Film formation from monodisperse acrylic latices 5. Drying and ageing in coalescing agent containing latex films

The influences of drying temperature, ageing time and ageing temperature on the film formation in coalescing agent containing latex films were investigated via turbidity measurements and atomic force microscopy. Coalescing agents used are 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (TEX) and ethylene glycol monobutyl ether (EB). Latex films were dried at different temperatures. At a drying temperature of 40 degrees C, the differences in immersion patterns of neat and 1% coalescing agent containing latex films are too small to show significant improvement in film formation during 1 h of drying. Increase of the temperature from 40 to 50 degrees C, however, causes an improvement in film formation. At higher temperatures (95 degrees C), fast removal of the liquid phase cannot be prevented by the addition of 1% coalescing agent. Although addition of higher amounts of coalescing agent results in an increase of particle deformation and film surface smoothness, it intensifies also the water absorption of dried films. Ageing below the MFFT does not result in a significant improvement of film formation in the presence of 1% coalescing agent. Above the MFFT, coalescing agents act more efficiently and cause an improvement in film formation. By addition of higher amounts of coalescing agent the completion of the film formation process is delayed: for example, by the addition of 15% EB, nearly 1 year of ageing at room temperature is required for an efficient result.     

Film formation from monodisperse acrylic latices, part 4: the role of coalescing agents in the film formation process

The role of coalescing agents in the film formation process is studied by means of the turbidity technique, i.e., analysis of light transmission and interference. The basic influence of coalescing agents is (a) lowering the minimum film formation temperature of the latex dispersion, (b) increasing the drying time and (c) improvement of coalescence. Application of coalescing agents also causes a change in polymer particle size as coalescing agents made of TEXANOL (2,2,4 trimethyl-1,3 pentanediol monoisobutyrate) and ethylene glycol monobutyl ether (EB) were used. Turbidity is shown to be a better method to optimize the amount of coalescing agent in a film formation process than the usual brass bar.     

Small-angle neutron scattering study of particle coalescence and SDS desorption during film formation from carboxylated acrylic latices

Four monodisperse core-shell latices were synthesized for small-angle neutron scattering (SANS) studies, differing by the acrylic acid content in the particle shell (1 or 4 wt%) and the T(g) of the acrylic core (around -40 or 10 degrees C). In a first part, the coalescence kinetics of the surfactant-free latices were studied. It was shown that coalescence was hindered by an increase in the acrylic acid content of the shell, pH of the latex, and Tg of the core. These results could be interpreted in terms of chain mobility in the shell and in the core. Upon coalescence, the hydrophilic phase was segregated in spherical, polydisperse domains with an average diameter of 110 nm. In a second part, labeled SDS was used to follow desorption of the surfactant during film formation. It was shown that desorption occurred early in the film formation process when the latex still contained around 20% of water. A small fraction of the surfactant remained irreversibly adsorbed at the particle surface.     

Film formation from nano‐sized polystyrene latex particles

This work reports on the steady state fluorescence (SSF) technique for studying film formation from surfactant‐free, nano‐sized polystyrene (PS) latex particles prepared via emulsion polymerization. The latex films were prepared from pyrene (P)‐labeled PS particles at room temperature and annealed at elevated temperatures in 5, 10, 15, 20 and 30 min time intervals above the glass transition temperature (T_g) of PS. During the annealing processes, the transparency of the film was improved considerably. Monomer and excimer fluorescence intensities, I_P and I_E respectively, from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of the latex films was monitored by using photon transmission intensity, I_tr. Void closure and interdiffusion stages were modeled and related activation energies were determined and found to be 10.3 and 50.3 kJ mol⁻¹. Void closure temperatures, T_v, were determined from the minima of I_tr value. Copyright © 2005 John Wiley & Sons, Ltd.     

Extraction of mercury by inert solvents from pure and mixed acids

The extraction of mercury by inert solvents has been investigated as a function of the hydrochloric and sulfuric acid concentration in the aqueous phase. It was found that the extraction of mercury with kerosene is adequate at low hydrochloric acid concentrations but decreases with the increasing acid concentration. In the case of sulfuric acid a maximum and/or a minimum are noticed. The presence of trace halides in the aqueous phase changes the shape of the relation between the distribution of mercury and the sulfuric acid concentration in the aqueous phase. The extraction of mercury by neutral, anion and cation exchange reagents was also investigated.     

Glass transition and film formation of VeoVa/vinyl acetate latices; role of water and co-solvents

The physical forces causing deformation of latex particles during the film formation process have been witley studied. However, the forces resisting particle deformation are still poorly characterized. It is clear that the extent of particle deformation is dependent on the viscoelastic nature of the polymer. In an emulsion, the latex particles will normally contain water, surfactants and “free” monomers which lead to plasticization of the polymer. Although this effect has been recognized, so far it has been studied only on films that had been dried and then partially or completely swollen by water. In this work, plasticization of the emulsion polymers by water and co-solvent has been quantified via differential scanning calorimetry investigation directly on the aqueous latex dispersions. More specifically, the plasticizing effect of water on VeoVa/vinyl acetate copolymer latices and its influence on minimum film-forming temperature (MFFT) has been studied. A linear correlation has been found between T_g and MFFT for the wet latices. This new direct method should help to improve our understanding of the forces resisting latex film formation. Additionally, the homogeneous distribution of the hydrophobic and hydrophilic monomers (VeoVa and vinyl acetate respectively) in the latex particles was verified via a ¹³C-NMR (nuclear magnetic resonance) study performed directly on the latices. This study confirmed that no significant core/shell type of morphology had influenced latex film formation.     

Quantum Monte Carlo study of small pure and mixed spin-polarized tritium clusters

We have investigated the stability limits of small spin-polarized clusters consisting of up to ten spin-polarized tritium T downward arrow atoms and the mixtures of T downward arrow with spin-polarized deuterium D downward arrow and hydrogen H downward arrow atoms. All of our calculations have been performed using the variational and diffusion Monte Carlo methods. For clusters with D downward arrow atoms, the released node procedure is used in cases where the wave function has nodes. In addition to the energy, we have also calculated the structure of small clusters using unbiased estimators. Results obtained for pure T downward arrow clusters are in good accordance with previous calculations, confirming that the trimer is the smallest spin-polarized tritium cluster. Our results show that mixed T downward arrow-H downward arrow clusters having up to ten atoms are unstable and that it takes at least three tritium atoms to bind one, two, or three D downward arrow atoms. Among all the considered clusters, we have found no other Borromean states except the ground state of the T downward arrow trimer.     

A fluorescence probe study of the mixed surfactant vesicles

Vesicle can be prepared from aqueous mixtures of simple commercially available, single-tailed canonic and anionic surfactants. In this work, the I3/I1 value, Ie/ Im value, and fluorescence lifetime of pyrene in different systems (see the preparation of samples) were determined. Hie essential affecting factors in the formation of vesicle can be deduced from the obtained results. It showed that large vesicle must form naturally before sonication in 0.082 M octyltrimethylammonium bromide and sodium laurate pH = 9.2 aqueous solution. While after sonication, only small vesicle exists, which can be proved further through electron microscope.     

Latex film formation and dissolution: A fluorescence study

A new technique based on steady state fluorescence (SSF) measurements is introduced for studying dissolution of polymer films. These films are formed from naphthalene (N) and pyrene (P) labeled poly(methyl methacrylate) (PMMA) latex particles, sterically stabilized by polyisobutylene (PIB). Annealing was performed above T_g at elevated temperatures for 30 min time intervals for film formation. Film formation from these latexes is monitored by the extent of energy transfer from N to P using SSF and by the transmitted photon intensity from these films using UV visible (UVV) methods. Desorption of P labeled PMMA chains was monitored in real-time by the change of pyrene fluorescence intensity. Dissolution experiments were performed in various solvents with different solubility parameters, δ, at room temperature. Diffusion coefficients, D, in various solvents were measured and found to be around 10⁻¹⁰ cm²/s. Strong relationships between D and δ were observed. Diffusion activation energy was measured by performing dissolution experiments in toluene-heptane mixtures at elevated temperatures and determined to be 24.4 kcal mol⁻¹.     

Fast transient fluorescence technique (FTRF) for studying vapor-induced latex film formation

A fast transient fluorescence (FTRF) technique was used to study latex film formation induced by organic solvent vapor. Seven different films with the same latex content were prepared separately from poly(methyl methacrylate) (PMMA) particles and exposed to vapor of various chloroform-heptane mixtures in seven different experiments. Latex films were prepared from pyrene (Py)-labeled latex particles and fluorescence lifetimes of Py were monitored during vapor-induced film formation. It was observed that pyrene lifetimes decreased as vapor exposure time increased. A Stern-Volmer kinetic analysis was used for low quenching efficiencies to interpret the decrease in pyrene lifetimes. A Prager-Tirrel model was employed to obtain back-and-forth frequencies, nu, of the reptating PMMA chains during latex film formation induced by solvent vapor. nu values were found to be correlated with chloroform content in vapor mixture. It was observed that polymer interdiffusion obeyed a t(1/2) law during film formation. The results of optical transmission experiments were found to support these findings.     

Dual-phase solid polymer electrolytes prepared from styrene–butadiene copolymer latices

A new dual-phase solid polymer electrolyte system has been proposed. In this system, a network of ion pathways is formed in a low-polarity, host polymer matrix. A series of electrolytes were prepared from styrene-butadiene copolymer latices with dissolved lithium salts. Polymer films were formed from these latices, and then impregnated with γ-butyrolactone (γ-BL) or γ-butyrolactone/dimethoxyethane mixture (γ-BL/DME), giving latex polymer electrolytes. The ionic conductivity of the polymer electrolyte system increased with increasing solvent content, although a distinct percolation threshold was not measured. Ionic conductivity also increased with the use of DME cosolvent, with the highest conductivity being 1.4 × 10^?4S/cm. Complex impedance diagrams are discussed. The diagrams show significant deviations from the ideal. TEM/SEM observations are consistent with the desired dual-phase morphology. © 1993 John Wiley & Sons, Inc.     

A study of the formation of silica-supported mixed magnesium-manganese spinel oxides from multicomponent gels

The effects of thermal treatment on composite materials prepared by the gelation of sols comprising large concentrations of metal oxide precursor salts have been investigated, in order to determine the compositional and thermal requirements for forming spinel magnesium manganates in such systems. The preparative technique has been found to give rise to derived gel materials in which the metal oxide phase, in the form of regular spherical particles, is dispersed throughout a continuous silica matrix. Silica-supported mixed magnesium and manganese spinel oxide phases were obtained for systems comprising at least 30 wt% metal nitrate after heating to temperatures between 700 and 850°C, but not without concomitant formation of Mn₂O₃ and modification of the silica network by magnesium.     

Large deformation of films from soft‐core/hard‐shell hydrophobic latices

Structured soft‐core/hard‐shell hydrophobic latices form rigid and transparent films under ambient conditions without the need of coalescing aids. The studied films have a composite structure, with the majority of soft poly(n‐butyl acrylate) dispersed in a continuous poly(methyl methacrylate) (PMMA) matrix. The matrix is formed by thin latex shells brought into intimate contact by surface forces. Despite the weakness of the interfaces between adjacent shells, the films exhibit high yield stress and surprising ductility. These properties result from a very specific PMMA matrix structure built from PMMA ligaments with a thickness of a few nanometers. Under these conditions, PMMA appears to shear without damage. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 224–234, 2003     

Void closure and interdiffusion processes during latex film formation from surfactant-free polystyrene particles: a fluorescence study

This study reports a steady state fluorescence (SSF) technique for studying film formation from surfactant-free polystyrene (PS) latex particles. The latex films were prepared from pyrene (P)-labeled PS particles at room temperature and annealed at elevated temperatures for 5-, 10-, 20-, and 30-min time intervals above the glass transition (T(g)) temperature of polystyrene. During the annealing processes, the transparency of the film changed considerably. Scattered light (I(sc)) and fluorescence intensity (I(0P)) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of latex films were monitored using photon transmission intensity, I(tr). Scanning electron microscopy (SEM) was used to detect variation in the physical structure of annealed films. Onset temperature for film formation, T(0), void closure, T(v), and healing temperatures, T(h), were determined and corresponding activation energies were measured. Void closure and interdiffusion stages were modeled and related activation energies were determined.     

A theoretical study of micro-domain formation in mixed lipid membranes

The thermodynamic stability of micro-clusters in a membrane built-up by charged and uncharged lipid molecules is discussed. A simple variational function is proposed in order to describe the essential structure of such lipid domains. Solvent-screened electrostatic repulsion between the lipid ionic head groups, short-range forces between the lipid hydrophobic taisl and entropic effects are taken into account. The stability conditions as well as the composition and the size of the lipid micro-domains are calculated and expressed as a function of molecular parameters for the membrane and its environment (for example, short-range forces, surface charge density of the lipid bilayer, ion concentration of the electrolyte solution in contact with the lipid membrane and temperature). As an application, the effect of micro-domain formation on the number of adsorbed ions on a charged lipid membrane has been calculated.     

Laser-induced fluorescence monitoring of higher alkanes production from pure methane using non-oxidative processes

A novel method for the study of non-oxidative methane conversion process into higher value hydrocarbon and hydrogen has been invented. The method involves the multiphoton dissociation of methane under the influence of the high power pulsed ultraviolet laser radiation at 355 nm wavelength at room temperature (293 K) and standard pressure (1 atm). The products generated as a result of methane conversion like ethane, ethylene, propane, propylene and isobutane are analyzed using an online gas chromatograph while the other species such as CH, CH₂ and C₂H₂, atomic and molecular hydrogen are characterized by real-time laser-induced fluorescence technique for the first time. A typical 7% conversion of methane into ethane has been achieved using 80 mJ of laser irradiation at 355 nm. The important features of this method are that it is non-oxidative, does not require any catalyst, high temperatures or pressures, which is normally the case in conventional techniques for methane conversion.     

Film formation from concentrated emulsions studied by simultaneous conductometry and gravimetry

We present a simple, yet effective, technique involving simultaneous conductometry and gravimetry, to study the drying process of films made from concentrated oil-in-water emulsions. We exemplify the technique by drying experiments on paraffin oil/Triton X100/brine emulsion films. The drying process is demonstrated to consist of three regimes: (1) evaporation of ‘free water’, (2) dehydration of the bi-liquid (o/w) foam and (3) the rupture of the foam structure into an inverted (w/o) emulsion. Conclusive statements about the morphology of the emulsion film in each of these stages are made based on observations using the above technique.