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1.
Int J Cosmet Sci ; 43(4): 484-493, 2021 Aug.
Article in English | MEDLINE | ID: mdl-34240435

ABSTRACT

OBJECTIVE: Green and sustainable trends are growing and with that the demand for naturally derived ingredients is rising. Dispersing agents are essential components of lipsticks due to their ability to wet pigment particles, reduce agglomerates and prevent re-agglomeration by stabilizing pigment particles. In this study, meadowfoam seed oil was evaluated as a pigment-dispersing agent for lipsticks and compared with castor oil and octyldodecanol. METHODS: Dispersions of Red 7 Lake were formulated with 20, 30 and 40% solid content using castor oil, octyldodecanol or meadowfoam seed oil. Particle size, viscosity, spreadability, wetting, oil absorption and colour were measured. Four of the nine dispersions were then formulated into lipsticks, including all the 30% pigment dispersions and the 40% dispersion with meadowfoam seed oil. Lipsticks were tested for hardness, pay-off, friction, rheology, colour and stability for 4 weeks. RESULTS: Average particle size was between 6 and 9 µm across the dispersions. The castor oil dispersions were more viscous, stickier and harder to spread than the other dispersions. The wetting contact angle was very low for all three dispersing agents, indicating that all of the oils wet the pigment well. The lipsticks varied in hardness, as expected, based on differences in the viscosity of the dispersing agents, and oil absorption of the powder. Red 7 Lake absorbed the highest amount of castor oil, which contributed to higher stick hardness. The castor oil lipstick and the meadowfoam seed oil lipstick containing 40% pigment were the hardest and most elastic. The octyldodecanol lipstick was the softest. Friction was the lowest for the meadowfoam seed oil lipstick containing 40% pigment, while pay-off was the highest for the octyldodecanol lipstick. The colour of the lipsticks as a stick and after being spread on paper was very similar. CONCLUSION: While the chemical composition and physicochemical properties of the dispersing agents were different, all three dispersing agents studied formed dispersions and lipsticks with appropriate characteristics. Meadowfoam seed oil's performance was qualitatively and quantitatively similar to castor oil and octyldodecanol. By modifying the amount of pigment and dispersing agent used, lipsticks that have similar characteristics to commercial products can be formulated.


OBJECTIF: Les tendances écologiques et durables sont en hausse, ainsi que la demande en ingrédients d'origine naturelle. Les agents de dispersion sont des composants essentiels des rouges à lèvres en raison de leur capacité à mouiller les particules pigmentaires, à réduire les agglomérats et à prévenir la réagglomération en stabilisant les particules pigmentaires. Dans cette étude, l'huile de graines de limnanthe a été évaluée en tant qu'agent de dispersion pigmentaire pour les rouges à lèvres et comparée à l'huile de ricin et à l'octyldodécanol. MÉTHODES: Les dispersions de Red 7 Lake ont été formulées avec une teneur solide de 20, 30 et 40 % à l'aide d'huile de ricin, d'octyldodécanol ou d'huile de graines de limnanthe. La taille des particules, la viscosité, la facilité d'étalement, le mouillage, l'absorption de l'huile et la couleur ont été mesurés. Quatre des neuf dispersions ont ensuite été formulées dans des rouges à lèvres, y compris toutes les dispersions pigmentaires à 30 % et la dispersion à 40 % avec l'huile de graines de limnanthe. Les rouges à lèvres ont été testés pour la dureté, le résultat, la friction, la rhéologie, la couleur et la stabilité pendant 4 semaines. RÉSULTATS: La taille moyenne des particules était comprise entre 6 et 9 µm dans les dispersions. Les dispersions d'huile de ricin étaient plus visqueuses, plus collantes et plus difficiles à étaler que les autres dispersions. L'angle de contact de mouillage était très faible pour les trois agents de dispersion, indiquant que toutes les huiles humidifient bien le pigment. La dureté des rouges à lèvres variait, comme attendu, en fonction des différences de viscosité des agents dispersants et de l'absorption de l'huile de la poudre. Red 7 Lake absorbe la plus grande quantité d'huile de ricin, ce qui contribue à une dureté du bâton plus élevée. Le rouge à lèvres à base d'huile de ricin et le rouge à lèvres à base d'huile de graines de limnanthe contenant 40 % de pigment étaient les plus durs et les plus élastiques. Le rouge à lèvres à base d'octyldodécanol était le plus mou. La friction était la plus basse pour le rouge à lèvres à base d'huile de graines de limnanthe contenant 40 % de pigment, tandis que le résultat était le plus élevé pour le rouge à lèvres à base d'octyldodécanol. La couleur des rouges à lèvres en bâton et après avoir été étalés sur du papier était très similaire. CONCULSION: Alors que la composition chimique et les propriétés physicochimiques des agents de dispersion étaient différentes, les trois agents de dispersion étudiés ont tous formé des dispersions et des rouges à lèvres ayant des caractéristiques appropriées. Les performances de l'huile de graines de limnanthe étaient qualitativement et quantitativement similaires à celles de l'huile de ricin et de l'octyldodécanol. En modifiant la quantité de pigment et d'agent dispersant utilisée, des rouges à lèvres ayant des caractéristiques similaires aux produits commerciaux peuvent être formulés.


Subject(s)
Color , Cosmetics/chemistry , Plant Oils/chemistry , Seeds/chemistry , Particle Size , Rheology
2.
Int J Mol Sci ; 22(3)2021 Jan 24.
Article in English | MEDLINE | ID: mdl-33498864

ABSTRACT

The paracrine and autocrine processes of the host response play an integral role in the success of scaffold-based tissue regeneration. Recently, the immunomodulatory scaffolds have received huge attention for modulating inflammation around the host tissue through releasing anti-inflammatory cytokine. However, controlling the inflammation and providing a sustained release of anti-inflammatory cytokine from the scaffold in the digestive inflammatory environment are predicated upon a comprehensive understanding of three fundamental questions. (1) How does the release rate of cytokine from the scaffold change in the digestive inflammatory environment? (2) Can we prevent the premature scaffold degradation and burst release of the loaded cytokine in the digestive inflammatory environment? (3) How does the scaffold degradation prevention technique affect the immunomodulatory capacity of the scaffold? This study investigated the impacts of the digestive inflammatory environment on scaffold degradation and how pre-mature degradation can be prevented using genipin crosslinking and how genipin crosslinking affects the interleukin-4 (IL-4) release from the scaffold and differentiation of naïve macrophages (M0). Our results demonstrated that the digestive inflammatory environment (DIE) attenuates protein retention within the scaffold. Over 14 days, the encapsulated protein released 46% more in DIE than in phosphate buffer saline (PBS), which was improved through genipin crosslinking. We have identified the 0.5 (w/v) genipin concentration as an optimal concentration for improved IL-4 released from the scaffold, cell viability, mechanical strength, and scaffold porosity, and immunomodulation studies. The IL-4 released from the injectable scaffold could differentiate naïve macrophages to an anti-inflammatory (M2) lineage; however, upon genipin crosslinking, the immunomodulatory capacity of the scaffold diminished significantly, and pro-inflammatory markers were expressed dominantly.


Subject(s)
Guided Tissue Regeneration/methods , Immunomodulation , Iridoids/pharmacology , Macrophages/drug effects , Tissue Scaffolds/chemistry , Animals , Cell Differentiation , Cells, Cultured , Collagen , Inflammation/drug therapy , Inflammation/prevention & control , Injections , Interleukin-4/immunology , Interleukin-4/metabolism , Iridoids/therapeutic use , Macrophages/immunology , Macrophages/metabolism , Macrophages/pathology , Mice , Musculoskeletal System/immunology , Porosity
3.
J Pharm Sci ; 109(9): 2719-2728, 2020 09.
Article in English | MEDLINE | ID: mdl-32473210

ABSTRACT

A new indole based chalcone molecule MOMIPP induced methuosis mediated cell death in gliobastoma and other cancer cell lines. But the drug was insoluble in water and had a very short plasma half-life. The purpose of this work was to develop a formulation that can provide sustained levels of MOMIPP in vivo. Initial studies established drug solubility in various solvents. N-methyl pyrrolidone (NMP) was determined as an excellent solvent for the drug. Subsequently a poloxamer-407 based thermoreversible gel containing NMP was used to develop the formulation. Rheological studies were performed via oscillatory temperature mode, continuous shear analysis, and oscillatory frequency mode experiments. The mechanical properties of the formulations were tested using a texture profile analyzer. The gelation temperature and time of formulations increased with increasing amounts of NMP. However, the viscosity at 20 °C and storage modulus decreased as the amount of NMP increased. Characterization studies helped to identify the gel formulation that was used to administer the drug orally, sub-cutaneously, and intra-peritoneally. When the gel was given intraperitoneally the target plasma and brain levels of over 5 µM was maintained for about 8 h. Thus, a thermoreversible gel formulation that can deliver MOMIPP in animal studies was successfully developed.


Subject(s)
Antineoplastic Agents , Hydrogels , Animals , Brain/metabolism , Gels , Indoles , Poloxamer/metabolism , Pyridines , Rheology , Temperature , Viscosity
4.
Dent Mater ; 36(7): 865-883, 2020 07.
Article in English | MEDLINE | ID: mdl-32451208

ABSTRACT

OBJECTIVE: The aim of this study was to develop bioactive and osseointegrable polyetheretherketone (PEEK)-based composite filaments melt-blended with novel amorphous magnesium phosphate (AMP) particles for 3D printing of dental and orthopedic implants. MATERIALS AND METHODS: A series of materials and biological analyses of AMP-PEEK were performed. Thermal stability, thermogravimetric and differential scanning calorimetry curves of as-synthesized AMP were measured. Complex viscosity, elastic modulus and viscous modulus were determined using a rotational rheometer. In vitro bioactivity was analyzed using SBF immersion method. SEM, EDS and XRD were used to study the apatite-forming ability of the AMP-PEEK filaments. Mouse pre-osteoblasts (MC3T3-E1) were cultured and analyzed for cell viability, proliferation and gene expression. For in vivo analyses, bare PEEK was used as the control and 15AMP-PEEK was chosen based on its in vitro cell-related results. After 4 or 12 weeks, animals were euthanized, and the femurs were collected for micro-computed tomography (µ-CT) and histology. RESULTS: The collected findings confirmed the homogeneous dispersion of AMP particles within the PEEK matrix with no phase degradation. Rheological studies demonstrated that AMP-PEEK composites are good candidates for 3D printing by exhibiting high zero-shear and low infinite-shear viscosities. In vitro results revealed enhanced bioactivity and superior pre-osteoblast cell function in the case of AMP-PEEK composites as compared to bare PEEK. In vivo analyses further corroborated the enhanced osseointegration capacity for AMP-PEEK implants. SIGNIFICANCE: Collectively, the present investigation demonstrated that AMP-PEEK composite filaments can serve as feedstock for 3D printing of orthopedic and dental implants due to enhanced bioactivity and osseointegration capacity.


Subject(s)
Dental Implants , Animals , Benzophenones , Ketones , Magnesium Compounds , Mice , Phosphates , Polyethylene Glycols , Polymers , Printing, Three-Dimensional , X-Ray Microtomography
5.
Soft Matter ; 15(38): 7616-7622, 2019 Oct 14.
Article in English | MEDLINE | ID: mdl-31482916

ABSTRACT

We studied the diffusion of charged gold nanoparticles within a semidilute solution of weakly charged polyelectrolyte, polyacrylic acid (PAA) of high molecular weight (Mw = 106 g mol-1) by using fluorescence correlation spectroscopy (FCS). Nanoparticle size (d) was varied between 5 nm to 40 nm and PAA volume fraction (φ) in water ranged from about 8φ* to 33φ*, where φ* is the overlap volume fraction. The reduced diffusion coefficient - defined as -D/Do, where D is the diffusion coefficient in PAA solution and Do is that in neat water - has a weak dependence on the particle size. D follows a power law of the form ∼φ-0.5, which can be explained by a mean-field hydrodynamic theory in porous medium. Additional, rheology measurements showed a zero shear rate viscosity and shear thinning, which are typical of high molecular weight polyelectrolytes.

6.
J Cosmet Sci ; 69(2): 83-100, 2018.
Article in English | MEDLINE | ID: mdl-29799807

ABSTRACT

The sales potential of cosmetic products is greatly determined by skin feel and skin sensory performance. To please the target audience, it is important to gather information about consumers' perception of products' sensory characteristics. In this study, six different emulsions were formulated. Samples represented three different types of emulsions, including steric-stabilized oil-in-water (O/W), liquid crystal-stabilized O/W, and water-in-oil emulsions, providing different skin feel and aesthetics. Emulsions within the same group differed in the emollients, providing similar sensory attributes. The aim was to have 50 consumers evaluate the emulsions' sensory characteristics. Using a check-all-that-apply (CATA) survey, consumers provided information about their perception of appearance, rub-out, pick-up, and afterfeel. Consumers effectively discriminated between the emulsions. Statistical analysis showed significant differences for 15 sensory attributes in the before, during, and after phases. Our findings suggest that emulsifiers, and not emollients, have the dominant role in determining the aesthetics of a skin care emulsion, similar to previous findings. The fact that untrained consumers provided similar results as trained panelists suggests the validity of the CATA survey and its reliability as a screening tool in the product development process. CATA questions may serve as a viable complimentary to descriptive sensory analysis performed by trained panelists.


Subject(s)
Consumer Behavior , Cosmetics , Surveys and Questionnaires/standards , Adolescent , Adult , Cosmetics/classification , Cosmetics/standards , Emollients/classification , Emollients/standards , Emulsifying Agents/classification , Emulsifying Agents/standards , Emulsions/classification , Emulsions/standards , Female , Humans , Male , Middle Aged , Rheology , Sensation , Young Adult
7.
Chemphyschem ; 16(13): 2810-2817, 2015 Sep 14.
Article in English | MEDLINE | ID: mdl-26275573

ABSTRACT

Despite the importance of fatty-acid methyl esters (FAMEs) as key components of various green solvents, detergents, plasticizers, and biodiesels, our understanding of these systems at the molecular level is limited. An enhanced molecular-level perspective of FAMEs will enable a detailed analysis of the polymorph and crystallization phenomena that adversely impact flow properties at low temperatures. Presented here, is the parameterization and validation of a charge-modified generalized amber force field (GAFF) for eight common FAMEs and two representative biodiesel mixtures. Our simulations accurately reproduce available experimental data (e.g. densities and self-diffusivity coefficients) and their trends, with respect to temperature and degree of unsaturation. Structural analyses from our simulations provide a more detailed picture of liquid-phase molecular ordering in FAMEs and confirm recent experimental hypotheses. This study provides a firm foundation to initiate further studies into the mechanisms that drive crystallization phenomena at the molecular level.

8.
Biophys J ; 108(1): 173-83, 2015 Jan 06.
Article in English | MEDLINE | ID: mdl-25564864

ABSTRACT

Fibrin is a biopolymer that gives thrombi the mechanical strength to withstand the forces imparted on them by blood flow. Importantly, fibrin is highly extensible, but strain hardens at low deformation rates. The density of fibrin in clots, especially arterial clots, is higher than that in gels made at plasma concentrations of fibrinogen (3-10 mg/mL), where most rheology studies have been conducted. Our objective in this study was to measure and characterize the elastic regimes of low (3-10 mg/mL) and high (30-100 mg/mL) density fibrin gels using shear and extensional rheology. Confocal microscopy of the gels shows that fiber density increases with fibrinogen concentration. At low strains, fibrin gels act as thermal networks independent of fibrinogen concentration. Within the low-strain regime, one can predict the mesh size of fibrin gels by the elastic modulus using semiflexible polymer theory. Significantly, this provides a link between gel mechanics and interstitial fluid flow. At moderate strains, we find that low-density fibrin gels act as nonaffine mechanical networks and transition to affine mechanical networks with increasing strains within the moderate regime, whereas high-density fibrin gels only act as affine mechanical networks. At high strains, the backbone of individual fibrin fibers stretches for all fibrin gels. Platelets can retract low-density gels by >80% of their initial volumes, but retraction is attenuated in high-density fibrin gels and with decreasing platelet density. Taken together, these results show that the nature of fibrin deformation is a strong function of fibrin fiber density, which has ramifications for the growth, embolization, and lysis of thrombi.


Subject(s)
Blood Platelets/chemistry , Fibrin/chemistry , Animals , Clot Retraction , Elastic Modulus , Fibrinogen/chemistry , Gels/chemistry , Linear Models , Materials Testing , Microscopy, Confocal , Models, Chemical , Polymers/chemistry , Rheology , Stress, Mechanical , Viscosity
9.
Phys Chem Chem Phys ; 17(6): 4367-78, 2015 Feb 14.
Article in English | MEDLINE | ID: mdl-25578464

ABSTRACT

We demonstrate that the true hydroxide conductivity in an e-beam grafted poly(ethylene-co-tetrafluoroethylene) [ETFE] anion exchange membrane (AEM) is as high as 132 mS cm(-1) at 80 °C and 95% RH, comparable to a proton exchange membrane, but with very much less water present in the film. To understand this behaviour we studied ion transport of hydroxide, carbonate, bicarbonate and chloride, as well as water uptake and distribution. Water uptake of the AEM in water vapor is an order of magnitude lower than when submerged in liquid water. In addition (19)F pulse field gradient spin echo NMR indicates that there is little tortuosity in the ionic pathways through the film. A complete analysis of the IR spectrum of the AEM and the analyses of water absorption using FT-IR led to conclusion that the fluorinated backbone chains do not interact with water and that two types of water domains exist within the membrane. The reduction in conductivity was measured during exposure of the OH(-) form of the AEM to air at 95% RH and was seen to be much slower than the reaction of CO2 with OH(-) as the amount of water in the film determines its ionic conductivity and at relative wet RHs its re-organization is slow.

10.
Langmuir ; 29(42): 12915-23, 2013 Oct 22.
Article in English | MEDLINE | ID: mdl-24063640

ABSTRACT

Chemical mechanical polishing (CMP) is an essential technology used in the semiconductor industry to polish and planarize a variety of materials for the fabrication of microelectronic devices (e.g., computer chips). During the high shear (~1,000,000 s(-1)) CMP process, it is hypothesized that individual slurry particles are driven together to form large agglomerates (≥0.5 µm), triggering a shear thickening effect. These shear-induced agglomerates are believed to cause defects during polishing. In this study, we examined the shear thickening of a 25 wt % fumed silica slurry with 0.17 M added KCl using in situ small-angle light scattering during rheological characterization (rheo-SALS). The salt-adjusted slurry displays a ~3-fold increase in viscosity at a critical shear rate of 20,000 s(-1) during a stepped shear rate ramp from 100 to 25,000 s(-1). As the shear rate is reduced back to 100 s(-1), the slurry displays irreversible thickening behavior with a final viscosity that is 100-times greater than the initial viscosity. Corresponding rheo-SALS images indicate the formation of micrometer scale structures (2-3 µm) that directly correlate with the discontinuous and irreversible shear thickening behavior of the fumed silica slurry; these micrometer scale structures are 10-times the nominal particle diameter (~0.2 µm). The scattering patterns from the 25 wt % slurry were corroborated through rheo-SALS examination of 27 and 29 wt % slurries (C(KCl) = 0.1 M). All slurries, regardless of ionic strength and solids loading, display scattering patterns that are directly associated with the observed thickening behavior. Scattering was only observable during and after thickening (i.e., no scattering was detected in the absence of thickening). This work serves as the first in situ observation of micrometer scale structures within the fumed silica CMP slurry while under shear.

11.
Langmuir ; 29(35): 10997-1004, 2013 Sep 03.
Article in English | MEDLINE | ID: mdl-23924434

ABSTRACT

The in situ formation and flow properties of methane hydrates formed from water-in-oil microemulsions composed of water, dodecane, and aerosol OT surfactant (AOT) were studied using a unique high pressure rheometer. AOT microemulsions have high stability (order of months), well-characterized composition, and yield reproducible results compared to hydrate studies in water-in-crude oil emulsions. Viscosity increases on the order of minutes upon hydrate formation, and then decreases on the order of hours. If significant unconverted water remained after the initial formation event, then viscosity increases for a time as methane slowly dissolves and converts additional water to hydrate. In addition to transient formation measurements, yield stresses and flow curves are measured for a set of experimental conditions. Hydrate slurry viscosity and yield stress increase with increasing water volume fraction, increasing initial pressure, decreasing temperature, and decreasing formation shear rate.

12.
J Colloid Interface Sci ; 396: 83-9, 2013 Apr 15.
Article in English | MEDLINE | ID: mdl-23484772

ABSTRACT

Suspensions of corn starch and water are the most common example of a shear thickening system. Investigations into the non-Newtonian flow behavior of corn starch slurries have ranged from simplistic elementary school demonstrations to in-depth rheological examinations that use corn starch to further elucidate the mechanisms that drive shear thickening. Here, we determine how much corn starch is required for the average person to ''walk on water'' (or in this case, run across a pool filled with corn starch and water). Steady shear rate rheological measurements were employed to monitor the thickening of corn starch slurries at concentrations ranging from 0 to 55 wt.% (0-44 vol.%). The steady state shear rate ramp experiments revealed a transition from continuous to discontinuous thickening behavior that exists at 52.5 wt.%. The rheological data was then compared to macro-scopic (~5 gallon) pool experiments, in which thickening behavior was tested by dropping a 2.1 kg rock onto the suspension surface. Impact-induced thickening in the ''rock drop'' study was not observed until the corn starch concentration reached at least 50 wt.%. At 52.5 wt.%, the corn starch slurry displayed true solid-like behavior and the falling rock ''bounced'' as it impacted the surface. The corn starch pool studies were fortified by steady state stress ramps which were extrapolated out to a critical stress value of 67,000 Pa (i.e., the force generated by an 80 kg adult while running). Only the suspensions containing at least 52.5 wt.% (42 vol.%) thickened to high enough viscosities (50-250 Pa s) that could reasonably be believed to support the impact of a man's foot while running. Therefore, we conclude that at least 52.5 wt.% corn starch is required to induce strong enough thickening behavior to safely allow the average person to ''walk on water''.


Subject(s)
Starch/chemistry , Suspensions/chemistry , Viscosity , Particle Size , Rheology , Zea mays
13.
Rev Sci Instrum ; 83(1): 015106, 2012 Jan.
Article in English | MEDLINE | ID: mdl-22299985

ABSTRACT

We present a novel setup for a high pressure rheometer operating with concentric cylinders geometry for in situ studies of hydrate formation and rheological characterization. The apparatus uses an external high pressure mixing cell to saturate water-in-oil emulsions with methane gas. The capability of mixing combined with a true rheometer design make this apparatus unique in terms of setup and sample formation. We have used the apparatus to form gas hydrates in situ from water-in-oil emulsions and characterize suspension rheological properties such as yield stress and shear-thinning behavior.

14.
ACS Appl Mater Interfaces ; 3(5): 1502-10, 2011 May.
Article in English | MEDLINE | ID: mdl-21456529

ABSTRACT

Gadolinium metal-organic framework (Gd MOF) nanoparticles are an interesting and novel class of nanomaterials that are being studied as a potential replacement for small molecule positive contrast agents in magnetic resonance imaging (MRI). Despite the tremendous interest in these nanoscale imaging constructs, there are limitations, particularly with respect to controlling the particle size, which need to be overcome before these nanoparticles can be integrated into in vivo applications. In an effort to control the size, shape, and size distribution of Gd MOF nanoparticles, hydrotropes were incorporated into the reverse microemulsion synthesis used to produce these nanoparticles. A study of how hydrotropes influenced the mechanism of formation of reverse micelles offered a great deal of information with respect to the physical properties of the Gd MOF nanoparticles formed. Specifically, this study incorporated the hydrotropes, sodium salicylate (NaSal), 5-methyl salicylic acid, and salicylic acid into the reverse microemulsion. Results demonstrated that addition of each of the hydrotropes into the synthesis of Gd MOFs provided a simple route to control the nanoparticle size as a function of hydrotrope concentration. Specifically, Gd MOF nanoparticles synthesized with NaSal showed the best reduction in size distributions in both length and width with percent relative standard deviations being nearly 50% less than nanoparticles produced via the standard route from the literature. Finally, the effect of the size of the Gd MOF nanoparticles with respect to their MRI relaxation properties was evaluated. Initial results indicated a positive correlation between the surface areas of the Gd MOF nanoparticles with the longitudinal relaxivity in MRI. In particular, Gd MOF nanoparticles with an average size of 82 nm with the addition of NaSal, yielded a longitudinal relaxivity value of 83.9 mM⁻¹ [Gd³âº] sec⁻¹, one of the highest reported values compared to other Gd-based nanoparticles in the literature to date.


Subject(s)
Contrast Media/chemical synthesis , Gadolinium/chemistry , Magnetic Resonance Imaging/methods , Metal Nanoparticles/chemistry , Nanotechnology/methods , Organic Chemicals/chemistry , Particle Size
15.
Langmuir ; 25(23): 13376-83, 2009 Dec 01.
Article in English | MEDLINE | ID: mdl-19852482

ABSTRACT

A quantitative study of the shear-induced phase separation of a polycation/anionic-nonionic micelle coacervate is presented. Simultaneous rheology and small-angle light scattering (SALS) measurements allow the elucidation of micrometer-scale phase separation under flow in three coacervate solutions. Below 18 degrees C, all three of the coacervate solutions are optically clear Newtonian fluids across the entire shear rate range investigated. Once a critical temperature range and/or shear rate is achieved, phase separation is observed in the small-angle light scattering images and the fluid exhibits shear thinning. Two definitive SALS patterns demonstrate the appearance of circular droplets at low shear rates near the critical temperature and ellipsoidal droplets at higher temperatures and shear rates. The shear-induced droplets range in size from approximately 1 to 4 mum. The ellipsoidal droplets have aspect ratios as high as 4. A conceptual picture in which shear flow extends the polyelectrolyte chains of the clear coacervate liquid phase is proposed. The extended chains create interpolyelectrolyte-micelle interactions and promote expulsion of small ions from the complex, resulting in the formation of micrometer-scale phase-separated droplets.

16.
Biotechnol Bioeng ; 104(2): 290-300, 2009 Oct 01.
Article in English | MEDLINE | ID: mdl-19472300

ABSTRACT

Effective and efficient breakdown of lignocellulosic biomass remains a primary barrier for its use as a feedstock for renewable transportation fuels. A more detailed understanding of the material properties of biomass slurries during conversion is needed to design cost-effective conversion processes. A series of enzymatic saccharification experiments were performed with dilute acid pretreated corn stover at initial insoluble solids loadings of 20% by mass, during which the concentration of particulate solids and the rheological property yield stress (tau(y)) of the slurries were measured. The saccharified stover liquefies to the point of being pourable (tau(y)

Subject(s)
Biomass , Bioreactors , Lignin/metabolism , Zea mays/metabolism , Energy-Generating Resources , Hydrolysis , Kinetics , Models, Chemical , Rheology
17.
Langmuir ; 24(15): 7718-26, 2008 Aug 05.
Article in English | MEDLINE | ID: mdl-18620438

ABSTRACT

The addition of positively charged, 30 nm diameter silica nanoparticles to cationic wormlike micellar solutions of cetyltrimethylammonium bromide and sodium nitrate is studied using a combination of rheology, small angle neutron scattering, dynamic light scattering, and cryo-transmission electron microscopy. The mixtures are single phase up to particle volume fractions of 1%. The addition of like-charged particles significantly increases the wormlike micelle (WLM) solution's zero shear rate viscosity, longest relaxation time, and storage modulus. The changes are hypothesized to originate from a close association of the particles with the micellar mesh. Small angle neutron scattering measurements with contrast matching demonstrate associations between particles mitigated by the WLMs. The effective interparticle interactions measured by SANS can explain the observed phase behavior. Dynamic light scattering measurements confirm the dynamic coupling of the particles to the micellar mesh.

18.
Phys Rev E Stat Nonlin Soft Matter Phys ; 73(2 Pt 1): 020504, 2006 Feb.
Article in English | MEDLINE | ID: mdl-16605317

ABSTRACT

The shear-induced microstructure of a shear-induced phase separating (SIPS) wormlike micellar solution is measured by combining small-angle neutron scattering with a shear cell capable of gap-resolved measurement in the 1-2 (velocity-velocity gradient) plane. Quantitative results show evidence for shear-induced microphase separation accompanied by shear banding. The results suggest both concentration fluctuations and gradients in segmental alignment occurring during SIPS.

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