On the Surface Tension and its Temperature Variation in Film-Forming Polymers

A thermal gradient bar has been used for convenient measurements of γ_c and dγ_c/dT in complex polymers used as film-formers. The technique yields both γ_c and its temperature variation in one experimental sequence well suited for rapid, routine applications. Surface tension data have been obtained for a styrene-acrylic terpolymer, and these have also been used to characterize the compatibility of external plasticizers for the polymer. The surface tension approach has shown that glyceryl dibenzoate, though compatible with the polymer at temperatures above ∼70°C becomes incompatible at use temperatures, and exudes to the polymer film surface. Measurements of moisture sensitivity in plasticized polymer samples have confirmed the incompatibility and illustrated one of the applications to which the gradient bar and its data generation potential may be put.     

PRODUCTION OF SUB-MICROMETER SIZE O/W EMULSIONS USING A HIGH-PRESSURE WET-TYPE JET MILL

Emulsions composed of sub-micrometer size droplets were obtained by a high-pressure wet-type jet mill. Liquid paraffin as dispersed phase, aqueous sucrose solution as continuous phase, and anionic sodium dodecyl sulfate as emulsifying agent were used as the model emulsification system. Droplet size distribution, Sauter mean diameter (d₃₂), geometric standard deviation of the droplet size distribution (σ_g), and emulsion viscosity (η_e) were investigated under the various combinations of process variables: dispersed phase volume fraction (Φ), dispersed phase viscosity (η_d), continuous phase viscosity (η_c), processing pressure, and number of passages through the wet-type jet mil. d₃₂ and σ_g were correlated with the process variables. For the entire experimental range, maximum droplet diameter was varied with d₃₂ in the range of 1.7-1.9-fold, and a correlation was proposed with K (=η_d/η_c) as a variable. Above a marginal value of d₃₂, at Φ ≥ 0.1, emulsions exhibited Newtonian behavior and could be described well by the Yaron and Gal-Or model. Below the marginal values, emulsions strongly depended on d₃₂ and exhibited a shear-thinning behavior. The relation between η_e and d₃₂ for such emulsions was modeled by use of particle Reynolds number.     

Fracture toughness of interfaces between glassy polymers in a trilayer geometry

We studied the fracture behavior of trilayer A/B/A assemblies based on polystyrene (PS) and poly(methylmethacrylate) (PMMA) where the central layer of the A polymer was confined (0.5–200 μm) between two thick plates of the B polymer (1– 3 mm). Diblock and random P(S-MMA) copolymers were used to provide a good stress transfer across the interfaces. Fracture experiments were performed with the double-cantilever beam method and the fracture mechanisms were observed by optical microscopy on microtomed slices of the damaged zone. The measured _c of the A/B interface fractured during the test was dependent on the molecular structure at the interface (random copolymer, diblock copolymer or no copolymer), on the crazing stress of the bulk materials and on the interfacial shear stresses. When the phase angle of the loading was even slightly positive, oblique crazes were observed in the PS increasing greatly _c. If PS was the central layer, this resulted in a very marked dependence of _c on the thickness of the central layer for a thickness range 10–200 μm which was not observed when the PMMA was the central layer. Thermal treatments modifying the interfacial shear stresses were also found to have a very strong effect on _c.     

Crystallinity and fusion of ethylene oxide/propylene oxide block copolymers: 1. Type PE copolymers

Lamella spacings, specific volumes and melting points have been determined for a series of well characterized poly(propylene oxide)/poly(ethylene oxide) type PE block copolymers with E-block length 40 chain units and P-block lengths 0 to 11 chain units. These properties are interpreted in terms of a stacked lamella model with alternating amorphous and crystalline layers. The crystalline lamella thickness is found to be about 25 E chain units, i.e. the crystals are predominantly of extended-chain type. The specific volume of the polymer in the amorphous lamellae is found to be lower than that of polymer of corresponding composition in the supercooled melt. The melting points are low compared to that of perfectly crystalline poly(ethylene oxide), i.e. 47 to 51°C compared with T⁰_m = 76°C. This is due to the positive free energy of formation from the melt of the amorphous layer (σ₅ 3.5 kJ/mol) and the crystalline/amorphous) interface (σ_o 3 kJ/mol).     

Drag on ensembles of fluid spheres translating in a power-law liquid at moderate Reynolds numbers

This work elucidates the role of power-law rheology on the sedimentation velocity of an ensemble of mono-size spherical Newtonian droplets (free from surfactants) translating in a power-law continuous phase numerically by solving the momentum equations of both phases. A simple sphere-in-sphere cell model has been used to account for inter-drop interactions. In particular, in this study, the effects of the Reynolds number (Re_o), the internal to external fluid characteristic viscosity ratio (k), the volume fraction of the dispersed phase (Φ) and the power-law index of the continuous phase (n_o) on the external flow field, pressure drag (C_dp), friction drag (C_df) and total drag (C_d) coefficients have been analyzed over wide ranges of parameters as follows: 1 ≤ Re_o ≤ 200, 0.1 ≤ k ≤ 50, 0.2 ≤ Φ ≤ 0.6 and 0.6 ≤ n_o ≤ 1.6. Based on the extensive numerical results obtained in this work, a simple predictive correlation has been proposed for the total drag coefficient, which can be used to predict the rate of sedimentation of ensembles of Newtonian fluid spheres in power-law liquids in a new application.     

The dominant time constant for distillation columns

It is shown that the dominant part of the dynamic composition response of two-product distillation columns can be approximated by a linear first-order response. This applies also for large perturbations to the column. The numerical value of this dominant time constant (τ_c) can be obtained from steady-state simulations. A simple analytical expression for small peturbations is derived which provides insight into the variation of τ_c with operating conditions. The time constant τ_c does not apply when there are changes in the internal flows only.     

CHARACTERISTICS OF MICROMETER AND SUBMICROMETER SIZE O/W EMULSIONS PRODUCED BY RAMOND SUPERMIXER®

A novel motionless mixer named the Ramond Supermixer® (RSM®) was employed to produce O/W emulsions composed of micrometer and submicrometer-size droplets. Liquid paraffin as dispersed phase, aqueous sucrose solution as continuous phase, and anionic sodium dodecyl sulfate as emulsifying agent were used as the model emulsification system. Pressure drop, droplet size distribution, Sauter mean diameter (d₃₂), and geometric standard deviation of the droplet size distribution (σ_g) were investigated under the various combinations of process variables; superficial liquid velocity, number of mixing units, number of passages through RSM®, dispersed phase viscosity (η_d), continuous phase viscosity (η_c), and dispersed phase volume fraction. Different modes of droplet size variations with process variables were obtained, with respect to micrometer- and submicrometer-size ranges, and theoretical explanations are forwarded. For the micrometer-size range, maximum droplet diameter (d_max) was proportional to d₃₂. For the submicrometer-size range, d_max varied with d₃₂ in the range of 1.53-2.19-fold, and a correlation is proposed with K (=η_d/η_c); d₃₂ and σ_g were well correlated with the process variables. Furthermore, a semi-empirical mechanistic model was developed for the formation of droplets obtained under inertial sub-range to interpret the effect of process variables.     

Peel Adhesion: Influence of Surface Energies and Adhesive Rheology

The adhesion properties of polymers are known to be influenced by both intermolecular forces operative at the interface and the rheological history of both bonding and unbonding. Recent adsorption and viscoelastic theories of adhesion and cohesion are implemented in a comprehensive examination of these phenomena. Eight peel force “master curves” extending over 14 decades of reduced rate and representing glassy state to flow region rheology are superimposed to provide a composite response envelope. Each master curve represents rate-temperature reduced adhesion of an alkyl acrylate adhesive (γ_c = 26 dyne/cm) to substrates ranging from low adhesion fluorinated polymers (γ_c = 15 to 17 dyne/cm) to polar poly-amide surfaces (γ_c = 45 dyne/cm) and glass. The rate dependent transition from interfacial to cohesive failure, a subject not treated by adsorption theory, is shown to be coincident with the onset of entanglement slippage within the polymeric adhesive. Thermodynamic criteria of polymer adhesion are shown to be applicable only to the flow region of polymeric response. This study indicates that measured surface tensions or calculated surface energies of polymeric solids do not properly account for the contributions of three dimensional network structure of the polymeric bulk phase to its total work of cohesion. Evidence of true interfacial failure of a polymer-polymer bond is supported by critical surface tension measurements.     

Co-operative diffusion of semi-dilute solutions, concentrated solutions and swollen networks for polystyrene in dibutylphthalate

The diffusion constant of solutions of polystyrenes of molecular weight ranging from 110 000 to 3.6 × 10⁶ in straight-chain-dibutylphthalate has been measured by photon correlation spectroscopy as a function of polymer volume fraction and temperature. In the semi-dilute range the co-operative diffusion constant D_c exhibits a much smaller increase with the polymer volume fraction Φ than theoretically predicted, except at high temperatures (T 100°C) where it follows a Φ^1/2 law characteristic of a marginal solvent. This effect can be described to an enhancement of the friction factor, which is also demonstrated by a decrease in D_c occurring at a volume fraction which increases with temperature. The same effect is observed in swollen networks but it is strongly reduced for swelling equilibrium conditions.     

Radiation-induced release of hydrogen from C:H films: basic regularities and mechanism

Model calculations of the process of interaction between accelerated ions and C:H films have shown that the kinetics of the ion irradiation-induced hydrogen release (IIIHR) from C:H films and the final hydrogen concentration (ρ_f) depend only on the characteristics of the irradiating ions. The hydrogen release the cross-section K, the saturation dose Φ_sat and the ion energy loss dE/dx are connected by simple linear relationships. The final hydrogen concentration ρ_f is proportional to the number of vacancies per broken bond (C_v/P_i). The IIIHR processes are well described by the following parameter: C_v/P_i, dE/dx and C′₀. In the proposed model for the given a-C:H film and ion irradiation the primarily characteristics of the IIIHR, such as Φ_sat and ρ_f, can be estimated ‘a priori’.     

The problem of correction for ohmic potential drop in linear potential sweep experiments and the derivation of s0 values for electrode surface processes

Rate constants or exchange current densities of electrode surface processes involving adatom arrays are conveniently evaluated by determining that sweep rate, s₀ (the reversibility parameter), in a linear potential sweep (LPS) experiment, below which the process just remains kinetically reversible, ie its overpotential is sensibly zero. Transition to irreversibility is characterized by peak potentials, E_p, becoming linear in the log of the sweep rate, s, following a region of independence of s for < s₀. A suitable extrapolation procedure enables s₀ to be evaluated. However, if s₀ is large and/or the resistivity of the solution is appreciable, the IR_u drop associated with uncompensated resistance in the measurement system can be comparable with the increase of E_p with log s, when s > s₀, rendering evaluation of s₀ inaccurate. While compensation or empirical correction for this may be made, it is desirable that the nature of the IR_u effect of the LPS I vs E profiles be understood in a more fundamental way. It is the purpose of this communication to provide such a treatment of this effect through evaluation of the actual time-dependent potential that becomes applied to the electrode, and to propose criteria based on the product of s₀, R_u and the reaction pseudocapacitance, C_φ for indicating the anticipated extent of the IR_u effect in the evaluation of s₀. While the transition in the E_p vs log s plot may be due to IR_u effects as well as to kinetic irreversibility, when the former are appreciable, it is shown that the corresponding transition in the value of C_φ with increasing log s can usually allow spurious IR_u and significant irreversibility effects to be distinguished.     

Crystallinity and fusion of ethylene oxide/propylene oxide block copolymers: 2. Type PEP copolymers

Lamella spacings, specific volumes and melting points have been determined for a series of well characterized poly(ethylene oxide)/poly(propylene oxide) type PEP block copolymers with E-block length 48 chain units and P-block lengths 0 to 7 chain units. These properties are interpreted in terms of a stacked lamella model with alternating amorphous and crystalline layers. Both extended-chain and once-folded-chain crystalline lamellae are found, the former with thickness about 32 E chain units and the latter with thickness about 21 E chain units. Compared with the specific volume of supercooled melt of the same composition the specific volume of the polymer in the amorphous lamellae is lower in the extended-chain polycrystals and higher in the once-folded-chain polycrystals. The melting points of the copolymers are low compared to that of perfectly crystalline poly(ethylene oxide), i.e. 37 to 55°C compared with T⁰_m = 76°C. This is due to the large positive free energy of formation from the melt of the crystalline/amorphous end interface (σ_o) and the amorphous layer (σ_a). For extended-chain polycrystals we find σ_o 3 kJ/mol and σ_a 3.5 kJ/mol; for once-folded-chain polycrystals we find σ_o 6 kJ/mol and σ_a 2 kJ/mol. We also find σ_o,x = 2.5 kJ/mol for a completely extended-chain end interface and σ_o,f = 10 kJ/mol for a completely folded-chain end interface.     

Physico-Chemical Criteria for Maximum Adhesion. Part II: A New Comprehensive Thermodynamic Analysis

In this paper, two parameters defined as the relative work of adhesion [W_A/γ_L] and the relative interfacial energy [γ_SL/γ_L] have been examined for their assumed usefulness in correlating the thermodynamic properties of the components of the system substrate/ adhesive with its practical performance (strength). It is shown that the minimum value of [γ_SL/γ_L] relevant to conditions for the maximum adhesion becomes zero only for those systems (relatively rare) for which interaction factor Φ₀ is equal to 1.0.

Several transition points were identified for boundary conditions acquired at θ = 0° and θ = 90° which can be used to predict the properties and performance of an adhesive joint. These transition points are: a_MIN—energy modulus of the system (E. M. S.), relevant to the minimum interfacial energy; a_S—E. M. S. where self-spreading of adhesive occurs; a_CRIT—E. M. S. relevant to conditions under which the thermodynamic work of adhesion becomes negative and the system exhibits a tendency for self-delaminating or has “zero-strength”; a_CF—E. M. S. beyond which the geometry of the interface at any interfacial void or boundary of the joint may be regarded as a crack tip.

It is shown that only in those systems for which Φ₀ = 1.0 can a minimum contact angle of 0° indicate a condition for the maximum strength. If Φ₀ is known, the optimum contact angle can be estimated and hence the optimum surface energy of the substrate (adjusted by surface treatment, etc.) for the maximum adhesion.     

Voidage profiles in magnetically fluidized beds

Voidage profiles in a fluidized bed of iron particles (230 μm) were investigated under the influence of an external uniform axial magnetic field. Passing a direct current through five solenoids generated uniform magnetic field. The five solenoids were arranged elaborately to get larger uniform magnetic space than that generated by Helmholtz electromagnet coils. A sensitive optical measuring system, based on detection of light reflected by particles, was used to measure local voidage in both dense and dilute phases.

Local voidage was measured as a function of superficial fluidizing air velocity, magnetic field intensity and the position in the bed. At a given magnetic field intensity and at the same position in the bed, the voidage was constant for a low air velocity range (in a fixed bed). The local voidage changed irregularly with increasing air velocity for an intermediate air velocity range (in a magnetically stabilized fluidized bed, MSFB). The local voidage changed linearly with increasing air velocity for a slightly high air velocity range (in a magnetized bubbling fluidized bed, MBFB). A general correlation was developed to predict the local solids fraction at the arbitrary position in the bed: (1−)=(1−)_c+[(1−)_w−(1−)_c](r/R)^B where (1−), (1−)_c and (1−)_w represent the local solids fraction at arbitrary position in the bed, at the bed center and on the bed wall; and B, (1−)_c and (1−)_w are the function of air velocity, distance from the distributor and magnetic field intensity.     

Conductive coating films based on low density In2O3 powders and polymer latexes

Several kinds of conductive coating films were prepared from a low-density indium(III) oxide powder (which was employed because it provides a much higher volume for the same weight) and polymer latexes. The low-density In₂O₃, which is an electrically conductive pigment, was prepared by pyrolysis followed by the combustion of water-swellable polymer microspheres imbibed with In(NO₃)₃, the precursor of In₂O₃. Either acrylamide/N,N'-methylenebisacrylamide or poly(vinylalcohol)/glutaricdialdehyde was used to generate spherical hydrogel particles. The polymer latexes with which the In₂O₃ was mixed had a soft core and a hard shell structure to ensure that the coating film has suitable mechanical properties in addition to conductivity. Acrylonitrile/butadiene/styrene copolymer ABS or acrylonitrile/butylacrylate/styrene copolymer ABAS latexes were used as binders for the conductive pigment. The powder coating followed by hot pressing, the water-borne coating consisting of low-density In₂O₃ and polymer latexes followed by curing, or the colloidal dispersion coating was used to deposit flexible conductive coating films on polyester sheets. The conductive pigment density and the polymer latexes' size and flowability are the factors that affect the characteristics of the film. We found that the colloidal suspension coating procedure based on ABAS latexes achieves better electrical and mechanical properties for the coating films. © 1996 John Wiley & Sons, Inc.     

A simple determination of counter-ionic permselectivity in an ion exchange membrane from bi-ionic membrane potential measurements: permselectivity of anionic species in a novel anion exchange membrane

A new method is proposed here for determining counter-ions permselectivity through an ion exchange membrane. The theoretical base of the method is Henderson equation. After simplifying at special experimental conditions, a linear relationship between the bi-ionic membrane potential term and concentration ratio, i.e., [exp(z_AF(−ΔE_T)/RT)−1]∝[C_A,L/C_B,L] can be obtained, from the slope of which, the permselectivity of counter-ions can be achieved. This method is very simple in operation and less time and money consuming. The method is exemplified by common 1–1, 2–2 and 2–1 counter-ions pair through a novel and published anion exchange membrane. The accuracy and the validity of the method is tested by three aspects: (1) the experimental [exp(z_AF(−ΔE_T)/RT)−1]∝[C_A,L/C_B,L] curve approaches a straight line (2) the predicted order of counter-ions conforms to the results evaluated in a practical electrodialysis process; and (3) the results calculate from different referenced counter-ions for the same counter-ions pair agree well with each other.     

The Effect of Interfacial Tension on the Adhesion of Cathodic E-coat to Aluminum Alloys

Adhesion of a cathodically electrodeposited paint (E-coat) to aluminum alloys, Alclad 2024-T3, AA 2024-T3 and AA 7075-T6, was investigated to examine the influence of interfacial tension at the paint/metal interface. The surface energy of an aluminum plate was modified by depositing a plasma polymer of a mixture of trimethyl silane (TMS) and one of three diatomic gases (O₂, N₂, and H₂) by cathodic plasma polymerization. The contact angle (Φ) of water on a modified surface changes as a function of the mole fraction of the diatomic gas. The plot of cos Φ_PP of a plasma polymer as a function of the mole fraction of the gas crosses the plot of cosΦ_EC of the E-coat. The difference, ΔCosΦ = cos Φ_PP - cosΦ_EC, is a parameter which indicates the level of interfacial tension at the paint/metal interface. ΔCosΦ = 0 represents the minimum interfacial tension. The adhesion of a cured E-coat on a panel was evaluated by the N-methyl pyrrolidinone (NMP) paint delamination time test. The maximum peak of adhesion test values plotted as a function of ΔCosΦ occurred around the zero point. ΔCos Φ = 0, indicating that maximum adhesion is obtained with minimum interfacial tension. Mixtures of TMS and N₂ on all three aluminum alloys studied consistently displayed longer delamination times in the NMP test than mixtures of TMS and O₂ or H₂.     

Water uptake of epoxy coatings modified with γ-APS silane monomer

Epoxy resin was modified by a silane monomer, γ-aminopropyltrimethoxy silane (γ-APS), and was used as the protective coatings for LY12 aluminum alloys. The aim of the modification is to reduce the water uptake of polymeric coatings. The water absorption of coatings was measured by coating capacitance method in 3.5 wt.% NaCl aqueous solution. The result indicates that water uptake of epoxy coatings modified with 1.0 wt.% γ-APS decreases compared with pure epoxy coatings, whereas larger amounts of sliane result in the deterioration in performance against water permeation, due to the excessive consumption of epoxide group in epoxy resin by amino-group in silane agent, thus reduce the cross-linking of epxoy coating as a result of presence of excessive curing agent (polyamide). T_g of silane-modified coatings increases slightly after immersion, extremely contrasting with that of pure epoxy coating, which was observed to decrease significantly after water permeation. The formation of Si–O–Si structure resulting from the hydrolysis and condensation of silane components during the immersion in aqueous media may be a reasonable explanation for the abnormal change in T_g of silane-modified coatings. In addition, all silane-modified coatings display better protection performance, which is characterized by higher charge transfer resistances (R_ct) and lower double layer capacitance (C_dl) at substrate/electrolyte interface.     

The influence of substrate absorbency on coating surface chemistry

The composition of the top surface of a coating layer can influence its functional properties or subsequent processing steps. The effect of the substrate absorbency on the coating surface chemistry is reported. Different coating systems containing a kaolin clay pigment, fine or coarse precipitated calcium carbonates, and a common latex binder were examined. The influence of a soluble polymer added into the coating was characterized. The surface chemistry was measured with attenuated total internal reflectance (ATR) and X-ray photoelectron spectroscopy (XPS).

Absorbent substrates generate bulky coatings with high voids and low gloss. Rapid dewatering by the absorbent substrate pulls the small particles, like latex binder, away from the top layers causing a low latex concentration at the surface. On non-absorbent substrates, the addition of the soluble polymer generates coating layers with higher void volume, lower gloss, and lower latex concentrations at the coating surface. However, on absorbent substrates, polymer addition causes coatings with lower void volumes and higher gloss. In this case, the rapid dewatering and mobility of particles is reduced by the polymer, which helps to retain the small particles at the surface. As a result, latex concentration at the surface increases with polymer addition on absorbent substrates.     

Al（OH）3@Zn（OH）2双层包覆氧化铁黄合成及其耐热性能研究

采用共沉淀法对铁黄颜料进行Al（OH）₃/Zn（OH）₂双层异相包覆,提升其耐热性能,并通过XRD、TG-DTA、FT-IR、SEM&EDS等手段对包覆前后铁黄颜料的微观结构进行表征。研究结果表明,包覆质量分数为40%的Al（OH）₃时铁黄颜料的耐热性能较好;第二层包覆Zn（OH）₂,最优包覆质量分数为30%,样品在240 ℃时色差值为1.84。XRD测试结果表明,Al（OH）₃和Zn（OH）₂包覆并没有改变氧化铁黄的特征峰,两者可能以无定形态包覆在铁黄粒子表面。SEM、EDS、FT-IR测试表明,Al（OH）₃/Zn（OH）₂已成功对铁黄颜料进行了包覆;此外,还出现了片状结构对应Al（OH）₃自身成核现象,包锌后出现了团聚现象。TG-DTA表征显示,包覆后样品升温脱水分两步,低温吸热峰对应包覆层物质的脱水,高温吸热峰偏向更高温度,对应包覆颜料耐热性能的提升。