Using Vesicular Dispersion for Stabilizing Suspensions of Dense Colloidal Particles against Sedimentation

Colloidal dispersions, like inks and paints, are often required to remain stable for long times, i.e., the dispersed colloidal particles should remain suspended. In most cases, a stable dispersion requires preventing the agglomeration of the suspended colloidal particles. If the particles agglomerate, their sizes will increase and rapid sedimentation will occur. Nevertheless, many colloidal particles of commercial interest have high densities. Thus, they quickly settle even without agglomeration. One novel approach to preventing the settling of high density particles is the use of close-packed vesicular dispersions (CPVDs) made of the surfactant DDAB (didodecyldimethylamine bromide). Previous work demonstrated the ability of these CPVDs to prohibit the settling of high density titania particles. However, only a limited range of particle sizes that were found to remain stable with CPVDs were investigated. Also, the effects of the method of preparation of the CPVDs was not fully explored, as an effecitve CPVD should be generated from the smallest possible amount of added DDAB. Thus, the impact of various preparation methods on the resulting properties of the DDAB vesicular dispersions are examined. DDAB vesicular dispersions are generated via stirring only to form primarily liposomes, sonication to break down large multi-layer vesicles, and extrusion through membranes to obtain specifically sized vesicles. Various light scattering and absorbance techniques are also used to probe the structure of the vesicular dispersions, important information needed for improving the ability of CPVDs to stabilize against sedimentation a broader range of colloidal particle sizes

Studies on Model Water-in-Oil (w/o) Emulsions: Phase Behavior, Emulsion Stability, and Hydrate Formation

Colloidal dispersions are widely encountered in several industrial settings including in ink, paint, and food formulations, as well as during subsea oil production. The present study focusses on the formation of hydrates in subsea oil pipelines from colloidal precursors that cause plugging and have tremendous environmental and economic consequences. Model systems for hydrate precursors are studied – water in cyclopentane emulsions stabilized by either SPAN 80 or AOT surfactants. The phase behavior, emulsion stability, and hydrate formation mechanisms are delineated using experimental techniques such as dynamic light scattering, spectroturbidimetry, and differential scanning calorimetry. The phase behavior is found to strongly depend upon the emulsion stabilizer with AOT systems displaying strong “solubilization” in contrast to SPAN 80 systems. Furthermore, for AOT systems the emulsion stability decreases with an increase in AOT concentration from 1 wt% to 5 wt %. For SPAN 80 systems, the emulsion stability is largely unaffected by its concentration. Additionally studies are underway to study the effect of temperature on emulsion stability and to identify the mechanisms for hydrate growth. Overall, the insights obtained from the present study will help in designing strategies for hydrate plug prevention, thereby, facilitating safe and economic oil production

Effect of Sodium Dodecyl Sulfate and Sodium Chloride on the Stability of Aqueous Dispersions of TiO2 Particles Against Aggregation and Sedimentation

Dispersions of TiO2 particles are widely used as the main pigment in white inks for inkjet printers due to its brightness and high opacity. The TiO2 particles, however, have a high density, and so the possible fast settling of these particles can cause maintenance problems for the printers and lower the printing quality. We studied the effect of sodium dodecyl sulfate (SDS), a commonly used dispersant, on the stability of 1 wt% TiO2 aqueous dispersions, both with and without NaCl, against aggregation and sedimentation. The sedimentation half time (t50), defined as the time need for the particles to sediment from an initial sample height of 1 cm to 0.5 cm, was determined for various SDS concentrations. t50 was found to first increase with an increase in SDS concentration, reach a plateau upon further increases in concentration, and then rapidly decrease for SDS concentrations above a critical value. A similar trend was observed in 100 mM NaCl, though the transitions in t50 occurred at different SDS concentrations. Particle sizes were measured using dynamic light scattering, both before and after redispersion of the sediment to the same or different SDS concentrations. These measurements confirm that coagulation, no aggregation and then flocculation occurs as the SDS concentration is increased, indicating the effect of micelles in the dispersion stability at high enough SDS concentrations

Stability of Aqueous Dispersions of Titanium Dioxide Against Sedimentation and Aggregation

Particles of titanium dioxide (TiO2) are widely used as white pigments in paints and inks, due to their brightness and high refractive index. Yet, with TiO2 having a high density (4.2 g/cm3), particles with typical sizes of 300 nm sediment rapidly even before significant agglomeration can occur. Thus, increasing the stability of TiO2 dispersions against sedimentation as well as aggregation is important. We studied the effect of sodium dodecyl sulfate (SDS), a commonly used dispersant, on the stability of aqueous dispersions of TiO2 with weight fractions from 0.01 to 40. The sedimentation time of each dispersion, defined to be the time for which the particles were found to settle from an initial sample of height of 1 cm to 0.5 cm, was obtained by visual observation. The sedimentation time for 40 wt% TiO2 exceeded 100 hours, but was less than 24 hours for 0.01 wt%. The viscosities of aqueous solutions with varying SDS concentrations were also measured, increasing by about 50% as the SDS concentrations increased from 0 mM to 200 mM. This increase in viscosity cannot therefore fully explain the observed increase in sedimentation time with increasing SDS concentration. The viscosity data were also used to determine the effective sizes of the SDS micelles. The effective diameter of micelles was raised from 3 nm to 6 nm and then remains constant as the SDS concentrations increased from 0 mM to 200 mM. Overall, the results show that the viscosity effects have little influence on the sedimentation behavior and the sedimentation time is increased with increasing TiO2 particle concentration

State diagrams for improving processing and storage of foods, biological materials, and pharmaceuticals (IUPAC Technical Report)

Supplemented temperature/composition phase diagrams include the non-equilibrium glass-transition temperature (Tg) curve and equilibrium ice-melting and solubility curves. The inclusion of the non-equilibrium curve allows one to establish relationships with the time coordinate and, thus, with the dynamic behavior of systems, provided that the thermal history of such systems is known. The objective of this report is to contribute to the potential applications of supplemented state diagrams for aqueous glass-formers, in order to describe the influence of water content, nature of vitrifying agents, and temperature on the physico-chemical properties of foods and biological and pharmaceutical products. These data are helpful to develop formulations, processing strategies, or storage procedures in order to optimize the stability of food ingredients and pharmaceutical formulations. Reported experimental data on phase and state transitions for several food and pharmaceutical systems were analyzed. Some methodological aspects and the effect of phase and state transitions on the main potential chemical reactions that can alter those systems during processing and/or storage are discussed.Fil: Buera, Maria del Pilar. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Industrias. Instituto de Tecnología de Alimentos y Procesos Químicos. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Tecnología de Alimentos y Procesos Químicos; ArgentinaFil: Roos, Yrjö. University College Cork; IrlandaFil: Levine, Harry. Food Polymer Science Consultancy; Estados UnidosFil: Slade, Louise. Food Polymer Science Consultancy; Estados UnidosFil: Corti, Horacio Roberto. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Reid, David S.. University of California at Davis; Estados UnidosFil: Auffret, Tony. taPrime Consulting; Reino UnidoFil: Angell, C. Austen. Arizona State University; Estados Unido

Access to recreational physical activities by car and bus : an assessment of socio-spatial inequalities in mainland Scotland

Obesity and other chronic conditions linked with low levels of physical activity (PA) are associated with deprivation. One reason for this could be that it is more difficult for low-income groups to access recreational PA facilities such as swimming pools and sports centres than high-income groups. In this paper, we explore the distribution of access to PA facilities by car and bus across mainland Scotland by income deprivation at datazone level. GIS car and bus networks were created to determine the number of PA facilities accessible within travel times of 10, 20 and 30 minutes. Multilevel negative binomial regression models were then used to investigate the distribution of the number of accessible facilities, adjusting for datazone population size and local authority. Access to PA facilities by car was significantly (p<0.01) higher for the most affluent quintile of area-based income deprivation than for most other quintiles in small towns and all other quintiles in rural areas. Accessibility by bus was significantly lower for the most affluent quintile than for other quintiles in urban areas and small towns, but not in rural areas. Overall, we found that the most disadvantaged groups were those without access to a car and living in the most affluent areas or in rural areas

The N276 glycosylation site is required for HIV-1 neutralization by the CD4 binding site specific HJ16 monoclonal antibody

Immunogen design for HIV-1 vaccines could be based on epitope identification of naturally occurring neutralizing antibodies in infected patients. A tier 2 neutralizing monoclonal antibody (mAb), HJ16 recognizes a new epitope in the CD4 binding site (CD4bs) region that only partially overlaps with the b12 epitope. We aimed to identify the critical binding site by resistance induction in a sensitive primary CRF02_AG strain. In four independent dose-escalation studies, the N276D mutation was consistently the only alteration found and it was confirmed to be responsible for resistance to HJ16 by sitedirected mutagenesis in envelopes (envs) of the homologous CRF02_AG, as well as of a subtype A and a subtype C primary isolate. This mutation removes an N-linked glycosylation site. The effect of N276D was very selective, as it failed to confer resistance to a range of other entry inhibitors. Remarkably, sensitivity to the CD4bs VRC01 and VRC03 mAbs was increased in the N276D mutated viruses. These data indicate that binding of the CD4bs specific HJ16 mAb critically depends on the interaction with the N276-glycan, thus indicating that HJ16 is the first glycan dependent CD4bs-specific mAb

“It’s my dream to work with Olympic athletes”: Neophyte sport psychologists’ expectations and initial experiences regarding service delivery

We examined trainee practitioners' initial experiences of applied sport psychology practice. Semi-structured interviews (4) were conducted over 6 months with 7 full-time MSc students before, during, and after the applied sport psychology module, when they were working with clients. Participants also kept reflective diaries over an 8-week period whilst working with clients. Findings included: (a) motivations and expectations of an ASP practice career, (b) perceptions of service delivery, (c) emotional demands, and (d) pivotal experiences. Findings extend previous literature on the initial stages of practitioner development, providing micro-level detail on aspects of the intense development process during this pivotal perio

MRI Discriminates Thrombus Composition and ST Resolution after Percutaneous Coronary Intervention in Patients with ST-Elevation Myocardial Infarction

Histological composition of material obtained by thrombus aspiration during percutaneous coronary intervention (PCI) in patients with ST-segment elevation acute myocardial infarction (STEMI) is highly variable. We aimed to characterize this material using magnetic resonance imaging (MRI) and to correlate MRI findings with the success of PCI in terms of ST-segment resolution. Thrombus aspiration during primary or rescue PCI was attempted in 100 consecutive STEMI patients, of whom enough material for MRI was obtained in 59. MR images were obtained at 9.4T and T1 and T2 values were measured. Patients with (n = 31) and without (n = 28) adequate ST resolution 120 min after PCI (≥70% of pre-PCI value) had similar baseline characteristics except for a higher prevalence of diabetes mellitus in the latter (10 vs. 43%, p = 0.003). T1 values were similar in both groups (1248±112 vs. 1307±85 ms, respectively, p = 0.7). T2 values averaged 31.2±10.3 and 36.6±12.2 ms; in thrombus from patients with and without adequate ST resolution (p = 0.09). After adjusting for diabetes and other baseline characteristics, lower T2 values were significantly associated with inadequate ST resolution (odds ratio for 1 ms increase 1.08, CI 95% 1.01–1.16, p = 0.027). Histology classified thrombus in 3 groups: coagulated blood (n = 38), fibrin rich (n = 9) and lipid-rich (n = 3). Thrombi composed mostly of coagulated blood were characterized as being of short (n = 10), intermediate (n = 15) or long evolution (n = 13), T2 values being 34.0±13.2, 31.9±8.3 and 31.5±7.9 ms respectively (p = NS). In this subgroup, T2 was significantly higher in specimens from patients with inadequate perfusion (35.9±10.3 versus 28.6±6.7 ms, p = 0.02). This can be of clinical interest as it provides information on the probability of adequate ST resolution, a surrogate for effective myocardial reperfusion