The swelling of a polymer glass by sorption of a small molecule penetrant is considered in a regime characterized by so-called case-II diffusion. Attention is focused on the polymer so that the swelling process can be investigated apart from diffusion. The model of Thomas and Windle (TW) is used to predict the surface swelling as a function of exposure time. This model assumes that the swelling is driven by the osmotic pressure which relaxes to zero as the surface penetrant volume fraction φs approaches its equilibrium value φe. The rate-controlling factor of the swelling process is the viscosity of the polymer η, which decreases with increasing surface sorption according to η=η0 exp(−mφ) where η0 is the viscosity of the unswollen polymer. For large values of M=mφe, φs is very small until a time τ is reached beyond which the swelling then accelerates rapidly towards its equilibrium value. This feature is absent if M<e. The time τ is estimated by asymptotic analysis. Rutherford backscattering spectrometry is used to investigate the surface swelling kinetics of polystyrene by iodohexane. The TW model tends to underestimate the swelling rate when φs is low and to overestimate it when φs is high. Nevertheless, the time for φs to approach its equilibrium value φe is approximated well by the TW model.

We consider front formation and steady-state front motion in a one-dimensional polymer system undergoing case-II diffusion. The polymer system approximates a polymer sheet whose thickness is very small compared with its lateral dimensions. The osmotic pressure of Thomas and Windle (TW) is used in the theoretical analysis. The transient problem of front formation is formulated. It is found that the original coupled system of partial differential equations proposed by TW can be reduced to one equation. An exact solution of this equation for a diffusion front moving with a velocity V is presented. The solution allows us to predict the dependence of the steady-state velocity on material parameters and the equilibrium concentration of penetrant outside the sheet. The concentration and pressure profile ahead of the moving front is obtained. We also show that the TW Model predicts the existence of a Fickian tail ahead of the steadily moving front. Conditions for the dominance of the Fickian tail are determined. The predicitions of our theoretical analysis are then compared with concentration profiles of iodohexane diffusing into polystyrene determined from Rutherford backscattering spectrometry.

This is a valuable book giving a good overview as well as a state-of-the-art account of several topics related to thermal aspects of electronic packaging. Chapter I, by Nakayama, is entitled: "Thermal Management of Electronic Equipment: A Review of Technology and Research Topics." The role of heat transfer engineering and fundamental research, toward establishing design criteria are discussed. An exposition of natural convection, forced convection and advanced schemes of cooling follows. An interesting account of the heat load in Japanese computers caps up the section. Yovanovich and Antonetti wrote the next Section on the application of thermal contact resistance theory to electronic packages. The study surveys mechanical joints and the role of surface roughness, crucial, for example, to the performance of various electrical connectors. Direct air cooling of electronic components is discussed by Moffat and Ortega under two major headings, 1. Forced Convection and II. Natural Convection. Analytical and numerical methods, and experimental data are presented in the first part.

BackgroundThe recalcitrance of cellulosic biomass is widely recognized as a key barrier to cost-effective biological processing to fuels and chemicals, but the relative impacts of physical, chemical and genetic interventions to improve biomass processing singly and in combination have yet to be evaluated systematically. Solubilization of plant cell walls can be enhanced by non-biological augmentation including physical cotreatment and thermochemical pretreatment, the choice of biocatalyst, the choice of plant feedstock, genetic engineering of plants, and choosing feedstocks that are less recalcitrant natural variants. A two-tiered combinatoric investigation of lignocellulosic biomass deconstruction was undertaken with three biocatalysts (Clostridium thermocellum, Caldicellulosiruptor bescii, Novozymes Cellic® Ctec2 and Htec2), three transgenic switchgrass plant lines (COMT, MYB4, GAUT4) and their respective nontransgenic controls, two Populus natural variants, and augmentation of biological attack using either mechanical cotreatment or cosolvent-enhanced lignocellulosic fractionation (CELF) pretreatment.ResultsIn the absence of augmentation and under the conditions tested, increased total carbohydrate solubilization (TCS) was observed for 8 of the 9 combinations of switchgrass modifications and biocatalysts tested, and statistically significant for five of the combinations. Our results indicate that recalcitrance is not a trait determined by the feedstock only, but instead is coequally determined by the choice of biocatalyst. TCS with C. thermocellum was significantly higher than with the other two biocatalysts. Both CELF pretreatment and cotreatment via continuous ball milling enabled TCS in excess of 90%.ConclusionBased on our results as well as literature studies, it appears that some form of non-biological augmentation will likely be necessary for the foreseeable future to achieve high TCS for most cellulosic feedstocks. However, our results show that this need not necessarily involve thermochemical processing, and need not necessarily occur prior to biological conversion. Under the conditions tested, the relative magnitude of TCS increase was augmentation > biocatalyst choice > plant choice > plant modification > plant natural variants. In the presence of augmentation, plant modification, plant natural variation, and plant choice exhibited a small, statistically non-significant impact on TCS.Electronic supplementary materialThe online version of this article (10.1186/s13068-019-1353-7) contains supplementary material, which is available to authorized users.

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