Evaporated Polymer Solutions Research Articles

Breath Figure Assembly on Evaporating Polymer Solution Droplets in Levitation

Breath Figure Assembly on Evaporating Polymer Solution Droplets in Levitation

Research progress in the deposition pattern of evaporating polymer solution

Research progress in the deposition pattern of evaporating polymer solution

Enhance understanding of rhythmic crystallization in confined evaporating polymer solution films: from environment to solution film and then to one period

An enhanced understanding of rhythmic crystallization in an evaporating polymer solution is explored from the environment to the film and to within one period.

On the Nature of the Breath Figures Self‐Assembly in Evaporated Polymer Solutions: Revisiting Physical Factors Governing the Patterning

AbstractThe breath‐figures self‐assembly process was studied. Polystyrene and polycarbonate were dissolved in a diversity of solvents including, acetone, dichloromethane, chloroform, carbon tetrachloride, tetrahydrofuran, toluene, xylenes, carbon disulfide, and N‐N dimethylformamide, and then were evaporated in a humid atmosphere. It was demonstrated that all solutions when sufficiently pre‐cooled gave rise to typical “breath‐figures” patterns. Thus, the decisive factor affecting the formation of the breath‐figures pattern is the temperature of the solution. Wetting properties of the manufactured patterns are reported.

Spin coating of an evaporating polymer solution

We consider a mathematical model of spin coating of a single polymer blended in a solvent. The model describes the one-dimensional development of a thin layer of the mixture as the layer thins due to flow created by a balance of viscous forces and centrifugal forces and evaporation of the solvent. In the model both the diffusivity of the solvent in the polymer and the viscosity of the mixture are very rapidly varying functions of the solvent mass fraction. Guided by numerical solutions an asymptotic analysis reveals a number of different possible behaviours of the thinning layer dependent on the nondimensional parameters describing the system. The main practical interest is in controlling the appearance and development of a “skin” on the polymer where the solvent concentration reduces rapidly on the outer surface leaving the bulk of the layer still with high concentrations of solvent. In practice, a fast and uniform drying of the film is required. The critical parameters controlling this behaviour are found to be the ratio of the diffusion to advection time scales ε, the ratio of the evaporation to advection time scales δ and the ratio of the diffusivity of the pure polymer and the initial mixture exp(−1/γ). In particular, our analysis shows that for very small evaporation with δ≪exp(-3/(4γ))ε3/4 skin formation can be prevented.

The effect of different stabilizers on the formation of self‐assembled porous film via the breath‐figure technique

AbstractThe Breath‐Figure technique was employed to imprint honeycomb structures in the polymer films via the condensation of water vapor on the surface of an evaporating polymer solution. Generally, the condensed water droplets can be stabilized by an end‐functional polymer or by particles added to the polymer solution. In this study, we carried out a systematic experiment on the effect of different stabilizers on the porous honeycomb structure under identical physical conditions. The end‐functional polymer produced a large area of regular spherical bubbles, whereas adding particles to the polymer solution leads to smaller arrays of the flattened bottom bubbles. The separation length between pores was larger for polymer/particle sample than that of the end‐functional polymer films. In the regular area of polymer/particle film many bubbles were not decorated by particles. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1430–1436, 2011

Interplay of kinetics and interfacial interactions in breath figure templating – A phenomenological interpretation

Breath Figure BF templating is an attractive technique for the production of polymer films with controlled porosity: upon the exposure to a moist airflow, monodisperse water droplets condense on the surface of evaporating polymer solution into ordered arrays, acting as a template for the final film structure. This work has been focused on polylactic acid (PDLLA), a biocompatible biodegradable polymer, and aims to provide a phenomenological interpretation of BF process based on the role of kinetics and the influence of interfacial tension. The effects of physical and chemical properties of solvents have been evaluated; the contribution of kinetics has been assessed by modifying the rate of film hardening from seconds to minutes, via different experimental set-up. Our experimental observations indicated that the interplay of kinetics and interfacial tension defines the structure of BF films: interfacial forces govern the physical interactions among water, solvent and polymer, but the dynamics of the process and thus the final pore structure is regulated by kinetics.

On the mechanism of patterning in rapidly evaporated polymer solutions: Is temperature-gradient-driven Marangoni instability responsible for the large-scale patterning?

Large-scale self-organization occurring on the scale of dozens of micrometers in rapidly evaporated polymer solutions based on amorphous polymers and chlorinated solvents was studied. Heating the substrate from below destroys the patterning. This contradicts the idea that self-organization is due to the jump in surface tension caused by a temperature gradient (temperature-gradient-driven Marangoni instability). We relate the patterning to the concentration-gradient- driven effects.

Mesoscopic Patterning in Evaporated Polymer Solutions: Poly(ethylene glycol) and Room‐Temperature‐Vulcanized Polyorganosilanes/‐siloxanes Promote Formation of Honeycomb Structures

AbstractPatterning in evaporated polymer solutions based on amorphous polymers and chlorinated solvents has been investigated. Bilayered films patterned on two scales, i.e., 50 and 5 µm, are obtained. The addition of polyorganosilane/‐siloxane to solutions destroys the large‐scale pattern. Poly(ethylene glycol) promotes the formation of more dense close‐packed structures on the mesoscopic scale (≈5 µm). Short‐range and mesoscopic (liquid‐like) ordering of the honeycomb structures on the characteristic scale of 5 µm is revealed with the statistical analysis of SEM images. Physical mechanisms responsible for patterning are discussed.magnified image

Self‐Assembly in Evaporated Polymer Solutions: Patterning on Two Scales

AbstractSelf‐assembly processes in intensively evaporated polymer solutions, based on chlorinated solvents and amorphous polymers, have been investigated under low and high humidity. Patterning on two scales, mesoscopic and microscopic, has been revealed. The strong dependence of the characteristic size of a mesoscopic pattern on the polymer solution concentration is revealed and studied. Various possible mechanisms of patterning on the two scales are discussed. It has been shown that the widespread hypothesis of micro‐patterning induced with water droplets needs further justification. The influence of substrate defects on the mesoscopic patterning is also investigated.

Self-assembled patterns obtained with evaporated polymer solutions and pre-stretched polymer substrates

We report patterns comprising non-spherical microscopic pores obtained under dewetting of polymer solutions of chlorinated solvents and amorphous polymers deposited on the pre-stretched polyethylene substrates. Patterns on meso- and microscopic scales were observed. Mesoscopically scaled pattern is practically insensitive to the mechanical strain, whereas small scale microscopic voids were highly deformed, and demonstrated the average eccentricity as high as 0.25. Introduction of PEG and RTV polyorganosiloxanes/silanes destroyed the large scale pattern, thus honeycomb pattern comprising non-spherical microscopic pores has been obtained. The patterns demonstrate a potential for polymer ferroelectret applications.

Film formation from polymer solution using inkjet printing method

AbstractThe factors determining the thin‐film shape from an evaporating polymer solution droplet are experimentally studied. The polystyrene/xylene droplets, whose diameter is controlled in the range of 30–100 μm with the mass fraction of 0.5–3.0 wt % are ejected onto a lyophobic substrate. The droplet on the substrate results in an axisymmetric or nonaxisymmetric ring‐like/dot‐like film. The film configuration is dominated by the evaporation rate and the film symmetry is governed by the local pinning time at the periphery. Various relationships are also found among the evaporation rate, pinning time, wetting diameter, and average solute concentration of which the nondimensionalization pronounces explicit relationships and similarity. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Controllable Organization of Quantum Dots into Mesoscale Wires and Cables via Interfacial Block Copolymer Self-Assembly

This paper describes morphology control and characterization of interfacial properties for the synergistic self-assembly of polymer-stabilized CdS quantum dots (QDs), referred to as PS-CdS, with polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymers at the air−water interface. This spontaneous process yields various hierarchical one-dimensional (1D) QD/polymer hybrid structures with widths commensurate with optical wavelengths, ∼300 nm, including wires, cables, branched wires, and rings incorporated along the lengths of cables. Control over predominant hybrid assemblies is achieved by varying the PS-CdS/PS-b-PEO blend composition and the concentration of the spreading solution, with higher PS-CdS fractions resulting in more uniform distributions of QDs throughout hybrid structures and higher spreading concentrations giving rise to a greater predominance of 1D structures relative to circular dots and island aggregates. Compression isotherms of QD/polymer assemblies at the air−water interface reveal that interfacial behavior of aggregates is also dependent on the spreading conditions and blend composition; for all spreading concentrations, a maximum is observed in plots of the limiting area vs PS-CdS weight fraction in the blends, suggesting a competition between the conformational effects of PS-b-PEO dilution and PS-CdS addition. In addition, we describe a mechanism of formation for QD/polymer assemblies, based on AFM data of structures obtained at the highest spreading concentration, in which self-assembly is initiated by dewetting of the evaporating polymer solution from the air−water interface.

Patterning in rapidly evaporated polymer solutions: Formation of annular structures under evaporation of the poor solvent

Patterning in the intensively evaporated polymer solutions based on polystyrene and poor solvent (acetone) was investigated. SEM and AFM studies demonstrated that annular elements of the surface topography are formed in this case, in contrast to the honeycomb patterns obtained under the evaporation of the good solvent (chloroform). The authors suggest that the theory of viscous dewetting developed by de Gennes explains the phenomenon satisfactorily.

Micropatterned Polymer Surfaces Induced by Nonsolvent

In this work, we present a facile method for fabricating polymer thin films with micropatterned surfaces by evaporating polymer solution containing a small amount of nonsolvent of polymer in air. Poly(methyl methacrylate) (PMMA) and polystyrene (PS) films with densely packed micropores on the surfaces were fabricated. This method was also used to prepare three-dimensional PMMA films with micropatterned surfaces. The effects of nonsolvent content; evaporation temperature; and interactions between the polymer, solvent, and nonsolvent on the specific patterns were investigated, and the formation mechanism of the pores is discussed. This simple route can potentially be used, for example, in the large-scale production of patterned surfaces, three-dimensional painting, and hydrophobicity-enhancing coatings.

Mechanisms of mesoscopic patterning in evaporated polymer films deposited on tilted and vertical substrates

Mesoscopic self-organization in evaporated polymer solutions was investigated. The structure of dried films was studied with optical and SEM microscopy. Formation of mesoscopic cells was studied in situ with a shadowgraph technique. Intensive migration of the vapor bubbles is an important factor in the formation of mesoscopic cells. A mechanism of mesoscopic network formation, based on the mass transport instability in evaporated film, was proposed. The impact of the solvent is discussed.

Self-assembly in evaporated polymer solutions: Influence of the solution concentration

Amorphous polymers were dissolved in chlorinated organic solvents and deposited on thin horizontal substrates. The solutions with various concentrations of polymers were deposited and evaporated under ambient conditions in a slow air current. Self-assembled oriented mesoscopically scaled patterns were observed. The patterns were studied with optical and atomic force microscopy. The concentration of the solution exerts a decisive influence on the mesoscopic cell characteristic dimension. Cell dimensions grow linearly with the polymer solution concentration for all kinds of tested polymers, chlorinated solvents and substrates. The dependence could be explained by a physical mechanism, based on the mass transport instability occurring under the intensive evaporation of the solvent. In situ FTIR study of the process was performed first. It was established with FTIR spectroscopy that film porosity is not due to water droplet condensation under evaporation.

Mesoscopic Patterning in Evaporated Polymer Solutions: New Experimental Data and Physical Mechanisms

Mesoscopic Patterning in Evaporated Polymer Solutions: New Experimental Data and Physical Mechanisms

Mesoscopic Patterning in Evaporated Polymer Solutions: New Experimental Data and Physical Mechanisms

Mesoscopically ordered patterns were obtained when polymer solutions were applied to tilted substrates and evaporated immediately under ambient conditions in a slow air current. The patterns were studied with optical, scanning electron, and atomic force microscopy. Shadowgraph visualization of the patterning was carried out, and visualization of the flow with an ink tracer was performed. Restrained and nonrestrained flows of the polymer solution gave rise to very similar patterning. The formation of the patterns on different solid substrates, including substrates wetted with silicon oil, was investigated. The concentration of the polymer solutions exerted an influence on the characteristic dimension of mesoscaled cells. A physical mechanism of the patterning is proposed. The mechanism is based on the mass transport instability occurring under the intensive evaporation of the solvent. The model satisfactorily explains the experimental findings.

Formation of honeycomb patterns in evaporated polymer solutions: Influence of the molecular weight

The influence of polymer molecular weight on the formation of honeycomb patterns obtained by evaporation of polystyrene solutions was investigated. Pattern structure was studied with scanning electron and atomic force microscopy. It was determined that molecular weight exerts a decisive influence on the patterns makeup. Pore size and depth, distance between pores and specific porosity depend strongly on the polymer's molecular weight.