Crystallization of weakly segregated poly(styrene-b-epsilon-caprolactone) diblock copolymer in thin films

The surface morphology and crystallization behavior of a weakly segregated symmetric diblock copolymer, poly(styrene-b-6-caprolactone) (PS-b-PCL), in thin films were investigated by optical microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy (AFM). When the samples were annealed in the molten state, surface-induced ordering, that is, relief structures with uniform thickness or droplets in the adsorbed monolayer, were observed depending on the annealing temperature. The polar PCL block preferred to wet the surface of a silicon wafer, while the PS block wet the air interface. This asymmetric wetting behavior led to the adsorbed monolayer with a PCL block layer having a thickness of around 4.0 nm. The crystallization of PCL blocks could overwhelm the microphase-separated structure because of the weak segregation. In situ observation of crystal growth indicated that the nucleation process preferred to occur at the edge of the thick parts of the film, that is, the relief structures or droplets. The crystal growth rate was presented by the time dependence of the distance between the tip of crystal clusters and the edge. At 22 and 17 degreesC, the average crystal growth rates were 55 +/- 10 and 18 +/- 4 nm/min, respectively.

Study on the origin of inverted phase in drying solution-cast block copolymer films

In a previous study, we reported observation of the novel inverted phase (the minority blocks comprising the continuum phase) in kinetically controlled phase separating solution-cast poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymer films [Zhang et al. Macromolecules 2000, 33, 9561-7]. In this study, we adopt the same approach to investigate the formation of inverted phase in a series of solution-cast poly(styrene-b-butadiene) (SB) asymmetric diblock copolymers having nearly equal polystyrene (PS) weight fraction (about 30 wt %) but different molecular weights. The microstructure of the solution-cast block copolymer films resulting from different solvent evaporation rates, R, was inspected, from which the kinetically frozen-in phase structures at qualitatively different block copolymer concentrations and correspondingly different effective interaction parameter, chieff, can be deduced. Our result shows that there is a threshold molecular weight or range of molecular weight below which the unusual inverted phase is accessible by controlling the solvent evaporation rate. In comparing the present result with that of our previous study on the SBS triblock copolymer, we find that the formation of the inverted phase has little bearing on the chain architecture. We performed numerical calculations for the free energy of block copolymer cylinders and found that the normal phase is always preferred irrespective of the interaction parameter and molecular weight, which suggests the formation of the inverted phase to have a kinetic origin.

How to form regular polymer microstructures by surface-pattern-directed dewetting

The substrates with regular patterns of self-assembly monolayers (SAMs) produced by microcontact printing with octadecyltrichlorosilane (OTS) was employed to direct thin polystyrene dewetting to fabricate ordered micrometer scale pattern. The pattern sizes and pattern fashion can be manipulated by controlling the experimental parameters. The pattern formation mechanisms have been discussed. The dewetting pattern can be transferred to form PDMS stamp for future microfabrication process.

Patterning thin polymer films by surface-directed dewetting and pattern transfer

The pattern evolution processes of thin polystyrene (PS) film on chemically patterned substrates during dewetting have been investigated experimentally. The substrates have patterns of self-assembly monolayers produced by microcontact printing with octadecyltrichlorosilane. Optical microscopy and atomic force microscopy images reveal that ordered micrometer scale pattern can be created by surface direct dewetting. Various pattern sizes and pattern complexities can be achieved by controlling the experimental parameters. The dewetting pattern has been transferred to form PDMS stamp for soft lithography.

Surface morphology control of immiscible polymer-blend thin films

The effects of the molecular weights (molecular weight of polystyrene, M-w,M-PS, varying from 2.9 to 129 k) on the surface morphologies of spin-coated and annealed polystyrene/poly (methyl methacrylate) (PS/PMMA = 50/50, w/w) blend films were investigated by atomic force microscopy and X-ray photoelectron spectroscopy. For the spin-coated films, when the M-w,M-PS varied from 2.9 to 129 k, three different kinds of surface morphologies (a nanophase-separated morphology, a PMMA cellular or network-like morphology whose meshes filled with PS, a sea-island like morphology) were observed and their formation mechanisms are discussed, respectively. Upon annealing, two different morphology-evolution processes were observed. It is found that a upper PS-rich phase layer is formed when M-w,M-PS < 4 k, and this behavior is mainly attributed to the low interfacial tension between PS and PMMA component. When M-w,M-PS > 4 k, the PS-rich phase forms droplets on top of the PMMA-rich phase layer which wets the SiOx substrate. These results indicate that the surface morphology of the polymer blend films can be controlled by the polymer molecular weight and annealing conditions.

Abnormal pressure dependence of the phase boundaries in TL/PEO/P(EO-b-DMS) ternary mixtures

The cloud-point temperatures (T-cl's) of both binary poly(ethylene oxide) (PEO)-poly(ethylene oxide-b-dimethylsiloxane) [P(EO-b-DMS)] and ternary[toluene/PEO/P(EO-b-DMS)] systems were determined by light scattering measurements at atmospheric pressure. The phase separation behavior upon cooling in the ternary system has been investigated at atmospheric pressure and under high pressure and compared to the phase behavior in the binary system. The phase transition temperatures have been obtained for all of the samples. As a result, the pressure induces compatibility in the binary mixtures, but for the ternary system, pressure not only can induce mixing but also can induce phase separation.

Thermodynamics of phase behavior in PEO/P(EO-b-DMS) homopolymer and block co-oligomer mixtures under pressure

The cloud-point temperatures (T-cl's) of poly(ethylene oxide) (PEO) and poly(ethylene oxide)-block-polydimethylsiloxane (P(EO-b-DMS)) homopolymer and block-oligomer mixtures were determined by turbidity measurements over a range of temperatures (105 to 130degrees), pressures (1 to 800 bar), and compositions (10-40 wt.-% PEO). The system phase separates upon cooling and T-cl was found to decrease with an increase in pressure for a constant composition. In the absence of special effects, this finding indicates negative excess volumes. Special attention was paid to the demixing temperatures as a function of the pressure for the different polymer mixtures and the plots in the T-phi plane (where phi signifies volume fractions). The cloud-point curves of the polymer mixture under pressures were observed for different compositions. The Sanchez-Lacombe (SL) lattice fluid theory was used to calculate the spinodals, the binodals, the Flory-Huggins (FH) interaction parameter, the enthalphy of mixing, and the volume changes of mixing. The calculated results show that modified P(EO-b-DMS) scaling parameters with the new combining rules can describe the thermodynamics of the PEO/P(EO-b-DMS) system well with the SL theory.

Preparation of macroporous functionalized polymer beads by a multistep polymerization and their application in zirconocene catalysts for ethylene polymerization

Macroporous functionalized. polymer beads of poly(4-vinylpyridine-co-1,4-divinylbenzene) [P(VPy-co-DVB)] were prepared by a multistep polymerization, including a polystyrene (PS) shape template by emulsifier-free emulsion polymerization, linear PS seeds by staged template suspension polymerization, and macroporous functionalized polymer beads of P(VPy-co-DVB) by multistep seeded polymerization. The polymer beads, having a cellular texture, were made of many small, spherical particles. The bead size was 10-50 mum, and the pore size was 0.1-1.5 mum. The polymer beads were used as supports for zirconocene catalysts in ethylene polymerization. They were very different from traditional polymer supports. The polymer beads could be exfoliated to yield many spherical particles dispersed in the resulting polyethylene particles during ethylene polymerization. The influence of the polymer beads on the catalytic behavior of the supported catalyst and morphology of the resulting polyethylene was investigated.

Determination of molecular weight and molecular sizes of polymers by high temperature gel permeation chromatography with a static and dynamic laser light scattering detector

Flow-mode static and dynamic laser light scattering (SLS/DLS) studies of polymers, including polystyrene, polyethylene, polypropylene and poly(dimethylsiloxane) (PDMS), in 1,2,4-trichlorobenzene (TCB) at 150 degreesC were performed on a high temperature gel permeation chromatography (GPC) coupled with a SLS/DLS detector. Both absolute molecular weight (M) and molecular sizes (radius of gyration, R-g and hydrodynamic radius, R-h) of polymers eluting from the GPC columns were obtained simultaneously. The conformation of different polymers in TCB at 150 degreesC were discussed according to the scaling relationships between R-g, R-h and M and the rho-ratio (p = R-g/R-h). Flow-mode DLS results of PDMS were verified by batch-mode DLS study of the same sample. The presented technique was proved to be a convenient and quick method to study the shape and conformation of polymers in solution at high temperature. However, the flow-mode DLS was only applicable for high molecular weight polymers with a higher refractive index increment such as PDMS.

Water-soluble fluorescent nanospheres as fluorosensor for detection of Cu2+

A novel water-soluble fluorescent nanosphere as fluorosensor was prepared by emulsifier-free emulsion copolymerization of styrene with naphthalimide derivative (A). The fluorosensor was high sensitive for detection of Cu2+. Comparied with other fluorosensors based on organic fluorophore, it has two advantages. First, there is no pollution to environment in the use of it. Second, it can be used repeatedly.

Study of PVT behavior of biaxially oriented polypropylene resins in the melting state

The PVT data of five kinds of biaxially oriented polypropylene (BOPP) Resins was measured by the PVT-100 apparatus. Thermal expansion coefficients (alpha) and isothermal compressibility (beta) were evaluated from Tait equation in the melting state and then compared with those fitted with the value of experiment. The results showed that it was reasonable to calculate alpha and beta with Tait equation in the melting state. At the same time, it was found that thermal expansion coefficients, isothermal compressibility and the melting temperature (T-m) of one of BOPP melts (S28C) were lower than those of the others in the same test conditions, indicating that the volume deformation of S28C resin is' less so that it could be realized to avoid arising surface defects of the film (biaxially oriented polypropylene film) due to. contracting, thereby decrease damage to the film in the subsequence process. Accordingly superior processing properties of S28C resin are confirmed from PVT. speciality.

Theoretical estimation of thermodynamic properties of the system PS/PPO on the basis of modified combining rule of Sanchez-Lacombe lattice fluid model

The three scaling parameters described in Sanchez-Lacombe lattice fluid theory (SLLFT), T*, P* and rho* of pure polystyrene (PS), pure poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and their mixtures are obtained by fitting corresponding experimental pressure volume-temperature data with equation-of-state of SLLFT. A modified combining rule in SLLFT used to match the volume per mer, v* of the PS/PPO mixtures was advanced and the enthalpy of mixing and Flory-Huggins (FH) interaction parameter were calculated using the new rule. It is found that the difference between the new rule and the old one presented by Sanchez and Lacombe is quite small in the calculation of the enthalpy of mixing and FH interaction parameter and the effect of volume-combining rule on the calculation of thermodynamic properties is much smaller than that of energy-combining rule. But the relative value of interaction parameter changes much due to the new volume-based combining rule. This effect can affect the position of phase diagram very much, which is reported elsewhere [Macromolecules 34 (2001) 6291]

Electrochemiluminescence of tris(2,2 '-bipyridyl)ruthenium (II) ion-exchanged in polyelectrolyte-silica composite thin-films

The organic-inorganic hybrid, PSS-silica composite material was developed for the immobilization of tris(2,2'-bipyridyl)ruthenium(II) (Ru(bpy)(3)(2+)) on glassy carbon electrode via ion-exchange (PSS stands for poly(sodium 4-styrene-sulfonate)). The electrochemiluminescence (ECL) and electrochemistry of Ru(bpy)(3)(2-) immobilized in the composite thin films have been investigated with tripropylamine (TPA) as the coreactant. The immobilized Ru(bpy)(3)(2-) underwent a surface process. The modified electrode was used for the ECL detection of TPA and showed high sensitivity. Detection limit was 0,1 mumol L-1 for TPA (S/N = 3) with a linear range from 0.5 mumol L-1 to 5 mmol L-1 (R = 0.998), Moreover, the resulting modified electrode was stable over six months and the good stability may be due to the strong interaction between Ru(bpy)(3)(2-) and the high ion-exchange able PSS-silica composite films on GCE. Compared with other materials. the PSS-silica composite films containing incorporated Ru(bpy)(3)(2-) showed improved sensitivity and long-term stability, Thus, such composite thin film can be a promising material for the construction of ECL sensor.

Morphology and thermal and mechanical properties of PBT/HIPS and PBT/HIPS-g-GMA blends

The modification of high-impact polystyrene (HIPS) was accomplished by melt-grafting glycidyl methacrylate (GMA) on its molecular chains. Fourier transform infrared spectroscopy and electron spectroscopy for chemical analysis were used to characterize the formation of HIPS-g-GMA copolymers. The content of GMA in HIPS-g-GMA copolymer was determined by using the titration method. The effect of the concentrations of GMA and dicumyl peroxide on the degree of grafting was studied. A total of 1.9% of GMA can be grafted on HIPS. HIPS-g-GNU was used to prepare binary blends with poly(buthylene terephthalate) (PBT), and the evidence of reactions between the grafting copolymer and PBT in the blends was confirmed by scanning electron microscopy (SEM), dynamic mechanical analysis, and its mechanical properties. The SEM result showed that the domain size in PBT/HIPS-g-GMA blends was reduced significantly compared with that in PBT/HIPS blends; moreover, the improved strength was measured in PBT/HIPS-g-GMA blends and results from good interfacial adhesion. The reaction between ester groups of PBT and epoxy groups of HIPS-g-GMA can depress crystallinity and the crystal perfection of PBT.

Theoretical representation of shear and pressure influence on the phase separation behavior of PVME/PS mixture

In the framework of lattice fluid model, the Gibbs energy and equation of state are derived by introducing the energy (E-s) stored during flow for polymer blends under shear. From the calculation of the spinodal of poly(vinyl methyl ether) (PVME) and polystyrene (PS) mixtures, we have found the influence of E., an equation of state in pure component is inappreciable, but it is appreciable in the mixture. However, the effect of E, on phase separation behavior is extremely striking. In the calculation of spinodal for the PVME/PS system, a thin, long and banana miscibility gap generated by shear is seen beside the miscibility gap with lower critical solution temperature. Meanwhile, a binodal coalescence of upper and lower miscibility gaps is occurred. The three points of the three-phase equilibrium are forecasted. The shear rate dependence of cloud point temperature at a certain composition is discussed. The calculated results are acceptable compared with the experiment values obtained by Higgins et at. However, the maximum positive shift and the minimum negative shift of cloud point temperature guessed by Higgins are not obtained, Furthermore, the combining effects of pressure and shear on spinodal shift are predicted.