Efficient removal of particulates from a rough surface
with a soft material through a “press and peel” method
(i.e., an adhesion and release approach) depends on good conformal
contact at the interface; a material should be sufficiently soft to
maximize contact with a particle while also conforming to rough surface
features to clean the entire substrate surface. Here, we investigate
the use of bottlebrush networksextremely soft elastomers composed
of macromolecules with polymeric side chainsas materials for
cleaning model substrates of varying roughness. Formed through free-radical
polymerization of mono- and dimethacrylate functionalized polysiloxanes,
these solvent-free supersoft elastomers exhibit moduli comparable
to those of solvated gels, allowing for a lower moduli regime of elastomers
to be used in contact experiments than previously possible. By varying
the macromonomer to cross-linker ratio, we study the effect of modulus
on conformal contact and cleaning for materials that are as soft as
gels while minimizing/negating physical and/or chemical concerns that
using a traditional material may involve (e.g., changes in component
concentrations, solvent evaporation, and syneresis). We study cleaning
efficacy by quantifying the conformal contact between soft materials
and rough substrates via a contact adhesion-based measurement. These
results give insight into the correlation between shear modulus and
conformal contact with surfaces of varying feature height. Not only
does a decrease in shear modulus leads to improved conformal contact
with rough surfaces, but also it facilitates adhesion to particulates
situated on the rough surface, thus aiding removal. We highlight this
property control with a case study illustrating the removal of an
artificial soil mixture from a rough, acrylic surface via peeling
rather than rubbing, which can cause damage to delicate surfaces.
We have developed soft, peelable organogels from 40% hydrolyzed poly(vinyl acetate) (40PVAc) and benzene-1,4-diboronic acid (BDBA). The organic liquids gelated include dimethyl sulfoxide, dimethylformamide, tetrahydrofuran, 2-ethoxyethanol, and methanol. The rheology of these soft materials can be tuned by altering the concentration of the polymer and/or crosslinker. Insights into the mechanisms leading to gelation were obtained from H NMR experiments, fluorescence measurements, and studies comparing properties of materials made from BDBA and phenylboronic acid, a molecule incapable of forming covalent crosslinks between the polymer chains. These organogels can be easily peeled off a surface, leaving no residue detectable by UV-vis spectroscopy. They are demonstrated to be effective at softening and removing deteriorated coatings from water-sensitive works of art and delicate surfaces. They have the needed characteristics to clean topographically complex surfaces: good contact with the surface, easy removal, and little to no residue after removal. A 2-ethoxyethanol organogel was used to remove oxidized varnish from a 16th century reliquary decorated with painted gold leaf, and an ethanol gel was used to remove solvent-resistant coatings from 16th and 18th century oil paintings.
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