Ernst Dieter von Meerwall

Self-diffusion in polymer systems, measured with field-gradient spin echo NMR methods

The steady gradient and pulsed gradient spin echo NMR Methods of measuring self-diffusion have for some twenty years been applied to the study of polymers. The methods are briefly described, and the principal results of this research are reviewed in three main areas: diffusion of polymers in the melt and in concentrated solutions, diffusion of polymer in dilute and semidilute solutions, and diffusion of penetrants and diluents in high polymers hosts. The theoretical interpretations of these experiments are included in the review, with particular attention to theories of dilute polymer solutions, the free-volume theory of diffusion in concentrated solutions, and power-law behavior postulated for various regimes.

Pulsed and Steady Field Gradient NMR Diffusion Measurements in Polymers

Abstract Some twenty years after the development of the steady and pulsed gradient spin-echo NMR methods of measuring self-diffusion, these techniques are now maturing and experiencing a surge of interest, much of it concentrated on polymer systems. The methods are briefly reviewed here, together with the most important results in polymers, with particular concentration on work described within the last few years. The research is divisible into three categories: diffusion of diluent and penetrant molecules in rubbery high polymers, diffusion of polymer molecules in dilute and semidilute solutions with liquid solvents, and diffusion of macromolecules dissolved in concentrated solutions or melts of equivalent or different polymers of arbitrary molecular weight. The review includes the main theoretical interpretations of the experiments, particularly the free-volume theory in its various forms and power-law behaviors postulated by recent refinements of tube/reptation and scaling theory. This article represen...

Interpreting pulsed-gradient spin-echo diffusion experiments in polydisperse specimens

Abstract Pulsed-gradient spin-echo diffusion measurements show the effects of even small molecular weight distributions provided that the echo attenuation is measured over a large range. Computer methods to test models of such polydispersity behavior and to extract diffusion coefficients from the data are described.

Mutual and self-diffusion of water in gelatin: experimental measurement and predictive test of free-volume theory

Abstract Self-diffusion of water in unhardened photographic gelatin is measured by pulsed-gradient n.m.r. spectroscopy. Mutual diffusion and activity of water in hardened and unhardened gelatin is measured by step-change gravimetric sorption methods. Predictions of mutual diffusion from the self-diffusion data and published thermodynamic data by using the Vrentas-Duda theory are in agreement with the measured mutual diffusivities. Hardening (i.e. crosslinking) of the gelatin reduces the diffusivity as predicted by an extension to the Vrentas-Duda theory. The water activity increases with crosslinking.

Mobility of a tackifying resin in a pressure‐sensitive adhesive

A detailed study of the mobility of a tackifying resin in a pressure-sensitive adhesive (PSA) has been done for the first time. The objective of this work is to relate changes in adhesive performance with tackifier loading to tackifier mobility. Tackifiers are low-molecular weight resins that improve the overall performance of PSAs. They increase the adhesive tack or the ability to form a bond of measurable strength after brief contact under slight applied pressure. In this study the diffusion of n-butyl ester of abietic acid (n-BEAA) in either polyisoprene (PI) (Mw = 195,000 Mw/Mn ∼ 1.05) or poly(ethylene-propylene) (PEP) (Mw = 40,000 Mw/Mn ∼ 2.30) was measured by Pulsed Gradient Spin Echo-Nuclear Magnetic Resonance (PGSE-NMR) as a function of both tackifier concentration and temperature. The concentration dependence of the tackifiers diffusion coefficient was weak for both systems. The weak variation in mobility with composition for the PI/n-BEAA system was consistent with that systems weak variation in tack with composition. On the other hand, blends of PEP/n-BEAA showed only modest variation in mobility, even though these adhesive systems showed appreciable enhancement of tack at intermediate compositions.

Molecular mobility of unfilled and carbon-black-filled isoprene rubber: proton NMR transverse relaxation and diffusion

Abstract In an effort to understand the effect of ultrasound on the devulcanization of gum and filled isoprene rubber vulcanizates, solid state NMR 1H transverse relaxation (T2) was employed to analyze rubber molecular mobility. The T2 relaxation decay of the unfilled and the black filled IR was successfully described by a two-component model. The short T2 component arose from the chemically crosslinked (gel) and physically entangled (heavy sol) network. The long T2 decay came from the unentangled sol and dangling network chain ends. Vulcanization decreased the molecular mobility; however, ultrasound devulcanization partially reversed this effect. Addition of processing oil in the filled IR significantly altered the dependence of T2 on the sol fraction. T2 and pulsed-gradient diffusion experiments were carried out on IR melt specimens after sonication with or without subsequent vulcanization. The lowered and broadened M-distribution produced results quantitatively related to earlier work in natural rubber.

Diffusion in polymer systems, measured with the pulsed-gradient NMR method☆

Abstract The pulsed-gradient spin-echo NMR method of measuring diffusion has long been used to investigate a large variety of non-glassy polymer systems. The large-gradient variant of this method, including several refinements as developed in the authors laboratory, is briefly reviewed. Several examples of recent work are presented: effects of molecular shape anisotropy of the diffusion of plasticizers in PVC above the glass transition; the retarding effects of the emerging branching on the diffusion of epoxies during curing; and the characterization of the sol remaining in bimodal PDMS networks after partial extraction.

Concentration-dependence of solvent diffusion in a colloidal suspension

Abstract We have used the large-pulsed-gradient NMR method supplemented by NMR relaxation to study the diffusivity D of water and cosolvent in a commercial poly(vinyl acetate)—water emulsion (Elmers Glue-All, Borden, Inc.), in samples with volatiles concentrations c between (water added) 100 and (drying) 5 wt%, in concentration equilibrium attained over several months. At high c , D ( c ) has the mild variation characteristic of obstruction by particles, while below c = 30% D drops by almost two orders of magnitude and cosolvent diffusion begins to dominate as water depletes. Diffusion becomes unmeasurable with this method near c = 6%, where the adhesive is translucent and rigid. We interpret the sharp drop in D ( c ) in terms of a topological transition between water-based emulsion and PV A-based porous but nearly impermeable solid. An elaboration of the Maxwell-Fricke model quantitatively accounts for the full c -dependence of D .