be dispersed in the oil or water phase and is functional over a
broad pH range.
“Consumer perception depends on lubricity,”explained Rhyta
Rounds of Fluid Dynamics, who provided an overview of lubricity measurements. But she also reminded the audience that the
consumer’s skin covers a broad range of moduli that depends,
among other things, on age, health and diet. Rounds explained
how lubricity analyzers are used in lubricity tests and provided
data demonstrating how two moisturizing lotions behave very
differently on skin.
Daphne Benderly, Presperse, provided attendees with a look
at how other industries view rheology. For example, viscosity
plays a critical role in engine oil development, with a high viscosity index meaning a relatively small change of viscosity with
temperature. In the coatings industry, shear rate is critical, since
a thin paint is easier to apply, but drips more. Therefore, chemists study shear-thinning behavior to design paints that are thick
enough not to drip and thin enough to spread easily. Benderly
concluded her presentation by noting that concepts and measurement techniques from other industries are transferable to the
Christina Teng of Princeton University explained how foams
could be employed for nanoparticle delivery. Inspired by whipped
cream, her team developed temperature-responsive foams that
contained cetyl alcohol, stearyl alcohol, polysorbate 60, propylene
glycol, an active ingredient, potassium hydroxide and water.
According to Teng, foam volume is greatly affected by ethanol concentration and just a small window of ethanol concentrations produce acceptable foams. She explained how Tween 20
produced higher foam volumes compared to Tween 60 and 80, as
well as PEG and PVA.
Yield stress; i.e., the stress above which a material flows, plays
a key role in product stability, processing and sensory characteristics, noted Jeffrey Martin of Johnson & Johnson. He reviewed
various test methods including flow curve, steady shear and amplitude sweep, before recommending researchers use amplitude
sweep (0.1-1 rad/s) as it is fast, easy and robust without requiring
How Does It Feel?
How it flows is one thing; more important is the relationship between rheological properties and skin feel, which was the topic of
a presentation by Geng Li of Energizer, who defined the skin feel
index and spectrum descriptive analysis. Li also gave attendees
new things to think about when developing products.
He explained that psycho-rheology, a term coined by M.R.
Wegener of Bristol University in 1997, is the study of the relationship between rheological and sensory properties of a material.
Via predictive modeling, psychorheological studies predict what
sensory characteristics and attributes appeal to the consumer.
“This saves time and money and makes product screening
faster,” insisted Li.
The speaker also described how Brummer’s window could be
a useful tool to not only predict a product’s skin feeling but also
to fulfill the consumer’s expectations.
Gail Vance Civille, Sensory Spectrum, reminded the audience
that when making rheological measurements, they must start
with the consumer—and was quick to assert that sensory measurements using panelists is a real science. Sensory properties are
the characteristics perceived through the senses, she explained,
and not the liking or preference of products.
“We sometimes think that consumers aren’t very bright,” observed Civille.“I just think that we don’t ask the right questions.”
“They can provide rich data for product development and
marketing,” Civille noted.
Bharath Rajaram, TA Instruments, reviewed the rheological
characterization of personal care products by detailing three different test methods: Tribology; interfacial rheology and orthogonal superposition. Tribology, the study of interacting surfaces in
relative motion, can be used to study solid and liquid lubrication;
lubricating oils and greases; friction, wear and surface damage;
and surface modifications and coatings, explained Rajaram. As a
result, tribology has a wide range of applications in the personal
care industry. He explained how researchers can use interfacial
rheology to compare such diverse products as makeup removers and hair sprays. Finally, orthogonal superposition enables researchers to monitor structural changes in materials, according
The Power of Polymers
But not all numbers are equal, warned Nava Dayan of Dr. Nava
“Interpretation of data can be far from the truth,” she warned
the audience.“We all arrive with different backgrounds.”
Dayan noted that study design, protocol and cells used can
greatly modify results. She warned that infinite dosing may not
reflect in use conditions and that thicker formulations may some-
times enhance the penetration of topical agents when applied
Joe Albanese, 3V