Heat-Sensitive Color Changing Slime: A DIY Guide

Let's Make Heat-Sensitive Color Changing Slime

In this project of the experiments corner, we are making heat-sensitive color changing slime and gaining knowledge about the properties of thermochromic materials.

Let's Make Heat-Sensitive Color Changing Slime

Good to Know!
If you saw a cup that changes color when a hot drink is put in it, you would probably think it is an illusion. However, such a situation is possible. So what could be the scientific explanation behind materials changing color by themselves depending on temperature change? The answer lies in a special chemical substance: thermochromic material.

What is a Thermochromic Material?
A thermochromic material is a type of smart material that changes color due to temperature change.

Objects appear in different colors depending on which wavelengths of light they absorb and reflect. When the temperature of thermochromic materials changes, their chemical or physical structures also change. Thus, they absorb and reflect different wavelengths of light. Therefore, they appear in different colors at different temperatures. The color change can be reversible, meaning a material that changes color when heated can return to its original color when cooled, or the color change may be irreversible.

There are basically two types of thermochromic materials: liquid crystals used in cell phones and screens, and organic substances called leuco dyes. Let's first explain how liquid crystals change color when the temperature changes.

LCD

Liquid crystals are used in LCD screens.

Solid materials with a crystalline structure, for example ice, turn into liquid when melted. However, during this process, the crystalline structure loses its inherent characteristics. In some substances, there is a transition phase between the solid crystalline structure and the liquid structure. This transition phase is called liquid crystal. Liquid crystals are materials that continue to exhibit the properties of crystalline solids.

When the temperature of liquid crystals is increased, the gaps between the molecules expand. This causes the wavelength of the light reflected by the material when interacting with light to change. Therefore, the color of the material changes when the temperature changes.

Another type of material that changes color with temperature change is leuco dyes. To be able to change color depending on temperature change, leuco dyes are obtained by mixing different chemicals. Leuco dyes can have two different chemical structures, one colorless and the other colored. Other chemicals present in leuco dyes enable their chemical structure to switch between these two forms depending on temperature.

Thermochromic materials are materials with many uses. Color changing toys and fabrics, baby bottles indicating that the temperature has reached the proper level are some examples of thermochromic materials used in our daily lives. There are also studies to coat windows with thermochromic materials to reduce heat loss.

In addition to these materials that change color depending on temperature, there are also materials that change color with different factors such as pH, electricity and mechanics. Promising studies are being carried out on the use of these materials, called chromic, in the development of next generation biosensors and early diagnosis of diseases such as Alzheimer's, Parkinson's and cancer.

What Do We Need?

PVA glue
Borax
Thermochromic powder
Glass jar
Heat resistant cup
Teaspoon
Tablespoon
Water
Heater

What Are We Doing?


What Happened?

When the slime we made using thermochromic material came into contact with the cup containing warm water, the chemical structure of the thermochromic substance in the slime changed under the effect of heat at the point of contact. The color of the thermochromic material we added to the slime was dark purple at room temperature. When we brought the slime into contact with the warm cup, the change in the chemical structure of the thermochromic material caused it to reflect the wavelengths that make up light purple tones, and the color of the slime turned light purple. As we removed the slime from the cup, while the temperature of the contacted part was decreasing, the chemical structure of the thermochromic material returned to its initial state. Thus, the color of the slime became dark purple as it was initially.

You can learn how slime is made and the reason behind its interesting properties from our previous Let's Make Slime activity.

Let's Think!
In what other situations can we use materials that can change color depending on temperature?