Rouse dynamics of colloids bound to polymer networks

We present experimental evidence of a transition in the short-time Brownian motion of colloids from diffusive to subdiffusive, Rouse-like. This transition is seen for particles that are bound, through physical adsorption, to transient polymer networks. The characteristic Rouse scaling of the mean square particle displacement with radical t, found in the experiments, is rationalized using an analytical bead-spring model of a large particle anchored to a set of polymer chains.     

Geometry- and rate-dependent adhesive failure of micropatterned surfaces

The dynamic nature of adhesive interface failure remains poorly understood, especially when the contact between the two surfaces is localized in microscopic points of adhesion. Here, we explore the dynamic failure of adhesive interfaces composed of a large number of micron-sized pillars against glass. Surprisingly, we find a large influence of the microcontact geometry; ordered arrays of these pillars exhibit significantly stronger adhesive properties than equivalent surfaces in which the pillars are disordered. This can be understood with a simple geometric argument that accounts for the number of adhesive bonds that needs to be broken simultaneously to propagate the crack front. Moreover, the adhesive strength in both cases depends largely on the velocity with which the surfaces are separated. This rate dependence is explained on the basis of a semi-phenomenological model that describes macroscopic failure as a consequence of microscopic bond-rupture events. Our results suggest that the dynamics of adhesive failure, in the limit explored here, is predominantly stress-driven and highly sensitive to local geometry effects.     

Comprehensive theory for star-like polymer micelles; combining classical nucleation and polymer brush theory

A comprehensive theory is proposed that combines classical nucleation and polymer brush theory to describe star-like polymer micelles. With a minimum of adjustable parameters, the model predicts properties such as critical micelle concentrations and micellar size distributions. The validity of the present theory is evidenced in direct comparison to experiments; this revealed that the proportionality constant in the Daoud-Cotton model is of the order of unity and that the star-limit is valid down to relatively short corona chains. Furthermore, we show that the predicted saddle points in the free energy correspond to those solutions that are accessible with self-consistent field methods for self-assembly.     

Markovian representation of a bilinear time series model and maximum likelihood estimation of the parameters

A bilinear time series (BLTS) model is expressed in the form of Akaike's Markovian representation in order to use the Kalman recursive estimation approach. It is shown that Akaike's Markovian representation of autoregressive moving average models of orderp and q (ARMA(p,q)) and that of the bilinear model are equivalent. This equivalence facilitates the maximum likelihood estimation of the parameters involved in the bilinear model, which otherwise is an unwieldy problem. The present approach can easily be extended to take into account missing observations     

Physical chemistry of supramolecular polymer networks

Supramolecular polymer networks are three-dimensional structures of crosslinked macromolecules connected by transient, non-covalent bonds; they are a fascinating class of soft materials, exhibiting properties such as stimuli-responsiveness, self-healing, and shape-memory. This critical review summarizes the current state of the art in the physical-chemical characterization of supramolecular networks and relates this knowledge to that about classical, covalently jointed and crosslinked networks. We present a separate focus on the formation, the structure, the dynamics, and the mechanics of both permanent chemical and transient supramolecular networks. Particular emphasis is placed on features such as the formation and the effect of network inhomogeneities, the manifestation of the crosslink relaxation dynamics in the macroscopic sample behavior, and the applicability of concepts developed for classical polymer melts, solutions, and networks such as the reptation model and the principle of time-temperature superposition (263 references).     

Simultaneous quantitation of IC87114, roflumilast and its active metabolite roflumilast N‐oxide in plasma by LC‐MS/MS: application for a pharmacokinetic study

A sensitive and reliable high‐performance liquid chromatography–mass spectrometry (LC–MS/MS) was developed and validated for simultaneous quantification IC87114, roflumilast (RFM), and its active metabolite roflumilast N‐oxide (RFN) using tolbutamide as an internal standard. The analytes were extracted by using liquid–liquid extraction and separated on a reverse phase C₁₈ column (50 mm × 3 mm i.d., 4.6 µ) using methanol: 2 mM ammonium acetate buffer, pH 4.0 as mobile phase at a flow rate 1 mL/min in gradient mode. Selective reaction monitoring was performed using the transitions m/z 398.3 > 145.9, 403.1 >186.9, 419.1 > 187.0 and 271.1 > 155.0 to quantify quantification IC87114, RFM, RFN and tolbutamide, respectively. The method was validated over the concentration range of 0.1–60 ng.mL^?1 for RFM and RFN and 6 to 2980 ng.mL^?1 for IC87114. Intra‐ and inter‐day accuracy and precision of validated method were within the acceptable limits of <15% at all concentrations. Coefficients of correlation (r²) for the calibration curves were >0.99 for all analytes. The quantitation method was successfully applied for simultaneous estimation of IC87114, RFM and RFN in a pharmacokinetic drug–drug interaction study in Wistar rats. Copyright © 2012 John Wiley & Sons, Ltd.     

Facile One‐Step Synthesis of Monodisperse Micron‐Sized Latex Particles with Highly Carboxylated Surfaces

A facile method for the aqueous synthesis of monodisperse and micronmeter‐sized colloids with highly carboxylated surfaces is presented. The method is applied to three different monomers, styrene, methyl methacrylate, and 2,2,2‐trifluoroethyl methacrylate, and illustrate tuning of the size and monodispersity in the reactions. High surface density of carboxylic acids of up to 10 COOH nm⁻² from potentiometric titrations, is achieved through copolymerization with itaconic acid. The versatility of this system is highlighted by creating highly fluorescent and monodisperse particles that can be index matched in aqueous solution and through surface modification via the carboxylic acid groups using standard amidation chemistry.

     

Supramolecular Assembly of Self‐Healing Nanocomposite Hydrogels

Hierarchical self‐assembly of transient composite hydrogels is demonstrated through a two‐step, orthogonal strategy using nanoparticle tectons interconnected through metal–ligand coordination complexes. The resulting materials are highly tunable with moduli and viscosities spanning many orders of magnitude, and show promising self‐healing properties, while maintaining complete optical transparency.

     

Study on using high injection voltage and spiral inflector in the central region of VEC

A feasibility study of using high injection voltage and spiral inflector in the present heavy ion central region of VEC is described. Conditions necessary for waist-to-waist transfer of the ion beam in the hole lens of main magnet have been obtained. The results of orbit studies of a variety of heavy ions indicate that a spiral inflector can be used in the central region.