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SURFACE LAYER MATRIX-ASSISTED LASER DESORPTION IONIZATION TIME OF FLIGHT MASS SPECTROMETRY (SL-MALDI-TOF MS) ANALYSIS OF POLYMER BLEND SURFACE COMPOSITION

Abstract Details

2017, Doctor of Philosophy, University of Akron, Polymer Science.
The composition of a polymer blend is generally different at the surface than in the bulk and the gradient in composition with depth has important implications for surface properties. The determination of the surface composition presents various challenges which continue to prompt the development of new techniques for quantifying the composition. Here the technique of surface layer matrix-assisted laser desorption ionization time-of-flight mass spectrometry (SL-MALDI-ToF-MS) has been further developed to address four specific questions of polymer blend surface behavior within the general category of surface composition determination. The first question is how chain length disparity affects surface segregation in the case that the disparity is quite small. While such segregation is known for blends containing low molecular weight additives or systems with large polydispersity, it has not been reported for anionically polymerized polymers that are viewed, in practice, as monodisperse. For 6 kDa polystyrene the number average molecular weight (Mn) at the surface is ca. 300 Da (5%) lower than that in the bulk and for 7 kDa polymethyl methacrylate the shift is ca. 500 Da. The second question is how chain-end functionalization effects not the location of chain ends at the surface, but rather the prevalence at the surface of any part of a chain having an end functionalization. A key issue of such an approach is understanding precisely where the functionalities ultimately reside and how this functionalization shifts the balance of forces that determine the distribution of chains with depth. The surface of a blend of 6 kDa polystyrene and 6 kDa polystyrene functionalized with hydroxymethyl ends is not only depleted of the higher energy end groups, but is depleted of any segments belonging to the functionalized chains. This is demonstrated using SL-MALDI-ToF-MS, which detects entire chains that have any repeat unit at the outer surface, and requires no labelling. This study was extended to the surfaces of blends of 6 kDa polystyrene and 6 kDa polystyrene functionalized with hydroxyethyl ends. Blends of all compositions less than 90 wt. % functionalized chains showed depletion. Finally, the challenge of determining lateral variations in the surface composition has been addressed with the development of SL-MALDI-ToF-MS imaging (SL-MALDI-ToF-MSI). Key to developing imaging capability was improving the lateral uniformity of the matrix deposition. This uniformity was achieved using solvent free sublimation of matrix and salt onto the sample’s surface. The capabilities of SL-MALDI-ToF-MSI were demonstrated by imaging the absence of material due to masking during material deposition, mechanical scribing or solvent perturbation at the surface of low molecular weight poly(methyl methacrylate) and polystyrene thin films. SL-MALDI-ToF MSI was made possible through the first uniform, solvent free simultaneous sublimation of matrix and salt onto the material’s surface.
Mark Foster, PhD (Advisor)
Chrys Wesdemiotis, PhD (Committee Member)
Ali Dhinojwala, PhD (Committee Chair)
Mesfin Tsige, PhD (Committee Member)
Min Younjin, PhD (Committee Member)
123 p.

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Citations

  • Hill, Hill, J. A. (2017). SURFACE LAYER MATRIX-ASSISTED LASER DESORPTION IONIZATION TIME OF FLIGHT MASS SPECTROMETRY (SL-MALDI-TOF MS) ANALYSIS OF POLYMER BLEND SURFACE COMPOSITION [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1514479406062149

    APA Style (7th edition)

  • Hill, Hill, Jacob. SURFACE LAYER MATRIX-ASSISTED LASER DESORPTION IONIZATION TIME OF FLIGHT MASS SPECTROMETRY (SL-MALDI-TOF MS) ANALYSIS OF POLYMER BLEND SURFACE COMPOSITION. 2017. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1514479406062149.

    MLA Style (8th edition)

  • Hill, Hill, Jacob. "SURFACE LAYER MATRIX-ASSISTED LASER DESORPTION IONIZATION TIME OF FLIGHT MASS SPECTROMETRY (SL-MALDI-TOF MS) ANALYSIS OF POLYMER BLEND SURFACE COMPOSITION." Doctoral dissertation, University of Akron, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1514479406062149

    Chicago Manual of Style (17th edition)