摘要:

The surface chemistry and thermodynamics of the nucleation, growth, configuration, and host–guest interactions of small particles within softenable substrates is investigated. It is found that novel subsurface particle monolayers form rather generally when inorganic materials are appropriately deposited onto softened (or subsequently softened) organic polymer substrates; partially embedded structures are generally formed by organic particulate materials, although these can also be embedded by exposure to a solvent vapour. For both rigid preformed particles spread onto the polymer surface, and for flexible growing clusters (as occur in vacuum deposition), the tendency for complete immersion is thermodynamically determined by the same simple inequality among the surface and interfacial tensions. Modelling of the polymer molecule configurations in the vicinity of subsurface particles predicts a novel entropic force of sufficient magnitude to explain why the particles form a monolayer a few tens of nm below the surface, rather than dispersing throughout the polymer, and why this structure is remarkably stable on extended heating. With the convenient fabrication technique of vacuum deposition, subsurface formation is further limited kinetically, by growth mode and sinking rate considerations, to generally low melting point inorganics and to certain ranges of deposition conditions; once subsurface particles are formed, their subsequent growth during the deposition process generally occurs at constant (nearly close-packed) surface coverage by a combination of material-capture and coalescence. After these nearly monodisperse particles grow beyond ~0.4 μm, they begin to bridge into a continuous subsurface structure. These vacuum-deposition phenomena are quantitatively explained by kinetic models of the formation and growth mechanisms.

ISSN:0008-4042    

DOI:10.1139/v85-031

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Evidence is presented which demonstrates that titanium dioxide does in fact photogenerate H2O2in the presence of the donor sodium formate. However, this H2O2has only a transient existence in aqueous dispersions. This was confirmed by experiments in which H2O2was injected into the dispersion. The reasons for the lability of H2O2are discussed and possible mechanisms presented. Electron paramagnetic resonance experiments using spin traps reveal that photolysis of TiO2dispersion generates •OH radicals in the donor-free case while •CO2radicals are observed in the presence of formate. These results are also consistent with H2O2generation.

ISSN:0008-4042    

DOI:10.1139/v85-032

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

In a dispersion polymerization process, the reaction mixture starts out as a homogeneous solution and the resulting polymer precipitates as spherical particles, stabilized by a steric barrier of dissolved polymer. The final polymer particle size is determined by the inherent polymer aggregation behaviour under a given set of conditions. In the present study styrene polymerization was studied in various solvents using cellulosic derivatives as the steric stabilizer. Some of these solvents in certain combinations allowed the direct preparation of particles in the micron size and their size distribution appeared to be highly dependent on the monomer–solvent–initiator system. Investigations of these factors have suggested that monodisperse particles up to 12 μm can be prepared in a single step; studies of several systems are delineated.

ISSN:0008-4042    

DOI:10.1139/v85-033

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Anodic and cathodic processes for rf and dc excited plasmas of silane gas differ in the relative role of charged and neutral radical species. By studying the thickness distribution of films deposited on substrates immersed in the plasma, the relative importance of these species as contributors to the film thickness is assessed. In addition, the impact of the different deposition processes on the spin density in the deposited hydrogenated amorphous silicon films and a key photoelectronic property, the hole range, is discussed.

ISSN:0008-4042    

DOI:10.1139/v85-034

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

A novel and simple method is described for evaluation of molecular weight – viscosity relationships for a polymer where only broad molecular weight distribution samples are available. The method demands measurement of the intrinsic viscosity and GPC chromatograms of several samples. Results of applying the procedure to bisphenol A – Diethyleneglycol (50:50) copolycarbonate are presented.

ISSN:0008-4042    

DOI:10.1139/v85-035

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Inverse gas chromatography was used to investigate the miscibility behaviour of molten polystyrene–poly(2,6-dimethyl-1,4-phenylene oxide) blends as a function of composition (0, 25, 50, 75, 85, and 100 wt.% PS). Specific retention volumes were measured for various solutes in pure and mixed stationary phases of these polymers at 240 °C. Infinite dilution weight fraction activity coefficients and Flory–Huggins polymer–solute (χ) and polymer–polymer (χ23′) interaction parameters were derived from these data.Negative polymer–polymer interaction parameters were obtained for blends containing more than 60 wt.% PS, suggesting strong intermolecular interactions in the molten state. This is in accord with the well-known compatibility of PS–PPO blends. However, positive χ23′ values were observed for blends containing less than 60 wt.% PS. This suggests weak intermolecular interactions, and perhaps some microheterogeneity in PS–PPO blends with a low PS content. In view of the single, composition dependentTgmeasured for each of these blends the microheterogeneity or microphase separation must be on a finer scale than that measured by the glass transition.

ISSN:0008-4042    

DOI:10.1139/v85-036

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The recombination dynamics of geminate cation–electron pairs in liquid hexane is studied by combining picosecond photoionization and infrared-stimulated charge dissociation measurements. The observed yield of free charge is determined by the product of the charge pair survival probability and the probability for infrared-stimulated charge dissociation. Experimental results are compared with transient solutions of the Smoluchowski equation governing diffusive recombination in a Coulomb well. Reasonable agreement with experiment can be reached by allowing for a radial distribution of initial pair separations. However, the stimulated dissociation yield exhibits a functional dependence on pair separation which complicates the analysis. A simple model of geminate charge pair dissociation by infrared stimulation is presented and its implications for these experiments are discussed.

ISSN:0008-4042    

DOI:10.1139/v85-037

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

The structural changes occurring in poly(methylvinylketone) when exposed to high temperatures have been investigated by high-resolution13C solid-state nmr. The degradation proceeds via the aldol condensation of pendant ketone groups to form a cyclic β-hydroxy ketone which is dehydrated to the cyclic α,β-unsaturated ketone. As the degradation continues there is the formation of polycyclic structures and aromatization of the sample.

ISSN:0008-4042    

DOI:10.1139/v85-038

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

Polymers and molecular solids are characterized by two fundamental features: the retention of molecular identity in the solid state and the occurrence of relatively weak interactions between the individual molecular entities. The weak interactions lead to a high degree of disorder caused both by defects and by thermally induced motions of the molecules. A model of charges injected into polymers and molecular solids is developed. Photoemission and transport measurements are utilized to evaluate the parameters in this model. Results for metal free phthalocyanine are presented as an illustrative example. For molecular glasses and aromatic pendant-group polymers this analysis predicts that disorder causes injected charges to form a Fermi glass of self-trapped polarons, i.e., they occupy localized states characterized by a high degree of local atomic and electronic polarization. Successful interpretations of photoemission spectra, contact charge exchange, and injected carrier drift mobilities verify this prediction. The boundary of the Fermi-glass region of localized-state molecular-ion behavior is identified by consideration of molecular crystals in which injected charges may occupy extended energy-band states at low temperatures.

ISSN:0008-4042    

DOI:10.1139/v85-039

出版商:NRC Research Press    

年代:1985

数据来源: NRC

摘要:

X-ray diffraction methods have been investigated as means of quantifying filler contents of paper. Both an "internal standard method" and an "absorption–diffraction method" were applied. Because of preferential orientation of the filler particles in commercial paper samples, the "internal standard method" was modified to include an empirical evaluation of the proportionality constant,K. Values ofKspecific for each filler material investigated (clay, calcite, talc, and titanium dioxide) were obtained by X-ray diffraction intensity measurements on standard papers containing different amounts of each filler. These values ofKwere then used to calculate the filler content of various commercial papers. The filler contents of these same commercial papers were also determined using the X-ray "absorption–diffraction method" and ash determination. Comparisons made among results from all these methods indicated that both X-ray methods give acceptable agreement with ash determination, but that the "absorption–diffraction method" is preferred due to its ease of application. In addition, the X-ray methods are more rapid and versatile than ash determination.

ISSN:0008-4042    

DOI:10.1139/v85-040

出版商:NRC Research Press    

年代:1985

数据来源: NRC