Publications

Kiple, L.,  Lee, T.,  Zavaglia, G.,  Meldrum, T.  Characterization of molecular environments and chemical exchange in acrylic paints via single-sided NMR. Prog. Org. Coat. 2023, 183, 107770. https://doi.org/10.1016/j.porgcoat.2023.107770

Abstract: Both oil and acrylic paints consist of pigments bound within a polymeric network; however, acrylic paints dry by evaporation of aqueous solvent, rather than curing chemically like oil paints. In this study, we used single-sided ¹H NMR relaxometry to characterize the molecular environments in both dry and wet acrylic paints by their molecular mobilities. We measured the transverse relaxation behaviors of paints with various pigment concentrations and conducted T₂–T₂ correlation measurements on wet paint to monitor exchange. In dry paint, we identified two transverse relaxation behaviors, indicating regions of greater and lesser mobility, which we attributed to amorphous and crystalline domains of the semi-crystalline acrylic polymer in the film. These polymer domains were not affected by pigment concentration. In wet paint, we characterized two different relaxation behaviors, which we hypothesize to originate from unique molecular environments in the acrylic binding medium. Additionally, we characterized two simultaneous exchange processes involving aqueous solvent in wet paint and showed the effects of pigment concentration on the exchange kinetics. Through non-invasive, non-destructive relaxometry measurements, we characterized the unique molecular environments in both dry and wet acrylic paints, which can be compared to molecular environments characterized by others in oil paints and can provide new insights into the physical properties of acrylics relevant to art conservation.

Kiple, L.,  Ballenger, J.,  Keating, K.,  Balachandra, A.,  Meldrum, T.  Automated optimization of spatial resolution for single-sided NMR. Magn. Reson. Chem. 2023, 61(7), 418. https://doi.org/10.1002/mrc.5352

Abstract: Single-sided NMR instruments utilize inhomogeneous magnetic fields with strong gradients to non-destructively probe physical properties of materials. The sensitive region of this type of magnet is often a thin slice above the magnet’s surface; measuring planar samples with high spatial resolution requires coplanarity between the sensitive region of the magnet and the sample region of interest. We developed an algorithmic approach to position flat samples coplanar with the magnet’s sensitive region. The efficient and objective positioning process utilizes an adjustable stage that offers control over three degrees of freedom, and the optimal position for each sample is found with a quadtree algorithm. We show this algorithm is effective for positioning samples with various relaxation behaviors. We report resolution values that describe position optimization, acquisition constraints, and final spatial resolution for each sample. Measurements after optimized positioning had appropriate spatial resolution to distinguish physical regions of layered samples with different physical properties, namely relaxation behavior. Our algorithmic positioning process can be implemented for planar samples in research and industrial settings to enhance spatial resolution of single-sided NMR measurements.

Kiple, Lyndi, "Characterizing Molecular Environments in Acrylic Paint Via Single-Sided NMR" (2023). Dissertations, Theses, and Masters Projects. William & Mary. Paper 1686662718. https://dx.doi.org/10.21220/s2-7g4z-np45

Abstract: Acrylic paint is a modern artistic material made of colored pigment and polymeric binder. Acrylic binder requires fundamental study at the molecular level to understand its physical properties for purposes of art conservation and general polymer chemistry. The research presented in this thesis uses single-sided nuclear magnetic resonance (NMR) as a non-invasive and non-destructive way to measure relaxation and self-diffusion, which provide insight to molecular mobility and physical properties of proton-containing samples. Specifically, this study relies on T2 relaxation to gain insight to regions within acrylic paint with different molecular mobilities. In both dry and wet paint, relaxometry data revealed two relaxation behaviors, each representing a region with unique binder mobility. Furthermore, the effect of pigment concentration on relaxation behavior of wet paint suggested molecules in acrylic binder undergo chemical exchange between these regions with differing mobilities. The characterization of local molecular environments in acrylic paint provides a foundation for future studies of acrylic polymers and contributes fundamental knowledge about the chemistry of acrylic paints to support their long-term preservation.