Whitepapers
Silicone's Hydrophilic Properties
NuSil recently completed a characterization of some preliminary materials
and found promising results regarding hydrophilic properties.
Silicone polymers are made up of repeating siloxane units (R2SiO). This
polymeric structure allows polysiloxanes to be modified to suit a variety
of applications. The R-substituent groups control the polymer’s chemical
and physical properties.
Contact Angle (CA) is the measure of the angle between the substrate surface
and the line tangent from the droplet to the touch of the surface. The
time-dependent CA for absorbent materials continuously changes as a function
of time, as the water wets out and/or penetrates into the surface.
The methods used in this characterization comprised curing each
silicone gel onto a glass slide. Then, a 6µL drop of water was dispensed
onto the gel surface and the angle was measured using a Ramé-hart
Model 200 goniometer at the gel/air interface at regular time
intervals for 180 seconds. Each test was performed in triplicate,
and the average CA for each time point was then plotted and compared for
each gel.
Results
-
Angle > 90 degrees at initial point of contact reveals
the hydrophobic element of the polymer matrix.
-
Dramatic increase in CA exposes the hydrophilic element
of PEO-modified polymer.
-
Final CA is well within the hydrophilic range (angle < 90
degrees).
The conclusion of the preliminary testing demonstrates the dynamic CA yields
data that clearly distinguishes between silicone types, as well
as the fact that PEO has complex surface effects with water.
Full information can be found here.
We are beginning Phase 2, which focuses on varying the hydrophilic constituents
and characterizing those materials.
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to MyNuSil or register for MyNuSil.
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Silicone Materials Series
Troubleshooting Silicone Materials Series:
Silicone Inhibition
Silicones are formulated to cure with a number of catalysts. Each catalyst
requires a certain set of conditions to cure, and these conditions are
typically included on the product profile or data sheet. Silicones can
contain chemical entities, known as cure inhibitors, which are added by
the manufacturer to adjust pot life (working time) and curing time. Again,
the cure conditions provided by the manufacturer account for these inhibitors
as a way to achieve complete cure.
Material preparation, device components and/or assembly processes can,
at times, compromise the cure of silicones. These “poisoning” effects
can range from a slight surface tack to a complete cure failure. Some inhibition
can be overcome, while other types permanently arrest cure. Tin-catalyzed
acetoxy cure adhesives are inhibited by isopropyl alcohol (a cleaning solvent
often used in medical device manufacturing). Once the alcohol is removed,
the cure proceeds.
The platinum catalyst used in addition-cured silicones is susceptible
to poisoning. Although there are many substances that can cause cure poisoning,
the following list includes many of the most common poisons:
- Sulfur-containing materials
- Rubber
- Latex
- Neoprene
- Buna N
- Natural rubber
- Polysulfides
- Sulfur compounds
- Organotin containing materials
- Condensation-cured silicones
- Acetoxy-cured silicones
- Oxime-cured silicones
- Plasticizers
- Other
- Plasticized polyvinyl chloride
- Plastisols
- Adhesive tapes
- Some amino groups
Curing a small amount of silicone in contact with a questionable material
can be an effective way to evaluate potential poisoning effects.
The next
troubleshooting article will focus on some process diagnostics
that can be useful in determining the source of the inhibition.
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New Products & Developments
RTV Gel Expands NuSil’s Line of Healthcare Silicone Materials
NuSil recently launched an extension to its line of healthcare gels. MED-6381
is ideal for use in healthcare applications that require an unfilled, room-temperature
vulcanizing (RTV) material.
The low cure temperature of this material makes it ideal for incorporating
heat-sensitive additives such as pharmaceutical compounds, biocides,
excipients and other functional fillers. The MED-6381 firm RTV gel cures
without heat and is filler-free. In addition, this pourable, three-component
gel can be molded or used as a soft, conformal coating.
NuSil’s MED-6381 is available in one-pint packaging. For more information,
visit www.nusil.com or call 805-684-8780.
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