Responsive liquid crystal elastomers for enhanced cell sheet alignment

Responsive, biocompatible substrates are of interest for directing the maturation and function of cells in vitro during cell culture. This can potentially provide cells and tissues with desirable properties for regenerative therapies. The present disclosure provides a scalable approach to attach, align and dynamically load cells on responsive liquid crystal elastomer (LCE) substrates. Monodomain LCEs exhibit reversible shape changes in response to cyclic stimulus, and when immersed in an aqueous medium on top of, for example, resistive heaters, shape changes are fast, reversible and produce minimal temperature changes in the surroundings

Rheological study of structural transitions in triblock copolymers in a liquid crystal solvent

Rheological properties of triblock copolymers dissolved in a nematic liquid crystal (LC) solvent demonstrate that their microphase separated structure is heavily influenced by changes in LC order. Nematic gels were created by swelling a well-defined, high molecular weight ABA block copolymer with the small-molecule nematic LC solvent 4-pentyl-4-cyanobiphenyl (5CB). The B midblock is a side-group liquid crystal polymer (SGLCP) designed to be soluble in 5CB and the A endblocks are polystyrene, which is LC-phobic and microphase separates to produce a physically cross-linked, thermoreversible, macroscopic polymer network. At sufficiently low polymer concentration a plateau modulus in the nematic phase, characteristic of a gel, abruptly transitions to terminal behavior when the gel is heated into its isotropic phase. In more concentrated gels, endblock aggregates persist into the isotopic phase. Dramatic changes in network structure are observed over small temperature windows (as little as 1 °C) due to tccche rapidly changing LC order near the isotropization point. The discontinuous change in solvent quality produces an abrupt change in viscoelastic properties for three polymers having different pendant mesogenic groups and matched block lengths

Director dynamics in liquid-crystal physical gels

Nematic liquid-crystal (LC) elastomers and gels have a rubbery polymer network coupled to the nematic director. While LC elastomers show a single, non-hydrodynamic relaxation mode, dynamic light-scattering studies of self-assembled liquid-crystal gels reveal orientational fluctuations that relax over a broad time scale. At short times, the relaxation dynamics exhibit hydrodynamic behavior. In contrast, the relaxation dynamics at long times are non-hydrodynamic, highly anisotropic, and increase in amplitude at small scattering angles. We argue that the slower dynamics arise from coupling between the director and the physically associated network, which prevents director orientational fluctuations from decaying completely at short times. At long enough times the network restructures, allowing the orientational fluctuations to fully decay. Director dynamics in the self-assembled gels are thus quite distinct from those observed in LC elastomers in two respects: they display soft orientational fluctuations at short times, and they exhibit at least two qualitatively distinct relaxation processes

A Comprehensive Study of Hydrolyzed Polyacrylamide as a Binder for Silicon Anodes.

Silicon anodes have a high theoretical capacity for lithium storage, but current composite electrode formulations are not sufficiently stable under long-term electrochemical cycling. The choice of polymeric binder has been shown to impact stability and capacity of silicon anodes for electrochemical energy storage. While several promising polymeric binders have been identified, there is a knowledge gap in how various physicochemical properties-including adhesion, mechanical integrity, and ion diffusion-impact electrochemical stability and performance. In this work, we comprehensively investigate the physical properties and performance of a molecular-weight series (3-20 × 106 g/mol) of partially hydrolyzed polyacrylamide (HPAM) in silicon anodes. We quantify the mechanical strength, electrolyte uptake, adhesion to silicon, copper, and carbon, as well as electrochemical performance and stability and find that HPAM satisfies many of the properties generally believed to be favorable, including good adhesion, high strength, and electrochemical stability. HPAM does not show any electrolyte uptake regardless of any molecular weight studied, and thin films of mid- and high-molecular-weight HPAM on silicon surfaces suppress lithiation of silicon. The resulting composite electrodes exhibit an electrochemical storage capacity greater than 3000 mAh/g initially and 1639 mAh/g after 100 cycles. We attribute capacity fade to failure of mechanical properties of the binder or an excess of the solid electrolyte interphase layer being formed at the Si surface. While the highest-molecular-weight sample was expected to perform the best given its stronger adhesion and bulk mechanical properties, we found that HPAM of moderate molecular weight performed the best. We attribute this to a trade-off in mechanical strength and uniformity of the resulting electrode. This work demonstrates promising performance of a low-cost polymer as a binder for Si anodes and provides insight into the physical and chemical properties that influence binder performance

Revisiting the capitalization of public transport accessibility into residential land value: an empirical analysis drawing on Open Science

Background: The delivery and effective operation of public transport is fundamental for a for a transition to low-carbon emission transport systems’. However, many cities face budgetary challenges in providing and operating this type of infrastructure. Land value capture (LVC) instruments, aimed at recovering all or part of the land value uplifts triggered by actions other than the landowner, can alleviate some of this pressure. A key element of LVC lies in the increment in land value associated with a particular public action. Urban economic theory supports this idea and considers accessibility to be a core element for determining residential land value. Although the empirical literature assessing the relationship between land value increments and public transport infrastructure is vast, it often assumes homogeneous benefits and, therefore, overlooks relevant elements of accessibility. Advancements in the accessibility concept in the context of Open Science can ease the relaxation of such assumptions. Methods: This thesis draws on the case of Greater Mexico City between 2009 and 2019. It focuses on the effects of the main public transport network (MPTN) which is organised in seven temporal stages according to its expansion phases. The analysis incorporates location based accessibility measures to employment opportunities in order to assess the benefits of public transport infrastructure. It does so by making extensive use of the open-source software OpenTripPlanner for public transport route modelling (≈ 2.1 billion origin-destination routes). Potential capitalizations are assessed according to the hedonic framework. The property value data includes individual administrative mortgage records collected by the Federal Mortgage Society (≈ 800,000). The hedonic function is estimated using a variety of approaches, i.e. linear models, nonlinear models, multilevel models, and spatial multilevel models. These are estimated by the maximum likelihood and Bayesian methods. The study also examines possible spatial aggregation bias using alternative spatial aggregation schemes according to the modifiable areal unit problem (MAUP) literature. Results: The accessibility models across the various temporal stages evidence the spatial heterogeneity shaped by the MPTN in combination with land use and the individual perception of residents. This highlights the need to transition from measures that focus on the characteristics of transport infrastructure to comprehensive accessibility measures which reflect such heterogeneity. The estimated hedonic function suggests a robust, positive, and significant relationship between MPTN accessibility and residential land value in all the modelling frameworks in the presence of a variety of controls. The residential land value increases between 3.6% and 5.7% for one additional standard deviation in MPTN accessibility to employment in the final set of models. The total willingness to pay (TWTP) is considerable, ranging from 0.7 to 1.5 times the equivalent of the capital costs of the bus rapid transit Line-7 of the Metrobús system. A sensitivity analysis shows that the hedonic model estimation is sensitive to the MAUP. In addition, the use of a post code zoning scheme produces the closest results compared to the smallest spatial analytical scheme (0.5 km hexagonal grid). Conclusion: The present thesis advances the discussion on the capitalization of public transport on residential land value by adopting recent contributions from the Open Science framework. Empirically, it fills a knowledge gap given the lack of literature around this topic in this area of study. In terms of policy, the findings support LVC as a mechanism of considerable potential. Regarding fee-based LVC instruments, there are fairness issues in relation to the distribution of charges or exactions to households that could be addressed using location based measures. Furthermore, the approach developed for this analysis serves as valuable guidance for identifying sites with large potential for the implementation of development based instruments, for instance land readjustments or the sale/lease of additional development rights

Well-Defined Liquid Crystal Gels from Telechelic Polymers

Well-defined liquid crystal networks with controlled molecular weight between cross-links and cross-link functionality were prepared by “click” cross-linking of telechelic polymers produced by ring-opening metathesis polymerization (ROMP). The networks readily swell in a small molecule liquid crystal, 5CB, to form LC gels with high swelling ratios. These gels exhibit fast, reversible, and low-threshold optic switching under applied electric fields when they are unconstrained between electrodes. For a given electric field, the LC gels prepared from shorter telechelic polymers showed a reduced degree of switching than their counterparts made from longer polymer strands. The reported approach provides control over important parameters for LC networks, such as the length of the network strands between cross-links, cross-linker functionality, and mesogen density. Therefore, it allows a detailed study of relationships between molecular structure and macroscopic properties of these scientifically and technologically interesting networks

Self-Assembly of Coil/Liquid-Crystalline Diblock Copolymers in a Liquid Crystal Solvent

Diblock copolymers having a random-coil polymer block (polystyrene, PS) connected to a side-group liquid crystal polymer (SGLCP) self-assemble in a nematic liquid crystal (LC), 4-pentyl-4′-cyanobiphenyl, into micelles with PS-rich cores and SGLCP-rich coronas. The morphologies of block copolymers with varying PS content are characterized as a function of temperature and concentration using small-angle neutron scattering, rheometry, and transmission electron microscopy. Unlike conventional solvents, the nematic LC can undergo a first-order transition between distinct fluid phases, accessing the regimes of both strong and slight selectivity in a single polymer/solvent pair. Micelles dissolve away above a microphase separation temperature (MST) that is often equal to the solution’s isotropization point, TNI. However, increasing or decreasing the polymer’s PS content can shift the MST to be above or below TNI, respectively, and in the former case, micelles abruptly swell with solvent at TNI. Comparable effects can be achieved by modulating the overall polymer concentration

Can Smartphone Location Data at the Point Level be Used to Estimate Traffic Volumes?: A Methodological Evaluation

The effective development of transport planning strategies relies on timely and comprehensive urban travel information. Manual or automatic traffic counts form a key input into many models but are available only for a limited set of locations and at a low frequency. The emergence of digital footprint data, particularly location data at the point level obtained from smartphones, has raised the possibility of replacing or supplementing traditional analytical methods and sources. However, the suitability of the data for these purposes is currently poorly understood. This study aims to assess the accuracy of estimating traffic counts and travel direction volumes by utilizing a sample of high-resolution smartphone location data. Counts will be derived and compared to 44 manual count points published by the Department of Transport in 2019 at various locations in and around Glasgow. The location data is provided by a private organization, Huq, which comprises 22 million records from 19,000 unique users for the same year in the study area. Two main challenges are addressed in the paper. The first is effectively extracting travel activity from the location data while mitigating the noise stemming from non-travel activities and imprecise or sparse location estimates. To address this, we construct and test a series of systematic buffers around traffic count points based on the characteristics of the road network and the immediate built environment. The second challenge concerns the heterogeneity in the quality and volume of the data produced by app users. We further examine whether it is possible to refine the estimates by inferring individual trips and the direction of travel based on the patterns of the location data. Preliminary results indicate that the proposed methodology explains between 36% and 70% of the variability of the manual traffic counts in a regression framework. This study establishes a methodological precedent and suggests directions for future research. Potential avenues include investigating additional years or cities, incorporating more temporally detailed traffic count data, integrating CCTV-based counts, evaluating alternative location data sources, and focusing on active travel modes

Public transport accessibility indicators to urban and regional services in Great Britain

Public transport accessibility to urban and regional services has been found to relate to various social and economic processes, such as unemployment, transport mode choice, property prices, and public health. A frequent type of measures representing accessibility are location-based. While these offer advantages, like flexibility and ease of interpretation, their estimation usually requires specialized skills and substantial computational resources. To lower these barriers, we have prepared a suite of accessibility indicators for key services across Great Britain at a spatially disaggregated level. The dataset includes ready-to-use public transport accessibility indicators for employment, general practitioners (GP, or family physician), hospitals, grocery stores, supermarkets, primary and secondary schools, and urban centres. It also includes the raw travel time matrix from each origin to every potential destination, a primary input for such indicator estimation. Altogether, this resource offers various levels of application, from direct input into a range of research topics to the foundation for creating comprehensive custom indicators

Towards Just Neighbourhoods: Leveraging Geospatial Data Science to Understand Night-Time Public Transport Variability in British Cities

Working towards equitable accessibility, sustainable mobility, and the decarbonisation of transport requires a better understanding of the challenges confronted by disadvantaged populations. These communities often rely on public transport, a sustainable form of mobility that is crucial for their daily needs, including commuting to and from workplaces. In the UK, nearly nine million individuals were engaged in night-time work in 2022, with a substantial percentage occupying low-paid positions (ONS, 2023). Coupled with the significant trend of poverty suburbanising in major British cities (Bailey & Minton, 2018)—areas typically less accessible than central locations—it's critical to investigate the impacts of public transport accessibility on these demographics, particularly during off-peak hours. However, the variability of public transport services at night in British cities remains poorly understood. This raises the question: How do night-time public transport service variations impact disadvantaged urban communities? To address this question, we exploited the increased computational resources, open-source software like 'R' and the 'R5R' package (Saraiva et al., 2021), as well as open-access data. These tools enabled the computation of detailed travel time matrices, allowing us to compare public transport service variations in larger British cities. We computed travel times from each lower super output area (LSOA) in England and Wales, or data zone (DZ) in Scotland, to all others during two periods: morning peak (7-10 a.m.) and night-time (9 p.m. to midnight). Later, we stratify these changes by disadvantaged community groups and model the accessibility poverty risk in a logistic regression. Our results confirm an expected overall decrease in night-time public transport services. Specifically, all subgroups within ‘Industrious’ and ‘Hard-pressed’ communities are at higher risk of experiencing accessibility poverty at night than ‘Other groups’ in British cities. This particularly affects ‘Endeavouring social renters’ and ‘Hard-pressed flat dwellers’ who have an odds ratio almost three times that of the rest of the urban population. Moreover, the odds for 'Primary sector workers' are ninefold. The latter can be understood because primary sector workers tend to be located in the countryside. These findings underscore the importance of further understanding disadvantaged communities' dual exclusion—firstly, by their geographic locations and secondly, by limitations restricting their participation in the night-time economy via public transport. It also highlights the critical role of advances in geospatial data science, open-source software and their communities in supporting the development of effective net-zero policies for equitable neighbourhoods and sustainable communities