The Fractionation of High-Polymeric Substances.

Cragg, L. H.; Hammerschlag, Hanna.

doi:10.1021/cr60122a002

Cited by 60 publications

(19 citation statements)

References 84 publications

(138 reference statements)

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“…We relate this to AFM measurements showing that particle interactions vary as the fluid is changed. Our results indicate that CS grains are covered by chemical agents behaving similarly to what was recently observed for polymer brushes [20] exhibiting a cosolvency effect [21,22]. These dangling polymers may be at the origin of the peculiar rheology in water and also of the rheology changes with fluid as observed for colloidal suspensions [e.g.…”

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confidence: 83%

“…4b shows the percentage of measurements with pulling events as a function of Φ m EtOH . We observe them for all ethanol concentrations with a minimum for ethanol, logical with amylose and amylopectin solubilities, and a maximum for intermediate concentrations, which indicates a cosolvency effect which is a solubilitymaximum at intermediate Φ m EtOH [20][21][22]. Fig.…”

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Dramatic effect of fluid chemistry on cornstarch suspensions: Linking particle interactions to macroscopic rheology

et al. 2017

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Suspensions of cornstarch in water exhibit strong dynamic shear-thickening. We show that partly replacing water by ethanol strongly alters the suspension rheology. We perform steady and nonsteady rheology measurements combined with atomic force microscopy to investigate the role of fluid chemistry on the macroscopic rheology of the suspensions and its link with the interactions between cornstarch grains. Upon increasing the ethanol content, the suspension goes through a yield-stress fluid state and ultimately becomes a shear-thinning fluid. On the cornstarch grain scale, atomic force microscopy measurements reveal the presence of polymers on the cornstarch surface, which exhibit a cosolvency effect. At intermediate ethanol content, a maximum of polymer solubility induces high microscopic adhesion which we relate to the macroscopic yield stress.Suspensions are mixtures of undissolved particles in a liquid. They are literally found all around us: mud, paints, pastes and blood [1]. The viscosity of a dense suspension can vary by orders of magnitude in a small shear rate interval [2]. Subjected to an increasing shear rate, dense suspensions first tend to become less viscous (shear-thinning) and then more viscous (shearthickening). The viscosity of some suspensions, especially non-Brownian ones, may increase so much that they effectively become solid [3]. Although standard rheology measurements provide a great tool to study this phenomenon [e.g. 4, 5], they are mainly limited to steadystate conditions.Many studies point out that dense suspensions exhibit remarkable dynamic phenomena emerging under non-steady-shear conditions: stable holes in thin vibrated layers [6], non-monotonic settling [7], dynamic compaction front [8] or fracturing [3]. Oscillatory rheology helps to describe some of these dynamic behaviours [9], but remains limited to constant volume conditions. Dynamic shear-thickening has been widely investigated [10], but its physical origin remains an active debate. Although several parameters seem to contribute to it (e.g. particles size [11], shape [12] or roughness [13]), it has become increasingly clear that frictional and non-contact interactions between particles play a key role [14,15]. Such interactions are easily modified in numerical simulations, but present a real challenge in experiments. Consequently, only few experimental studies addressthe role of particle-particle interactions in dense suspensions rheology [e.g. 5, 16] however lacking systematic variation of these interactions. Moreover, direct measurements of these interactions in relation to the rheology are also lacking so far.Here, we directly probe the microscopic interactions between individual particles and explore their link with * adeline.pons@normalesup.org the macroscopic rheology for dense cornstarch (CS) suspensions. The archetypical suspension of CS grains in water exhibits a strong dynamic shear-thickening [3,[6][7][8]. Interestingly, Taylor [17] shows that replacing water by polypropylene glycol in CS suspensions completely su...

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Dramatic effect of fluid chemistry on cornstarch suspensions: Linking particle interactions to macroscopic rheology

et al. 2017

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“…Decalin is distilled from this chamber by way of condenser (4) (tap water cooled) into the sample chamber (2). The samples are placed in nickelchromium wire gauze baskets (5). Chamber (2) is heated to within 10°C of the desired temperature by hotplate (6) with the remainder of the heat supplied by heat tape (7) which is controlled to within f0.2"C. Sample aliquots are removed via the stopcock (11).…”

Section: Methodsmentioning

confidence: 99%

Use of a sequential extraction technique to determine the MWD of bulk UHMWPE

Kusy

Whitley

1986

J of Applied Polymer Sci

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SynopsisThe molecular weight distribution (MWD) of bulk ultrahigh molecular weight polyethylene (UHMWPE) was determined by an increasing temperature sequential extraction technique. Using decahydronapthalene (decalin) as the solvent, 5 g samples of UHMWPE were fractionated stepwise from room temperature to 190°C in 10Co increments. Results via high temperature capillary viscometry show that intrinsic viscosity ( [ q ] ) ranges from 12.0 to 37.0 dL/g or that the viscosity average molecular weight ( a o , r a n g e s from approximately 1.6 to 7.4 X lo6. When the integral distribution is plotted against M, on logarithmic probability graph paper, a straight line (i.e., a Wesslau distribution) results. Although the present methodology is tedious, many previous problems which have led to degradation are overcome by this technique.

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“…No method was known to fractionate polymers exclusively on a chemical composition basis. 1 These techniques were based on the fact that the solubility of polymers in a given solvent decreases with increasing molecular weight and that solvent power depends on solvent temperature and on the ratio of solvent to nonsolvent in a binary mixture.…”

Section: Introductionmentioning

confidence: 99%