A pH‐sensitive,strong double‐network hydrogel: Poly(ethylene glycol) methyl ether methacrylates–poly(acrylic acid)

We here describe new double network (DN) hydrogels with excellent mechanical strength and high sensitivity to pH changes. The first polymer network has a bottle brush structure and is formed from oligo‐monomers of poly(ethylene glycol) methyl ether methacrylate (PEGMA). Poly(acrylic acid) (PAA) is used as the second network. This double network features strong intermolecular interactions between the neutral poly(ethylene glycol) (PEG) side chains of PPEGMA and the non‐ionized carboxylic acid groups of the PAA second network. When immersed in solutions with a pH below ～4 the DN hydrogels have a low swelling ratio and are opaque as a result of solvent‐polymer phase separation driven by the formation of dense hydrogen‐bonded clusters. The compression strength (～8 MPa) is at least 14 times higher than the analogous single networks. When immersed in solutions with a pH >4, the hydrogels are transparent and exhibit a high swelling ratio with a compression strength of ～1 MPa. The PEG side chain length can be readily controlled without greatly altering the overall DN topology by choosing PEGMA monomers having different PEG side chain lengths. Longer PEG side branches give higher compression and tensile strengths at pH <4 when hydrogen bonded clusters form. The robust nature of these DN gels over a wide pH range may be useful for applications such as artificial muscles and controlled release devices. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Recursive constructions of small regular graphs of given degree and girth

We revisit and generalize a recursive construction due to Sachs involving two graphs which increases the girth of one graph and the degree of the other. We investigate the properties of the resulting graphs in the context of cages and construct families of small graphs using geometric graphs, Paley graphs, and techniques from the theory of Cayley maps.     

Modeling joints with clearance and friction in multibody dynamic simulation of automotive differentials

Defects in kinematic joints can sometimes highly influence the simulation response of the whole multibody system within which these joints are included. For instance, the clearance, the friction, the lubrication and the flexibility affect the transient behaviour, reduce the component life and produce noise and vibration for classical joints such as prismatics, cylindrics or universal joints. In this work, a new 3D cylindrical joint model which accounts for the clearance, the misalignment and the friction is presented. This formulation has been used to represent the link between the planet gears and the planet carrier in an automotive differential model.     

Effect of Shift Reagents on Infrared Spectra

Abstract

Introduction

We have shown previously¹ that when Eu(fod)₃?d₂₇ shift reagent is added to the erythro and threo esters of 2,3-diphenyl-3-hydroxypropanoic acid, the vicinal coupling constants, J₂₃, vary in a manner which indicates bidentate coordination.