Materials manufacturing industries seek efficient, economic, and sustainable compounds for stabilizing dispersed systems such as emulsions. In this study, novel, abundant biobased hydrocolloids spruce galactoglucomannans (GGM) and birch glucuronoxylans (GX) were obtained from a forestry biorefining process and characterized as versatile stabilizers of rapeseed oil-in-water emulsions. For the first time, GGM and GX isolated by pressurized hot water extraction (PHWE) of spruce and birch saw meal, respectively, were studied in emulsions. The PHWE wood hemicelluloses-polysaccharides with relatively low molar mass-facilitated the formation of emulsions with small average droplet size and efficiently prevented droplet coalescence. GGM and GX lowered the surface tension of emulsions' oil-water interface and increased the viscosity of the continuous phase. However, viscosity of the wood hemicellulose-based systems was low compared to that of commercial polymeric stabilizers. GGM-stabilized emulsions with varying oil volume fractions were characterized in terms of their rheological properties, including large amplitude oscillation shear (LAOS) measurements, and compared to emulsions prepared with a classical small-molecular surfactant, Tween20. The physical emulsion stabilization mechanisms of GGM and GX are suggested as steric repulsion assisted by Pickering-type stabilization. Wood hemicelluloses have potential as highly promising future bioproducts for versatile industrial applications involving colloidal systems and soft materials.

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The leading nonlinear stress response in a periodically strained concentrated colloidal dispersion is studied experimentally and by theory. A thermosensitive microgel dispersion serves as well-characterized glass-forming model, where the stress response at the first higher harmonic frequency (3ω for strain at frequency ω) is investigated in the limit of small amplitude. The intrinsic nonlinearity at the third harmonic exhibits a scaling behavior which has a maximum in an intermediate frequency window and diverges when approaching the glass transition. It captures the (in-) stability of the transient elastic structure. Elastic stresses in-phase with the third power of the strain dominate the scaling. Our results qualitatively differ from previously derived scaling behavior in dielectric spectroscopy of supercooled molecular liquids. This might indicate a dependence of the nonlinear response on the symmetry of the external driving under time reversal.

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Analytical solutions for the normal stress differences in large-amplitude oscillatory shear flow (LAOS), for continuum or molecular models, normally take the form of the first few terms of a series expansion in the shear rate amplitude. Here, we improve the accuracy of these truncated expansions by replacing them with rational functions called Padé approximants. Specifically, we examine replacing the truncated expansion for the corotational Jeffreys fluid with its Padé approximants for the normal stress differences. We begin by extending the Goddard integral expansion (GIE) from its third [J Non-Newt Fluid Mech 166, 1081 (2011)] to its fifth order term in the shear rate amplitude. We then explore the Padé approximants for this extension. We uncover the best approximant, the [3,4] approximant, and compare this with both the GIE and the exact solution [Macromol Theory Simul 24, 352 (2015)]. We use Ewoldt grids to show the stunning accuracy of our [3,4] approximant in LAOS. We quantify this accuracy with an objective function and then map its onto Pipkin space. We find the [3,4] approximant to be a simple accurate expression for the normal stress differences in LAOS. Our applications illustrate how to use our new approximant reliably. For this, we use the Spriggs relations to generalize our best approximant to multimode, and then, we compare with measurements on molten high-density polyethylene, and on dissolved polyisobutylene in isobutylene oligomer.