The Secret of Smart Paper

Abstract

In this Activity, students learn about special papers that use microencapsulation-such as grocery store receipts, carbonless lab notebooks, and some questionnaires-that they encounter every day. Students will perform a hands-on exploration of three-part carbonless copy paper, learning about the paper through their own personal observations. BackgroundNearly everyone has filled out a carbonless copy form. You write on one sheet, yet two, three, or more copies are produced. The technology of how carbonless copy paper works is the basis for this activity. The "secret" is that dye precursors coat the back of one paper sheet and the color developer (which changes the reactant from colorless to colored) coats the front of the next paper sheet. A microcapsule (3-8 µm diam, usually made of gelatin) houses the dye precursor, preventing the dye from turning color until mechanical force from a pencil or pen breaks open the microcapsule. (See ref 1 for animation.) The dye precursor generally reacts with acid to go from colorless to colored (2). Crystal violet lactone is a common precursor: upon reaction with acid, its phthalide bond breaks, changing the molecule's hybridization from sp 3 (tetrahedral) to sp 2 (planar) resulting in color formation (2, 3). The color developer is usually a clay (e.g., bentonite or attapulgite), which tends to produce hydrogen ions (3). For three-part carbonless copy paper the middle sheet is coated on both sides: the front with color developer, the back with microcapsules. A third sheet will be coated on the front with color developer. This pattern can continue to create many copies. In an analogous use, microcapsules are being tried to target medicine to certain diseased cells. For instance, in typical cancer treatment, toxic drugs are given that harm many cells in the body, leading to negative side effects (e.g., hair loss, and tingly, painful fingers). Targeting a drug to affect only cancer cells saves patients from many negative side effects. Integrating the Activity into Your CurriculumThis activity introduces encapsulation, specifically showing students how microencapsulation works and how it is useful for making identical copies without a photocopy machine. Students can discuss further applications for this technology and explore other ways this technology is used, such as in medicines (4) and scratch-and-sniff stickers.

JCE Classroom Activity #110: Artistic Anthocyanins and Acid–Base Chemistry

“…The papers can be cut into smaller pieces to allow students to practice before working on the larger pieces of paper. Excess cabbage juice liquid extract can be used as a liquid indicator for other related demonstrations. − …”

“…The pH conditions determine the protonation states of their ketone and hydroxyl substituents, which in turn leads to color changes. The use of anthocyanins from red cabbage juice has been previously reported for classroom activities in which students can visualize color changes that occur when the anthocyanins are exposed to different pH conditions. , More sophisticated possibilities include staining paper to have a desired color by using an anthocyanin solution with a particular pH value, dipping anthocyanin-stained paper into solutions with different pH values, and writing messages in invisible acid–base ink that are revealed when an anthocyanin solution is applied . In this activity, rather than staining paper with an anthocyanin solution or dipping the paper into solutions to change color, students are immersed in creating their own artworks on an easily prepared, dry anthocyanin-stained canvas using brushes with common colorless acids and bases as unconventional “paints”.…”

“…1,2 More sophisticated possibilities include staining paper to have a desired color by using an anthocyanin solution with a particular pH value, 3 dipping anthocyanin-stained paper into solutions with different pH values, 4 and writing messages in invisible acidÀbase ink that are revealed when an anthocyanin solution is applied. 5 In this activity, rather than staining paper with an anthocyanin solution or dipping the…”