Nondestructive In Situ Detection of Chemical Reactions at the Buried Interface between Polyurethane and Isocyanate-Based Primer

Zhang, Shuqing; Andre, John S.; Hsu, Lorraine; Toolis, Amy; Esarey, Samuel L.; Chen, Zhan

doi:10.1021/acs.macromol.0c01862

Cited by 30 publications

(38 citation statements)

References 74 publications

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“…Figure displays the SFG spectra collected from the primer surface in the wavenumber region of 2050–2400 cm –1 using the ppp and ssp polarization combinations of the input laser beams and the output signal beam. A distinct peak around 2250 cm –1 was observed in each spectrum, which is assigned to the characteristic NCO stretching signal . In Figure a and b, a noticeable decrease in terms of the intensity of this peak in both the ssp and the ppp spectra was observed from the primer surface with 4-h exposure to the atmosphere compared to that with no atmosphere exposure.…”

Section: Resultsmentioning

confidence: 87%

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Investigation of the Atmospheric Moisture Effect on the Molecular Behavior of an Isocyanate-Based Primer Surface

et al. 2021

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A primer coating is engineered to facilitate compatibility between products like adhesives, sealants, and potting compounds and targeted substrates. Prolonged exposure of isocyanate-based primer surfaces to the environment is known to negatively affect the interfacial adhesion between itself and the products subsequently applied on top of it. However, the molecular behavior behind this observed phenomenon remained to be further investigated. In this study, sum frequency generation (SFG) vibrational spectroscopy, a nonlinear optical spectroscopic technique, was applied to study the surface of an isocyanate-based primer exposed to different environments at the molecular level. Atmospheric moisture was considered to be a potential factor in impairing the adhesion performance of the primer, and thus, time-and humidity-dependent experiments were executed to monitor the molecular behavior at the primer surface using SFG. In addition, 180°peel testing experiments were conducted to measure the adhesion properties of primers after being exposed to the corresponding conditions to correlate to SFG results and establish a chemical structure−macroscopic performance relationship. This study on the changes at the primer surface in different environments with varied humidity levels as a function of time aims to provide an in-depth understanding of the moisture effect on isocyanatebased primers. These learnings may also be helpful toward exploring a broader range of coatings and surface layers and improving customer product use guidelines.

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Section: Resultsmentioning

confidence: 87%

“…Our lab previously researched the mechanism of the adhesion enhancement at the interface between an isocyanate-based primer and a polyurethane potting compound . The research confirmed the formation of chemical bonding at the buried primer/potting compound interface, which contributed to the enhanced adhesion performance.…”

Section: Introductionmentioning

confidence: 80%

Investigation of the Atmospheric Moisture Effect on the Molecular Behavior of an Isocyanate-Based Primer Surface

et al. 2021

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“…In this research, we applied sum frequency generation (SFG) vibrational spectroscopy to study the molecular structure at the buried graphene/PT interfaces. SFG is a coherent, second-order nonlinear optical spectroscopy that utilizes the chemical selectivity of IR and Raman spectroscopies to detect molecular structures including functional group orientation at a medium where the inversion symmetry is broken. − In a typical SFG experiment, a visible laser beam with a fixed frequency and a frequency-tunable IR beam overlap both spatially and temporally at the sample interface where two photons are combined; a third photon with the sum of the two input photons’ energies is generated. According to the selection rules of SFG spectroscopy, only a medium with no inversion symmetry can generate an SFG signal under the electric-dipole approximation. ,,,,, In the bulk environment, most of the polymer molecules are randomly distributed and thus form an isotropic sample that possesses inversion symmetry, which will not generate an SFG signal.…”

Section: Introductionmentioning

confidence: 99%

Molecular Orientations at Buried Conducting Polymer/Graphene Interfaces

Guo

et al. 2021

Macromolecules

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Graphene and semiconducting polymers have been extensively researched for use in many microelectronic devices. For both devices with layered structures and graphene–semiconducting polymer composite materials, molecular interactions between graphene and semiconducting polymers play significant roles in determining the interfacial properties and impact the device performance. In this research, molecular orientations of polymer backbones of three polythiophenes (PTs) with different side-chain lengths at the buried PT/graphene interfaces were determined using sum frequency generation (SFG) vibrational spectroscopy. It was found that the longer the PT side chain, the larger the PT backbone tilt angle measured. Therefore, the PT backbone with a longer side-chain length adopts a more lying-down pose on graphene. The same trend for orientation tilt angles of PTs with different side-chain lengths at PT/CaF2 interfaces was observed. When comparing the same PT backbone orientation, PT at the PT/graphene interface generally lies down more compared to that at the PT/CaF2 interface, due to stronger π–π interactions between the PT backbone conjugated rings and graphene. The different PT backbone orientations at interfaces are likely caused by varied interactions between the PT backbone and the substrate and between side chains and the substrate, as well as intermolecular and intramolecular interactions between PT molecules (including side chains and backbones). The determination of PT backbone orientations at buried interfaces helps to understand molecular interactions at these interfaces, aiding in the design of polymer/graphene interfaces with optimal structure and improved properties.

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“…This study used a commercial SFG spectrometer from EKSPLA and all the SFG spectra were collected using ssp (s-polarized sum frequency signal, s-polarized input green beam, and p-polarized IR beam) polarization combinations. [78][79][80] In this work, to collect SFG spectra, right-angle CaF 2 prisms (Altos Photonics, Bozeman, MT) were used as substrates. PI and DIP materials used for SFG study were prepared by dissolving 1 g of the appropriate PDMS and the calculated amount of salt based on stoichiometry in separate 5 mL aliquots tetrahydrofuron (THF).…”

Section: Methodsmentioning

confidence: 99%

Enabling Tunable Water‐Responsive Surface Adaptation of PDMS via Metal–Ligand Coordinated Dynamic Networks

Zhang

Crisci

Finlay

et al. 2022

Adv Materials Inter

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emerging as an enabling technology. [1][2][3][4] The combination of flexibility and responsiveness allows applications in various fields, including wearable electronics, soft robotics, drug delivery, biomedical devices, and biomimetic design. [5][6][7][8][9][10] Among various material options, polymers play an essential role in fabricating flexible sensors and soft actuators due to their tailorability and the potential of integrating multiple functionalities, such as adaptive response to signals (e.g., chemical, mechanical, electrical), energy harvesting and storage, and biochemical sensing. [3,10] Adding responsive functionality to a polymer often involves methods such as copolymerizing monomers with different capability, attaching layers of active materials to a polymer matrix, building in molecular orientation or internal polarization, introducing structural heterogeneity by combining amorphous and crystalline domain or multi-layer assembly, and preparing composites by hybridizing organic and inorganic materials. [2,[11][12][13][14] Among various techniques, utilizing dynamic chemistry to enable polymer responsivity has received significant attention in the past few decades. [15,16] Reversible interactions, including dynamic covalent bonding, hydrogen bonding, ionic bonding, π-π stacking, and metal-ligand coordination, are susceptible to environmental variation and can achieve multiple physical and chemical responses via bond breaking and reforming. [17][18][19][20][21] Fascinating material properties arise from disrupting the equilibrium state of dynamic bonding, for example: polymers with spiropyran go through force-induced covalent-bond activation and give rise to visible color and fluorescence; supramolecular polymers containing metal-ligand motifs can self-heal by exposing to ultraviolet irradiation; and polymers functionalized by self-complementary hydrogen bonded ureidopyrimidinone (UPy) moieties shows shape-memory effect through temperature change. [22][23][24] Among these options, metal-ligand coordination bonding is particularly appealing to realize a particular desired response, because of the ease of tuning the stability of the bond.One of the most popular polymers for fabricating sensors and actuators is polydimethylsiloxane (PDMS). [2,7] It commonly serves as an essential substrate or a responsive component due to the attractive physical and chemical properties, including low Polymers are at the core of emerging flexible sensor and soft actuator technology. Ideal candidates not only respond to external stimuli but also have programmable response intensity and speed. Incorporating dynamic interactions into polymers has been widely studied. However, most research has focused on synthesis methods and on optical and mechanical effects of these interactions. Here, a new and tunable method of enabling environmentally adaptive polymers are introduced. Specifically, polar functionalities are "hidden" within polydimethylsiloxane (PDMS). When unveiled, these polar functionalities change the hydrophilicity ...

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Nondestructive In Situ Detection of Chemical Reactions at the Buried Interface between Polyurethane and Isocyanate-Based Primer

Cited by 30 publications

References 74 publications

Investigation of the Atmospheric Moisture Effect on the Molecular Behavior of an Isocyanate-Based Primer Surface

Investigation of the Atmospheric Moisture Effect on the Molecular Behavior of an Isocyanate-Based Primer Surface

Molecular Orientations at Buried Conducting Polymer/Graphene Interfaces

Enabling Tunable Water‐Responsive Surface Adaptation of PDMS via Metal–Ligand Coordinated Dynamic Networks

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