Adaptive, Bayesian Experimental Design to Efficiently Determine the Critical Micelle Concentration of a Surfactant

Surfactants are widely used for industrial applications, yet more environmentally friendly surfactants with enhanced properties are demanded. A key thermodynamic property governing the behavior of a surfactant in an aqueous solution is its critical micelle concentration (CMC). Below the CMC, increasing the surfactant concentration reduces the surface tension of the solution; above the CMC, the water–air interface becomes saturated with adsorbed surfactant, leading excess surfactant to self-assemble into micelles and the surface tension to plateau. Many physicochemical properties of a surfactant solution exhibit sharp changes at the CMC. The conventional experimental protocol to determine the CMC of a surfactant is labor-intensive and time-consuming: (1) prepare many surfactant solutions spanning a wide concentration range and then (2) measure the surface tension of each solution. Herein, we adopt Bayesian experimental design (BED) to determine the CMC of a surfactant more efficiently─even without prior knowledge of its order of magnitude. BED follows an experiment-model-design feedback loop: (1) prepare a surfactant solution and measure its surface tension; (2) use all surface tension data thus far to obtain a posterior distribution over thermodynamic models of the surface tension isotherm of the surfactant; and (3) pick the surfactant concentration for the next experiment to maximize expected information gain about the CMC. We show that BED efficiently gathers information about the CMC using two surfactants (octyl-β-d-thioglucopyranoside and Triton X-100) as test cases. Broadly, BED can reduce the time, effort, cost, and chemical waste to determine the CMC of surfactants and drive an autonomous laboratory for surfactant discovery and characterization.

pubs.acs.org

‘Reimagining matter’: Nobel laureate invents machine that harvests water from dry air

Omar Yaghi’s invention uses ambient thermal energy and can generate up to 1,000 litres of clean water every day A Nobel laureate’s environmentally friendly invention that provides clean water if central supplies are knocked out by a hurricane or drought, could be a life saver for vulnerable islands, its founder says. The invention, by the chemist Prof Omar Yaghi, uses a type of science called reticular chemistry to create molecularly engineered materials, which can extract moisture from the air and harvest water even in arid and desert conditions. Continue reading...

theguardian.com

Adaptive Allocation of Monte Carlo Samples for Efficient, Multifidelity Computational Screening of Metal–Organic Frameworks

For applications in gas sensing, purification, and capture, we often wish to search a large set of metal–organic frameworks (MOFs) for the top-K in terms of their Henry coefficients for an adsorbate. A molecular simulation to predict the Henry coefficient of a MOF constitutes a Monte Carlo integration where each sample consists of inserting an adsorbate in the MOF at a random position, orientation, and configuration, then calculating the MOF–adsorbate interaction energy. Our idea is to leverage top-K arm identification algorithms, developed for the multi-armed bandit problem in reinforcement learning, to sequentially and adaptively allocate adsorbate insertions among the MOFs, in a data-driven manner, to obtain the most accurate top-K subset under a fixed insertion budget. By analogy, each MOF is a slot machine in a casino that, upon pulling its arm (inserting an adsorbate), offers a stochastic reward (a noisy estimate of its Henry coefficient) sampled from a static, unknown probability distribution. Each adaptive allocation algorithm (1) proceeds in a feedback loop of (i) allocate adsorbate insertions to MOF(s), (ii) update the running estimates of the Henry coefficients of the MOF(s), then (iii) judiciously allocate adsorbate insertions to the next MOF(s); (2) sequentially dials-up the fidelities of ongoing molecular simulations in the MOFs, giving a multifidelity computational screening; and (3) circumvents the need to hand-craft structural or chemical features of the MOFs for decision making. As a case study, we implement, benchmark, and analyze the sequential halving, successive accepts and rejects, and narrowing exploration (our proposed heuristic) algorithms to adaptively allocate xenon insertions to screen a set of ca. 300 MOFs for the top-K Xe Henry coefficient subset over differing insertion budgets. Provided with a sufficient budget, we find that these adaptive insertion algorithms can significantly reduce (by a factor of 2–3) the simple regret (sum of true minus empirical top-K true Henry coefficients) and error in the top-K subset of MOFs output by a computational screening. By another metric, adaptive insertion allocation provided a ca. 60% discount on the computational cost to identify the top-K MOFs with less than 5% error. We thereby demonstrate that top-K arm identification algorithms may generally be useful for more efficiently screening materials for various properties via Monte Carlo molecular simulations. This efficiency improvement is especially important when adopting more computationally expensive, sophisticated force fields or even ab initio calculations for the potential energy of configurations to lend higher-fidelity screenings.

pubs.acs.org

Conductive Covalent Organic Frameworks as Chemiresistive Sensor Arrays for the Detection and Differentiation of Gasotransmitters

This paper describes a chemiresistive sensor array using four structurally analogous, but chemically distinct, conductive covalent organic frameworks (COFs) (M-COF-DC-8, M = Fe, Co, Ni, and Cu) capable of detecting and differentiating four important gaseous analytes: nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H2S), and ammonia (NH3). The COFs were synthesized from the condensation of 2,3,9,10,16,17,23,24-octaamino-metallophthalocyanine precursors with pyrenetetraone linkers resulting in chemically robust and electrically conductive materials. Chemiresistive sensing experiments, together with machine learning to parse the response pattern of the sensor array, show that the M-COF-DC-8 (M = Fe, Co, Ni, Cu) materials can detect and differentiate this suite of oxidizing and reducing gases at parts-per-million concentrations, with theoretical limits of detection (LOD) in the parts-per-billion range in dry N2. Importantly, the COF array containing M-COF-DC-8 (M = Co, Ni, Cu) retains its ability to detect and differentiate these analytes in air and humidity under low power consumption. Spectroscopic investigations reveal that the synthetic control over the identity of the metallophthalocyanine core efficiently tunes material–analyte interactions and, therefore, emergent device performance. The use of highly tunable COFs as the active material in sensor arrays enables low-power, sensitive, and real-time gas detection with future applications in healthcare and personal protection.

pubs.acs.org

Optimizing Mixtures of Metal–Organic Frameworks for Robust and Bespoke Passive Atmospheric Water Harvesting

Atmospheric water harvesting (AWH) is a method to obtain clean water in remote or underdeveloped regions including, but not limited to, those with an arid or desert climate. For passive (i.e., relying...

pubs.acs.org

How a Puzzle About Fractions Got Brain Scans Rolling (Gift Article)

A story of bowling pins, patterns and medical miracles.

nytimes.com

Inferring the cross-sectional area profile of an unseen solid in a draining tank from liquid level dynamics

We aim to reconstruct the horizontal cross-sectional area profile of an exogenous, heavy, unseen solid contained in a tank from measurements of the li…

sciencedirect.com

The "Skeleton Flower" Turns From White to Translucent When Exposed to Water

The Diphelleia grayi or “Skeleton Flower” is finally a reason to look forward to rainy days. This rare flower transforms into a translucent beauty [its skeletal form] when exposed to water, its white ...

thisiscolossal.com