Everyone knows that if you spill water on your pants they get wet. Well, not if the pants have been treated with a stain repellent finish. The dramatic differences in behavior between stain resistant and untreated 100% cotton fabrics have been used to develop a scientific discovery activity suitable for audiences ranging from elementary school students to adults. The activity demonstrates how changes in the 100% cotton fabric that are too small to see or feel can make big differences in how the fabric performs.

One of the most high profile trends in textile finishing is the addition of stain repellent properties to cotton fabrics. These finishes, in combination with wrinkle resistant finishes, appeared first in men’s business casual pants and have spread to children’s pants, women’s pants and shirts for both men and women. Aggressive advertising by apparel manufacturers has insured high public awareness of the benefits of garments made with stain repellent finishes.

The science behind how these finishes work is interesting from two viewpoints. First, the differences in treated and untreated fabrics are too small to be seen by eye or even with all but the most sophisticated microscopy techniques. For this reason, many of the garments are labeled with trade names including the word ‘nano’ and may be the general public’s closest contact with nanotechnology. Secondly, these fabrics demonstrate principles of surface energy and wetting very dramatically in contrast with untreated 100% cotton fabrics. While untreated 100% cotton is highly absorbent, 100% cotton fabric treated for stain repellence is not wettable by most common liquids.

This paper provides instructions for a scientific inquiry activity and suggestions on tailoring the activity to a wide range of audiences. Since most people have experience with fabrics and staining in everyday life, participants were able to relate to the activity immediately.

Materials and Methods:

Materials:
100% cotton twill fabrics (bottom weight):
-1 treated with stain resistant finish, grey. Donated by VF Corporation.
-1 untreated, khaki. Purchased at JoAnn Fabrics
Staining materials such as:
-Grape juice
-Kool-aid®
-Spaghetti sauce
-Mustard
-Chocolate Sauce
-Ketchup
-Water – either running water or in squirt bottles

Method:
Cut both the treated and the untreated fabric samples into 4 inch by 4 inch squares with pinking shears. Make enough samples for each participant to have one square of each fabric. Transfer staining materials to low flow dropper/squirt bottles to minimize mess. Retain the original containers as part of the display for the activity. Cover the work surface with newspaper or a waterproof table cloth to facilitate clean up. A dishpan full of warm soapy water and several wash clothes were supplied as well.

Supply each participant with a piece of untreated and a piece of stain resistant fabric and asked the participant to identify any differences that they can see or feel between the materials. Ask the participants what will happen if they spill something on the fabrics. For more formal/classroom settings, explain that this is the hypothesis – what a scientist predicts will happen. Next, invite participants to put a few drops of any of the stain materials that they choose onto the fabrics and observe the results. Liquids such as water, grape juice, or salad oil will bead up on the treated fabric and roll off if the fabric is tilted. These same liquids will soak into the untreated cotton fabric immediately. Figure 1 is a worksheet that was used with third graders.

Explain the differences between the two materials. The detail of the explanation will depend on the audience but should emphasize that a treatment has been added to the fabric at a level that is too small to see or feel. Since it is so small and has such a large affect, this treatment is truly an example of nanotechnology. The size scale of the material involved in the treatment is about 1/1000th of the size of the cotton fibers. The treatment is similar to the coating on a non-stick frying in that nothing sticks to it. If we were able to see the treatment, it would look like tiny whiskers sticking off of the surface of the cotton fibers. For more sophisticated audiences, concepts of covalent bonding to durably attach the treatment to the surface and surface chemistry can be incorporated.

Depending on the time available participants can now try additional stains. All liquid materials will bead up and roll off the treated fabric. Sometimes drops of liquid will even bounce off the treated fabric. Encourage participants to leave thicker staining materials such as ketchup, mustard, or chocolate sauce on both fabrics for a few minutes. These sauces will not bead up on the fabric because they are too viscous. On the untreated cotton, however, a stain will start to form around where the sauce was dropped as water and oils wick into the fabric. This will not happen on the treated fabric. The sauces will not roll off the treated fabrics, but can be chased off with a stream of water from a squirt bottle or a tap. If participants attempt to wipe the sauces off of the treated fabrics, the wiping motion can actually grind the sauces into the fabric and cause a stain. Grinding some stains in can provide further evidence that the stain resistant coating is comprised of fine whiskers. If a sauce gets past the whiskers by being ground in by wiping it is difficult to remove.

Figure 2: Co-Author Catherine Jordan and Cornell University Textile and Apparel students hosting the stain resistant fabric exploration during the American Chemical Society 2004 National Chemical Week mall event.

RESULTS AND DISCUSSION:

IInitial trials of this experiment were conducted in three settings: during ACS chemistry week at a local shopping mall event (Fig.1) and during Prof. Frey’s research group meeting with a group of 6 graduate and undergraduate students and in a 3rd grade classroom with 20 8-10 year olds. The experiment was easy for all participants to grasp and overall, participants seemed to enjoy interacting with the fabrics and staining materials. The experiment was also essentially self adapting to the participants level of interest. Some rushing mall shoppers were satisfied by squirting a little grape juice on to the fabric and marveling that it rolled off of the stain repellent sample while graduate students were determined to test the limits of repellency and found additional staining materials to test. Third graders were also interested in trying some of their classroom materials and juices from their lunch boxes on the fabrics. The experiment did turn out to be messy and low flow bottles for staining materials were very important in preventing younger participants from staining their own clothing.

The experiment was highly repeatable: grape juice always beaded on the treated fabric and always spread on the untreated fabric. The experiment also allowed for a variety of levels of inquiry. Participants could investigate a range of liquid materials from water based to oil based and also a range of viscosity from water thin to paste-like. Highly viscous materials like mustard that could not bead up to minimize contact with the stain resistant fabric would stain the fabric if they were ground in, but could be washed off the fabric by running water.

CONCLUSIONS:
Anecdotally, many participants were able to relate this experience back to their own experiences. Younger children were familiar with being scolded for spilling things onto their clothing. Adults were familiar with stains in laundry, stains making clothes unwearable and the immediate embarrassment of spending the day with a splash of morning coffee on your shirt. This activity could be followed up with activities on detergency and stain removal for more detailed study of textile behavior.

It was difficult to measure the accuracy of information taken away from this activity, particularly in the very informal mall setting. We are optimistic, however, that our participants have an increased appreciation for how textile finishing processes can dramatically change garment properties. The experiment was easy to set up and run. Leaders could be trained very rapidly. All materials were safe to handle and inexpensive except for the treated fabric. The treated fabric is not currently readily available in fabric stores. The one drawback to this experiment is that it can be messy and potentially stain participants clothing.

http://www.nanotex.com/
Microscopic revolution, Textile Month, October, 2003 p. 10-12.
http://www.vfc.com/