Optimization of single‐zone drying of polymer solution coatings using mathematical modeling

Optimal conditions for drying polymer–solvent coatings result from a trade‐off between minimizing the residual solvent level and creating defects. This article describes an application of automated constrained optimization with a detailed mathematical drying model to find the optimal drying conditions for a prototypical coating in a single‐zone oven. The optimization process seeks oven conditions that minimize the residual solvent level for a fixed oven residence time without boiling the solvent within the coating. The optimal oven conditions include the air temperature and coating‐side and substrate‐side heat‐transfer coefficients. The conditions are constrained to physically reasonable values. According to our results, the optimal coating‐side heat‐transfer coefficient is always equal to or greater than the optimal substrate‐side heat‐transfer coefficient. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 149–165, 2000     

Phase dynamics and wetting layer formation mechanisms of pattern-directed phase separation in binary polymer mixture films with asymmetry compositions

Focusing on the binary polymer mixture films under the off-critical condition, the phase dynamics and wetting layer formation mechanisms of pattern-directed phase separation are numerically investigated. The simulated results demonstrate that, for different compositions, the polymer mixtures on the strip patterned surface can exhibit various phase morphologies in the strips of the bulk, which can be used to tailor the microscopic structures of films. The evolutions of these phase structures in the strips of the bulk obey almost the same power law with an exponent of 1/3, i.e., the Lifshitz-Slyozov growth law for the films with various off-critical degrees. It is found that the wetting layer thickness near the patterned surface grows logarithmically at the initial stages, just like the wetting layer formation mechanism of the polymer mixture near the surface with an isotropic potential. This revels that only patterning the surface potential may not change the growth law of the wetting layer. The simulated results also indicate that the diffusion of the component in the direction parallel to the surface originates from the edge of the strips.     

Pattern formation and morphology in the course of drying a droplet of a ternary polymer solution

A micro‐structured polymer film was prepared by drying a droplet of a ternary polymer solution of polystyrene (PS), poly(vinyl pyrrolidone) (PVP), and chloroform. Within a certain weight ratio of PS to PVP an ordered pattern of cylindrical PVP domains was formed on the film surface. The diameter of the individual PVP domains was in the order of 2–3 μm. The effect of polymer weight ratios on the surface morphology was investigated by atomic force microscopy. Additionally, scanning electron microscopy of cross‐sections of the polymer composite film yielded supplementary information on the bulk morphology and revealed an unexpected complex structure underneath the surface pattern. The reasons for this formation mechanism possibly included aspects of phase separation, convective transport in a drying droplet, and the continuous increase of viscosity during solvent evaporation. At a certain solvent concentration in the evaporation path, it will lead to a vitrification of any structure. The “evolution time”, the time between the onset of phase separation and this “point of vitrification”, will determine the resulting film morphology. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Confinement of a polymer chain: An entropic study by Monte Carlo method

The properties of macromolecules in presence of an interface could be considerably modified due to confinement effects. When phase separations are performed in nanoconfined domains, the concurrent presence of high‐energy interfaces and conformational entropy constraints of the macromolecules causes profound differences in polymer aggregation behavior. Here, thermodynamics of a polymer chain in solution, confined by a three‐dimensional cubic interface, is studied by means of Monte Carlo method, focusing on the chain conformational entropy penalty arising from the excluded volume effects. The presented method might become a general tool for a preliminary evaluation of the thermodynamic effects due to the confinement of a polymer system. Further, the interface effects on Thermally Induced Phase Separation (TIPS) of polymer solutions, confined by High‐Pressure Homogenization, are experimentally studied, regarding final morphologies. It is confirmed how peculiar polymer morphologies are obtained only when the TIPS develops under nanoconfinement degrees above a threshold one. © 2017 American Institute of Chemical Engineers AIChE J, 64: 416–426, 2018     

水分散涂料的常温成膜

叙述了常温成膜水分散涂料的成膜。     

Mechanism of bubble formation in step-emulsification devices

Step-emulsification device is an emerging technology for bubble generation, which is convenient for numbering-up. However, the mechanism of bubble formation in such devices remains unclear. In this article, the mechanism of bubble formation in step-emulsification devices is investigated by using a high-speed camera. First, the evolution of gas–liquid interface with time during bubble formation is observed. Second, the variation of characteristic parameters of bubbles, such as bubble's volume V_B and generation frequency f, with gas and liquid flow rates is described under various liquid viscosities and step widths. Meanwhile, the coupling law of interface evolution with characteristic parameters of bubbles is explored. Finally, the basic guideline for generation of monodispersed bubbles in step-emulsification is put forward: low liquid viscosity. Connecting the interface evolution with the characteristic parameters, predictive models for bubble's volume, and generation frequency in step-emulsification are proposed, respectively.     

Surface concentration effects in the drying of solvent-coated polymer films

The effect of changing the solvent surface concentration on the initial rate of solvent removal from solvent-coated polymer films is investigated. An analytical perturbation so-lution is developed for the nonlinear problem, and predictions are made for different surface concentrations and different diffusivity–concentration dependencies. © 1996 John Wiley & Sons, Inc.     

热诱导相分离法制备高分子微孔膜的原理与进展

简述了热诱导相分离 (TIPS)法制备高分子微孔膜的相平衡热力学及相分离动力学原理 ,并对国内外研究进展进行了评述     

Pattern formation in polymer films under the mask

This paper presents a straightforward method for patterning thin films of polymers, i.e. a prepatterned mask is used to induce self-assembly of polymers and the resulting pattern is the same as the lateral structures in the mask on a submicrometre length scale. The patterns can be formed at above T_g+30 °C in a short time and the external electric field is not crucial. Electrostatic force is assumed to be the driving force for the pattern transfer. Viscous fingering and novel stress-relief lateral morphology induced under the featureless mask are also observed and the formation mechanisms are discussed.     

Effect of confinement on the bubble points of hydrocarbons in nanoporous media

The bubble point of reservoir petroleum fluids in nanoporous media is an important parameter in shale oil production. We present experimental results on the bubble points of octane and decane confined in controlled‐pore glasses (CPGs) with pore sizes of 4.3 and 38.1 nm. Differential scanning calorimetry (DSC) is used to measure the temperature at which the vapor phase begins to form (i.e., the bubble point). We find that the bubble point is dramatically affected by pore diameter: at 38.1 nm the confinement effect is insignificant, but at 4.3 nm two distinct bubble points appear, suggesting two distinct populations of evaporating fluid. Deviations are as great as ±15 K for both peaks relative to the bulk bubble point for 4.3 nm CPGs. Thermogravimetric analysis is consistent with DSC, supporting the validity of these results. Based on these experiments and previous simulations, we propose a two‐state model for the nanoconfined hydrocarbons. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1772–1780, 2016     

Monte Carlo simulations of phase separation in thin polymer blend films: scaling properties of morphological measures

Surface directed phase separation in thin polymer blend film has been studied with Monte Carlo simulations using a simple model based on reptation method. Time evolution of phase structure was characterized quantitatively by morphological measures (the Minkowski functionals) in addition to the inspection of concentration versus depth profiles. It was shown that the dynamical scaling hypothesis holds for the Minkowski functionals describing morphologies at the early stages of phase separation in thin films. Two time regimes with different scaling exponents (0.25, 0.33) were found for the growth of the characteristic length scale in the system corresponding to various transport mechanisms (diffusion along- and normally to the interface). Fast decrease in the morphological measures observed at the end of phase separation was attributed to the confinement of the thin film.     

Effect of polymer properties on bubble growth in polymer–paperboard composites

Foamed paperboard is a composite material used in thermally insulated food packaging and beverage containers. The paperboard is sandwiched between a layer of low‐density polyethylene and a barrier layer, and the low‐density film is foamed through heating. The moisture inside the paperboard vaporizes and serves as the driving force for creating the foam. The bubble growth on the paper surface has been tracked with high‐speed photography. The number of generated bubbles has been found to depend on the number of pores on the surface of the paperboard; there is little or no dependence on the properties of the polymer, at least across the range of properties studied. In contrast, the thickness of the foam is relatively insensitive to the paperboard properties but has a strong dependence on the thickness of the initial polymer film, the nature of the polymer, and the speed at which it is extruded onto the paperboard. It is believed that some of these variations arise from differences in the degree of adhesion between the polymer and the paperboard. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Formation and characterization of perfluorocyclobutyl polymer thin films

Perfluorocyclobutyl (PFCB) polymers are a new class of materials that show promise as selective layer materials in the development of composite membranes for gas separations, such as carbon dioxide/methane (α_{pure gas} = 38.6) and oxygen/nitrogen (α_{pure gas} = 4.8) separations. In many of the flat sheet applications, a thin film of the selective layer that is free of major defects must be coated onto a support membrane. A focus of this study was to elucidate the impacts of solvents, polymer concentration, and dip‐coating withdrawal speed on PFCB thin film thickness and uniformity. An extension was proposed to the Landau–Levich model to estimate the polymer film thickness. The results show that the extended model fits the thickness‐withdrawal speed data well above about 55 mm/min, but, at lower withdrawal speeds, the data deviated from the model. This deviation could be explained by the phenomenon of polymer surface excess. Static surface excesses of polymer solutions were estimated by applying the Gibbs adsorption equation using measured surface tension data. Prepared films were characterized by ellipsometry. Refractive index was found to increase with decreasing film thickness below about 50 nm, indicating densification of ultrathin films prepared from PFCB solutions below the overlap concentration. Atomic force microscopy was used to characterize surface morphologies. Films prepared from tetrahydrofuran and chloroform yielded uniform nanolayers. However, films prepared using acetone as solvent yielded a partial dewetting pattern, which could be explained by a surface depletion layer of pure solvent between the bulk PFCB/acetone solution and the substrate. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

双进双出气泡泵输送性能

吸收式热泵是回收利用低品位热能的方式之一。在扩散吸收式热变换器中借由双进双出气泡泵引入扩散气体,以此代替机械泵,实现全热驱动。本文采用工质为水-甲酸钾-R134a,通过改变动力压头、发生温度和扩散气体流量,对扩散吸收式热变换器系统中气泡泵的输送性能进行动力压头分别为0.42和0.55 m的两组试验研究。其中制冷剂流量、气相流量、提升效率这3项参数的不确定度分别为0.06078 g/s、0.06081 g/s、1.64799。结果表明,提高温度与动力压头、降低扩散气体流量,均可增大气泡泵的提升效率,这些研究结果将为后续的气泡泵设计提供重要的参考依据。     

Phase‐inversion applications beyond membrane formation. I. Lithography films

Polymeric films cast from a polymer solution can develop a bulk porosity, if the conditions are favorable for phase inversion (PI), a physical chemical process based on fluid–fluid demixing of which there are two known major variants: wet and dry PI. As the formation of polymeric coatings often involves a polymeric solution or gel precursor, dry or wet PI phenomena may affect the structure formation of the final solvent‐free coating. In this article we identify the situations under which lithographic films can develop a PI structure and focus on solid polymer layers undergoing postcasting wet processing. Examples are provided from the wet processing of a fractionated epoxy novolac resin currently used in lithographic patterning. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2145–2157, 2000     

A capacitance study of pseudo-fickian diffusion in glassy polymer coatings

The permeation and sorption of water in eight coatings below the glass transition temperature was monitored using capacitance measurements. For each coating deviations from ideal-fickian diffusion were observed. The diffusion rate was found to decrease considerably. This anomalous (or non-fickian) behaviour is known in literature as pseudo-fickian diffusion or two-stage sorption. To analyse the measurements further a new method is developed. The data were transformed to a time-dependent diffusion rate. The analysis resulted in a new pseudofickian diffusion model, which could also be represented by a spectral distribution of diffusion rates. The results agree well with the relaxation model of Berens and Hopfenberg. It is shown that the Berens-Hopfenberg model, in particular, and pseudo-fickian behaviour, in general,can be understood as diffusion influenced by free-volume relaxation.     

Filler effect on formation and properties of interpenetrating polymer networks based on polyurethane and polyesteracrylate

The formation processes of unfilled and filled interpenetrating polymer networks (IPNs) and some of their physico-mechanical properties have been investigated. The IPN formation kinetics and the constituent network curing rates determine the rate and degree of microphase separation. This in turn determines the boundary layer composition and structure. Introduction of filler into the IPN during formation affects greatly the crosslinking reaction and the microphase segregation of homopolymers. It has been shown that the degree of phase segregation in filled IPNs differs from that in unfilled ones. All the fillers were found to shorten the time of internal stress appearance and to increase its value for IPNs with predominantly high-modulus component content. Some filled IPNs were shown to have greater thermodynamic stability than unfilled ones.     

Thermodynamic Modeling of Phase Diagrams in Binary Alkali Silicate Systems

A thermodynamic modeling of phase diagrams in binary alkali silicate systems is described by using the Gibbs free energy of the phases. Simple models employing regular, quasi-regular, and subregular solution models were applied to describe the liquid phase. The interaction parameters of the liquid phases were obtained by using the liquidus curves of silica (and subliquidus data) through a multiple linear regression method. The present calculated liquidus curves agree very well with Cs₂O—SiO₂ and Rb₂O—SiO₂ systems. In the K₂O—, Na₂O—, and Li₂O—SiO₂ systems, the calculations permitted discrimination between sets of data and, based upon the calculation choices, could be correctly made to select the most appropriate phase diagram. Also, the spinodals were calculated where phase separation can occur by a spinodal decomposition process.     

Effect of polymer-filler surface interactions on the phase separation in polymer blends

For the blends of chlorinated polyethylene and copolymer of ethylene with vinyl acetate, the effect of the introducing filler (fumed silica) on the phase behavior of the blends was investigated. It was found that introducing filler in polymer blends depending on its amount lead either to the increase or to the decrease in the temperature of phase separation. At the filler concentration where both components transit into the state of a border layers, the phase separation temperature increases. This effect was explained by the change of the total thermodynamic interaction parameter in the ternary system polymer-polymer-filler. At lower concentration of a filler, the possible effect is the redistribution of the blend components according to their molecular masses between filler surface (in the border layer) and in the bulk that may diminish the phase separation temperature.Effect of the filler on the phase behavior was explained by the simultaneous action of two mechanisms: by changing the thermodynamics of interaction near the surface due to selective adsorption of one of the components and by the redistribution of components according to their molecular masses between the boundary region (near the surface) and in the matrix.The measurements of the kinetics of phase separation and calculation of the parameters of the activation energy are in agreement with proposed mechanisms.