Breath figure patterns prepared by spin coating in a dry environment

We introduce a novel method for fabricating breath figure patterns on a homopolymer film by spin coating of polymer solutions with various solvents. The homopolymers employed in this study were cellulose acetate butyrate, monocarboxylated end-functional polystyrene, and poly(methyl methacrylate). Breath figure patterns were generated even when a water-miscible solvent such as tetrahydrofuran (THF) was used as a solvent. We even succeeded in generating breath figure patterns by spin coating even under a dry environment (relative humidity less than 30%), when water was directly added into THF solution. With the combination of the spin coating method, pores with a few hundred nanometers to several micrometers have been generated. We found that the pore size becomes larger with increasing water content in THF solution and decreasing rotating speed. This is equivalent to increasing humidity and decreasing evaporation speed, respectively, in the conventional method, which is direct solvent evaporation under a humid environment. Thus, compared with the conventional method for making breath figure patterns, this method would be very convenient for fabricating large-scale films with various pore sizes.     

A facile approach to fabricate hierarchically structured poly(3‐hexylthiophene‐2,5‐diyl) films

Microstructured surfaces have great potentials to improve the performances and efficiency of optoelectronic devices. In this work, a simple robust approach based on surface instabilities was presented to fabricate poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) films with ridge‐like/wrinkled composite microstructures. Namely, the hierarchically patterned films were prepared by spin coating the P3HT/tetrahydrofuran (THF) solution on a polydimethylsiloxane (PDMS) substrate to form stable ridge‐like structures, followed by solvent vapor swelling to create surface wrinkles with the orientation guided by the ridge‐like structures. During spin coating of the P3HT/THF solution, the ridge‐like structures were generated by the in‐situ template of the THF swelling‐induced creasing structures on the PDMS substrate. To our knowledge, it is the first report that the creasing structures are used as a recoverable template for patterning films. The crease‐templated ridge‐like structures were well modulated by the THF swelling time, the modulus of the PDMS substrate, the P3HT/THF solution concentration and the selective/blanket exposure of the PDMS substrate to O₂ plasma. UV–vis and fluorescence spectrometry measurements indicated that the light absorption and fluorescent emission were improved on the hierarchically patterned P3HT films, which can be utilized to enhance the efficiencies of organic solar cells. Furthermore, this simple versatile method based on the solvent swelling‐induced crease as the in‐situ recoverable template has been extended to pattern other spin‐coated films with different compositions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 928–939     

The morphology and structure of PS‐b‐P4VP block copolymer films by solvent annealing: effect of the solvent parameter

Lamellae (symmetric) forming polystyrene‐b‐poly(4‐vinylpyridine) (PS‐b‐P4VP) block copolymers (BCPs) were used to produce nanostructured thin films by solvent (toluene) casting (spin‐coating) onto silicon substrates. As expected, strong micellization of PS‐P4VP in toluene results in poorly ordered hexagonally structures films. Following deposition the films were solvent annealed in various solvents and mixtures thereof. A range of both morphologies including micelle and microphase separated structures were observed. It was found that nanostructures typical of films of regular thickness (across the substrate) and demonstrating microphase separation occurred only for relatively few solvents and mixtures. The data demonstrate that simple models of solvent annealing based on swelling of the polymer promoting higher polymer chain mobility are not appropriate and more careful rationalization is required to understand these data. Analysis suggests that regular phase separated films can only be achieved when the copolymer Hildebrand solubility parameter is very similar to the value of the solvent. It is suggested that the solvent anneal method used is best considered as a liquid phase technique rather than a vapor phase method. The results show that solvent annealing methods can be a very powerful means to control structure and in some circumstances dominate other factors such as surface chemistry and surface energies. Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of film thickness controlled by ink‐jet printing method on the optical properties of an electroluminescent polymer

Ink‐jet printing (IJP) represents a highly promising liquid processed polymer deposition method for the film preparation of functional polymers in photo‐electronic devices. In this report, the results on the IJP of a fluorene‐based electroluminescent polymer, poly(9,9‐dihexylfluorene‐alt‐2,5‐dioctyloxybenzene) (PF6OC8), from a piezoelectric droplet generator are presented. The polymer film thickness has been found to show an approximate linear relation with the number of droplets per unit area; it is thus convenient to control the film thickness by the space of printed dots in IJP process. In comparison, spin coating approach is also used to prepare polymer films with different thicknesses by varying solution concentration and spinning speed. However, it is found that spin coating is difficult to control the film thickness quantitatively. The influence of film thickness on the photoluminescence (PL) properties of PF6OC8 films prepared by IJP and spin coating is comparatively investigated. For both ink‐jet printed and spin coated films, the intensity of PL spectra first increases and then decreases with increase in the film thickness, probably due to the exciton quenching in thicker films. When the polymer film thickness is at nanoscale, the major peak in the PL spectrum is the 0–0 vibronic emission at about 420 nm, and with increase in the film thickness, the 0–1 vibronic peak at about 440 nm becomes dominant. The red‐shifted PL spectra with increase in film thickness show the change from the 2D exciton state to the 3D one. Copyright © 2009 John Wiley & Sons, Ltd.     

Spin coating process of sol-gel silicate films deposition: Effect of spin speed and processing temperature

The effect of two factors having the most important influence on spin coating process of sol-gel films: the spin speed and the temperature (of the substrate and the applied solution) during film deposition is discussed. It is shown, that film thickness and thickness uniformity are determined by centrifugal driving force dynamics, viscous polymer rheology, solvent evaporation dynamics, and film porous microstructure.     

The relationship between end‐group concentrations and stability of spin‐coated thin polymer films investigated by ToF‐SIMS depth profiling

Stable and unstable spin‐coated polymer films were prepared using various solvents and substrates. The relationship between polymer end‐group concentrations and stability of spin‐coated polymer films was revealed by time‐of‐flight secondary ion mass spectrometry depth profiling. A high concentration of bromine end groups at the interface between the polymer and the substrate helped to prevent the dewetting of films. In contrast, the bromine end groups were found to be more evenly distributed in unstable thin films. The extent to which the bromine end groups segregate to the interface depended on the competitive interactions between the polymer, the solvent and the substrate. Stronger polymer–solvent and solvent–substrate interactions prevented the segregation of the bromine end groups to the interface, resulting in unstable polymer films. Copyright © 2013 John Wiley & Sons, Ltd.     

Solvent vapor annealing of block copolymer thin films: removal of processing history

The ordering processes of PS-b-P2VP block copolymer thin films with different processing histories were studied during solvent vapor annealing by in situ grazing incidence small-angle X-ray scattering (GISAXS). We compared cylinder-forming PS-b-P2VP thin films with 34 kg/mol molecular weight that were prepared in three different ways: spin coating, spin coating and subsequent solvent vapor annealing where the solvent vapor was removed instantaneously, and spin coating and subsequent solvent vapor annealing where the solvent vapor was removed slowly. Block copolymer thin films retained the morphology resulting from the different “processing histories” at smaller swelling ratios. This processing history was erased when the samples reached a higher swelling ratio (~1.4). After the solvent was slowly removed from the swollen film, the surface morphology was characterized by ex situ AFM. All samples showed the same morphology after solvent annealing regardless of the initial morphology, indicating the morphology of solvent annealed samples is determined by the polymer concentration in the swollen film and the solvent vapor removal rate, but not the processing history.     

Surface characterizations of spin-coated films of ethylcellulose and hydroxypropyl methylcellulose blends

Films of pure ethylcellulose (EC) and hydroxypropyl methylcellulose (HPMC) polymers and EC/HPMC blends were prepared from solutions by spin coating where isopropyl alcohol (IPA), water, and IPA/water cosolvent were used as solvents. Surface structures of the films were investigated using optical microscopy, atomic force microscopy (AFM), and Raman mapping and spectroscopy. For the films prepared from EC/HPMC blend solutions using the IPA/water cosolvent, different domain structures such as islands or pits and phase separation between EC and HPMC were observed by optical microscopy and AFM. The nature of the polymer components on the surface of the films was identified by Raman mapping and spectroscopy. Experimental results also indicated that polymer composition, solvent, and temperature during spin coating had significant impacts on surface structures of the films.     

Acrylic polymer/silica organic–inorganic hybrid emulsions for coating materials: Role of the silane coupling agent

Acrylic polymer/silica organic–inorganic hybrid emulsions were synthesized by a simple method, that is, a conventional emulsion polymerization and subsequent sol–gel process, to provide water‐based coating materials. The acrylic polymer emulsions contained a silane coupling agent monomer, such as methacryloxypropyltriethoxysilane, to form highly solvent‐resistant hybrid films. On the other hand, the hybrid films from the surface‐modified polymer emulsions, in which the silane coupling agent was located only on the surface of the polymer particles and the particle core was not crosslinked, did not exhibit high solvent resistance. A honeycomblike array structure, which was derived from the polymer particles (diameter ≈ 50 nm) and the silica domain, on the hybrid film surfaces was observed by atomic force microscopy. The crosslinked core part and silane coupling agent containing the shell part of the polymer particles played important roles in attaining high solvent resistance. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4736–4742, 2006     

Structural Evolution of an Organic Semiconducting Molecule onto a Soft Substrate

The structural organization and evolution of the organic semiconducting molecule 2,7‐dioctyloxy[1]benzothieno[3,2‐b]‐benzothiophene on a soft matrix is studied. Thin films of a blend formed from polystyrene and the molecule were prepared by spin‐coating onto silicon substrates, which were subsequently studied by using a combination of microscopy and scattering techniques. The organic semiconducting molecule segregated to the surface and developed a phase with a different structure to the bulk, as in the case of a substrate induced phase observed previously. Under a solvent vapor annealing procedure, the growth of micrometer‐sized tetragonal crystals onto the polymer surface was observed, which was not evidenced for the silicon substrates.     

Control of the interchain pi-pi interaction and electron density distribution at the surface of conjugated poly(3-hexylthiophene) thin films

Interchain interaction, i.e., pi-pi stacking, can benefit the carrier transport in conjugated regio-regular poly(3-hexylthiophene) (P3HT) thin films. However, the existence of the insulating side hexyl chains in the surface region may be detrimental to the charge transfer between the polymer backbone and overlayer molecules. The control of the molecular orientation in the surface region is expected to alter the distribution of the pi electron density at the surface to solve such problems, which can be achieved by controlling the solvent removal rate during solidification. The evidence that the pi-electron density distribution at the outermost surface can be controlled is demonstrated by the investigation using the powerful combination of near edge X-ray absorption fine structure spectroscopy, ultraviolet photoelectron spectroscopy, and the most surface-sensitive technique: Penning ionization electron spectroscopy. From the spectroscopic studies, it can be deduced that the slower removal rate of the solvent makes the polymer chains even at the surface have sufficient time to adopt a more nearly equilibrium structure with edge-on conformation. Thus, the side hexyl chains extend outside the surface, which buries the pi-electron density contributed from the polymer backbone. Contrarily, the quench of obtaining a thermo-equilibrium structure in the surface region due to the faster removal of the solvent residual can lead to the surface chain conformation without persisting to the strong bulk orientation preference. Therefore, the face-on conformation of the polymer chain at the surface of thin films coated with high spin coating speed facilitate the electron density of the polymer backbone exposed outside the surface. Finally, thickness dependence of the surface electronic structure of P3HT thin films is also discussed.     

Photo‐optical properties and photo‐orientation phenomena in an immiscible blend of cholesteric copolymer with azobenzene‐containing polymer

Novel side chain liquid crystalline polymer blends containing immiscible non‐chiral and cholesteric polymers were prepared. A non‐chiral polymer was used containing azobenzene side groups capable of E–Z photoisomerization. Phase behaviour and miscibility properties of the blends were studied. Thin films of the blends were prepared by spin‐coating; it was shown that just after preparation these films are optically isotropic and homogeneous. Photo‐ and chiro‐optical properties of the films as well as photo‐orientation phenomena induced by the action of polarized light were investigated. It was found that the photo‐optical behavior of these films is rather complicated and considerably different from the properties of both individual components. This difference is associated with the strong influence of blend morphology on the photo‐optical properties.     

Electrochemical sensing with electrodes modified with molecularly imprinted polymer films

This article summarises our work on the development of voltammetric sensors based on molecularly imprinted polymers. Several recognition elements and integration strategies were used:1.membranes electropolymerised at the electrode surface; 2.casting of polymeric membranes by drop-coating a solution of pre-formed polymer (polyphosphazene) and template in a low-boiling-point solvent on to the electrode surface; 3.preparation of composite membranes containing conductive material (graphite or carbon black), acrylic-type molecularly imprinted polymers (small particle size), and PVC as binder; and 4.in-situ polymerisation of a thin layer of acrylic imprinted polymer deposited on the electrode surface by spin coating.All the options evaluated offer the possibility of controlling electrode characteristics such as hydrophobic/hydrophilic character, permeability, or film thickness, which are essential for obtaining good sensor performance.     

Effects of evaporation velocity and film thickness on poly(3‐hexylthiophene) thin films processed from aggregate dispersions in binary solvent mixtures

Aggregate dispersions of P3HT in two series of solvent mixtures, chloroform:dichloromethane and toluene:dichloromethane, are used to study the impact of the evaporation velocity and film thickness on the P3HT films processed using two spin‐coating speeds (1000 rpm and 2000 rpm). The structural order and surface morphology were investigated with UV/Vis absorption spectroscopy and atomic force microscopy techniques. There is no evidence that the characteristics of the liquid phase P3HT dispersions impact the structures of the films, which is in agreement with a previous study of drop cast P3HT films that were dried over much longer time periods. An association is observed between the extent of aggregation in the liquid phase and the thickness and surface roughness parameters of the films. However, the structural order does not correlate with the thickness of the films, which was previously reported for polymer films processed from amorphous polymer solutions in pure organic solvents. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 330–343     

Molecularly imprinted polymer as a novel solid‐phase microextraction coating for the selective enrichment of trace imidazolinones in rice,peanut, and soil

The development and application of an imazethapyr molecularly imprinted polymer‐based solid‐phase microextraction coating were investigated. A novel molecularly imprinted polymer coating with imazethapyr as template was firstly prepared by a one‐step in situ polymerization method, and demonstrated specific selectivity to imidazolinone herbicides in complicated samples. The structural characteristics and extraction performance of the imazethapyr molecularly imprinted polymer coating were studied. The molecularly imprinted polymer coating was homogeneous, dense, and heat and solvent resistant. Adsorption capacity experiments showed that the molecularly imprinted polymer coating could selectively extract imazethapyr and its structural analogs, and the maximum adsorption capacity was 2.5 times as much as that of the nonimprinted polymer coating. A method for the determination of five imidazolinones by imazethapyr molecularly imprinted polymer solid‐phase microextraction coupled with high‐performance liquid chromatography was developed. The linear range was 0.50–50 μg/L for imazameth, imazamox, imazapyr acid, and imazethapyr, and 1.0–100 μg/L for imazaquin acid, and the detection limits were within the range of 0.070–0.29 μg/L. The method was applied to simultaneous and multiresidual determinations of trace imidazolinones in rice, peanut, and soil samples with satisfactory recoveries of 60.6–99.5, 79.1–123, and 61.3–116%, respectively, and relative standard deviations of 0.40–10%, which indicated that this method was suitable for the trace analysis of imidazolinones in complex food and environmental samples.     

Porous structures of polymer films prepared by spin coating with mixed solvents under humid condition

We investigate the effects of interfacial energy between water and solvent as well as polymer concentration on the formation of porous structures of polymer films prepared by spin coating of cellulose acetate butyrate (CAB) in mixed solvent of tetrahydrofuran (THF) and chloroform under humid condition. The interfacial energy between water and the solvent was gradually changed by the addition of chloroform to the solvent. At a high polymer concentration (0.15 g/cm3 in THF), porous structures were limited only at the top surfaces of CAB films, regardless of interfacial energies, due to the high viscosity of the solution. At a medium concentration (approximately 0.08 g/cm3 in THF), CAB film had relatively uniform pores at the top surface and very small pores inside the film because of the mixing of the water droplets with THF solution. When chloroform was added to THF, pores at the inner CAB film had a comparable size with those at the top surface because of the reduced degree of the mixing between the water droplets and the mixed solvent. A further decrease in polymer concentration (0.05 g/cm3 in THF) caused the final films to have a two-layer porous structure, and the size of pores at each layer was almost the same.     

磷酸铁纳米薄膜复合光波导氨气传感元件的制备

将硝酸铁和甲醇、磷酸溶液按一定比例混合后,通过旋涂法制备了磷酸铁（FePO₄）纳米薄膜,测定了匀胶机转速对膜厚及烘干温度对膜厚和折射率的影响,并发现薄膜的烘干温度超过150 ℃时,薄膜的厚度（130 nm）和折射率(1.7)变化不大。将该薄膜固定在钾离子交换玻璃光波导表面,研制出FePO₄膜/K⁺交换玻璃复合光波导。酸碱指示剂溴百里酚兰（BTB）作为敏感试剂,固定在复合光波导表面,研制了BTB膜-FePO₄膜/K⁺交换玻璃复合光波导氨气传感元件。采用自装的光波导气体传感检测系统对不同浓度的氨气进行了检测。结果表明,该传感元件能够检测0.35 mg/m³浓度的氨气,并具有响应（10 s）及恢复（90 s）速度快、可逆性好、连续使用等特点。     

Determination of Volatile Organic Compounds by a Novel Polymer Spin-Coated Thin Film and Surface Plasmon Resonance

Here, the synthesis, characterization, and volatile organic compound (VOCs) sensing of a 1,3-dimethyl polyphenylene vinylene polymer is reported. The synthesis was performed by a Witting condensation through the reaction of 1,4-terphthaldehyde with the phosphonium chloride of meta-xylene. The material was characterized by infrared spectroscopy, elemental analysis, and thermogravimetric analyses. Thin films of the polymer were prepared by spin coating at speeds from 1000 to 5000?rpm. Ultraviolet–visible spectroscopy and surface plasmon resonance were used to characterize the spin-coated films. The thicknesses of the films were estimated by fitting the curves and were between 4.5 and 24.5?nm depending on the speed. The refractive index of the new polymer was 1.72. The polymer spin-coated films were exposed to volatile organic vapors to characterize their sensing properties by surface plasmon resonance as a function of time. The results showed that the new material responded rapidly, sensitively, and reversibly to VOCs.     

Responsive Gels with the Polymer Containing Alternating Naphthalene Diimide and Fluorinated Alkyl Chains: Gel Formation and Responsiveness as Well as Electrical Conductivity of Polymer Thin Films

A new electroactive polymer 1 with alternating NDI (naphthalene diimide) moieties and fluorinated alkyl chains was prepared and characterized. Gels of polymer 1 were formed in several solvents. Interestingly, gels of polymer 1 exhibited responsiveness toward N₂H₄, F^? and CN^?. Absorption and ESR spectroscopic studies revealed that such responsiveness is owing to the reduction of NDI moieties into the respective NDI^.?. In addition, thin films of polymer 1 were easily prepared with spin‐coating technique and the electrical conductivity of thin films reached 52.4 S/m after exposure to N₂H₄ vapor.