Paper Humidity Sensor With PEDOT:PSS Films

ISEF Category: Chemistry

Subcategory: Materials Chemistry  ·  Difficulty: Intermediate  ·  Setup: School Lab  ·  Time: 1 to 2 Months

The Hook

A thin film can act like a tiny weather reporter. Change the humidity, and its electrical behavior can shift fast. That makes paper-based conductive films a smart target for a low-cost sensor project. You can test how a simple additive changes that response.

What Is It?

PEDOT:PSS is a conductive polymer blend. That sounds fancy, but the idea is simple. You coat a paper strip with a material that can carry charge, then watch how well it conducts electricity when the air gets wetter. Think of it like a road for electrons. If the road gets wider, smoother, or more connected, current moves more easily.

Sorbitol is a secondary dopant, which means it helps change how the conductive material forms a film. In this project, you are not just asking whether the film conducts. You are asking how humidity changes that conductivity, and whether sorbitol makes the sensor more sensitive, more stable, or both. That gives you a real materials science question, not just a demo.

Why This Is a Good Topic

This is a strong science fair topic because you can change one material variable, measure a clear electrical response, and compare it across humidity conditions. The project connects to real needs like low-cost environmental sensing, smart packaging, and flexible electronics. You can learn film preparation, resistance measurement, calibration, data cleaning, and basic modeling without needing a full research lab.

Research Questions

• How does sorbitol concentration affect the conductivity of PEDOT:PSS films on paper?
• What is the effect of relative humidity on the resistance of PEDOT:PSS paper films?
• Does adding sorbitol change the sensitivity of PEDOT:PSS films to humidity?
• To what extent does paper type change the humidity response of PEDOT:PSS films?
• Which drying condition gives the most stable conductivity after humidity cycling?
• How does repeated humidity exposure affect the reversibility of the film's electrical response?
• To what extent does film thickness change the slope of the conductivity versus humidity curve?

Basic Materials

• PEDOT:PSS aqueous dispersion with product data sheet.
• Sorbitol powder or solution.
• Plain printer paper, cardstock, and filter paper for substrate comparison.
• Conductive silver paint or copper tape for contacts.
• Digital multimeter with resistance measurement.
• Ruler or calipers for measuring electrode spacing.
• Digital kitchen scale with 0.1 g accuracy.
• Small spray bottle or pipette for film deposition.
• Clear storage container with lid for simple humidity chamber.
• Hygrometer for checking relative humidity.
• Thermometer for room conditions.
• Notebook or spreadsheet for recording readings.

Advanced Materials

• Four-point probe setup or spring-loaded probe heads.
• Source measure unit or benchtop multimeter with stable current mode.
• Precision humidity chamber or sealed chamber with humidity control packs.
• Lab balance with 0.001 g accuracy.
• Hot plate or drying oven with controlled settings.
• Surface profiler or optical microscope for film uniformity checks.
• Contact angle tool if available for substrate wetting studies.
• SEM or AFM access for film morphology if your school can support it.
• Fresh PEDOT:PSS batches with and without additives for repeatability testing.

Software & Tools

• Python: Fits calibration curves, runs finite-difference models, and compares humidity response across samples.
• Google Sheets: Organizes raw resistance, humidity, and replicate data for quick plotting.
• Jupyter Notebook: Keeps code, notes, and graphs in one place for modeling and analysis.
• ImageJ: Measures film coverage, crack patterns, or drop-cast area from photos.
• SciPy: Helps with curve fitting, regression, and basic statistical tests.

Experiment Steps

1. Define the main variable you will change, such as sorbitol level, paper type, or film thickness.
2. Choose one electrical signal to track, then decide how you will convert raw resistance into a comparable metric.
3. Plan a humidity calibration method that gives you multiple stable humidity points and a clear control sample.
4. Design electrode geometry and film layout so every sample has the same measurement path.
5. Build a data model that predicts how humidity should alter conductivity, then test whether your measurements match it.
6. Set up repeat trials and cycling tests so you can judge sensitivity, drift, and reversibility.

Common Pitfalls

• Using uneven drop-cast films, which creates patchy conductivity and hides the real humidity effect.
• Measuring with loose or shifting contacts, which adds contact resistance that looks like a film change.
• Letting paper absorb water differently from sample to sample, which confuses humidity response with substrate swelling.
• Comparing readings before the film reaches equilibrium, which makes the sensor seem more sensitive than it really is.
• Skipping a blank or baseline sample, which makes it hard to tell whether sorbitol improved the film or just changed the starting resistance.

What Makes This Competitive

A stronger project will do more than show that resistance changes with humidity. You can stand out by separating film effects from contact effects, comparing multiple substrates, and using a real calibration curve with error bars. A Python model that predicts the trend, then explains where the data bends or drifts, adds depth. If you also test reversibility and long-term stability, your project starts to look like sensor research, not a classroom demo.

Project Variations

• Test different paper substrates, such as printer paper, filter paper, and coated paper, to see how porosity changes humidity response.
• Compare sorbitol with another benign additive, such as glycerol, to study how the dopant changes conductivity and recovery.
• Add a modeling angle by fitting your data to a diffusion or percolation-based curve and checking which model best matches the sensor behavior.

Learn More

• PubMed: Search review articles on PEDOT:PSS films, humidity sensors, and conductive polymers.
• NIH PubChem: Look up sorbitol and related additives for safety, structure, and basic chemical properties.
• NIST Chemistry WebBook: Check reference data and measurement terms used in materials analysis.
• MIT OpenCourseWare: Search materials science and electrical measurement lectures for background on conductivity and thin films.
• Synthetic Metals: Search for peer-reviewed articles on PEDOT:PSS film structure, doping, and sensing behavior.
• NOAA National Centers for Environmental Information: Use humidity and climate data ideas to think about real-world sensor applications.