Water-dispersible sulfopolyesters are a major class of film-forming and solution-modifying polymers, which are routinely used in applications such as inks, adhesives, coatings, and personal care products. Since these polyesters are designed to be used as waterborne dispersions, understanding their colloidal interactions in dispersions is critical for their application. By using a range of commercially available water-dispersible sulfopolyesters as a model system, we investigated the relationship between their molecular composition, colloidal interactions, and phase equilibria. We established how these polyesters undergo different molecular configurations and nanoaggregated states, depending on the nature of the liquid medium. For example, the polyesters are in a solvated molecular form in certain organic solvents, whereas they self-assemble into compact nanoaggregates in water. We found that the interactions of these nanoaggregates follow the classical DLVO theory of critical colloidal coagulation where the stability of these nanoparticles is extremely sensitive to multivalent electrolytes (i.e., C ∝ z). By using static, dynamic, and electrophoretic light scattering, we correlate their nanoscale intermolecular and interparticle interactions with corresponding macroscale phase behavior in both organic medium and water, based on the theoretical framework of second virial coefficients. We present a model for nanoaggregate formation in water based on the critical surface charge density of these nanoparticles. Such fundamental understanding of colloidal interactions could be used to efficiently control and improve the colloidal stability and film-formation ability of these polyesters and may enable the design of novel high-performance surfactant-free waterborne dispersion systems.
When a sessile droplet of a complex
mixture evaporates, its nonvolatile components may deposit into various
patterns. One such phenomena, the coffee ring effect, has been a topic
of interest for several decades. Here, we identify what we believe
to be a fascinating phenomenon of droplet pattern deposition for another
well-known beveragewhat we have termed a “whiskey web”.
Nanoscale agglomerates were generated in diluted American whiskeys
(20–25% alcohol by volume), which later stratified as microwebs
on the liquid–air interface during evaporation. The web’s
strandlike features result from monolayer collapse, and the resulting
pattern is a function of the intrinsic molecular constituents of the
whiskey. Data suggest that, for our conditions (diluted 1.0 μL
drops evaporated on cleaned glass substrates), whiskey webs were unique
to diluted American whiskey; however, similar structures were generated
with other whiskeys under different conditions. Further, each product
forms their own distinct pattern, demonstrating that this phenomenon
could be used for sample analysis and counterfeit identification.
Structurally colored sulfopolyester films with higher fraction of hydrophilic groups experience higher “coffee-ring erosion” as a result of water droplet deposition.
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