+ Site Statistics
+ Search Articles
+ Subscribe to Site Feeds
Most Shared
PDF Full Text
+ PDF Full Text
Request PDF Full Text
+ Follow Us
Follow on Facebook
Follow on Twitter
Follow on LinkedIn
+ Translate
+ Recently Requested

Sticky or Slippery Wetting: Network Formation Conditions Can Provide a One-Way Street for Water Flow on Platinum-cured Silicone

Sticky or Slippery Wetting: Network Formation Conditions Can Provide a One-Way Street for Water Flow on Platinum-cured Silicone

Acs Applied Materials and Interfaces 8(22): 14252-14262

In the course of studies on Sylgard 184 (S-PDMS), we discovered strong effects on receding contact angles (CAs), θrec, while cure conditions have little effect on advancing CAs. Network formation at high temperatures resulted in high θadv of 115-120° and high θrec ≥ 80°. After network formation at low temperatures (≤25 °C), θadv was still high but θrec was 30-50°. Uncertainty about compositional effects on wetting behavior resulted in similar experiments with a model D(V)D(H) silicone elastomer (Pt-PDMS) composed of a vinyl-terminated poly(dimethylsiloxane) (PDMS) base and a polymeric hydromethylsilane cross-linker. Again, network formation at high temperature (∼100 °C) resulted in high CAs, while low-temperature curing retained high advancing CAs but gave low receding CAs (θrec 30-50°). These changes in receding CAs translate to strong effects on water adhesion, wp, which is the actual work required to separate a liquid (water) from a surface: wp ∝ (1 + θrec). When the values θrec 84° for high-temperature and θrec 50° for low-temperature network formation are used, wp is ∼1.5 times higher for curing at low temperature. The origin of low receding contact angles was investigated by attenuated total reflectance IR spectroscopy. Absorptions for Si-OH hydrogen-bonded to water (3350 cm(-1)) were stronger for low- versus high-temperature curing. This result is attributed to faster hydrosilylation during curing at higher temperatures that consumes Si-H before autoxidation to Si-OH. Sharp bands at 3750 and 3690 cm(-1) due to isolated -Si-OH are more prominent for Pt-PDMS than those for S-PDMS, which may be due to an effect of functionalized nanofiller. To explore the impact of wp on water droplet flow, gradient coatings of S-PDMS and Pt-PDMS elastomers were prepared by coating a slide, maintaining opposite ends at high and low temperatures and thus forming a thermal gradient. When the slide was tilted, a droplet moved easily on the high-temperature end (slippery surface) but became pinned at the low-temperature end (sticky surface) and did not move when the slide was rotated 180°. The surface was therefore a "one-way street" for water droplet flow. Theory provides fundamental understanding for slippery/sticky behavior for gradient S-PDMS and Pt-PDMS coatings. A model for network formation is based on hydrosilylation at high temperature and condensation curing of Si-OH from autoxidation of Si-H at low temperatures. In summary, network formation conditions strongly affect receding contact angles and water adhesion for Sylgard 184 and the filler-free mimic Pt-PDMS. These findings suggest careful control of curing conditions is important to silicones used in microfluidic devices or as biomedical materials. Network-forming conditions also impact bulk mechanical properties for Sylgard 184, but the range that can be obtained has not been critically examined for specific applications.

(PDF emailed within 0-6 h: $19.90)

Accession: 058905267

Download citation: RISBibTeXText

PMID: 27175918

DOI: 10.1021/acsami.6b02066

Related references

Effect of wetting conditions and flow rate on bubble formation at orifices submerged in water. Colloids and Surfaces A: Physicochemical and Engineering Aspects 290(1-3): 41-49, 2006

Slippery and Sticky Graphene in Water. Acs Nano 2019, 2019

Surface science and wetting dynamics of hydrosilation- and alkoxysilane-cured polydimethylsiloxane and relevance to silicone biomedical applications. Abstracts of Papers American Chemical Society 223(1-2): POLY 279, 2002

Slippery or sticky boundary conditions: control of wrinkling in metal-capped thin polymer films by selective adhesion to substrates. Physical Review Letters 99(18): 188302, 2007

Designing robust alumina nanowires-on-nanopores structures: superhydrophobic surfaces with slippery or sticky water adhesion. Journal of Colloid and Interface Science 409: 18-24, 2013

Street Orientation and Side of the Street Greatly Influence the Microclimatic Benefits Street Trees Can Provide in Summer. Journal of Environmental Quality 45(1): 167-174, 2018

Interaction between perfluorcarbon liquid and heavy silicone oil: risk factor for "sticky oil" formation. Current Eye Research 37(7): 563-566, 2012

Study of wetting at the silicone oil/water/fibre interface. Colloids and Surfaces A: Physicochemical and Engineering Aspects 147(3): 317-329, 1999

A cleaning solution for silicone intraocular lenses: "sticky silicone oil". British Journal of Ophthalmology 92(11): 1522-1527, 2008

Slippery to Sticky Transition of Hydrophobic Nanochannels. Nano Letters 15(11): 7497-7502, 2015

Forming Sticky Droplets from Slippery Polymer Zwitterions. Advanced Materials 29(38), 2017

Colour changes of light-cured composite resin after exposure to water and photographic wetting agent. Restorative Dentistry 7(2): 38-39, 1991

Sticky Places in Slippery Space: A Typology of Industrial Districts. Economic Geography 72(3): 293-313, 1996

The nucleosome: a transparent, slippery, sticky and yet stable DNA-protein complex. European Physical Journal. E, Soft Matter 19(3): 251-262, 2006

Biomimetic polyimide nanotube arrays with slippery or sticky superhydrophobicity. Journal of Colloid and Interface Science 344(2): 541-546, 2010