PDMS elastomer surfaces

Plasma treatment of PDMS followed by adsorption of self-assembled silane monolayers has enabled us to controllably modify the surface energy of elastomer surfaces as described in the section on the Johnson, Kendall, and Roberts approach to deriving the surface free energy of solids. A similar treatment of silicon substrates has produced a useful, low—hysteresis model substrate for contact angle study. There are three types of PDMS contact angle substrates usually studied fluids baked or otherwise chemisorbed on solids such as glass or metals cross-linked coatings on flexible substrates, such as paper or plastic film PDMS elastomer surfaces. 

For many applications, it is desirable that the adhesive layer accept printable elements readily in its fully cured state. This characteristic usually requires the layer to be soft in its cured form. Adhesive thin films composed of low-modulus PDMS elastomer meet this requirement well18 and can guide transfer of elements to a target quickly (without exposure to heat or light). Surprisingly, the direction of transfer can be well defined even when the composition of the adhesive is identical to that of the stamp. Successful transfer is thus determined by several factors surface chemistry, conformability (modulus), geometrical/mechanical factors (e.g., adhesive film thickness), and others. 

In order to homogenize the elastomer surface properties, thermal aging of PDMS was sometimes carried out (at 115°C for 12 h) [170]. 

Fig. 11. Normalised enhanced adhesive strength wyw as a function of the surface density, a, for two PDMS elastomers in contact with silicon wafers covered with irreversibly adsorbed chains. Wis the thermodynamic work of adhesion, W=2y, with ythe surface tension of PDMS, 7=21.6 mN m"1 at 25 °C. The filled symbols correspond to a molecular weight between crosslinks in the elastomer Mc=24.2 kg mol-1 while Mc=10.2 kg mol-1 for the open symbols. The adhesive strength, G, has been measured by peel tests performed at a very low velocity of the propagation of fracture, 0.17 im/s. The molecular weight of the surface anchored chains is Mw=242 kg mol-1...

The adhesion between PDMS chains irreversibly adsorbed on silica and crosslinked PDMS elastomers has been investigated in a systematic way in our group [118-120] over a wider range of surface densities than in the early work by... 

Fig. 16. Universal curve giving the enhanced adhesive strength, G-W, normalized by the optimum enhanced adhesive strength, Gopt-W, as a function of the normalized surface density, G/aopt (o0pt is the surface density leading to the maximum adhesive strength) for different irreversibly adsorbed PDMS layers in contact with PDMS elastomers. Peel tests with a fracture velocity of 0.017 pm/s have been used to measure G. The molecular weights of the surface chains, Mw and the molecular weights between crosslinks of the elastomers, Mc, are the following ...

To make samples for the adhesion experiments, a crosslinked PDMS elastomer substrate was oxidized by a 30 min exposure to UV/ozone [21-24], using a Jelight Company Model 42 UVO-Cleaner. A thin layer of polystyrene (M = 38000 g mol ) with a trimethoxysilyl end group was spin-cast onto this oxidized elastomer from a solution in toluene. These functionalized chains were grafted onto the oxidized PDMS surface by annealing for 1.5 h at 125 °C, and the excess polystyrene chains were removed by rinsing the sample in toluene... 

J.Y Park, D. Ahn, YY Choi, C.M. Hwang, S. Takayama, S.H. Lee, S. Lee, Surface chemistry modifications of PDMS elastomers with boiling water improves cellular adhesion. Sens. Actuators B 173 (2012)765-771. 

Fumed silica is widely used for the reinforcement of polydimethylsiloxane (PDMS) elastomers. The intermolecular interaction of the filler surface with the PDMS matrix controls this process [1, 2] so that understanding which factors influence the interaction at the filler/PDMS interface has become a crucial point for further development of the technology. Among the factors of interest there are the... 

Emulsions play a role in some aspects of polysiloxane technology. Polymerization has been carried out in emulsions, " and room temperature-cured PDMS elastomers have been obtained from aqueous dispersions. PolyCvinyl pyrrolidone) dispersions have been prepared in reactive PDMS media. Microemulsions containing PDMS also find use in applications such as cosmetics. One novel study involved a surfactant solution in a polysiloxane, droplets of which bounced on a vertically vibrated liquid surface. When the amplitude of the vibration exceeded a threshold value, a polysiloxane-water-polysiloxane double emulsion was formed ... 

Whether bonded or physically adsorbed or embedded, surface polymers dangle from the polymer surface, as do the chains in any PDMS elastomer. Such chains are important with regard to mechanical properties such as adhesion, adhesion hysteresis, and tack ( stickiness ). Their rheological and dielectric behavior have been modeled using molecular dynamics. ... 

Self-healing is often used in a broader sense, to mean reconstruction of the entire polymer instead of just its surface. A relevant example here is a PDMS elastomer that contains microencapsulated PDMS resin and microencapsulated cross linker. If this type of PDMS is damaged, both capsules rupture and the newly formed elastomer mends the damaged area. 

PDMS elastomer that reports localized compression by force-induced ring opening of spiropyran. The elastomer was subjected to (a) tension, and (b-d) rolling of patterned objects across its surface. 

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