Influence of prepolymers molecular weight on the viscoelastic properties of aqueous HEUR solutions

Barmar, Mohammad; Ribitsch, Volker; Kaffashi, Babak; Barikani, Mehdi; Sarreshtehdari, Z.; Pfragner, J.

doi:10.1007/s00396-003-0968-0

Cited by 39 publications

(50 citation statements)

References 22 publications

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“…9 Excess diisocyanate is used to control the molecular weight and to generate an isocyanatefunctionalized polymer that is then exposed to alkyl-amine or -alcohol. 9,[10][11][12][13][14][15][16][17][18] The resultant polymer is called a SG-HEUR. 9 Unlike uni-HEURs, the hydrophilic segment of SGHEURs consists of multiple PEG polymers that are separated by diisocyanate segments.…”

Section: Rheologymentioning

confidence: 99%

“…24 When not in a micelle or loop, the external hydrophobes "dangle" in the continuous phase. 23 When the concentration of HEUR exceeds the critical aggregation concentration (CAC), a dynamic three-dimensional associative network is formed [13][14]21,23 ( Figure 4). …”

Section: Rheologymentioning

confidence: 99%

“…The length of the external hydrophobes and the molecular weight of the HEURs influence the strength of the associative network. Longer external hydrophobes promote network formation (lower CAC) 13,15 and strengthen the network (increase viscosity).…”

Section: Rheologymentioning

confidence: 99%

“…16 As the molecular weight of HEURs increases, external hydrophobe concentration relative to that of lower molecular weight HEUR (holding the weight fraction of HEUR constant) decreases, 10 which decreases the number of bridges (decreases low-shear Newtonian viscosity and increases CAC). [11][12][13]15,18,26 Also, as an extension of the molecular weight effect, HEURs with higher polydispersity indexes (PDI) have higher lower viscosities than those with lower PDI. 17 However, the viscosity can increase with increasing molecular weight until the number average molecular weight ( ) exceeded 18 kDa.…”

Section: Shear Thickening Newtonianmentioning

confidence: 99%

“…27 When HEUR concentration is high, latex particles are dispersed throughout the system and the rheology shows Newtonian, shear thickening, and shear thinning behaviors. [13][14]21,23 Yet, when HEUR concentration is low, latex particles can approach one another and flocculate. 1 The bridging of latex particles by HEURs maintains the flocculated structures (bridging flocculation mechanism), though when shear is applied the flocculates are separated.…”

Section: Rheology and Phase Behavior Of Waterborne Latex / Heur Mixturesmentioning

confidence: 99%

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Syneresis and Rheology Mechanisms of a Latex-HEUR Associative Thickener System

Smith

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Syneresis and Rheology Mechanisms of a Latex-HEUR Associative Thickener SystemTravis Bruno Smith Rheology modifiers are used in paints and coatings to ease their application to a surface, prevent sagging once applied, and allow the leveling of brushstrokes, among other benefits. The early rheology modifiers were hydroxyethyl celluloses (HECs), a type of non-associative thickener that is relatively inexpensive and synthesized from cellulose, which is abundant. However, coatings that are modified with HECs tend to suffer from poor leveling and syneresis (phase separation). HECs have since been replaced with associative thickeners (ATs). These thickeners, when properly formulated, produce stable dispersions that have improved rheological properties, yet, unlike HECs, are sensitive to changes to the coating formulation. This drawback has encouraged research that attempts to predict the phase behavior and rheology of systems that are modified with ATs.This work is concerned with the phase behavior and rheology of waterborne latex / hydrophobically-modified ethoxylated urethane (HEUR) AT systems. When latex volume fraction is held constant, the amount of HEUR (and surfactant) in the mixture determines whether the system experiences syneresis. Dispersion phase diagrams (DPDs) of such systems have been previously studied, but the rheology of the mixtures used to prepare the DPDs have not been studied in any detail. A study on the rheology of phase separated latex / HEUR mixtures that were prepared with commercial materials was done at Cal Poly and showed a correlation between syneresis and complex rheology. However, v a proper analysis was limited because the compositions and chemical structures of the commercial materials were not well known.To better understand the relationships between phase behavior and rheology, waterborne latex / HEUR mixtures were prepared from latex and HEURs that were made at Cal Poly. Three series of mixtures were studied: commercial latex / commercial HEUR (I), commercial latex / Cal Poly HEUR (II), and Cal Poly latex / Cal Poly HEUR (III).The latex volume fraction was held constant at 0.25 and the concentration of HEUR was varied from 0-2.0 wt%. Mixtures were allowed to equilibrate for 7 days, syneresis was measured on day 7, and steady-state viscosities over a shear rate range of 0.01-1000 s -1 were determined on days 7-9 with a DHR-2 rheometer (TA Instruments) that was outfitted with 40 mm, 2 o cone. The mixtures were also studied by microscopy and dynamic oscillatory testing. The chemical structures of the Cal Poly HEURs were determined by proton nuclear magnetic resonance spectroscopy ( 1 H NMR) and the molecular weight by gel permeation chromatography (GPC).From this study, a correlation between syneresis and complex rheology was observed in I. Similar trends were observed in phase-separated II and dispersed (not phase-separated) III, though II with over 0.4 wt% HEUR were ejected from the cone / plate geometry at 1-100 s -1 and III did not demonstrate syneresis. Further investi...

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Section: Rheologymentioning

confidence: 99%

Section: Rheologymentioning

confidence: 99%

Section: Rheologymentioning

confidence: 99%

Section: Shear Thickening Newtonianmentioning

confidence: 99%

Section: Rheology and Phase Behavior Of Waterborne Latex / Heur Mixturesmentioning

confidence: 99%

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Syneresis and Rheology Mechanisms of a Latex-HEUR Associative Thickener System

Smith

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Influence of fluorinated segments of variable length on the thickening properties of a model HASE skeleton

Oddes

Amigoni

Givenchy

et al. 2011

J of Applied Polymer Sci

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Introduction of fluorocarbon segments in an associative thickener copolymer (ethyl acrylate (EA)/ methacrylic acid/macromonomer) was achieved by the substitution of EA with either trifluoroethyl acrylate, 2-perfluorobutylethyl acrylate, or 2-perfluorooctylethyl acrylate. The thickening properties were evaluated by rheological flow experiments in aqueous medium as well as in 10 wt % of sodium dodecyl sulfate (SDS) aqueous solution. Whereas in the literature no particular attention is devoted to the impact of the ethylene moieties in hydrophobically modified alkali-soluble emulsion (HASE) skeleton, our study reveals they contribute significantly to the performances when modified by an incompatible fluorocarbon segment. Moreover, the synthesis process has a huge influence by inducing a specific distribution of the fluorinated acrylates in the macromolecule. The amount of substitution is also important and even 20 mol % of EA substituted reveals a great impact on the rheological properties of the copolymer solutions. Whereas an SDS aqueous medium generally destroys almost all the hydrocarbon interactions from the macromonomer, the total replacement of ethyl groups by trifluoroethyl groups with a cosolvent process, leads to emulsions with an equivalent thickening effect than the reference hydrocarbon HASE used. This result is quite encouraging for research work on the synthesis of HASE with increased biocompatibility.

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On the Relationship Between Plateau Modulus and Shear Relaxation Time in Transient Networks

West

Kindt

2015

Macromol. Theory Simul.

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The linear rheology of unentangled Maxwellian transient networks formed from reversibly associating telechelic polymers can be characterized by a plateau modulus and a shear relaxation time. The concentration dependences of both these properties have been modeled using a variety of theories. An expression is introduced here that allows the concentration dependence of shear relaxation time to be determined (to within a constant, the microscopic chain lifetime) directly from the concentration dependence of the plateau modulus, subject to some approximations. This prediction is tested against experimental results for hydrophobic ethoxylated urethane (HEUR) and against results of simple‐model simulations. The nature of the approximations needed to derive this relationship and the scope of its applicability are discussed.

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Influence of prepolymers molecular weight on the viscoelastic properties of aqueous HEUR solutions

Cited by 39 publications

References 22 publications

Syneresis and Rheology Mechanisms of a Latex-HEUR Associative Thickener System

Syneresis and Rheology Mechanisms of a Latex-HEUR Associative Thickener System

Influence of fluorinated segments of variable length on the thickening properties of a model HASE skeleton

On the Relationship Between Plateau Modulus and Shear Relaxation Time in Transient Networks

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