3 research outputs found
Polydopamine and Polydopamine–Silane Hybrid Surface Treatments in Structural Adhesive Applications
Numerous studies
have focused on the remarkable adhesive properties
of polydopamine, which can bind to substrates with a wide range of
surface energies, even under aqueous conditions. This behavior suggests
that polydopamine may be an attractive option as a surface treatment
in structural bonding applications, where good bond durability is
required. Here, we assessed polydopamine as a surface treatment for
bonding aluminum plates with an epoxy resin. A model epoxy adhesive
consisting of diglycidyl ether of bisphenol A (DGEBA) and Jeffamine
D230 polyetheramine was employed, and lap shear measurements (ASTM
D1002 10) were made (i) under dry conditions to examine initial bond
strength and (ii) after exposure to hot/wet (63 °C in water for
14 days) conditions to assess bond durability. Surprisingly, our results
showed that polydopamine alone as a surface treatment provided no
benefit beyond that obtained by exposing the substrates to an alkaline
solution of tris buffer used for the deposition of polydopamine. This
implies that polydopamine has a potential Achilles’ heel, namely,
the formation of a weak boundary layer that was identified using X-ray
photoelectron spectroscopy (XPS) of the fractured surfaces. In fact,
for longer deposition times (2.5 and 18 h), the tris buffer-treated
surface outperformed the polydopamine surface treatments, suggesting
that tris buffer plays a unique role in improving adhesive performance
even in the absence of polydopamine. We further showed that the use
of polydopamine–3-aminopropyltriethoxysilane (APTES) hybrid
surface treatments provided significant improvements in bond durability
at extended deposition times relative to both polydopamine and an
untreated control
Expanded Functionality of Polymers Prepared Using Metal-Free Ring-Opening Metathesis Polymerization
Photoredox-mediated
metal-free ring-opening metathesis polymerization
(MF-ROMP) is an alternative to traditional metal-mediated ROMP that
avoids the use of transition metal initiators while also enabling
temporal control over the polymerization. Herein, we explore the effect
of various additives on the success of the polymerization in order
to optimize reaction protocols and identify new functionalized monomers
that can be utilized in MF-ROMP. The use of protected alcohol monomers
allows for homo- and copolymers to be prepared that contain functionality
beyond simple alkyl groups. Several other functional groups are also
tolerated to varying degrees and offer insight into future directions
for expansion of monomer scope
Synthesis and Characterization of Aminopropyltriethoxysilane-Polydopamine Coatings
Polydopamine
coatings are of interest due to the fact that they
can promote adhesion to a broad range of materials and can enable
a variety of applications. However, the polydopamine–substrate
interaction is often noncovalent. To broaden the potential applications
of polydopamine, we show the incorporation of 3-aminopropyltriethoxysilane
(APTES), a traditional coupling agent capable of covalent bonding
to a broad range of organic and inorganic surfaces, into polydopamine
coatings. High energy X-ray photoelectron spectroscopy (HE-XPS), conventional
XPS, near-edge X-ray absorption fine structure (NEXAFS), Fourier transform
infrared-attenuated total reflectance (FTIR-ATR), and ellipsometry
measurements were used to investigate changes in coating chemistry
and thickness, which suggest covalent incorporation of APTES into
polydopamine. These coatings can be deposited either in Tris buffer
or by using an aqueous APTES solution as a buffer without Tris. APTES–dopamine
hydrochloride deposition from solutions with molar ratios between
0:1 and 10:1 allowed us to control the coating composition across
a broad range