"The beaker is crying."
Kana looked at glassware with water droplets.
Toma laughed. "It's just water remaining."
Rei approached. "But how it 'remains' is the problem."
"What do you mean?"
"Look," Rei showed another beaker. "This one has water flowing as a film."
"This one has droplets remaining."
Kana compared. "You're right. What's different?"
"Hydrophilic and hydrophobic," Rei explained.
"Hydrophilic is water-friendly. Hydrophobic dislikes water."
Toma supplemented. "Glass is naturally hydrophilic."
"But when dirty, it becomes hydrophobic."
Kana wrote in her notebook. "Dirt = hydrophobic substance?"
"Oil and organic matter," Rei answered. "Repel water."
Milia entered the room. "Talking about interfacial chemistry?"
"Yeah. How to wash glass."
Milia nodded. "Basic for experiments, but deep."
Kana asked. "Why is hydrophilic good?"
Rei explained. "Remaining droplets cause errors in next experiment."
"If it flows as film, it dries completely."
Toma added. "Droplets might contain residues from previous experiment."
"Contamination."
Milia took out detergent. "Wash with this."
"Surfactant."
Kana was interested. "How does it work?"
Milia drew a molecular model. "One end is hydrophilic, the other hydrophobic."
"Amphiphilic molecule."
Rei continued. "Hydrophobic end sticks to oil dirt."
"Hydrophilic end faces water."
"Oil appears to dissolve in water."
Kana understood. "It's a mediator."
Toma proposed an experiment. "Let's actually wash."
Put detergent water in dirty beaker.
Shaking it, foam formed.
"Foam wraps around dirt," Milia explained.
Rinsing, water flowed as a film.
"Clean," Kana was impressed.
Rei showed another method. "There's also acid washing."
"Chromic-sulfuric acid mixture."
Toma warned. "Dangerous though."
"But completely oxidizes organic matter."
Milia supplemented. "Last resort."
Kana asked. "Other ways to make it hydrophilic?"
"Plasma treatment," Rei answered. "Activates surface."
"Silane coupling," Milia added.
"Silane?"
"Silicon compound. Chemically bonds to glass surface."
Rei explained. "Used when wanting hydrophobic."
"Wait, the reverse too?" Kana was surprised.
"Depends on case," Toma said. "Like water-repellent coating."
Milia organized. "Controlling interface properties is interfacial chemistry."
"Can choose hydrophilic or hydrophobic."
Kana thought. "So the crying beaker had become hydrophobic?"
"Likely had oil contamination," Rei diagnosed.
"If washed with detergent?"
"It heals," Toma laughed.
Kana actually washed it. Rinsed with water.
This time, no droplets remained.
"It stopped crying."
Milia smiled. "Glass is honest."
"Surface condition is immediately visible."
Rei added. "That's why pre-experiment cleaning is important."
"Accurate data comes from clean equipment."
Toma became philosophical. "Chemistry is particular about details."
"Small dirt creates large errors."
Kana held glassware to the light. "Transparent and clean."
"This is proof of hydrophilicity."
Milia said finally. "Surface chemistry is invisible but important."
"One molecular layer difference changes properties."
Rei supplemented. "The nanometer world."
"But affects macroscopic results."
Kana began cleaning up. "I'll wash more carefully from now on."
Toma agreed. "Won't make beakers cry."
Outside the window, rain was falling. Water droplets flowed on glass. Proof of hydrophilicity.