An IMI-NFG Outreach Activity

for Engaging Students in Glass Science

(Pre-College and even University) through

inquiry, participation and wonder

William R. Heffner & Himanshu Jain

International Materials Institute for Glass

Lehigh University, Bethlehem, PA

Exploring Glass and Material Science

through Candy and Common Materials

AAPT 2012 Winter Meeting Workshop

Ontario, CA February 5, 2012

Approach:

A collection of interrelated experiments using sugar glass (hard candy) – a material

that students can both make and use to explore many aspects of glass science.

Objectives and Approach of Program

Priorities: • low cost and within the resources of a typical high school student

• yet capture relevant and significant principles of glass science

• simple enough for the young student to perform independently

• interesting enough to hold their attention

• rich enough to mimic activities done by the material scientist

• developed by glass scientists and refined through student collaboration

• inter-related experiments for prolonged engagement & accumulated learning

•Available free to all on our website:

http://www.lehigh.edu/imi/

Primary Objective:

To engage young students with the glass science through a series of

hands-on activities with glass.

Outline of Experiments and Activities Today

• Overview of Sugar Glass System

• Material Synthesis – making of candy glass

• Pulling “glass” fibers and a fiber drawing tower

• Optical characterization

Refractive Index Measurement

• Density measurements

• Crystallization

Birefringence and Detecting Ordering

Mechanisms & growth rates in sugar glass

Crystallization in PET

• Glass Transition

Thermal Methods

Electrical conductivity

•Demonstration Videos - time permitting

For more experiments and details see IMI website:

http://www.lehigh.edu/imi/

Material Science – The Sucrose Water Phase Diagram

Student can construct the phase diagram using solubility, freezing point depression and

boiling point data for this system. See Mathlouthi and Reiser (ed.), Sucrose Properties and Applications (1995).

I II

III

high viscosity

xtals slow to form

=> considerable

metastable range

> 20% supersat.

Stable for hours

Material Science – The Sucrose Water Phase Diagram

Student can construct the phase diagram using solubility, freezing point depression and

boiling point data for this system. See Mathlouthi and Reiser (ed.), Sucrose Properties and Applications (1995).

I II

III

Heat to:

Dissolve

Boil to:

Reduce H2O

Cool quickly to

Avoid Xtals &

Make Glass

Material Science – The Sucrose Water Phase Diagram

Student can construct the phase diagram using solubility, freezing point depression and

boiling point data for this system. See Mathlouthi and Reiser (ed.), Sucrose Properties and Applications (1995).

I II

III

Heat to:

Dissolve

Boil to:

Reduce H2O

Cool quickly to

Make Glass

Avoid Xtals

Problem with Sucrose: Very prone to crystallization at low water content, even during cooking!

Recommend:

2:1 sucrose to corn syrup (by wt.)

for good glass with some crystal tendency 7

Example of how mixing allows tailoring performance of resulting glass

The Making of Hard Candy (Glass) – Material Synthesis

Phenomenological approach

Sucrose, Corn Syrup and Water are combined and

cooked-

• first to dissolve into a single liquid phase &

• then to remove most of the water.

Solution temp provides measure of the water content.

Boil to ~ 150° C.

Cost ~ $5 in materials

for many batches

Data from Food Industries Manual, 24th ed, (1997).

Drawing glassy “candy fibers” has never

failed to excite and captivate – whether young

(middle school), high school or even adult!

Typical Science Camp Activity or

Teacher Workshop

examples, properties and structure of glass

applications e.g. optics and fiber optics

making of candy glass

fiber pulling

Candy Glass – A Favorite for the Science Camp

Multiple camps and workshops have provided a wonderful testing ground for what works!

Fiber Drawing Tower – Mimics Optical Fiber Manufacturing Process

Opportunity to explore –

glass melting, visco-elasticity, heat transfer by radiation, and much more

L

a

m

p

20 W

L

a

m

p

20 W

Thermocouple

Probe

Dimmer

Switch

Voltage

Controller

Fiber Spool

(Plastic Jar)

Fixed or Sliding

Holder

Sugar Glass Rod

Monitor or Control

Heat input

Temperature

Draw rate

Candy Rod Preform heated by 20W Lamps

Estimated cost - $20 for Tower and lamps, $10 for dimmer switch control

Pfund’s Method

Refractive Index of Candy Glass via Pfund’s Method

Tara Schneider, REU(2005)

n=sqrt(d2+16h2)/d

Requires:

•Slab of candy glass ~ 1 cm thick

•laser pointer ($5.00)

•metric ruler or caliper ($10.00)

•ring stand and clamp to hold laser

With practice Tara was able to achieve a std dev of ~ 0.015 (~1%),

sufficient to see the index increase of candy glass with boiling temperature.

Easy Refractive Index of Flat Glass Pieces

Using a Gem Refractometer

Gem refractometers are now available for ~ $100

They provide a very quick and convenient

approach to measuring refractive index of

common glass items (slides, prisms, windows,

etc.) without any construction. Good for ~ 0.5%

accuracy.

Also based on total internal reflection at critical angle, so a good follow on to

Pfund’s experiment. Trick is the high index hemispherical lens in the unit.

Student Spectrometer for more accurate Refractive Index

Using the Min. Deviation Method

REU student Sean Kelley (2006) develops

method for making sugar glass prisms from

microscope slide molds and determining

index of refraction to four place precision.

index method provides σ ~ 0.0015 (0.1%)

No significant dependence of index on sucrose/ corn syrup ratio.

Candy Glass - Index vs Corn Syrup Content

1.510

1.515

1.520

1.525

1.530

1.535

1.540

1.545

1.550

0 20 40 60 80 100

Percent Corn Syrup

Ind

ex (

Avg

)

avg

Candy Glass - Index vs Corn Syrup Content

1.510

1.515

1.520

1.525

1.530

1.535

1.540

1.545

1.550

0 20 40 60 80 100

Percent Corn Syrup

Ind

ex (

Avg

)

avg-candy

Sucrose

±2σ

Having spectrometer, cost is a box of

microscope slides ($20) and epoxy ($3).

Specific Gravity = (wt of glass) / (wt of displaced water)

= (wt of glass) / {(wt of glass & water) – (wt of glass)}

Glass

water

water

fixed volume

Density Apparatus – Low Cost Student-built Pycnometer

Utilizes Centigram Balance – available in most high school labs

and salsa jar with hole and epoxied washer for stiffening - no other costs

For candy glass measurements must be made before candy dissolves (much).

REU, Sean Kelly (2006)

Polariscope constructed from two polarizing sheets can be used to demonstrate

the amorphous nature of glass compared to a ordered, birefringent solid such as

a quartz crystal.

Birefringence –Tool for Observing

Structure in Transparent Materials

Also flow induced order can be

demonstrated in glassy plastic.

Similar to method used by glass

blowers to check for residual

stress.

Glass slide –

only edges visible

Calcite Crystal –

very bright

at this orientation

Excellent Examples of Crystal Growth from Sugar Glass

Two Distinct Mechanisms

Interior Crystal Growth

From melt at elevated

temperatures

Surface Crystal Growth

At room temperature

with moisture (humidity)

microscope slides provide

convenient observation platform

Crystalization in 50% RH Chamber

(Recipe3)

0

2

4

6

8

10

12

0 5 10 15 20 25 30

days in 50% RH

Cry

sta

l w

idth

(m

m)

12/07 (143C)

12/05 (145C)

Quantitative Crystal Growth Expt. Moisture mediated surface crystallization at Room Temp

Need only: glass slides, camera,

ruler and 50% Rel. Humidity Jar

Growth of outer crystal ring

after 6 days at 50% RH

High School science project:

Awards at County Sci. Fair & Jr. Acad. of Sci.

Cookie jar with

sat. solution MgSO4

for 50% RH chamber

Batch A (143 C)

Batch B (145 C)

Rate =

0.4 mm/day

Student used Image J freeware and calculate crystal area.

Devitrification in Molten Solutions Finding the maximum crystal growth temperature

From NIH at: http://rsbweb.nih.gov/ij/ Oven cost ~ $20 with temp probe

T uniformity

± 1°C typical

Home-made Microscope Hot Stage

For existing lab microscope

- transmission & reflection

Uses 2-20W cylindrical heaters

and dimmer switch control

< $40 in cost

Photos taken through eyepiece

with hand held digital camera

& crossed polars.

Enhancing crystal growth studies in molten sugar solutions

75x mag 2.5X obj,

5x eyepiece 20x obj, 10x eye

Observing Crystal Growth (125 C)

20 min 50 min

Photographed at 100X magnification through eyepiece with hand held digital camera

Multiple Crystal Morphologies

Interesting range of crystal morphologies observed under higher magnification with home-built hot stage. Levenson and Hartel reported some of the same morphologies in their 2004 paper. D.A. Levenson, R.W. Hartel, Journal of Food Engineering, “Nucleation of amorphous sucrose-corn syrup mixtures”

Photographed at 200X magnification through eyepiece with hand held digital camera

Another Common Glassy material for Crystal Growth - PET

PET is one of the common plastic materials

used for beverage and other food packaging.

It can be identified by the recycling code 1.

• glassy state at room temperature

• Tg near 80 C

• easily observable crystallization near 135 C

• Tm ~ 220 C.

Demonstration of Crystallization from Amorphous PET

appearance to 130 C All white by 135 C )

Simple equipment includes:

GE Hotplate ($20, Wal-Mart)

Aluminum plate with hole drilled for

Thermocouple to monitor temperature

TC meter ($30, Harbor Freight)

Glass Petri Dish cover

Abrupt melting at 237 C

Crystallization occurs abruptly

near 132 C providing a great demo.

Crystallization in PET under microscopic examination

lamellar region in sharp contrast to sucrose crystallization Pre crystal

clear region

~8 u pitch

Milky crystal region

Lamella phase described well for students at

http://en.wikipedia.org/wiki/Crystallization_of_polymers

Getting a handle on the Glass Transition

Advantages

•Low Cost

•Student Assembled

•Can observe what’s happening

Bath

Temp

Differential

Temp, ΔT

Enabling student

to explore both:

Glass transition

Crystal Melting

and

Candy sample Reference

Beaker filled

with oil

Thermal Analysis (DTA) for the Home Experimenter

Observing Tg of Sugar Glass

$12

The Initial, Basic Student DTA •Hot Plate from the lab with

•digital cooking thermometer

•digital meter with TC probe ($30)

•two test tubes and beaker

•cooking oil and

•hand made holder

Our initial manual data:

The experimentalist can literally watch what

is taking place as T rises!

Provides student access to the glass

transition and opportunity to explore their

own curiosities.

Quickly stimulating desire for more data,

more experiments!

Improved DTA - Automated Data Collection

Adding Parallax Microcontroller

and thermocouple module provides

flexible, low cost data logging

solution for approximately $100.

Careful attention to thermal history

provide some excellent data.

Heating and Cooling Curves :

Stearic Acid a crystalline standard material

with moderately low melting point (~ 70 C).

Saucepan with

water & ice

Cooling Option Too!

Note: Tm identified with kink in

heating curve at ~ 70 C in

good agreement with literature

and comparison DSC.

Significant under-cooling

observed on the cooling scan.

Influence of Thermal History on DTA – Sugar Glass

Experiments illustrate

A) good repeatability with careful control of thermal history (long wait after quench)

B) large influence of changing thermal history (see 1 hr wait)

Both valuable hands on lessons for the student of glass sciences

PET chips cut from the top of a Nestle water bottle with oil to provide thermal

contact. Clear Tg near the 73° value from DSC as well as crystallization

exotherm near 135° C. Scans at ~ 10° C/min.

Tg

Txtal

Exo

Example Data – PET

Exo

Hand-made probe and ultra low current

amplifier capable of measuring

resistances in the100 G Ω range.

Designed with a $3 ultra low current IC

chip keeping total cost < $50.

Op Amps Open Additional Opportunities for the Experimenter

Electrical Conductivity Shows Signature of Tg

And a lot more ideas waiting to grow into quantitative experiments!

Summary

• Developed Curriculum of Hands-On Learning Activities to explore Glass Science

• Inter-related and build around candy glass & common materials materials synthesis physical property measurements crystal growth – both surface and from melts glass transition (DTA and conductivity)

• Designed to engage student in real glass science through hands on participation

• With quantitative results and open ended possibilities

• Tested and Student-hardened through Science Camps, Student Science Projects,

REU Activities and Teacher Workshops

• Leveraged through Website for open access & wide distribution

• An ongoing & growing effort – visit us often for exciting updates and Share your own ideas and thoughts!

http://www.lehigh.edu/imi/

Acknowledgements:

REU students:

Tara Schneider (2006), Sean Kelly (2007)

Sarah Horst (2009),

Nick Ward, Jordan Davis, Adam Kohn and Paul Sihelnik (2010)

High school students (science projects):

Jung Hyun (Gloria) Noh (2007, 2008)

Isha Jain (2001)

Sarah Wing – IMI-NFG Coordinator , video assistant and enthusiastic

supporter of all education and outreach

NSF’s International Materials Institute for New Functionality in Glass

(IMI-NFG): DMR-0409588 and DMR-0844014.

Demonstrations

Polariscope - Observing Order

in Transparent Materials (1:39)

Candy Fiber Drawing Tower (1:45)

Writing Crystals with Light (1:13) http://rm1.cc.lehigh.edu:8080/asxgen/dept/IMI/EdVideo/CrystalWriting_768.wmv

Questions and Comments