Journal of Polymer Science, Part B: Polymer Physics

Nanocomposites were prepared with different grades of nitrile rubber with acrylonitrile contents of 19, 34, and 50%, with styrene–butadiene rubber (23% styrene content), and with polybutadiene rubber with Na‐montmorillonite clay. The clay was modified with stearyl amine and was characterized by X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and transmission electron microscopy (TEM). The XRD studies showed an increase in the gallery gap upon the modification of the filler by stearyl amine. The intercalation of the amine chains into the clay gallery gap was confirmed by the presence of some extra peaks (2928, 2846, and 1553 cm⁻¹) in the FTIR spectra. The clay–rubber nanocomposites were characterized by TEM and XRD. The mechanical properties were studied for all the compositions. An improvement in the mechanical properties with the degree of filler loading up to a certain level was observed. The changes in the mechanical properties, with changes in the nature and polarity of the rubbers, were explained with the help of XRD and TEM results. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1573–1585, 2004

Water and ion transport in thin sheets of initially dry, ionic, hydrophilic crosslinked polymers was modelled throughout the dynamic swelling process. The water transport was expressed in terms of a non‐Fickian equation with a diffusion term containing a Fujitatype concentration‐dependent diffusion coefficient coupled with a pseudoconvective term arising from the reasonable assumption that the stress in ionic polymers is proportional to the total number of ionized pendant groups in the polymer. Ion transport was expressed in terms of generalized Fickian equations with water concentration‐dependent diffusion coefficients. These equations were solved with appropriate boundary conditions to establish the water uptake as a function of time, pH and ionic strength in a citrate‐phosphate‐borate buffer solution. A new dimensionless number, the Stress Swelling number, A, was defined to quantify the relative importance of stress in the overall swelling process. Water uptake was a strong function of A. © 1994 John Wiley & Sons, Inc.

Fourier‐transform infrared (FTIR) spectral studies were carried out on a polyurethane in styrene solutions at styrene concentrations from 30 to 90% (w/w). NH vibrations were studied in the stretching and bending regions. The results demonstrated that the NH groups of the polyurethane can hydrogen bond not only with the CO groups but also with other groups in this system. The investigation of the vibrations of the monosubstituted aromatic rings confirms that some aromatic rings of the styrene are hydrogen bonded with the NH groups of the polyurethane. With the results of Part 1 of this series, the mole fractions of “free” NH groups and of NH groups H‐bonded to CO groups and to the π orbitals of the aromatic rings were obtained. These results are useful in elucidating why a physical gel appears in this system. © 1994 John Wiley & Sons, Inc.

We investigate the dewetting of aqueous, evaporating polymer [poly(acrylic acid)] solutions cast on glassy hydrophobic (polystyrene) substrates. As in ordinary dewetting, the evaporating films initially break up through the nucleation of holes that perforate the film, but the rapidly growing holes become unstable and form nonequilibrium patterns resembling fingering patterns that arise when injecting air into a liquid between two closely spaced plates (Hele–Shaw patterns). This is natural because the formation of holes in thin films is similar to air injection into a polymer film where the thermodynamic driving force of dewetting is the analogue of the applied pressure in the flow measurement. The patterns formed in the rapidly dewetting and evaporating polymer films become frozen into a stable glassy state after most of the solvent (water) has evaporated, leaving stationary patterns that can be examined by atomic force microscopy and optical microscopy. Similar patterns have been observed in water films evaporating from mica substrates, block copolymer films, and modest hole fingering has also been found in the dewetting of dry polymer films. From these varied observations, we expect this dewetting‐induced fingering instability to occur generally when the dewetting rate and film viscosity are sufficiently large. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2825–2832, 2002

The pressure‐volume‐temperature properties of poly(ether ether ketone) (PEEK) were studied experimentally at temperatures of 400°C and pressures to 200 MPa. Specific volume data were fitted successfully to the empirical Tait equation for T < T_g and T > T_m and to the theoretical Simha‐Somcynsky equation of state for the melt. The pressure dependence of the glass‐transition temperature is about 0.57–0.59°C/MPa and that of the melting point 0.483°C/MPa. The pressure dependence of the melting point, the specific volume of the melt at T_m, and the specific volume of the crystal at T_m determined from x‐ray diffraction data at elevated temperatures were combined in the Clapeyron equation to calculate a heat of fusion of 161 ± 20 J/g for the PEEK crystal. This value is somewhat higher than the previously reported value of 130 J/g.

A gravimetric method for determining precisely the solubility of gases in polymers at high pressure is described. The solubilities of N₂ and CO₂ in low‐density polyethylene (LDPE); CO₂ in polycarbonate (PC); and N₂, CH₄, C₂H₆, and CO₂ in polysulfone (PSUL) have been measured as a function of pressure up to 50 atm. Most of the measured sorption isotherms agreed closely with published data, but reproducible and time‐dependent hysteresis in the sorption of CO₂, C₂H₆, and CH₄ in glassy polymers, PC, and PSUL, was observed in this study for the first time. Like the well known conditioning effect of high‐pressure CO₂ on the sorption capacity of glassy polymers, these hysteresis phenomena are believed to be due to the plasticizing effect of sorbed gases. On the basis of the current data, the dual‐mode sorption model including the plasticization by sorbed gas is discussed and a primitive equation for the concentration of sorbed gases in a quasiequilibrium state of sorption or desorption is proposed.

Sorption and dilation in the system poly(ethyl methacrylate) (PEMA) and carbon dioxide are reported for pressures up to 50 atm over the temperature range 15–85°C. The sorption isotherms were obtained gravimetrically. The dilation accompanying sorption was measured directly with a cathetometer. At low temperatures the sorption and dilation isotherms were concave toward the pressure axis in the low‐pressure region and turned to convex with increasing pressure. As the experimental temperature approached and exceeded the glass transition temperature of 61°C, both isotherms became convex or linear over the whole range of pressure. Partial molar volumes of CO₂ in PEMA were obtained from sorption and dilation data, which were described well by the extended dual‐mode sorption and dilation models developed recently. The temperature dependence of the dual‐mode parameters and the isothermal glass transition are discussed.

Các tính chất của nanocomposite polyurethane (PU) với ba loại organoclay khác nhau đã được so sánh dựa trên độ ổn định nhiệt, tính chất cơ học, hình thái và khả năng thẩm thấu khí. Hexadecylamine–montmorillonite, dodecyltrimethyl ammonium–montmorillonite, và Cloisite 25A được sử dụng làm organoclay để tạo ra các phim PU hybrid. Các tính chất được kiểm tra như một hàm của nồng độ organoclay trong polymer nền. Hình ảnh vi kính điện tử truyền dẫn cho thấy hầu hết các lớp đất sét được phân tán đồng nhất vào polymer nền ở quy mô nano, mặc dù một số hạt đất sét bị kết tụ. Hơn nữa, việc thêm chỉ một lượng nhỏ organoclay cũng đủ để cải thiện độ ổn định nhiệt và các tính chất cơ học của các phim PU hybrid, trong khi khả năng thẩm thấu khí thì giảm. Ngay cả những polymer có nồng độ organoclay thấp (3-4 wt %) cũng cho thấy giá trị độ bền và mô đun cao hơn nhiều so với PU nguyên chất. Khả năng thẩm thấu khí đã giảm theo tỷ lệ với sự gia tăng lượng organoclay trong nền PU. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 670–677, 2002; DOI 10.1002/polb.10124

The equilibrium sorption and swelling behavior of four different polymers—poly(methyl methacrylate), poly(tetrafluoroethylene), poly(vinylidene fluoride), and the random copolymer tetrafluoroethylene–perfluoromethylvinylether–in supercritical CO₂—are studied at different temperatures (from 40 to 80 °C) and pressures (up to 200 bar). Swelling is measured by visualization, and sorption through a gravimetric technique. From these data, the behavior of amorphous and semicrystalline polymers can be compared, particularly in terms of partial molar volume of CO₂ in the polymer matrix. Both poly(methyl methacrylate) and the copolymer of tetrafluoroethylene exhibit a behavior typical of rubbery systems. On the contrary, polymers with a considerable degree of crystallinity, such as poly(tetrafluoroethylene) and poly (vinylidene fluoride), show larger values of partial molar volume. These can be related to the limited mobility of the polymer chains in a semicrystalline matrix, which causes the structure to “freeze” during the sorption process into a nonequilibrium state that can differ significantly from the actual thermodynamic equilibrium. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1531–1546, 2006

The field of organic thin films and devices is progressing at an extremely rapid pace. Organic–metal and organic–organic interfaces play crucial roles in charge injection into, and transport through, these devices. Their electronic structure, chemical properties, and electrical behavior must be fully characterized and understood if the engineering and control of organic devices are to reach the levels obtained for inorganic semiconductor devices. This article provides an extensive, although admittedly nonexhaustive, review of experimental work done in our group on the electronic structure and electrical properties of interfaces between films of π‐conjugated molecular films and metals. It introduces several mechanisms currently believed to affect the formation of metal–organic interface barriers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2529–2548, 2003