Overview

• Grade Level: AP Chemistry / AP Environmental Science / Engineering / History of Science (grades 10-12)

• Time Required: Single class (45 minutes); bell-ringer option (10 minutes); extension (2 additional class periods)

• Historical Period: 1941-1948, Maria Telkes at MIT and the US Office of Scientific Research and Development during World War II, and the postwar scaling to permanent solar desalination installations

• Modern Connection: The 30 May 2026 Light: Science and Applications paper (vol. 15, art. 246) by Chunlei Guo's group at the University of Rochester's Institute of Optics, demonstrating a femtosecond-laser-etched superwicking black-metal panel that performs solar desalination with approximately 100 percent salt recovery in solid form, eliminating the hyper-saline brine waste stream that has constrained industrial desalination since the 1960s

Learning Objectives

Students will be able to:

1. Describe Maria Telkes's wartime solar-still design, including the inflatable plastic envelope, the principle of evaporation-and-condensation, and the deployment of the device as standard equipment on US Navy lifeboats by 1944.

1. Explain in their own words why conventional reverse-osmosis and thermal-distillation desalination plants produce a hyper-saline brine waste stream and what ecological problems result from discharging that brine into coastal waters.

1. Summarise the experimental design and key findings of the 2026 Light: Science and Applications paper, including the femtosecond-laser-etched black-metal surface, the coffee-ring-effect-driven salt migration, the approximately 100 percent salt recovery in solid form, and the proposed use of the recovered solid as a feedstock for battery-grade lithium and other minerals.

1. Construct an argument about whether the Rochester laser-textured-surface approach represents a fundamentally new technology or an engineering refinement of Telkes's 1942 wartime concept, distinguishing the underlying physics from the engineering implementation.

Before Reading

Anticipation Questions

1. Seawater is approximately 3.5 percent dissolved salt by mass. If you wanted to extract a litre of fresh water from a kilogram of seawater, how much salt would you have to do something with? Predict three possible fates for that salt and rank them by environmental damage.

1. The Telkes solar still was deployed on US Navy lifeboats by 1944 and is credited with saving 'several thousand' lives. What does it mean for an engineering decision (the choice to put a still on every lifeboat) to save thousands of lives without anyone tracking who exactly was saved?

1. The 'coffee ring effect' is the brown rim left at the edge of a dried coffee spill. Where else in everyday life have you seen this effect, and what does it tell you about the physics of evaporation at the edge of a thin liquid film?

Key Vocabulary

• Solar still: A device that uses sunlight to evaporate water from a saline source, condense the fresh-water vapour on a cooler surface, and collect the condensate, leaving the dissolved salts behind.

• Desalination: The general process of removing dissolved salts from seawater or brackish water to produce fresh water. Industrial methods include reverse osmosis, thermal distillation, and solar thermal.

• Reverse osmosis: A pressure-driven membrane filtration process in which seawater is forced at high pressure through a semipermeable membrane that allows water molecules through but rejects dissolved salt ions. The dominant industrial desalination method since the 1980s.

• Brine: The hyper-saline concentrated waste stream produced by conventional desalination plants. Typically discharged back into the ocean near the plant, where it sinks, concentrates locally, and damages marine ecosystems.

• Femtosecond laser: A laser that emits pulses on a femtosecond (10^-15 second) timescale, used to ablate or texture material surfaces with extreme precision and minimal thermal damage to surrounding regions.

• Superwicking: A surface property in which a liquid spreads across the surface as a thin film by capillary action against gravity, much faster than ordinary capillary wetting.

• Coffee-ring effect: The fluid-dynamical phenomenon in which solid suspended particles are deposited at the perimeter of an evaporating droplet of suspension, characterised in a 1997 Nature paper by Deegan and colleagues at the University of Chicago.

• Battery-grade lithium: Lithium of sufficient purity (typically 99.5 percent or higher) and crystal form to be used in lithium-ion battery cathodes, currently a constraint on grid-scale battery manufacture.

During Reading

Guided Questions

1. Identify the date and the institutional context in which Maria Telkes was assigned to design a portable solar still. Why was the US Office of Scientific Research and Development willing to fund the project?

1. Describe in your own words the physical-chemistry principle that makes a solar still work. Why is sunlight required (rather than, say, a hot plate)?

1. Trace the engineering scaling of the Telkes still from a single-survivor inflatable balloon (1942) to a permanent installation in the US Virgin Islands (postwar). What engineering questions had to be answered at each step?

1. Identify the lead author and institution of the 2026 Light: Science and Applications paper. What is a femtosecond laser, and what does it do to the metal panel?

1. The Rochester paper achieves approximately 100 percent salt recovery in solid form. What is the conventional fate of dissolved salts in industrial desalination, and why is the solid-recovery alternative significant?

After Reading

Discussion Questions

1. The story argues that the 'thermodynamics is identical' between the Telkes balloon and the Rochester panel, while 'the engineering shift is in what happens to the salt.' Is this distinction useful for understanding what counts as a scientific breakthrough? Defend your position.

1. (Genuinely debatable.) Industrial desalination has been constrained by the brine problem since the 1960s. The Rochester device is currently a laboratory demonstration. What kind of evidence would convince you that the Rochester approach can scale to deployment? Pick a milestone and defend it.

1. Telkes is sometimes called the founder of solar thermal energy storage and was nicknamed 'The Sun Queen,' yet she is much less famous in the popular history of science than her male contemporaries. Why might that be, and is the gap closing?

1. The Rochester paper notes that the recovered salt is mineral-rich enough to be a candidate source of battery-grade lithium. If desalination plants in the 2030s also become lithium mines, what does that mean for how cities and regions plan their water and energy infrastructure?

1. The OSRD assigned Telkes to design the still because soldiers were dying. The Rochester team designs theirs to solve an ecological waste-disposal problem. What does that say about how engineering priorities evolve between wartime and peacetime?

The Parallel

1. List the structural features that are similar between Telkes's 1942 wartime solar still and the 2026 Rochester laser-etched panel. List the features that are different. Which list is longer, and which is more important?

1. Both halves of the story rely on the same physical-chemistry principle (evaporation-condensation separation of water from dissolved salt). What technological refinements between 1942 and 2026 made the 100-percent-salt-recovery industrial-scale version possible?

1. Could there be an analogous 'wartime invention, peacetime mineral-recovery rebirth' story in a different field? Suggest one example (radar, nylon, synthetic ammonia, penicillin, nuclear power) and defend it.

Activities

Bell-Ringer (10 minutes)

Project two images side by side: a wartime photograph of Maria Telkes's inflatable plastic solar still in the hand of a Navy testing officer (or the patent diagram) and a contemporary photograph of the Rochester laser-textured black-metal panel with visible salt-deposit migration on the panel surface. Ask students: 'These two devices, 84 years apart, do the same thing. What is it? And what is different about how they do it?' Have them write two sentences. Use the responses to introduce the lesson.

Single Class (45 minutes)

• 0 to 5 minutes: Bell-ringer recap.

• 5 to 18 minutes: Read the historical half of the story aloud. Students fill out a guided-reading organiser with three columns: 'Telkes's background and MIT appointment,' 'The OSRD wartime assignment,' 'The 1944 deployment and postwar scaling.'

• 18 to 32 minutes: Read the modern half aloud. Students extend the organiser with two more columns: 'Femtosecond-laser-etched surface and superwicking' and '100 percent salt recovery and mineral-feedstock proposition.'

• 32 to 42 minutes: Whole-class four-corners discussion of After Reading question 1 (is the engineering-versus-physics distinction useful). Students move to a corner marked 'A breakthrough has to be physics,' 'Engineering is its own breakthrough,' 'The distinction is artificial,' or 'It depends on what you mean by breakthrough.'

• 42 to 45 minutes: Exit ticket. One sentence: 'The most important difference between the 1942 still and the 2026 panel is: ___.'

Extension Activity

Solar-engineering essay (3 to 5 pages, two class periods): students pick one Telkes invention (the wartime solar still, the Dover Sun House solar-heated home, the solar oven, the night-air cooling system) and write a structured essay describing the physical-chemistry principle it relied on, the wartime or postwar problem it was designed to solve, the engineering refinements that allowed it to scale, and the modern descendants that build on the same principle. Citation of at least three primary or near-primary sources required.

Primary Source Connections

• Maria Telkes, "Distilling Water with Sunshine," Distillation / various wartime OSRD technical reports (1942-1944). Type: technical engineering report. The original wartime documentation of the solar-still design and deployment.

• Maria Telkes, "Solar Heat Storage," Journal of Solar Energy Science and Engineering (1949) and related postwar papers. Type: scientific publication. The postwar foundational papers in solar thermal storage.

• Eleanor Raymond and Maria Telkes, the Dover Sun House (1948), Dover, Massachusetts. Type: surviving built environment. The first solar-heated house, designed by Raymond with thermal storage by Telkes.

• Chunlei Guo et al., "Mineral-rich additive-free solar desalination without brine," Light: Science and Applications 15 (2026), article 246. Type: peer-reviewed paper. Open access.

• The Maria Telkes papers, held at the Schlesinger Library at the Radcliffe Institute for Advanced Study, Harvard University. Type: institutional archive.

• The PBS American Experience documentary 'The Sun Queen' (2023). Type: biographical documentary. The most accessible popular synthesis of Telkes's life and work.

Standards Alignment

C3 Framework

• Dimension 1 (Developing Questions): Compelling question: 'How does an engineering innovation move from a wartime single-survivor application to a peacetime industrial-scale solution, and what does the path tell us about the relationship between physics and engineering?' Supporting questions about the role of national-emergency funding, gender and immigration in mid-twentieth-century US science, and the constraints on industrial-scale desalination.

• Dimension 2 (Applying Concepts): Chemistry (evaporation-condensation thermodynamics, solubility, crystallisation). Engineering (laser surface texturing, capillary wetting, material durability). Environmental science (marine pollution from brine outfalls, the desalination plant as point source).

• Dimension 3 (Evaluating Sources): The story is accompanied by a populated evidence manifest with twelve verified claims and direct source URLs.

• Dimension 4 (Communicating Conclusions): The structured four-corners discussion and the extension essay both require sustained argumentation and source evaluation.

AP Alignment

• AP Chemistry: Big Idea 5 (Reactions) and Big Idea 6 (Bond energies and enthalpy). Phase transitions, the energetics of evaporation, solubility products of mineral salts.

• AP Environmental Science: Unit 6 (Energy Resources and Consumption) and Unit 8 (Aquatic and Terrestrial Pollution). The brine-discharge problem, solar thermal energy, water-resource engineering.

• AP Physics: Unit 4 (Thermodynamics). Heat of vaporisation, blackbody absorption of solar radiation.

• AP Research / AP History of Science: A case study in how a single physical-chemistry principle moves through eighty years of engineering refinement.