Search

We have studied ion transport in electrolytes created by blending two different polymers and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The polymers covered in this study are poly(ethylene oxide) (PEO), poly(1,3,6-trioxocane) (P(2EO-MO)), and poly(1,3-dioxolane) (P(EO-MO)). Ion transport is quantified by the product κρ+which is defined as the efficacy of the electrolytes, where κ is conductivity and ρ+is the current fraction determined by the Bruce-Vincent method. Polymer blends can be either one-phase or macrophase-separated. We used small-angle neutron scattering (SANS) to distinguish between these two possibilities. The random phase approximation (RPA) was used to interpret SANS data from one-phase blends. The effect of added salt on polymer blend thermodynamics is quantified by an effective Flory-Huggins interaction parameter. All polymer blends were one-phase in the absence of salt. Adding salt in small concentrations results in macrophase separation in all cases. One-phase systems were observed in the PEO/P(EO-MO)/LiTFSI blends at high salt concentrations. In most of the polymer blend electrolytes, the measured κρ+was either lower than or comparable to that of the homopolymer electrolytes. An exception to this was one-phase PEO/P(EO-MO)/LiTFSI blends electrolytes at high salt concentrations.

We investigate a polyacetal-based electrolyte, poly(1,3,6-Trioxocane) (P(2EO-MO)) mixed with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt, and report full electrochemical characterization of the transport parameters and a thermodynamic property in comparison to the previously reported poly(ethylene oxide) (PEO) electrolyte data [D. Gribble et al., J. Electrochem. Soc., 166, A3228 (2019)]. While the steady-state current fraction (?+) of P(2EO-MO) electrolyte is greater than that of PEO electrolyte in the entire salt concentration window we explored, the rigorously defined transference number using Newman s concentrated solution theory ( + t 0) appears to be similar to that of PEO electrolyte. On the basis of full electrochemical characterization, we calculate the salt concentration profile as a function of position in the cell and predict limiting current density (iLL) as a function of salt concentration. Experimental data were compared to the predicted values. The non-monotonic behaviors were observed both in prediction and experimental results with offset peak positions. We find that the limiting current density of P (2EO-MO) electrolyte is systematically lower than that of PEO electrolyte in most of the salt concentrations with the exception of rav = 0.05. It is noteworthy that even though one measure of electrolyte efficacy (?+) is superior in P(2EO-MO) electrolyte, the limiting current density, which is another metric of electrolyte efficacy at high currents, is not greater in P(2EO-MO).

The success of poly(ethylene oxide) (PEO) in solid-state polymer electrolytes for lithium-ion batteries is well established. Recently, in order to understand this success and to explore possible alternatives, we studied polyacetal electrolytes to deepen the understanding of the effect of the local chemical structure on ion transport. Advanced molecular dynamics techniques using newly developed, tailored interaction potentials have helped elucidate the various coordination environments of ions in these systems. In particular, the competition between cation-anion pairing and coordination by the polymer has been explored using free-energy sampling (metadynamics). At equivalent reduced temperatures, with respect to the polymer-specific glass-transition temperature, two-dimensional free-energy plots reveal the existence of multiple coordination environments for the lithium (Li) ions in these systems and their relative stabilities. Furthermore, we observe that the Li-ion movement in PEO follows a serial, stepwise pathway when moving from one coordination state to another, whereas this happens in a more continuous and concerted fashion in a polyacetal such as poly(1,3-dioxalane) [P(EO-MO)]. The implication is that interconversion between coordination states of the Li ions may be easier in P(EO-MO). However, the overarching observation from our free-energy analysis is that Li-ion coordination is dominated by the polymer (in either case) and contact-ion pairs are rare. We rationalize the observed higher increase in glass-transition temperature (Tg) with salt loading in polyacetals as due to intermolecular Li-ion coordination involving multiple polymer chains, rather than just one chain for PEO-based electrolytes. This interchain coupling in the polyacetals, resulting in the higherTg, works against any gains due to variations in Li-ion coordination that might enhance transport processes over PEO. Further research is required to overcome the interdependence between local coordination and macroscopic properties to compete with PEO electrolytes at the same absolute working temperature.

Identifying plastics capable of chemical recycling to monomer (CRM) is the foremost challenge in creating a sustainable circular plastic economy. Polyacetals are promising candidates for CRM but lack useful tensile strengths owing to the low molecular weights produced using current uncontrolled cationic ring-opening polymerization (CROP) methods. Here, we present reversible-deactivation CROP of cyclic acetals using a commercial halomethyl ether initiator and an indium(III) bromide catalyst. Using this method, we synthesize poly(1,3-dioxolane) (PDXL), which demonstrates tensile strength comparable to some commodity polyolefins. Depolymerization of PDXL using strong acid catalysts returns monomer in near-quantitative yield and even proceeds from a commodity plastic waste mixture. Our efficient polymerization method affords a tough thermoplastic that can undergo selective depolymerization to monomer.

Polyacetal electrolytes have been demonstrated as promising alternatives to liquid electrolytes and poly(ethylene oxide) (PEO) for rechargeable lithium-ion batteries; however, the relationship between polymer structure and ion motion is difficult to characterize. Here, we study structure-property trends in ion diffusion with respect to polymer composition for a systematic series of five polyacetals with varying ratios of ethylene oxide (EO) to methylene oxide (MO) units, denoted as P(xEO-yMO), and PEO. We first use 7Li and 19F pulsed-field-gradient NMR spectroscopy to measure cation and anion self-diffusion, respectively, in polymer/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt mixtures. At 90 °C, we observe modest changes in Li+ diffusivity across all polymer compositions, while anion (TFSI-) self-diffusion coefficients decrease significantly with increasing MO content. At a given reduced temperature (T - Tg), all polyacetal electrolytes exhibit faster Li+ self-diffusion than PEO. Intriguingly, P(EO-MO) and P(EO-2MO) also show slower TFSI- anion self-diffusion than PEO at a given reduced temperature. Molecular dynamics simulations reveal that shorter distances between acetal oxygen atoms (O-CH2-O) compared to ether oxygens (O-CH2-CH2-O) promote more diverse, often asymmetric, Li+ coordination environments. Raman spectra reveal that anion-rich ion clusters in P(EO-MO) and P(EO-2MO) lead to decreased anion diffusivity, which along with increased cation diffusivity, support the viability of polyacetals as high-performance polymer electrolytes.

Polymer electrolytes mitigate safety concerns surrounding flammable liquid electrolytes in lithium-ion batteries. Poly(ethylene oxide) (PEO) electrolytes demonstrate viable conductivity values (∼1 × 10-3 S/cm) at elevated temperatures (>70 °C) but a relatively low Li+ current fraction (≤0.2) because strong Li+ coordination inhibits cation mobility. We have developed a series of polyacetal electrolytes by systematically varying methylene oxide (MO) and ethylene oxide (EO) units in the polymer backbone. These materials maintain high oxygen-to-carbon ratios like PEO but offer improved ion transport, revealing trends of decreasing conductivity and increasing current fraction with respect to polymer composition. In particular, the increasing current fraction measured via the Bruce-Vincent method suggests that MO units improve Li+ mobility relative to anion mobility. We calculate an overall efficacy (product of conductivity and current fraction) for each polymer/salt composition and identify two polymers - P(EO-MO) and P(EO-2MO) - that outperform PEO at high and low salt concentrations, respectively.

This study shows that it is possible to obtain homogeneous mixtures of two chemically distinct polymers with a lithium salt for electrolytic applications. This approach is motivated by the success of using mixtures of organic solvents in modern lithium-ion batteries. The properties of mixtures of a polyether, poly(ethylene oxide) (PEO), a poly(ether-acetal), poly(1,3,6-trioxocane) (P(2EO-MO)), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt were studied by small-angle neutron scattering (SANS) and electrochemical characterization in symmetric cells. The SANS data are used to determine the miscibility window and quantify the effect of added salt on the thermodynamic interactions between the polymers. In the absence of salt, PEO/P(2EO-MO) blends are homogeneous and characterized by attractive interactions, i.e., a negative Flory-Huggins interaction parameter, χ. The addition of small amounts of salt results in a positive effective Flory-Huggins interaction parameter, χeff, and macrophase separation. Surprisingly, miscible blends and negative χeff parameters are obtained when the salt concentration is increased beyond a critical value. The electrochemical properties of PEO/P(2EO-MO)/LiTFSI blends at a given salt concentration were close to those obtained in PEO/LiTFSI electrolytes at the same salt concentration. This suggests that in the presence of PEO the electrochemical properties exhibited by P(2EO-MO) chains are similar to those of PEO chains. This work opens the door to a new direction for creating new and improved polymer electrolytes either by combining existing polymers and salt or by synthesizing new polymers with the specific aim of including them in miscible polymer blend electrolytes.

Background: High quality data pertaining to the size of the transgender and gender diverse (TGD) population are scant, however, several recently published studies may provide more reliable contemporary estimates. Aims: To summarize the estimated number and proportion of TGD individuals overall and across age groups, based on most accurate data. Methods: This systematic review focused on recent studies (published from 2009 through 2019) that utilized sound methodology in assessing the proportion of TGD people in the general population. Publications were included if they used clear definitions of TGD status, and calculated proportions based on a well-defined sampling frame. Nineteen eligible publications represented two broad categories of studies: those that used data from large health care systems; and those that identified TGD individuals from population surveys. Results: Among health system-based studies, TGD persons were identified using relevant diagnostic codes or clinical notes. The proportions of individuals with a TGD-relevant diagnosis or other recorded evidence ranged between 17 and 33 per 100,000 enrollees. In population surveys TGD status was ascertained based on self-report with either narrow or broad definitions. The survey-based estimates were orders of magnitude higher and consistent across studies using similar definitions. When the surveys specifically inquired about transgender identity, the estimates ranged from 0.3% to 0.5% among adults, and from 1.2% to 2.7% among children and adolescents. When the definition was expanded to include broader manifestations of gender diversity, the corresponding proportions increased to 0.5-4.5% among adults and 2.5-8.4% among children and adolescents. Upward temporal trends in the proportion of TGD people were consistently observed. Conclusions: Current data indicate that people who self-identify as TGD represent a sizable and increasing proportion of the general population. This proportion may differ, depending on inclusion criteria, age, and geographic location, but well-conducted studies of similar type and design tend to produce comparable results.

BACKGROUND: Non-adherence to dialysis recommendations is common and associated with poor outcomes. We used data from a cohort of in-center hemodialysis patients to determine whether patients reported difficulties with adherence were associated with achievement of clinical targets for treatment recommendations. PATIENTS AND METHODS: We included 799 in-center patients receiving hemodialysis from February 2010 to October 2016 at Emory Dialysis (Atlanta, GA, USA). Patient-reported difficulty with adherence (yes vs no) across multiple domains (coming to dialysis, completing dialysis sessions, fluid restrictions, diet restrictions, taking medications) was obtained from baseline social worker assessments. Achievement of clinical targets for coming to dialysis (missing ≥3 expected sessions), completing dialysis sessions (shortening >3 sessions by ≥15 min), fluid restrictions (mean interdialytic weight gain ≥3 kg), diet restrictions (mean potassium ≥5.0 mEq/L, mean phosphate >5.5 mg/dL), and taking medications (mean phosphate >5.5 mg/dL) was estimated over the following 12 weeks, using electronic medical record data. Crude agreement was assessed, and multivariable logistic regression was used to estimate the associations between these measures. RESULTS: Agreement between reported difficulty in adherence and failure to achieve clinical targets was generally poor across all domains (percent agreement: 52.9-65.3%). After adjustment, patients reporting difficulty with fluid restrictions were 62% more likely to have mean interdialytic weight gain ≥3 kg than those not reporting difficulty (OR: 1.62, 95% CI: 1.08, 2.43). Patients reporting difficulty with coming to dialysis were 41% more likely to miss ≥3 expected dialysis sessions over 12 weeks (OR: 1.41, 95% CI: 0.96, 2.07); however, this association was not statistically significant. There were no significant associations between reported difficulty and failure to achieve clinical targets in other categories. CONCLUSION: While reported difficulty with only fluid restrictions and coming to dialysis were associated with failure to achieve clinical targets in our study, the general lack of agreement between reported difficulty with adherence and failure to achieve clinical targets highlights a gap that could be explored to develop and target educational interventions aimed at increasing adherence among dialysis patients.

Recent studies of language policy and bilingual education have focused on federal level legislation (Wiley and García in Mod Lang J 100:48-63, 2016. 10.1111/modl.12303), and immediate consequences of state level policy. Although Critical Race Theory (CRT) has been employed to analyze the structural impact of local policy on minoritized communities (Davila and Aviles de Bradley in Educ Found 24:39-58, 2010), few studies have explicitly connected CRT and language policy, or applied CRT to state level law. In this study, I apply CRT, specifically the theory of whiteness as property (Harris in Harv Law Rev 106:1-63, 1993), and the theory of raciolinguistic ideologies to three Washington State laws related to bilingual education: the Transitional Bilingual Instruction Act, the Seal of Biliteracy law, and the Dual Language Grant Program Bill. I utilize a Critical Discourse Analysis to examine the laws, related legislative reports, and materials such as guidelines created by Washington school districts. Results of this analysis suggest that the discourse embedded in these laws and related documents upholds whiteness as a form of property. Further, I relate these findings to language planning, and suggest that language education policy-makers employ racial impact reports (Fathi in Gonzaga Law Rev 47:531-545, 2009) in order to re-center race, racism and racial inequity in language planning.

Drawing on the concept of figured worlds, we examined how four preservice teachers in a monoglossically oriented teacher preparation program developed their professional identities and sense of agency as dual language teachers. Figured worlds are socially constructed and culturally recognized realms with a story line and actors who also actively change these story lines in the course of narrating them and participating in them. Drawing on interviews and observations, we showed how four teachers' personal linguistic, racial, and cultural backgrounds interacted with external affordances, including their own language ideologies and those present in their contexts, leading to the (re)construction of their figured worlds of dual language teaching. These figured worlds were mainly reshaped to include family connections and student empowerment and made salient the limitations of the teachers' engagement with the centrality of race, power, and immigrant rights in their language ideologies.

The current study surveys medical and doctoral psychology students (N = 100) from an urban northeastern university regarding knowledge and attitudes toward elderly sexuality and aging using the Facts on Aging Quiz, the Aging Sexuality Knowledge and Attitudes Scale, and measures of interest in gerontology, academic/clinical exposure to aging and sexuality, and contact with elders. The current study found that psychology students demonstrated greater aging knowledge than medical students; however, both groups showed gaps in knowledge about sexuality. Married students had greater academic/clinical exposure and greater knowledge about aging but less permissive attitudes toward elderly sexuality. Generally, knowledge about aging was the strongest correlate of knowledge about sexuality. Level of knowledge about sexuality was not associated with attitudes. Attitudes toward sexuality and aging may be more strongly tied to demographic variables reflective of religious beliefs or adherence to sociocultural norms. (Contains 5 tables.)