Characteristic changes of pH during the alkalization of latex dispersions of the ethyl acrylate — methacrylic acid copolymers

The titration curves of latex dispersions of ethyl acrylate — methacrylic acid copolymers have a rather complex shape which indicates a strong dependence of the apparent dissociation constant of carboxylic groups on the degree of neutralization and copolymer composition. These dependences seem to be related to changes in the macroscopic structure (swelling and disintegration) of dispersion particles during alkalization.     

Equilibrium sorption of crystal violet by carboxymethylated cellulose with low degree of substitution

Cellulose fabric samples were carboxymethylated for different duration. The degree of substitution was changing through a maximum value during the reaction time.The equilibrium sorption of a cationic dye by cellulosic fibers of different degrees of carboxymethylation was investigated in buffered and in unbuffered systems. The sorption isotherms were interpreted by two kinds of approximations based upon Langmuir isotherm. From the sorption data extrapolated to zero dye concentration affinities were calculated. The temperature dependence of affinities gave the values of heat and entropy of dyeing which were changing along the reaction time similarly to the degree of substitution.     

Sorption properties of celluloses in binary liquid mixtures

The adsorption capacity for methanol-benzene andn-propanol-water mixtures was measured on two kinds of microcrystalline celluloses and cotton linters. Excess adsorption isotherms were obtained; the free energy of displacement was calculated from the isotherms. The enthalpy of displacement for one crystalline cellulose was measured by flow calorimetry. The entropic function of displacement was derived from the enthalpy and free energy of displacement. The preferential adsorption of methanol andn-propanol was characterized by the adsorption equilibrium constant.On leave from the Department of Physical and Colloid Chemistry, Wageningen Agricultural University, The Netherlands     

CPS LG 313 Phenylalkanol — adsorbates on silica as types of immobilized drugs 1. Chemiadsorption on activated silica surfaces

The chemiadsorption of phenylalkanols onto a porous silica support (d _pore 10 nm) viaSi-O-C bonds was studied. The silica support was activated prior to the alcohol adsorption by annealing or by the introduction ofSi-Cl groups. Different reaction conditions were applied, namely time, temperature, solvent and drug-support ratio. The yield of chemiadsorption was dependent on both the reaction conditions and the structure of the alcohols. Long alkyl chains, especially those with an alcohol OH-group positioned in the vicinity of bulky substituents, reduce the yield considerably. Using chlorinated silica, a reasonable yield of chemiadsorption can be obtained even at relatively low reaction temperatures.Dedicated to Professor Dr. Dr. h. c. Armin Weiss on the occassion of his 60th birthday.     

On the collision efficiency approach to flocculation

The collision efficiency approach to flocculation is analyzed on the basis of a model describing the probability of aggregation by polymer bridging. The model allows for the effect of the randomness of distribution of polymer over particles as well as the effect of simultaneous coagulation and weak flocculation. It is argued that the collision efficiency approach is applicable to a rather limited range of experimental systems and provides a qualitative understanding rather than a quantitative theory of the relationship between flocculation and adsorption.     

Heat of micelle formation: Effect of counterions with concentrated,diffused, and separated electric charges

Heats of micelle formation were estimated from calorimetric measurements of anionic surfactants to see if there is any effect of the electrical charge of the counterion on micelle formation from the viewpoint of enthalpy change. The cationic counterions used are Na⁺ and Cu²⁺ for the concentrated electric charge, MV²⁺ for the diffused and 1,1-(1,)-alkanediyl)bispyridiniumions n=2, 4, 6, 8, 10, 12, 14 for the separated. The heat of micelle formation was obtained by subtracting an enthalpy change of dissolution of surfactant solid precipitated below the micelle temperature range (MTR or Krafft point) from a heat of complete dissolution of the precipitated surfactant solid around the MTR. The heats thus evaluated were found to be much more temperature-dependent than counterion-dependent. They were compared with the enthalpy change calculated from the CMC change with temperature, and the big difference between them was discussed from a thermodynamic point of view.     

Displacement processes on hydrophilic/hydrophobic surfaces in methanol-water mixtures

The adsorption from methanol/water and the enthalpy of displacement of methanol by water were studied on K-60 silica gel, on graphitized PRINTEX-80, and onn-alkylammonium vermiculites. The adsorption between the hydrophobized silicate layers was followed by x-ray measurements. The excess isotherms of alkylammonium vermiculites in methanol/water exhibit two maxima corresponding to the two steps of the individual isotherm. The equilibrium constant of the exchange of water by methanol is calculated. For calculating the adsorption capacities and molar adsorption potentials, a new equation is proposed which combines the adsorption excess quantities with free energy and enthalpy functions.     

Force-length relation for a short freely jointed chain: mass and volume dependence

We evaluate the force-length relation for short model chains. It is shown that this relation is markedly different when evaluated for static and dynamic model chains with rigid segments. The relation also differs for chains with rigid segments when they are isolated and coupled to a canonical heatbath, respectively. Furthermore, it is derived that the variation of the masses along the chain only has a small influence on the force-length relation. On the other hand, restricting the motion of the chain by walls perpendicular to the chain extension has a pronounced effect. We especially find that in this situation the chain has a finite equilibrium length.Dedicated to Professor W. Pechhold on the occasion of his 60th birthday     

Polyacrylamide Na-kaolinite interactions: Effect of electrolyte concentration on polymer adsorption

The variation in polyacrylamide adsorption on Na-kaolinite as a function of the electrolyte concentration of the clay suspension, was determined under three pH conditions, where the clays display varying charge characteristics. Interpretation of the results is based on two arguments: non-charged polyacrylamide adsorption is restricted to the edge faces of the colloidal platelets and hydrogen bonding between the amide groups of the polymer and the isolated hydroxyl sites of these faces is the mode of surface attachment. At constant pH, when Na-kaolinite bears charged surface groups, the polymer adsorption, which is related to the density of the anchoring sites, parallels the state of ionization of the edge surface. The mechanism by which the salt modifies the adsorption properties of the kaolinite in neutral medium is not established with certainty. Nevertheless, no polymer-clay association occurs if the surface is entirely uncharged. This result is in line with the fact that while hydroxyl groups are engaged in internal hydrogen bonds, they cannot hydrogen-bond to the polyacrylamide. Variations in the clay-polymer affinity are attributed to a modification of the interfacial structure of the adsorbed polymer, associated with changes in the surface density of the anchoring groups.     

Thermodynamics of adsorption of acetone on active carbon supported metal adsorbents

Adsorption of acetone on active carbon and active carbon supported metals (Ni, Cu, Zn and Cd) have been studied as a function of temperature. Thermodynamic parameters such as G ⁰, H ⁰, and S ⁰ are calculated from virial and Langmuir isotherm expressions. It is observed that active carbon supported metals have more adsorption affinity for acetone as compared to active carbon. Results show that the increase in adsorption affinity for active carbon supported metals is not due to configurational factors affecting the entropy of adsorption, but because of enhanced enthalpy of adsorption. XRD spectra show that active carbon supported metals adsorbents are amorphous and metal residues are present on the surface of active carbon in its reduced form. From adsorption data, isosteric heats and molar entropies of adsorption were calculated as a function of coverages and temperature. The values of isosteric heats of adsorption were found to be higher for active carbon supported metals, which may be due to the chemisorption of adsorbate molecules with metal sites present on the surface of active carbon. The extent of coordination of adsorbate molecules with metal sites is discussed on the basis of the acidic character of metal.     

Network properties of mixtures of protonated and deuterated polyethylene

Mixtures of protonated and deuterated polyethylene were irradiated in the melt. The degree of crystallinity, the degree of crosslinking, as well as the enthalpyH and the melting pointT _M were determined. No significant differences in the degree of crosslinking between protonated and deuterated chains were found. The mass specific entropyS of the uncrosslinked samples remained constant and independent of the deuterium concentration. For the crosslinked samples, a netpoint entropy was postulated. A weaker Van der Waals interaction could explain the decrease in melting temperature by deuteration (for weakly crosslinked samples).     

Molecular properties of acetone and some of its chloroderivatives adsorbed at the surface of water

The relations between the electric surface potential (V) and the surface tension () of aqueous solutions of acetone, chloroacetone, 1,3-dichloroacetone, and their concentration were investigated. The vertical components of dipole moments of the above mentioned compounds were determined using the Helmholtz equation. The calculations were carried out on the basis of surface excess values, which were obtained from surface tension measurements and surface potential changes. Once the vertical component of dipole moments were found and the orientation of adsorbed molecules was assumed, the local dielectric permittivities of the surface monolayer were estimated.     

Modelling adsorbent heterogeneity for adsorption from binary liquid mixtures

It is demonstrated that the detailed structure of the surface energy or selectivity distribution function is not critical to obtaining adequate analytical expressions for surface excess isotherms for adsorption from binary liquid mixtures on heterogeneous adsorbents. The gamma and the uniform selectivity distribution functions, which are very different in form, were successfully used in conjunction with the monolayer-pore filling model for adsorption on a homogeneous site to describe adsorption of various binary liquid mixtures on silica gel. Both models described the salient features of the surface characteristics of the silica gel.     

Electrical properties of planar bimolecular surfactant membrane

Planar bimolecular film of the triple long-chain salt(dihexadecyldimethylammonium hexadecanesulfonate) was found to be formed in the electrolyte solutions was carried out at different temperatures by the transient D. C. method. In four electrolyte solutions of Li⁺, Na⁺, K⁺, and Cs⁺ chlorides, the resistance of the membrane was very high (up to 10⁷ ohm·cm²). From the temperature-dependence of conductivity, the activation energy of ion transfer through the film was calculated by the Arrhenius equation. The magnitude of the activation energy was related with the size of the crystallographic radius.The authors acknowledge financial support from the Swiss National Science Foundation.     

Diffusion-based adhesive bonds between phases in fibrous composites

In this paper the mesophase developed between main phases in fibrous composites was studied assuming that it constitutes a diffuse boundary. This type of mesophase is normally developed in polymer-polymer adjacent phases and it it useful for the study of modern composites disposing a coupling agent between main phases. At the high temperature of reaction of phases during the casting process both neighboring phases are partly liquified, allowing a two-way movement of elements of either phase whose intensity and extent depends on the particular diffusion characteristics of either phase and the affinities between them.The characteristics of this diffusion reaction were studied and their influence on the development and the properties of the adhesion between phases were established, especially for fiber composites. Interesting results were derived concerning the extent of the diffusive mesophase and its mechanical properties, as well as its contribution on the global mechanical behavior of the composite. Finally, the results were found to be in agreement with previously established models.     

The action of indomethacin on neutral and positively charged monolayers

The penetration ability of indomethacin in neutral and positively charged monolayers has been studied. Neutral monolayers of cholesterol and dipalmitoyl phosphatidyl choline present a slight but significant increase of surface pressure. The presence of stearylamine in the films results in an increase of surface pressure due to an electrostatic effect between the carboxylic anion of indomethacin and the polar head group of the stearylamine. These values can afford a reference point to choose the best lipid composition of liposomes encapsulating indomethacin to avoid the drug causing leakage of liposomes.     

Photo-induced electron transfer in surfactant solutions containing thionine dye

The mechanism of photovoltage generation in the micellar solution of nonionic surfactants incorporating thionine dye involves charge-transfer (CT) or electron donor acceptor (EDA) interaction; the dye acts as the electron acceptor and the surfactants act as the electron donors. This is well corroborated by the spectral studies of the systems. The thermodynamic and spectral properties of the complexes are presented. The photovoltage generation, the spectral shifts due to complexation, and the thermodynamic properties of the complexes are found to be well correlated.     

Morphology and optical properties of liquid crystals embedded in polyester resin matrix

This paper reports on morphological, thermo-optical, and electro-optical results of UV-cured polyester resin film containing liquid-crystal nematic and cholesteric domains. Electro-optic measurements were performed in an applied d.c. electric field. The morphological structure of PDLC film is modified by the various methods of their preparation. Size-distribution curves drawn vs the duration of the initial cooling obtained for cholesteric liquid crystal domains are presented.     

Chemical deposition coatings from emulsifier-free anionic polymer emulsion onto anodized aluminum plate under stirring conditions

The chemical deposition from an anionic acrylic copolymer emulsion onto an anodized aluminum plate was carried out under various stirring conditions. The amount of polymer deposited was affected by the stirring rate. At higher stirring rates, the surface flatness of the obtained coating decreased, but the transparency (which was affected by the traces of bubbles, due to evolution of hydrogen gas from the surface of the plate in the deposition process) was improved. Under optimum stirring conditions an excellent coating having a flat surface and good transparency was obtained.Part CXVIII of the series Studies on Suspension and Emulsion.     

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.