Supplementary Material
A. Materials
The formulations for three lab-scale gums are indicated in Table S1. These were created
in order to directly compare the rheological fingerprint of commercial chewing and bubble gum
with materials of known compositions. Additionally, a commercially available confectionary
wax, Wack-o-wax Mr. Stache (available at http://shop.tootsie.com), was utilized for certain
studies and is referred to as “W1.”
Table S1. Formulations of lab scale gums
Sample
Base
Calcium
carbonate
Sorbitol
Glycerine
Medium
Chain
Triglycerides
Flavorings
wt%
V1
40%
---
57%
3%
---
---
V2
30%
10%
55%
3%
---
2%
V3
30%
5%
55%
3%
5%
2%
B. Results
1. Thermal Characterization
Thermal analysis was conducted on two representative gum bases – a chewing gum base
and a bubble gum base – using a Thermal Analysis Q1000 DSC (TA Instruments). The DSC
traces upon second heating at a ramp rate of 10 °C/min are shown in Figure S1a below,
confirming the presence of a thermal transition between 30 °C and 40 °C that appears mostly
crystalline. We also performed DSC on some of the pure components of the gum bases such as
poly(isobutylene), low and high molecular weight poly(vinyl acetate) (PVAc), and rosin esters,
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the traces of which are shown in Figure S1b. For the PVAc and rosin esters, a clear glass
transition temperature can be seen in this same temperature window between 30 °C and 40 °C.
Figure S1. Differential scanning calorimetry (DSC) curves upon second heating at a ramp rate of 10 °C/min for a) a
chewing gum base and a bubble gum base and b) low molecular weight poly(isobutylene) (PIB), low and high molecular
weight poly(vinyl acetate) (PVAc), and rosin esters. The gum bases show thermal transitions between 30 °C and 40 °C
that appear predominately crystalline, while the PVAc and rosin esters show glass transitions in this same temperature
window.
2. Linear Viscoelasticity
Strain sweeps of chewing and bubble gums were conducted at frequencies of 0.05 rad/s
and 500 rad/s to target the low and high frequency regimes, respectively. The results for C1 are
shown in Figure S2. In the low frequency regime, C1 demonstrated a higher critical strain
(0.37%) than in the high frequency regime (0.07%), although in both frequency regimes, the
linear region is rather small as discussed in the body of the paper.
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Figure S2. Storage and loss moduli for chewing gum C1 measured during small amplitude oscillatory shear. The
critical strain is defined as the strain at which G' decreases by 10%. At both low and high frequencies, the critical
strain was found to be < 0.5%.
The elastic moduli of all chewing gums, bubble gums, lab-scale gums, and the wax at
three different frequencies are shown in Figure S3. This data was obtained during LAOS tests at
strains that were well within the linear region; hence, only three data points per sample were
collected. Although somewhat sparse, this data demonstrates two key features: 1) at a given
frequency, the elastic modulus deviates by over a magnitude between commercial products
without large deviations in sensory feel or performance and 2) all samples behave like critical
gels.
Finally, Figure S4 demonstrates that in shear creep conducted over 100 s at a stress of
100 Pa, all chewing and bubble gums show similar responses. Further testing must be done to
verify these are in the linear regime.
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Figure S3. Storage modulus versus frequency for chewing gums, bubble gums, lab-scale gums, and wax.
3. Nonlinear Viscoelasticity
Here we provide supplementary results to compare chewing gums, bubble gums, labscale gums, and a commercial wax in a series of rheological tests that probe nonlinearity in shear
and extension. Figure S5 shows results for start-up of steady shear at a constant shear rate of
1.732 s−1 for all samples but V3. Once a constant strain rate was achieved, all chewing and
bubble gums have relatively constant viscosities, ranging from 1000 to 6000 Pa-s, until the point
of edge failure. Conversely, the lab-scale gums and wax demonstrate higher viscosities (> 8000
Pa-s), and the viscosities of V1 and W1 decrease with time. The latter observation was attributed
to both yielding and slip.
Figure S6 shows the LAOS response of all chewing gums, bubble gums, lab-scale gums,
and the wax at the frequency  = 1 rad/s in terms of the first-harmonic (cycle-averaged) complex
modulus, G1* . As noted in the body of the paper, all samples show a nonlinear, monotonic
decrease of both elasticity and dissipation, but we only plot G1* for the sake of simplicity.
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The start-up of steady uniaxial extension was deemed a key attribute in differentiating
between chewing and bubble gums. Chewing gums failed at extensional stresses ≤ 2.0x106 Pa-s
while most bubble gums withstood higher stresses (> 2.0x106 Pa-s) with similar strains at break.
Additionally, both chewing and bubble gums strain hardened leading up to the failure point. The
responses of V1, V2, and W1 are shown in Figure S7 for comparison. Sample V1 shows
qualitatively similar extensional behavior to the chewing and bubble gums with strain hardening
and a high strain at break. Conversely, W1 yielded almost immediately, strain softened, and
broke at a Hencky strain of ~ 0.4. V2 showed a combination of these two behaviors – yielding
and strain softening at lower strains, yet strain hardening close to a large strain at break (ε ~ 5.4).
Figure S4. Shear creep results of chewing and bubble gums at a stress of 100 Pa showing critical gel-like behavior
for all samples. Inconsistencies at times < 0.04 s (denoted by the dotted line) are attributed to finite start-up time of
the instrument.
C. Fitting
The dynamic frequency data for C1 and B1 were fit to the Rouse and critical gel models by first
fitting the critical gel equation to G  for ω < 10 rad/s and using equation 2 in the main text to
calculate G  . Then, we minimized the following equation using the Microsoft Excel Solver tool:
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log(R )  log(D  G )
2
i
i
i
(S1)
i
In equation S1, Di is the experimental data point (for either G  or G  ) at a frequency i and Ri
and Gi are the Rouse and critical gel model fits at this frequency, respectively.
Figure S5. Transient viscosity measured during start-up of steady shear for chewing gums, bubble gums, lab scale
gums, and wax at a Hencky strain rate of 1.732 s−1. Experimental concerns included yielding, slip, and edge failure.
Inconsistencies at times < 0.04 s (denoted by the dotted line) are attributed to finite start-up time of the instrument.
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Figure S6. 1st harmonic average moduli for chewing gums, bubble gums, lab-scale gums and wax measured during
*
large amplitude oscillatory shear. The relative values of G1 change in the nonlinear viscoelastic regime.
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Figure S7. Transient extensional viscosity measured during start-up of steady uniaxial extension for lab scale
gums and wax at a Hencky strain rate of 1 s−1. The lab scale gums and waxes show distinct behavior from the
chewing and bubble gums. Inconsistencies at times < 0.04 s (denoted by the dotted line) are attributed to finite
start-up time of the instrument.
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