Photochromism of 4‐cyanophenylazobenzene in liquid crystalline‐coil AB diblock copolymers: the influence of microstructure

The UV and V spectral features of an AB diblock copolymer composed of polystyrene and a poly(1,2 & 3,4)isoprene‐based polymer with a pendant liquid crystalline 4‐cyanophenylazobenzene (Az) group in comparison with those of a corresponding LC polyisoprene homopolymer are reported. The orientational and photochromic behavior of an AB diblock copolymer in thin films shows distinct differences from that of a corresponding Az homopolymer. This can be attributed to the influence of the phase separated polymer coil microdomain of polystyrene in the AB block copolymer film.     

Controlling the size of nanostructures in thin films via blending of block copolymers and homopolymers

The effects of molecular weight and concentration of poly (methyl methacrylate) (PMMA) homopolymer or symmetric short polystyrene-block-poly (methyl methacrylate) (PS-b-PMMA) diblock copolymer on the size of the nanostructures of its blends with symmetric long PS-b-PMMA diblock copolymer have been investigated by atomic force microscopy. By careful controlling of the film thickness, solvent selectivity, and annealing time, PMMA cylindrical microdomains oriented normal to the film surface were obtained in all thin films. With the addition of both low- and high-molecular-weight PMMA homopolymers, the cylindrical domain sizes increased although it was less obvious for the lower molecular weight homopolymer. In contrast to the homopolymer, adding the short chain diblock copolymer resulted in a decrease in the cylindrical domain size, which was ascribed to the reduction of the interfacial tension and increase in the stretching energy.     

Atomic force microscopy investigation of asymmetric diblock copolymer morphologies in thin films

Microphase separation and the resulting morphology of asymmetric diblock copolymers of poly(ε-caprolactone) (PCL) in thin films have been investigated by atomic force microscopy. Copolymers consisted of a short block of PCL (M_n∼2500-4500 g/mole) and a longer second block of poly(methyl methacrylate) (PMMA), poly(styrene) (PS) or poly(cyclohexene oxide) (PCHO). Tendency for microphase separation above the glass transition temperature of the second block (PMMA, PS or PCHO) resulted in a pitted morphology on the surface of the thin films. This tendency was strongest for PMMA and weakest for PCHO. The presence of up to 54% PMMA homopolymer in PCL-PMMA block copolymer did not prevent the formation of such pitted morphology on the surface. The effect of the chemical structure of the second block and the possible orientations of the block copolymer molecules in thin films are discussed.     

Fabrication of nanoporous templates from diblock copolymer thin films on alkylchlorosilane-neutralized surfaces

The fabrication of nanoporous templates from poly(styrene)-b-poly(methyl methacrylate) diblock copolymer thin films (PS-b-PMMA, volume ratio 70:30) on silicon requires precise control of interfacial energies to achieve a perpendicular orientation of the PMMA cylindrical microdomains relative to the substrate. To provide a simple, rapid, yet tunable approach for surface neutralization, we investigated the self-assembled ordering of PS-b-PMMA diblock copolymer thin films on silicon substrates modified with a partial monolayer of octadecyldimethyl chlorosilane (ODMS), i.e., a layer of ODMS with a grafting density less than the maximum possible monolayer surface coverage. We demonstrate herein the fabrication of nanoporous PS templates from annealed PS-b-PMMA diblock copolymer thin films on these partial ODMS SAMs.     

Control of the microdomain orientation in block copolymer thin films with homopolymers for lithographic application

Block copolymer lithography is a promising method for fabricating periodical nanopatterns of less than 20 nm by self-assembly and can be applicable for fabricating patterned magnetic media with a recording density over 1 Tb/in.2. We found a simple technique to control the orientation of cylindrical microdomains in thin films. Simply by mixing polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymers with the homopolymer (PS or PMMA) of the major component, we could align the cylindrical microdomains perpendicular to the film surface. The added homopolymer induces conformational entropic relaxation of the block chains in microdomain space and stabilizes the perpendicular orientation of hexagonally packed cylindrical microdomains. Thus formed perpendicular cylinders can be readily aligned in a regular array with a grating substrate.     

Monte Carlo simulation of AB diblock copolymer between surface and substrate and comparison of experimental results

The morphologies of AB diblock copolymer film between the substrate and surface were investigated via Monte Carlo simulations on simple cubic lattices. The morphological dependence of the diblock copolymer thin film on the thickness, as well as the composition and interactive intensity has been mainly studied. With the increase of A‐segments fraction, various microdomain morphologies including regular parallel stripe‐like, mesh‐like, and normal lamella near the region of the surface were generated in this work. The morphology of thin films of asymmetric diblock copolymer was found to form cylinders in a bulk system when L_z was equal to 30. The morphologies of PS‐b‐PDMS diblock copolymer films have been studied via atomic force microscopy (AFM) and transition electron microscopy (TEM) measurements. The surface morphology of the PS‐b‐PDMS copolymer thin film shows a mesh‐like microphase separated structure, and PDMS continuous phase protruded on the PS dispersed phase. The surface composition of PS‐b‐PDMS copolymer thin films was measured by means of X‐ray photoelectron spectroscopy (XPS) and ATR‐IR. The comparison results show that the experimental observations are in good agreement with the simulation results. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1835–1845, 2006     

Morphologies of Diblock Copolymer/Homopolymer Blend Films

Summary: Using bond length fluctuation and cavity diffusion algorithm, the morphologies of diblock copolymer/homopolymer blend films, AB/C and AB/A, confined between two hard walls are studied via Monte Carlo (MC) simulation on a cubic lattice. For the AB/C film, the C homopolymer is supposed to be more compatible with the A block than with the B block, while A and B are mutually incompatible. Effects of the composition of the diblock copolymer/homopolymer mixture, the symmetry of the diblock copolymer chain, the film thickness and the selective wall field on morphologies are studied in detail. Furthermore, the simulated results are compared with that of corresponding ABA and ABC triblock copolymer thin films. Comparisons with experiments and SCF theory also show good agreement. The results indicate that both the AB/C and AB/A can be used to prepare porous AB diblock copolymer membranes, the size of the pore channel can be controlled by the volume fraction of homopolymer C or homopolymer A.

Morphology of A₆B₁₄/C₁₀ polymer blend film.     

Using neutron reflectivity to determine the dynamic properties of a copolymer in a homopolymer matrix

A protocol for using neutron reflectivity to monitor the dynamic properties of a copolymer in a homopolymer matrix is described. This technique may be used to monitor a broad range of systems, as long as the copolymer and homopolymer form a miscible blend at low copolymer concentrations. Moreover, with knowledge of the Flory–Huggins interaction parameter between the copolymer and homopolymer, the molecular dynamic parameters of the copolymer, such as the tracer diffusion coefficient, segmental friction factor, and longest relaxation time, can be quantitatively determined. This technique is demonstrated by the determination of these parameters for a series of styrene/methyl methacrylate alternating copolymers dispersed in a matrix of deuterated poly(methyl methacrylate). Interestingly, the segmental friction factor of these alternating copolymers is significantly different from that of similar diblock copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3235–3247, 2004     

The Formation of Ordered Nanoholes in Binary,Chemically Similar,Symmetric Diblock Copolymer Blend Films

Summary: Binary symmetric diblock copolymer blends, that is, low‐molecular‐weight poly(styrene‐block‐methyl methacrylate) (PS‐b‐PMMA) and high‐molecular‐weight poly(styrene‐block‐methacrylate) (PS‐b‐PMA), self‐assemble on silicon substrates to form structures with highly ordered nanoholes in thin films. As a result of the chemically similar structure of the PMA and the PMMA block, the PMMA chain penetrates through the large PMA block that absorbs preferentially on the polar silicon substrate. This results in the formation of nanoholes in the PS continuous matrix.

An atomic force microscopy image of the thin film obtained from the blend of low‐molecular‐weight PS‐b‐PMMA and high‐molecular‐weight PS‐b‐PMA. The regular array of nanoholes in the films surface is clearly visible.     

Modification of the morphology of P(S-b-EO) templated thin TiO2 films by swelling with PS homopolymer

For the controlled modification of sol-gel-templated polymer nanocomposites, which are transferred to a nanostructured, crystalline TiO2 phase by a calcination process, the addition of a single homopolymer was investigated. For the preparation, the homopolymer polystyrene (PS) is added in different amounts to the diblock copolymer P(S-b-EO) acting as a templating agent. The homopolymer/diblock copolymer blend system is combined with sol-gel chemistry to provide and attach the TiO2 nanoparticles to the diblock copolymer. So-called good-poor solvent-pair-induced phase separation leads to the formation of nanostructures by film preparation via spin coating. The fabricated morphologies are studied as a function of added homopolymer before and after calcination with atomic force microscopy, field emission scanning electron microscopy, and grazing incidence small-angle X-ray scattering. The observed behavior is discussed in the framework of controlling the block copolymer morphologies by the addition of homopolymers. At small homopolymer concentrations, the increase in homopolymer concentration changes the structure size, whereas at high homopolymer concentrations, a change in morphology is triggered. Thus, the behavior of a pure polymer system is transferred to a more complex hybrid system.     

Order‐order transitions of a triblock copolymer with a homopolymer (ABC/A) blend film induced by saturated solvent vapor annealing

The morphology transition of binary mixtures of polystyrene‐block‐poly(butadiene)‐block‐poly(2‐vinylpyridine)(SBV) triblock and polystyrene (PS) homopolymer thin films was investigated as a function of the volume fraction of added homopolymer and the annealing time in benzene vapor. It was found that the weight ratio of PS in the blends influenced the transition process. When PS content was >5%, the order‐order transition (OOT) of core‐shell cylinders (C) →sphere in “diblock Gyroid” (sdG) → sphere in lamella (sL) → sphere (S) was observed, which was similar to ABC triblock copolymer except for the increased surface area of the PS phase. When PS content reached to 10–30%, the OOT in the sequence of C → sL → S was observed. The disappearance of the Gyroid phase is due to the change of the effective volume fraction. Further increasing the PS content, C phase also disappeared and sL → S was expected to take place. © 2014 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2014 , 52, 1030–1036     

Dewetting of thin polystyrene films absorbed on epoxy coated substrates

Various characteristics of dewetting of thin polystyrene (PS) films absorbed on highly cross-linked epoxy-coated and silicon oxide covered substrates are studied as a function of PS film thickness (20h(c1) whereas the spinodal dewetting (SD) occurs through the growth of surface undulations for hh(c2) while the SD mechanism is observed for h相似文献   

Thin film confinement reduces compatibility in symmetric ternary block copolymer/homopolymer blends

The thin film phase behavior of ternary blends consisting of symmetric poly(styrene) (PS)-b-poly(dimethylsiloxane)(PDMS), PS, and PDMS was investigated using X-ray reflectivity (XRR) and atomic force microscopy (AFM). This system is strongly segregated, and the homopolymers are approximately the same length as the corresponding blocks of the copolymer. The XRR and AFM data are used to quantify changes in domain spacing (L) and morphology evolution with increasing homopolymer content (Φ _H). In 100 nm thick films, from Φ _H = 0 to 0.20, the system maintains a perfect parallel lamellar structure and domains swell as predicted based on theory; however, from Φ _H = 0.30 to 0.50, a morphology transition to a “dot pattern” morphology (tentatively identified as perforated lamellae) and mixed morphologies were observed before macrophase separation. In thicker films, dot patterns were observed for a broad range of Φ _H before macrophase separation. The absence of the bicontinuous microemulsion phase reported for bulk blends and thin films of perpendicular lamellae and the presence of dot patterns/perforated lamellae are attributed to preferential migration of the PDMS homopolymer to the wetting layers located at the substrate and free air interfaces, which leads to an asymmetric composition within the film and morphology transition. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1443–1451     

Conformational change in an isolated single synthetic polymer chain on a mica surface observed by atomic force microscopy

The random coil conformation of an isolated conventional synthetic polymer chain was clearly imaged by atomic force microscopy (AFM). The sample used was a poly(styrene)-block-poly(methyl methacrylate) diblock copolymer. A very dilute solution of the copolymer with benzene was spread on a water surface. The structure thus formed on water was subsequently transferred and deposited onto mica at various surface pressures and observed under AFM. The AFM images obtained with films deposited at a low surface pressure (<0.1 mN/m) showed a single polystyrene (PS) block chain aggregated into a single PS particle with a single poly(methyl methacrylate) (PMMA) block chain emanating from the particle. Immediately after the deposition, the single PMMA block chain aggregated to form a condensed monolayer around the polystyrene particles. However, after exposing the deposited film to highly humid air for 1 day, the PMMA chains spread out so that the single PMMA block chain could be identified as a random coil on the substrate. The thin water layer formed on the mica substrate in humid air may enable the PMMA block chain to be mobilized on the substrate, leading to the conformational rearrangement from the condensed monolayer conformation to an expanded and elongated coil. The elongation of the PMMA chain was highly sensitive to the humidity; the maximum elongation was obtained at 79% relative humidity. The elongation was a slow process and took about 20 h.     

Morphologies in solvent-annealed thin films of symmetric diblock copolymer

We have systematically studied the thin film morphologies of symmetric poly(styrene)-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer after annealing to solvents with varying selectivity. Upon neutral solvent vapor annealing, terraced morphology is observed without any lateral structures on the surfaces. When using PS-selective solvent annealing, the film exhibits macroscopically flat with a disordered micellar structure. While PMMA-selective solvent annealing leads to the dewetting of the film with fractal-like holes, with highly ordered nanoscale depressions in the region of undewetted films. In addition, when decreasing the swelling degree of the film in the case of PMMA-selective solvent annealing, hills and valleys are observed with the coexistence of highly ordered nanoscale spheres and stripes on the surface, in contrast to the case of higher swelling degree. The differences are explained qualitatively on the basis of polymer-solvent interaction parameters of the different components.     

Coupling of microphase separation and dewetting in weakly segregated diblock co-polymer ultrathin films

We have studied the coupling behavior of microphase separation and autophobic dewetting in weakly segregated poly(ε-caprolactone)-block-poly(L-lactide) (PCL-b-PLLA) diblock co-polymer ultrathin films on carbon-coated mica substrates. At temperatures higher than the melting point of the PLLA block, the co-polymer forms a lamellar structure in bulk with a long period of L ～ 20 nm, as determined using small-angle X-ray scattering. The relaxation procedure of ultrathin films with an initial film thickness of h = 10 nm during annealing has been followed by atomic force microscopy (AFM). In the experimental temperature range (100-140 °C), the co-polymer dewets to an ultrathin film of itself at about 5 nm because of the strong attraction of both blocks with the substrate. Moreover, the dewetting velocity increases with decreasing annealing temperatures. This novel dewetting kinetics can be explained by a competition effect of the composition fluctuation driven by the microphase separation with the dominated dewetting process during the early stage of the annealing process. While dewetting dominates the relaxation procedure and leads to the rupture of the ultrathin films, the composition fluctuation induced by the microphase separation attempts to stabilize them because of the matching of h to the long period (h ～ 1/2L). The temperature dependence of these two processes leads to this novel relaxation kinetics of co-polymer thin films.     

Structure evolution in layers of polymer blend nanoparticles

The early stages of phase evolution, not available for nanometer polymer blend films spin-cast from solutions of incompatible mixtures, have been examined for films prepared from nanoparticles of deuterated polystyrene/ poly(methyl methacrylate) blends (1:1 mass fraction of dPS/PMMA) with PS-PMMA diblock copolymer additives. The initial phase arrangement, confined to the size of nanoparticles, has provided the homogeneity of the initial film composition. The early stages of structure formation, promoted by annealing and traced with atomic and lateral force microscopy (AFM, LFM) as well as secondary ion mass spectroscopy (SIMS), resulted in bilayers, observed commonly for as-prepared solvent-cast blends. The initiated capillary instability of the upper dPS-rich layer depended on copolymer additives, which enhanced the lateral structures pinning the dewetting process.     

Double/single phase segregation and vertical stratification induced by crystallization in all‐crystalline tri/diblock copolymers and homopolymer blends of poly(3‐hexylthiophene) and poly(ethylene glycol)

Distinct stratified and non‐stratified morphologies were developed in poly(3‐hexylthiophene) (P3HT) and poly(ethylene glycol) (PEG)‐based homopolymer blends and diblock and triblock copolymer systems. By applying X‐ray photoelectron spectroscopy, only a double‐percolation mechanism including assembling of P3HT chains into the nanofibers in solution aging process with a marginal solvent like p‐xylene as well as crystallization of PEG phase in the cast thin films resulted in vertical stratification and networked fibrils. In cast thin films whose PEG phase, due to low molecular weight or being constrained between two rigid P3HT blocks in triblock copolymers was not crystallized, a non‐stratified discrete fibrillar morphology was acquired. Crystallization of PEGs in the thin films mainly participated in networking and expelling pre‐organized P3HT fibrils to the film surface. By performing the solution aging step in a good solvent such as o‐dichlorobenzene, the P3HTs remained in a coily‐like conformation, and casting the corresponding thin films reflected the non‐stratified discrete granular and featureless morphologies. Assembling the P3HT chains in the presence of PEG phase in cast films at most led to the low‐crystalline granules instead of highly crystalline nanofibrils. No significant crystallization in either homopolymer blends or block copolymer systems conduced to a featureless morphology with homogeneous distribution of existed materials. The surface morphology and ordering in various morphologies were studied employing atomic force microscopy, grazing incidence X‐ray diffraction, and ultraviolet–visible analyses. Copyright © 2016 John Wiley & Sons, Ltd.     

Multiscale dewetting of triblock copolymer thin film induced by solvent vapor

Multiscale dewetting of poly(styrene‐b‐ethylene/butylenes‐b‐styrene) (SEBS) triblock copolymer thin films induced by volatile solvent vapor treatment were observed in this study. Film rupture occurred at first and produced macroscopic holes. Near‐regular droplets (which represented a compromise between complete disorder and perfect order) could be formed at the last stage. The mechanism of solvent‐driven dewetting was discussed by comparing with that of thermal‐induced dewetting. Similar to thermal‐induced dewetting, the block copolymer thin films initially break up through the nucleation of holes that perforated the films. The rapid growing holes became unstable and formed nonequilibrium fingering patterns. The films exhibit autophobic or autodewetting phenomena. The velocity of the holes growth was nearly a constant (3.3 μm/min). The stages of the dewetting were quite similar to that found for homopolymer and block copolymer thin films dewetting on solid or liquid substrates under thermal treatment. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2874–2884, 2005     

PTHF-b-PMMA/PVC共混体系的相容性和结晶行为

研究了具有焓效应的聚四氢呋喃-聚甲基丙烯酸甲酯两嵌段共聚物与聚氯乙烯PTHF-b-PMMA/PVC)共混体系的相容性和结晶行为. 结果表明, 其相容性比AB/A型嵌段共聚物共混体系的相容性要好得多; 与PTHF部分相容的PVC对PTHF微区的结晶行为可产生很大的影响. 应用有关理论和模型很好地解释了结晶行为的这种变化.