Limited-supply diffusion in the liquid polystyrene–glassy poly(phenylene oxide) pair. Further results in extended times scale (original) (raw)
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Liquid‐Glassy Polymer Diffusion: Effects of Liquid Molecular Weight and Temperature
Macromolecular Chemistry and Physics, 2007
We examine mechanistic aspects of the diffusion between a series of liquid polystyrenes (PS) and a glassy poly(phenylene oxide) (PPO) matrix, through the use of confocal Raman microspectroscopy. The results show that the diffusion kinetics has Fickean characteristics, similar to those found in liquid‐liquid polymer diffusion. No signatures of the linear regime typical of the case‐II diffusion mechanism were found. Overall, these observations are consistent with the claim that case‐II is unlikely to occur in liquid‐glassy polymer diffusion.magnified image
Liquid−Glassy Polymer Diffusion: Rate-Controlling Step and Diffusion Mechanism
Macromolecules, 2005
We investigate the diffusion mechanism at a liquid-glassy polymer interphase, produced in this case between poly(vinyl methyl ether) (PVME) as the liquid polymer and polystyrene (PS) as the glassy matrix. The evolution of the interphase was directly measured by using confocal Raman microspectroscopy in the depth-profiling mode. Diffusion experiments were performed in the range 85-125°C, with the specific purpose of encompassing the glass transition temperature (T g) of the glassy matrix (PS, 100°C). In this way, direct evidence about the effect of the physical state of the (glassy or liquid) PS matrix on the diffusion modes was obtained. We found that the diffusion experiments performed at temperatures below the matrix T g (liquid-glassy polymer diffusion) are controlled by the same parameters and show the same features as those performed at temperatures above the matrix Tg (liquidliquid polymer diffusion). Furthermore, a Fickean diffusion model developed for liquid-liquid polymer diffusion correlates precisely with the whole set of data, including liquid-glassy polymer diffusion experiments, without invoking case II diffusion theory. It is concluded that the diffusion-controlling step of the process is placed at the liquid PVME-PS interphase. These observations are in marked contrast with interpretations from other authors that used the context of case II to explain the mechanisms that control the evolution of these interphases, an idea often proposed to interpret experimental results for this polymer pair. The origin of the discrepancy is discussed.
Raman depth-profiling characterization of a migrant diffusion in a polymer
Journal of Membrane Science, 2011
a b s t r a c t Raman depth-profiling microspectroscopy provides rich information on chemical/physical characterization in a non-destructive mode with micrometric resolution. However, refraction causes distortions to the data obtained thereby. A method to determine the diffusivity of an additive in low linear density polyethylene (LLDPE) with Raman depth profiling is proposed, combining the latest developments on data treatment of refraction distorted profiles. The method is compared with the results obtained analysing the cross section of the sample, with a maximum 32% relative error between both methods. The main benefits, characteristics of this method, a discussion of the experimental errors, as well as perspectives for future work are highlighted.
Liquid−Liquid Limited-Supply Diffusion Studies in the Polystyrene−Poly(vinyl methyl ether) Pair
Macromolecules, 2004
Liquid-liquid diffusion at the interphase between poly(vinyl-methyl ether) (PVME) and polystyrene (PS) was experimentally studied using confocal Raman microspectroscopy. A combination of a specially designed experimental setup and a direct and precise quantification for the corrections to be applied to the Raman measurements allowed us to measure directly the PVME concentration along the diffusion path for a wide range of diffusion times. An already proposed and tested liquid-liquid diffusion model (based on liquid dynamics controlled by monomeric friction coefficients) was used to correlate and predict the detailed shape of the PVME concentration profiles and the diffusion rates as functions of diffusion time and temperature. The results obtained allowed us to discern among several approaches previously proposed in the literature to calculate monomeric friction coefficients in this system. Only the approach that considers independent monomeric friction coefficient values for PS and PVME (obtained from tracer diffusion measurements) gave good agreement between experimental results and model calculations. Calculations performed using literature data for a common monomeric friction coefficient for both PS and PVME (obtained from estimated blend viscosity data) do not agree with experimental measurements. The success of the model used for this work clearly ruled out the need for combinations of Fickean and Case II models used previously to describe PS-PVME polymer diffusion.
Diffusive Mixing of Polymers Investigated by Raman Microspectroscopy and Microrheology
Langmuir, 2010
Diffusive mixing in a model polymer blend of limited miscibility (i.e., the pair polydimethylsiloxane/polyisobutene) is investigated. The diffusion process is followed in the actual droplet-based microstructure of the polymer blend, as opposed to the ideal planar geometry used in previous studies (Brochard et al. Macromolecules 1983, 16, 1638 Composto et al. Nature 1987, 328, 234). In our experiments we combine Raman microspectroscopy and video particletracking microrheology. The first technique allows us to monitor local concentration of the two polymers with high spatial resolution both inside and outside a micrometer-size droplet of the dispersed phase. In addition, microrheology enables to follow how the local viscosity inside the droplet changes during the diffusion. The polymer viscosity inside the droplet is determined by video tracking the Brownian motion of a polystyrene bead microinjected into the droplet. The microspectroscopic and microrheological data are combined to estimate the concentration dependence of the monomer friction factor of the two species, which is a key parameter to calculate the interdiffusion coefficient D. Numerical calculations based on such concentration-dependent interdiffusion coefficient D and several alternative models of the polymer diffusion are compared to the experimental concentration profiles. A satisfactory agreement is found for the socalled "slow theory" (Brochard et al.). A phenomenological model improving the agreement of the model with the experimental data is also presented.
Interphase Evolution in Polymer Films by Confocal Raman Microspectroscopy
Applied Spectroscopy, 2006
Liquid-glassy polymer diffusion is an important topic in polymer physics, with several mechanistic aspects that still remain unclear. Here we describe the use of confocal Raman microspectroscopy (CRM) to study directly several features of interphase evolution in a system of this type. The interphase studied was generated by contact between liquid polystyrene (PS) and glassy polyphenylene oxide (PPO). Interphase evolution on thin films made from these polymers was followed by depth profiling in combination with immersion optics. We also applied regularized deconvolution to improve the spatial resolution of the measurements. With the help of these techniques, we examined interphase PPO concentration profiles and kinetics of interphase evolution in the range 120–180 °C, well below the glass transition temperature of the PPO-based films (185 °C). Overall, the experiment captures the most important features needed to discern the mechanistic factors that control this process. In this sens...
Macromolecules, 2001
The diffusion of a liquid polymer into a glassy polymer matrix has been studied in a range of temperatures below the glassy matrix glass transition temperature (T g) and for different diffusion times. The liquid polymer used is low-molecular-weight polystyrene (PS) with a narrow molecular weight distribution, and the glassy matrix is poly(phenylene oxide); the two are miscible at any concentration. A simple physical diffusion model is proposed to correlate and predict diffusion rates, assuming a relatively rapid dissolution of the high-Tg polymer at the liquid-solid interface and a relatively slow diffusion process that produces a thick interphase. The local chemical compositions, local glass transition temperatures, and local PS monomeric friction coefficients change markedly along the diffusion path across the interphase; these changes are well predicted by the diffusion model and have also been experimentally verified. The large changes in local T g values cause huge changes in the PS monomeric friction factor across the interphase, and this fact explains the asymmetrical local chemical composition profiles experimentally measured for the PS-rich interphase. The results obtained by other authors for the diffusion of liquid polymers and bulky plasticizers into glassy matrixes are analyzed and discussed on the basis of the diffusion model predictions, and it is found that all of them behave following the same pattern as was observed in our experiments. It is concluded that the Case II diffusion mechanism must not be expected for the diffusion of liquid polymers into glassy matrixes, because of the negligible osmotic pressure. Furthermore, all of the analyzed data for diffusion of liquid polymers and bulky plasticizers into glassy matrixes show evidence for relatively rapid dissolution of the glassy matrix at the interface, together with a relatively slow diffusion process across the interphase.
Macromolecules, 2009
We report a diffusion study on a series of interphases formed between a polystyrene-rich (PS) liquid layer and a poly(phenylene oxide) (PPO) glassy matrix. Diffusion was promoted by annealing the polymer pair at several temperatures below the glass transition temperature of the PPO matrix, in experiments where the liquid component was supplied from an unlimited source. Depth PS concentration profiles were obtained via optical sectioning through the glassy layer with confocal Raman microspectroscopy. The PS profiles measured in all the samples had sharp diffusion fronts followed by a region with relatively uniform PS concentration. From the time evolution of the PS front advance, we directly obtained the time-scaling laws for interphase kinetics which are interpreted in the context of the Fickean and case II diffusion theories. Despite some recent studies reporting the occurrence of case II in this particular system, our results and analysis show conclusively that interphase kinetics are, on the contrary, markedly Fickean. Results previously published by other authors on this polymer pair are also analyzed with the aim of offering a unified view about the mechanism that controls interphase evolution at the molecular level.
Macromolecular …, 2000
A generalized method for calculating diffusion rates in polydisperse systems, valid in the concentrated regime, is outlined. In the formulation of the method the discrete variable that describes the molecular size, is replaced by a continuous variable in the same range. This replacement diminishes the number of degrees of freedom but keeping the essential physics of the original statement. The effects of monomeric friction coef®cient, Flory-Huggins thermodynamic interaction parameter, individual species molecular weights, local molecular weights distribution and local T g are consistently included in the model. The method is used to calculate concentration distribution pro®les generated by diffusion of polydisperse polymers blends, and experimentally tested. For this purpose polystyrene with discrete (bimodal and tetramodal) molecular weight distributions and polystyrene with wide and continuous molecular weight distributions were used to simulate polydisperse systems. They are allowed to diffuse in a blend of polyphenylene oxide and polystyrene. The simulated concentration pro®les are compared with results obtained by using two experimental techniques based on independent physical properties, which give complementary information: Raman spectroscopy and DMA. The total PS concentration pro®les calculated using the proposed method agree well with Raman spectroscopy results. Simulated DMA resultsÐwhich are sensitive to the PS species molecular weight distributionÐobtained using the concentration pro®les calculated for each PS molecular weight species, agree well with the experimental DMA results. Calculations based on average molecular weights on the other hand, give incorrect results.
Journal of Polymer Engineering, 2005
Attenuated Total Reflection (ATR) spectroscopy was used to study the interdiffusion mechanism at the interface of Polystyrene (PS) and Poly(vinyl methyl ether) (PVME), at temperatures above and below the glass transition temperature (T g) of PS, but in the miscible region. One molecular weight of PVME and 13 molecular weights of PS, both below and above the critical molecular weights of PS were used to investigate the effect of molecular weight on mutual diffusion process both below and above the critical molecular weight for entanglements of PS. To extract the diffusion coefficient from experimental data, we used the approach suggested by Jabbari and Pepas. Both Fickian and Case-II diffusion were necessary to fit the PVME concentration profile for the various molecular weights. The experimental results were also compared with the slow-mode and the fast mode theories2-3.