Structural alterations of branched versus linear mixed-surfactant micellar systems with the addition of a complex perfume mixture and dipropylene glycol as cosolvent.

Personal care products commonly contain perfume mixtures, consisting of numerous perfume raw materials (PRMs), and cosolvents. The lipophilicity and structure of an individual PRM is known to affect its localization within the surfactant self-assembly as well as the micellar geometry. However, because multiple PRMs are used in formulations, significant intermolecular interactions between the PRMs and between the PRMs and the surfactant tail may also influence the location of the PRMs and their effects on the self-assembly. Herein, two anionic/zwitterionic mixed-surfactant systems (sodium trideceth-2 sulfate (ST2S)/cocamidopropyl betaine (CAPB) and sodium laureth-3 sulfate/CAPB) were formulated with a cosolvent (dipropylene glycol (DPG)) and 12 PRMs of varying structures and lipophilicities. This 12 PRM accord is simpler than a fully formulated perfume but more complex than a single perfume molecule. The geometric variations in the self-assemblies were evaluated using small-angle neutron scattering, perfume head space concentrations were determined using gas chromatography-mass spectrometry, and perfume localization was identified using NMR spectroscopy. The addition of the perfume accord caused enlargement of the micelles in both surfactant systems, with a greater change observed for ST2S/CAPB formulations. Furthermore, the addition of DPG to ST2S/CAPB resulted in micelle shrinkage. The micelle geometries and PRM localization in the micelles were affected by the degree of branching in the surfactant tail.

Effects of a Multicomponent Perfume Accord and Dilution on the Formation of ST2S/CAPB Mixed-Surfactant Microemulsions.

Perfume mixtures contain perfume raw materials (PRMs) with varying structures and hydrophobicities, which influence PRM localization within a surfactant-based formulation and thereby affect the phase behavior. In rinse-off products, the addition of water can further affect the phase behavior. In this study, a mixture of 12 PRMs was used as the oil phase in an aqueous system consisting of sodium trideceth-2 sulfate as a primary surfactant, cocamidopropyl betaine as a cosurfactant, and dipropylene glycol as a cosolvent. A series of phase diagrams were constructed with increasing water content, simulating the use conditions for rinse-off products, to determine how the phase boundaries shift with dilution. Using these phase diagrams, the compositions of interest in the micelle without perfume, micelle with perfume, microemulsion, and micelle-microemulsion transition regions were identified at each dilution level. The structural changes were probed through combined small-angle neutron scattering (SANS) and cryo-transmission electron microscopy analyses. The SANS results showed that ellipsoidal micelles were maintained as the perfume content and the dilution level increased. With ≥50 wt % water, increasing the perfume content increased the micelle volume. Interestingly, a higher rate of volume increase was observed at ≥70 wt % water. Notably, the volumes of the micelles with and without perfume increased steadily with dilution, whereas the volumes of the assemblies in the transition region and the microemulsion region increased more rapidly once diluted to 70 and 80 wt % water, respectively.

Phase Behavior of Poloxamer 188 Aqueous Solutions at Subzero Temperatures: A Neutron and X-ray Scattering Study.

Phase transitions of poloxamer 188 (P188) aqueous solutions at freezing temperatures are investigated using small-angle neutron scattering (SANS) and small- and wide-angle X-ray scatterings (SAXS and WAXS). It is shown that P188 solution (10%) undergoes the following sequence of phase transitions during cooling from 25 to -150 °C: micelle solution, solution of monomers, two-phase mixture of liquid crystalline mesophase + ice, and finally crystalline P188 + ice. Formation of the liquid crystalline phase during freezing is likely to be triggered by water freezing to ice and corresponding freeze concentration of the remaining solution. During heating of the frozen solutions, the sequence of the phase transitions is reversed: crystalline P188 + ice, liquid crystalline mesophase + ice, monomer solution + ice, monomer solution, and finally micelle solution. Similar phase transitions are detected for dilute solutions of P188 (1%) except that micelle formation is not observed at 25 °C, consistent with the literature reported critical micelle concentration (CMC) at this temperature. The present study provides new insight into P188 aqueous solutions at freezing temperatures and has practical implications on the design and development of pharmaceutical formulations.

Investigating the effect of a simplified perfume accord and dilution on the formation of mixed-surfactant microemulsions.

The phase analysis of a mixed surfactant system is much more complex than that for a single surfactant system. The addition of fragrance further enhances the complexity of such colloidal systems. The wide variation in structure and log P values of perfume raw materials influence its partitioning into the micellar phase. Herein, we have created a simplified perfume accord consisting of three perfume raw materials (3-PRM) and investigated its loading within a mixed-surfactant system consisting of sodium trideceth-2 sulfate/ST2S and cocamidopropyl betaine/CAPB, along with citric acid and dipropylene glycol. We performed a systematic phase diagram analysis and identified the isotropic phases and compositions of interest. Select compositions from the phase diagram were further investigated to learn how the geometry of the surfactant self-assembly and the localization of the PRMs within the surfactant self-assembly changed when water or perfume is added. A combined small-angle neutron scattering/SANS and NMR methodology was used to identify variation in colloidal domains and positioning of perfume molecules at varying dilutions/rinse off scenarios. The results obtained were utilized to better distinguish distorted micelles from true microemulsions. The systematic investigation here provides a fundamental understanding about the self-assembly, encapsulation and perfume release from a commercially relevant mixed surfactant system.

Screening lengths and osmotic compressibility of flexible polyelectrolytes in excess salt solutions.

We report results of small angle neutron scattering measurements made on sodium polystyrene sulfonate in aqueous salt solutions. The correlation length (ξ) and osmotic compressibility are measured as a function of polymer (c) and added salt (cS) concentrations, and the results are compared with scaling predictions and the random-phase approximation (RPA). In Dobrynin et al.'s scaling model the osmotic pressure consists of a counter-ion contribution and a polymer contribution. The polymer contribution is found to be two orders of magnitude smaller than expected from the scaling model, in agreement with earlier observations made on neutral polymers in good solvent condition. RPA allows the determination of single-chain dimensions in semidilute solutions at high polymer and added salt concentrations, but fails for cS≤ 2 M. The χ parameter can be modelled as the sum of an intrinsic contribution (χ0) and an electrostatic term: χ∼χ0 + K'/√cS, where χ0 > 0.5 is consistent with the hydrophobic nature of the backbone of NaPSS. The dependence of χelec∼ 1/√cS disagrees with the random-phase approximation (χelec∼ 1/cs), but agrees with the light scattering results in dilute solution and Dobrynin et al.'s scaling treatment of electrostatic excluded volume.

Molecular partitioning in ternary solutions of cellulose.

Neutron scattering measurements on the structure and dynamics of ternary solutions of microcrystalline cellulose (MC) in mixtures of an ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate and a polar organic solvent dimethylformamide (DMF) have shown that MC can be fully dissolved in solvent mixtures. Data also show the molecular partitioning of IL into coexisting states. The structure partitioning is manifested as IL adsorbed to cellulose molecules with additional IL self-assembled to form clusters in solution, while the dynamics partitioning shows dynamical heterogeneities of the IL with slow dynamics resembling neat IL and fast dynamics being coupled with the solvent. The composition dependence of the molecular partitioning results in a solubility gap in dilute cellulose solutions and a phase boundary criterion of the molar ratio of IL / MC ∼ 3 in more concentrated regimes. The two characteristics together define the main features of the dissolution phase diagram of ternary cellulose mixtures of MC / IL / DMF at the room temperature.

Aggregation and Solubility of a Model Conjugated Donor-Acceptor Polymer.

In conjugated polymers, solution-phase structure and aggregation exert a strong influence on device morphology and performance, making understanding solubility crucial for rational design. Using atomistic molecular dynamics (MD) and free-energy sampling algorithms, we examine the aggregation and solubility of the polymer PTB7, studying how side-chain structure can be modified to control aggregation. We demonstrate that free-energy sampling can be used to effectively screen polymer solubility in a variety of solvents but that solubility parameters derived from MD are not predictive. We then study the aggregation of variants of PTB7 including those with linear (octyl), branched (2-ethylhexyl), and cleaved (methyl) side chains, in a selection of explicit solvents and additives. Energetic analysis demonstrates that while side chains do disrupt polymer backbone stacking, solvent exclusion is a critical factor controlling polymer solubility.

Viscoplastic fracture transition of a biopolymer gel.

Physical gels are swollen polymer networks consisting of transient crosslink junctions associated with hydrogen or ionic bonds. Unlike covalently crosslinked gels, these physical crosslinks are reversible thus enabling these materials to display highly tunable and dynamic mechanical properties. In this work, we study the polymer composition effects on the fracture behavior of a gelatin gel, which is a thermoreversible biopolymer gel consisting of denatured collagen chains bridging physical network junctions formed from triple helices. Below the critical volume fraction for chain entanglement, which we confirm via neutron scattering measurements, we find that the fracture behavior is consistent with a viscoplastic type process characterized by hydrodynamic friction of individual polymer chains through the polymer mesh to show that the enhancement in fracture scales inversely with the squared of the mesh size of the gelatin gel network. Above this critical volume fraction, the fracture process can be described by the Lake-Thomas theory that considers fracture as a chain scission process due to chain entanglements.

pyPRISM: A Computational Tool for Liquid-State Theory Calculations of Macromolecular Materials.

The Polymer Reference Interaction Site Model (PRISM) theory describes the equilibrium spatial-correlations of liquid-like polymer systems including melts, blends, solutions, block copolymers, ionomers, liquid crystalline polymers, and nanocomposites. Using PRISM theory, one can calculate thermodynamic (second virial coefficients, Flory-Huggins χ interaction parameters, potentials of mean force) and structural (pair correlation functions, structure factors) data for these macromolecular materials. Here, we present a Python-based, open-source framework, pyPRISM, for conducting PRISM theory calculations. This framework aims to simplify PRISM-based studies by providing a user-friendly scripting interface for setting up and numerically solving the PRISM equations. pyPRISM also provides data structures, functions, and classes that streamline PRISM calculations, allowing pyPRISM to be extended for use in other tasks, such as the coarse-graining of atomistic simulation force-fields or the modeling of experimental scattering data. The goal of this framework is to reduce the barrier to correctly and appropriately using PRISM theory and to provide a platform for rapid calculations of the structure and thermodynamics of polymeric fluids and nanocomposites.

Surface interaction parameter measurement of solvated polymers via model end-tethered chains.

We present a method for the direct measurement of the relative energy of interaction between a solvated polymer and a solid interface. By tethering linear chains covalently to the surface, we ensured the idealized and constant configuration of polymer molecules for measurement, modeling, and parameter estimation. For the case of amine-terminated polystyrene bound to a glycidoxypropyl silane film submerged in cyclohexane-d12, we estimated the χ parameter for the temperature range 10.7 °C to 52.0 °C, and found a downward sloping trend that crosses the χ = 0.5 threshold at 37 °C to 40 °C, in agreement with solution estimates for the same system. We simultaneously estimated the surface interaction parameter χs at each temperature, finding a decreasing affinity of the chains for the surface with increasing temperature, consistent with empirical observations. The theoretical model shows some limitations in a stronger solvent (toluene-d8) that prevent rigorous parameter estimation, but we demonstrate a qualitative change in χ and χs towards stronger solvency and weaker surface interaction with increasing temperature.

The lack of obstructive coronary artery disease on coronary CT angiography safely reduces downstream cost and resource utilization during subsequent chest pain presentations.

OBJECTIVE: The purpose of this study is to investigate the cost and resource use due to chest pain (CP) evaluations after initial coronary CT angiography (CCTA) stratified by coronary artery disease (CAD) burden. METHODS: We examined 1518 patients referred for CCTA from January 2005 to July 2012 for downstream evaluation after CCTA during a median follow-up of 351 days. Results were stratified by CAD burden as quantified on CCTA into no CAD, nonobstructive CAD (<50% stenosis), or obstructive CAD (≥50% stenosis). The incidence of ischemic testing at the time of recurrent evaluation (defined as a composite of clinic visit, emergency department encounter, or ischemic testing after the index CCTA for CP, atypical CP, or angina defined by ICD-9 code), the testing modality used, and frequency of testing were abstracted and used to calculate the direct costs of downstream utilization. Major adverse cardiovascular events defined as all-cause mortality, nonfatal myocardial infarction, stroke, or revascularization >90 days from CCTA were abstracted using ICD-9 codes and Social Security Death Index query. RESULTS: A total of 174 patients (11.5%) underwent evaluation for CP after index CCTA with a higher rate of subsequent clinical visits among obstructive CAD patients compared to those with nonobstructive CAD and no CAD (17.8% vs 13.9% vs. 7.5%; P < .001). A significant reduction in the incidence of repeat ischemic testing was observed in patients with no CAD and nonobstructive CAD (P = .002). This resulted in a lower per-patient cost in the nonobstructive CAD and no CAD patients (median [interquartile range 25-75]: $2952 [$307-2952] and $235 [$0-2880]) when compared with patients with obstructive CAD (median [interquartile range 25-75]: $5832 [$5498-17,459]; P < .001). Major adverse cardiovascular events were not different in the 90 patients that underwent repeat testing at the time of CP evaluation when compared with the 84 patients for whom testing was deferred. CONCLUSION: Absence of CAD on initial CCTA was associated with lower costs and decreased downstream utilization compared to the presence of nonobstructive and obstructive CAD on CCTA during median follow-up of 351 days.

Thermally-induced transition of lamellae orientation in block-copolymer films on 'neutral' nanoparticle-coated substrates.

Block-copolymer orientation in thin films is controlled by the complex balance between interfacial free energies, including the inter-block segregation strength, the surface tensions of the blocks, and the relative substrate interactions. While block-copolymer lamellae orient horizontally when there is any preferential affinity of one block for the substrate, we recently described how nanoparticle-roughened substrates can be used to modify substrate interactions. We demonstrate how such 'neutral' substrates can be combined with control of annealing temperature to generate vertical lamellae orientations throughout a sample, at all thicknesses. We observe an orientational transition from vertical to horizontal lamellae upon heating, as confirmed using a combination of atomic force microscopy (AFM), neutron reflectometry (NR) and rotational small-angle neutron scattering (RSANS). Using molecular dynamics (MD) simulations, we identify substrate-localized distortions to the lamellar morphology as the physical basis of the novel behavior. In particular, under strong segregation conditions, bending of horizontal lamellae induce a large energetic cost. At higher temperatures, the energetic cost of conformal deformations of lamellae over the rough substrate is reduced, returning lamellae to the typical horizontal orientation. Thus, we find that both surface interactions and temperature play a crucial role in dictating block-copolymer lamellae orientation. Our combined experimental and simulation findings suggest that controlling substrate roughness should provide a useful and robust platform for controlling block-copolymer orientation in applications of these materials.

Critical examination of the colloidal particle model of globular proteins.

Recent studies of globular protein solutions have uniformly adopted a colloidal view of proteins as particles, a perspective that neglects the polymeric primary structure of these biological macromolecules, their intrinsic flexibility, and their ability to sample a large configurational space. While the colloidal perspective often serves as a useful idealization in many cases, the macromolecular identity of proteins must reveal itself under thermodynamic conditions in which the native state is no longer stable, such as denaturing solvents and high protein concentrations where macromolecules tend to have screened excluded volume, charge, and hydrodynamic interactions. Under extreme pH conditions, charge repulsion interactions within the protein chain can overcome the attractive hydrogen-bonding interactions, holding it in its native globular state. Conformational changes can therefore be expected to have great significance on the shear viscosity and other rheological properties of protein solutions. These changes are not envisioned in conventional colloidal protein models and we have initiated an investigation of the scattering and rheological properties of model proteins. We initiate this effort by considering bovine serum albumin because it is a globular protein whose solution properties have also been extensively investigated as a function of pH, temperature, ionic strength, and concentration. As we anticipated, near-ultraviolet circular dichroism measurements and intrinsic viscosity measurements clearly indicate that the bovine serum albumin tertiary structure changes as protein concentration and pH are varied. Our findings point to limited validity of the colloidal protein model and to the need for further consideration and quantification of the effects of conformational changes on protein solution viscosity, protein association, and the phase behavior. Small-angle Neutron Scattering measurements have allowed us to assess how these conformational changes influence protein size, shape, and interprotein interaction strength.

Safe and rapid disposition of low-to-intermediate risk patients presenting to the emergency department with chest pain: a 1-year high-volume single-center experience.

BACKGROUND: Coronary CT angiography (CTA) is a powerful tool for the evaluation of chest pain in the emergency department (ED). Some debate persists regarding its cost-effectiveness in a low-to-intermediate risk population. OBJECTIVE: This study sought to evaluate the safety and cost-effectiveness of coronary CTA for low-to-intermediate risk patients presenting to the ED with chest pain in a closed-loop referral system. METHODS: Chest pain patients were evaluated in the ED via a local rapid coronary CTA protocol and tracked prospectively for ED throughput, disposition, chest pain recidivism, and cost utilization as compared with an age-matched cohort evaluated for chest pain treated with usual care. RESULTS: One hundred eighty-three patients underwent the rapid coronary CTA protocol compared with an age-matched cohort of 184 patients treated with usual care. The median follow-up period for major adverse cardiovascular events in the coronary CTA group was 9.0 months (range, 1.8-14.5 months) and 11.1 months (range, 0-14.0 months) for the age-matched cohort. The median ED length of stay (LOS) was 5.8 hours (range, 2.6-12.3 hours) for the rapid coronary CTA cohort and 12.2 hours (range, 1.7-40.3 hours) for the age-matched cohort (P < .001). The median time to performance of coronary CTA was 2.5 hours (range, 0.4-8.7 hours) with a median time from coronary CTA performance to disposition of 2.9 hours (range, 0.8-8.6 hours). Total median hospital LOS was 5.9 hours (range, 2.7-124 hours) in the rapid coronary CTA cohort compared with 25.0 hours (range, 1.2-208 hours) in the age-matched cohort (P < .001). Hospital admission was more common in the age-matched cohort (98.9% vs 9.3%; P < .001). There was a significant reduction in total payer cost in coronary CTA group when compared to usual care ($182,064.55 vs $685,190.77; P < .001). CONCLUSIONS: Coronary CTA for ED risk stratification and disposition within a closed referral system resulted in the shortest ED LOS published to date while being safe and cost-effective.

Effect of Coronary Computed Tomography Angiography Disease Burden on the Incidence of Recurrent Chest Pain.

Introduction. The purpose of this study is to investigate chest pain evaluations after initial coronary computed tomography angiography (CCTA) based upon coronary artery disease (CAD) burden. Methods. CCTA results of 1,518 patients were grouped based on the CCTA results into no CAD, nonobstructive CAD (<50% maximal diameter stenosis), or obstructive CAD (≥50% stenosis). Chest pain evaluation after initial CCTA and rates of major adverse cardiovascular events (MACE) defined as the incidence of all-cause mortality, nonfatal MI, ischemic stroke, and late revascularization (>90 days following CCTA) were evaluated. Results. MACE rates were higher with obstructive CAD compared to nonobstructive CAD and no CAD (8.9% versus 0.7%, P < 0.001; 8.9 versus 1.6%, P < 0.001). One hundred seventy-four patients (11.5%) underwent evaluation for chest pain after index CCTA with rates significantly higher with obstructive CAD compared to both nonobstructive CAD and no CAD (7.5% versus 13.9% versus 17.8%, P < 0.001). The incidence of repeat testing was more frequent in patients with obstructive CAD (no CAD 36.5% versus nonobstructive CAD 54.9% versus obstructive CAD 67.7%, P = 0.015). Conclusion. Absence of obstructive disease on CCTA is associated with lower rates of subsequent evaluations for chest pain and repeat testing with low MACE event rates over a 22-month followup.

Thermally reversible surface morphology transition in thin diblock copolymer films.

Many phase transitions exhibit ordering transitions at the boundary of the material that are distinct from its interior where intermolecular interactions can be significantly different. The present work considers the existence of a surface thermodynamic order-order transition between two distinct morphologies in thin block copolymer (BCP) films that are of interest in nanomanufacturing applications. Specifically, we find a thermally reversible interfacial transition between sphere-like structures and cylinders in flow-coated films of poly(styrene-block-methyl methacrylate) (PS-b-PMMA), where the BCP forms a cylinder microphase in the bulk. We present direct evidence from atomic force microscopy (AFM) of ion-etched films and grazing-incidence small-angle X-ray scattering (GISAXS) on films without etching, which shows that the order-order transition is restricted to the outer layer of the film, while the film interior remains in the cylinder state. Moreover, we find this order-order transition to be insensitive to film thickness over the range investigated (40-170 nm). This morphological transition is of importance in characterizing the thermodynamics and dynamics of thin BCP films used as templates in nanomanufacturing applications.

Challenges in fabrication of mesoporous carbon films with ordered cylindrical pores via phenolic oligomer self-assembly with triblock copolymers.

Mesoporous phenol formaldehyde (PF) polymer resin and carbon films are prepared by a solution self-assembly of PF oligomers with amphiphilic triblock copolymers. After thermopolymerization of the PF to cross-link the network, the films show an ordered morphology as determined by X-ray diffraction and grazing incidence small-angle X-ray scattering (GISAXS). Our results show that the amphiphilic triblock copolymer template greatly influences the stability of the final porous mesostructures. The pyrolysis of the two-dimensional (2-D) hexagonal films with p6mm symmetry templated by Pluronic F127 yields a disordered porous structure following the template removal. Conversely, films templated by Pluronic P123 can exhibit well-ordered cylindrical pores after the template removal, but the solution composition range to yield ordered cylindrical mesopores is significantly reduced (nearly 70%) for thin films in comparison to bulk powders. We propose two dominant difficulties in fabricating well-ordered cylindrical mesopores in films: first, the stress from contraction during the pyrolysis can lead to a collapse of the mesostructure if the wall thickness is insufficient, and second, the surface wetting behavior in thin films leads to a small compositional range.

Target patterns induced by fixed nanoparticles in block copolymer films.

It is well-known that thin films of cylinder-forming block copolymers (BCP) can exhibit a transition from a perpendicular to a parallel cylinder orientation with respect to the supporting solid substrate upon varying film thickness. We show that wave-like oscillations between these morphologies can be induced through the introduction of nanoparticles (NP) into flow-coated and annealed BCP films where the particles span the film thickness and are fixed by irreversible adsorption to the supporting substrate. We hypothesize that these novel "target" patterns arise from residual stresses that build up in the film while undergoing thermal treatment and film formation, and we support this hypothesis by showing the suppression of this type of pattern formation in films that are first thermally annealed near their glass transition T(g) to relax residual stress. Similar undulating height patterns are also observed in heated homopolymer films with nanoparticles, consistent with our thermally induced stress hypothesis of the target pattern formation in BCP films and pointing to the general nature of wave-like thermally induced height variations in heated heterogeneous polymer films. Similar wave patterns should be induced by lithographically etched substrate patterns arising in device fabrication using BCP materials, which makes the phenomena of technological interest. These target patterns also potentially provide valuable information about the presence of residual stresses in cast films that arise during their processing.

Surface morphology diagram for cylinder-forming block copolymer thin films.

We investigate the effect of the ordering temperature (T) and film thickness (h(f)) on the surface morphology of flow-coated block copolymer (BCP) films of asymmetric poly(styrene-block-methyl methacrylate). Morphology transitions observed on the ordered film surface by atomic force microscopy (AFM) are associated with a perpendicular to a parallel cylinder BCP microphase orientation transition with respect to the substrate with increasing h(f). "Hybrid" surface patterns for intermediate h(f) between these limiting morphologies are correspondingly interpreted by a coexistence of these two BCP microphase orientations so that two "transitional" h(f) exist for each T. This explanation of our surface patterns is supported by both neutron reflectivity and rotational SANS measurements. The transitional h(f) values as a function of T define upper and lower surface morphology transition lines, h(fu) (T) and h(fl) (T), respectively, and a surface morphology diagram that should be useful in materials fabrication. Surprisingly, the BCP film surface morphology depends on the method of film formation (flow-coated versus spun-cast films) so that nonequilibrium effects are evidently operative. This morphological variability is attributed primarily to the trapping of residual solvent (toluene) within the film (quantified by neutron reflectivity) due to film vitrification while drying. This effect has significant implications for controlling film structure in nanomanufacturing applications based on BCP templates.

Orientational order in block copolymer films zone annealed below the order--disorder transition temperature.

We report measurements of rapid ordering and preferential alignment in block copolymer films zone annealed below the order-disorder transition temperature. The orientational correlation lengths measured after approximately 5 h above the glass-transition temperature ( approximately 2 microm) were an order of magnitude greater than that obtained under equivalent static annealing. The ability to rapidly process polymers with inaccessible order-disorder transition temperatures suggests zone annealing as a route toward more robust nanomanufacturing methods based on block copolymer self-assembly.