Chapter Four · failure evidence
What Colloidal & Suspension Rheology got wrong, from 47 dissertations
The records document widespread experimental, modeling, and processing failures encountered across colloidal dispersions, complex pastes, and polymeric fluids. Practitioners frequently struggle with printable viscosity bounds in additive manufacturing, constitutive equation breakdowns in structured fluids, severe measurement artifacts in rheometry, and high resistance during mixing and flow. These records come from PhD theses at 17 institutions, 2021 to 2026. Each links to its thesis. They were extracted by language models reading the full text, so treat each as a lead to read, not a verdict.
Inkjet and direct-write printing fail when ink viscosity and yield stress fall outside operational limits
Formulations with insufficient viscosity or yield stress suffer from liquid spreading, poor shape fidelity post-deposition, and uncontrolled pore infiltration. Conversely, overly viscous, dilatant, or shear-thickening inks cause nozzle clogging, droplet formation failure, and tunneling through the surrounding matrix.
Tried and failed
semi-solid extrusion 3D printing applied to low-concentration single-component biopolymer hydrogels. Outcome: unstable. Reason: insufficient viscosity and low yield stress caused spreading and loss of shape fidelity post-deposition
Semi-solid extrusion-based 3D printing of biopolymer hydrogels and their applications in food · Iowa State
Tried and failed
pneumatic extrusion bioprinting applied to time-dependent viscous hydrogel precursor. Outcome: unstable. Reason: viscosity changed over time, causing bioink deposition rate per unit distance to continuously decrease
Tried and failed
vertical orientation fused deposition modeling printing applied to nanocomposite polymer blend filaments. Outcome: unstable. Reason: highly sensitive complex viscosity behavior during deposition prevented successful structural printing
Tried and failed
direct extrusion of undiluted clay paste applied to additive manufacturing of functional pastes. Reason: excessive paste viscosity prevented extrusion through the print nozzle
Considered and rejected
Considered and rejected: Rejected using 3D inkjet printing (CeraPrinter X-Series) for membrane fabrication due to powder agglomeration and unstable colloidal ink rheology
Recovering materials from end-of-life lithium-ion batteries · Imperial
Considered and rejected
Considered and rejected: Rejected 70 wt% polymer formulations in ethyl acetate for 3D printing due to excessive viscosity exceeding the 10 Pa·s continuous printing threshold.
Photochemical 3D Printing of Prototype Medical Devices from Poly(Propylene Fumarate)-Based Copolyesters · DukeSpace
Considered and rejected
Considered and rejected: Rejected dropper-based droplet drying for traditional binder due to excessive viscosity clogging the dropper.
Considered and rejected
Considered and rejected: Rejected pure cyclohexane slip casting suspension for direct ink writing due to excessively low viscosity and dilatant behavior at high solid loadings (>55 vol%)
Near-Net Shaping and Additive Manufacturing of Ultra-High Temperature Ceramics via Colloidal Processing · Virginia Tech
Lost to a baseline
Inkjet-printed PEDOT:PSS on nitrocellulose exhibited ~6x lower ON current in modulus compared to dispense-printed PEDOT:PSS due to low-viscosity ink dispersion in pores.
A printable Organic Electrochemical Transistor on paper for biochemical sensing · IRIS - POLITO - prod
Considered and rejected
Considered and rejected: Rejected inkjet/jetting processes for polymer solutions because high dynamic viscosity (Z ~ 0.05) prevents droplet formation in the viscous dissipation regime.
Sensor-based Characterization and Control of Additive Biomanufacturing Processes · Virginia Tech
Considered and rejected
Considered and rejected: Viscosity ratios eta_ink >> eta_matrix were rejected because the ink tunneled through the matrix during extrusion rather than forming cohesive spherical nodes
Embedded 3D Printing of Polymeric and Ceramic Lattices · Harvard
Considered and rejected
Considered and rejected: Commercial inkjet printers without electrostatic field, rejected due to poor handling of high-viscosity inks and microscale cracking.
Real-time monitoring of neuronal cells through electrohydrodynamic patterning of flexible graphene microelectrodes · Iowa State
Considered and rejected
Considered and rejected: Rejected inkjet printing of P(VDF-TrFE) using Dimatix printer due to strict 10–12 mPas ink viscosity constraints not met by dissolution process.
Considered and rejected
Considered and rejected: Rejected standard inkjet printing because it requires pressure and is limited to low-viscosity materials (5 to 20 mPa·s).
The E-jet printing of organic inks on organic substrates · Iowa State
Considered and rejected
Considered and rejected: Rejected matching ink viscosity across particle sizes in favor of matching ink solids content (50 wt%), because shear-thinning profiles converged at high shear rates (>10 s⁻¹).
Considered and rejected
Considered and rejected: Rejected using pure cell inks without microparticles for STEP due to their lower storage modulus, loss modulus, yield stress, and apparent viscosity.
Programmable Assembly of Genetically Engineered Human Tissues · Harvard
Standard constitutive rheology models fail to capture microstructural changes and non-Newtonian behavior
Classical models such as Carreau, Casson, and Herschel-Bulkley break down when fluid microstructures are altered by aeration, incomplete polymer hydration, or shear-induced deformation. These constitutive equations generate unphysical zero-shear viscosities, non-monotonic fitting errors, and unstable flow index predictions under low shear rates.
Tried and failed
Empirical Carreau rheology model parameter fitting applied to incompletely hydrated polymer solutions. Reason: Poor hydration and microgels caused non-monotonic, scattered low-shear viscosity data that violated model assumptions
Database, Spreadsheet, and Models for Polymer Chemical Enhanced Oil Recovery · UT Austin
Considered and rejected
Considered and rejected: Rejected arbitrary viscosity partitioning in Burgers transient rheological models (e.g. fixing eta_KM / eta_M = 1/10), because it lacks experimental physical basis and cannot be generalized across differing forcing timescales.
Fire and ice: investigating links between mantle dynamics and ice sheet stability · Imperial
Tried and failed
Casson rheological model fitting applied to aerated complex fluid shear viscosity. Outcome: did not generalise. Reason: standard suspension constitutive model failed across tested shear rates once micro-aeration altered the fluid microstructure
Tried and failed
empirical droplet size scaling models applied to high-viscosity fluid atomization. Outcome: did not generalise. Reason: shear-thinning non-Newtonian behavior invalidated constant-viscosity assumptions
Airblast atomization : the effect of linear scale on the mean drop size · Cranfield
Tried and failed
Herschel-Bulkley rheological model applied to low shear rate multiphase flow simulation. Reason: Predicts infinite viscosity at near-zero shear rates, causing unrealistic velocity profiles and transport errors
Rheological characterization of complex drilling fluid and the effects on drilling hydraulics · UT Austin
Tried and failed
Herschel-Bulkley model fitting at low shear rates applied to colloidal hydrogel rheology data. Outcome: unstable. Reason: low shear rate stress instabilities produced inconsistent and unphysical flow index values (>1)
Synthetic, rheological, and morphological control of one-dimensional CdS and Sb₂S₃ nanomaterials · UT Austin
Considered and rejected
Considered and rejected: Rejected assuming clusters are strictly rigid under flow in the viscosity model, introducing cluster flexibility/rigidity attenuation scaling with cluster size.
Protein-protein interactions and rheological properties of monoclonal antibodies at high concentration · UT Austin
Considered and rejected
Considered and rejected: Rejected using Cross, Sisko, or Carreau-Yasuda models due to excessive parameters not broadly applicable across disparate colloidal regimes
Predicting the Flow Rate and Extensional Behavior of Colloidal Dispersions for 3D Printing Applications · Texas Tech
Elevated suspension viscosity impairs fluid mixing, coating uniformity, and continuous handling
Highly viscous and shear-thickening composite suspensions generate excessive mechanical energy dissipation and impede secondary emulsification and polymer dissolution. High resistance to flow also leads to inhomogeneous liquid distribution in binders, irregular coating profiles, and severe dispersion difficulties.
Considered and rejected
Considered and rejected: Rejected continuous flow mode for the semi-solid Na-S flow battery in favor of intermittent aliquot flow due to high suspension viscosity causing mechanical energy dissipation.
Electrochemical Flow System for Li-Ion Battery Recycling and Energy Storage · Virginia Tech
Considered and rejected
Considered and rejected: Rejected liquid sucrose aqueous solutions as binders because high viscosity led to inhomogeneous liquid distribution and excessively delayed disintegration times
Novel drug-loaded paper tablets for improved oral drug delivery Neuartige Papiertabletten mit Wirkstoffbeladung für verbesserte orale Arzneimittelverabreichung · open_UMR Marburg DSpace 10.0
Considered and rejected
Considered and rejected: Rejected protein concentrations above 2% w/v for microneedle coating due to excessive viscosity causing irregular coating.
Metal-Organic Frameworks for Long-term Vaccine Storage · Georgia Tech
Considered and rejected
Considered and rejected: Rejected primary emulsion formulations with 1.5%–4% psyllium husk because high viscosity hindered secondary emulsification mixing.
Ultrasound-Assisted Novel Double Emulsion Containing Grape Pomace Polyphenols as a Delivery System to Encapsulate Vitamin E and Omega-3 for Food and Dietary Supplement Applications · Carleton University Institutional Repository
Considered and rejected
Considered and rejected: Rejected testing polymer concentrations above 11–16 wt% in cloud point and dissolution tests due to rapid solution viscosity increase preventing adequate mixing
Solvent-Enabled Molecular Recycling of Polyolefins · DSpace at SUNY Buffalo
Considered and rejected
Considered and rejected: Direct mixing of concentrated CNC/CNF gels into polymer solutions rejected due to poor dispersion and lower gel modulus than composite reverse dialysis
Rheological Characterization of Cellulose Nanomaterials for Quality Control and Processing · Georgia Tech
Considered and rejected
Considered and rejected: Rejected PAN/LDH composite suspensions with higher LDH contents (≥12.6 wt.%) due to shear-thickening behavior, particle aggregation, and increased suspension viscosity.
Nanostructured Adsorbents for Selective Lithium Recovery: Mechanisms, Fabrication, Performance Evaluation, and Applications in Desalination · Virginia Tech
Rheometrical characterization suffers from measurement artifacts, wall slip, and phase separation
Smooth test geometries induce significant wall slip and sample ejection at elevated shear rates, leading to severe underestimation of viscosity. In addition, lack of solvent density matching induces gravitational sedimentation while discontinuous shear thickening produces extreme stress fluctuations that disrupt steady-state rheometry.
Tried and failed
non-standard polymer dissolution and mixing protocols applied to polymer rheology and viscosity characterization. Reason: incorrect sample preparation caused severe artificial overestimation of low-shear viscosity
Database, Spreadsheet, and Models for Polymer Chemical Enhanced Oil Recovery · UT Austin
Tried and failed
suspension characterization without solvent density matching applied to dilute colloidal gel systems. Outcome: unstable. Reason: gravitational sedimentation caused sample failure at low volume fractions without precise solvent density matching
Microscopic characterization of macroscopic colloidal gel rheology · MIT
Tried and failed
strain-controlled rheometry applied to discontinuous shear thickening colloidal suspensions. Outcome: unstable. Reason: extreme stress fluctuations and critical shear rate variability prevented capturing controlled states across the discontinuity
Microscopic characterization of macroscopic colloidal gel rheology · MIT
Tried and failed
Environmental and mechanical conditioning of yield-stress fluids applied to concentrated colloidal dispersions. Reason: Treatments failed to reliably recreate cohesive structural failure or control rheological breakdown
Extrusion Printing of Carbon Nanotube Inks, from Rheology to Electronics · MIT
Tried and failed
rotational rheometry with smooth plate geometry applied to yield-stress capillary suspension inks. Outcome: unstable. Reason: smooth geometries induced severe wall slip and sample ejection at high shear rates, underestimating viscosity
Direct ink writing of aqueous electrochemical energy storage devices · Imperial
Lost to a baseline
Liquid handler viscosity determination underestimated capillary viscometer measurements by ~7 cSt offset due to measurement shear thinning or pressure conversion models.
Synthesis and application of novel hyperbranched polymers · University of Nottingham Repository
Colloidal stability and redispersion predictions fail due to shifting sedimentation regimes and agglomeration
Extrapolating long-term suspension stability from initial settling rates fails because sedimentation mechanisms transition through different physical regimes over time. Furthermore, conventional dewatering treatments like freeze drying and filter pressing cause severe particle agglomeration and impurity retention that prevent redispersion.
Tried and failed
extrapolating long-term stability from initial settling rate applied to colloidal suspension stability estimation. Outcome: did not generalise. Reason: sedimentation mechanisms shift across different regimes over time
Investigation on the performance of nanofluids due to preparation effects and operational conditions. · Cranfield
Lost to a baseline
Filter-pressing and freeze drying failed to match ultrasonic dewatering for redispersion ease; filter-pressed samples retained impurities/residues and freeze-dried samples exhibited severe agglomeration that precluded optical and SEM image analysis even after 5 minutes of mixing.
Dewatering of Cellulose Nanomaterials using Ultrasound · Georgia Tech
Left open by the authors
Problems the authors named and did not get to.
Left open
Design ionic liquid cations with enhanced Li+ chelating affinity, reduced viscosity, and high chemical stability for lithium-bromine flow batteries. Blocker: Requires chemical synthesis, wet-lab validation, and electrochemical testing facilities
Left open
Apply colloidal synthesis to fabricate MoSe2-carbon heterostructures and evaluate their cycling stability in batteries. Blocker: Requires wet-lab chemical synthesis and battery testing apparatus
Left open
Extend bulk polymer rheology models to predict in-situ apparent viscosity within porous media. Blocker: Requires porous media coreflood experimental data and rheological laboratory measurements for validation.
Left open
Incorporate additive manufacturing microstructural heterogeneities into dynamic failure models to predict spall strength and shock dispersion. Blocker: None
Left open
Measure physical properties and viscosity changes when incorporating tardigrade disordered proteins into pharmaceutical formulations. Blocker: Requires a wet lab and rheological measurement apparatus to formulate and test protein solutions
Intrinsically Disordered Proteins & Regions in Viruses and Possibly Pharmaceuticals · UT Austin
Left open
Systematically vary polymer cross-linker density at fixed particle volume fraction to test the polymer-reinforced aggregate hypothesis. Blocker: Requires a wet lab, chemical synthesis of cross-linked polymers/silica dispersions, and a strain-controlled rheometer.
Left open
Perform rheological testing on pAA-lactose-C12 and pAA-lactose-C16 polymers to verify shear thinning and viscosity properties. Blocker: Requires physical synthesized polymer samples and specialized rheology measurement equipment/services (Formulaction).
Surface-Active Synthetic Glycocalyx and Lipid Layer Analogs for the Treatment of Dry Eye Disease · Cornell
Left open
Evaluate the effects of polymer molar mass on dense paste mixing behavior using viscosity-matched binders across different viscosities in RAM. Blocker: Requires a physical chemistry/materials wet lab, Resonant Acoustic Mixer (RAM), and formulation chemicals.
Formulation and Process Considerations for the Manufacturing of Dense Pastes · Georgia Tech
Left open
Investigate scalings of normal stress differences, complex modulus, and friction coefficients near the frictional shear jamming critical point. Blocker: Requires a physical rheometer and custom piezoelectric transducer apparatus for dense colloidal suspensions
UNDERSTANDING AND TUNING THE RHEOLOGY OF DENSE SUSPENSIONS VIA ITS MICROSTRUCTURE · Cornell
Left open
Investigate the breakdown of the quasi-static assumption and measure the effects of fluid viscosity on fractal landscape dynamics. Blocker: Requires experimental laboratory apparatus and physical soft jammed emulsion systems to vary strain rate and fluid viscosity.
A fractal landscape dynamics approach to understanding particle motion in soft jammed materials · Penn
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