Peroxide radical treatments of a perfluorinated ionomer used in polymer electrolyte membrane (PEM) fuel cells and its small molecule analogues were carried out, along with analysis of the resultant products. Molecules containing terminal carboxylic acids degraded at least 1 order of magnitude faster than noncarboxylate materials; all of the systems did show peroxide-initiated degradation nonetheless. Product analysis suggests that terminal carboxylic acids react according to a sequential chain shortening, consistent with previous studies. Cleavage of side chains from both polymer and model compounds was also observed to be important and in fact may be the dominate pathway in low carboxyl content commercial PEM membranes, based on the following comparison of reactivity and concentration. The relative reactivities of carboxylic chain ends and ether linkages is approximately 500, as calculated using model compounds fluoride generation rates. Commercial perfluorosulfonic acid (PFSA) products contain minimal carboxylic acid end groups, and the side chain concentrations are of 2−3 orders of magnitude higher than carboxylic acid end groups.

Time-resolved adsorption behavior of a human immunoglobin G (hIgG) protein on a hydrophobized gold surface is investigated using multitechniques:  quartz crystal microbalance/dissipation (QCM-D) technique; combined surface plasmon resonance (SPR) and Love mode surface acoustic wave (SAW) technique; combined QCM-D and atomic force microscopy (AFM) technique. The adsorbed hIgG forms interfacial structures varying in organization from a submonolayer to a multilayer. An “end-on” IgG orientation in the monolayer film, associated with the surface coverage results, does not corroborate with the effective protein thickness determined from SPR/SAW measurements. This inconsistence is interpreted by a deformation effect induced by conformation change. This conformation change is confirmed by QCM-D measurement. Combined SPR/SAW measurements suggest that the adsorbed protein barely contains water after extended contact with the hydrophobic surface. This limited interfacial hydration also contributed to a continuous conformation change in the adsorbed protein layer. The viscoelastic variation associated with interfacial conformation changes induces about 1.5 times overestimation of the mass uptake in the QCM-D measurements. The merit of combined multitechnique measurements is demonstrated.

We show the theoretical and experimental combination of acoustic and optical methods for the in situ quantitative evaluation of the density, the viscosity and the thickness of soft layers adsorbed on chemically tailored metal surfaces. For the highest sensitivity and an operation in liquids, a Love mode surface acoustic wave (SAW) sensor with a hydrophobized gold coated sensing area is the acoustic method, while surface plasmon resonance (SPR) on the same gold surface as the optical method is monitored simultaneously in a single set-up for the real-time and label-free measurement of the parameters of adsorbed soft layers, which means for layers with a predominant viscous behavior. A general mathematical modeling in equivalent viscoelastic transmission lines is presented to determine the correlation between experimental SAW signal shifts and the waveguide structure including the presence of the adsorbed layer and the supporting liquid from which it segregates. A methodology is presented to identify from SAW and SPR simulations the parameters representatives of the soft layer. During the absorption of a soft layer, thickness or viscosity changes are observed in the experimental ratio of the SAW signal attenuation to the SAW signal phase and are correlated with 2 the theoretical model. As application example, the simulation method is applied to study the thermal behavior of physisorbed PNIPAAm, a polymer whose conformation is sensitive to temperature, under a cycling variation of temperature between 20 and 40• C. Under the assumption of the bulk density and the bulk refractive index of PNIPAAm, thickness and viscosity of the film are obtained from simulations; the viscosity is correlated to the solvent content of the physisorbed layer.3

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A dual temperature-responsive triblock polymer (Poly(N-isopropyl acrylamide)-block-poly(N,N-dimethyl acrylamide)-block-poly(acrylamide-co-acrylonitrile) (P(AM-co-AN)-b-PDMA-b-PNIPAM) (NDAA) was obtained by sequential reversible addition–fragmentation chain transfer (RAFT) polymerization ,with the uncharged UCST temperature-sensitive block P (AM-co-AN) and the...

This study evaluates the microscopic changes of paulownia solid wood panels subjected to thermal compression via characterizing the changes in wood microstructure. The panels, with dimensions of 500 mm × 100 mm × 20 mm, were hot-pressed in a tangential direction by using a laboratory-type hot press at a temperature of either 150 °C or 170 °C and a pressure of 2 MPa for 45 min. Microscopic investigations conducted by light microscopy showed that slightly more damage occurred in the samples compressed at 170 °C and 2 MPa than at 150 °C and 2 MPa, and that the distribution of deformation in the panels was not uniform in the growth rings of the two treatment groups. The cell collapse was not observed in the microstructure of paulownia wood after the thermal compression. Cell shapes and their arrangement in the growth ring alongside loading direction were interpreted as effective factors governing the non-uniform distribution of damage and the lack of cell collapse in the microstructure.

A generalized model for the prediction of mat pressuredensity relationship of wood-based composites was developed. Based on the compression models for fiber assembly, this model treats the composite mat structure as a system of bending units, thus making element bending the dominant mechanism during early stage of mat consolidation. The consolidation behavior of fiber, strand, and particle mats were experimentally investigated. Satisfactory agreement was found between the model predictions and experimental results. Combined with the compression model, the entire strand mat consolidation can be predicted based on the properties of the wood constituents.

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