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Effect of Poly(ethylene oxide) Molecular Weight on the Pinning and Pillar Formation of Evaporating Sessile Droplets: The Role of the Interface

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Original languageEnglish
Pages (from-to)5908-5918
Number of pages11
JournalLangmuir
Volume31
Issue number21
Early online date26 Mar 2015
DOIs
Publication statusPublished - 2015

Abstract

We report on the drying press of sessile droplets of aqueous poly(ethylene oxide) (PEO) solutions studied by contact angle analysis. Liquid samples Were prepared with the same initial concentration of four different molecular weights, M-w, of PEO, Droplets with initial volumes of between: 1 and 5 mu L were left to evaporate while temperature, pressure, and relative humidity were kept constant Residues were formed with,either a disklike puddle Or a distinctive tall conical pillar shape The latter occurred following a four stage deposition process: pinned drying, during which the contact line is stationary, pseudodewetting, where the receding contact line is hid-need by precipitation, bootstrap building; eluting which the liquid droplet is lifted on freshly precipitated solid; and late drying Contact angle analysis allowed us to monitor all stages during drying and consider transitions between stages for different molecular weights. We illustrate the mechanisms taking place during the crucial stages of pinning and depinning revealing the effect of adhesion and contact line friction for high molecular weights and its influence on the final morphology of the dried PEO solute. To this end, we performed PEO solution droplet evaporation on PEO and PTFE films demonstrating the importance of interfacial interaction phenomena We show that the formation of disklike puddles for high molecular weights on glass is associated with continuous droplet contact line pinning. ThiS' results from the strong adhesion due to the interdigitation of the loops and tails of a polymer layer (adsorbed on glass during evaporation) with the polymer gel network inside the droplet that form as water evaporates.

    Research areas

  • SOFT POLYMER INTERFACES, GLASS SURFACES, CONTACT-ANGLE, LIQUID-DROPS, FRICTION, ADHESION, LAYERS, EQUILIBRIUM, SUPPRESSION, ATTACHMENT

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