Dramatic Increase In Viscosity Research Articles

Water-in-Oil Emulsion Temporal and Spatial Evolution at Static Conditions and Its Impact on Pipeline Restart

Summary Understanding emulsion evolution at static conditions is crucial for production operations, such as pipeline operations during the shut-in and restart process and separator optimal design. This study experimentally investigated the temporal and spatial evolution of water-in-oil emulsion properties under static conditions. Numerical simulations were conducted to study their impacts on pipeline restart operations. The experiments were conducted in graduated glass cylinders, with mineral oil and tap water as the testing fluids and Span® 80 as the surfactant. Different water cuts, mixing speeds, and surfactant concentrations were investigated. Along with idle time at static conditions, the mixture demonstrated two layers, namely an upper oil layer and a lower emulsion layer, except for the lowest surfactant concentration that gave a third additional free-water layer at the bottom. Experimental results showed a dramatic increase in viscosity in the emulsion layer with time and depth, which was closely related to the increase in the water volumetric fraction. The increase rate slowed down and plateaued out with time. The increase rate is also related to water cut, mixing speed, and surfactant concentration. Experimental results also show that the relationships between the viscosity and water cut for separated emulsion follow the master curve of viscosity and water cut for homogeneous emulsion. This suggests that one can estimate the viscosity using the master curve given the water volumetric fraction. The numerical simulation was conducted for pipelines with a valley configuration and with the fluid properties obtained from the experimental measurements. It demonstrates that a higher pressure is required to restart the flow to the original flow rate. It also shows that the flow rate may not be able to resume its original value given the same pressure boundaries due to the accumulation of dense emulsion layers in the horizontal and upward inclined sections. For example, for a 16-m pipe, the flow cannot be restarted given the same inlet pressure (100 Pa). It can only resume 4.6% of the original flow rate when the pressure is elevated to 300 Pa.

Shear thickening in presence of adhesive contact forces: The singularity of cornstarch

Hypothesis: A number of dense particle suspensions experience a dramatic increase in viscosity with the shear stress, up to a solid-like response. This shear-thickening process is understood as a transition under flow of the nature of the contacts – from lubricated to frictional – between initially repellent particles. Most systems are now assumed to fit in with this scenario, which is questionable.Experiment: Using an in-house pressure sensor array, we provide a spatio-temporal map of the normal stresses in the flows of two shear-thickening fluids: a stabilized calcium carbonate suspension, known to fit in with the standard scenario, and a cornstarch suspension, which spectacular thickening behavior remains poorly understood.Findings: We evidence in cornstarch a unique, stable heterogeneous structure, which moves in the velocity direction and does not appear in calcium carbonate. Its nature changes from a stress wave to a rolling solid jammed aggregate at high solid fraction and small gap width. The modeling of these heterogenities points to an adhesive force between cornstarch particles at high stress, also evidenced in microscopic measurements. Cornstarch being also attractive at low stress, it stands out of the classical shear-thickening frame, and might be part of a larger family of adhesive and attractive shear-thickening fluids.

Engineering Advanced Environmentally Friendly Corrosion Inhibitors, Their Mechanisms, and Biological Effects in Live Zebrafish Embryos

Carbon steel is one of the most used construction materials and makes up the bulk of steel production in the world. However, this alloy is vulnerable to corrosion, which reduces its safety and costs trillions of dollars worldwide in terms of corrosion protection and infrastructure maintenance. Corrosion inhibitors are among the cheapest and most effective methods to minimize corrosion and maximize the shelf life of this ubiquitous alloy; however, they are often harmful to the environment. Currently there are no reports in terms of engineering design methodology to develop highly effective, advanced corrosion inhibitors. The possible synergistic behavior of a surface-active quaternary ammonium with a tailored carboxylate compound provides a rational molecular design toward delivering corrosion inhibitors to a metal surface through controlled speciation in solution. Here we show how entrapment and delivery of the anion inhibitor through speciation and micellar formation can lead to high inhibition efficiency, as determined by potentiodynamic polarization and electrochemical impedance spectroscopy. In particular, we demonstrate how NMR spectroscopy, pfg NMR diffusion measurements, and Cryo-TEM, taken together with molecular dynamic simulations, can reveal the micellar formation and its concentration dependence, with wormlike micelles evident at higher concentrations correlating with a dramatic increase in viscosity. This new organic corrosion inhibitor, cetrimonium 4-ethoxy cinnamate, provides significantly higher corrosion inhibition efficiency compared with the 4-hydroxy cinnamate analogue and with reduced toxic impact in the zebrafish embryo compared to the surface active CTAB often used as an antimicrobial.

Spherical hybrid filler BN@Al2O3 via chemical adhesive for enhancing thermal conductivity and processability of silicon rubber

AbstractHexagonal boron nitride (h‐BN) is an ideal candidate material for electrical and electronic systems due to its excellent performance. However, the addition of platelet‐like h‐BN leads to a dramatic increase of viscosity of composites and anisotropic thermal conductivity of composites. Herein, modified h‐BN (m‐BN) was coated onto spherical α‐Al2O3 via chemical adhesive, and core‐shell structured hybrid spherical filler (m‐BN@Al2O3) was prepared. Furthermore, the microstructure, rheology, mechanical properties, and thermal conductivity of hybrid filler/polydimethylsiloxane (PDMS) were studied. At 60 vol% filler loading, the thermal conductivity of m‐BN@Al2O3/PDMS is up to 2.23 W·m−1·K−1, which is 86% higher than that of Al2O3/PDMS and the ratio of in‐plane diffusivity to through‐plane diffusivity decreases from 2.0 to 1.0. At meanwhile, the viscosity of m‐BN@Al2O3/PDMS is about one fourth of the viscosity of m‐BN/Al2O3/PDMS. This simple and versatile strategy opens a pavement for enhancing the thermal conductivity of polymer and has great potential in high‐frequency communication.

Understanding the multiple interactions of inertinite during pyrolysis/carbonisation with vitrinite: A study of two Australian coals of different rank

Macerals (vitrinite and inertinite) were separated from two Australian coals to study interactions during coking. Macerals were blended in various ratios, and their viscoelastic properties and expansion/contraction behaviour measured using rheometry. The minimum viscosity of a vitrinite concentrate (VC) from a high-rank coking coal (vitrinite reflectance Rvo = 1.54%) increased according to an expected exponential trend with increasing amounts of added inertinite concentrate (IC), suggesting no interaction. Volatile release rates (VRR), obtained from thermogravimetric analysis, were the same as that predicted based on the assumption that vitrinite and inertinite behave independently. For a medium-rank coal (Rvo = 1.19%), increasing proportions of its corresponding inertinite also increased viscosity, but the extent that it increased was much less than expected. VRR from these blends were lower than expected from a mass average of the components. When the IC from the high-rank coal blended with the VC of the medium-rank coal, a dramatic increase in viscosity occurred along with retention of volatile matter. These observations have been attributed to inertinite displaying varying degrees of volatile adsorption and softening/deformation. It is evident that inertinite and vitrinite interact in multiple ways during pyrolysis, which could have competing influences on viscosity and, therefore expansion behaviour.

Polyurethane coatings cured via azide-alkyne cycloaddition using reduced-viscosity poly(alkynyl carbamate) prepolymers

Alternative crosslinking polyurethanes (ACPUs) were created by reacting a commercial allophanate-modified polyisocyanate with propargyl alcohol to yield a poly(alkynyl carbamate); a polyazide co-reactant was created from an acrylic polyol. Conversion of the polyisocyanate into the corresponding poly(propargyl carbamate) resulted in a dramatic viscosity increase. Poly(alkynyl carbamate) prepolymers with lower viscosities were designed by replacing various fractions of the propargyl alcohol with commercial glycol ether plasticizers, ethylene glycol monoethyl ether (EGMEE), diethylene glycol monomethyl ether (DEGMEE), and diethyleneglycol monobutyl ether (DEGBE). Triethylene glycol monopropargyl ether was also studied to provide plasticization with no sacrifice of alkyne functionality. For each commercial glycol ether plasticizer, viscosity was unaffected or increased at a loading level of 10 mol%. At 25 mol%, average viscosity reduction was 36 %, with DEGBE yielding the greatest reduction at 55 %. At 33 mol%, no further decreases were observed. Triethylene glycol monopropargyl ether yielded a 76 % reduction in viscosity at 33 mol%; 100 mol% substitution yielded no further reduction. Coatings produced from the modified poly(alkynyl carbamate)s were softer and displayed lower glass transition temperatures compared to a polyisocyanate/polyol control and a 100 % propargylated poly(alkynyl carbamate)/polyazide control. Solvent resistance of the modified coatings was the same as the controls except for those created from DEGBE and from DEGMEE at 33 mol%.

Densities, viscosities and spectroscopic study of partially CO2-loaded nonaqueous blends of 2-butoxyethanol with 2-(ethylamino)ethanol and 2-(butylamino)ethanol at temperatures of (293.15 to 353.15) K

Nonaqueous CO2 absorbents, composed of secondary alkanolamines and 2-alkoxyethanols, have attracted much attention for an energy-efficient CO2 capture process. In this work, densities and viscosities of partially CO2-loaded mixtures of 2-(butylamino)ethanol (BAE) + 2-butoxyethanol (EGBE) and 2-(ethylamino)ethanol (EAE) + EGBE were measured at atmospheric pressure over the temperature range of (293.15 to 353.15) K with amine mass fraction (w1) of (0.10, 0.30 and 0.50) containing various CO2 loading. With increasing CO2 loadings, significant increases in both density and viscosity were observed. Dimensionless ρloaded·ρCO2-free−1 and ηloaded·ηCO2-free−1 from the CO2-free and CO2-loaded systems were fitted by proposed correlations as a function of temperature, amine concentration and CO2 loading. The calculated values of density and viscosity from the correlations are in good agreement with the experimental results, with AADs within 0.15% and 1.60% for density and viscosity respectively. The dramatic increase in viscosity of carbonated solutions was interpreted by the intermolecular interactions and the formation of ionic products in the mixtures based on the FTIR spectral results.

Rheological analysis of nitrate molten salts with suspended particles for solar thermal plants

Binary alkali nitrate molten salts are currently the heat transfer fluid (HTF) and thermal energy storage (TES) media of choice in commercial solar thermal energy (STE) power plants. This paper studies the rheological properties of binary alkali nitrate molten salts containing two distinct classes of suspended particles with unique practical applications and dynamics. Phase change salt slurries (liquid/solid suspensions) can appear during plant start-up after local freezing in pipes. Molten salt-nanoparticle suspensions are being proposed in the literature as an advanced HTF with enhanced properties. The phase change slurries were analyzed by rheological measurement of off-eutectic salt mixtures at sub-liquidus temperatures combined with determination of solid fraction through differential scanning calorimeter (DSC) testing in a novel approach. Molten salts with a range of silica nanoparticle loadings were also studied in the rheometer. Both suspension types exhibit non-Newtonian, shear thinning behavior, with a dramatic increase in viscosity compared to the base fluid. Additionally, both suspension types show that measured viscosity depends on the shear history, but the trends in viscosity with shear history differs between the two systems. The increase in viscosity with solid volume fraction of the nanofluid is significantly higher than that of a partially-crystallized salt slurry at a given volume fraction. Particle aggregation, particle/cluster aspect ratio, cluster breakage and restructuring are considered as determining factors in the observed rheological behavior. Deviations from classical effective medium theories of well-dispersed systems are discussed. Differing trends suggest that unique physical phenomena govern the rheological behaviors of the molten salt mixtures with different suspended solid particles. Thus, engineers and scientists must exercise caution when extrapolating rheological results to unique applications. • Molten salt slurries and nanoparticle suspensions are investigated experimentally. • Rheology and calorimetry are combined to determine the viscosity dependence on solid volume fraction. • Viscosity of molten salt nanofluids follows a modified Batchelor expansion. • Viscosity depends on suspension type and shear history, and exhibits shear thinning/thickening.

Investigating the nature of discontinuous shear thickening: Beyond a mean-field description

Dense suspensions can undergo a dramatic increase in viscosity at a critical value of the shear stress. This phenomenon, termed discontinuous shear thickening (DST), has been attributed to an increase in the fraction of particle interactions becoming frictional with increasing shear stress, and a successful mean-field theory has been developed to explain various accompanying rheological properties. On a microscopic scale, however, conventional structural analysis measures such as the grain-position pair correlation function show no significant changes with the onset of DST, though recent work has shown that similar analysis in the dual space of contact forces does lead to marked changes at this transition. Furthermore, experimental results have suggested the existence of higher-order microscopic correlations and the importance of incorporating fluctuations away from a mean-field description. To this end, we use a higher-order cluster analysis tool to study the force networks obtained from simulations of dense suspensions to construct an effective interaction potential in force space. We show that there are significant changes occurring in this potential as a function of density and stress close to DST. We discuss the implications of these observations on an emergent field theory of the DST transition.

Synthesis and Characterization of Amphiphilic Hairy Nanoparticles with pH and Ionic Dual‐Responsiveness

Recently, polymeric shell hybrid nanoparticles with multiresponse to external triggers have attracted much interests in academic researches and technical industries. This work provided a novel of amphiphilic hairy nanoparticles (APNPs) with distinct pH and ionic dual‐responsiveness based on silica nanoparticles as the core, amphiphilic‐polymeric chains containing amine‐moieties, and carboxylic groups as the layer by a facile emulsion polymerization. The structural parameters of APNPs were characterized by combining thermal gravimetric analysis, infrared spectroscopy, proton nuclear magnetic resonance, transmission electronic microscopy, and dynamic light scattering. The polymeric shell in water was compressed due to proton‐transference from carboxylic groups to amine‐moieties, where APNPs behaved as colloidal particles. By adding HCl, carboxyl groups were deionized, whereas the electrostatic repulsion of protonated amine‐moieties between the neighboring chains expanded the polymeric shell, and thus APNPs self‐assembled into a typical viscoelastic fluid. APNPs reconstructed into branch‐like viscoelastic gel in the presence of cationic ions under alkaline environment. Such transformation was reversible by adjusting the pH of APNPs dispersion. APNPs might have potential application in enhanced oil recovery of unconventional reservoirs because of their original low viscosity for desirable injectivity from ground to micro‐nanopores of subsurface, and the dramatic increase in viscosity for mobility control triggered by pH and ionic ions. POLYM. ENG. SCI., 60:563–574, 2020. © 2019 Society of Plastics Engineers

Spray-assisted assembled spherical boron nitride as fillers for polymers with enhanced thermally conductivity

Owing to its unique properties, such as electrical insulation, high thermal conductivity, high breakdown strength, physical and chemical stability, boron nitride has been used widely as fillers to improve the thermal conductivity of polymers. However, the addition of very small boron nitride leads to a dramatic increase of viscosity of polymer composites. The increased viscosity will limit the amount of boron nitride in polymers, which results in limited increase of thermal conductivity for polymer composites. To this end, we developed a spray-assisted self-assembly method to prepare spherical boron nitride. The spherical boron nitride improves the thermal conductivity of polydimethylsiloxane, in contrast to boron nitride platelets, which is attributed to its structural characteristics. The thermal conductivity of spherical boron nitride/polydimethylsiloxane is up to 2.30 W/mK, almost four times of that of platelet-like BN/polydimethylsiloxane composite at the 50 wt% filler content. This simple and versatile method is therefore directly relevant to the future design of practical polymer composites for heat removal of modern electronics.

Experiences in numerical simulation of wax deposition in oil and multiphase pipelines: Theory versus reality

Wax deposition in pipelines transporting waxy oils and multiphase fluids is a significant flow assurance issue. The main problems caused by wax deposition include dramatic viscosity increase or complete “gelling” of crude oil.The present study shows a review of existing literature references concerning the problem of wax deposition, the main driving forces behind the phenomenon and the relative mathematical models developed. In addition, the application of the main mathematical models to real field data is presented in order to compare the numerical results with measured field values. In fact, wax deposition models, generally, are validated using experimental data, obtained from laboratory deposition tests; anyway, since the scale-up of the data to the real field cases is a problem, it is more advisable to compare models’ predictions to real field data. Four sets of field data have been simulated, two involving one phase wax deposition and two related to wax deposition from multiphase flow.

The Mayonnaise Effect.

Structuring caused by the mixing of liquids or the addition of solutes to a solvent causes the viscosity to increase. The classical example is mayonnaise: a mixture of two low-viscosity liquids, water and oil, is structured through the addition of a surfactant creating a dispersed phase, causing the viscosity to increase a thousand-fold. The dramatic increase in viscosity in highly concentrated solutions is a long-standing unsolved problem in physical chemistry. Here we will show that this viscosity increase can be understood in terms of the solute-induced structuring of the first solvation shell, leading to a jamming transition at a critical concentration. As the jamming transition is approached, the viscosity naturally increases according to a Vogel-Fulcher-Tammann type expression. This result calls into question the validity of the Jones-Dole B-coefficient as an indicator of the structure making or breaking ability of solutes.

Universal glass-forming behavior of in vitro and living cytoplasm

Physiological processes in cells are performed efficiently without getting jammed although cytoplasm is highly crowded with various macromolecules. Elucidating the physical machinery is challenging because the interior of a cell is so complex and driven far from equilibrium by metabolic activities. Here, we studied the mechanics of in vitro and living cytoplasm using the particle-tracking and manipulation technique. The molecular crowding effect on cytoplasmic mechanics was selectively studied by preparing simple in vitro models of cytoplasm from which both the metabolism and cytoskeletons were removed. We obtained direct evidence of the cytoplasmic glass transition; a dramatic increase in viscosity upon crowding quantitatively conformed to the super-Arrhenius formula, which is typical for fragile colloidal suspensions close to jamming. Furthermore, the glass-forming behaviors were found to be universally conserved in all the cytoplasm samples that originated from different species and developmental stages; they showed the same tendency for diverging at the macromolecule concentrations relevant for living cells. Notably, such fragile behavior disappeared in metabolically active living cells whose viscosity showed a genuine Arrhenius increase as in typical strong glass formers. Being actively driven by metabolism, the living cytoplasm forms glass that is fundamentally different from that of its non-living counterpart.

Thermometer Effect: Origin of the Mixed Alkali Effect in Glass Relaxation.

Despite the dramatic increase of viscosity as temperature decreases, some glasses are known to feature room-temperature relaxation. However, the structural origin of this phenomenon-known as the "thermometer effect"-remains unclear. Here, based on accelerated molecular dynamics simulations of alkali silicate glasses, we show that both enthalpy and volume follow stretched exponential decay functions upon relaxation. However, we observe a bifurcation of their stretching exponents, with β=3/5 and 3/7 for enthalpy and volume relaxation, respectively, in agreement with Phillips's topological diffusion-trap model. Based on these results, we demonstrate that the thermometer effect is a manifestation of the mixed alkali effect. We show that relaxation is driven by the existence of stressed local structural instabilities in mixed alkali glasses. This driving force is found to be at a maximum when the concentrations of each alkali atom equal each other, which arises from a balance between the concentration of each alkali atom and the magnitude of the local stress that they experience.

PH reversible micelle transition of a tertiary amine-based gemini surfactant in aqueous solution

ABSTRACTIn this work, we prepared a tertiary amide-based gemini surfactant (DSTAPA), which contained two pH-sensitive tertiary amide head groups. Then the molecule state distribution and self-assembly transition of the surfactant in aqueous solution were investigated under different pH conditions. The DSTAPA molecules were on the states of double cationic (DSTAPAH2+), single cationic (DSTAPAH+), and double tertiary amine groups (DSTAPA) under acidic, neutral, and basic conditions, respectively. With the variation of the molecule states, the sample was water-like below pH of 6.8 and immediately transformed to gel-like fluid between pH of 6.8 and 7.8, then changed to white precipitate with the further increase of pH value. Furthermore, the microstructure and regulation mechanism were investigated by rheological measurements, dynamic light scattering, and cryogenic transmission electron microscopy. The appearance and micelle transitions of the DSTAPA aqueous solution are actually owing to the spherical–worm-like micelle transition, leading to dramatic viscosity increase and hydrogel formation. This transition was completely reversible and repeated for at least three cycles. Finally, a reasonable mechanism of the transition was proposed based on the viewpoints of the molecular states and micelle structures. The DSTAPA aqueous system with pH-reversible property has a great potential application in oil and gas production.

Effects of Surface-Modified Alkyl Chain Length of Silica Fillers on the Rheological and Thermal Mechanical Properties of Underfill

Due to the increased packaging density as well as the size reduction of the gap between the chip and the substrate in modern flip-chip technology, there is an increasing demand for the use of nanosized silica particles as fillers into underfill to further improve its comprehensive performance. However, silica nanoparticles (SNPs) cannot uniformly disperse into the polymer matrix and usually cause some negative issues, such as a dramatic increase in viscosity and a significant decrease in the glass transition temperature as a result of their excessive surface energy and surface hydrophilic silanol groups. Surface modification with alkyl chains is an effective way to facilitate a uniform dispersion of nanofillers in polymer matrix since suitable repulsive forces can optimize spacing among nanoparticles by decreasing interactions between nanoparticles and changing the surface property of nanoparticles from hydrophilic to hydrophobic. In this paper, SNPs surface-modified by alkyl groups of different lengths were prepared and used as fillers to study the role of the surface alkyl chain length in the rheological and thermal–mechanical properties of underfill nanocomposites. It was found that surface alkyl chains could improve the dispersion of SNPs in epoxy matrix, and thus contributed to decrease the viscosity and enhance the glass transition temperature of underfill nanocomposites. With an increase in the surface alkyl chain length, the viscosity of underfill nanocomposites increased and the glass transition temperature shifted to a higher temperature. This paper sets the way toward the choice of an alkyl chain of proper length as filler surface functional group to improve the comprehensive performance of underfill.

Autoclave foaming of chemically modified polylactide

Polylactide has emerged as one of the most promising biopolymers due to its good mechanical properties, as reflected by the continual increase in its production volume per year. However, one of the main drawbacks of polylactide is its low melt strength, which is disadvantageous in terms of foaming. To overcome this issue, in this study, several chemical modifiers that induce crosslinking, chain extension or grafting were incorporated by reactive extrusion, which greatly affected the foaming process by increasing the molecular weight and thereby the melt properties of polylactide. By means of gel permeation chromatography, an increase in the molecular weight was observed in the modified polylactides. Elongational viscosity measurements indicate a dramatic viscosity increase for polylactide modified with a multifunctional epoxide and an organic peroxide. With pressure-induced batch foaming, almost all modifications, with the exception of styrene maleic anhydride, led to a decrease in foam density compared to the neat polylactide.

Rheological characteristics of mixed kaolin–sand slurry, impacts of pH, temperature, solid concentration and kaolin–sand mixing ratio

Significant amount of slurry waste is produced from mineral processing plants globally constituting high levels of both kaolin and sand in aqueous suspension. Large quantities of slurry and mine tailings require efficient handling, transportation and storage system. The transportation and treatment of kaolin–sand slurry is dependent on its rheological behaviour which is a function of temperature, total solid concentration and pH. In this study, the effects of total solid concentration, pH and temperature on rheological behaviour of kaolin–sand mixture were investigated. These parameters were varied to analyse the viscosity, yield stress, flow index and shear force requirements of the mixed kaolin–sand suspension as a function of these varying parameters. Experimental rheological investigation conducted on rotational stress-controlled rheometer equipped with Peltier concentric cylinder system showed that the kaolin–sand mixture suspension is shear thickening in nature. The shear stress-rate rheograms for the kaolin–sand suspension can be modelled by the Herschel–Bulkley model with high levels of accuracy for pH range of 4–11, temperature range of 20–50 °C and solid concentration of 5–50 %. Solid concentration of the suspension was found to significantly affect the rheological behaviour of the mixture where higher kaolin–sand slurry concentration resulted in greater viscosity and the trend becoming less predictable for solid concentration greater than 50 % by weight. pH was another factor affecting the rheological behaviour of kaolin–sand slurry. pH of 3 or less resulted in the dramatic increase of viscosity of the suspension possibly due to the isoelectric point of the mixture system found between pH of 3 and 4.

Thermosensitive hexanoyl glycol chitosan-based ocular delivery system for glaucoma therapy

Conventional eye drops quickly move away from the surface of the eye; as a result, ocular bioavailability is very limited. To overcome this issue, we developed a thermosensitive hexanoyl glycol chitosan (HGC) as a carrier for topical drug delivery to the eye. Here, we modulated the degree of N-hexanoylation to control the thermogelling behavior and prepared a new ocular formulation of HGC for glaucoma therapy. The viscosity of the aqueous formulation sharply and significantly increases at body temperature. The results from cytotoxicity evaluation showed that HGC is non-toxic at up to 1.25wt.%. In vivo experiments demonstrated that HGC is maintained on the preocular surface for a comparatively longer period of time due to its enhanced viscosity at body temperature. As a result, when brimonidine was loaded, the formulation exhibited attractive bioavailability properties as well as more prolonged period of lowered intra-ocular pressure (14h) compared with Alphagan P, the marketed medication for brimonidine treatment. Statement of SignificanceIn this manuscript, hexanoyl glycol chitosan (HGC) was synthesized by the N-hexanoylation of glycol chitosan. We have observed that an aqueous solution of HGC exhibited a dramatic increase in viscosity as the temperature increased. The HGC-based formulation showed prolonged retention on the preocular surface and enhanced drug availability and efficacy.