Surface Glass Transition Temperature Research Articles

On the scaling law of the evolution of lap-shear strength with healing temperature at amorphous polymer−polymer interfaces and surface glass transition

The evolution of lap-shear strength (σ) with healing temperature Th at symmetric and asymmetric amorphous polymer−polymer interfaces formed of the samples with vitrified bulk has been investigated. It has been found that the square root of the lap-shear strength behaves with respect to healing temperature as σ1/2 ~ Th both at symmetric and asymmetric interfaces. Basing on this scaling law between σ and Th, the values of the surface glass transition temperature \( \left( {T_{\rm{g}}^{\rm{surface}}} \right) \) have been estimated for a number of amorphous polymers by the extrapolation of the experimental curves σ1/2 ~ Th for symmetric polymer−polymer interfaces and, in some cases, for asymmetric, both compatible and incompatible, polymer−polymer interfaces, to zero strength. A significant reduction in surface glass transition temperature \( T_{\rm{g}}^{\rm{surface}} \) with respect to the glass transition temperature of the polymer bulk \( \left( {T_{\rm{g}}^{\rm{bulk}}} \right) \), reported earlier, has been confirmed by the use of the new proposed approach. The quasi-equilibrium surface glass transition temperature \( T_{\rm{g}}^{\rm{surface}} \) of amorphous polystyrene (PS) has been predicted in the framework of an Arrhenius approach using the plot “logarithm of healing time − reciprocal surface glass transition temperature \( T_{\rm{g}}^{\rm{surface}}\prime \prime \) and the activation energy of the surface alpha-relaxation of PS has been calculated.

Surface glass transition of miscible amorphous polymers blends

The surface glass transition temperature (Tgsurface) of the bulk samples of miscible blends formed of amorphous polystyrene (PS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) has been characterised in terms of an adhesion approach we proposed recently. Tgsurface has been measured as the temperature transition “occurrence of autoadhesion–nonoccurrence of autoadhesion” by employing a lap-shear joint mechanical testing method. The effect of the reduction in Tgsurface with respect to the glass transition temperature of the bulk (Tgbulk), which had been observed earlier in pure homopolymers, has been found to exist in the blends of PS with PPO as well. The values of this effect for the blends have been compared with those for pure homopolymers, and the differences found have been discussed.

New simple method of measuring the surface glass transition temperature of polymers

AbstractA lap‐shear joint mechanical testing method has been probed to measure the surface glass transition temperature (T) of the thick bulk films of high‐molecular‐weight polymers. As T, the temperature transition “occurrence of autoadhesion–nonoccurrence of autoadhesion” has been proposed. The influence of chain flexibility, of molecular architecture, of polymer morphology, and of chain ends concentration on the T has been investigated. The correlation between the reduction in T with respect to the glass transition temperature of the bulk (T) and the intensity of the intermolecular interaction in the polymer bulk in amorphous polymers has been found. The effect of surface roughness on T has been discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2012–2021, 2010

Nanoscopic adhesion test for polymers by a light-lever system

Polymer nano-adhesion between a cantilever tip coated with polymer and a flat polymer film was studied by a light-lever system using an atomic force microscope. The polymer interface was adhered at a temperature above the surface glass transition temperature for a given time. Nano-adhesion force (Fnano), at which the tip was detached from the surface, was estimated from the deflection of the lever with a known spring constant. Nano-adhesion strength (GN) was simply obtained dividing Fnano by the contact area, which was estimated on the basis of Johnson-Kendall-Roberts theory. The time evolution of the interfacial thickness was independently examined by dynamic secondary ion mass spectrometry. Interestingly, GN increased with increasing interfacial thickness. However, it can be hardly judged whether GN is proportional to the interfacial thickness with the exponent of 1 or 2. Then, temperature dependence of GN was examined. Above the bulk glass transition temperature, the relation between temperature and GN was well expressed by a Williams-Landel-Ferry type equation. This means that the nano-adhesion strength is governed by friction between segments. Once this is accepted, GN should be proportional to the interfacial thickness with the exponent of 2.

Probing the Surface Glass Transition Temperature of Polymer Films via Organic Semiconductor Growth Mode, Microstructure, and Thin-Film Transistor Response

Organic semiconductor-based thin-film transistors (TFTs) have been extensively studied for organic electronics. In this study, we report on the influence of the polymer gate dielectric viscoelastic properties on overlying organic semiconductor film growth, film microstructure, and TFT response. From the knowledge that nanoscopically-confined thin polymer films exhibit glass-transition temperatures that deviate substantially from those of the corresponding bulk materials, we show here that pentacene (p-channel) and cyanoperylene (n-channel) films grown on polymeric gate dielectrics at temperatures well-below their bulk glass transition temperatures [T(g)(b)] exhibit morphological/microstructural transitions and dramatic OTFT performance discontinuities at well-defined temperatures [associated with a polymer "surface glass transition temperature," or T(g)(s)]. These transitions are characteristic of the particular polymer architecture and independent of film thickness or overall film cooperative chain dynamics. Our results demonstrate that TFT measurements represent a new and sensitive methodology to probe polymer surface viscoelastic properties.

A modified cyclone stickiness test for characterizing food powders

A cyclone stickiness test device from a preliminary work was modified and used for characterizing stickiness behaviour of food powders. This test device employed the principle of particle dynamics in cyclone section of a spray dryer. The device was more compacted and consisted of temperature–humidity controlled air generator and cyclone test chamber. Characteristic temperature–humidity curves were determined and served as the maximum test conditions. Skim milk powder was used as a model for stickiness testing. The sample was subjected to various air conditions in the cyclone and stickiness conditions were determined. Surface moisture content and glass transition temperature at sticky point were also analysed. It was found that as the particle surface temperature increased humidity at which stickiness occurred decreased. Stickiness curve was drawn to separate between sticky and non-sticky conditions. The curve of glass transition temperature vs equilibrium surface moisture content at sticky points was obtained. It was found that the sticky curve laid at 11.4 °C above the glass transition temperature line.

ゴムのシミュレーション技術 高分子材料の表面・界面における粗視化シミュレーション

Recently the physical properties of the surface and the interface of polymeric materials are analyzed by several experimental methods in a few nanometer scales. On the other hand, the analysis is also needed from the point of view of polymer chain. Our group studied the phenomena of polymer materials in the point of view of polymer chain dynamics using the coarse-grained molecular dynamics simulation. In this review, we show two topics listed below; the local glass transition temperature at the surface and interface, and the polymer chain dynamics at the friction force microscopy using atomic force microscopy. In the first topics, we studied the local dynamics of polymer chains. The surface and interfacial glass transition temperatures which are also estimated by the experiments are measured by the mean square displacement analysis. In the second topics, we study the model simulation of the friction force to the polymer surface by probe tip in atomic force microscopy. In the series of simulation, we can observe the chain withdrawing and it is one of the important origin of the friction.

Surface glass transition in bimodal polystyrene mixtures

Using the cluster-embedding method of V. Zaporojchenko et al. (Macromolecules 34, 1125 (2000)), we measured the glass transition temperature T (g) at the polystyrene/vacuum interface of bimodal mixtures of monodisperse polystyrenes of 3.5k and 1000k. Embedding of approximately 1 nm Au clusters was monitored in situ by X-ray photoelectron spectroscopy (XPS). The clusters were formed by evaporation of Au onto the polymer surface. Only one glass transition was observed in the mixtures. The surface glass transition temperatures are correlated to but are below the bulk values of the mixtures and obey the Gordon-Taylor equation. The results suggest that the earlier reported molecular-weight dependence of the surface glass transition is not due to segregation of short chains to the surface.

Effect of protein concentration on the surface composition, water sorption and glass transition temperature of spray-dried skim milk powders

The effects of dilution of protein content in skim milk (34–8.5% protein content), by lactose addition, on the surface composition, water sorption property and glass transition temperatures of spray-dried powders were investigated. The X-ray photoelectron spectroscopy (XPS) study of spray-dried powders showed preferential migration of proteins toward the surface of the milk particles whereas the lactose remained in the bulk. Sorption studies showed that the lower protein concentration in milk powders is linked to an increased water adsorption property and lowering of water activity ( a w) for lactose crystallization. Analysis of glass transition temperature ( T g) of the powders sorbed at different humidities showed no distinct change in T g values, indicating the dominant effect of lactose on the glass transition temperature of all the powders.

Stickiness of maltodextrins using probe tack test during in-situ drying

A probe tack test was used to map the level of stickiness of droplets containing 20 and 40 wt% of maltodextrins DE5, DE10 and DE18 as they dried at 40 and 78 °C. As skin formation progressed, the stickiness increased to a maximum then decreased in most cases until the droplet was no longer sticky (non-adhesive state). The results show the expected trends; lower DE maltodextrins (higher molecular weight) were sticky for only a short time over a narrow range of bulk moisture contents, and addition of glycerol and maltodextrin DE18 to maltodextrin DE5 act as plasticisers resulting in a broadening of the stickiness profiles. Glass transition temperatures were measured for each maltodextrin at a range of moisture contents. They indicate that the solutions should be sticky when, in fact, the probe tack tests show that they are non-adhesive. This indicates a difference between the surface and the bulk measured moisture content and possibly also temperature, as expected in a drying system. However, because surface moisture content and temperature can not be measured, the stickiness results were not able to be directly related to the surface glass transition temperature of the maltodextrins.

Design and characterization of modified urethane lacquer coating

A new series of natural lacquer/polyurethane (LPU) blended films were synthesized. The new lacquer/polyurethane films have very good visual color and detected gloss, fast drying time, strong weather resistance, especially against UV light and water, and a better pencil lead hardness (8H). The gel ratio increases with drying time and becomes stable after 6 months (more than 99%). The surface glass transition temperature ( T gs) obtained from a rigid-body pendulum physical properties testing (RPT) instrument showed that the new LPU films dried for 6 months have higher T gs than polyurethane (PU) films in the following order: LPU 100 > LPU 90 > LPU 80 > LPU 70 > LPU 60 > LPU 50 > PU. Differential scanning calorimeter (DSC) results showed the same tendency as T g but without a great gap in the LPU series except for polyurethane. Thermogravimetric analysis (TGA) showed that when the ratio of natural lacquer is more than 50%, the 50% weight loss temperatures increase about 100 °C. In addition, the reaction between lacquer and polyurethane is discussed based on the IR and NMR measurements.

Glass transition and thermal expansivity of polystyrene thin films

We have studied glass transition temperature and thermal expansivity of polystyrene thin films supported on silicon substrate using X-ray reflectivity and inelastic neutron scattering techniques. In annealing experiments, we have found that the reported apparent negative expansivity of polymer thin films is caused by unrelaxed structure due to insufficient annealing. Using well-annealed films, we have evaluated glass transition temperature T g and thermal expansivity as a function of film thickness. The glass transition temperature decreases with film thickness and is constant below about 10 nm, suggesting the surface glass transition temperature of 355 K, which is lower than that in bulk. We have also found that the thermal expansivity in the glassy state decreases with film thickness even after annealing. The decrease has been attributed to hardening of harmonic force constant arising from chain confinement in a thin film. This idea has been confirmed in the inelastic neutron scattering measurements.

Applications of the Cyclone Stickiness Test for Characterization of Stickiness in Food Powders

The cyclone stickiness test (CST) technique was applied to measure the stickiness temperature and relative humidity of whey, honey, and apple juice powders. A moisture sorption isotherm study was conducted to analyze the surface moisture content of whey powder. The glass transition temperatures of the sample powder were analyzed using differential scanning calorimetry (DSC). The stickiness results of these products were found within 20°C above their surface glass transition temperatures, which is well within the normal temperature range for glass transition in general. The results obtained by the CST technique were found consistent with DSC values.

Free-volume distribution and glass transition of nano-scale polymeric films

Positron annihilation spectroscopy has been used to measure the ortho-positronium lifetime variation with respect to the temperature in an 80-nm polystyrene film on Si in different depths. The surface and interface glass transition temperatures were found to be significantly suppressed by 18 and 12 K at the depth of 5 and 70 nm from the surface, respectively. The observed T g-depth dependence is interpreted as a different degree of free-volume distributions at the surface and the interface with Si.

Investigation of the drastic change in the sputter rate of polymers at low ion fluence

The polymer sputter rate dependence on ion fluence and ion chemistry (Ar, N2, O2) at 1keV energy was investigated using a quartz crystal microbalance (QCM) which allowed to do real time etch rate measurements and to study kinetics of sputtering. The obtained sputter rates differed drastically from polymer to polymer showing, that the chemical structure of polymer is an important factor in the polymer etch yield. A decrease in the sputter rate was observed up to ion fluence of 5×1014–5×1015cm−2 (depending on the polymer type and ion chemistry) followed by the saturation in the rate at prolonged ion bombardment. Polymer removal was accompanied by the formation of degradation products, cross-linking or branching, modification of the surface chemical structure, which was studied in situ using XPS. The dependence of the surface glass transition temperature, Tgs on the ion fluence was studied using the method based on the embedding of metallic nanoparticles. The correlation between chemical yield data and ablation rate is discussed.

Measurement of surface glass transition temperature of amorphous cefditoren pivoxil granules by inverse gas chromatography

The aim of the present study is to increase the knowledge about the molecular mobility of cefditoren pivoxil (CDTR-PI) on the granules surface by studying the glass transition temperature (Tg) of the drug using inverse gas chromatography (IGC), and to clarify the inhomogeneity of the granule resulting in the physical stability of them. The Tg of the granulated amorphous CDTR-PI and the granulated CDTR-PI with polymers were measured by inverse gas chromatography (IGC) and differential scanning calorimetry (DSC). There was no difference among samples in the Tg measured by DSC. However, the Tg measured by IGC were different among samples; the value of CDTR-PI with hydroxypropylcellulose (HPC-L) was lower than the others, and showed a tendency similar to spray-dried samples. It was suggested that IGC measured the surface transition temperatures of granules that was impossible to measure by DSC. By comparison with the influence of the Tg on the surface and the whole granule on the crystallization rates of them, the surface Tg strongly affected the physicochemical stability of granules compared to those of the whole.

Investigation of the Surface Glass Transition Temperature by Embedding of Noble Metal Nanoclusters into Monodisperse Polystyrenes

Chain mobility in a near surface region at a polystyrene/vacuum interface was investigated by embedding of noble metal nanosized clusters. The embedding process was monitored in situ by X-ray photoelectron spectroscopy. The embedding of nanosized clusters needs long-range chain mobility of the polymer. Therefore, the embedding process is a probe for the glass transition in a near surface region. The clusters used in this study are formed by the dewetting of evaporated noble metals onto the polymer surface. First, methodical influences on the embedding process were investigated. An onset embedding temperature T* was defined. T* increases with a heating rate comparable to Tg(bulk) determined with a differential scanning calorimeter. Furthermore, T* increases with nominal metal coverage which results in increasing average cluster radius. The cluster size distribution was investigated by transmission electron microscopy. It is shown that T* is an upper limit for Tg in a near surface region with a depth of a few nanometers. With optimized probe conditions, embedding processes were performed on monodisperse polystyrene (Mw = 3−1000 kg/mol). The T* values fit quite well with the Fox−Flory relation, but with a saturation temperature of approximately 8 K below the bulk value. ΔT = Tg(bulk) − T* increases with molecular weight. This molecular weight dependence of T* will be discussed in terms of several models. The chain end segregation model can be ruled out. To investigate the kinetics of the embedding process, isothermal experiments were performed. From these experiments surface viscosities were derived, which are well below bulk values.

A direct comparison of surface and bulk chain-relaxation in polystyrene.

Near-edge X-ray absorption fine-structure (NEXAFS) spectroscopy was used to measure simultaneously the relaxation rates of polystyrene (PS) molecules at the free surface and in the bulk. The samples were uniaxially stretched and annealed at temperatures below the bulk glass transition temperature of PS. The surface and bulk chain relaxation was monitored by measuring the partial-electron and the fluorescence NEXAFS yields, respectively, both parallel and perpendicular to the stretching direction. The decay of the optical birefringence was also measured to provide an independent measure of the bulk relaxation. Relaxation of PS chains was found to occur faster on the surface relative to the bulk. The magnitude of the surface glass transition temperature suppression over the bulk was estimated based on the information on the temperature dependence of the rates.

Mechanisms of argon ion-beam surface modification of polystyrene

The surface characteristics of polymers are important factors determining their interfacial properties and their technological performance. Changes in physical and chemical properties of a polymer film may be induced by subjecting the material to a variety of surface modification techniques, one of which is ion-beam modification. In order to understand the underlying mechanisms X-ray photoelectron spectroscopy (XPS) was used to study the alterations of the polystyrene (PS) surface after Ar-ion treatment under well controlled conditions with low ion doses from 10 12 to 10 16 cm −2. The ion bombardment leads to surface functionalization, loss of aromaticity, and free radical formation. Induced surface cross-linking and the formation of polar groups raised the surface glass transition temperature of PS film.

Etching rate and structural modification of polymer films during low energy ion irradiation

Various polymers were sputtered with low energy Ar + ions of 1 keV in order to determine their etching rate. Hydrocarbons, oxygenated, fluorinated and nitrogen-containing glassy polymers with a broad range of the glass transition temperature ( T g) were chosen. The etching rate was measured using a profilometer, and X-ray photoelectron spectroscopy. At the same time the surface chemical modification, and the surface glass transition temperature were studied. Comparing the sputter rate to the various polymer properties a correlation among the T g, cross-link density, and sputter rate was found. In addition, the sputter rate as a function of the integral ion fluence proved to exhibit a sharp increase in the initial regime of very low fluence. The results are discussed in terms of the characteristics of the polymers.