Effects of simulated acid rain on the surface tension of selected leaves

In this study the effect of simulated acid rain on the surface tension of leaves of selected crop plants is reported. The contact angle measurements of liquids (water and n-propanol mixtures) on various plant leaves (bean, mustard, lettuce, cress) showed that the acid rain effect can be investigated when analyses of the surface tension of leaves are estimated. Acid rain was found to give rise to a change in the polar surface tension of leaves, while the apolar surface tension was unaffected. This effect was strongest in bean leaves, which suggests that this is related to the polar surface tension of leaves.     

Interaction of polysilicic acid with monolayers of substances containing quaternary ammonium groups

The action of polysilicic acid on monolayers of a quaternary ammonium salt and a phospholipid spread on substrates of various pH values was studied. The films of benzyl dimethyl hexadecyl ammonium chloride were considerably affected above pH 2. No interaction was observed, at any pH, between silicic acid and dipalmitoyl phosphatidyl serine.The results support the existence of ionic interactions between dissociated silanol groups and tetra-alkylammonium groups. The involvement of hydrogen bonds is ruled out.     

Determination of dispersive and nondispersive components of the surface free energy of glass fibers

The dispersive component _s ^d of the surface free energy of glass fibers and its interaction energy with alkanes, benzene, 1-nitropropane, ethyleneglycol, glycerol, formamide, and water were quantitatively determined by the tensiometric method within two liquids. The values of nondispersive interaction energy I _SL ^p were found to be a linear function of the square root of the nondispersive component of the surface free energy of liquids. This suggests that the nondispersive interaction energy may be represented by the geometric mean of the nondispersive component of the surface free energy of a solid and a liquid. The slope gave the nondispersive component _s ^p of the surface free energy. The _s ^p values are 33 and 14 mJ/m² for the untreated and aminosilane-treated fibers, respectively, suggesting that organophilic character has developed on the surface after aminosilane treatment. The _s ^p value was almost similar after the treatment, probably because of the polar characteristics of amino groups.     

The dynamik contact angle II. Investigation of the adsorption mechanism based on the measurement of the preceding contact angles

The structure of the adsorption layer at the solid/gas interface is characterized, as a function of conditioning concentration, by the measurement of preceding contact angles. The contact angles were determined tensiometrically (plate method) and cinema tographically (capillary rise method) in the system glass or mercury/n-dodecyl ammonium chloride solution/air, respectively. In the dependence of contact angle on concentration, four regions are provable. These regions correlate with the surfactants, which are bound to adsorption in a heteropolar mode or by van der Waals forces of interaction, with the formation of layer-like coverage and with bilayers. Special attention was given to the fact that loosely bound surfactants are transferred from the solid/gas interface to the liquid/gas interface and cause a reduction of the preceding contact angle.Publication No. 1077 from the Research Institut of Mineral Processing, Academy of Sciences of the GDR, Freiberg, G.D.R.     

“Belt-loop” model of chain entanglement

A simple model of an entangled chain is proposed. Statistical properties of the model are examined based on the partition function derived to include geometrical constraints imposed by entanglements. The model chain statistics results, for long chains, in a modified Gaussian function. The new statistics applied in the affine network theory yield stress-strain dependence, which qualitatively agrees with experimental data obtained for uniaxial extension and compression. Non-linear Mooney-Rivlin plots with a maximum appearing in the compression region are predicted for unswollen networks. With increasing swelling, non-linearity decreases. The proposed explanation of these phenomena is based on the restraints imposed on entangled chains, rather than on network junctions, unlike in the Flory-Erman theory. No arbitrary parameters are involved in the model.     

Theory of swelling of a crosslinked substance in equilibrium with a solvent in various phases

In this paper the thermodynamic theory of a body in a liquid, crystalline or vaporized solvent is treated. The equilibrium swelling curves are discussed for the different states of the solvent. The slopes of the swelling curves are dependent on the differential enthalpy of dilution of the solvent and, additionally, on the enthalpies of vaporization, crystallization and sublimation of the solvent related to the state of the swelling agent. The slopes of the swelling curves are determined by the differential heat of vaporization, the differential heat of solution of the solvent or the differential heat of fusion according to the state of the swelling agent. Directly below the melting pointT _m,1, or directly above the boiling pointT _b,1 of the solvent the swelling curves change their slopes with a sharp bend. This phenomenon can be used to determine (₁/w ₁) at constant temperature and pressure, which means the change of the chemical potential ₁, with the change of the weight fractionw ₁ of the solvent. Using a simplified statistical thermodynamic relation it is possible to describe the principal courses of the swelling curves in all states of the solvent.     

The dynamic contact angle I. Dependence of the receding contact angle on velocity in the surfactant-containing three-phase system

Spontaneous three-phase contact (tpc) motion is investigated in order to determine the dependence of the static contact angle on tpc velocity in surfactant-containing systems after recession. To interpret the experimental results, the molecular-kinetic sitechanging theory and the hydrodynamic theory were considered. It is shown that, especially at very high tpc velocities, the experimental results are not thoroughly described by these theories. The deviations are explained as a surfactant transfer from the liquid/gas to the solid/gas interface which, under insufficient afterdiffusion, leads to an increase in surface tension and to a changed surface rheology. This mechanism could be governed by a model.     

EPR study of free radicals in a main chain thermotropic polymer

Free radicals were generated in a rigid rod-like copolymer via mechanical route and by gamma radiation. The (EPR) method was used for studying free radicals formed at 123 K. The spectra of free radicals observed and the influence of molecular motions on the transport of radical centers in the fracture surface layer are discussed.     

Viscoelastic behaviour during gelation of various molar-mass polyvinylchloride solutions and polymerization temperatures

The gel formation of various 10% molar-mass polyvinyl-chloride (PVC) sample solutions and polymerization temperatures in di-(2-ethylhexyl)phthalate (DOP) was studied by measuring dynamic moduli as functions of gelation (or ageing) time and frequency. The propensity to form gels increases with increasing molar mass and decreasing polymerization temperature. Extraction of a commercial PVC with acetone separates it into a relatively highly crystalline and a nearly non-crystalline polyvinyl chloride.     

The problem of intrinsic birefringence and chain conformation in polycarbonate from bisphenol-A

The PC-monomer is found to be a good example for elucidating the problems engendered by more complex monomers when the orientation behavior is investigated. The discrepancies found in the literature regarding the intrinsic birefringence can be fully resolved with the following assumptions:The carbonyl-unit is neither in the trans nor in the cis configuration, and the absorption band at 1364 cm^–1 is a mixture of in-phase and out-of-phase symmetric bending vibrations of the isopropyl methyl-groups. Planar and helical chain conformations are found which are thought to build up the amorphous phase. It is demonstrated that the crystal structure as known from literature can be realized by the planar conformations.Dedicated to Prof. E. W. Fischer on the occasion of his 60^th birthday     

The influence of surfactants on latex flocculation with poly(diallyldimethyl ammonium chloride)

Aqueous latex was flocculated by mixtures of poly(diallyldimethyl ammonium chloride), PDADMAC, and anionic surfactants. Sodium dodecyl sulfate, (SDS), and Aerosol OT influenced flocculation whereas nonionic Tergitol NP-10 did not. The flocculation domains were correlated with properties of the polymer-surfactant complexFlocculation was never observed above the CMC of the corresponding surfactant solution without polymer or latex. At SDS concentrations greater than 10^–3.6 M the flocculation boundary corresponded to the first appearance of insoluble polymer-surfactant complex which was characterized by dynamic light scattering and microelectrophoresis. Under these conditions latex (diameter 570 nm) and dispersed polymer-surfactant complex particles (diameters between 30 and 2 000 nm) displayed simultaneous homo and heteroflocculation. The boundaries of the flocculation domains at low surfactant concentration were determined by the ratio of polymer to latex and by the net electrostatic charge of the soluble polymer-surfactant complex. On the other hand, the mechanisms controlling flocculation boundaries in the dispersed polymer-surfactant domain require further clarification.     

Eigenvectors of the polyethylene chain with conformational defects calculated semianalytically by Green's function

Eigenvectors of vibrating polyethylene chains with (200) and (110) folds have been calculated by solving the phonon-scattering problem exactly with the method of Green's function. The results are applied to analyze the resonance modes of the (200) fold (ggtgg: 1353, 1356, 1374 cm^–1) and the (110) fold (approximately ggggtg: 820, 1288, 1342, 1348, 1372, 1374 cm^–1) in terms of the characteristic vibrations of smaller subunits of the (200) fold (gg, gtg) and the (110) fold (ggggtg, gggg, gtg) which can be identified spectroscopcally.Dedicated to Prof. Dr. W. Pechhold on the occasion of his 60th birthday     

Effect of coexistent hydrocarbon phase on the volume behavior of adsorbed film and micelle of dodecyltrimethylammonium chloride

Interfacial tension () between aqueous dodecyltrimethylammonium chloride (DTAC) solution and benzene was measured as a function of pressure (p) and concentration. The/p was observed to change discontinuously at the critical micelle concentration; this indicates that the micelle formation of DTAC in the aqueous solution coexisting with benzene can be treated like the appearance of a macroscopic phase. It was shown by drawing the vs.A curves that hydrocarbon, such as benzene, cyclohexane, and hexane, make the adsorbed film of DTAC expand. The volume behavior of the micelle with benzene molecules solubilized was found to bear a strong resemblance to that of the adsorbed film at the water/benzene interface. The difference in the molar volume value of adsorbed DTAC among the coexistent hydrocarbon phases was attributed to the difference in the contribution of the hydrocarbon molecules to the interfacial excess volume; the number of the solubilized hydrocarbon molecules was evaluated to be one or two a micelle.     

Conformational change of poly(L-lysine) and poly(L-ornithine) and cooperative binding of sodium alkanesulfonate surfactants with different chain length

Conformations of poly(L-lysine) (PLL) and poly(L-ornithine) (PLO) were examined in aqueous solutions of sodium alkanesulfontates (C_nSO₃Na, n=9, 10, 11, 12) in the presence of 0.02 M NaCl by circular dichroism (CD) spectroscopy. These surfactants induce the-structure for PLL and the-helix for PLO. The binding of surfactants on the polypeptides was measured potentiometrically with a surfactant ion electrode and was found to be highly cooperative. The cooperativity increases with increasing chain length of surfactant. The behavior accompanying the surfactant binding and the conformational change indicated that the conformational change requires a certain amount of bound surfactants in the case of C₉SO₃Na and starts immediately on binding of surfactant in the case of C_{1 2}SO₃Na. The clustering of bound surfactants due to the cooperative binding as well as neutralization of polypeptides contributes to their conformational change. A slow conformational change of PLO was found in the time scale of hours, sometimes days, for C₉- and C₁₀SO₃Na at low concentrations, but the binding process reached the equilibrium quickly. This slow mode might occur due to the slow interaction between surfactant/polypeptide complexes.     

Equilibrium and non-equilibrium melting of branched polyethylene relating to defect incorporation within crystals

New equilibrium melting point data, for polyethylene containing chain defects, are tested in the light of random copolymer predictions. A simplified expression for the melting point depression of random copolymers containing small amounts of non-crystallizable units is derived. Non-equilibrium melting data for rapidly quenched polyethylene samples are also reported. The fusion enthalpyH(X), and the surface free energy _e for crystals containing defects are evaluated using crystallinity, equilibrium meltingtemperatures and X-ray long period data. It is shown that increasing defect penetration within crystals induces a decrease ofH(X) withX in accordance with theoretical predictions. Finally _e is, similarly, shown to decrease with increasing number of chain defects attached to the crystal surface.     

On the theory of photoadsorption kinetics of a-Se colloids: The thermal activation energy and compensation effect

In this study, a model is developed to explain in microscopic terms the results obtained from thermally activated photoadsorption experiments in a-Se colloids. The observed compensation effect can be described for two different cases. At low efficiency adsorption, the process is controlled by the potential at the boundary layer. In the high efficiency adsorption case, the process is controlled by diffusion transport.On leave from Center of Technological Education, Holon, Israel     

Participation of electrolyte cations in albumin adsorption onto negatively charged polymer latices

The participation of electrolyte cations in the adsorption of bovine serum albumin (BSA) onto polymer latices was investigated. The latices used were hydrophobic polystyrene (PS), and hydrophilic copolymers, i.e., styrene (St)/2-hydroxyethyl methacrylate(HEMA) copolymer [P(St/HEMA)] and styrene/acrylamide (AAm) copolymer [P(St/AAm)]. Three kinds of electrolyte cations (Na⁺, Ca²⁺, Mg²⁺) were used as the chloride. The amount of BSA adsorbed in every cation medium showed a maximum near the isoelectric point (iep, pH about 5) of the protein. The amounts of BSA adsorbed onto copolymer latices (except in the acidic pH region lower than the iep) were considerably smaller than that onto PS latex because of the steric repulsion and the decrease in the hydrophobic interaction between BSA and copolymer latices. In the acidic pH region, there was little difference in the amount of BSA adsorbed in every cation medium. However, in the pH region higher than the iep, the amounts of BSA adsorbed (particularly onto PS latex) in divalent cations (Ca²⁺ and Mg²⁺) media were relatively greater compared with that in a monovalent (Na⁺) one. This result was interpreted on the basis of the differences in such effects of electrolyte cations as dehydration power, suppression of the electrostatic repulsion, and binding affinity to BSA molecule. Ion Chromatographic estimation of the amounts of electrolyte cations captured upon BSA adsorption (in pH > 5) revealed that divalent cations were incorporated into the contact interface between the latex and BSA molecule so as to prevent the accumulation of anion charge and facilitate the protein adsorption.     

Interactions of proteins with uniform colloidal hematite and chromium hydroxide particles. I. Adsorption

The adsorption of ovalbumin, -globulin, and lysozyme on uniform spherical hematite and chromium hydroxide particles in aqueous media has been studied as a function of the pH at a constant ionic strength. The uptake of ovalbumin and -globulin was greatest at their isoelectric points and differed little at 10^–2 and 10^–3 mol dm^–3 NaNO₃. The adsorption of lysozyme was strongly influenced by the ionic strength.The deposition of ovalbumin on hematite in the presence of Mg (NO₃)₂ was significantly greater than that with NaNO₃ under otherwise comparable conditions. Dialysis experiments with ovalbumin against magnesium nitrate solutions showed Mg²⁺ to be specifically bound to the protein.The shapes of isotherms indicated monolayer coverage for ovalbumin and multilayer coating for lysozyme for both adsorbents. The shapes of isotherms of -globulin on hematite point to a rearrangement of the protein on the particle surface, while a monolayer was found on chromium hydroxide particles.Supported by the NSF Grant CHE-9108420Part of a Ph.D. thesis     

Anionic graft polymerization of vinyl monomers initiated by metallized aromatic rings of graphite powder

Anionic graft polymerizations of methyl methacrylate (MMA) and styrene from graphite powder initiated by metallized aromatic rings on the surface were investigated. Metalation of the surface was achieved by the reaction of polycondensed aromatic rings of graphite withn-butyllithium (BuLi) in N,N,N,N-tetramethylethylenediamine (TMEDA) or hexamethylphosphorous triamide (HMPT) at 0 °C., Anionic polymerizations of MMA and styrene were initiated by metallized graphite, and these polymers were grafted onto the surface. The conversion and percentage of grafting increased by increasing the amount of BuLi used for metalation. When 0.20 g of graphite was treated with 0.4–0.5 mmol of BuLi in TMEDA, the percentage of grafting of PMMA and polystyrene reached the maximum value: PMMA 52.8% (PMMA/graphite =0.528 g/1.0 g) and polystyrene 37.2% (polystyrene/graphite=0.372 g/1.0 g). Grafting of polymers was also confirmed by infrared spectra. Although no metalation of graphite proceeded in toluene, graphite could be metallized even in toluene by the addition of crown ether as a complexing cation agent. The stability of graphite powder in organic solvent dispersion was found to be improved remarkably by grafting of polymer onto the surface.     

Interpretation of adsorption excess quantities: the absolute surface excess concentration

The concept of absolute surface excess of adsorption accounts for the expansion of compression of the volume of a pure liquid under the influence of a solid surface. The absolute surface excess amount of substance can prove to be a powerful measure of the adsorption at a solid/binary liquid interface, too. The contributions of the composition and volumetric effects to the adsorption can be separated from each other in this concept, and both of them are experimentally accessible quantities.