization rates were higher under continuously moist conditions (—33 kPa) compared with wetting and drying cycles. After 6 months of incubation, a continuously moist seleniferous soil had lost approximately 21% of the Se inventory, whereas the same soil incubated under wetting and drying cycles had dissipated 7% of the total Se. Incubation under anoxia (N₂ atmosphere) increased evolution of dimethyl selenide (DMSe) 1.4‐fold compared with aerated conditions. When soil samples were incubated under static versus continuously mixed conditions, the latter treatment enhanced volatilization 1.8‐fold. This was attributed to increased availability of the Se to the methylating soil microbiota. The optimum aggregate size to promote volatilization of Se was 0.53 mm when compared to 0.15, 1, and 2 mm. The application of saline well water (7.5 dS m^‐1) over 6 months, compared with deionized water, had little effect on volatilization rates of Se from a highly saline (22 dS mr^‐1) seleniferous dewatered sediment. Each of these parameters should be considered in promoting volatilization of Se as a bioremediation approach in the cleanup of seleniferous sediments.     

La Flora Delle Gole di Popoli (Pescara)

Abstract

Flora of Popoli's gorges (Central Italy). — The results of floristic research developed from 1967 to 1969 at the Popoli's gorges (province of Pescara, in Abruzzo, Central Italy) are reported. Short accounts on the geographic position, on the geology and climate of the gorges are given, together with the floristic index of 696 entities, 4 of which are new for Abruzzo. For each species the biological and the phytogeographical categories are indicated; and for the whole of the flora the biological spectrum. This shows that this flora is a submediterranean one, with altitude influences. Critical remarks are developed about the taxonomy and distribution in the region of Abruzzo of several species wich looked particularly significant to the author.     

Dry under water: Comparative morphology and functional aspects of air‐retaining insect surfaces

Superhydrophobic surfaces prevent certain body parts of semiaquatic and aquatic insects from getting wet while submerged in water. The air layer on these surfaces can serve the insects as a physical gill. Using scanning electron microscopy, we investigated the morphology of air‐retaining surfaces in five insect species with different levels of adaptation to aquatic habitats. We found surfaces with either large and sparse hairs (setae), small and dense hairs (microtrichia), or hierarchically structured surfaces with both types of hairs. The structural parameters and air‐film persistence of these surfaces were compared. Air‐film persistence varied between 2 days in the beetle Galerucella nymphaea possessing only sparse setae and more than 120 days in the bugs Notonecta glauca and Ilyocoris cimicoides possessing dense microtrichia (up to 6.6 × 10⁶ microtrichia per millimeter square). From our results, we conclude that the density of the surface structures is the most important factor that affects the persistence of air films. Combinations of setae and microtrichia are not decisive for the overall persistence of the air film but might provide a thick air store for a short time and a thin but mechanically more stable air film for a long time. Thus, we assume that a dense cover of microtrichia acts as a “backup system” preventing wetting of the body surface in case the air–water interface is pressed toward the surface. Our findings might be beneficial for the development of biomimetic surfaces for long‐term air retention and drag reduction under water. In addition, the biological functions of the different air retention capabilities are discussed. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

The Effect of Canopy Wetting on Plant Water Status, CO2 Fixation, Ion Content and Growth Rate of 'Baccara' Roses

The effect of canopy wetting of rose (Rosa hybrida) plants on transpiration rate, stomatal resistance, plant water potential, ion concentration in leaves, and several growth parameters was investigated. Plants were grown in a greenhouse and their canopies were exposed to wetting cycles during the daytime. Canopy wetting decreased transpiration rate and increased diffusive resistance to water vapor transfer. Plant water potential was only slightly increased by wetting, mainly in the spring. Canopy wetting did not prevent the decrease in CO₂ fixation, which took place before midday when plant water potential dropped below – 10 bars during a rise in radiation intensity. The concentrations of Cl^? and Ca²⁺ decreased in wetted leaves, while the concentration of Na⁺ was increased and other cations were hardly affected. Canopy wetting inhibited growth rate of rose shoots and flower formation, and increased the average flower weight.